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The Project Gutenberg eBook of Lichens
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Title: Lichens
Author: Annie Lorrain Smith
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*** START OF THE PROJECT GUTENBERG EBOOK LICHENS ***
Cambridge Botanical Handbooks
Edited by A. C. Seward and A. G. Tansley
This eBook is for the use of anyone anywhere in the United States and most
other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms of
the Project Gutenberg License included with this eBook or online at
www.gutenberg.org. If you are not located in the United States, you will
have to check the laws of the country where you are located before using
this eBook.
Title: Lichens
Author: Annie Lorrain Smith
Release date: March 14, 2020 [eBook #61616]
Most recently updated: October 17, 2024
Language: English
Other information and formats: www.gutenberg.org/ebooks/61616
Credits: Produced by Chris Curnow and the Online Distributed
Proofreading Team at http://www.pgdp.net (This file was
produced from images generously made available by The
Internet Archive)
*** START OF THE PROJECT GUTENBERG EBOOK LICHENS ***
Cambridge Botanical Handbooks
Edited by A. C. Seward and A. G. Tansley
Page 4
LICHENS
CAMBRIDGE UNIVERSITY PRESS
C. F. CLAY, Manager
LONDON: FETTER LANE, E.C.4
LONDON: H. K. LEWIS AND CO., Ltd.,
136, Gower Street, W.C.1
LONDON: WHELDON & WESLEY, Ltd.,
28, Essex Street, Strand, W.C.2
NEW YORK: THE MACMILLAN CO.
BOMBAY }
CALCUTTA } MACMILLAN AND CO., Ltd.
MADRAS }
TORONTO: THE MACMILLAN CO. OF CANADA, Ltd.
TOKYO: MARUZEN-KABUSHIKI-KAISHA
ALL RIGHTS RESERVED
LICHENS
CAMBRIDGE UNIVERSITY PRESS
C. F. CLAY, Manager
LONDON: FETTER LANE, E.C.4
LONDON: H. K. LEWIS AND CO., Ltd.,
136, Gower Street, W.C.1
LONDON: WHELDON & WESLEY, Ltd.,
28, Essex Street, Strand, W.C.2
NEW YORK: THE MACMILLAN CO.
BOMBAY }
CALCUTTA } MACMILLAN AND CO., Ltd.
MADRAS }
TORONTO: THE MACMILLAN CO. OF CANADA, Ltd.
TOKYO: MARUZEN-KABUSHIKI-KAISHA
ALL RIGHTS RESERVED
LICHENS
Page 5
BY
ANNIE LORRAIN SMITH, F.L.S.
ACTING ASSISTANT, BOTANICAL DEPARTMENT, BRITISH MUSEUM
CAMBRIDGE:
AT THE UNIVERSITY PRESS
1921
PRINTED IN GREAT BRITAIN
ANNIE LORRAIN SMITH, F.L.S.
ACTING ASSISTANT, BOTANICAL DEPARTMENT, BRITISH MUSEUM
CAMBRIDGE:
AT THE UNIVERSITY PRESS
1921
PRINTED IN GREAT BRITAIN
Page 6
PREFACE
The publication of this volume has been delayed owing to war
conditions, but the delay is the less to be regretted in that it has allowed the
inclusion of recent work on the subject. Much of the subject-matter is of
common knowledge to lichenologists, but in the co-ordination and
arrangement of the facts the original papers are cited throughout. The
method has somewhat burdened the pages with citations, but it is hoped
that, as a book of reference, its value has been enhanced thereby. The
Glossary includes terms used in lichenology, or those with a special
lichenological meaning. The Bibliography refers only to works consulted in
the preparation of this volume. To save space, etc., the titles of books and
papers quoted in the text are generally translated and curtailed: full citations
will be found in the Bibliography. Subject-matter has been omitted from the
index: references of importance will be found in the Table of Contents or in
the Glossary.
I would record my thanks to those who have generously helped me
during the preparation of the volume: to Lady Muriel Percy for taking notes
of spore production, and to Dr Cavers for the loan of reprints. Prof. Potter
and Dr Somerville Hastings placed at my disposal their photographs of the
living plants. Free use has been made of published text-figures which are
duly acknowledged.
I have throughout had the inestimable advantage of being able to consult
freely the library and herbarium of the British Museum, and have thus been
able to verify references to plants as well as to literature. A special debt of
gratitude is due to my colleagues Mr Gepp and Mr Ramsbottom for their
unfailing assistance and advice.
A. L. S.
London, February, 1920
The publication of this volume has been delayed owing to war
conditions, but the delay is the less to be regretted in that it has allowed the
inclusion of recent work on the subject. Much of the subject-matter is of
common knowledge to lichenologists, but in the co-ordination and
arrangement of the facts the original papers are cited throughout. The
method has somewhat burdened the pages with citations, but it is hoped
that, as a book of reference, its value has been enhanced thereby. The
Glossary includes terms used in lichenology, or those with a special
lichenological meaning. The Bibliography refers only to works consulted in
the preparation of this volume. To save space, etc., the titles of books and
papers quoted in the text are generally translated and curtailed: full citations
will be found in the Bibliography. Subject-matter has been omitted from the
index: references of importance will be found in the Table of Contents or in
the Glossary.
I would record my thanks to those who have generously helped me
during the preparation of the volume: to Lady Muriel Percy for taking notes
of spore production, and to Dr Cavers for the loan of reprints. Prof. Potter
and Dr Somerville Hastings placed at my disposal their photographs of the
living plants. Free use has been made of published text-figures which are
duly acknowledged.
I have throughout had the inestimable advantage of being able to consult
freely the library and herbarium of the British Museum, and have thus been
able to verify references to plants as well as to literature. A special debt of
gratitude is due to my colleagues Mr Gepp and Mr Ramsbottom for their
unfailing assistance and advice.
A. L. S.
London, February, 1920
Page 7
CONTENTS
PAGE
Glossary xix
Errata xxii
Introduction xxiii
CHAPTER I
HISTORY OF LICHENOLOGY
A. Introductory 1
B. Period I. Previous to 1694 2
C. Period II. 1694-1729 5
D. Period III. 1729-1780 6
E. Period IV. 1780-1803 9
F. Period V. 1803-1846 10
G. Period VI. 1846-1867 15
H. Period VII. 1867 and after 18
CHAPTER II
CONSTITUENTS OF THE LICHEN THALLUS
I. LICHEN GONIDIA
1. GONIDIA IN RELATION TO THE THALLUS
A. Historical account of Lichen Gonidia 21
B. Gonidia contrasted with Algae 22
C. Culture Experiments with the Lichen Thallus 24
D. Theories as to the Origin of Gonidia 25
E. Microgonidia 26
F. Composite Nature of Thallus 27
G. Synthetic Cultures 27
H. Hymenial Gonidia 30
PAGE
Glossary xix
Errata xxii
Introduction xxiii
CHAPTER I
HISTORY OF LICHENOLOGY
A. Introductory 1
B. Period I. Previous to 1694 2
C. Period II. 1694-1729 5
D. Period III. 1729-1780 6
E. Period IV. 1780-1803 9
F. Period V. 1803-1846 10
G. Period VI. 1846-1867 15
H. Period VII. 1867 and after 18
CHAPTER II
CONSTITUENTS OF THE LICHEN THALLUS
I. LICHEN GONIDIA
1. GONIDIA IN RELATION TO THE THALLUS
A. Historical account of Lichen Gonidia 21
B. Gonidia contrasted with Algae 22
C. Culture Experiments with the Lichen Thallus 24
D. Theories as to the Origin of Gonidia 25
E. Microgonidia 26
F. Composite Nature of Thallus 27
G. Synthetic Cultures 27
H. Hymenial Gonidia 30
Page 8
I. Nature of Association between Alga and Fungus 31
a. Consortium and symbiosis
b. Different forms of association
J. Recent views on Symbiosis and Parasitism 36
2. PHYSIOLOGY OF THE SYMBIONTS
A. Nutrition of Lichen Algae 39
a. Character of algal cells
b. Supply of nitrogen
c. Effect on the alga
d. Supply of carbon
e. Nutrition within the symbiotic plant
f. Affinities of lichen gonidia
B. Nutrition of Lichen Fungi 44
C. Symbiosis of other Plants 45
II. LICHEN HYPHAE
A. Origin of Hyphae 46
B. Development of Lichenoid Hyphae 47
C. Culture of Hyphae Without Gonidia 49
D. Continuity of Protoplasm in Hyphal Cells 51
III. LICHEN ALGAE
A. Types of Algae 51
a. Myxophyceae associated with Phycolichens
b. Chlorophyceae associated with Archilichens
B. Changes induced in the Alga 60
a. Myxophyceae
b. Chlorophyceae
C. Constancy of Algal Constituents 63
D. Displacement of Algae Within the Thallus 64
a. Normal displacement
b. Local displacement
E. Non-gonidial Organisms associated with Lichen Hyphae 65
F. Parasitism of Algae on Lichens 65
CHAPTER III
MORPHOLOGY
a. Consortium and symbiosis
b. Different forms of association
J. Recent views on Symbiosis and Parasitism 36
2. PHYSIOLOGY OF THE SYMBIONTS
A. Nutrition of Lichen Algae 39
a. Character of algal cells
b. Supply of nitrogen
c. Effect on the alga
d. Supply of carbon
e. Nutrition within the symbiotic plant
f. Affinities of lichen gonidia
B. Nutrition of Lichen Fungi 44
C. Symbiosis of other Plants 45
II. LICHEN HYPHAE
A. Origin of Hyphae 46
B. Development of Lichenoid Hyphae 47
C. Culture of Hyphae Without Gonidia 49
D. Continuity of Protoplasm in Hyphal Cells 51
III. LICHEN ALGAE
A. Types of Algae 51
a. Myxophyceae associated with Phycolichens
b. Chlorophyceae associated with Archilichens
B. Changes induced in the Alga 60
a. Myxophyceae
b. Chlorophyceae
C. Constancy of Algal Constituents 63
D. Displacement of Algae Within the Thallus 64
a. Normal displacement
b. Local displacement
E. Non-gonidial Organisms associated with Lichen Hyphae 65
F. Parasitism of Algae on Lichens 65
CHAPTER III
MORPHOLOGY
Page 9
I. GENERAL ACCOUNT OF LICHEN STRUCTURE
ORIGIN OF LICHEN STRUCTURES
A. Forms of Cell-Structure 67
B. Types of Thallus 68
a. Endogenous thallus
b. Exogenous thallus
II. STRATOSE THALLUS
1. CRUSTACEOUS LICHENS
A. General Structure 70
B. Saxicolous Lichens 70
a. Epilithic lichens
aa. Hypothallus or protothallus
bb. Formation of crustaceous tissues
cc. Formation of areolae
b. Endolithic lichens
c. Chemical nature of the substratum
C. Corticolous Lichens 77
a. Epiphloeodal lichens
b. Hypophloeodal lichens
2. SQUAMULOSE LICHENS
A. Development of the Squamule 79
B. Tissues of Squamulose Thallus 81
3. FOLIOSE LICHENS
A. Development of foliose Thallus 82
B. Cortical Tissues 82
a. Types of cortical structure
b. Origin of variation in cortical structure
c. Loss and renewal of cortex
d. Cortical hairs
C. Gonidial Tissues 87
D. Medulla and Lower Cortex 88
a. Medulla
b. Lower cortex
c. Hypothallic structures
ORIGIN OF LICHEN STRUCTURES
A. Forms of Cell-Structure 67
B. Types of Thallus 68
a. Endogenous thallus
b. Exogenous thallus
II. STRATOSE THALLUS
1. CRUSTACEOUS LICHENS
A. General Structure 70
B. Saxicolous Lichens 70
a. Epilithic lichens
aa. Hypothallus or protothallus
bb. Formation of crustaceous tissues
cc. Formation of areolae
b. Endolithic lichens
c. Chemical nature of the substratum
C. Corticolous Lichens 77
a. Epiphloeodal lichens
b. Hypophloeodal lichens
2. SQUAMULOSE LICHENS
A. Development of the Squamule 79
B. Tissues of Squamulose Thallus 81
3. FOLIOSE LICHENS
A. Development of foliose Thallus 82
B. Cortical Tissues 82
a. Types of cortical structure
b. Origin of variation in cortical structure
c. Loss and renewal of cortex
d. Cortical hairs
C. Gonidial Tissues 87
D. Medulla and Lower Cortex 88
a. Medulla
b. Lower cortex
c. Hypothallic structures
Page 10
E. Structures for Protection and Attachment 91
a. Cilia
b. Rhizinae
c. Haptera
F. Strengthening Tissues of Stratose Lichens 95
a. Produced by development of cortex
b. Produced by development of veins or nerves
III. RADIATE THALLUS
1. CHARACTERS OF RADIATE THALLUS
2. INTERMEDIATE TYPES OF THALLUS
3. FRUTICOSE AND FILAMENTOUS THALLUS
A. General Structure of Thallus 101
Cortical Structures
a. The fastigiate cortex
b. The fibrous cortex
B. Special strengthening Structures 103
a. Sclerotic strands
b. Chondroid axis
C. Survey of Mechanical Tissues 105
D. Reticulate Fronds 106
E. Rooting Base in Fruticose Lichens 108
IV. STRATOSE-RADIATE THALLUS
1. STRATOSE OR PRIMARY THALLUS
A. General Characteristics 111
B. Tissues of Primary Thallus 112
a. Cortical tissue
b. Gonidial tissue
c. Medullary tissue
d. Soredia
2. RADIATE OR SECONDARY THALLUS
A. Origin of the Podetium 114
B. Structure of the Podetium 114
a. Cilia
b. Rhizinae
c. Haptera
F. Strengthening Tissues of Stratose Lichens 95
a. Produced by development of cortex
b. Produced by development of veins or nerves
III. RADIATE THALLUS
1. CHARACTERS OF RADIATE THALLUS
2. INTERMEDIATE TYPES OF THALLUS
3. FRUTICOSE AND FILAMENTOUS THALLUS
A. General Structure of Thallus 101
Cortical Structures
a. The fastigiate cortex
b. The fibrous cortex
B. Special strengthening Structures 103
a. Sclerotic strands
b. Chondroid axis
C. Survey of Mechanical Tissues 105
D. Reticulate Fronds 106
E. Rooting Base in Fruticose Lichens 108
IV. STRATOSE-RADIATE THALLUS
1. STRATOSE OR PRIMARY THALLUS
A. General Characteristics 111
B. Tissues of Primary Thallus 112
a. Cortical tissue
b. Gonidial tissue
c. Medullary tissue
d. Soredia
2. RADIATE OR SECONDARY THALLUS
A. Origin of the Podetium 114
B. Structure of the Podetium 114
Page 11
a. General structure
b. Gonidial tissue
c. Cortical tissue
d. Soredia
C. Development of the Scyphus 117
a. From abortive apothecia
b. From polytomous branching
c. From arrested growth
d. Gonidia of the scyphus
e. Species without scyphi
D. Branching of the Podetium 119
E. Perforations and Reticulation of the Podetium 120
F. Rooting Structures of Cladoniae 121
G. Haptera 122
H. Morphology of the Podetium 122
I. Pilophorus and Stereocaulon 125
V. STRUCTURES PECULIAR TO LICHENS
1. AERATION STRUCTURES
A. Cyphellae and Pseudocyphellae 126
a. Historical
b. Development of cyphellae
c. Pseudocyphellae
d. Occurrence and distribution
B. Breathing-Pores 129
a. Definite breathing-pores
b. Other openings in the thallus
C. General Aeration of the Thallus 132
2. CEPHALODIA
A. Historical and Descriptive 133
B. Classification 135
I. CEPHALODIA VERA
II. PSEUDOCEPHALODIA
C. Algae that form Cephalodia 136
D. Development of Cephalodia 137
a. Ectotrophic
b. Endotrophic
c. Pseudocephalodia
b. Gonidial tissue
c. Cortical tissue
d. Soredia
C. Development of the Scyphus 117
a. From abortive apothecia
b. From polytomous branching
c. From arrested growth
d. Gonidia of the scyphus
e. Species without scyphi
D. Branching of the Podetium 119
E. Perforations and Reticulation of the Podetium 120
F. Rooting Structures of Cladoniae 121
G. Haptera 122
H. Morphology of the Podetium 122
I. Pilophorus and Stereocaulon 125
V. STRUCTURES PECULIAR TO LICHENS
1. AERATION STRUCTURES
A. Cyphellae and Pseudocyphellae 126
a. Historical
b. Development of cyphellae
c. Pseudocyphellae
d. Occurrence and distribution
B. Breathing-Pores 129
a. Definite breathing-pores
b. Other openings in the thallus
C. General Aeration of the Thallus 132
2. CEPHALODIA
A. Historical and Descriptive 133
B. Classification 135
I. CEPHALODIA VERA
II. PSEUDOCEPHALODIA
C. Algae that form Cephalodia 136
D. Development of Cephalodia 137
a. Ectotrophic
b. Endotrophic
c. Pseudocephalodia
Page 12
E. Autosymbiotic Cephalodia 140
3. SOREDIA
A. Structure and Origin of Soredia 141
a. Scattered soredia
b. Isidial soredia
c. Soredia as buds
B. Soralia 144
a. Form and occurrence of soralia
b. Position of soraliferous lobes
c. Deep-seated soralia
C. Dispersal and Germination of Soredia 147
D. Evolution of Soredia 148
4. ISIDIA
A. Form and Structure of Isidia 149
B. Origin and Function of Isidia 151
VI. HYMENOLICHENS
A. Affinity with other Plants 152
B. Structure of Thallus 153
C. Sporiferous Tissues 154
CHAPTER IV
REPRODUCTION
I. REPRODUCTION BY ASCOSPORES
A. Historical Survey 155
B. Forms of Reproductive Organs 156
a. Apothecia
b. Perithecia
C. Development of Reproductive Organs 159
1. DISCOLICHENS
a. Carpogonia of gelatinous lichens
b. Carpogonia of non-gelatinous lichens
c. General summary
d. Hypothecium and paraphyses
e. Variations in apothecial development
aa. Parmeliae
3. SOREDIA
A. Structure and Origin of Soredia 141
a. Scattered soredia
b. Isidial soredia
c. Soredia as buds
B. Soralia 144
a. Form and occurrence of soralia
b. Position of soraliferous lobes
c. Deep-seated soralia
C. Dispersal and Germination of Soredia 147
D. Evolution of Soredia 148
4. ISIDIA
A. Form and Structure of Isidia 149
B. Origin and Function of Isidia 151
VI. HYMENOLICHENS
A. Affinity with other Plants 152
B. Structure of Thallus 153
C. Sporiferous Tissues 154
CHAPTER IV
REPRODUCTION
I. REPRODUCTION BY ASCOSPORES
A. Historical Survey 155
B. Forms of Reproductive Organs 156
a. Apothecia
b. Perithecia
C. Development of Reproductive Organs 159
1. DISCOLICHENS
a. Carpogonia of gelatinous lichens
b. Carpogonia of non-gelatinous lichens
c. General summary
d. Hypothecium and paraphyses
e. Variations in apothecial development
aa. Parmeliae
Page 13
bb. Pertusariae
cc. Graphideae
dd. Cladoniae
2. PYRENOLICHENS
a. Development of the perithecium
b. Formation of carpogonia
D. Apogamous Reproduction 174
E. Discussion of Lichen Reproduction 177
a. The Trichogyne
b. The Ascogonium
F. Final Stages of Apothecial Development 181
a. Open or closed apothecia
b. Emergence of ascocarp
G. Lichen Asci and Spores 184
a. Historical
b. Development of the ascus
c. Development of the spores
d. Spore germination
e. Multinucleate spores
f. Polaribilocular spores
II. SECONDARY SPORES
A. Reproduction by Oidia 189
B. Reproduction by Conidia 190
a. Rare instances of conidial formation
b. Comparison with Hyphomycetes
C. Campylidium and Orthidium 191
III. SPERMOGONIA OR PYCNIDIA
A. Historical Account of Spermogonia 192
B. Spermogonia as Male Organs 193
C. Occurrence and Distribution 193
a. Relation to thallus and apothecia
b. Form and size
c. Colour
D. Structure 196
a. Origin and growth
b. Form and types of spermatiophores
c. Periphyses and sterile filaments
E. Spermatia or Pycnidiospores 201
a. Origin and form
cc. Graphideae
dd. Cladoniae
2. PYRENOLICHENS
a. Development of the perithecium
b. Formation of carpogonia
D. Apogamous Reproduction 174
E. Discussion of Lichen Reproduction 177
a. The Trichogyne
b. The Ascogonium
F. Final Stages of Apothecial Development 181
a. Open or closed apothecia
b. Emergence of ascocarp
G. Lichen Asci and Spores 184
a. Historical
b. Development of the ascus
c. Development of the spores
d. Spore germination
e. Multinucleate spores
f. Polaribilocular spores
II. SECONDARY SPORES
A. Reproduction by Oidia 189
B. Reproduction by Conidia 190
a. Rare instances of conidial formation
b. Comparison with Hyphomycetes
C. Campylidium and Orthidium 191
III. SPERMOGONIA OR PYCNIDIA
A. Historical Account of Spermogonia 192
B. Spermogonia as Male Organs 193
C. Occurrence and Distribution 193
a. Relation to thallus and apothecia
b. Form and size
c. Colour
D. Structure 196
a. Origin and growth
b. Form and types of spermatiophores
c. Periphyses and sterile filaments
E. Spermatia or Pycnidiospores 201
a. Origin and form
Page 14
b. Size and structure
c. Germination
d. Variation in pycnidia
F. Pycnidia with Macrospores 204
G. General Survey 205
a. Sexual or asexual
b. Comparison with fungi
c. Influence of symbiosis
d. Value in diagnosis
CHAPTER V
PHYSIOLOGY
I. CELLS AND CELL PRODUCTS
A. Cell-membranes 209
a. Chitin
b. Lichenin and allied carbohydrates
c. Cellulose
B. Contents and Products of the Fungal Cells 213
a. Cell-substances
b. Calcium Oxalate
c. Importance of calcium oxalate
C. Oil-cells 215
a. Oil-cells of endolithic lichens
b. Oil-cells of epilithic lichens
c. Significance of oil-formation
D. Lichen-acids 221
a. Historical
b. Occurrence and examination of acids
c. Character of acids
d. Causes of variation in quantity and quality
e. Distribution of acids
E. Chemical grouping of acids 225
I. ACIDS OF THE FAT SERIES
II. ACIDS OF THE BENZOLE SERIES
Subseries I. Orcine derivatives
Subseries II. Anthracene derivatives
F. Chemical Reagents as Tests for Lichens 228
G. Chemical Reactions in Nature 229
II. GENERAL NUTRITION
c. Germination
d. Variation in pycnidia
F. Pycnidia with Macrospores 204
G. General Survey 205
a. Sexual or asexual
b. Comparison with fungi
c. Influence of symbiosis
d. Value in diagnosis
CHAPTER V
PHYSIOLOGY
I. CELLS AND CELL PRODUCTS
A. Cell-membranes 209
a. Chitin
b. Lichenin and allied carbohydrates
c. Cellulose
B. Contents and Products of the Fungal Cells 213
a. Cell-substances
b. Calcium Oxalate
c. Importance of calcium oxalate
C. Oil-cells 215
a. Oil-cells of endolithic lichens
b. Oil-cells of epilithic lichens
c. Significance of oil-formation
D. Lichen-acids 221
a. Historical
b. Occurrence and examination of acids
c. Character of acids
d. Causes of variation in quantity and quality
e. Distribution of acids
E. Chemical grouping of acids 225
I. ACIDS OF THE FAT SERIES
II. ACIDS OF THE BENZOLE SERIES
Subseries I. Orcine derivatives
Subseries II. Anthracene derivatives
F. Chemical Reagents as Tests for Lichens 228
G. Chemical Reactions in Nature 229
II. GENERAL NUTRITION
Page 15
A. Absorption of Water 229
a. Gelatinous lichens
b. Crustaceous lichens
c. Foliose lichens
d. Fruticose lichens
B. Storage of Water 232
C. Supply of Inorganic Food 232
a. In foliose and fruticose lichens
b. In crustaceous lichens
D. Supply of Organic Food 235
a. From the substratum
b. From other lichens
c. From other vegetation
III. ASSIMILATION AND RESPIRATION
A. Influence of Temperature 238
a. High temperature
b. Low temperature
B. Influence of Moisture 239
a. On vital functions
b. On general development
IV. ILLUMINATION OF LICHENS
A. Effect of Light on the Thallus 240
a. Sun lichens
b. Colour-changes due to light
c. Shade lichens
d. Varying shade conditions
B. Effect of Light on Reproductive Organs 244
a. Position and orientation of fruits with regard to light
b. Influence of light on colour of fruits
V. COLOUR OF LICHENS
A. Origin of Lichen-Colouring 245
a. Colour given by the algal constituent
b. Colour due to lichen-acids
c. Colour due to amorphous substances
d. Enumeration of amorphous pigments
e. Colour due to infiltration
a. Gelatinous lichens
b. Crustaceous lichens
c. Foliose lichens
d. Fruticose lichens
B. Storage of Water 232
C. Supply of Inorganic Food 232
a. In foliose and fruticose lichens
b. In crustaceous lichens
D. Supply of Organic Food 235
a. From the substratum
b. From other lichens
c. From other vegetation
III. ASSIMILATION AND RESPIRATION
A. Influence of Temperature 238
a. High temperature
b. Low temperature
B. Influence of Moisture 239
a. On vital functions
b. On general development
IV. ILLUMINATION OF LICHENS
A. Effect of Light on the Thallus 240
a. Sun lichens
b. Colour-changes due to light
c. Shade lichens
d. Varying shade conditions
B. Effect of Light on Reproductive Organs 244
a. Position and orientation of fruits with regard to light
b. Influence of light on colour of fruits
V. COLOUR OF LICHENS
A. Origin of Lichen-Colouring 245
a. Colour given by the algal constituent
b. Colour due to lichen-acids
c. Colour due to amorphous substances
d. Enumeration of amorphous pigments
e. Colour due to infiltration
Page 16
CHAPTER VI
BIONOMICS
A. Growth and Duration of Lichens 252
B. Season of Fruit Formation 255
C. Dispersal and Increase 256
a. Dispersal of crustaceous lichens
b. Dispersal of foliose lichens
c. Dispersal of fruticose lichens
D. Erratic Lichens 258
E. Parasitism 260
a. General statement
b. Antagonistic symbiosis
c. Parasymbiosis
d. Parasymbiosis of fungi
e. Fungi parasitic on lichens
f. Mycetozoa parasitic on lichens
F. Diseases of Lichens 268
a. Caused by parasitism
b. Caused by crowding
c. Caused by adverse conditions
G. Harmful Effect of Lichens 269
H. Gall-Formation 270
CHAPTER VII
PHYLOGENY
I. GENERAL STATEMENT
A. Origin of Lichens 272
B. Algal Ancestors 273
C. Fungal Ancestors 273
a. Basidiolichens
b. Ascolichens
II. THE REPRODUCTIVE ORGANS
A. Theories of Descent in Ascolichens 273
B. Relation of Lichens to Fungi 275
a. Pyrenocarpineae
BIONOMICS
A. Growth and Duration of Lichens 252
B. Season of Fruit Formation 255
C. Dispersal and Increase 256
a. Dispersal of crustaceous lichens
b. Dispersal of foliose lichens
c. Dispersal of fruticose lichens
D. Erratic Lichens 258
E. Parasitism 260
a. General statement
b. Antagonistic symbiosis
c. Parasymbiosis
d. Parasymbiosis of fungi
e. Fungi parasitic on lichens
f. Mycetozoa parasitic on lichens
F. Diseases of Lichens 268
a. Caused by parasitism
b. Caused by crowding
c. Caused by adverse conditions
G. Harmful Effect of Lichens 269
H. Gall-Formation 270
CHAPTER VII
PHYLOGENY
I. GENERAL STATEMENT
A. Origin of Lichens 272
B. Algal Ancestors 273
C. Fungal Ancestors 273
a. Basidiolichens
b. Ascolichens
II. THE REPRODUCTIVE ORGANS
A. Theories of Descent in Ascolichens 273
B. Relation of Lichens to Fungi 275
a. Pyrenocarpineae
Page 17
b. Coniocarpineae
c. Graphidineae
d. Cyclocarpineae
III. THE THALLUS
A. General Outline of Development of Thallus 281
a. Preliminary considerations
b. Course of evolution in Hymenolichens
c. Course of evolution in Ascolichens
B. Comparative Antiquity of Algal Symbionts 282
C. Evolution of Phycolichens 283
a. Gloeolichens
b. Ephebaceae and Collemaceae
c. Pyrenidiaceae
d. Heppiaceae and Pannariaceae
e. Peltigeraceae and Stictaceae
D. Evolution of Archilichens 287
a. Thallus of Pyrenocarpineae
b. Thallus of Coniocarpineae
c. Thallus of Graphidineae
d. Thallus of Cyclocarpineae
AA. LECIDEALES
aa. Coenogoniaceae
bb. Lecideaceae and Gyrophoraceae
cc. Cladoniaceae
1. Origin of Cladonia
2. Evolution of the primary thallus
3. Evolution of the secondary thallus
4. Course of podetial development
5. Variation in Cladonia
6. Causes of variation
7. Podetial development and spore-dissemination
8. Pilophorus, Stereocaulon and Argopsis
BB. LECANORALES
aa. Course of Development
bb. Lecanoraceae
cc. Parmeliaceae
dd. Usneaceae
ee. Physciaceae
CHAPTER VIII
SYSTEMATIC
c. Graphidineae
d. Cyclocarpineae
III. THE THALLUS
A. General Outline of Development of Thallus 281
a. Preliminary considerations
b. Course of evolution in Hymenolichens
c. Course of evolution in Ascolichens
B. Comparative Antiquity of Algal Symbionts 282
C. Evolution of Phycolichens 283
a. Gloeolichens
b. Ephebaceae and Collemaceae
c. Pyrenidiaceae
d. Heppiaceae and Pannariaceae
e. Peltigeraceae and Stictaceae
D. Evolution of Archilichens 287
a. Thallus of Pyrenocarpineae
b. Thallus of Coniocarpineae
c. Thallus of Graphidineae
d. Thallus of Cyclocarpineae
AA. LECIDEALES
aa. Coenogoniaceae
bb. Lecideaceae and Gyrophoraceae
cc. Cladoniaceae
1. Origin of Cladonia
2. Evolution of the primary thallus
3. Evolution of the secondary thallus
4. Course of podetial development
5. Variation in Cladonia
6. Causes of variation
7. Podetial development and spore-dissemination
8. Pilophorus, Stereocaulon and Argopsis
BB. LECANORALES
aa. Course of Development
bb. Lecanoraceae
cc. Parmeliaceae
dd. Usneaceae
ee. Physciaceae
CHAPTER VIII
SYSTEMATIC
Page 18
I. CLASSIFICATION
A. Work of Successive Systematists 304
a. Dillenius and Linnaeus
b. Acharius
c. Schaerer
d. Massalongo and Koerber
e. Nylander
f. Müller-Argau
g. Reinke
h. Zahlbruckner
B. Families and Genera of Ascolichens 311
C. Hymenolichens 342
II. NUMBER AND DISTRIBUTION
1. ESTIMATES OF NUMBER
2. GEOGRAPHICAL DISTRIBUTION
A. General Survey 343
B. Lichens of Polar Regions 345
C. Lichens of the Temperate Zones 348
D. Lichens of Tropical Regions 352
III. FOSSIL LICHENS
CHAPTER IX
ECOLOGY
A. General Introduction 356
B. External Influences 357
a. Temperature
b. Humidity
c. Wind
d. Human Agency
C. Lichen Communities 362
1. ARBOREAL 363
a. Epiphyllous
b. Corticolous
c. Lignicolous
A. Work of Successive Systematists 304
a. Dillenius and Linnaeus
b. Acharius
c. Schaerer
d. Massalongo and Koerber
e. Nylander
f. Müller-Argau
g. Reinke
h. Zahlbruckner
B. Families and Genera of Ascolichens 311
C. Hymenolichens 342
II. NUMBER AND DISTRIBUTION
1. ESTIMATES OF NUMBER
2. GEOGRAPHICAL DISTRIBUTION
A. General Survey 343
B. Lichens of Polar Regions 345
C. Lichens of the Temperate Zones 348
D. Lichens of Tropical Regions 352
III. FOSSIL LICHENS
CHAPTER IX
ECOLOGY
A. General Introduction 356
B. External Influences 357
a. Temperature
b. Humidity
c. Wind
d. Human Agency
C. Lichen Communities 362
1. ARBOREAL 363
a. Epiphyllous
b. Corticolous
c. Lignicolous
Page 19
2. TERRICOLOUS 367
a. On calcareous soil
b. On siliceous soil
c. On bricks
d. On humus
e. On peaty soil
f. On mosses
g. On fungi
3. SAXICOLOUS 371
a. Characters of mineral substrata
b. Colonization on rocks
c. Calcicolous
d. Silicicolous
4. OMNICOLOUS LICHENS 376
5. LOCALIZED COMMUNITIES 378
a. Maritime lichens
b. Sand-dune lichens
c. Mountain lichens
d. Tundra lichens
e. Desert lichens
f. Aquatic lichens
D. Lichens as Pioneers 392
a. Soil-formers
b. Outposts of vegetation
CHAPTER X
ECONOMIC AND TECHNICAL
A. Lichens as Food 395
a. Food for insects
b. Insect mimicry of lichens
c. Food for the higher animals
d. Food for man
B. Lichens as Medicine 405
a. Ancient remedies
b. Doctrine of “signatures”
c. Cure for hydrophobia
d. Popular remedies
C. Lichens as Poisons 410
D. Lichens used in Tanning, Brewing and Distilling 411
E. Dyeing Properties of Lichens 411
a. Lichens as dye-plants
a. On calcareous soil
b. On siliceous soil
c. On bricks
d. On humus
e. On peaty soil
f. On mosses
g. On fungi
3. SAXICOLOUS 371
a. Characters of mineral substrata
b. Colonization on rocks
c. Calcicolous
d. Silicicolous
4. OMNICOLOUS LICHENS 376
5. LOCALIZED COMMUNITIES 378
a. Maritime lichens
b. Sand-dune lichens
c. Mountain lichens
d. Tundra lichens
e. Desert lichens
f. Aquatic lichens
D. Lichens as Pioneers 392
a. Soil-formers
b. Outposts of vegetation
CHAPTER X
ECONOMIC AND TECHNICAL
A. Lichens as Food 395
a. Food for insects
b. Insect mimicry of lichens
c. Food for the higher animals
d. Food for man
B. Lichens as Medicine 405
a. Ancient remedies
b. Doctrine of “signatures”
c. Cure for hydrophobia
d. Popular remedies
C. Lichens as Poisons 410
D. Lichens used in Tanning, Brewing and Distilling 411
E. Dyeing Properties of Lichens 411
a. Lichens as dye-plants
Page 20
b. The orchil lichen, Roccella
c. Purple dyes: orchil, cudbear and litmus
d. Other orchil lichens
e. Preparation of orchil
f. Brown and yellow dyes
g. Collecting of dye-lichens
h. Lichen colours and spectrum characters
F. Lichens in Perfumery 418
a. Lichens as perfumes
b. Lichens as hair-powder
G. Some minor Uses of Lichens 420
Appendix 421
Addendum 422
Bibliography 423
Index 448
c. Purple dyes: orchil, cudbear and litmus
d. Other orchil lichens
e. Preparation of orchil
f. Brown and yellow dyes
g. Collecting of dye-lichens
h. Lichen colours and spectrum characters
F. Lichens in Perfumery 418
a. Lichens as perfumes
b. Lichens as hair-powder
G. Some minor Uses of Lichens 420
Appendix 421
Addendum 422
Bibliography 423
Index 448
Page 21
GLOSSARY
Acrogenous, borne at the tips of hyphae; see spermatium, 312.
Allelositismus, Norman’s term to describe the thallus of Moriolaceae
(mutualism), 313.
Amorphous cortex, formed of indistinct hyphae with thickened walls; cf.
decomposed cortex.
Amphithecium, thalline margin of the apothecium, 157.
Antagonistic symbiosis, hurtful parasitism of one lichen on another, 261 et
seq.
Apothecium, open or disc-shaped fructification, 11, 156 et passim. Veiled
apothecium, 169. Closed or open at first, 182.
Archilichens, lichens in which the gonidia are bright green
(Chlorophyceae), 52, 55 et passim.
Ardella, the small spot-like apothecium of Arthoniaceae, 158.
Areola (areolate), small space marked out by lines or chinks on the surface
of the thallus, 73 et passim.
Arthrosterigma, septate tissue-like sterigma (spermatiophore), 197.
Ascogonium, the cell or cells that produce ascogenous hyphae, 180 et seq.
Ascolichens, lichens in which the fungus is an Ascomycete, 159, 173 et
passim.
Ascus, enlarged cell in which a definite number of spores (usually 8) are
developed; cf. theca, 157, 184.
Ascyphous, podetia without scyphi, 119 et passim.
Biatorine, apothecia that are soft or waxy, and often brightly coloured, as in
Biatora, 158.
Blasteniospore, see polarilocular spore.
Acrogenous, borne at the tips of hyphae; see spermatium, 312.
Allelositismus, Norman’s term to describe the thallus of Moriolaceae
(mutualism), 313.
Amorphous cortex, formed of indistinct hyphae with thickened walls; cf.
decomposed cortex.
Amphithecium, thalline margin of the apothecium, 157.
Antagonistic symbiosis, hurtful parasitism of one lichen on another, 261 et
seq.
Apothecium, open or disc-shaped fructification, 11, 156 et passim. Veiled
apothecium, 169. Closed or open at first, 182.
Archilichens, lichens in which the gonidia are bright green
(Chlorophyceae), 52, 55 et passim.
Ardella, the small spot-like apothecium of Arthoniaceae, 158.
Areola (areolate), small space marked out by lines or chinks on the surface
of the thallus, 73 et passim.
Arthrosterigma, septate tissue-like sterigma (spermatiophore), 197.
Ascogonium, the cell or cells that produce ascogenous hyphae, 180 et seq.
Ascolichens, lichens in which the fungus is an Ascomycete, 159, 173 et
passim.
Ascus, enlarged cell in which a definite number of spores (usually 8) are
developed; cf. theca, 157, 184.
Ascyphous, podetia without scyphi, 119 et passim.
Biatorine, apothecia that are soft or waxy, and often brightly coloured, as in
Biatora, 158.
Blasteniospore, see polarilocular spore.
Page 22
Byssoid, slender, thread-like, as in the old genus Byssus.
Campylidium, supposed new type of fructification in lichens, 191.
Capitulum, the globose apical apothecium of Coniocarpineae; cf.
mazaedium, 319.
Carpogonium, primordial stage of fructification, 160, 164 et passim.
Cephalodium, irregular outgrowth from the thallus enclosing mostly blue-
green algae; or intruded packet of algae within the thallus, 11, 133 et
passim.
Chrondroid, hard and tough like cartilage, a term applied to strengthening
strands of hyphae, 104, 114.
Chroolepoid, like the genus Chroolepis (Trentepohlia).
Chrysogonidia, yellow algal cells (Trentepohlia).
Cilium, hair-like outgrowth from surface or margin of thallus, or margin of
apothecium, 91.
Consortium (consortism), mutual association of fungus and alga (Reinke);
also termed “mutualism,” 31, 313.
Corticolous, living on the bark of trees, 363.
Crustaceous, crust-like closely adhering thallus, 70-79.
Cyphella, minute cup-like depression on the under surface of the thallus
(Sticta, etc.), 11, 126.
Decomposed, term applied to cortex formed of gelatinous indistinct hyphae
(amorphous), 73-81 et passim, 357.
Determinate, thallus with a definite outline, 72.
Dimidiate, term applied to the perithecium, when the outer wall covers
only the upper portion, 159.
Discoid, disc-like, an open rounded apothecium, 156.
Discolichens, in which the fructification is an apothecium, 160 et seq.
Dual hypothesis, the theory of two organisms present in the lichen thallus,
27 et seq.
Campylidium, supposed new type of fructification in lichens, 191.
Capitulum, the globose apical apothecium of Coniocarpineae; cf.
mazaedium, 319.
Carpogonium, primordial stage of fructification, 160, 164 et passim.
Cephalodium, irregular outgrowth from the thallus enclosing mostly blue-
green algae; or intruded packet of algae within the thallus, 11, 133 et
passim.
Chrondroid, hard and tough like cartilage, a term applied to strengthening
strands of hyphae, 104, 114.
Chroolepoid, like the genus Chroolepis (Trentepohlia).
Chrysogonidia, yellow algal cells (Trentepohlia).
Cilium, hair-like outgrowth from surface or margin of thallus, or margin of
apothecium, 91.
Consortium (consortism), mutual association of fungus and alga (Reinke);
also termed “mutualism,” 31, 313.
Corticolous, living on the bark of trees, 363.
Crustaceous, crust-like closely adhering thallus, 70-79.
Cyphella, minute cup-like depression on the under surface of the thallus
(Sticta, etc.), 11, 126.
Decomposed, term applied to cortex formed of gelatinous indistinct hyphae
(amorphous), 73-81 et passim, 357.
Determinate, thallus with a definite outline, 72.
Dimidiate, term applied to the perithecium, when the outer wall covers
only the upper portion, 159.
Discoid, disc-like, an open rounded apothecium, 156.
Discolichens, in which the fructification is an apothecium, 160 et seq.
Dual hypothesis, the theory of two organisms present in the lichen thallus,
27 et seq.
Page 23
Effigurate, having a distinct form or figure; cf. placodioid, 80, 201.
Endobasidial, Steiner’s term for sporophore with a secondary sporiferous
branch, 200.
Endogenous, produced internally, as spores in an ascus, 179; see also under
thallus.
Endolithic, embedded in the rock, 75.
Endosaprophytism, term used by Elenkin for destruction of the algal
contents by enzymes of the fungus, 36.
Entire, term applied to the perithecium when completely surrounded by an
outer wall, 159.
Epilithic, growing on the rock surface, 70.
Epiphloeodal, thallus growing on the surface of the bark, 77.
Epiphyllous, growing on leaves, 363.
Epithecium, upper layer of thecium (hymenium), 158.
Erratic lichens, unattached and drifting, 259.
Exobasidial, Steiner’s term for sporophore without a secondary sporiferous
branch, 200.
Exogenous, produced externally, as spores on tips of hyphae; see also under
thallus.
Fastigiate cortex, formed of clustered parallel hyphal branches vertical to
long axis of thallus, 82.
Fat-cells, specialized hyphal cells containing fat or oil, 75, 215 et passim.
Fibrous cortex, formed of hyphae parallel with long axis of thallus, 82.
Filamentous, slender thallus with radiate structure, 101 et seq.
Foliose, lichens with a leafy form and stratose in structure, 82-97.
Foveolae, Foveolate, pitted, 373.
Fruticose, upright or pendulous thallus, with radiate structure, 101 et seq.
Fulcrum, term used by Steiner for sporophore, 200.
Endobasidial, Steiner’s term for sporophore with a secondary sporiferous
branch, 200.
Endogenous, produced internally, as spores in an ascus, 179; see also under
thallus.
Endolithic, embedded in the rock, 75.
Endosaprophytism, term used by Elenkin for destruction of the algal
contents by enzymes of the fungus, 36.
Entire, term applied to the perithecium when completely surrounded by an
outer wall, 159.
Epilithic, growing on the rock surface, 70.
Epiphloeodal, thallus growing on the surface of the bark, 77.
Epiphyllous, growing on leaves, 363.
Epithecium, upper layer of thecium (hymenium), 158.
Erratic lichens, unattached and drifting, 259.
Exobasidial, Steiner’s term for sporophore without a secondary sporiferous
branch, 200.
Exogenous, produced externally, as spores on tips of hyphae; see also under
thallus.
Fastigiate cortex, formed of clustered parallel hyphal branches vertical to
long axis of thallus, 82.
Fat-cells, specialized hyphal cells containing fat or oil, 75, 215 et passim.
Fibrous cortex, formed of hyphae parallel with long axis of thallus, 82.
Filamentous, slender thallus with radiate structure, 101 et seq.
Foliose, lichens with a leafy form and stratose in structure, 82-97.
Foveolae, Foveolate, pitted, 373.
Fruticose, upright or pendulous thallus, with radiate structure, 101 et seq.
Fulcrum, term used by Steiner for sporophore, 200.
Page 24
Gloeolichens, lichens in which the gonidia are Gloeocapsa or
Chroococcus, 284, 373, 389.
Gonidium, the algal constituent of the lichen thallus, 20-45 et passim.
Gonimium, blue-green algal cell (Myxophyceae), constituent of the lichen
thallus, 52.
Goniocysts, nests of gonidia in Moriolaceae, 313.
Gyrose, curved backward and forward, furrowed fruit of Gyrophora, 184.
Hapteron, aerial organ of attachment, 94, 122.
Haustorium, outgrowth or branch of a hypha serving as an organ of
suction, 32.
Helotism, state of servitude, term used to denote the relation of alga to
fungus in lichen organization, 38, 40.
Heteromerous, fungal and algal constituents of the thallus in definite strata,
13, 68, 305 et passim.
Hold-fast, rooting organ of thallus, 109, 122 et passim.
Homobium, interdependent association of fungus and alga, 31.
Homoiomerous, fungal and algal constituents more or less mixed in the
thallus, 13, 68, 305 et passim.
Hymenial gonidia, algal cells in the hymenium, 30, 314, 315, 327.
Hymenium, apothecial tissue consisting of asci and paraphyses; cf.
thecium, 157.
Hymenolichens, lichens of which the fungal constituent is a
Hymenomycete, 152-154, 342.
Hypophloeodal, thallus growing within the bark, 78, 364.
Hypothallus, first growth of hyphae (proto- or pro-thallus) persisting as
hyphal growth at base or margin of the thallus, 70, 257 et passim.
Hypothecium, layer below the thecium (hymenium), 157.
Intricate cortex, composed of hyphae densely interwoven but not
coalescent, 83.
Chroococcus, 284, 373, 389.
Gonidium, the algal constituent of the lichen thallus, 20-45 et passim.
Gonimium, blue-green algal cell (Myxophyceae), constituent of the lichen
thallus, 52.
Goniocysts, nests of gonidia in Moriolaceae, 313.
Gyrose, curved backward and forward, furrowed fruit of Gyrophora, 184.
Hapteron, aerial organ of attachment, 94, 122.
Haustorium, outgrowth or branch of a hypha serving as an organ of
suction, 32.
Helotism, state of servitude, term used to denote the relation of alga to
fungus in lichen organization, 38, 40.
Heteromerous, fungal and algal constituents of the thallus in definite strata,
13, 68, 305 et passim.
Hold-fast, rooting organ of thallus, 109, 122 et passim.
Homobium, interdependent association of fungus and alga, 31.
Homoiomerous, fungal and algal constituents more or less mixed in the
thallus, 13, 68, 305 et passim.
Hymenial gonidia, algal cells in the hymenium, 30, 314, 315, 327.
Hymenium, apothecial tissue consisting of asci and paraphyses; cf.
thecium, 157.
Hymenolichens, lichens of which the fungal constituent is a
Hymenomycete, 152-154, 342.
Hypophloeodal, thallus growing within the bark, 78, 364.
Hypothallus, first growth of hyphae (proto- or pro-thallus) persisting as
hyphal growth at base or margin of the thallus, 70, 257 et passim.
Hypothecium, layer below the thecium (hymenium), 157.
Intricate cortex, composed of hyphae densely interwoven but not
coalescent, 83.
Page 25
Isidium, coral-like outgrowth on the lichen thallus, 149-151.
Lecanorine, apothecium with a thalline margin as in Lecanora, 158.
Lecideine, apothecium usually dark-coloured or carbonaceous and without
a thalline margin, 158.
Leprose, mealy or scurfy, like the old form genera, Lepra, Lepraria, 191.
Lichen-acids, organic acids peculiar to lichens, 221 et seq.
Lignicolous, living on wood or trees, 366.
Lirella, long narrow apothecium of Graphideae, 158.
Mazaedium, fructification of Coniocarpineae, the spores lying as a
powdery mass in the capitulum, 176.
Medulla, the loose hyphal layer in the interior of the thallus, 88 et passim.
Meristematic, term applied by Wainio to growing hyphae, 48.
Microgonidia, term applied by Minks to minute greenish bodies in lichen
hyphae, 26.
Multi-septate, term applied to spores with numerous transverse septa, 316
et seq.
Murali-divided, Muriform, term applied to spores divided like the
masonry of a wall, 187.
Oidium, reproductive cell formed by the breaking up of the hyphae, 189.
Oil-cell, hyphal cell containing fat globules, 215.
Orculiform, see polarilocular.
Orthidium, supposed new type of fructification in lichens, 192.
Palisade-cells, the terminal cells of the hyphae forming the fastigiate
cortex, 82, 83.
Panniform, having a felted or matted appearance, 260.
Paraphysis, sterile filament in the hymenium, 157.
Parasymbiosis, associated harmless but not mutually useful growth of two
organisms, 263.
Lecanorine, apothecium with a thalline margin as in Lecanora, 158.
Lecideine, apothecium usually dark-coloured or carbonaceous and without
a thalline margin, 158.
Leprose, mealy or scurfy, like the old form genera, Lepra, Lepraria, 191.
Lichen-acids, organic acids peculiar to lichens, 221 et seq.
Lignicolous, living on wood or trees, 366.
Lirella, long narrow apothecium of Graphideae, 158.
Mazaedium, fructification of Coniocarpineae, the spores lying as a
powdery mass in the capitulum, 176.
Medulla, the loose hyphal layer in the interior of the thallus, 88 et passim.
Meristematic, term applied by Wainio to growing hyphae, 48.
Microgonidia, term applied by Minks to minute greenish bodies in lichen
hyphae, 26.
Multi-septate, term applied to spores with numerous transverse septa, 316
et seq.
Murali-divided, Muriform, term applied to spores divided like the
masonry of a wall, 187.
Oidium, reproductive cell formed by the breaking up of the hyphae, 189.
Oil-cell, hyphal cell containing fat globules, 215.
Orculiform, see polarilocular.
Orthidium, supposed new type of fructification in lichens, 192.
Palisade-cells, the terminal cells of the hyphae forming the fastigiate
cortex, 82, 83.
Panniform, having a felted or matted appearance, 260.
Paraphysis, sterile filament in the hymenium, 157.
Parasymbiosis, associated harmless but not mutually useful growth of two
organisms, 263.
Page 26
Parathecium, hyphal layer round the apothecium, 157.
Peltate, term applied to orbicular and horizontal apothecia in the form of a
shield, 336.
Perithecium, roundish fructification usually with an apical opening
(ostiole) containing ascospores, 158 et passim.
Pervious, referring to scyphi with an opening at the base (Perviae), 118.
Phycolichens, lichens in which the gonidia are blue-green (Myxophyceae),
52 et passim.
Placodioid, thallus with a squamulose determinate outline, generally
orbicular; cf. effigurate, 80.
Placodiomorph, see polarilocular.
Plectenchyma (Plectenchymatous), pseudoparenchyma of fungi and
lichens, 66 et passim.
Pleurogenous, borne laterally on hyphal cells; see spermatium, 312.
Pluri-septate, term applied to spores with several transverse septa, 321 et
seq.
Podetium, stalk-like secondary thallus of Cladoniaceae, 114, 293 et seq.
Polarilocular, Polaribilocular, two-celled spores with thick median wall
traversed by a connecting tube, 188, 340-341.
Polytomous, arising of several branches of the podetium from one level,
118.
Proper margin, the hyphal margin surrounding the apothecium, 157.
Prothallus, Protothallus, first stages of hyphal growth; cf. hypothallus, 71.
Pycnidiospores, stylospores borne in pycnidia, 198 et passim.
Pycnidium, roundish fructification, usually with an opening at the apex,
containing sporophores and stylospores; cf. spermogonium, 192 et seq.
Pyrenolichens, in which the fructification is a closed perithecium, 173 et
passim.
Radiate thallus, the tissues radiate from a centre, 98 et seq.
Peltate, term applied to orbicular and horizontal apothecia in the form of a
shield, 336.
Perithecium, roundish fructification usually with an apical opening
(ostiole) containing ascospores, 158 et passim.
Pervious, referring to scyphi with an opening at the base (Perviae), 118.
Phycolichens, lichens in which the gonidia are blue-green (Myxophyceae),
52 et passim.
Placodioid, thallus with a squamulose determinate outline, generally
orbicular; cf. effigurate, 80.
Placodiomorph, see polarilocular.
Plectenchyma (Plectenchymatous), pseudoparenchyma of fungi and
lichens, 66 et passim.
Pleurogenous, borne laterally on hyphal cells; see spermatium, 312.
Pluri-septate, term applied to spores with several transverse septa, 321 et
seq.
Podetium, stalk-like secondary thallus of Cladoniaceae, 114, 293 et seq.
Polarilocular, Polaribilocular, two-celled spores with thick median wall
traversed by a connecting tube, 188, 340-341.
Polytomous, arising of several branches of the podetium from one level,
118.
Proper margin, the hyphal margin surrounding the apothecium, 157.
Prothallus, Protothallus, first stages of hyphal growth; cf. hypothallus, 71.
Pycnidiospores, stylospores borne in pycnidia, 198 et passim.
Pycnidium, roundish fructification, usually with an opening at the apex,
containing sporophores and stylospores; cf. spermogonium, 192 et seq.
Pyrenolichens, in which the fructification is a closed perithecium, 173 et
passim.
Radiate thallus, the tissues radiate from a centre, 98 et seq.
Page 27
Rhagadiose, deeply chinked, 74; cf. rimose.
Rhizina, attaching “rootlet,” 92-94.
Rimose, Rimulose, cleft or chinked into areolae, 73.
Rimose-diffract, widely cracked or chinked, 74.
Scutellate, shaped like a platter, 156.
Scyphus, cup-like dilatation of the podetium, 111, 117.
Signature, a term in ancient medicine to signify the resemblance of a plant
to any part of the human body, 406, 409.
Soralium, group of soredia surrounded by a definite margin, 144.
Soredium, minute separable particle arising from the gonidial tissue of the
thallus, and consisting of algae and hyphae, 141.
Spermatium, spore-like body borne in the spermogonium, regarded as a
non-motile male cell or as a pycnidiospore, 201.
Spermogonium, roundish closed receptacle containing spermatia, 192.
Sphaeroid-cell, swollen hyphal cell, containing fat globules, 215.
Squamule, a small thalline lobe or scale, 74 et passim.
Sterigma, Nylander’s term for the spermatiophore, 197.
Stratose thallus, where the tissues are in horizontal layers, 70.
Stratum, a layer of tissue in the thallus, 70.
Symbiont, one of two dissimilar organisms living together, 32.
Symbiosis, a living together of dissimilar organisms, also termed
commensalism, 31, 32 et seq.
Tegulicolous, living on tiles, 369.
Terebrator, boring apparatus, term used by Lindau for the lichen
“trichogyne,” 179.
Thalline margin, an apothecial margin formed of and usually coloured like
the thallus; cf. amphithecium.
Rhizina, attaching “rootlet,” 92-94.
Rimose, Rimulose, cleft or chinked into areolae, 73.
Rimose-diffract, widely cracked or chinked, 74.
Scutellate, shaped like a platter, 156.
Scyphus, cup-like dilatation of the podetium, 111, 117.
Signature, a term in ancient medicine to signify the resemblance of a plant
to any part of the human body, 406, 409.
Soralium, group of soredia surrounded by a definite margin, 144.
Soredium, minute separable particle arising from the gonidial tissue of the
thallus, and consisting of algae and hyphae, 141.
Spermatium, spore-like body borne in the spermogonium, regarded as a
non-motile male cell or as a pycnidiospore, 201.
Spermogonium, roundish closed receptacle containing spermatia, 192.
Sphaeroid-cell, swollen hyphal cell, containing fat globules, 215.
Squamule, a small thalline lobe or scale, 74 et passim.
Sterigma, Nylander’s term for the spermatiophore, 197.
Stratose thallus, where the tissues are in horizontal layers, 70.
Stratum, a layer of tissue in the thallus, 70.
Symbiont, one of two dissimilar organisms living together, 32.
Symbiosis, a living together of dissimilar organisms, also termed
commensalism, 31, 32 et seq.
Tegulicolous, living on tiles, 369.
Terebrator, boring apparatus, term used by Lindau for the lichen
“trichogyne,” 179.
Thalline margin, an apothecial margin formed of and usually coloured like
the thallus; cf. amphithecium.
Page 28
Thallus, vegetative body or soma of the lichen plant, 11, 421. Endogenous
thallus in which the alga predominates, 68. Exogenous thallus in which
the fungus predominates, 69.
Theca, enlarged cell containing spores; cf. ascus.
Thecium, layer of tissue in the apothecium consisting of asci and
paraphyses; cf. hymenium, 157.
Trichogyne, prolongation of the egg-cell in Florideae which acts as a
receptive tube; septate hypha in lichens arising from the ascogonium,
160, 177-181, 273.
Woronin’s hypha, a coiled hypha occurring in the centre of the fruit
primordium, 159, 163.
thallus in which the alga predominates, 68. Exogenous thallus in which
the fungus predominates, 69.
Theca, enlarged cell containing spores; cf. ascus.
Thecium, layer of tissue in the apothecium consisting of asci and
paraphyses; cf. hymenium, 157.
Trichogyne, prolongation of the egg-cell in Florideae which acts as a
receptive tube; septate hypha in lichens arising from the ascogonium,
160, 177-181, 273.
Woronin’s hypha, a coiled hypha occurring in the centre of the fruit
primordium, 159, 163.
Page 29
ERRATA
p. 24. For Baranetsky read Baranetzky.
p. 277. For Ascolium read Acolium.
p. 318. For Lepolichen coccophora read coccophorus.
Transcriber’s Note: The errata have been corrected.
p. 24. For Baranetsky read Baranetzky.
p. 277. For Ascolium read Acolium.
p. 318. For Lepolichen coccophora read coccophorus.
Transcriber’s Note: The errata have been corrected.
Page 30
INTRODUCTION
Lichens are, with few exceptions, perennial aerial plants of somewhat
lowly organization. In the form of spreading encrustations, horizontal leafy
expansions, of upright strap-shaped fronds or of pendulous filaments, they
take possession of the tree-trunks, palings, walls, rocks or even soil that
afford them a suitable and stable foothold. The vegetative body, or thallus,
which may be extremely long-lived, is of varying colour, white, yellow,
brown, grey or black. The great majority of lichens are Ascolichens and
reproduction is by ascospores produced in open or closed fruits (apothecia
or perithecia) which often differ in colour from the thallus. There are a few
Hymenolichens which form basidiospores. Vegetative reproduction by
soredia is frequent.
Lichens abound everywhere, from the sea-shore to the tops of high
mountains, where indeed the covering of perpetual snow is the only barrier
to their advance; but owing to their slow growth and long duration, they are
more seriously affected than are the higher plants by chemical or other
atmospheric impurities and they are killed out by the smoke of large towns:
only a few species are able to persist in somewhat depauperate form in or
near the great centres of population or of industry.
The distinguishing feature of lichens is their composite nature: they
consist of two distinct and dissimilar organisms, a fungus and an alga,
which, in the lichen thallus, are associated in some kind of symbiotic union,
each symbiont contributing in varying degree to the common support: it is a
more or less unique and not unsuccessful venture in plant-life. The algae—
Chlorophyceae or Myxophyceae—that become lichen symbionts or
“gonidia” are of simple structure, and, in a free condition, are generally to
be found in or near localities that are also the customary habitats of lichens.
The fungus is the predominant partner in the alliance as it forms the fruiting
bodies. It belongs to the Ascomycetes[1], except in a few tropical lichens
(Hymenolichens), in which the fungus is a Basidiomycete. These two types
of plants (algae and fungi) belonging severally to many different genera and
species have developed in their associated life this new lichen organism,
Lichens are, with few exceptions, perennial aerial plants of somewhat
lowly organization. In the form of spreading encrustations, horizontal leafy
expansions, of upright strap-shaped fronds or of pendulous filaments, they
take possession of the tree-trunks, palings, walls, rocks or even soil that
afford them a suitable and stable foothold. The vegetative body, or thallus,
which may be extremely long-lived, is of varying colour, white, yellow,
brown, grey or black. The great majority of lichens are Ascolichens and
reproduction is by ascospores produced in open or closed fruits (apothecia
or perithecia) which often differ in colour from the thallus. There are a few
Hymenolichens which form basidiospores. Vegetative reproduction by
soredia is frequent.
Lichens abound everywhere, from the sea-shore to the tops of high
mountains, where indeed the covering of perpetual snow is the only barrier
to their advance; but owing to their slow growth and long duration, they are
more seriously affected than are the higher plants by chemical or other
atmospheric impurities and they are killed out by the smoke of large towns:
only a few species are able to persist in somewhat depauperate form in or
near the great centres of population or of industry.
The distinguishing feature of lichens is their composite nature: they
consist of two distinct and dissimilar organisms, a fungus and an alga,
which, in the lichen thallus, are associated in some kind of symbiotic union,
each symbiont contributing in varying degree to the common support: it is a
more or less unique and not unsuccessful venture in plant-life. The algae—
Chlorophyceae or Myxophyceae—that become lichen symbionts or
“gonidia” are of simple structure, and, in a free condition, are generally to
be found in or near localities that are also the customary habitats of lichens.
The fungus is the predominant partner in the alliance as it forms the fruiting
bodies. It belongs to the Ascomycetes[1], except in a few tropical lichens
(Hymenolichens), in which the fungus is a Basidiomycete. These two types
of plants (algae and fungi) belonging severally to many different genera and
species have developed in their associated life this new lichen organism,
Page 31
different from themselves as well as from all other plants, not only
morphologically but physiologically. Thus there has arisen a distinct class,
with families, genera and species, which through all their varying forms
retain the characteristics peculiar to lichens.
In the absence of any “visible” seed, there was much speculation in early
days as to the genesis of all the lower plants and many opinions were
hazarded as to their origin. Luyken[2], for instance, thought that lichens
were compounded of air and moisture. Hornschuch[3] traced their origin to a
vegetable infusorium, Monas Lens, which became transformed to green
matter and was further developed by the continued action of light and air,
not only to lichens, but to algae and mosses, the type of plant finally
evolved being determined by the varying atmospheric influences along with
the chemical nature of the substratum. An account[4] is published of Nees
von Esenbeck, on a botanical excursion, pointing out to his students the
green substance, Lepraria botryoides, which covered the lower reaches of
walls and rocks, while higher up it assumed the grey lichen hue. This
afforded him sufficient proof that the green matter in that dry situation
changed to lichens, just as in water it changed to algae. An adverse criticism
by Dillenius[5] on a description of a lichen fructification is not inappropriate
to those early theorists: “Ex quo apparet, quantum videre possint homines,
si imaginatione polleant.”
A constant subject of speculation and of controversy was the origin of the
green cells, so dissimilar to the general texture of the thallus. It was thought
finally to have been established beyond dispute that they were formed
directly from the colourless hyphae and, as a corollary, Protococcus and
other algal cells living in the open were considered to be escaped gonidia
or, as Wallroth[6] termed them, “unfortunate brood-cells,” his view being
that they were the reproductive organs of the lichen plant that had failed to
develop.
It was a step forward in the right direction when lichens were regarded as
transformed algae, among others by Agardh[7], who believed that he had
followed the change from Nostoc lichenoides to the lichen Collema
limosum. Thenceforward their double resemblance, on the one hand to
algae, on the other to fungi, was acknowledged, and influenced strongly the
trend of study and investigation.
morphologically but physiologically. Thus there has arisen a distinct class,
with families, genera and species, which through all their varying forms
retain the characteristics peculiar to lichens.
In the absence of any “visible” seed, there was much speculation in early
days as to the genesis of all the lower plants and many opinions were
hazarded as to their origin. Luyken[2], for instance, thought that lichens
were compounded of air and moisture. Hornschuch[3] traced their origin to a
vegetable infusorium, Monas Lens, which became transformed to green
matter and was further developed by the continued action of light and air,
not only to lichens, but to algae and mosses, the type of plant finally
evolved being determined by the varying atmospheric influences along with
the chemical nature of the substratum. An account[4] is published of Nees
von Esenbeck, on a botanical excursion, pointing out to his students the
green substance, Lepraria botryoides, which covered the lower reaches of
walls and rocks, while higher up it assumed the grey lichen hue. This
afforded him sufficient proof that the green matter in that dry situation
changed to lichens, just as in water it changed to algae. An adverse criticism
by Dillenius[5] on a description of a lichen fructification is not inappropriate
to those early theorists: “Ex quo apparet, quantum videre possint homines,
si imaginatione polleant.”
A constant subject of speculation and of controversy was the origin of the
green cells, so dissimilar to the general texture of the thallus. It was thought
finally to have been established beyond dispute that they were formed
directly from the colourless hyphae and, as a corollary, Protococcus and
other algal cells living in the open were considered to be escaped gonidia
or, as Wallroth[6] termed them, “unfortunate brood-cells,” his view being
that they were the reproductive organs of the lichen plant that had failed to
develop.
It was a step forward in the right direction when lichens were regarded as
transformed algae, among others by Agardh[7], who believed that he had
followed the change from Nostoc lichenoides to the lichen Collema
limosum. Thenceforward their double resemblance, on the one hand to
algae, on the other to fungi, was acknowledged, and influenced strongly the
trend of study and investigation.
Page 32
The announcement[8] by Schwendener[9] of the dual hypothesis solved
the problem for most students, though the relation between the two
symbionts is still a subject of controversy. The explanation given by
Schwendener, and still held by some[10], that lichens were merely fungi
parasitic on algae, was indeed a very inadequate conception of the lichen
plant, and it was hotly contested by various lichenologists. Lauder
Lindsay[11] dismissed the theory as “merely the most recent instance of
German transcendentalism applied to the Lichens.” Earlier still,
Nylander[12], in a paper dealing with cephalodia and their peculiar gonidia,
had denounced it: “Locum sic suum dignum occupat algolichenomachia
inter historias ridiculas, quae hodie haud paucae circa lichenes, majore
imaginatione quam scientia, enarrantur.” He never changed his attitude and
Crombie[13], wholly agreeing with his estimate of these “absurd tales,”
translates a much later pronouncement by him[14]: “All these allegations
belong to inept Schwendenerism and scarcely deserve even to be reviewed
or castigated so puerile are they—the offspring of inexperience and of a
light imagination. No true science there.” Crombie[15] himself in a first
paper on this subject declared that “the new theory would necessitate their
degradation from the position they have so long held as an independent
class.” He scornfully rejected the whole subject as “a Romance of
Lichenology, or the unnatural union between a captive Algal damsel and a
tyrant Fungal master.” The nearest approach to any concession on the algal
question occurs in a translation by Crombie[16] of one of Nylander’s papers.
It is stated there that a saxicolous alga (Gongrosira Kütz.) had been found
bearing the apothecia of Lecidea herbidula n. sp. Nylander adds: “This
algological genus is one which readily passes into lichens.” At a later date,
Crombie[17] was even more comprehensively contemptuous and wrote:
“whether viewed anatomically or biologically, analytically or synthetically,
it is instead of being true science, only the Romance of Lichenology.” These
views were shared by many continental lichenologists and were indeed, as
already stated, justified to a considerable extent: it was impossible to regard
such a large and distinctive class of plants as merely fungi parasitic on the
lower algae.
Controversy about lichens never dies down, and that view of their
parasitic nature has been freshly promulgated among others by the
the problem for most students, though the relation between the two
symbionts is still a subject of controversy. The explanation given by
Schwendener, and still held by some[10], that lichens were merely fungi
parasitic on algae, was indeed a very inadequate conception of the lichen
plant, and it was hotly contested by various lichenologists. Lauder
Lindsay[11] dismissed the theory as “merely the most recent instance of
German transcendentalism applied to the Lichens.” Earlier still,
Nylander[12], in a paper dealing with cephalodia and their peculiar gonidia,
had denounced it: “Locum sic suum dignum occupat algolichenomachia
inter historias ridiculas, quae hodie haud paucae circa lichenes, majore
imaginatione quam scientia, enarrantur.” He never changed his attitude and
Crombie[13], wholly agreeing with his estimate of these “absurd tales,”
translates a much later pronouncement by him[14]: “All these allegations
belong to inept Schwendenerism and scarcely deserve even to be reviewed
or castigated so puerile are they—the offspring of inexperience and of a
light imagination. No true science there.” Crombie[15] himself in a first
paper on this subject declared that “the new theory would necessitate their
degradation from the position they have so long held as an independent
class.” He scornfully rejected the whole subject as “a Romance of
Lichenology, or the unnatural union between a captive Algal damsel and a
tyrant Fungal master.” The nearest approach to any concession on the algal
question occurs in a translation by Crombie[16] of one of Nylander’s papers.
It is stated there that a saxicolous alga (Gongrosira Kütz.) had been found
bearing the apothecia of Lecidea herbidula n. sp. Nylander adds: “This
algological genus is one which readily passes into lichens.” At a later date,
Crombie[17] was even more comprehensively contemptuous and wrote:
“whether viewed anatomically or biologically, analytically or synthetically,
it is instead of being true science, only the Romance of Lichenology.” These
views were shared by many continental lichenologists and were indeed, as
already stated, justified to a considerable extent: it was impossible to regard
such a large and distinctive class of plants as merely fungi parasitic on the
lower algae.
Controversy about lichens never dies down, and that view of their
parasitic nature has been freshly promulgated among others by the
Page 33
American lichenologist Bruce Fink[18]. The genetic origin of the gonidia has
also been restated by Elfving[19]: the various theories and views are
discussed fully in the chapter on the lichen plant.
Much of the interest in lichens has centred round their symbiotic growth.
No theory of simple parasitism can explain the association of the two
plants: if one of the symbionts is withdrawn—either fungus or alga—the
lichen as such ceases to exist. Together they form a healthy unit capable of
development and change: a basis for progress along new lines. Permanent
characters have been formed which are transmitted just as in other units of
organic life.
A new view of the association has been advanced by F. and Mme
Moreau[20]. They hold that the most characteristic lichen structures—more
particularly the cortex—have been induced by the action of the alga on the
fungus. The larger part of the thallus might therefore be regarded as
equivalent to a gall: “it is a cecidium, an algal cecidium, a generalized
biomorphogenesis.”
The morphological characters of lichens are of exceptional interest,
conditioned as they are by the interaction of the two symbionts, and new
structures have been evolved by the fungus which provides the general
tissue system. Lichens are plants of physiological symbiotic origin, and that
aspect of their life-history has been steadily kept in view in this work. There
are many new requirements which have had to be met by the lichen hyphae,
and the differences between them and the true fungal hyphae have been
considered, as these are manifested in the internal economy of the
compound plant, and in its reaction to external influences such as light,
heat, moisture, etc.
The pioneers of botanical science were of necessity occupied almost
exclusively with collecting and describing plants. As the number of known
lichens gradually accumulated, affinities were recognized and more or less
successful efforts were made to tabulate them in classes, orders, etc. It was
a marvellous power of observation that enabled the early workers to arrange
the first schemes of classification. Increasing knowledge aided by improved
microscopes has necessitated changes, but the old fundamental “genus”
Lichen is practically equivalent to the Class Lichenes.
also been restated by Elfving[19]: the various theories and views are
discussed fully in the chapter on the lichen plant.
Much of the interest in lichens has centred round their symbiotic growth.
No theory of simple parasitism can explain the association of the two
plants: if one of the symbionts is withdrawn—either fungus or alga—the
lichen as such ceases to exist. Together they form a healthy unit capable of
development and change: a basis for progress along new lines. Permanent
characters have been formed which are transmitted just as in other units of
organic life.
A new view of the association has been advanced by F. and Mme
Moreau[20]. They hold that the most characteristic lichen structures—more
particularly the cortex—have been induced by the action of the alga on the
fungus. The larger part of the thallus might therefore be regarded as
equivalent to a gall: “it is a cecidium, an algal cecidium, a generalized
biomorphogenesis.”
The morphological characters of lichens are of exceptional interest,
conditioned as they are by the interaction of the two symbionts, and new
structures have been evolved by the fungus which provides the general
tissue system. Lichens are plants of physiological symbiotic origin, and that
aspect of their life-history has been steadily kept in view in this work. There
are many new requirements which have had to be met by the lichen hyphae,
and the differences between them and the true fungal hyphae have been
considered, as these are manifested in the internal economy of the
compound plant, and in its reaction to external influences such as light,
heat, moisture, etc.
The pioneers of botanical science were of necessity occupied almost
exclusively with collecting and describing plants. As the number of known
lichens gradually accumulated, affinities were recognized and more or less
successful efforts were made to tabulate them in classes, orders, etc. It was
a marvellous power of observation that enabled the early workers to arrange
the first schemes of classification. Increasing knowledge aided by improved
microscopes has necessitated changes, but the old fundamental “genus”
Lichen is practically equivalent to the Class Lichenes.
Page 34
The study of lichens has been a slow and gradual process, with a
continual conflict of opinion as to the meaning of these puzzling plants—
their structure, reproduction, manner of subsistence and classification as
well as their relation to other plants. It has been found desirable to treat
these different subjects from a historical aspect, as only thus can a true
understanding be gained, or a true judgment formed as to the present
condition of the science. It is the story of the evolution of lichenology as
well as of lichens that has yielded so much of interest and importance.
The lichenologist may claim several advantages in the study of his
subject: the abundant material almost everywhere to hand in country
districts, the ease with which the plants are preserved, and, not least, the
interest excited by the changes and variations induced by growth
conditions; there are a whole series of problems and puzzles barely touched
on as yet that are waiting to be solved.
In field work, it is important to note accurately and carefully the nature of
the substratum as well as the locality. Crustaceous species should be
gathered if possible along with part of the wood or rock to which they are
attached; if they are scraped off, the pieces may be reassembled on gummed
paper, but that is less satisfactory. The larger forms are more easily secured;
they should be damped and then pressed before being laid away: the
process flattens them, but it saves them from the risk of being crushed and
broken, as when dry they are somewhat brittle. Moistening with water will
largely restore their original form. All parts of the lichen, both thallus and
fruit, can be examined with ease at any time as they do not sensibly alter in
the herbarium, though they lose to some extent their colouring: the blue-
grey forms, for instance, often become a uniform dingy brownish-grey.
Microscopic examination in the determination of species is necessary in
many instances, but that disability—if it ranks as such—is shared by other
cryptogams, and may possibly be considered an inducement rather than a
deterrent to the study of lichens. For temporary examination of microscopic
preparations, the normal condition is best observed by mounting them in
water. If the plants are old and dry, the addition of a drop or two of potash
—or ammonia—solution is often helpful in clearing the membranes of the
cells and in restoring the shrivelled spores and paraphyses to their natural
forms and dimensions.
continual conflict of opinion as to the meaning of these puzzling plants—
their structure, reproduction, manner of subsistence and classification as
well as their relation to other plants. It has been found desirable to treat
these different subjects from a historical aspect, as only thus can a true
understanding be gained, or a true judgment formed as to the present
condition of the science. It is the story of the evolution of lichenology as
well as of lichens that has yielded so much of interest and importance.
The lichenologist may claim several advantages in the study of his
subject: the abundant material almost everywhere to hand in country
districts, the ease with which the plants are preserved, and, not least, the
interest excited by the changes and variations induced by growth
conditions; there are a whole series of problems and puzzles barely touched
on as yet that are waiting to be solved.
In field work, it is important to note accurately and carefully the nature of
the substratum as well as the locality. Crustaceous species should be
gathered if possible along with part of the wood or rock to which they are
attached; if they are scraped off, the pieces may be reassembled on gummed
paper, but that is less satisfactory. The larger forms are more easily secured;
they should be damped and then pressed before being laid away: the
process flattens them, but it saves them from the risk of being crushed and
broken, as when dry they are somewhat brittle. Moistening with water will
largely restore their original form. All parts of the lichen, both thallus and
fruit, can be examined with ease at any time as they do not sensibly alter in
the herbarium, though they lose to some extent their colouring: the blue-
grey forms, for instance, often become a uniform dingy brownish-grey.
Microscopic examination in the determination of species is necessary in
many instances, but that disability—if it ranks as such—is shared by other
cryptogams, and may possibly be considered an inducement rather than a
deterrent to the study of lichens. For temporary examination of microscopic
preparations, the normal condition is best observed by mounting them in
water. If the plants are old and dry, the addition of a drop or two of potash
—or ammonia—solution is often helpful in clearing the membranes of the
cells and in restoring the shrivelled spores and paraphyses to their natural
forms and dimensions.
Page 35
If serial microtome sections are desired, more elaborate methods are
required. For this purpose Peirce[21] has recommended that “when dealing
with plants that are dry but still alive, the material should be thoroughly
wetted and kept moist for two days, then killed and fixed in a saturated
solution of corrosive sublimate in thirty-five per cent. alcohol.” The
solution should be used hot: the usual methods of dehydrating and
embedding in paraffin are then employed with extra precautions on account
of the extremely brittle nature of lichens.
Another method that also gave good results has been proposed by
French[22]: “first the lichen is put into 95 per cent. alcohol for 24 hours, then
into thin celloidin and thick celloidin 24 hours each. After this the
specimens are embedded in thick celloidin which is hardened in 70 per cent.
alcohol for 24 hours and then cut.” French advises staining with borax
carmine: it colours the fungal part pale carmine and the algal cells a
greenish-red shade.
Modern research methods of work are generally described in full in the
publications that are discussed in the following chapters. The student is
referred to these original papers for information as to fixing, embedding,
staining, etc.
Great use has been made of reagents in determining lichen species. They
are extremely helpful and often give the clinching decision when
morphological characters are obscure, especially if the plant has been much
altered by the environment. It must be borne in mind, however, that a
species is a morphological rather than a physiological unit, and it is not the
structures but the cell-products that are affected by reagents. Those most
commonly in use are saturated solutions of potash and of bleaching-powder
(calcium hypochlorite). The former is cited in text-books as KOH or simply
as K, the latter as CaCl or C. The C solution deteriorates quickly and must,
therefore, be frequently renewed to produce the required reaction, i.e. some
change of colour. These two reagents are used singly or, if conjointly, K
followed by C. The significance of the colour changes has been considered
in the discussion on lichen-acids.
Iodine is generally cited in connection with its staining effect on the
hymenium of the fruit; the blue colour produced is, however, more general
than was at one time supposed and is not peculiar to lichens; the asci of
required. For this purpose Peirce[21] has recommended that “when dealing
with plants that are dry but still alive, the material should be thoroughly
wetted and kept moist for two days, then killed and fixed in a saturated
solution of corrosive sublimate in thirty-five per cent. alcohol.” The
solution should be used hot: the usual methods of dehydrating and
embedding in paraffin are then employed with extra precautions on account
of the extremely brittle nature of lichens.
Another method that also gave good results has been proposed by
French[22]: “first the lichen is put into 95 per cent. alcohol for 24 hours, then
into thin celloidin and thick celloidin 24 hours each. After this the
specimens are embedded in thick celloidin which is hardened in 70 per cent.
alcohol for 24 hours and then cut.” French advises staining with borax
carmine: it colours the fungal part pale carmine and the algal cells a
greenish-red shade.
Modern research methods of work are generally described in full in the
publications that are discussed in the following chapters. The student is
referred to these original papers for information as to fixing, embedding,
staining, etc.
Great use has been made of reagents in determining lichen species. They
are extremely helpful and often give the clinching decision when
morphological characters are obscure, especially if the plant has been much
altered by the environment. It must be borne in mind, however, that a
species is a morphological rather than a physiological unit, and it is not the
structures but the cell-products that are affected by reagents. Those most
commonly in use are saturated solutions of potash and of bleaching-powder
(calcium hypochlorite). The former is cited in text-books as KOH or simply
as K, the latter as CaCl or C. The C solution deteriorates quickly and must,
therefore, be frequently renewed to produce the required reaction, i.e. some
change of colour. These two reagents are used singly or, if conjointly, K
followed by C. The significance of the colour changes has been considered
in the discussion on lichen-acids.
Iodine is generally cited in connection with its staining effect on the
hymenium of the fruit; the blue colour produced is, however, more general
than was at one time supposed and is not peculiar to lichens; the asci of
Page 36
many fungi react similarly though to a less extent. The medullary hyphae in
certain species also stain blue with iodine.
certain species also stain blue with iodine.
Page 37
CHAPTER I
HISTORY OF LICHENOLOGY
A. Introductory
The term “lichen” is a word of Greek origin used by Theophrastus in his
History of Plants to signify a superficial growth on the bark of olive-trees.
The name was given in the early days of botanical study not to lichens, as
we understand them, but to hepatics of the Marchantia type. Lichens
themselves were generally described along with various other somewhat
similar plants as “Muscus” (Moss) by the older writers, and more definitely
as “Musco-fungus” by Morison[23]. In a botanical work published in 1700
by Tournefort[24] all the members of the vegetable kingdom then known
were for the first time classified in genera, and the genus Lichen was
reserved for the plants that have been so designated since that time, though
Dillenius[25] in his works preferred the adjectival name Lichenoides.
A painstaking historical account of lichens up to the beginning of modern
lichenology has been written by Krempelhuber[26], a German lichenologist.
He has grouped the data compiled by him into a series of Periods, each one
marked by some great advance in knowledge of the subject, though, as we
shall see, the advance from period to period has been continuous and
gradual. While following generally on the lines laid down by
Krempelhuber, it will be possible to cite only the more prominent writers
and it will be of much interest to British readers to note especially the work
of our own botanists.
Krempelhuber’s periods are as follows:
I. From the earliest times to the end of the seventeenth
century.
II. Dating from the arrangement of plants into classes
called genera by Tournefort in 1694 to 1729.
HISTORY OF LICHENOLOGY
A. Introductory
The term “lichen” is a word of Greek origin used by Theophrastus in his
History of Plants to signify a superficial growth on the bark of olive-trees.
The name was given in the early days of botanical study not to lichens, as
we understand them, but to hepatics of the Marchantia type. Lichens
themselves were generally described along with various other somewhat
similar plants as “Muscus” (Moss) by the older writers, and more definitely
as “Musco-fungus” by Morison[23]. In a botanical work published in 1700
by Tournefort[24] all the members of the vegetable kingdom then known
were for the first time classified in genera, and the genus Lichen was
reserved for the plants that have been so designated since that time, though
Dillenius[25] in his works preferred the adjectival name Lichenoides.
A painstaking historical account of lichens up to the beginning of modern
lichenology has been written by Krempelhuber[26], a German lichenologist.
He has grouped the data compiled by him into a series of Periods, each one
marked by some great advance in knowledge of the subject, though, as we
shall see, the advance from period to period has been continuous and
gradual. While following generally on the lines laid down by
Krempelhuber, it will be possible to cite only the more prominent writers
and it will be of much interest to British readers to note especially the work
of our own botanists.
Krempelhuber’s periods are as follows:
I. From the earliest times to the end of the seventeenth
century.
II. Dating from the arrangement of plants into classes
called genera by Tournefort in 1694 to 1729.
Page 38
III. From Micheli’s division of lichens into different
orders in 1729 to 1780.
IV. The definite and reasoned establishment of lichen
genera based on the structure of thallus and fruit by Weber in
1780 to 1803.
V. The arrangement of all known lichens under their
respective genera by Acharius in 1803 to 1846.
VI. The recognition of spore characters in classification
by De Notaris in 1846 to 1867.
A seventh period which includes modern lichenology, and which dates
after the publication of Krempelhuber’s History, was ushered in by
Schwendener’s announcement in 1867 of the hypothesis as to the dual
nature of the lichen thallus. Schwendener’s theory gave a new impulse to
the study of lichens and strongly influenced all succeeding investigations.
B. Period I. Previous to 1694
Our examination of lichen literature takes us back to Theophrastus, the
disciple of Plato and Aristotle, who lived from 371 to 284 b.c., and who
wrote a History of Plants, one of the earliest known treatises on Botany.
Among the plants described by Theophrastus, there are evidently two
lichens, one of which is either an Usnea or an Alectoria, and the other
certainly Roccella tinctoria, the last-named an important economic plant
likely to be well known for its valuable dyeing properties. The same or
somewhat similar lichens are also probably alluded to by the Greek
physician Dioscorides, in his work on Materia Medica, a.d. 68. About the
same time Pliny the elder, who was a soldier and traveller as well as a
voluminous writer, mentions them in his Natural History which was
completed in 77 a.d.
During the centuries that followed, there was little study of Natural
History, and, in any case, lichens were then and for a long time after
considered to be of too little economic value to receive much attention.
orders in 1729 to 1780.
IV. The definite and reasoned establishment of lichen
genera based on the structure of thallus and fruit by Weber in
1780 to 1803.
V. The arrangement of all known lichens under their
respective genera by Acharius in 1803 to 1846.
VI. The recognition of spore characters in classification
by De Notaris in 1846 to 1867.
A seventh period which includes modern lichenology, and which dates
after the publication of Krempelhuber’s History, was ushered in by
Schwendener’s announcement in 1867 of the hypothesis as to the dual
nature of the lichen thallus. Schwendener’s theory gave a new impulse to
the study of lichens and strongly influenced all succeeding investigations.
B. Period I. Previous to 1694
Our examination of lichen literature takes us back to Theophrastus, the
disciple of Plato and Aristotle, who lived from 371 to 284 b.c., and who
wrote a History of Plants, one of the earliest known treatises on Botany.
Among the plants described by Theophrastus, there are evidently two
lichens, one of which is either an Usnea or an Alectoria, and the other
certainly Roccella tinctoria, the last-named an important economic plant
likely to be well known for its valuable dyeing properties. The same or
somewhat similar lichens are also probably alluded to by the Greek
physician Dioscorides, in his work on Materia Medica, a.d. 68. About the
same time Pliny the elder, who was a soldier and traveller as well as a
voluminous writer, mentions them in his Natural History which was
completed in 77 a.d.
During the centuries that followed, there was little study of Natural
History, and, in any case, lichens were then and for a long time after
considered to be of too little economic value to receive much attention.
Page 39
In the sixteenth century there was a great awakening of scientific interest
all over Europe, and, after the printing-press had come into general use, a
number of books bearing on Botany were published. It will be necessary to
chronicle only those that made distinct contributions to the knowledge of
lichens.
The study of plants was at first entirely from a medical standpoint and
one of the first works, and the first book on Natural History, printed in
England, was the Grete Herball[27]. It was translated from a French work,
Hortus sanitatis, and published by Peter Treveris in Southwark. One of the
herbs recommended for various ailments is “Muscus arborum,” the tree-
moss (Usnea). A somewhat crude figure accompanies the text.
Ruel[28] of Soissons in France, Dorstenius[29], Camerarius[30] and
Tabernaemontanus[31] in Germany followed with works on medical or
economic botany and they described, in addition to the tree-moss, several
species of reputed value in the art of healing now known as Sticta (Lobaria)
pulmonaria, Lobaria laetevirens, Cladonia pyxidata, Evernia prunastri and
Cetraria islandica. Meanwhile L’Obel[32], a Fleming, who spent the latter
part of his life in England and is said to have had charge of a physic garden
at Hackney, was appointed botanist to James I. He published at Antwerp a
large series of engravings of plants, and added a species of Ramalina to the
growing list of recognized lichens. Dodoens[33], also a Fleming, records not
only the Usnea of trees, but a smaller and more slender black form which is
easily identifiable as Alectoria jubata. He also figures Lichen pulmonaria
and gives the recipe for its use.
The best-known botanical book published at that time, however, is the
Herball of John Gerard[34] of London, Master in Chirurgerie, who had a
garden in Holborn. He recommends as medicinally valuable not only
Usnea, but also Cladonia pyxidata, for which he coined the name “cuppe-
or chalice-moss.” About the same time Schwenckfeld[35] recorded, among
plants discovered by him in Silesia, lichens now familiar as Alectoria
jubata, Cladonia rangiferina and a species of Peltigera.
Among the more important botanical writers of the seventeenth century
may be cited Colonna[36] and Bauhin[37]. The former, an Italian, contributes,
in his Ecphrasis, descriptions and figures of three additional species easily
all over Europe, and, after the printing-press had come into general use, a
number of books bearing on Botany were published. It will be necessary to
chronicle only those that made distinct contributions to the knowledge of
lichens.
The study of plants was at first entirely from a medical standpoint and
one of the first works, and the first book on Natural History, printed in
England, was the Grete Herball[27]. It was translated from a French work,
Hortus sanitatis, and published by Peter Treveris in Southwark. One of the
herbs recommended for various ailments is “Muscus arborum,” the tree-
moss (Usnea). A somewhat crude figure accompanies the text.
Ruel[28] of Soissons in France, Dorstenius[29], Camerarius[30] and
Tabernaemontanus[31] in Germany followed with works on medical or
economic botany and they described, in addition to the tree-moss, several
species of reputed value in the art of healing now known as Sticta (Lobaria)
pulmonaria, Lobaria laetevirens, Cladonia pyxidata, Evernia prunastri and
Cetraria islandica. Meanwhile L’Obel[32], a Fleming, who spent the latter
part of his life in England and is said to have had charge of a physic garden
at Hackney, was appointed botanist to James I. He published at Antwerp a
large series of engravings of plants, and added a species of Ramalina to the
growing list of recognized lichens. Dodoens[33], also a Fleming, records not
only the Usnea of trees, but a smaller and more slender black form which is
easily identifiable as Alectoria jubata. He also figures Lichen pulmonaria
and gives the recipe for its use.
The best-known botanical book published at that time, however, is the
Herball of John Gerard[34] of London, Master in Chirurgerie, who had a
garden in Holborn. He recommends as medicinally valuable not only
Usnea, but also Cladonia pyxidata, for which he coined the name “cuppe-
or chalice-moss.” About the same time Schwenckfeld[35] recorded, among
plants discovered by him in Silesia, lichens now familiar as Alectoria
jubata, Cladonia rangiferina and a species of Peltigera.
Among the more important botanical writers of the seventeenth century
may be cited Colonna[36] and Bauhin[37]. The former, an Italian, contributes,
in his Ecphrasis, descriptions and figures of three additional species easily
Page 40
recognized as Physcia ciliaris, Xanthoria parietina and Ramalina calicaris.
Kaspar Bauhin, a professor in Basle, who was one of the most advanced of
the older botanists, was the first to use a binomial nomenclature for some of
his plants. He gives a list in his Pinax of the lichens with which he was
acquainted, one of them, Cladonia fimbriata, being a new plant.
John Parkinson’s[38] Herball is well known to English students; he adds
one new species for England, Lobaria pulmonaria, already recorded on the
Continent. Parkinson was an apothecary in London and held the office of
the King’s Herbarist; his garden was situated in Long Acre. How’s[39]
Phytographia is notable as being the first account of British plants compiled
without reference to their healing properties. Five of the plants described by
him are lichen species: “Lichen arborum sive pulmonaria” (Lobaria
pulmonaria), “Lichen petraeus tinctorius” (Roccella), “Muscus arboreus”
(Usnea), “Corallina montana” (Cladonia rangiferina) and “Muscus
pixoides” (Cladonia). Several other British species were added by
Merrett[40], who records in his Pinax, “Muscus arboreus umbilicatus”
(Physcia ciliaris), “Muscus aureus tenuissimus” (Teloschistes flavicans),
“Muscus caule rigido” (Alectoria) and “Lichen petraeus purpureus”
(Parmelia omphalodes), the last-named, a rock lichen, being used, he tells
us, for dyeing in Lancashire.
Merret or Merrett was librarian to the Royal College of Physicians. His
Pinax was undertaken to replace How’s Phytographia published sixteen
years previously and then already out of print. Merrett’s work was issued in
1666, but the first impression was destroyed in the great fire of London and
most of the copies now extant are dated 1667. He arranged the species of
plants in alphabetical order, but as the work was not critical it fell into
disuse, being superseded by John Ray’s Catalogus and Synopsis. To Robert
Plot[41] we owe the earliest record of Cladonia coccifera which had hitherto
escaped notice; it was described and figured as a new and rare plant in the
Natural History of Staffordshire[41]. Plot was the first Custos of Ashmole’s
Museum in Oxford and he was also the first to prepare a County Natural
History.
The greatest advance during this first period was made by Robert
Morison[42], a Scotsman from Aberdeen. He studied medicine at Angers in
France, superintended the Duke of Orleans’ garden at Blois, and finally,
Kaspar Bauhin, a professor in Basle, who was one of the most advanced of
the older botanists, was the first to use a binomial nomenclature for some of
his plants. He gives a list in his Pinax of the lichens with which he was
acquainted, one of them, Cladonia fimbriata, being a new plant.
John Parkinson’s[38] Herball is well known to English students; he adds
one new species for England, Lobaria pulmonaria, already recorded on the
Continent. Parkinson was an apothecary in London and held the office of
the King’s Herbarist; his garden was situated in Long Acre. How’s[39]
Phytographia is notable as being the first account of British plants compiled
without reference to their healing properties. Five of the plants described by
him are lichen species: “Lichen arborum sive pulmonaria” (Lobaria
pulmonaria), “Lichen petraeus tinctorius” (Roccella), “Muscus arboreus”
(Usnea), “Corallina montana” (Cladonia rangiferina) and “Muscus
pixoides” (Cladonia). Several other British species were added by
Merrett[40], who records in his Pinax, “Muscus arboreus umbilicatus”
(Physcia ciliaris), “Muscus aureus tenuissimus” (Teloschistes flavicans),
“Muscus caule rigido” (Alectoria) and “Lichen petraeus purpureus”
(Parmelia omphalodes), the last-named, a rock lichen, being used, he tells
us, for dyeing in Lancashire.
Merret or Merrett was librarian to the Royal College of Physicians. His
Pinax was undertaken to replace How’s Phytographia published sixteen
years previously and then already out of print. Merrett’s work was issued in
1666, but the first impression was destroyed in the great fire of London and
most of the copies now extant are dated 1667. He arranged the species of
plants in alphabetical order, but as the work was not critical it fell into
disuse, being superseded by John Ray’s Catalogus and Synopsis. To Robert
Plot[41] we owe the earliest record of Cladonia coccifera which had hitherto
escaped notice; it was described and figured as a new and rare plant in the
Natural History of Staffordshire[41]. Plot was the first Custos of Ashmole’s
Museum in Oxford and he was also the first to prepare a County Natural
History.
The greatest advance during this first period was made by Robert
Morison[42], a Scotsman from Aberdeen. He studied medicine at Angers in
France, superintended the Duke of Orleans’ garden at Blois, and finally,
Page 41
after his return to this country in 1669, became Keeper of the botanic
garden at Oxford. In the third volume of his great work[42] on Oxford
plants, which was not issued till after his death, the lichens are put in a
separate group—“Musco-fungus”—and classified with some other plants
under “Plantae Heteroclitae.” The publication of the volume projects into
the next historical period.
Long before this date John Ray had begun to study and publish books on
Botany. His Catalogue of English Plants[43] is considered to have
commenced a new era in the study of the science. The Catalogue was
followed by the History of Plants[44], and later by a Synopsis of British
Plants[45], and in all of these books lichens find a place. Two editions of the
Synopsis appeared during Ray’s lifetime, and to the second there is added
an Appendix contributed by Samuel Doody which is entirely devoted to
Cryptogamic plants, including not a few lichens—still called “Mosses”—
discovered for the first time. Doody, himself an apothecary, took charge of
the garden of the Apothecaries’ Society at Chelsea, but his chief interest
was Cryptogamic Botany, a branch of the subject but little regarded before
his day. Pulteney wrote of him as the “Dillenius of his time.”
Among Doody’s associates were the Rev. Adam Buddle, James Petiver
and William Sherard. Buddle was primarily a collector and his herbarium is
incorporated in the Sloane Herbarium at the British Museum. It contains
lichens from all parts of the world, many of them contributed by Doody,
Sherard and Petiver. Only a few of them bear British localities: several are
from Hampstead where Buddle had a church.
The Society of Apothecaries had been founded in 1617 and the members
acquired land on the river-front at Chelsea, which was extended later and
made into a Physick Garden. James Petiver[46] was one of the first
Demonstrators of Plants to the Society in connection with the garden, and
one of his duties was to conduct the annual herborizing tours of the
apprentices in search of plants. He thus collected a large herbarium on the
annual excursions, as well as on shorter visits to the more immediate
neighbourhood of London. He wrote many tracts on Natural History
subjects, and in these some lichens are included. He was one of the best
known of Ray’s correspondents, and owing to his connection with the
Physic Garden received plants from naturalists in foreign countries.
garden at Oxford. In the third volume of his great work[42] on Oxford
plants, which was not issued till after his death, the lichens are put in a
separate group—“Musco-fungus”—and classified with some other plants
under “Plantae Heteroclitae.” The publication of the volume projects into
the next historical period.
Long before this date John Ray had begun to study and publish books on
Botany. His Catalogue of English Plants[43] is considered to have
commenced a new era in the study of the science. The Catalogue was
followed by the History of Plants[44], and later by a Synopsis of British
Plants[45], and in all of these books lichens find a place. Two editions of the
Synopsis appeared during Ray’s lifetime, and to the second there is added
an Appendix contributed by Samuel Doody which is entirely devoted to
Cryptogamic plants, including not a few lichens—still called “Mosses”—
discovered for the first time. Doody, himself an apothecary, took charge of
the garden of the Apothecaries’ Society at Chelsea, but his chief interest
was Cryptogamic Botany, a branch of the subject but little regarded before
his day. Pulteney wrote of him as the “Dillenius of his time.”
Among Doody’s associates were the Rev. Adam Buddle, James Petiver
and William Sherard. Buddle was primarily a collector and his herbarium is
incorporated in the Sloane Herbarium at the British Museum. It contains
lichens from all parts of the world, many of them contributed by Doody,
Sherard and Petiver. Only a few of them bear British localities: several are
from Hampstead where Buddle had a church.
The Society of Apothecaries had been founded in 1617 and the members
acquired land on the river-front at Chelsea, which was extended later and
made into a Physick Garden. James Petiver[46] was one of the first
Demonstrators of Plants to the Society in connection with the garden, and
one of his duties was to conduct the annual herborizing tours of the
apprentices in search of plants. He thus collected a large herbarium on the
annual excursions, as well as on shorter visits to the more immediate
neighbourhood of London. He wrote many tracts on Natural History
subjects, and in these some lichens are included. He was one of the best
known of Ray’s correspondents, and owing to his connection with the
Physic Garden received plants from naturalists in foreign countries.
Page 42
Sherard, another of Doody’s friends, had studied abroad under Tournefort
and was full of enthusiasm for Natural Science. It was he who brought
Dillenius to England and finally nominated him for the position of the first
Sherardian Professor of Botany at Oxford. Another well-known
contemporary botanist was Leonard Plukenet[47] who had a botanical
garden at Old Palace Yard, Westminster. He wrote several botanical works
in which lichens are included.
Morison is the only one of all the botanists of the time who recognized
lichens as a group distinct from mosses, algae or liverworts, and even he
had very vague ideas as to their development. Malpighi[48] had noted the
presence of soredia on the thallus of some species, and regarded them as
seeds. Porta[49], a Neapolitan, has been quoted by Krempelhuber as
probably the first to discover and place on record the direct growth of lichen
fronds from green matter on the trunks of trees.
C. Period II. 1694-1729
The second Period is ushered in with the publication of a French work,
Les Élémens de Botanique by Tournefort[50], who was one of the greatest
botanists of the time. His object was—“to facilitate the knowledge of plants
and to disentangle a science which had been neglected because it was found
to be full of confusion and obscurity.” Up to this date all plants were
classified or listed as individual species. It was Tournefort who first
arranged them in groups which he designated “genera” and he gave a
careful diagnosis of each genus.
Les Élémens was successful enough to warrant the publication a few
years later of a larger Latin edition entitled Institutiones[51] and thus fitted
for a wider circulation. Under the genus Lichen, he included plants “lacking
flowers but with a true cup-shaped shallow fruit, with very minute pollen or
seed which appeared to be subrotund under the microscope.” Not only the
description but the figures prove that he was dealing with ascospores and
not merely soredia, though under Lichen along with true members of the
“genus” he has placed a Marchantia, the moss Splachnum and a fern. A few
lichens were placed by him in another genus Coralloides.
and was full of enthusiasm for Natural Science. It was he who brought
Dillenius to England and finally nominated him for the position of the first
Sherardian Professor of Botany at Oxford. Another well-known
contemporary botanist was Leonard Plukenet[47] who had a botanical
garden at Old Palace Yard, Westminster. He wrote several botanical works
in which lichens are included.
Morison is the only one of all the botanists of the time who recognized
lichens as a group distinct from mosses, algae or liverworts, and even he
had very vague ideas as to their development. Malpighi[48] had noted the
presence of soredia on the thallus of some species, and regarded them as
seeds. Porta[49], a Neapolitan, has been quoted by Krempelhuber as
probably the first to discover and place on record the direct growth of lichen
fronds from green matter on the trunks of trees.
C. Period II. 1694-1729
The second Period is ushered in with the publication of a French work,
Les Élémens de Botanique by Tournefort[50], who was one of the greatest
botanists of the time. His object was—“to facilitate the knowledge of plants
and to disentangle a science which had been neglected because it was found
to be full of confusion and obscurity.” Up to this date all plants were
classified or listed as individual species. It was Tournefort who first
arranged them in groups which he designated “genera” and he gave a
careful diagnosis of each genus.
Les Élémens was successful enough to warrant the publication a few
years later of a larger Latin edition entitled Institutiones[51] and thus fitted
for a wider circulation. Under the genus Lichen, he included plants “lacking
flowers but with a true cup-shaped shallow fruit, with very minute pollen or
seed which appeared to be subrotund under the microscope.” Not only the
description but the figures prove that he was dealing with ascospores and
not merely soredia, though under Lichen along with true members of the
“genus” he has placed a Marchantia, the moss Splachnum and a fern. A few
lichens were placed by him in another genus Coralloides.
Page 43
Tournefort’s system was of great service in promoting the study of
Botany: his method of classification was at once adopted by the German
writer Rupp[52] who published a Flora of plants from Jena. Among these
plants are included twenty-five species of lichens, several of which he
considered new discoveries, no fewer than five being some form of Lichen
gelatinosus (Collema). Buxbaum[53], in his enumeration of plants from
Halle, finds place for forty-nine lichen species, with, in addition, eleven
species of Coralloides; and Vaillant[54] in listing the plants that grew in the
neighbourhood of Paris gives thirty-three species for the genus Lichen of
which a large number are figured, among them species of Ramalina,
Parmelia, Cladonia, etc.
In England, however, Dillenius[55], who at this time brought out a third
edition of Ray’s Synopsis and some years later his own Historia Muscorum,
still described most of his lichens as “Lichenoides” or “Coralloides”; and no
other work of note was published in our country until after the Linnaean
system of classification and of nomenclature was introduced.
D. Period III. 1729-1780
Lichens were henceforth regarded as a distinct genus or section of plants.
Micheli[56], an Italian botanist, Keeper of the Grand Duke’s Gardens in
Florence, realized the desirability of still further delimitation, and he broke
up Tournefort’s large comprehensive genera into numerical Orders. In the
genus Lichen, he found occasion for 38 of these Orders, determined mainly
by the character of the thallus, and the position on it of apothecia and
soredia. He enumerates the species, many of them new discoveries, though
not all of them recognizable now. His great work on Plants is enriched by a
series of beautiful figures. It was published in 1729 and marks the
beginning of a new Period—a new outlook on botanical science. Micheli
regarded the apothecia of lichens as “floral receptacles,” and the soredia as
the seed, because he had himself followed the development of lichen fronds
from soredia.
The next writer of distinction is the afore-mentioned Dillen or Dillenius.
He was a native of Darmstadt and began his scientific career in the
University of Giessen. His first published work[57] was an account of plants
Botany: his method of classification was at once adopted by the German
writer Rupp[52] who published a Flora of plants from Jena. Among these
plants are included twenty-five species of lichens, several of which he
considered new discoveries, no fewer than five being some form of Lichen
gelatinosus (Collema). Buxbaum[53], in his enumeration of plants from
Halle, finds place for forty-nine lichen species, with, in addition, eleven
species of Coralloides; and Vaillant[54] in listing the plants that grew in the
neighbourhood of Paris gives thirty-three species for the genus Lichen of
which a large number are figured, among them species of Ramalina,
Parmelia, Cladonia, etc.
In England, however, Dillenius[55], who at this time brought out a third
edition of Ray’s Synopsis and some years later his own Historia Muscorum,
still described most of his lichens as “Lichenoides” or “Coralloides”; and no
other work of note was published in our country until after the Linnaean
system of classification and of nomenclature was introduced.
D. Period III. 1729-1780
Lichens were henceforth regarded as a distinct genus or section of plants.
Micheli[56], an Italian botanist, Keeper of the Grand Duke’s Gardens in
Florence, realized the desirability of still further delimitation, and he broke
up Tournefort’s large comprehensive genera into numerical Orders. In the
genus Lichen, he found occasion for 38 of these Orders, determined mainly
by the character of the thallus, and the position on it of apothecia and
soredia. He enumerates the species, many of them new discoveries, though
not all of them recognizable now. His great work on Plants is enriched by a
series of beautiful figures. It was published in 1729 and marks the
beginning of a new Period—a new outlook on botanical science. Micheli
regarded the apothecia of lichens as “floral receptacles,” and the soredia as
the seed, because he had himself followed the development of lichen fronds
from soredia.
The next writer of distinction is the afore-mentioned Dillen or Dillenius.
He was a native of Darmstadt and began his scientific career in the
University of Giessen. His first published work[57] was an account of plants
Page 44
that were to be found near Giessen in the different months of the year.
Mosses and lichens he has assigned to December and January. Sherard
induced him to come to England in 1721, and at first engaged his services
in arranging the large collections of plants which he, Sherard, had brought
from Smyrna or acquired from other sources.
Three years after his arrival Dillenius had prepared the third edition of
Ray’s Synopsis for the press, but without putting his name on the title-
page[58]. Sherard explained, in a letter to Dr Richardson of Bierly in
Yorkshire, that “our people can’t agree about an editor, they are unwilling a
foreigner should put his name to it.” Dillenius, who was quite aware of the
prejudice against aliens, himself writes also to Dr Richardson: “there being
some apprehension (me being a foreigner) of making natives uneasy if I
should publicate it in my name.” Lichens were already engaging his
attention, and descriptions of 91 species were added to Ray’s work. So well
did this edition meet the requirements of the age, that the Synopsis remained
the text-book of British Botany until the publication of Hudson’s Flora
Anglica in 1762.
William Sherard died in 1728. He left his books and plates to the
University of Oxford with a sum of money to endow a Professorship of
Botany. In his will he had nominated Dr Dillenius for the post. The great
German botanist was accordingly appointed and became the first Sherardian
Professor of Botany, though he did not remove to Oxford till 1734. The
following years were devoted by him to the preparation of Historia
Muscorum, which was finally published in 1741. It includes an account of
the then known liverworts, mosses and lichens. The latter—still considered
by Dillenius as belonging to mosses—were grouped under three genera,
Usnea, Coralloides and Lichenoides. The descriptions and figures are
excellent, and his notes on occasional lichen characteristics and on localities
are full of interest. His lichen herbarium, which still exists at Oxford,
mounted with the utmost care and neatness, has been critically examined by
Nylander and Crombie[59] and many of the species identified.
Dillenius was ignorant of, or rejected, Micheli’s method of classification,
adopting instead the form of the thallus as a guide to relationship. He also
differed from him in his views as to propagation, regarding the soredia as
the pollen of the lichen, and the apothecia as the seed-vessels, or even in
certain cases as young plants.
Mosses and lichens he has assigned to December and January. Sherard
induced him to come to England in 1721, and at first engaged his services
in arranging the large collections of plants which he, Sherard, had brought
from Smyrna or acquired from other sources.
Three years after his arrival Dillenius had prepared the third edition of
Ray’s Synopsis for the press, but without putting his name on the title-
page[58]. Sherard explained, in a letter to Dr Richardson of Bierly in
Yorkshire, that “our people can’t agree about an editor, they are unwilling a
foreigner should put his name to it.” Dillenius, who was quite aware of the
prejudice against aliens, himself writes also to Dr Richardson: “there being
some apprehension (me being a foreigner) of making natives uneasy if I
should publicate it in my name.” Lichens were already engaging his
attention, and descriptions of 91 species were added to Ray’s work. So well
did this edition meet the requirements of the age, that the Synopsis remained
the text-book of British Botany until the publication of Hudson’s Flora
Anglica in 1762.
William Sherard died in 1728. He left his books and plates to the
University of Oxford with a sum of money to endow a Professorship of
Botany. In his will he had nominated Dr Dillenius for the post. The great
German botanist was accordingly appointed and became the first Sherardian
Professor of Botany, though he did not remove to Oxford till 1734. The
following years were devoted by him to the preparation of Historia
Muscorum, which was finally published in 1741. It includes an account of
the then known liverworts, mosses and lichens. The latter—still considered
by Dillenius as belonging to mosses—were grouped under three genera,
Usnea, Coralloides and Lichenoides. The descriptions and figures are
excellent, and his notes on occasional lichen characteristics and on localities
are full of interest. His lichen herbarium, which still exists at Oxford,
mounted with the utmost care and neatness, has been critically examined by
Nylander and Crombie[59] and many of the species identified.
Dillenius was ignorant of, or rejected, Micheli’s method of classification,
adopting instead the form of the thallus as a guide to relationship. He also
differed from him in his views as to propagation, regarding the soredia as
the pollen of the lichen, and the apothecia as the seed-vessels, or even in
certain cases as young plants.
Page 45
Shortly after the publication of Dillenius’ Historia, appeared Haller’s[60]
Systematic and Descriptive list of plants indigenous to Switzerland. The
lichens are described as without visible leaves or stamens but with
“corpuscula” instead of flowers and leaves. He arranged his lichen species,
160 in all, under seven different Orders: 1. “Lichenes Corniculati and
Pyxidati”; 2. “L. Coralloidei”; 3. “L. Fruticosi”; 4. “L. Pulmonarii”; 5. “L.
Crustacei” (with flower-shields); 6. “L. Scutellis” (with shields but with
little or no thallus); and 7. “L. Crustacei” (without shields).
This period extends till near the end of the eighteenth century, and thus
includes within its scope the foundation of the binomial system of naming
plants established by Linnaeus[61]. The renowned Swedish botanist rather
scorned lichens as “rustici pauperrimi,” happily translated by Schneider[62]
as the “poor trash of vegetation,” but he named and listed about 80 species.
He divided his solitary genus Lichen into sections: 1. “Leprosi tuberculati”;
2. “Leprosi scutellati”; 3. “Imbricati”; 4. “Foliacei”; 5. “Coriacei”; 6.
“Scyphiferi”; 7. “Filamentosi.” By this ordered sequence Linnaeus showed
his appreciation of development, beginning, as he does, with the leprose
crustaceous thallus and continuing up to the most highly organized
filamentous forms. He and his followers still included the genus Lichen
among Algae.
A voluminous History of Plants had been published in 1751 by Sir John
Hill[63], the first superintendent to be appointed to the Royal Gardens, Kew.
In the History lichens are included under the Class “Mosses,” and are
divided into several vaguely limited “genera”—Usnea, tree mosses,
consisting of filaments only; Platysma, flat branched tree mosses, such as
lung-wort; Cladonia, the orchil and coralline mosses, such as Cladonia
furcata; Pyxidium, the cup-mosses; and Placodium, the crustaceous, friable
or gelatinous forms. A number of plants are somewhat obscurely described
under each genus. Not only were these new Lichen genera suggested by
him, but among his plants are such binomials as Usnea compressa,
Platysma corniculatum, Cladonia furcata and Cladonia tophacea; other
lichens are trinomial or are indicated, in the way then customary, by a
whole sentence. Hill’s studies embraced a wide variety of subjects; he had
flashes of insight, but not enough concentration to make an effective
application of his ideas. In his Flora Britannica[64], which was compiled
after the publication of Linnaeus’s Species Plantarum, he abandoned his
Systematic and Descriptive list of plants indigenous to Switzerland. The
lichens are described as without visible leaves or stamens but with
“corpuscula” instead of flowers and leaves. He arranged his lichen species,
160 in all, under seven different Orders: 1. “Lichenes Corniculati and
Pyxidati”; 2. “L. Coralloidei”; 3. “L. Fruticosi”; 4. “L. Pulmonarii”; 5. “L.
Crustacei” (with flower-shields); 6. “L. Scutellis” (with shields but with
little or no thallus); and 7. “L. Crustacei” (without shields).
This period extends till near the end of the eighteenth century, and thus
includes within its scope the foundation of the binomial system of naming
plants established by Linnaeus[61]. The renowned Swedish botanist rather
scorned lichens as “rustici pauperrimi,” happily translated by Schneider[62]
as the “poor trash of vegetation,” but he named and listed about 80 species.
He divided his solitary genus Lichen into sections: 1. “Leprosi tuberculati”;
2. “Leprosi scutellati”; 3. “Imbricati”; 4. “Foliacei”; 5. “Coriacei”; 6.
“Scyphiferi”; 7. “Filamentosi.” By this ordered sequence Linnaeus showed
his appreciation of development, beginning, as he does, with the leprose
crustaceous thallus and continuing up to the most highly organized
filamentous forms. He and his followers still included the genus Lichen
among Algae.
A voluminous History of Plants had been published in 1751 by Sir John
Hill[63], the first superintendent to be appointed to the Royal Gardens, Kew.
In the History lichens are included under the Class “Mosses,” and are
divided into several vaguely limited “genera”—Usnea, tree mosses,
consisting of filaments only; Platysma, flat branched tree mosses, such as
lung-wort; Cladonia, the orchil and coralline mosses, such as Cladonia
furcata; Pyxidium, the cup-mosses; and Placodium, the crustaceous, friable
or gelatinous forms. A number of plants are somewhat obscurely described
under each genus. Not only were these new Lichen genera suggested by
him, but among his plants are such binomials as Usnea compressa,
Platysma corniculatum, Cladonia furcata and Cladonia tophacea; other
lichens are trinomial or are indicated, in the way then customary, by a
whole sentence. Hill’s studies embraced a wide variety of subjects; he had
flashes of insight, but not enough concentration to make an effective
application of his ideas. In his Flora Britannica[64], which was compiled
after the publication of Linnaeus’s Species Plantarum, he abandoned his
Page 46
own arrangement in favour of the one introduced by Linnaeus and accepted
again the single genus Lichen.
Sir William Watson[65], a London apothecary and physician of scientific
repute at this period, proposed a rearrangement and some alteration of
Linnaeus’s sections. He had failed to grasp the principle of development,
but he gives a good general account of the various groups. Watson was the
progenitor of those who decry the makers and multipliers of species. So in
regard to Micheli, who had increased the number to “298,” he writes: “it is
to be regretted, that so indefatigable an author, one whose genius
particularly led him to scrutinize the minuter subjects of the science, should
have been so solicitous to increase the number of species under all his
genera: an error this, which tends to great confusion and embarrassment,
and must retard the progress and real improvement of the botanic science.”
Linnaeus however in redressing the balance earned his full approbation:
“He has so far retrenched the genus (Lichen) that in his general enumeration
of plants he recounts only 80 species belonging to it.”
Linnaeus’s binomial system was almost at once adopted by the whole
botanical world and the discovery and tabulation of lichens as well as of
other plants proceeded apace. Scopoli’s[66] Flora Carniolica, for instance,
published in 1760, still adhered to the old descriptive method of
nomenclature, but a second edition, issued twelve years later, is based on
the new system: it includes 54 lichen species.
About this time Adanson[67] proposed a new classification of plants,
dividing them into families, and these again into sections and genera. He
transferred the lichens to the Family “Fungi,” and one of his sections
contains a number of lichen genera, the names of these being culled from
previous workers, Dillenius, Hill, etc. A few new ones are added by himself,
and one of them, Graphis, still ranks as a good genus.
In England, Hudson[68], who was an apothecary and became sub-librarian
of the British Museum, followed Linnaeus both in the first and later editions
of the Flora Anglica. He records 102 lichen species. Withering[69] was also
engaged, about this time, in compiling his Arrangement of Plants. He
translated Linnaeus’s term “Algae” into the English word “Thongs,” the
lichens being designated as “Cupthongs.” In later editions, he simply
classifies lichens as such. Lightfoot[70], whose descriptive and economic
again the single genus Lichen.
Sir William Watson[65], a London apothecary and physician of scientific
repute at this period, proposed a rearrangement and some alteration of
Linnaeus’s sections. He had failed to grasp the principle of development,
but he gives a good general account of the various groups. Watson was the
progenitor of those who decry the makers and multipliers of species. So in
regard to Micheli, who had increased the number to “298,” he writes: “it is
to be regretted, that so indefatigable an author, one whose genius
particularly led him to scrutinize the minuter subjects of the science, should
have been so solicitous to increase the number of species under all his
genera: an error this, which tends to great confusion and embarrassment,
and must retard the progress and real improvement of the botanic science.”
Linnaeus however in redressing the balance earned his full approbation:
“He has so far retrenched the genus (Lichen) that in his general enumeration
of plants he recounts only 80 species belonging to it.”
Linnaeus’s binomial system was almost at once adopted by the whole
botanical world and the discovery and tabulation of lichens as well as of
other plants proceeded apace. Scopoli’s[66] Flora Carniolica, for instance,
published in 1760, still adhered to the old descriptive method of
nomenclature, but a second edition, issued twelve years later, is based on
the new system: it includes 54 lichen species.
About this time Adanson[67] proposed a new classification of plants,
dividing them into families, and these again into sections and genera. He
transferred the lichens to the Family “Fungi,” and one of his sections
contains a number of lichen genera, the names of these being culled from
previous workers, Dillenius, Hill, etc. A few new ones are added by himself,
and one of them, Graphis, still ranks as a good genus.
In England, Hudson[68], who was an apothecary and became sub-librarian
of the British Museum, followed Linnaeus both in the first and later editions
of the Flora Anglica. He records 102 lichen species. Withering[69] was also
engaged, about this time, in compiling his Arrangement of Plants. He
translated Linnaeus’s term “Algae” into the English word “Thongs,” the
lichens being designated as “Cupthongs.” In later editions, he simply
classifies lichens as such. Lightfoot[70], whose descriptive and economic
Page 47
notes are full of interest, records 103 lichens in the Flora Scotica, and
Dickson[71] shortly after published a number of species from Scotland,
some of them hitherto undescribed. Dickson was a nurseryman who settled
in London, and his avocations kept him in touch with plant-lovers and with
travellers in many lands.
E. Period IV. 1780-1803
The inevitable next advance was made by Weber[72] who at the time was
a Professor at Kiel. In a first work dealing with lichens he had followed
Linnaeus; then he published a new method of classification in which the
lichens are considered as an independent Order of Cryptogamia, and that
Order, called “Aspidoferae,” he subdivided into genera. His ideas had been
partly anticipated by Hill and by Adanson, but the work of Weber indicates
a more correct view of the nature of lichens. He established eight fairly
well-marked genera, viz. Verrucaria, Tubercularia, Sphaerocephalum and
Placodium, which were based on fruit-characters, the thallus being
crustaceous and rather insignificant, and a second group Lichen, Collema,
Cladonia and Usnea, in which the thallus ranked first in importance.
Though Weber’s scheme was published in 1780, it did not at first secure
much attention. The great authority of Linnaeus dominated so strongly the
botany of the period that for a long time no change was welcomed or even
tolerated.
In our own country Relhan at Cambridge and Sibthorp[73] at Oxford were
making extensive studies of plants. The latter was content to follow
Linnaeus in his treatment of lichens. Relhan[74] also grouped his lichens
under one genus though, in a second edition of his Flora, he broke away
from the Linnaean tradition and adopted the classification of Acharius.
Extensive contributions to the knowledge of English plants generally
were made by Sir James Edward Smith[75] who, in 1788, founded the
Linnean Society of London of which he was President until his death in
1828. He began his great work, English Botany, in 1790 with James
Sowerby as artist. Smith’s and Sowerby’s part of the work came to an end
in 1814; but a supplement was begun in 1831 by Hooker who had the
assistance of Sowerby’s sons in preparing the drawings. Nearly all the
Dickson[71] shortly after published a number of species from Scotland,
some of them hitherto undescribed. Dickson was a nurseryman who settled
in London, and his avocations kept him in touch with plant-lovers and with
travellers in many lands.
E. Period IV. 1780-1803
The inevitable next advance was made by Weber[72] who at the time was
a Professor at Kiel. In a first work dealing with lichens he had followed
Linnaeus; then he published a new method of classification in which the
lichens are considered as an independent Order of Cryptogamia, and that
Order, called “Aspidoferae,” he subdivided into genera. His ideas had been
partly anticipated by Hill and by Adanson, but the work of Weber indicates
a more correct view of the nature of lichens. He established eight fairly
well-marked genera, viz. Verrucaria, Tubercularia, Sphaerocephalum and
Placodium, which were based on fruit-characters, the thallus being
crustaceous and rather insignificant, and a second group Lichen, Collema,
Cladonia and Usnea, in which the thallus ranked first in importance.
Though Weber’s scheme was published in 1780, it did not at first secure
much attention. The great authority of Linnaeus dominated so strongly the
botany of the period that for a long time no change was welcomed or even
tolerated.
In our own country Relhan at Cambridge and Sibthorp[73] at Oxford were
making extensive studies of plants. The latter was content to follow
Linnaeus in his treatment of lichens. Relhan[74] also grouped his lichens
under one genus though, in a second edition of his Flora, he broke away
from the Linnaean tradition and adopted the classification of Acharius.
Extensive contributions to the knowledge of English plants generally
were made by Sir James Edward Smith[75] who, in 1788, founded the
Linnean Society of London of which he was President until his death in
1828. He began his great work, English Botany, in 1790 with James
Sowerby as artist. Smith’s and Sowerby’s part of the work came to an end
in 1814; but a supplement was begun in 1831 by Hooker who had the
assistance of Sowerby’s sons in preparing the drawings. Nearly all the
Page 48
lichens recorded by Smith are published simply as Lichen, and his Botany
thus belongs to the period under discussion, though in time it stretches far
beyond.
Continental lichenologists had been more receptive to new ideas, and
other genera were gradually added to Weber’s list, notably by Hoffmann[76]
and Persoon[77].
For a long time little was known of the lichens of other than European
countries. Buxbaum[78] in the East, Petiver[79] and Hans Sloane[80] in the
West made the first exotic records. The latter notes how frequently lichens
grew on the imported Jesuit’s bark, and he quaintly suggests in regard to
some of these species that they may be identical with the “hyssop that
springeth out of the wall.” It was not however till towards the end of the
eighteenth century that much attention was given to foreign lichens, when
Swartz[81] in the West Indies and Desfontaines[82] in N. Africa collected and
recorded a fair number. Swartz describes about twenty species collected on
his journey through the West Indian Islands (1783-87).
Interest was also growing in other aspects of lichenology. Georgi[83], a
Russian Professor, was the first to make a chemical analysis of lichens. He
experimented on some of the larger forms and extracted and examined the
mucilaginous contents of Ramalina farinacea, Platysma glaucum, Lobaria
pulmonaria, etc., which he collected from birch and pine trees. About this
time also the French scientists Willomet[84], Amoreux and Hoffmann jointly
published theses setting forth the economic value of such lichens as were
used in the arts, as food, or as medicine.
F. Period V. 1803-1846
The fine constructive work of Acharius appropriately begins a new era in
the history of lichenology. Previous writers had indeed included lichens in
their survey of plants, but always as a somewhat side issue. Acharius made
them a subject of special study, and by his scientific system of classification
raised them to the rank of the other great classes of plants.
Acharius was a country doctor at Wadstena on Lake Mälar in Sweden, as
he himself calls it, “the country of lichens.” He was attracted to the study of
them by their singular mode of growth and organization, both of thallus and
thus belongs to the period under discussion, though in time it stretches far
beyond.
Continental lichenologists had been more receptive to new ideas, and
other genera were gradually added to Weber’s list, notably by Hoffmann[76]
and Persoon[77].
For a long time little was known of the lichens of other than European
countries. Buxbaum[78] in the East, Petiver[79] and Hans Sloane[80] in the
West made the first exotic records. The latter notes how frequently lichens
grew on the imported Jesuit’s bark, and he quaintly suggests in regard to
some of these species that they may be identical with the “hyssop that
springeth out of the wall.” It was not however till towards the end of the
eighteenth century that much attention was given to foreign lichens, when
Swartz[81] in the West Indies and Desfontaines[82] in N. Africa collected and
recorded a fair number. Swartz describes about twenty species collected on
his journey through the West Indian Islands (1783-87).
Interest was also growing in other aspects of lichenology. Georgi[83], a
Russian Professor, was the first to make a chemical analysis of lichens. He
experimented on some of the larger forms and extracted and examined the
mucilaginous contents of Ramalina farinacea, Platysma glaucum, Lobaria
pulmonaria, etc., which he collected from birch and pine trees. About this
time also the French scientists Willomet[84], Amoreux and Hoffmann jointly
published theses setting forth the economic value of such lichens as were
used in the arts, as food, or as medicine.
F. Period V. 1803-1846
The fine constructive work of Acharius appropriately begins a new era in
the history of lichenology. Previous writers had indeed included lichens in
their survey of plants, but always as a somewhat side issue. Acharius made
them a subject of special study, and by his scientific system of classification
raised them to the rank of the other great classes of plants.
Acharius was a country doctor at Wadstena on Lake Mälar in Sweden, as
he himself calls it, “the country of lichens.” He was attracted to the study of
them by their singular mode of growth and organization, both of thallus and
Page 49
reproductive organs, for which reason he finally judged that lichens should
be considered as a distinct Order of Cryptogamia.
In his first tentative work[85] he had followed his great compatriot
Linnaeus, classifying all the species known to him under the one genus
Lichen, though he had progressed so far as to divide the unwieldy Genus
into Families and these again into Tribes, these latter having each a tribal
designation such as Verrucaria, Opegrapha, etc. He established in all
twenty-eight tribes which, at a later stage, he transformed into genera after
the example of Weber.
Acharius, from the beginning of his work, had allowed great importance
to the structure of the apothecia as a diagnostic character though scarcely
recognizing them as true fruits. He gave expression to his more mature
views first in the Methodus Lichenum[86], then subsequently in the larger
Lichenographia Universalia[87]. In the latter work there are forty-one
genera arranged under different divisions; the species are given short and
succinct descriptions, with habitat, locality and synonymy. No material
alteration was made in the Synopsis Lichenum[88], a more condensed work
which he published a few years later.
The Cryptogamia are divided by Acharius into six “Families,” one of
which, “Lichenes,” is distinguished, he finds, by two methods of
propagation: by propagula (soredia) and by spores produced in apothecia.
He divides the family into classes characterized solely by fruit characters,
and these again into orders, genera and species, of which diagnoses are
given. With fuller knowledge many changes and rearrangements have been
found necessary in the application and extension of the system, but that in
no way detracts from the value of the work as a whole.
In addition to founding a scientific classification, Acharius invented a
terminology for the structures peculiar to lichens. We owe to him the names
and descriptions of “thallus,” “podetium,” “apothecium,” “perithecium,”
“soredium,” “cyphella” and “cephalodium,” the last word however with a
different meaning from the one now given to it. He proposed several others,
some of which are redundant or have fallen into disuse, but many of his
terms as we see have stood the test of time and have been found of service
in allied branches of botany.
be considered as a distinct Order of Cryptogamia.
In his first tentative work[85] he had followed his great compatriot
Linnaeus, classifying all the species known to him under the one genus
Lichen, though he had progressed so far as to divide the unwieldy Genus
into Families and these again into Tribes, these latter having each a tribal
designation such as Verrucaria, Opegrapha, etc. He established in all
twenty-eight tribes which, at a later stage, he transformed into genera after
the example of Weber.
Acharius, from the beginning of his work, had allowed great importance
to the structure of the apothecia as a diagnostic character though scarcely
recognizing them as true fruits. He gave expression to his more mature
views first in the Methodus Lichenum[86], then subsequently in the larger
Lichenographia Universalia[87]. In the latter work there are forty-one
genera arranged under different divisions; the species are given short and
succinct descriptions, with habitat, locality and synonymy. No material
alteration was made in the Synopsis Lichenum[88], a more condensed work
which he published a few years later.
The Cryptogamia are divided by Acharius into six “Families,” one of
which, “Lichenes,” is distinguished, he finds, by two methods of
propagation: by propagula (soredia) and by spores produced in apothecia.
He divides the family into classes characterized solely by fruit characters,
and these again into orders, genera and species, of which diagnoses are
given. With fuller knowledge many changes and rearrangements have been
found necessary in the application and extension of the system, but that in
no way detracts from the value of the work as a whole.
In addition to founding a scientific classification, Acharius invented a
terminology for the structures peculiar to lichens. We owe to him the names
and descriptions of “thallus,” “podetium,” “apothecium,” “perithecium,”
“soredium,” “cyphella” and “cephalodium,” the last word however with a
different meaning from the one now given to it. He proposed several others,
some of which are redundant or have fallen into disuse, but many of his
terms as we see have stood the test of time and have been found of service
in allied branches of botany.
Page 50
Lichens were studied with great zest by the men of that day. Hue[89]
recalls a rather startling incident in this connection: Wahlberg, it is said, had
informed Dufour that he had sent a large collection of lichens from Spain to
Acharius who was so excited on receiving them, that he fell ill and died in a
few days (Aug. 14th, 1819). Dufour, however, had added the comment that
the illness and death might after all be merely a coincidence.
Among contemporary botanists, we find that De Candolle[90] in the
volume he contributed to Lamarck’s French Flora, quotes only from the
earlier work of Acharius. He had probably not then seen the Methodus, as
he uses none of the new terms; the lichens of the volume are arranged under
genera which are based more or less on the position of the apothecia on the
thallus. Flörke[91], the next writer of consequence, frankly accepts the
terminology and the new view of classification, though differing on some
minor points.
Two lists of lichens, neither of particular note, were published at this time
in our country: one by Hugh Davies[92] for Wales, which adheres to the
Linnaean system, and the other by Forster[93] of lichens round Tonbridge.
Though Forster adopts the genera of Acharius, he includes lichens among
algae. A more important publication was S. F. Gray’s[94] Natural
Arrangement of British Plants. Gray, who was a druggist in Walsall and
afterwards a lecturer on botany in London, was only nominally[95] the
author, as it was mainly the work of his son John Edward Gray[96],
sometime Keeper of Zoology in the British Museum. Gray was the first to
apply the principles of the Natural System of classification to British plants,
but the work was opposed by British botanists of his day. The years
following the French Revolution and the Napoleonic wars were full of bitter
feeling and of prejudice, and anything emanating, as did the Natural
System, from France was rejected as unworthy of consideration.
In the Natural Arrangement, Gray followed Acharius in his treatment of
lichens; but whereas Acharius, though here and there confusing fungus
species with lichens, had been clear-sighted enough to avoid all
intermixture of fungus genera, with the exception of one only, the sterile
genus Rhizomorpha, Gray had allowed the interpolation of several, such as
Hysterium, Xylaria, Hypoxylon, etc. He had also raised many of Acharius’s
subgenera and divisions to the rank of genera, thus largely increasing their
recalls a rather startling incident in this connection: Wahlberg, it is said, had
informed Dufour that he had sent a large collection of lichens from Spain to
Acharius who was so excited on receiving them, that he fell ill and died in a
few days (Aug. 14th, 1819). Dufour, however, had added the comment that
the illness and death might after all be merely a coincidence.
Among contemporary botanists, we find that De Candolle[90] in the
volume he contributed to Lamarck’s French Flora, quotes only from the
earlier work of Acharius. He had probably not then seen the Methodus, as
he uses none of the new terms; the lichens of the volume are arranged under
genera which are based more or less on the position of the apothecia on the
thallus. Flörke[91], the next writer of consequence, frankly accepts the
terminology and the new view of classification, though differing on some
minor points.
Two lists of lichens, neither of particular note, were published at this time
in our country: one by Hugh Davies[92] for Wales, which adheres to the
Linnaean system, and the other by Forster[93] of lichens round Tonbridge.
Though Forster adopts the genera of Acharius, he includes lichens among
algae. A more important publication was S. F. Gray’s[94] Natural
Arrangement of British Plants. Gray, who was a druggist in Walsall and
afterwards a lecturer on botany in London, was only nominally[95] the
author, as it was mainly the work of his son John Edward Gray[96],
sometime Keeper of Zoology in the British Museum. Gray was the first to
apply the principles of the Natural System of classification to British plants,
but the work was opposed by British botanists of his day. The years
following the French Revolution and the Napoleonic wars were full of bitter
feeling and of prejudice, and anything emanating, as did the Natural
System, from France was rejected as unworthy of consideration.
In the Natural Arrangement, Gray followed Acharius in his treatment of
lichens; but whereas Acharius, though here and there confusing fungus
species with lichens, had been clear-sighted enough to avoid all
intermixture of fungus genera, with the exception of one only, the sterile
genus Rhizomorpha, Gray had allowed the interpolation of several, such as
Hysterium, Xylaria, Hypoxylon, etc. He had also raised many of Acharius’s
subgenera and divisions to the rank of genera, thus largely increasing their
Page 51
number. This oversplitting of well-defined genera has somewhat weakened
Gray’s work and he has not received from later writers the attention he
deserves.
The lichens of Hooker’s[97] Flora Scotica, which is synchronous with
Gray’s work, number 195 species, an increase of about 90 for Scotland
since the publication of Lightfoot’s Flora more than 40 years before.
Hooker also followed Acharius in his classification of lichens both in the
Flora Scotica and in the Supplement to English Botany[98], which was
undertaken by the younger Sowerbys and himself. To that work Borrer
(1781-1862), a keen lichenologist, supplied many new and rare lichens
collected mostly in Sussex.
It is a matter of regret that Greville should have so entirely ignored
lichens in his great work on Scottish Cryptogams[99]. The two species of
Lichina are the only ones he figured, and these he took to be algae. He[100]
was well acquainted with lichens, for in the Flora Edinensis he lists 128
species for the Edinburgh district, arranging the genera under “Lichenes”
with the exception of Opegrapha and Verrucaria which are placed with the
fungus genus Poronia in “Hypoxyla.” Though he cites the publications of
Acharius, he does not employ his scientific terms, possibly because he was
writing his diagnoses in English. Two other British works of this time still
remain to be chronicled: Hooker’s[101] contributions to Smith’s English
Flora and Taylor’s[102] work on lichens in Mackay’s Flora Hibernica.
Through these the knowledge of the subject was very largely extended in
our country.
The classification of lichens and their place in the vegetable kingdom
were now firmly established on the lines laid down by Acharius. Fries[103]
in his important work Lichenographia Europaea more or less followed his
distinguished countryman. The uncertainty as to the position and
relationship of lichens had rendered the task of systematic arrangement one
of peculiar difficulty and had unduly absorbed attention; but now that a
satisfactory order had been established in the chaos of forms, the way was
clear for other aspects of the study. Several writers expressed their views by
suggesting somewhat different methods of classification, others wrote
monographs of separate groups, or genera. Fée[104] published an Essay on
the Cryptogams (mostly lichens) that grew on officinal exotic barks;
Gray’s work and he has not received from later writers the attention he
deserves.
The lichens of Hooker’s[97] Flora Scotica, which is synchronous with
Gray’s work, number 195 species, an increase of about 90 for Scotland
since the publication of Lightfoot’s Flora more than 40 years before.
Hooker also followed Acharius in his classification of lichens both in the
Flora Scotica and in the Supplement to English Botany[98], which was
undertaken by the younger Sowerbys and himself. To that work Borrer
(1781-1862), a keen lichenologist, supplied many new and rare lichens
collected mostly in Sussex.
It is a matter of regret that Greville should have so entirely ignored
lichens in his great work on Scottish Cryptogams[99]. The two species of
Lichina are the only ones he figured, and these he took to be algae. He[100]
was well acquainted with lichens, for in the Flora Edinensis he lists 128
species for the Edinburgh district, arranging the genera under “Lichenes”
with the exception of Opegrapha and Verrucaria which are placed with the
fungus genus Poronia in “Hypoxyla.” Though he cites the publications of
Acharius, he does not employ his scientific terms, possibly because he was
writing his diagnoses in English. Two other British works of this time still
remain to be chronicled: Hooker’s[101] contributions to Smith’s English
Flora and Taylor’s[102] work on lichens in Mackay’s Flora Hibernica.
Through these the knowledge of the subject was very largely extended in
our country.
The classification of lichens and their place in the vegetable kingdom
were now firmly established on the lines laid down by Acharius. Fries[103]
in his important work Lichenographia Europaea more or less followed his
distinguished countryman. The uncertainty as to the position and
relationship of lichens had rendered the task of systematic arrangement one
of peculiar difficulty and had unduly absorbed attention; but now that a
satisfactory order had been established in the chaos of forms, the way was
clear for other aspects of the study. Several writers expressed their views by
suggesting somewhat different methods of classification, others wrote
monographs of separate groups, or genera. Fée[104] published an Essay on
the Cryptogams (mostly lichens) that grew on officinal exotic barks;
Page 52
Flörke[105] took up the difficult genus Cladonia; Wallroth[106] also wrote on
Cladonia; Delise[107] on Sticta, and Chevalier[108] published a long and
elaborate account of Graphideae.
Wallroth and Meyer at this time published, simultaneously, important
studies on the general morphology and physiology of lichens. Wallroth[109]
had contemplated an even larger work on the Natural History of Lichens,
but only two of the volumes reached publication. In the first of these he
devoted much attention to the “gonidia” or “brood-cells” and established
the distinction between the heteromerous and homoiomerous distribution of
green cells within the thallus; he also describes with great detail the
“morphosis” and “metamorphosis” of the vegetative body. In the second
volume he discusses their physiology—the contents and products of the
thallus, colouring, nutrition, season of development, etc.—and finally the
pathology of these organisms. He made no great use of the compound
microscope, and his studies were confined to phenomena that could be
observed with a single lens.
Meyer’s[110] work contains a still more exact study of the anatomy and
physiology of lichens; he also devotes many passages to an account of their
metamorphoses, pointing out that species alter so much in varying
conditions, that the same one at different stages may be placed even in
different genera; he however carries his theory of metamorphosis too far
and unites together widely separated plants. Meyer was the first to describe
the growth of the lichen from spores, though his description is somewhat
confused. Possibly the honour of having first observed their germination
should be given to a later botanist, Holle[111]. The works of both Wallroth
and Meyer enjoyed a great and well-merited reputation: they were standard
books of consultation for many years. Koerber[112], who devoted a long
treatise to the study of gonidia, confirmed Wallroth’s theories: he
considered at that time that the gonidia in the soredial condition were
organs of propagation.
Mention should be made here of the many able and keen collectors who,
in the latter half of the eighteenth century and the beginning of the
nineteenth, did so much to further the knowledge of lichens in the British
Isles. Among the earliest of these naturalists are Richard Pulteney (1730-
1801), whose collection of plants, now in the herbarium of the British
Cladonia; Delise[107] on Sticta, and Chevalier[108] published a long and
elaborate account of Graphideae.
Wallroth and Meyer at this time published, simultaneously, important
studies on the general morphology and physiology of lichens. Wallroth[109]
had contemplated an even larger work on the Natural History of Lichens,
but only two of the volumes reached publication. In the first of these he
devoted much attention to the “gonidia” or “brood-cells” and established
the distinction between the heteromerous and homoiomerous distribution of
green cells within the thallus; he also describes with great detail the
“morphosis” and “metamorphosis” of the vegetative body. In the second
volume he discusses their physiology—the contents and products of the
thallus, colouring, nutrition, season of development, etc.—and finally the
pathology of these organisms. He made no great use of the compound
microscope, and his studies were confined to phenomena that could be
observed with a single lens.
Meyer’s[110] work contains a still more exact study of the anatomy and
physiology of lichens; he also devotes many passages to an account of their
metamorphoses, pointing out that species alter so much in varying
conditions, that the same one at different stages may be placed even in
different genera; he however carries his theory of metamorphosis too far
and unites together widely separated plants. Meyer was the first to describe
the growth of the lichen from spores, though his description is somewhat
confused. Possibly the honour of having first observed their germination
should be given to a later botanist, Holle[111]. The works of both Wallroth
and Meyer enjoyed a great and well-merited reputation: they were standard
books of consultation for many years. Koerber[112], who devoted a long
treatise to the study of gonidia, confirmed Wallroth’s theories: he
considered at that time that the gonidia in the soredial condition were
organs of propagation.
Mention should be made here of the many able and keen collectors who,
in the latter half of the eighteenth century and the beginning of the
nineteenth, did so much to further the knowledge of lichens in the British
Isles. Among the earliest of these naturalists are Richard Pulteney (1730-
1801), whose collection of plants, now in the herbarium of the British
Page 53
Museum, includes many lichens, and Hugh Davies (1739-1821), a
clergyman whose Welsh plants also form part of the Museum collection.
The Rev. John Harriman (1760-1831) sent many rare plants from
Egglestone in Durham to the editors of English Botany and among them
were not a few lichens. Edward Forster (1765-1849) lived in Essex and
collected in that county, more especially in and near Epping Forest, and
another East country botanist, Dawson Turner (1775-1858), though chiefly
known as an algologist, gave considerable attention to lichens. In Scotland
the two most active workers were Charles Lyell (1767-1849), of Kinnordy
in Forfarshire, and George Don (1798-1856), also a Forfar man. Don was a
gardener and became eventually a foreman at the Chelsea Physic Garden.
Sir Thomas Gage of Hengrave Hall (1781-1823) botanized chiefly in his
own county of Suffolk; but most of his lichens were collected in South
Ireland and are incorporated in the herbarium of the British Museum. Miss
Hutchins also collected in Ireland and sent her plants for inclusion in
English Botany. But in later years, the principal lichenologist connected
with that great undertaking was W. Borrer, who spent his life in Sussex: he
not only supplied a large number of specimens to the authors, but he
himself discovered and described many new lichens.
American lichenologists were also extremely active all through this
period. The comparatively few lichens of Michaux’s[113] Flora grouped
under “Lichenaceae” were collected in such widely separated regions as
Carolina and Canada. A few years later Mühlenberg[114] included no fewer
than 184 species in his Catalogue of North American Plants. Torrey[115] and
Halsey[116] botanized over a limited area near New York, and the latter, who
devoted himself more especially to lichens, succeeded in recording 176
different forms, old and new. These two botanists were both indebted for
help in their work to Schweinitz, a Moravian brother, who moved from one
country to another, working and publishing, now in America and now in
Europe. His name is however chiefly associated with fungi. Later American
lichenology is nobly represented by Tuckerman[117] who issued his first
work on lichens in 1839, and who continued for many years to devote
himself to the subject. He followed at first the classification and
nomenclature that had been adopted by Fée, but as time went on he
associated himself with all that was best and most enlightened in the
growing science.
clergyman whose Welsh plants also form part of the Museum collection.
The Rev. John Harriman (1760-1831) sent many rare plants from
Egglestone in Durham to the editors of English Botany and among them
were not a few lichens. Edward Forster (1765-1849) lived in Essex and
collected in that county, more especially in and near Epping Forest, and
another East country botanist, Dawson Turner (1775-1858), though chiefly
known as an algologist, gave considerable attention to lichens. In Scotland
the two most active workers were Charles Lyell (1767-1849), of Kinnordy
in Forfarshire, and George Don (1798-1856), also a Forfar man. Don was a
gardener and became eventually a foreman at the Chelsea Physic Garden.
Sir Thomas Gage of Hengrave Hall (1781-1823) botanized chiefly in his
own county of Suffolk; but most of his lichens were collected in South
Ireland and are incorporated in the herbarium of the British Museum. Miss
Hutchins also collected in Ireland and sent her plants for inclusion in
English Botany. But in later years, the principal lichenologist connected
with that great undertaking was W. Borrer, who spent his life in Sussex: he
not only supplied a large number of specimens to the authors, but he
himself discovered and described many new lichens.
American lichenologists were also extremely active all through this
period. The comparatively few lichens of Michaux’s[113] Flora grouped
under “Lichenaceae” were collected in such widely separated regions as
Carolina and Canada. A few years later Mühlenberg[114] included no fewer
than 184 species in his Catalogue of North American Plants. Torrey[115] and
Halsey[116] botanized over a limited area near New York, and the latter, who
devoted himself more especially to lichens, succeeded in recording 176
different forms, old and new. These two botanists were both indebted for
help in their work to Schweinitz, a Moravian brother, who moved from one
country to another, working and publishing, now in America and now in
Europe. His name is however chiefly associated with fungi. Later American
lichenology is nobly represented by Tuckerman[117] who issued his first
work on lichens in 1839, and who continued for many years to devote
himself to the subject. He followed at first the classification and
nomenclature that had been adopted by Fée, but as time went on he
associated himself with all that was best and most enlightened in the
growing science.
Page 54
Travellers and explorers in those days of high adventure were constantly
sending their specimens to European botanists for examination and
determination, and the knowledge of exotic lichens as of other classes of
plants grew with opportunity. Among the principal home workers in foreign
material, at this time, may be cited Fée[118] who described a very large
series on officinal barks (Cinchona, etc.) so largely coming into use as
medicines; he also took charge of the lichens in Martius’s[119] Flora of
Brazil. Montagne[120] named large collections, notably those of Leprieur
collected in Guiana, and Hooker[121] and Walker Arnott determined the
plants collected during Captain Beechey’s voyage, which included lichens
from many different regions.
G. Period VI. 1846-1867
The last work of importance, in which microscopic characters were
ignored, was the Enumeratio critica Lichenum Europaeum by Schaerer[122],
a veteran lichenologist, who rather sadly realized at the end the limitations
of that work, as he asks the reader to accept it “such as it is.” Many years
previously, Eschweiler[123] in his Systema and Fée[124] in his account of
Cryptogams on Officinal Bark, had given particular attention to the internal
structure as well as to the outward form of the lichen fructification. Fée,
more especially, had described and figured a large number of spores; but
neither writer had done more than suggest their value as a guide in the
determination of genera and species.
It was an Italian botanist, Giuseppe de Notaris[125], a Professor in
Florence, who took up the work where Fée had left it. His comparative
studies of both vegetative and reproductive organs convinced him of the
great importance of spore characters in classification, the spore being, as he
rightly decided, the highest and ultimate product of the lichen plant. In his
microscopic examination of the various recognized genera, he found that
while, in some genera, the spores conformed to one distinct type, in others
their diversities in form, septation or colour gave a decisive reason for the
establishment of new genera, while minor differences in size, etc. of the
spores proved to be of great value in distinguishing species. The spore
standard thus marks a new departure in lichenology. De Notaris published
the results of his researches in a fragment of a projected larger work that
sending their specimens to European botanists for examination and
determination, and the knowledge of exotic lichens as of other classes of
plants grew with opportunity. Among the principal home workers in foreign
material, at this time, may be cited Fée[118] who described a very large
series on officinal barks (Cinchona, etc.) so largely coming into use as
medicines; he also took charge of the lichens in Martius’s[119] Flora of
Brazil. Montagne[120] named large collections, notably those of Leprieur
collected in Guiana, and Hooker[121] and Walker Arnott determined the
plants collected during Captain Beechey’s voyage, which included lichens
from many different regions.
G. Period VI. 1846-1867
The last work of importance, in which microscopic characters were
ignored, was the Enumeratio critica Lichenum Europaeum by Schaerer[122],
a veteran lichenologist, who rather sadly realized at the end the limitations
of that work, as he asks the reader to accept it “such as it is.” Many years
previously, Eschweiler[123] in his Systema and Fée[124] in his account of
Cryptogams on Officinal Bark, had given particular attention to the internal
structure as well as to the outward form of the lichen fructification. Fée,
more especially, had described and figured a large number of spores; but
neither writer had done more than suggest their value as a guide in the
determination of genera and species.
It was an Italian botanist, Giuseppe de Notaris[125], a Professor in
Florence, who took up the work where Fée had left it. His comparative
studies of both vegetative and reproductive organs convinced him of the
great importance of spore characters in classification, the spore being, as he
rightly decided, the highest and ultimate product of the lichen plant. In his
microscopic examination of the various recognized genera, he found that
while, in some genera, the spores conformed to one distinct type, in others
their diversities in form, septation or colour gave a decisive reason for the
establishment of new genera, while minor differences in size, etc. of the
spores proved to be of great value in distinguishing species. The spore
standard thus marks a new departure in lichenology. De Notaris published
the results of his researches in a fragment of a projected larger work that
Page 55
was never completed. Though his views were overlooked for a time, they
were at length fully recognized and further elaborated by Massalongo[126] in
Italy, by Norman[127] in Norway, by Koerber[128] in Germany and by
Mudd[129] in our own country. Massalongo had drawn up the scheme of a
great Scolia Lichenographica, but like de Notaris, he was only able to
publish a part. After twelve years of ill-health, in which he struggled to
continue his work, he died at the early age of 36.
Lindsay[130], Mudd and Leighton[131] were at this time devoting great
attention to British lichens. Lauder Lindsay’s Popular History of British
Lichens, with its coloured plates and its descriptive and economic account
of these plants has enabled many to acquire a wide knowledge of the group.
Mudd’s Manual, a more complete and extremely valuable contribution to
the subject, followed entirely on the lines of Massalongo’s work. From his
large experience in the examination of lichens he came to the conclusion
that: “Of all organs furnished by a given group of plants, none offer so
many real, constant and physiological characters as the spores of lichens,
for the formation of a simple and natural classification.”
Meanwhile, a contemporary writer, William Nylander, was rising into
fame. He was born at Uleaborg in Finland[132] in 1822 and became
interested in lichens very early in his career. His first post was the
professorship of botany at Helsingfors; but in 1863 he gave up his chair and
removed to Paris where he remained, except for short absences, until his
death. One of his excursions brought him to London in 1857 to examine
Hooker’s herbarium. He devoted his whole life to the study of lichens, and
from 1852, the date of his first lichen publication, which is an account of
the lichens of Helsingfors, to the end of his life he poured out a constant
succession of books or papers, most of them in Latin. One of his earliest
works was an Essay on Classification[133] which he elaborated later, but
which in its main features he never altered. He relied, in his system, on the
structure and form of thallus, gonidia and fructifications, more especially on
those of the spermogonia (pycnidia), but he rejected ascospore characters
except so far as they were of use in the diagnosis of species. He failed by
being too isolated and by his unwillingness to recognize results obtained by
other workers. In 1866 he had discovered the staining reactions of potash
and hypochlorite of lime on certain thalli, and though these are at times
unreliable owing to growth conditions, etc., they have generally been of real
were at length fully recognized and further elaborated by Massalongo[126] in
Italy, by Norman[127] in Norway, by Koerber[128] in Germany and by
Mudd[129] in our own country. Massalongo had drawn up the scheme of a
great Scolia Lichenographica, but like de Notaris, he was only able to
publish a part. After twelve years of ill-health, in which he struggled to
continue his work, he died at the early age of 36.
Lindsay[130], Mudd and Leighton[131] were at this time devoting great
attention to British lichens. Lauder Lindsay’s Popular History of British
Lichens, with its coloured plates and its descriptive and economic account
of these plants has enabled many to acquire a wide knowledge of the group.
Mudd’s Manual, a more complete and extremely valuable contribution to
the subject, followed entirely on the lines of Massalongo’s work. From his
large experience in the examination of lichens he came to the conclusion
that: “Of all organs furnished by a given group of plants, none offer so
many real, constant and physiological characters as the spores of lichens,
for the formation of a simple and natural classification.”
Meanwhile, a contemporary writer, William Nylander, was rising into
fame. He was born at Uleaborg in Finland[132] in 1822 and became
interested in lichens very early in his career. His first post was the
professorship of botany at Helsingfors; but in 1863 he gave up his chair and
removed to Paris where he remained, except for short absences, until his
death. One of his excursions brought him to London in 1857 to examine
Hooker’s herbarium. He devoted his whole life to the study of lichens, and
from 1852, the date of his first lichen publication, which is an account of
the lichens of Helsingfors, to the end of his life he poured out a constant
succession of books or papers, most of them in Latin. One of his earliest
works was an Essay on Classification[133] which he elaborated later, but
which in its main features he never altered. He relied, in his system, on the
structure and form of thallus, gonidia and fructifications, more especially on
those of the spermogonia (pycnidia), but he rejected ascospore characters
except so far as they were of use in the diagnosis of species. He failed by
being too isolated and by his unwillingness to recognize results obtained by
other workers. In 1866 he had discovered the staining reactions of potash
and hypochlorite of lime on certain thalli, and though these are at times
unreliable owing to growth conditions, etc., they have generally been of real
Page 56
service. Nylander, however, never admitted any criticism of his methods;
his opinions once stated were never revised. He rejected absolutely the
theory of the dual nature of lichens propounded by Schwendener without
seriously examining the question, and regarded as personal enemies those
who dared to differ from him. The last years of his life were passed in
complete solitude. He died in March 1899.
Owing to the very inadequate powers of magnification at the service of
scientific workers, the study of lichens as of other plants was for long
restricted to the collecting, examining and classifying of specimens
according to their macroscopic characters; the microscopic details observed
were isolated and unreliable except to some extent for spore characters.
Special interest is therefore attached to the various schemes of
classification, as each new one proposed reflects to a large extent the
condition of scientific knowledge of the time, and generally marks an
advance. It was the improvement of the microscope from a scientific toy to
an instrument of research that opened up new fields of observation and gave
a new impetus to the study of a group of plants that had proved a puzzle
from the earliest times.
Tulasne was one of the pioneers in microscopic botany. He made a
methodical study of a large series of lichens[134] and traced their
development, so far as he was able, from the spore onwards. He gave
special attention to the form and function of spermogonia and spermatia,
and his work is enriched by beautiful figures of microscopic detail. Lauder
Lindsay[135] also published an elaborate treatise on spermogonia, on their
occurrence in the lichen kingdom and on their form and structure. The
paper embodies the results of wide microscopic research and is a mine of
information regarding these bodies.
Much interesting work was contributed at this time by Itzigsohn[136],
Speerschneider[137], Sachs[138], Thwaites[139], and others. They devoted
their researches to some particular aspect of lichen development and their
several contributions are discussed elsewhere in this work.
Schwendener[140] followed with a systematic study of the minute
anatomy of many of the larger lichen genera. His work is extremely
important in itself and still more so as it gradually revealed to him the
composite character of the thallus.
his opinions once stated were never revised. He rejected absolutely the
theory of the dual nature of lichens propounded by Schwendener without
seriously examining the question, and regarded as personal enemies those
who dared to differ from him. The last years of his life were passed in
complete solitude. He died in March 1899.
Owing to the very inadequate powers of magnification at the service of
scientific workers, the study of lichens as of other plants was for long
restricted to the collecting, examining and classifying of specimens
according to their macroscopic characters; the microscopic details observed
were isolated and unreliable except to some extent for spore characters.
Special interest is therefore attached to the various schemes of
classification, as each new one proposed reflects to a large extent the
condition of scientific knowledge of the time, and generally marks an
advance. It was the improvement of the microscope from a scientific toy to
an instrument of research that opened up new fields of observation and gave
a new impetus to the study of a group of plants that had proved a puzzle
from the earliest times.
Tulasne was one of the pioneers in microscopic botany. He made a
methodical study of a large series of lichens[134] and traced their
development, so far as he was able, from the spore onwards. He gave
special attention to the form and function of spermogonia and spermatia,
and his work is enriched by beautiful figures of microscopic detail. Lauder
Lindsay[135] also published an elaborate treatise on spermogonia, on their
occurrence in the lichen kingdom and on their form and structure. The
paper embodies the results of wide microscopic research and is a mine of
information regarding these bodies.
Much interesting work was contributed at this time by Itzigsohn[136],
Speerschneider[137], Sachs[138], Thwaites[139], and others. They devoted
their researches to some particular aspect of lichen development and their
several contributions are discussed elsewhere in this work.
Schwendener[140] followed with a systematic study of the minute
anatomy of many of the larger lichen genera. His work is extremely
important in itself and still more so as it gradually revealed to him the
composite character of the thallus.
Page 57
Several important monographs date from this period: Leighton[141]
reviewed all the British “Angiocarpous” lichens with special reference to
their “sporidia” though without treating these as of generic value. He
followed up this monograph by two others, on the Graphideae[142] and the
Umbilicarieae[143], and Mudd[144] published a careful study of the British
Cladoniae. On the Continent Th. Fries[145] issued a revision of Stereocaulon
and Pilophoron and other writers contributed work on smaller groups.
H. Period VII. 1867 and after
Modern lichenology begins with the enunciation of Schwendener’s[146]
theory of the composite nature of the lichen plant. The puzzling
resemblance of certain forms to algae, of others to fungi, had excited the
interest of botanists from a very early date, and the similarity between the
green cells in the thallus, and certain lower forms of algae had been again
and again pointed out. Increasing observation concerning the life-histories
of these algae and of the gonidia had eventually piled up so great a number
of proofs of their identity that Schwendener’s announcement must have
seemed to many an inevitable conclusion, though no one before had
hazarded the astounding statement that two organisms of independent origin
were combined in the lichen.
The dual hypothesis, as it was termed, was not however universally
accepted. It was indeed bitterly and scornfully rejected by some of the most
prominent lichenologists of the time, including Nylander[147], J. Müller and
Crombie[148]. Schwendener held that the lichen was a fungus parasitic on an
alga, and his opponents judged, indeed quite rightly, that such a view was
wholly inadequate to explain the biology of lichens. It was not till a later
date that the truer conception of the “consortium” or “symbiosis” was
proposed. The researches undertaken to prove or disprove the new theories
come under review in Chapter II.
Stahl’s work on the development of the carpogonium in lichens gave a
new direction to study, and notable work has been done during the last forty
years in that as in other branches of lichenology.
Exploration of old and new fields furnished the lichen-flora of the world
with many new plants which have been described by various systematists—
reviewed all the British “Angiocarpous” lichens with special reference to
their “sporidia” though without treating these as of generic value. He
followed up this monograph by two others, on the Graphideae[142] and the
Umbilicarieae[143], and Mudd[144] published a careful study of the British
Cladoniae. On the Continent Th. Fries[145] issued a revision of Stereocaulon
and Pilophoron and other writers contributed work on smaller groups.
H. Period VII. 1867 and after
Modern lichenology begins with the enunciation of Schwendener’s[146]
theory of the composite nature of the lichen plant. The puzzling
resemblance of certain forms to algae, of others to fungi, had excited the
interest of botanists from a very early date, and the similarity between the
green cells in the thallus, and certain lower forms of algae had been again
and again pointed out. Increasing observation concerning the life-histories
of these algae and of the gonidia had eventually piled up so great a number
of proofs of their identity that Schwendener’s announcement must have
seemed to many an inevitable conclusion, though no one before had
hazarded the astounding statement that two organisms of independent origin
were combined in the lichen.
The dual hypothesis, as it was termed, was not however universally
accepted. It was indeed bitterly and scornfully rejected by some of the most
prominent lichenologists of the time, including Nylander[147], J. Müller and
Crombie[148]. Schwendener held that the lichen was a fungus parasitic on an
alga, and his opponents judged, indeed quite rightly, that such a view was
wholly inadequate to explain the biology of lichens. It was not till a later
date that the truer conception of the “consortium” or “symbiosis” was
proposed. The researches undertaken to prove or disprove the new theories
come under review in Chapter II.
Stahl’s work on the development of the carpogonium in lichens gave a
new direction to study, and notable work has been done during the last forty
years in that as in other branches of lichenology.
Exploration of old and new fields furnished the lichen-flora of the world
with many new plants which have been described by various systematists—
Page 58
by Nylander, Babington, Arnold, Müller, Th. Fries, Stizenberger, Leighton,
Crombie and many others, and their contributions are scattered through
contemporary scientific journals. The number of recorded species is now
somewhere about 40,000, though, in all probability, many of these will be
found to be growth forms. Still, at the lowest computation, the number of
different species is very large.
Systematic literature has been enriched by a series of important
monographs, too numerous to mention here. While treating definite groups,
they have helped to elucidate some of the peculiar biological problems of
the symbiotic growth.
Morphology, since Schwendener’s time, has been well represented by
Zukal, Reinke, Lindau, Fünfstück, Darbishire, Hue, and by an increasing
number of modern writers whose work is duly acknowledged under each
subject of study. Hesse and Zopf, and more recently Lettau, have been
engaged in the examination of those unique products, the lichen acids,
while other workers have investigated lichen derivatives such as fats.
Ecology of lichens has also been receiving increased attention. Problems of
physiology, symbiosis, etc., are not yet considered to be solved and are
being attacked from various sides.
British lichenologists since 1867 have been mainly engaged on field
work, with the exception of Lauder Lindsay who published after that date a
second great paper on the spermogonia of crustaceous lichens. Leighton in
his Lichen Flora and Crombie in numerous publications gave the lead in
systematic work, and with them were associated a band of indefatigable
collectors. Among these may be recalled Alexander Croall (1809-85), a
parish schoolmaster in Scotland whose Plants of Braemar include many of
the rarer mountain lichens. Henry Buchanan Holl (1820-86), a surgeon in
London, collected in the Scottish Highlands as well as in England and
Wales. William Joshua (1828-98) worked mostly in the Western counties of
Somerset and Gloucestershire. Charles Du Bois Larbalestier, who died in
1911, was a keen observer and collector during many years; he discovered a
number of new species in his native Jersey, in Cambridgeshire and also in
Connemara; his plants were generally sent to Nylander to be determined
and described. He issued two sets of lichens, one of Channel Island plants,
the other of more general British distribution, and he had begun the issue of
Cambridgeshire lichens. Isaac Carroll (1828-80), an Irish botanist, issued a
Crombie and many others, and their contributions are scattered through
contemporary scientific journals. The number of recorded species is now
somewhere about 40,000, though, in all probability, many of these will be
found to be growth forms. Still, at the lowest computation, the number of
different species is very large.
Systematic literature has been enriched by a series of important
monographs, too numerous to mention here. While treating definite groups,
they have helped to elucidate some of the peculiar biological problems of
the symbiotic growth.
Morphology, since Schwendener’s time, has been well represented by
Zukal, Reinke, Lindau, Fünfstück, Darbishire, Hue, and by an increasing
number of modern writers whose work is duly acknowledged under each
subject of study. Hesse and Zopf, and more recently Lettau, have been
engaged in the examination of those unique products, the lichen acids,
while other workers have investigated lichen derivatives such as fats.
Ecology of lichens has also been receiving increased attention. Problems of
physiology, symbiosis, etc., are not yet considered to be solved and are
being attacked from various sides.
British lichenologists since 1867 have been mainly engaged on field
work, with the exception of Lauder Lindsay who published after that date a
second great paper on the spermogonia of crustaceous lichens. Leighton in
his Lichen Flora and Crombie in numerous publications gave the lead in
systematic work, and with them were associated a band of indefatigable
collectors. Among these may be recalled Alexander Croall (1809-85), a
parish schoolmaster in Scotland whose Plants of Braemar include many of
the rarer mountain lichens. Henry Buchanan Holl (1820-86), a surgeon in
London, collected in the Scottish Highlands as well as in England and
Wales. William Joshua (1828-98) worked mostly in the Western counties of
Somerset and Gloucestershire. Charles Du Bois Larbalestier, who died in
1911, was a keen observer and collector during many years; he discovered a
number of new species in his native Jersey, in Cambridgeshire and also in
Connemara; his plants were generally sent to Nylander to be determined
and described. He issued two sets of lichens, one of Channel Island plants,
the other of more general British distribution, and he had begun the issue of
Cambridgeshire lichens. Isaac Carroll (1828-80), an Irish botanist, issued a
Page 59
first fascicle of Lichenes Hibernici containing 40 numbers. More recently
Lett[149] has reported 80 species and varieties from the Mourne Mountains
in Ireland. Other more extensive sets were issued by Mudd and by
Leighton, and later by Crombie and by Johnson. All these have been of
great service to the study of lichenology in our country. Other collectors of
note are Curnow (Cornwall), Martindale (Westmoreland), and E. M.
Holmes whose valuable herbarium has been secured by University College,
Nottingham.
The publication of the volume dealing with Lichenes in Engler and
Prantl’s Pflanzenfamilien has proved a boon to all who are interested in the
study of lichens. Fünfstück[150] prepared the introduction, an admirable
presentation of the morphological and physiological aspects of the subject,
while Zahlbruckner[151], with equal success, took charge of the section
dealing with classification.
Lett[149] has reported 80 species and varieties from the Mourne Mountains
in Ireland. Other more extensive sets were issued by Mudd and by
Leighton, and later by Crombie and by Johnson. All these have been of
great service to the study of lichenology in our country. Other collectors of
note are Curnow (Cornwall), Martindale (Westmoreland), and E. M.
Holmes whose valuable herbarium has been secured by University College,
Nottingham.
The publication of the volume dealing with Lichenes in Engler and
Prantl’s Pflanzenfamilien has proved a boon to all who are interested in the
study of lichens. Fünfstück[150] prepared the introduction, an admirable
presentation of the morphological and physiological aspects of the subject,
while Zahlbruckner[151], with equal success, took charge of the section
dealing with classification.
Page 60
CHAPTER II
CONSTITUENTS OF THE LICHEN THALLUS
I. LICHEN GONIDIA
CONSTITUENTS OF THE LICHEN THALLUS
I. LICHEN GONIDIA
Page 61
Fig. 1. Physcia aipolia Nyl. Vertical section of thallus. a, cortex;
b, algal layer; c, medulla; d, lower cortex. × 100 (partly
diagrammatic).
The thallus or vegetative body of lichens differs from that of other green
plants in the sharp distinction both of form and colour between the
assimilative cells and the colourless tissues, and in the relative positions
these occupy within the thallus: in the greater number of lichen species the
green chlorophyll cells are confined to a narrow zone or band some way
beneath and parallel with the surface (Fig. 1); in a minority of genera they
are distributed through the entire thallus (Fig. 2); but in all cases the tissues
remain distinct. The green zone can be easily demonstrated in any of the
larger lichens by scaling off the outer surface cells, or by making a vertical
section through the thallus. The colourless cells penetrate to some extent
among the green cells; they also form the whole of the cortical and
medullary tissues.
b, algal layer; c, medulla; d, lower cortex. × 100 (partly
diagrammatic).
The thallus or vegetative body of lichens differs from that of other green
plants in the sharp distinction both of form and colour between the
assimilative cells and the colourless tissues, and in the relative positions
these occupy within the thallus: in the greater number of lichen species the
green chlorophyll cells are confined to a narrow zone or band some way
beneath and parallel with the surface (Fig. 1); in a minority of genera they
are distributed through the entire thallus (Fig. 2); but in all cases the tissues
remain distinct. The green zone can be easily demonstrated in any of the
larger lichens by scaling off the outer surface cells, or by making a vertical
section through the thallus. The colourless cells penetrate to some extent
among the green cells; they also form the whole of the cortical and
medullary tissues.
Page 62
Fig. 2. Collema nigrescens Ach. Vertical section of thallus. a,
chains of the alga Nostoc; b, fungal filaments. × 600.
These two different elements we now know to consist of two distinct
organisms, a fungus and an alga. The green algal cells were at one time
considered to be reproductive bodies, and were called “gonidia,” a term still
in use though its significance has changed.
1. GONIDIA IN RELATION TO THE THALLUS
A. Historical account of Lichen Gonidia
There have been few subjects of botanical investigation that have roused
so much speculation and such prolonged controversy as the question of
these constituents of the lichen plant. The green cells and the colourless
filaments which together form the vegetative structure are so markedly
dissimilar, that constant attempts have been made to explain the problem of
chains of the alga Nostoc; b, fungal filaments. × 600.
These two different elements we now know to consist of two distinct
organisms, a fungus and an alga. The green algal cells were at one time
considered to be reproductive bodies, and were called “gonidia,” a term still
in use though its significance has changed.
1. GONIDIA IN RELATION TO THE THALLUS
A. Historical account of Lichen Gonidia
There have been few subjects of botanical investigation that have roused
so much speculation and such prolonged controversy as the question of
these constituents of the lichen plant. The green cells and the colourless
filaments which together form the vegetative structure are so markedly
dissimilar, that constant attempts have been made to explain the problem of
Page 63
their origin and function, and thereby to establish satisfactorily the
relationship of lichens to other members of the Plant Kingdom.
In gelatinous lichens, represented by Collema, of which several species
are common in damp places and grow on trees or walls or on the ground,
the chains of green cells interspersed through the thallus have long been
recognized as comparable with the filaments of Nostoc, a blue-green
gelatinous alga, conspicuous in wet weather in the same localities as those
inhabited by Collema. So among early systematists, we find Ventenat[152]
classifying the few lichens with which he was acquainted under algae and
hazarding the statement that a gelatinous lichen such as Collema was only a
Nostoc changed in form. Some years later Cassini[153] in an account of
Nostoc expressed a somewhat similar view, though with a difference: he
suggested that Nostoc was but a monstrous form of Collema, his argument
being that, as the latter bore the fruit, it was the normal and perfect
condition of the plant. A few years later Agardh[154] claimed to have
observed the metamorphosis of Nostoc up to the fertile stage of a lichen,
Collema limosum. But long before this date, Scopoli[155] had demonstrated
a green colouring substance in non-gelatinous lichens by rubbing a
crustaceous or leprose thallus between the fingers; and Persoon[156] made
use of this green colour characteristic of lichen crusts to differentiate these
plants from fungi. Sprengel[157] went a step further in exactly describing the
green tissue as forming a definite layer below the upper cortex of foliaceous
lichens.
The first clear description and delimitation of the different elements
composing the lichen thallus was, however, given by Wallroth[158]. He drew
attention to the great similarity between the colourless filaments of the
lichen and the hyphae of fungi. The green globose cells in the
chlorophyllaceous lichens he interpreted as brood-cells or gonidia,
regarding them as organs of reproduction collected into a “stratum
gonimon.” To the same author we owe the terms “homoiomerous” and
“heteromerous,” which he coined to describe the arrangement of these
green cells in the tissue of the thallus. In the former case the gonidia are
distributed equally through the structure; in the latter they are confined to a
distinct zone.
relationship of lichens to other members of the Plant Kingdom.
In gelatinous lichens, represented by Collema, of which several species
are common in damp places and grow on trees or walls or on the ground,
the chains of green cells interspersed through the thallus have long been
recognized as comparable with the filaments of Nostoc, a blue-green
gelatinous alga, conspicuous in wet weather in the same localities as those
inhabited by Collema. So among early systematists, we find Ventenat[152]
classifying the few lichens with which he was acquainted under algae and
hazarding the statement that a gelatinous lichen such as Collema was only a
Nostoc changed in form. Some years later Cassini[153] in an account of
Nostoc expressed a somewhat similar view, though with a difference: he
suggested that Nostoc was but a monstrous form of Collema, his argument
being that, as the latter bore the fruit, it was the normal and perfect
condition of the plant. A few years later Agardh[154] claimed to have
observed the metamorphosis of Nostoc up to the fertile stage of a lichen,
Collema limosum. But long before this date, Scopoli[155] had demonstrated
a green colouring substance in non-gelatinous lichens by rubbing a
crustaceous or leprose thallus between the fingers; and Persoon[156] made
use of this green colour characteristic of lichen crusts to differentiate these
plants from fungi. Sprengel[157] went a step further in exactly describing the
green tissue as forming a definite layer below the upper cortex of foliaceous
lichens.
The first clear description and delimitation of the different elements
composing the lichen thallus was, however, given by Wallroth[158]. He drew
attention to the great similarity between the colourless filaments of the
lichen and the hyphae of fungi. The green globose cells in the
chlorophyllaceous lichens he interpreted as brood-cells or gonidia,
regarding them as organs of reproduction collected into a “stratum
gonimon.” To the same author we owe the terms “homoiomerous” and
“heteromerous,” which he coined to describe the arrangement of these
green cells in the tissue of the thallus. In the former case the gonidia are
distributed equally through the structure; in the latter they are confined to a
distinct zone.
Page 64
Wallroth’s terminology and his views of the function of the gonidia were
accepted as the true explanation for many years, the opinion that they were
solely reproductive bodies being entirely in accordance with the well-
known part played by soredia in the propagation of lichens—and soredia
always include one or more green cells.
B. Gonidia contrasted with Algae
In describing the gonidia of the Graphideae Wallroth[159] had pointed out
their affinity with the filaments of Chroolepus (Trentepohlia) umbrina. He
considered these and other green algae when growing loose on the trunks of
trees to be but “unfortunate brood-cells” which had become free and,
though capable of growth and increase, were unable to form again a lichen
plant.
Further observations on gonidia were made by E. Fries[160]: he found that
the green cells escaped from the lichen matrix and produced new
individuals; and also that the whole thallus in moist localities might become
dissolved into the alga known as Protococcus viridis; but, he continues,
“though these Protococcus cells multiplied exceedingly, they never could
rise again to the perfect lichen.” Kützing[161], in a later account of
Protococcus viridis, also recognized its affinity with lichens; he stated that
he could testify from observation that, according to the amount of moisture
present, it would develop, either in excessive moisture to a filamentous
alga, or in drier conditions “to lichens such as Lecanora subfusca or
Xanthoria parietina.”
A British botanist, G. H. K. Thwaites[162], at one time superintendent of
the botanical garden at Peradeniya in Ceylon, published a notable paper on
lichen gonidia in which he pointed out that as in Collema the green
constituents of the thallus resembled the chains of Nostoc, so in the non-
gelatinous lichens, the green globose cells were comparable or identical
with Pleurococcus, and Thwaites further observed that they increased by
division within the lichen thallus. He insisted too that in no instance were
gonidia reproductive organs: they were essential component parts of the
vegetative body and necessary to the life of the plant. In a further paper on
Chroolepus ebeneus Ag., a plant consisting of slender dark-coloured felted
filaments, he described these filaments as being composed of a central
accepted as the true explanation for many years, the opinion that they were
solely reproductive bodies being entirely in accordance with the well-
known part played by soredia in the propagation of lichens—and soredia
always include one or more green cells.
B. Gonidia contrasted with Algae
In describing the gonidia of the Graphideae Wallroth[159] had pointed out
their affinity with the filaments of Chroolepus (Trentepohlia) umbrina. He
considered these and other green algae when growing loose on the trunks of
trees to be but “unfortunate brood-cells” which had become free and,
though capable of growth and increase, were unable to form again a lichen
plant.
Further observations on gonidia were made by E. Fries[160]: he found that
the green cells escaped from the lichen matrix and produced new
individuals; and also that the whole thallus in moist localities might become
dissolved into the alga known as Protococcus viridis; but, he continues,
“though these Protococcus cells multiplied exceedingly, they never could
rise again to the perfect lichen.” Kützing[161], in a later account of
Protococcus viridis, also recognized its affinity with lichens; he stated that
he could testify from observation that, according to the amount of moisture
present, it would develop, either in excessive moisture to a filamentous
alga, or in drier conditions “to lichens such as Lecanora subfusca or
Xanthoria parietina.”
A British botanist, G. H. K. Thwaites[162], at one time superintendent of
the botanical garden at Peradeniya in Ceylon, published a notable paper on
lichen gonidia in which he pointed out that as in Collema the green
constituents of the thallus resembled the chains of Nostoc, so in the non-
gelatinous lichens, the green globose cells were comparable or identical
with Pleurococcus, and Thwaites further observed that they increased by
division within the lichen thallus. He insisted too that in no instance were
gonidia reproductive organs: they were essential component parts of the
vegetative body and necessary to the life of the plant. In a further paper on
Chroolepus ebeneus Ag., a plant consisting of slender dark-coloured felted
filaments, he described these filaments as being composed of a central
Page 65
strand which closely resembled the alga
Chroolepus, and of a surrounding sheath of
dark-coloured cells (Fig. 3): “occasionally,” he
writes, “the internal filament protrudes beyond
the investing sheath, and may then be seen to
consist of oblong cells containing the peculiar
reddish oily-looking endochrome of
Chroolepus.” Thwaites placed this puzzling
plant in a new genus, Cystocoleus, at the same
time pointing out its affinity with the lichen
genus Coenogonium. The plant is now known as
Coenogonium ebeneum. Thwaites was on the
threshold of the discovery as to the true nature
of the relationship between the central filament
Fig. 3. Coenogonium ebeneum and the investing sheath, but he failed to take
A. L. Sm. Tip of lichen filament, the next forward step.
the alga overgrown by dark
fungal hyphae × 600. Very shortly after, Von Flotow[163] published
his views on some other lichen gonidia. He had
come to the conclusion that the various species
of the alga, Gloeocapsa, so frequently found in damp places, among mosses
and lichens, were merely growth stages of the gonidia of Ephebe pubescens,
and bore the same relation to Ephebe as did Lepra viridis (Protococcus) to
Parmelia. The gonidium of Ephebe is the gelatinous filamentous blue-green
alga Stigonema (Fig. 4), and the separate cells are not unlike those of
Gloeocapsa. Flotow had also demonstrated that the same type of gonidium
was enclosed in the cephalodia of Stereocaulon. Sachs[164], too, gave
evidence as to the close connection between Nostoc and Collema. He had
observed numerous small clumps of the alga growing in proximity to
equally abundant thalli of Collema, with every stage of development
represented from one to the other. He found cases where the gelatinous coils
of Nostoc chains were penetrated by fine colourless filaments “as if invaded
by a parasitic fungus.” Later these threads were seen to be attached to some
cell of the Nostoc trichome. Sachs concluded, however, from very careful
examination at the time, that the colourless filaments were produced by the
green cells. As growth proceeded, the coloured Nostoc chains became
massed towards the upper surface, while the colourless filaments tended to
Chroolepus, and of a surrounding sheath of
dark-coloured cells (Fig. 3): “occasionally,” he
writes, “the internal filament protrudes beyond
the investing sheath, and may then be seen to
consist of oblong cells containing the peculiar
reddish oily-looking endochrome of
Chroolepus.” Thwaites placed this puzzling
plant in a new genus, Cystocoleus, at the same
time pointing out its affinity with the lichen
genus Coenogonium. The plant is now known as
Coenogonium ebeneum. Thwaites was on the
threshold of the discovery as to the true nature
of the relationship between the central filament
Fig. 3. Coenogonium ebeneum and the investing sheath, but he failed to take
A. L. Sm. Tip of lichen filament, the next forward step.
the alga overgrown by dark
fungal hyphae × 600. Very shortly after, Von Flotow[163] published
his views on some other lichen gonidia. He had
come to the conclusion that the various species
of the alga, Gloeocapsa, so frequently found in damp places, among mosses
and lichens, were merely growth stages of the gonidia of Ephebe pubescens,
and bore the same relation to Ephebe as did Lepra viridis (Protococcus) to
Parmelia. The gonidium of Ephebe is the gelatinous filamentous blue-green
alga Stigonema (Fig. 4), and the separate cells are not unlike those of
Gloeocapsa. Flotow had also demonstrated that the same type of gonidium
was enclosed in the cephalodia of Stereocaulon. Sachs[164], too, gave
evidence as to the close connection between Nostoc and Collema. He had
observed numerous small clumps of the alga growing in proximity to
equally abundant thalli of Collema, with every stage of development
represented from one to the other. He found cases where the gelatinous coils
of Nostoc chains were penetrated by fine colourless filaments “as if invaded
by a parasitic fungus.” Later these threads were seen to be attached to some
cell of the Nostoc trichome. Sachs concluded, however, from very careful
examination at the time, that the colourless filaments were produced by the
green cells. As growth proceeded, the coloured Nostoc chains became
massed towards the upper surface, while the colourless filaments tended to
Page 66
occupy the lower part of the thallus. He calculated that during the summer
season the metamorphosis from Nostoc to a fertile Collema thallus took
from three to four months. He judged that in favourable conditions the
change would inevitably take place, though if there should be too great
moisture no Collema would be formed. His study of Cladonia was less
successful as he mistook some colonies of Gloeocapsa for a growth
condition of Cladonia gonidia, an error corrected later by Itzigsohn[165].
But before this date Itzigsohn[166] had
published a paper setting forth his views on
thallus formation, which marked a distinct
advance. He did not hazard any theory as to the
origin of gonidia, but he had observed spermatia
growing, much as did the cells of Oscillaria: by
increase in length, and, by subsequent
branching, filaments were formed which
surrounded the green cells; these latter had
meanwhile multiplied by repeated division till
finally a complete thallus was built up, the
filamentous tissue being derived from the
spermatia, while the green layer came from the
original gonidium. In contrasting the
development with that of Collema, he represents Fig. 4. Ephebe pubescens Nyl.
Nostoc as a sterile product of a lichen and, like Tip of lichen filament × 600.
the gonidia of other lichens, only able to form a
lichen thallus when it encounters the fructifying
spermatia.
Braxton Hicks[167], a London doctor, some time later, made experiments
with Chroococcus algae which grew in plenty on the bark of trees, and
followed their development into a lichen thallus. He further claimed to have
observed a Chlorococcus, which was associated with a Cladonia, divide
and form a Palmella stage.
C. Culture Experiments with the Lichen Thallus
It had been repeatedly stated that the gonidia might become independent
of the thallus, but absolute proof was wanting until Speerschneider[168],
season the metamorphosis from Nostoc to a fertile Collema thallus took
from three to four months. He judged that in favourable conditions the
change would inevitably take place, though if there should be too great
moisture no Collema would be formed. His study of Cladonia was less
successful as he mistook some colonies of Gloeocapsa for a growth
condition of Cladonia gonidia, an error corrected later by Itzigsohn[165].
But before this date Itzigsohn[166] had
published a paper setting forth his views on
thallus formation, which marked a distinct
advance. He did not hazard any theory as to the
origin of gonidia, but he had observed spermatia
growing, much as did the cells of Oscillaria: by
increase in length, and, by subsequent
branching, filaments were formed which
surrounded the green cells; these latter had
meanwhile multiplied by repeated division till
finally a complete thallus was built up, the
filamentous tissue being derived from the
spermatia, while the green layer came from the
original gonidium. In contrasting the
development with that of Collema, he represents Fig. 4. Ephebe pubescens Nyl.
Nostoc as a sterile product of a lichen and, like Tip of lichen filament × 600.
the gonidia of other lichens, only able to form a
lichen thallus when it encounters the fructifying
spermatia.
Braxton Hicks[167], a London doctor, some time later, made experiments
with Chroococcus algae which grew in plenty on the bark of trees, and
followed their development into a lichen thallus. He further claimed to have
observed a Chlorococcus, which was associated with a Cladonia, divide
and form a Palmella stage.
C. Culture Experiments with the Lichen Thallus
It had been repeatedly stated that the gonidia might become independent
of the thallus, but absolute proof was wanting until Speerschneider[168],
Page 67
who had turned his attention to the subject, made direct culture experiments
and was able to follow the liberation of the green cells. He took a thinnish
section of the thallus of Hagenia (Physcia) ciliaris, and, by keeping it
moist, he was able to observe that the gonidial cells increased by division;
the moist condition at the same time caused the colourless filaments to die
away. This method of investigation was to lead to further results. It was
resorted to by Famintzin and Baranetzky[169] who made cultures of gonidia
extracted from three different lichens, Physcia (Xanthoria) parietina,
Evernia furfuracea and Cladonia sp. They were able to observe the growth
and division of the green cells and, in addition, the formation of zoospores.
They recognized the development as entirely identical with that of the
unicellular green alga, Cystococcus humicola Naeg. Baranetzky[170]
continued the experiments and made cultures of the blue-green gonidia of
Peltigera canina and of Collema pulposum. In both instances he succeeded
in isolating them from the thallus and in growing them in moist air as
separate organisms. He adds that “many forms reckoned as algae, may be
considered as vegetating lichen gonidia such as Cystococcus, Polycoccus,
Nostoc, etc.” Meanwhile Itzigsohn[171] had further demonstrated by similar
culture experiments that the gonidia of Peltigera canina corresponded with
the algae known as Gloeocapsa monococca Kütz., and as Polycoccus
punctiformis Kütz.
D. Theories as to the Origin of Gonidia
Though the relationship between the gonidia within the thallus and free-
living algal organisms seemed to be proved beyond dispute, the manner in
which gonidia first originated had not yet been discovered. Bayrhoffer[172]
attacked this problem in a study of foliose and other lichens. According to
his observations, certain colourless cells or filaments, belonging to the
“gonimic” layer, grew in a downward direction and formed at their tips a
faintly yellowish-green cell; it gradually enlarged and was at length thrown
off as a free globose gonidium, which represented the female cell. Other
filaments from the “lower fibrous layer” of the thallus at the same time
grew upwards and from them were given off somewhat similar gonidia
which functioned as male cells. His observations and deductions were
fanciful, but it must be remembered that the attachment between hypha and
alga in lichens is in many cases so close as to appear genetic, and also it
and was able to follow the liberation of the green cells. He took a thinnish
section of the thallus of Hagenia (Physcia) ciliaris, and, by keeping it
moist, he was able to observe that the gonidial cells increased by division;
the moist condition at the same time caused the colourless filaments to die
away. This method of investigation was to lead to further results. It was
resorted to by Famintzin and Baranetzky[169] who made cultures of gonidia
extracted from three different lichens, Physcia (Xanthoria) parietina,
Evernia furfuracea and Cladonia sp. They were able to observe the growth
and division of the green cells and, in addition, the formation of zoospores.
They recognized the development as entirely identical with that of the
unicellular green alga, Cystococcus humicola Naeg. Baranetzky[170]
continued the experiments and made cultures of the blue-green gonidia of
Peltigera canina and of Collema pulposum. In both instances he succeeded
in isolating them from the thallus and in growing them in moist air as
separate organisms. He adds that “many forms reckoned as algae, may be
considered as vegetating lichen gonidia such as Cystococcus, Polycoccus,
Nostoc, etc.” Meanwhile Itzigsohn[171] had further demonstrated by similar
culture experiments that the gonidia of Peltigera canina corresponded with
the algae known as Gloeocapsa monococca Kütz., and as Polycoccus
punctiformis Kütz.
D. Theories as to the Origin of Gonidia
Though the relationship between the gonidia within the thallus and free-
living algal organisms seemed to be proved beyond dispute, the manner in
which gonidia first originated had not yet been discovered. Bayrhoffer[172]
attacked this problem in a study of foliose and other lichens. According to
his observations, certain colourless cells or filaments, belonging to the
“gonimic” layer, grew in a downward direction and formed at their tips a
faintly yellowish-green cell; it gradually enlarged and was at length thrown
off as a free globose gonidium, which represented the female cell. Other
filaments from the “lower fibrous layer” of the thallus at the same time
grew upwards and from them were given off somewhat similar gonidia
which functioned as male cells. His observations and deductions were
fanciful, but it must be remembered that the attachment between hypha and
alga in lichens is in many cases so close as to appear genetic, and also it
Page 68
often happens that as the gonidium multiplies it becomes free from the
hypha.
In his Mémoire sur les Lichens, Tulasne[173] described the colourless
filaments as being fungal in appearance. The green cells he recognized as
organs of nutrition, and once and again in his paper he states that they arose
directly by a sort of budding process from the medullary or cortical
filaments, either laterally or at the apex. This apparently reasonable view of
their origin was confirmed by other writers on the subject: by
Speerschneider[174] in his account of the anatomy of Usnea barbata, by de
Bary[175], and by Schwendener[176] in their earlier writings. But even while
de Bary accepted the hyphal origin of the gonidia, he noted[177] that,
accompanying Opegrapha atra and other Graphideae, on the bark were to
be found free Chroolepus cells similar to the gonidia in the lichen thallus.
He added that gonidia of certain other lichens in no way differed from
Protococcus cells; and as for the gelatinous lichens he declared that “either
they were the perfect fruiting form of Nostocaceae and Chroococcaceae—
hitherto looked on as algae—or that these same Nostocaceae and
Chroococcaceae are algae which take the form of Collema, Ephebe, etc.,
when attacked by an ascomycetous fungus.”
All these investigators, and other lichenologists such as Nylander[178],
still regarded the free-living organisms identified by them as similar to the
green cells of the thallus, as only lichen gonidia escaped from the matrix
and vegetating in an independent condition.
The old controversy has in recent years been unexpectedly reopened by
Elfving[179] who has sought again to prove the genetic origin of the green
cells. His method has been to examine a large series of lichens by making
sections of the growing areas, and he claims to have observed in every case
the hyphal origin of the gonidia: not only of Cystococcus but also of
Trentepohlia, Stigonema and Nostoc. In the case of Cystococcus, the
gonidium, he says, arises by the swelling of the terminal cell of the hypha to
a globose form, and by the gradual transformation of the contents to a
chlorophyll-green colour, with power of assimilation. In the case of
filamentous gonidia such as Trentepohlia, the hyphal cells destined to
become gonidia are intercalary. In Peltigera the cells of the meristematic
plectenchyma become transformed to blue-green Nostoc cells.
hypha.
In his Mémoire sur les Lichens, Tulasne[173] described the colourless
filaments as being fungal in appearance. The green cells he recognized as
organs of nutrition, and once and again in his paper he states that they arose
directly by a sort of budding process from the medullary or cortical
filaments, either laterally or at the apex. This apparently reasonable view of
their origin was confirmed by other writers on the subject: by
Speerschneider[174] in his account of the anatomy of Usnea barbata, by de
Bary[175], and by Schwendener[176] in their earlier writings. But even while
de Bary accepted the hyphal origin of the gonidia, he noted[177] that,
accompanying Opegrapha atra and other Graphideae, on the bark were to
be found free Chroolepus cells similar to the gonidia in the lichen thallus.
He added that gonidia of certain other lichens in no way differed from
Protococcus cells; and as for the gelatinous lichens he declared that “either
they were the perfect fruiting form of Nostocaceae and Chroococcaceae—
hitherto looked on as algae—or that these same Nostocaceae and
Chroococcaceae are algae which take the form of Collema, Ephebe, etc.,
when attacked by an ascomycetous fungus.”
All these investigators, and other lichenologists such as Nylander[178],
still regarded the free-living organisms identified by them as similar to the
green cells of the thallus, as only lichen gonidia escaped from the matrix
and vegetating in an independent condition.
The old controversy has in recent years been unexpectedly reopened by
Elfving[179] who has sought again to prove the genetic origin of the green
cells. His method has been to examine a large series of lichens by making
sections of the growing areas, and he claims to have observed in every case
the hyphal origin of the gonidia: not only of Cystococcus but also of
Trentepohlia, Stigonema and Nostoc. In the case of Cystococcus, the
gonidium, he says, arises by the swelling of the terminal cell of the hypha to
a globose form, and by the gradual transformation of the contents to a
chlorophyll-green colour, with power of assimilation. In the case of
filamentous gonidia such as Trentepohlia, the hyphal cells destined to
become gonidia are intercalary. In Peltigera the cells of the meristematic
plectenchyma become transformed to blue-green Nostoc cells.
Page 69
A study was also made by him of the formation of cephalodia[180], the
gonidia of which differ from those of the “host” thallus. In Peltigera
aphthosa he claims to have traced the development of these bodies to the
branching and mingling of the external hairs which, in the end, form a ball
of interwoven hyphae. The central cells of the ball are then gradually
differentiated into Nostoc cells, which increase to form the familiar chains.
Elfving allows that the gonidia mainly increase by division within the
thallus, and that they also may escape and live as free organisms. His views
are unsupported by direct culture experiments which are the real proof of
the composite nature of the thallus.
E. Microgonidia
Another attempt to establish a genetic origin for lichen gonidia was made
by Minks[181]. He had found in his examination of Leptogium myochroum
that the protoplasmic contents of the hyphae broke up into a regular series
of globular corpuscles which had a greenish appearance. These minute
bodies, called by him microgonidia, were, he states, at first few in number,
but gradually they increased and were eventually set free by the
mucilaginous degeneration of the cell wall. As free thalline gonidia, they
increased in size and rapidly multiplied by division. Minks was at first
enthusiastically supported by Müller[182] who had found from his own
observations that microgonidia might be present in any of the lichen hyphae
and in any part of the thallus, even in the germinating tube of the lichen
spore, and was in that case most easily seen when the spores germinated
within the ascus. He argued that as spores originated within the ascus, so
microgonidia were developed within the hyphae. Minks’s theories were
however not generally accepted and were at last wholly discredited by
Zukal[183] who was able to prove that the greenish bodies were contracted
portions of protoplasm in hyphae that suffered from a lowered supply of
moisture, the green colour not being due to any colouring substance, but to
light effect on the proteins—an outcome of special conditions in the
vegetative life of the plant. Darbishire[184] criticized Minks’s whole work
with great care and he has arrived at the conclusion that the microgonidium
may be dismissed as a totally mistaken conception.
F. Composite Nature of Thallus
gonidia of which differ from those of the “host” thallus. In Peltigera
aphthosa he claims to have traced the development of these bodies to the
branching and mingling of the external hairs which, in the end, form a ball
of interwoven hyphae. The central cells of the ball are then gradually
differentiated into Nostoc cells, which increase to form the familiar chains.
Elfving allows that the gonidia mainly increase by division within the
thallus, and that they also may escape and live as free organisms. His views
are unsupported by direct culture experiments which are the real proof of
the composite nature of the thallus.
E. Microgonidia
Another attempt to establish a genetic origin for lichen gonidia was made
by Minks[181]. He had found in his examination of Leptogium myochroum
that the protoplasmic contents of the hyphae broke up into a regular series
of globular corpuscles which had a greenish appearance. These minute
bodies, called by him microgonidia, were, he states, at first few in number,
but gradually they increased and were eventually set free by the
mucilaginous degeneration of the cell wall. As free thalline gonidia, they
increased in size and rapidly multiplied by division. Minks was at first
enthusiastically supported by Müller[182] who had found from his own
observations that microgonidia might be present in any of the lichen hyphae
and in any part of the thallus, even in the germinating tube of the lichen
spore, and was in that case most easily seen when the spores germinated
within the ascus. He argued that as spores originated within the ascus, so
microgonidia were developed within the hyphae. Minks’s theories were
however not generally accepted and were at last wholly discredited by
Zukal[183] who was able to prove that the greenish bodies were contracted
portions of protoplasm in hyphae that suffered from a lowered supply of
moisture, the green colour not being due to any colouring substance, but to
light effect on the proteins—an outcome of special conditions in the
vegetative life of the plant. Darbishire[184] criticized Minks’s whole work
with great care and he has arrived at the conclusion that the microgonidium
may be dismissed as a totally mistaken conception.
F. Composite Nature of Thallus
Page 70
Schwendener[185] meanwhile was engaged on his study of lichen
anatomy. Though at first he adhered to the then accepted view of the genetic
connection between hyphae and gonidia, his continued examination of the
vegetative development led him to publish a short paper[186] in which he
announced his opinion that the various blue-green and green gonidia were
really algae and that the complete lichen in all cases represented a fungus
living parasitically on an alga: in Ephebe, for example, the alga was a form
of Stigonema, in the Collemaceae it was a species of Nostoc. In those
lichens enclosing bright green cells, the gonidia were identical with
Cystococcus humicola, while in Graphideae the brightly coloured
filamentous cells were those of Chroolepus (Trentepohlia). This statement
he repeated in an appendix to the larger work on lichens[187] and again in
the following year[188] when he described more fully the different gonidial
algae and the changes produced in their structure and habit by the action of
the parasite: “though eventually the alga is destroyed,” he writes, “it is at
first excited to more vigorous growth by contact with the fungus, and in the
course of generations may become changed beyond recognition both in size
and form.” In support of his theory of the composite constitution of the
thallus, Schwendener pointed out the wide distribution and frequent
occurrence in nature of the algae that become transformed to lichen gonidia.
He claimed as further proof of the presence of two distinct organisms that,
while the colourless filaments react in the same way as fungi on the
application of iodine, the gonidia take the stain of algal membranes.
G. Synthetic Cultures
Schwendener’s “dual hypothesis,” as it was termed, excited great interest
and no little controversy, the reasons for and against being debated with
considerable heat. Rees[189] was the first who attempted to put the matter to
the proof by making synthetic cultures. For this purpose he took spores
from the apothecium of a Collema and sowed them on pure cultures of
Nostoc, and as a result obtained the formation of a lichen thallus, though he
did not succeed in producing any fructification. He observed further that the
hyphal filaments from the germinating spore died off when no Nostoc was
forthcoming.
anatomy. Though at first he adhered to the then accepted view of the genetic
connection between hyphae and gonidia, his continued examination of the
vegetative development led him to publish a short paper[186] in which he
announced his opinion that the various blue-green and green gonidia were
really algae and that the complete lichen in all cases represented a fungus
living parasitically on an alga: in Ephebe, for example, the alga was a form
of Stigonema, in the Collemaceae it was a species of Nostoc. In those
lichens enclosing bright green cells, the gonidia were identical with
Cystococcus humicola, while in Graphideae the brightly coloured
filamentous cells were those of Chroolepus (Trentepohlia). This statement
he repeated in an appendix to the larger work on lichens[187] and again in
the following year[188] when he described more fully the different gonidial
algae and the changes produced in their structure and habit by the action of
the parasite: “though eventually the alga is destroyed,” he writes, “it is at
first excited to more vigorous growth by contact with the fungus, and in the
course of generations may become changed beyond recognition both in size
and form.” In support of his theory of the composite constitution of the
thallus, Schwendener pointed out the wide distribution and frequent
occurrence in nature of the algae that become transformed to lichen gonidia.
He claimed as further proof of the presence of two distinct organisms that,
while the colourless filaments react in the same way as fungi on the
application of iodine, the gonidia take the stain of algal membranes.
G. Synthetic Cultures
Schwendener’s “dual hypothesis,” as it was termed, excited great interest
and no little controversy, the reasons for and against being debated with
considerable heat. Rees[189] was the first who attempted to put the matter to
the proof by making synthetic cultures. For this purpose he took spores
from the apothecium of a Collema and sowed them on pure cultures of
Nostoc, and as a result obtained the formation of a lichen thallus, though he
did not succeed in producing any fructification. He observed further that the
hyphal filaments from the germinating spore died off when no Nostoc was
forthcoming.
Page 71
Bornet[190] followed with his record of successful cultures. He selected
for experiment the spores of Physcia (Xanthoria) parietina and was able to
show that hyphae produced from the germinating spore adhered to the free-
growing cells of Protococcus[191] viridis and formed the early stages of a
lichen thallus. Woronin[192] contributed his observations on the gonidia of
Parmelia (Physcia) pulverulenta which he isolated from the thallus and
cultivated in pure water. He confirmed the occurrence of cell division in the
gonidia and also the formation of zoospores, these again forming new
colonies of algae identical in all respects with the thalline gonidia. He was
able to see the germinating tube from a lichen spore attach itself to a
gonidium, though he failed in his attempts to induce further growth. In our
own country Archer[193] welcomed the new views on lichens, and attempted
cultures but with very little success. Further synthetic cultures were made
by Bornet[194], Treub[195] and Borzi[196] with a series of lichen spores. They
also were able to observe the first stages of the thallus. Borzi observed
spores of Physcia (Xanthoria) parietina scattered among Protococcus cells
on the branch of a tree. The spores had germinated and the first branching
hyphae had already begun to encircle the algae.
for experiment the spores of Physcia (Xanthoria) parietina and was able to
show that hyphae produced from the germinating spore adhered to the free-
growing cells of Protococcus[191] viridis and formed the early stages of a
lichen thallus. Woronin[192] contributed his observations on the gonidia of
Parmelia (Physcia) pulverulenta which he isolated from the thallus and
cultivated in pure water. He confirmed the occurrence of cell division in the
gonidia and also the formation of zoospores, these again forming new
colonies of algae identical in all respects with the thalline gonidia. He was
able to see the germinating tube from a lichen spore attach itself to a
gonidium, though he failed in his attempts to induce further growth. In our
own country Archer[193] welcomed the new views on lichens, and attempted
cultures but with very little success. Further synthetic cultures were made
by Bornet[194], Treub[195] and Borzi[196] with a series of lichen spores. They
also were able to observe the first stages of the thallus. Borzi observed
spores of Physcia (Xanthoria) parietina scattered among Protococcus cells
on the branch of a tree. The spores had germinated and the first branching
hyphae had already begun to encircle the algae.
Page 72
Fig. 5. Endocarpon pusillum Hedw.
Asci and spores, with hymenial
gonidia × 320 (after Stahl).
Fig. 6. Endocarpon pusillum Hedw. Spore germinating in contact
with hymenial gonidia × 320 (after Stahl).
Asci and spores, with hymenial
gonidia × 320 (after Stahl).
Fig. 6. Endocarpon pusillum Hedw. Spore germinating in contact
with hymenial gonidia × 320 (after Stahl).
Page 73
Additional evidence in favour of the theory of the independent origin of
the colourless filaments and the green cells was furnished by Stahl’s[197]
research on hymenial gonidia in Endocarpon (Fig. 5). By making synthetic
cultures of the mature spores with these bodies, he was able to observe not
only the germination of the spores and the attachment of the filaments to the
gonidia (Fig. 6), but also the gradual building up of a complete lichen
thallus to the formation of perithecia and spores.
Fig. 7. Germination of spore of Physcia parietina De Not. in
contact with Protococcus viridis Ag. × 950 (after Bornet).
Fig. 8. Physcia parietina De Not. Vertical section of thallus obtained by synthetic
culture × 130 (after Bonnier).
the colourless filaments and the green cells was furnished by Stahl’s[197]
research on hymenial gonidia in Endocarpon (Fig. 5). By making synthetic
cultures of the mature spores with these bodies, he was able to observe not
only the germination of the spores and the attachment of the filaments to the
gonidia (Fig. 6), but also the gradual building up of a complete lichen
thallus to the formation of perithecia and spores.
Fig. 7. Germination of spore of Physcia parietina De Not. in
contact with Protococcus viridis Ag. × 950 (after Bornet).
Fig. 8. Physcia parietina De Not. Vertical section of thallus obtained by synthetic
culture × 130 (after Bonnier).
Page 74
Some years later Bonnier[198] made an interesting series of synthetic
cultures between the spores of lichens germinated in carefully sterilized
conditions, and algae taken from the open (Figs. 7 and 8). Separate control
cultures of spores and algae were carried on at the same time, with the
result that in one case lichen hyphae alone, in the other algae were
produced. The various lichen spores with which he experimented were
sown in association with the following algae:
(1) Protococcus.
Pure synthetic cultures of Physcia (Xanthoria) parietina were begun in
August 1884 on fragments of bark. In October 1886 the thallus was several
centimetres in diameter, and some of the lobes were fruited.
Physcia stellaris was also grown on bark; in one case both thallus and
apothecia were developed.
Parmelia acetabulum, another corticolous species, formed only a minute
thallus about 5 mm. in diameter, but entirely identical with normally
growing specimens.
(2) Pleurococcus.
Lecanora (Rinodina) sophodes, sown on rock in 1883, reached in 1886 a
diameter of 13 mm. with fully developed apothecia.
Lecanora ferruginea and L. subfusca after three years’ culture formed
sterile thalli only.
Lecanora coilocarpa in four years, and L. caesio-rufa in three years
formed very small thalli without fructification.
(3) Trentepohlia (Chroolepus).
Opegrapha vulgata in two years had developed thallus and apothecia.
The control culture of the spores formed, as in nature, a considerable felt of
mycelium in the interstices of the bark, but no pycnidia or apothecia.
Graphis elegans. Only the beginning of a differentiated thallus was
obtained with this species.
Verrucaria muralis (?)[199] gave in less than a year a completely
developed thallus.
cultures between the spores of lichens germinated in carefully sterilized
conditions, and algae taken from the open (Figs. 7 and 8). Separate control
cultures of spores and algae were carried on at the same time, with the
result that in one case lichen hyphae alone, in the other algae were
produced. The various lichen spores with which he experimented were
sown in association with the following algae:
(1) Protococcus.
Pure synthetic cultures of Physcia (Xanthoria) parietina were begun in
August 1884 on fragments of bark. In October 1886 the thallus was several
centimetres in diameter, and some of the lobes were fruited.
Physcia stellaris was also grown on bark; in one case both thallus and
apothecia were developed.
Parmelia acetabulum, another corticolous species, formed only a minute
thallus about 5 mm. in diameter, but entirely identical with normally
growing specimens.
(2) Pleurococcus.
Lecanora (Rinodina) sophodes, sown on rock in 1883, reached in 1886 a
diameter of 13 mm. with fully developed apothecia.
Lecanora ferruginea and L. subfusca after three years’ culture formed
sterile thalli only.
Lecanora coilocarpa in four years, and L. caesio-rufa in three years
formed very small thalli without fructification.
(3) Trentepohlia (Chroolepus).
Opegrapha vulgata in two years had developed thallus and apothecia.
The control culture of the spores formed, as in nature, a considerable felt of
mycelium in the interstices of the bark, but no pycnidia or apothecia.
Graphis elegans. Only the beginning of a differentiated thallus was
obtained with this species.
Verrucaria muralis (?)[199] gave in less than a year a completely
developed thallus.
Page 75
Bonnier also attempted cultures with species of Collema and Ephebe, but
was unsuccessful in inducing the formation of a lichen plant.
H. Hymenial Gonidia
Reference has already been made to the minute green cells which were
originally described by Nylander[200] as occurring in the perithecia of a few
Pyrenolichens as free gonidia, i.e. unentangled with lichen hyphae.
Fuisting[201] found them in the perithecium of Polyblastia (Staurothele)
catalepta at a very early stage of its development when the perithecial
tissues were newly differentiated from those of the surrounding thallus. The
gonidia enclosed in the perithecium differed in no wise from those of the
thallus: they had become mechanically enclosed in the new tissue; and
while those in the outer compact layers died off, those in the centre of the
structure, where a hollow space arises, were subject to very active division,
becoming smaller in the process and finally filling the cavity. Winter’s[202]
researches on similar lichens confirmed Fuisting’s conclusions: he
described them as similar to the thalline gonidia but lighter in colour and of
smaller size, measuring frequently only 2·3 µ in diameter, though this size
increased to about 7 µ when cultivated outside the perithecium.
Stahl[203] sufficiently demonstrated the importance of these gonidia in
supplying the germinating spores with the necessary algae. They come to lie
in vertical rows between the asci and, owing to pressure, assume an
elongate form[204] (Figs. 5 and 6). They have been seen in very few lichens,
in Endocarpon and Staurothele, both rather small genera of Pyrenolichens,
and, so far as is known, in two Discolichens, Lecidea phylliscocarpa and L.
phyllocaris, the latter recorded from Brazil by Wainio[205], and, on account
of the inclusion of gonidia in the hymenium, placed by him in a section,
Gonothecium.
I. Nature of Association between Alga and Fungus
a. Consortium and Symbiosis. These cultures had established
convincingly the composite nature of the lichen thallus, and Schwendener’s
opinion, that the relationship between the two organisms was some varying
degree of parasitism, was at first unhesitatingly accepted by most botanists.
was unsuccessful in inducing the formation of a lichen plant.
H. Hymenial Gonidia
Reference has already been made to the minute green cells which were
originally described by Nylander[200] as occurring in the perithecia of a few
Pyrenolichens as free gonidia, i.e. unentangled with lichen hyphae.
Fuisting[201] found them in the perithecium of Polyblastia (Staurothele)
catalepta at a very early stage of its development when the perithecial
tissues were newly differentiated from those of the surrounding thallus. The
gonidia enclosed in the perithecium differed in no wise from those of the
thallus: they had become mechanically enclosed in the new tissue; and
while those in the outer compact layers died off, those in the centre of the
structure, where a hollow space arises, were subject to very active division,
becoming smaller in the process and finally filling the cavity. Winter’s[202]
researches on similar lichens confirmed Fuisting’s conclusions: he
described them as similar to the thalline gonidia but lighter in colour and of
smaller size, measuring frequently only 2·3 µ in diameter, though this size
increased to about 7 µ when cultivated outside the perithecium.
Stahl[203] sufficiently demonstrated the importance of these gonidia in
supplying the germinating spores with the necessary algae. They come to lie
in vertical rows between the asci and, owing to pressure, assume an
elongate form[204] (Figs. 5 and 6). They have been seen in very few lichens,
in Endocarpon and Staurothele, both rather small genera of Pyrenolichens,
and, so far as is known, in two Discolichens, Lecidea phylliscocarpa and L.
phyllocaris, the latter recorded from Brazil by Wainio[205], and, on account
of the inclusion of gonidia in the hymenium, placed by him in a section,
Gonothecium.
I. Nature of Association between Alga and Fungus
a. Consortium and Symbiosis. These cultures had established
convincingly the composite nature of the lichen thallus, and Schwendener’s
opinion, that the relationship between the two organisms was some varying
degree of parasitism, was at first unhesitatingly accepted by most botanists.
Page 76
Reinke[206] was the first to point out the insufficiency of this view to
explain the long continued healthy life of both constituents, a condition so
different from all known instances of the disturbing or fatal parasitism of
one individual on another. He recognized in the association a state of
mutual growth and interdependence, that had resulted in the production of
an entirely new type of plant, and he suggested Consortium as a truer
description of the connection between the fungus and the alga. This term
had originally been coined by his friend Grisebach in a paper[206] describing
the presence of actively growing Nostoc algae in healthy Gunnera stems;
and Reinke compared that apparently harmless association with the similar
phenomenon in the lichen thallus. The comparison was emphasized by him
in a later paper[207] on the same subject, in which he ascribes to each
“consort” its function in the composite plant, and declares that if such a
mutual life of Alga and Ascomycete is to be regarded as one of parasitism,
it must be considered as reciprocal parasitism; and he insists that “much
more appropriate for this form of organic life is the conception and title of
Consortium.” In a special work on lichens, Reinke[208] further elaborated
his theory of the physiological activity and mutual service of the two
organisms forming the consortium.
Frank[209] suggested the term Homobium as appropriate, but it is faulty
inasmuch as it expresses a relationship of complete interdependence, and it
has been proved that the fungus partly, and the alga entirely, have the power
of free growth.
A wider currency was given to this view of a mutually advantageous
growth by de Bary[210]. He followed Reinke in refusing to accept as
satisfactory the theory of simple parasitism, and adduced the evident
healthy life of the algal cells—the alleged victims of the fungus—as
incompatible with the parasitic condition. He proposed the happily
descriptive designation of a Symbiosis or conjoint life which was mostly
though not always, nor in equal degree, beneficial to each of the partners or
symbionts.
b. Different Forms of Association. The type of association between the
two symbionts varies in different lichens. Bornet[211], in describing the
development of the thallus in certain members of the Collemaceae, found
that though as a rule the two elements of the thallus, as in some species of
explain the long continued healthy life of both constituents, a condition so
different from all known instances of the disturbing or fatal parasitism of
one individual on another. He recognized in the association a state of
mutual growth and interdependence, that had resulted in the production of
an entirely new type of plant, and he suggested Consortium as a truer
description of the connection between the fungus and the alga. This term
had originally been coined by his friend Grisebach in a paper[206] describing
the presence of actively growing Nostoc algae in healthy Gunnera stems;
and Reinke compared that apparently harmless association with the similar
phenomenon in the lichen thallus. The comparison was emphasized by him
in a later paper[207] on the same subject, in which he ascribes to each
“consort” its function in the composite plant, and declares that if such a
mutual life of Alga and Ascomycete is to be regarded as one of parasitism,
it must be considered as reciprocal parasitism; and he insists that “much
more appropriate for this form of organic life is the conception and title of
Consortium.” In a special work on lichens, Reinke[208] further elaborated
his theory of the physiological activity and mutual service of the two
organisms forming the consortium.
Frank[209] suggested the term Homobium as appropriate, but it is faulty
inasmuch as it expresses a relationship of complete interdependence, and it
has been proved that the fungus partly, and the alga entirely, have the power
of free growth.
A wider currency was given to this view of a mutually advantageous
growth by de Bary[210]. He followed Reinke in refusing to accept as
satisfactory the theory of simple parasitism, and adduced the evident
healthy life of the algal cells—the alleged victims of the fungus—as
incompatible with the parasitic condition. He proposed the happily
descriptive designation of a Symbiosis or conjoint life which was mostly
though not always, nor in equal degree, beneficial to each of the partners or
symbionts.
b. Different Forms of Association. The type of association between the
two symbionts varies in different lichens. Bornet[211], in describing the
development of the thallus in certain members of the Collemaceae, found
that though as a rule the two elements of the thallus, as in some species of
Page 77
Collema itself, persisted intact side by side, there was in other members of
the genus an occasional parasitism: short branches from the main hyphae
applied themselves by their tips to some cell of the Nostoc chain (Fig. 9).
The cell thus seized upon began to increase in size, and the plasma became
granular and gathered at the side furthest away from the point of
attachment. Finally the contents were used up, and nothing was left but an
empty membrane adhering to the fungus hypha. In another species the
hypha penetrated the cell. These instances of parasitism are most readily
seen towards the edge of the thallus where growth is more active; towards
the centre the attached cells have become absorbed, and only the shortened
broken chains attest their disappearance. The other cells of the chains
remain uninjured.
Fig. 9. Physma chalazanum Arn. Cells of Nostoc chains
penetrated and enlarged by hyphae × 950 (after Bornet).
In Synalissa, a small shrubby gelatinous genus, the hypha, as described
by Bornet and by Hedlund[212], pierces the outer wall of the gelatinous alga
(Gloeocapsa) and swells inside to a somewhat globose haustorium which
rests in a depression of the plasma (Fig. 10). The alga, though evidently
undamaged, is excited to a division which takes place on a plane that passes
through the haustorium; the two daughter-cells then separate, and in so
doing free themselves from the hypha.
the genus an occasional parasitism: short branches from the main hyphae
applied themselves by their tips to some cell of the Nostoc chain (Fig. 9).
The cell thus seized upon began to increase in size, and the plasma became
granular and gathered at the side furthest away from the point of
attachment. Finally the contents were used up, and nothing was left but an
empty membrane adhering to the fungus hypha. In another species the
hypha penetrated the cell. These instances of parasitism are most readily
seen towards the edge of the thallus where growth is more active; towards
the centre the attached cells have become absorbed, and only the shortened
broken chains attest their disappearance. The other cells of the chains
remain uninjured.
Fig. 9. Physma chalazanum Arn. Cells of Nostoc chains
penetrated and enlarged by hyphae × 950 (after Bornet).
In Synalissa, a small shrubby gelatinous genus, the hypha, as described
by Bornet and by Hedlund[212], pierces the outer wall of the gelatinous alga
(Gloeocapsa) and swells inside to a somewhat globose haustorium which
rests in a depression of the plasma (Fig. 10). The alga, though evidently
undamaged, is excited to a division which takes place on a plane that passes
through the haustorium; the two daughter-cells then separate, and in so
doing free themselves from the hypha.
Page 78
Fig. 10. Synalissa symphorea Nyl. Algae
(Gloeocapsa) with hyphae from the internal
thallus × 480 (after Bornet).
Hedlund followed the process of association between the two organisms
in the lichens Micarea (Biatorina) prasina and M. denigrata (Biatorina
synothea), crustaceous species which inhabit trunks of trees or palings. In
these the alga, one of the Chlorophyceae, has assumed the character of a
Gloeocapsa but on cultivation it was found to belong to the genus
Gloeocystis. The cells are globose and rather small; they increase by the
division of the contents into two or at most four portions which become
rounded off and covered with a membrane before they become free from
the mother-cell. The lichen hypha, on contact with any one of the green
cells, bores through the outer membrane and swells within to a haustorium,
as in the gonidia of Synalissa.
(Gloeocapsa) with hyphae from the internal
thallus × 480 (after Bornet).
Hedlund followed the process of association between the two organisms
in the lichens Micarea (Biatorina) prasina and M. denigrata (Biatorina
synothea), crustaceous species which inhabit trunks of trees or palings. In
these the alga, one of the Chlorophyceae, has assumed the character of a
Gloeocapsa but on cultivation it was found to belong to the genus
Gloeocystis. The cells are globose and rather small; they increase by the
division of the contents into two or at most four portions which become
rounded off and covered with a membrane before they become free from
the mother-cell. The lichen hypha, on contact with any one of the green
cells, bores through the outer membrane and swells within to a haustorium,
as in the gonidia of Synalissa.
Page 79
Fig. 11. Gonidia from Ramalina
reticulata Nyl. A, gonidium pierced and
cell contents shrinking × 560; B, older
stage, the contents of gonidium
exhausted × 900 (after Peirce).
Fig. 12. Pertusaria globulifera Nyl. Fungus and gonidia from
gonidial zone × 500 (after Darbishire).
Penetrating haustoria were demonstrated by Peirce[213] in his study of the
gonidia of Ramalina reticulata. In the first stage the tip of a hypha had
pierced the outer wall of the alga, causing the protoplasm to contract away
reticulata Nyl. A, gonidium pierced and
cell contents shrinking × 560; B, older
stage, the contents of gonidium
exhausted × 900 (after Peirce).
Fig. 12. Pertusaria globulifera Nyl. Fungus and gonidia from
gonidial zone × 500 (after Darbishire).
Penetrating haustoria were demonstrated by Peirce[213] in his study of the
gonidia of Ramalina reticulata. In the first stage the tip of a hypha had
pierced the outer wall of the alga, causing the protoplasm to contract away
Page 80
from the point of contact (Fig. 11). More advanced stages showed the
extension of the haustorium into the centre of the cell, and, finally, the
complete disappearance of the contents. In many cases it was found that
penetration equally with clasping of the alga by the filament sets up an
irritation which induces cell-division, and the alga, as in Synalissa, thus
becomes free from the fungus. Hue[214] has recorded instances of
penetration in an Antarctic species, Physcia puncticulata. It is easy, he says,
to see the tips of the hyphae pierce the sheath of the gonidium and penetrate
to the nucleus.
Lindau[215] has described the association between fungus and alga in
Pertusaria and other crustaceous forms as one of contact only (Fig. 12). He
found that the cell-membrane of the two adhering organisms was unbroken.
Occasionally the algal cell showed a slight indentation, but was otherwise
unchanged. The hyphal branch was somewhat swollen at the tip where it
touched the alga, and the wall was slightly thinner. The attachment between
the two cells was so close, however, that pressure on the cover-glass failed
to separate them.
Generally the hypha simply surrounds the gonidium with clasping
branches. Many algae also lie free in the gonidial zone, and Peirce[216]
claims that these are larger, more deeply coloured and in every way
healthier looking than those in the grasp of the fungus. He ignores,
however, the case of the soredial algae which though very closely invested
by the fungus are yet entirely healthy, since on their future increase depends
in many cases the reproduction of new individual lichens.
In a recent study of a crustaceous sandstone lichen, “Caloplaca pyracea,”
Claassen[217] has sought to prove a case of pure parasitism. The rock was at
first covered with the green cells of Cystococcus sp. Later there appeared
greyish-white patches on the green, representing the invasion of the lichen
fungus. These patches increased centrifugally, leaving in time a bare patch
in the centre of growth which was again colonized by the green alga. The
lichen fruited abundantly, but wherever it encroached the green cells were
more or less destroyed. The true explanation seems to be that the green cells
were absorbed into the lichen thallus, though enough of them persisted to
start new colonies on any bare piece of the stone. In the same way large
patches of Trentepohlia aurea have been observed to be gradually invaded
extension of the haustorium into the centre of the cell, and, finally, the
complete disappearance of the contents. In many cases it was found that
penetration equally with clasping of the alga by the filament sets up an
irritation which induces cell-division, and the alga, as in Synalissa, thus
becomes free from the fungus. Hue[214] has recorded instances of
penetration in an Antarctic species, Physcia puncticulata. It is easy, he says,
to see the tips of the hyphae pierce the sheath of the gonidium and penetrate
to the nucleus.
Lindau[215] has described the association between fungus and alga in
Pertusaria and other crustaceous forms as one of contact only (Fig. 12). He
found that the cell-membrane of the two adhering organisms was unbroken.
Occasionally the algal cell showed a slight indentation, but was otherwise
unchanged. The hyphal branch was somewhat swollen at the tip where it
touched the alga, and the wall was slightly thinner. The attachment between
the two cells was so close, however, that pressure on the cover-glass failed
to separate them.
Generally the hypha simply surrounds the gonidium with clasping
branches. Many algae also lie free in the gonidial zone, and Peirce[216]
claims that these are larger, more deeply coloured and in every way
healthier looking than those in the grasp of the fungus. He ignores,
however, the case of the soredial algae which though very closely invested
by the fungus are yet entirely healthy, since on their future increase depends
in many cases the reproduction of new individual lichens.
In a recent study of a crustaceous sandstone lichen, “Caloplaca pyracea,”
Claassen[217] has sought to prove a case of pure parasitism. The rock was at
first covered with the green cells of Cystococcus sp. Later there appeared
greyish-white patches on the green, representing the invasion of the lichen
fungus. These patches increased centrifugally, leaving in time a bare patch
in the centre of growth which was again colonized by the green alga. The
lichen fruited abundantly, but wherever it encroached the green cells were
more or less destroyed. The true explanation seems to be that the green cells
were absorbed into the lichen thallus, though enough of them persisted to
start new colonies on any bare piece of the stone. In the same way large
patches of Trentepohlia aurea have been observed to be gradually invaded
Page 81
by the dark coloured hyphae of Coenogonium ebeneum. In time the whole
of the alga is absorbed and nothing is to be seen but the dark felted lichen.
The free alga as such disappears, but it is hardly correct to describe the
process as one of destruction.
This algal genus Trentepohlia (Chroolepus) forms the gonidia of the
Graphideae, Roccelleae, etc. It is a filamentous aerial alga which increases
by apical growth. In the Graphideae, many of which grow on trees beneath
the outer bark (hypophloeodal), the association between the two symbionts
may be of the simplest character, but was considered by Frank[218] to be of
an advanced type. According to his observations and to those of Lindau[219],
the fungal hyphae penetrate first between the cells of the periderm. The
alga, frequently Trentepohlia umbrina, tends to grow down into any cracks
of the surface. It goes more deeply in when preceded by the hyphae. In
some species both organisms maintain their independent growth, though
each shows increased vigour when it comes into contact with the other. In
some instances the cells of the alga are clasped by the fungus which causes
the disintegration of the filament. The cells lose their bright yellow or
reddish colour and are changed in appearance to greenish lichen gonidia;
but no penetration by haustoria has ever been observed in Trentepohlia.
Bachmann’s[220] study of a similar gonidium in a calcicolous species of
Opegrapha confirms Frank’s results. The algae had pierced not only
between the looser lime granules but also through a crystal of calcium
carbonate, and occupied nests scooped out in the rock by means of acid
formed and excreted by their filaments. When association took place with
the fungus, the algal cells were more restricted to a gonidial zone; but some
of the cells, having been pushed aside by the hyphae, had started new
centres of gonidia. On contact with the hyphae there was a tendency to bud
out in a yeast-like growth.
In the thallus of the Roccelleae, the algal filament, also a Trentepohlia, is
broken up into separate cells, but in the Coenogoniaceae, whether the
gonidium be a Cladophora as in Racodium, or a Trentepohlia as in
Coenogonium, the filaments remain intact and are invested more or less
closely by the hyphae.
of the alga is absorbed and nothing is to be seen but the dark felted lichen.
The free alga as such disappears, but it is hardly correct to describe the
process as one of destruction.
This algal genus Trentepohlia (Chroolepus) forms the gonidia of the
Graphideae, Roccelleae, etc. It is a filamentous aerial alga which increases
by apical growth. In the Graphideae, many of which grow on trees beneath
the outer bark (hypophloeodal), the association between the two symbionts
may be of the simplest character, but was considered by Frank[218] to be of
an advanced type. According to his observations and to those of Lindau[219],
the fungal hyphae penetrate first between the cells of the periderm. The
alga, frequently Trentepohlia umbrina, tends to grow down into any cracks
of the surface. It goes more deeply in when preceded by the hyphae. In
some species both organisms maintain their independent growth, though
each shows increased vigour when it comes into contact with the other. In
some instances the cells of the alga are clasped by the fungus which causes
the disintegration of the filament. The cells lose their bright yellow or
reddish colour and are changed in appearance to greenish lichen gonidia;
but no penetration by haustoria has ever been observed in Trentepohlia.
Bachmann’s[220] study of a similar gonidium in a calcicolous species of
Opegrapha confirms Frank’s results. The algae had pierced not only
between the looser lime granules but also through a crystal of calcium
carbonate, and occupied nests scooped out in the rock by means of acid
formed and excreted by their filaments. When association took place with
the fungus, the algal cells were more restricted to a gonidial zone; but some
of the cells, having been pushed aside by the hyphae, had started new
centres of gonidia. On contact with the hyphae there was a tendency to bud
out in a yeast-like growth.
In the thallus of the Roccelleae, the algal filament, also a Trentepohlia, is
broken up into separate cells, but in the Coenogoniaceae, whether the
gonidium be a Cladophora as in Racodium, or a Trentepohlia as in
Coenogonium, the filaments remain intact and are invested more or less
closely by the hyphae.
Page 82
Fig. 13. Outer edge of Phycopeltis expansa Jenn.,
the alga attacked by hyphae and passing into
separate gonidia × 500 (after Vaughan Jennings).
A somewhat different type of association takes place between alga and
fungus in Strigula complanata, an epiphyllous lichen more or less common
in tropical regions. Cunningham[221], who found it near Calcutta, described
the algal constituent and placed it in a new genus, Mycoidea (Cephaleuros).
It forms small plate-like expansions on the surface of the leaf, and also
penetrates below the cuticle, burrowing between that and the epidermal
cells; occasionally, as observed by Cunningham, rhizoid-like growths pierce
deeper into the tissue—into and below the epidermal layer. Very frequently,
in the wet season, a fungus takes possession of the alga and slender
colourless hyphae creep along its surface by the side of the cell rows,
sending out branches which grow downwards. Marshall Ward[222] described
the same lichen from Ceylon. He states that the alga may be attacked at any
stage, and if it is in a very young condition it is killed by the fungus; at a
more advanced period of growth it continues to develop as an integral part
of the lichen thallus, but with more frequently divided and smaller cells.
Vaughan Jennings[223] observed Strigula complanata in New Zealand
associated with a closely allied chroolepoid alga Phycopeltis expansa. He
also noted the growth of the fungus over the alga breaking up the plates of
tissue and separating the cells which, from yellow, change to a green colour
and become rounded off (Fig. 13). The mature lichen, a white thallus dotted
with black fruits, contrasts strikingly with the yellow membranous alga.
Lichen formation usually begins near the edge of the leaf and the margin of
the thallus itself is marked by a green zone showing where the fungus has
recently come into contact with the alga.
the alga attacked by hyphae and passing into
separate gonidia × 500 (after Vaughan Jennings).
A somewhat different type of association takes place between alga and
fungus in Strigula complanata, an epiphyllous lichen more or less common
in tropical regions. Cunningham[221], who found it near Calcutta, described
the algal constituent and placed it in a new genus, Mycoidea (Cephaleuros).
It forms small plate-like expansions on the surface of the leaf, and also
penetrates below the cuticle, burrowing between that and the epidermal
cells; occasionally, as observed by Cunningham, rhizoid-like growths pierce
deeper into the tissue—into and below the epidermal layer. Very frequently,
in the wet season, a fungus takes possession of the alga and slender
colourless hyphae creep along its surface by the side of the cell rows,
sending out branches which grow downwards. Marshall Ward[222] described
the same lichen from Ceylon. He states that the alga may be attacked at any
stage, and if it is in a very young condition it is killed by the fungus; at a
more advanced period of growth it continues to develop as an integral part
of the lichen thallus, but with more frequently divided and smaller cells.
Vaughan Jennings[223] observed Strigula complanata in New Zealand
associated with a closely allied chroolepoid alga Phycopeltis expansa. He
also noted the growth of the fungus over the alga breaking up the plates of
tissue and separating the cells which, from yellow, change to a green colour
and become rounded off (Fig. 13). The mature lichen, a white thallus dotted
with black fruits, contrasts strikingly with the yellow membranous alga.
Lichen formation usually begins near the edge of the leaf and the margin of
the thallus itself is marked by a green zone showing where the fungus has
recently come into contact with the alga.
Page 83
More recently Hans Fitting[224] has described “Mycoidea parasitica” as it
occurs on evergreen leaves in Java. The alga, a species of Cephaleuros,
though at first an epiphyte, becomes partially parasitic at maturity. It
penetrates below the cuticle to the outer epidermal cells and may even reach
the tissue below. When it is joined by the lichen fungus, both constituents
grow together to form the lichen. Fitting adds that the leaf is evidently but
little injured. In this lichen the alga in the grip of the fungus loses its
independence and may be killed off: it is an instance of something like
intermittent parasitism.
J. Recent views on Symbiosis and Parasitism
No hyphal penetration of the bright-green algal cell by means of
haustoria had been observed by the earlier workers, Bornet[225],
Bonnier[226] and others, though they followed Schwendener[227] in
regarding the relationship as one of host and parasite. Lindau, also, after
long study accepted parasitism as the only adequate explanation of the
associated growth, though he never found the fungus actually preying on
the alga.
In recent years interest in the subject has been revived by the researches
of Elenkin[228], a Russian botanist who claims to have established a case for
parasitism or rather “endosaprophytism.” He has demonstrated by means of
staining reagents the presence in the thallus of large numbers of dead algal
cells. A few empty membranes are to be found in the cortex and in the
gonidial zone, but the larger proportion occur below the gonidial zone and
partly in the medulla. He describes the lower layer as a “necral” or
“hyponecral” zone, and he considers that the hyphae draw their
nourishment chiefly from dead algal material. The fungus must therefore be
regarded in this case as a saprophyte rather than a parasite. The algae, he
considers, may have perished from want of sufficient light and air or they
may have been destroyed by an enzyme produced by the fungus. The latter
he thinks is the more probable, as dead cells are frequently present among
the living algae of the gonidial zone. To the action of the enzyme he also
attributes the angular deformed appearance of many gonidia and the paler
colour and gradual disintegration of their contents which are finally used up
as endosaprophytic nourishment by the fungus. Dead algal cells were more
occurs on evergreen leaves in Java. The alga, a species of Cephaleuros,
though at first an epiphyte, becomes partially parasitic at maturity. It
penetrates below the cuticle to the outer epidermal cells and may even reach
the tissue below. When it is joined by the lichen fungus, both constituents
grow together to form the lichen. Fitting adds that the leaf is evidently but
little injured. In this lichen the alga in the grip of the fungus loses its
independence and may be killed off: it is an instance of something like
intermittent parasitism.
J. Recent views on Symbiosis and Parasitism
No hyphal penetration of the bright-green algal cell by means of
haustoria had been observed by the earlier workers, Bornet[225],
Bonnier[226] and others, though they followed Schwendener[227] in
regarding the relationship as one of host and parasite. Lindau, also, after
long study accepted parasitism as the only adequate explanation of the
associated growth, though he never found the fungus actually preying on
the alga.
In recent years interest in the subject has been revived by the researches
of Elenkin[228], a Russian botanist who claims to have established a case for
parasitism or rather “endosaprophytism.” He has demonstrated by means of
staining reagents the presence in the thallus of large numbers of dead algal
cells. A few empty membranes are to be found in the cortex and in the
gonidial zone, but the larger proportion occur below the gonidial zone and
partly in the medulla. He describes the lower layer as a “necral” or
“hyponecral” zone, and he considers that the hyphae draw their
nourishment chiefly from dead algal material. The fungus must therefore be
regarded in this case as a saprophyte rather than a parasite. The algae, he
considers, may have perished from want of sufficient light and air or they
may have been destroyed by an enzyme produced by the fungus. The latter
he thinks is the more probable, as dead cells are frequently present among
the living algae of the gonidial zone. To the action of the enzyme he also
attributes the angular deformed appearance of many gonidia and the paler
colour and gradual disintegration of their contents which are finally used up
as endosaprophytic nourishment by the fungus. Dead algal cells were more
Page 84
easily seen, he tells us, in crustaceous lichens associated with
“Pleurococcus” or “Cystococcus”; they were much less frequent in the
larger foliose or fruticose lichens. Dead cells of Trentepohlia were also
difficult to find.
In a second paper Elenkin records one clear instance of a haustorium
entering an algal cell, and says he found some evidence of hyphal branches
penetrating otherwise uninjured gonidia, round holes being visible in their
outer wall, but he holds that it is the cell-wall of the alga that is mainly
dissolved by the ferment and then used as food by the hyphae.
No allowance has been made by Elenkin for the normal wasting common
to all organic beings: the lichen fungus is continually being renewed,
especially in the cortical structures, and the alga must also be subject to
change. He[229] claims, nevertheless, that his observations have proved that
the one symbiont is always preying on the other, either as a parasite or as a
saprophyte. He has likened the conception of symbiosis to that of a balance
between two organisms, “a moveable equilibrium of the symbionts.” If, he
says, we could conceive a state where the conditions of life would be
equally favourable for both partners there would be true mutualism, but in
practice one only is favoured and gains the upper hand, using its advantage
to prey on the other. Unless the balance is redressed, the complete
destruction of the weaker is certain, and is followed in time by the death of
the stronger. The fungus being the dominant partner, the balance, he
considers, is tipped in its favour.
Elenkin’s conclusions are not borne out by the long continued and
healthy life of the lichen. There is no record of either symbiont having
succumbed to the other, and the alga, when set free, is unchanged and able
to resume its normal development. Without the alga the fungus cannot form
the ascigerous fruit. Is that because as a parasite within the lichen it has
degenerated past recovery, or has it become so adapted to symbiosis that in
saprophytic conditions it fails to develop?
Another Russian lichenologist, U. N. Danilov[230], records results which
would seem to support the theory of parasitism. He found that from the
clasping hyphae minute haustoria were produced, which penetrate the algal
cell-wall, and branch when within the outer membrane, thus forming a
delicate network over the plasma; secondary haustoria arising from this
“Pleurococcus” or “Cystococcus”; they were much less frequent in the
larger foliose or fruticose lichens. Dead cells of Trentepohlia were also
difficult to find.
In a second paper Elenkin records one clear instance of a haustorium
entering an algal cell, and says he found some evidence of hyphal branches
penetrating otherwise uninjured gonidia, round holes being visible in their
outer wall, but he holds that it is the cell-wall of the alga that is mainly
dissolved by the ferment and then used as food by the hyphae.
No allowance has been made by Elenkin for the normal wasting common
to all organic beings: the lichen fungus is continually being renewed,
especially in the cortical structures, and the alga must also be subject to
change. He[229] claims, nevertheless, that his observations have proved that
the one symbiont is always preying on the other, either as a parasite or as a
saprophyte. He has likened the conception of symbiosis to that of a balance
between two organisms, “a moveable equilibrium of the symbionts.” If, he
says, we could conceive a state where the conditions of life would be
equally favourable for both partners there would be true mutualism, but in
practice one only is favoured and gains the upper hand, using its advantage
to prey on the other. Unless the balance is redressed, the complete
destruction of the weaker is certain, and is followed in time by the death of
the stronger. The fungus being the dominant partner, the balance, he
considers, is tipped in its favour.
Elenkin’s conclusions are not borne out by the long continued and
healthy life of the lichen. There is no record of either symbiont having
succumbed to the other, and the alga, when set free, is unchanged and able
to resume its normal development. Without the alga the fungus cannot form
the ascigerous fruit. Is that because as a parasite within the lichen it has
degenerated past recovery, or has it become so adapted to symbiosis that in
saprophytic conditions it fails to develop?
Another Russian lichenologist, U. N. Danilov[230], records results which
would seem to support the theory of parasitism. He found that from the
clasping hyphae minute haustoria were produced, which penetrate the algal
cell-wall, and branch when within the outer membrane, thus forming a
delicate network over the plasma; secondary haustoria arising from this
Page 85
network protrude into the interior and rob the cell-contents. He observed
gonidia filled with well-developed hyphae and these, after having exhausted
one cell, travel onwards to others. Some gonidia under the influence of the
fungus had become deformed and were finally killed. As a proof of this
latter statement he adduces the presence in the thallus of some gonidia
containing shrivelled protoplasm, of others entirely empty. He considers, as
further evidence in favour of parasitism, the finding of empty membranes as
well as of colourless gonidia filled with the hyphal network. This
description hardly tallies with the usual healthy appearance of the gonidial
zone in the normal thallus, and it has been suggested that where the fungus
filled the algal cell, it was as a saprophyte preying on dead material.
The gradual perishing of algal cells in time by natural decay and their
subsequent absorption by the fungus is undisputed. It is open to question
whether the varying results recorded by these workers have any further
significance.
These observations of Elenkin and Danilov have been proved to be
erroneous by Paulson and Somerville Hastings[231]. They examined the
thalli of several lichens (Xanthoria parietina, Cladonia sp., etc.) collected
in early spring when vegetative growth in these plants was found to be at its
highest activity. They found an abundant increase of gonidia within the
thallus, which they regarded as sporulation of the algae, and the most
careful methods of staining failed to reveal any case of penetration of the
gonidia by the hyphae.
Nienburg[232] has published some recent observations on the association
of the symbionts. In the wide cortex of a Pertusaria he found not only the
densely compact hyphae, but also isolated gonidia. In front of these latter
there was a small hollow cavity and, behind, parallel hyphae rich in
contents. These gonidia had originated from the normal gonidial zone. They
were moved upward by special hyphae called by Nienburg “push-hyphae.”
After their transportation, the algae at once divide and the products of
division pass to a resting stage and become the centre of a new thalline
growth. A somewhat similar process was noted towards the apex of Evernia
furfuracea. Radial hyphae pushed up the cortex, leaving a hollow space
over the gonidial zone. Into the space isolated algae were thrust by “push-
hyphae.” In this lichen he also observed the penetration of the algal cell by
gonidia filled with well-developed hyphae and these, after having exhausted
one cell, travel onwards to others. Some gonidia under the influence of the
fungus had become deformed and were finally killed. As a proof of this
latter statement he adduces the presence in the thallus of some gonidia
containing shrivelled protoplasm, of others entirely empty. He considers, as
further evidence in favour of parasitism, the finding of empty membranes as
well as of colourless gonidia filled with the hyphal network. This
description hardly tallies with the usual healthy appearance of the gonidial
zone in the normal thallus, and it has been suggested that where the fungus
filled the algal cell, it was as a saprophyte preying on dead material.
The gradual perishing of algal cells in time by natural decay and their
subsequent absorption by the fungus is undisputed. It is open to question
whether the varying results recorded by these workers have any further
significance.
These observations of Elenkin and Danilov have been proved to be
erroneous by Paulson and Somerville Hastings[231]. They examined the
thalli of several lichens (Xanthoria parietina, Cladonia sp., etc.) collected
in early spring when vegetative growth in these plants was found to be at its
highest activity. They found an abundant increase of gonidia within the
thallus, which they regarded as sporulation of the algae, and the most
careful methods of staining failed to reveal any case of penetration of the
gonidia by the hyphae.
Nienburg[232] has published some recent observations on the association
of the symbionts. In the wide cortex of a Pertusaria he found not only the
densely compact hyphae, but also isolated gonidia. In front of these latter
there was a small hollow cavity and, behind, parallel hyphae rich in
contents. These gonidia had originated from the normal gonidial zone. They
were moved upward by special hyphae called by Nienburg “push-hyphae.”
After their transportation, the algae at once divide and the products of
division pass to a resting stage and become the centre of a new thalline
growth. A somewhat similar process was noted towards the apex of Evernia
furfuracea. Radial hyphae pushed up the cortex, leaving a hollow space
over the gonidial zone. Into the space isolated algae were thrust by “push-
hyphae.” In this lichen he also observed the penetration of the algal cell by
Page 86
haustoria of the fungus. He considers that the alga reaps advantage but also
suffers harm, and he proposes the term helotism to express the relationship.
An instructive case of the true parasitism of a fungus on an alga has been
described by Zukal[233] in the case of Endomyces scytonemata which he
calls a “half-lichen.” The mature fungus formed small swellings on the
filaments of the Scytonema and, when examined, the hyphae were seen to
have attacked the alga, penetrating the outer gelatinous sheath and then
using up the contents of the green cells. It is only after the alga has been
destroyed and absorbed, that asci are formed by the fungus. Zukal contrasts
the development of this fungus with the symbiotic growth of the two
constituents in Ephebe where both grow together for an indefinite time.
Mere associated growth however even between a fungus and an alga does
not constitute a lichen. An instance of such growth is described by
Sutherland[234] in an account of marine microfungi. One of these, a species
of Mycosphaerella, was found on Pelvetia canaliculata, and Sutherland
claims that as no apparent injury was done to the alga, it was a case of
symbiosis and that there was formed a new type of lichen. The mycelium,
always intercellular, pervaded the whole host-plant, and the fungal fruits
were invariably formed on the algal receptacles close to the oogonia. Their
position there is, of course, due to the greater food supply at that region.
Both fungus and alga fruited freely. A closer analogy could have been found
by the writer in the smut fungus which grows with the host-cereal until
fruiting time; or with the mycorrhiza of Calluna which also pervades every
part of the host-plant without causing any injury. In the true lichen, the alga,
though constituting an important part of the vegetative body, takes no part
in reproduction, except by division and increase of the vegetative cells
within the thallus. The fruiting bodies are always of a modified fungal
nature.
2. PHYSIOLOGY OF THE SYMBIONTS
The occurrence of isolated cases of parasitism—the fungus preying on
the alga—in any case leaves the general problem unsolved. The whole
question turns on the physiological activity and requirements of the two
component elements of the thallus. From what sources do they each procure
suffers harm, and he proposes the term helotism to express the relationship.
An instructive case of the true parasitism of a fungus on an alga has been
described by Zukal[233] in the case of Endomyces scytonemata which he
calls a “half-lichen.” The mature fungus formed small swellings on the
filaments of the Scytonema and, when examined, the hyphae were seen to
have attacked the alga, penetrating the outer gelatinous sheath and then
using up the contents of the green cells. It is only after the alga has been
destroyed and absorbed, that asci are formed by the fungus. Zukal contrasts
the development of this fungus with the symbiotic growth of the two
constituents in Ephebe where both grow together for an indefinite time.
Mere associated growth however even between a fungus and an alga does
not constitute a lichen. An instance of such growth is described by
Sutherland[234] in an account of marine microfungi. One of these, a species
of Mycosphaerella, was found on Pelvetia canaliculata, and Sutherland
claims that as no apparent injury was done to the alga, it was a case of
symbiosis and that there was formed a new type of lichen. The mycelium,
always intercellular, pervaded the whole host-plant, and the fungal fruits
were invariably formed on the algal receptacles close to the oogonia. Their
position there is, of course, due to the greater food supply at that region.
Both fungus and alga fruited freely. A closer analogy could have been found
by the writer in the smut fungus which grows with the host-cereal until
fruiting time; or with the mycorrhiza of Calluna which also pervades every
part of the host-plant without causing any injury. In the true lichen, the alga,
though constituting an important part of the vegetative body, takes no part
in reproduction, except by division and increase of the vegetative cells
within the thallus. The fruiting bodies are always of a modified fungal
nature.
2. PHYSIOLOGY OF THE SYMBIONTS
The occurrence of isolated cases of parasitism—the fungus preying on
the alga—in any case leaves the general problem unsolved. The whole
question turns on the physiological activity and requirements of the two
component elements of the thallus. From what sources do they each procure
Page 87
the materials essential to them as living organisms? It is chiefly a question
of nutrition.
A. Nutrition of Algae
a. Character of Algal Cells. Gonidia are chlorophyll-containing bodies
and assimilate carbon-dioxide from the atmosphere by photosynthesis as do
the chlorophyll cells of other plants. They also require water and mineral
salts which, in a free condition, they absorb from their immediate
surroundings, but which, in the lichen thallus, they must obtain from the
fungal hyphae. If the nutriment supplied to them in their inclosed position
be greater or even equal to what the cells could procure as free-living algae,
then they undoubtedly gain rather than lose by their association with the
fungus, and are not to be considered merely as victims of parasitism.
b. Supply of Nitrogen. Important contributions on the subject of algal
nutrition have been made by Beyerinck[235] and Artari[236]. The former
conducted a series of culture experiments with green algae, including the
gonidia of Physcia (Xanthoria) parietina. He successfully isolated the
lichen gonidia and, at first, attempted to grow them on gelatine with an
infusion of the Elm bark from which he had taken the lichen. Growth was
very slow and very feeble until he added to the culture-medium a solution
of malt-extract which contains peptones and sugar. Very soon he obtained
an active development of the gonidia, and they multiplied rapidly by
division[237] as in the lichen thallus. This proved to him conclusively the
great advantage to the algae of an abundant supply of nitrogen.
Artari in his work has demonstrated that there are two different
physiological races of green algae: (1) those that absorb peptones—which
he designates peptone-algae—and (2) those that do not so absorb peptones.
He tested the cells of Cystococcus humicola taken from the thallus of
Physcia parietina, and found that they belonged to the peptone group and
were therefore dependent on a sufficiency of nitrogenous material to attain
their normal vigorous growth. It was also discovered by Artari that the one
race can be made by cultivation to pass over to the other: that ordinary
algae can be educated to live on peptones, and peptone-algae to do without.
We learn further from Beyerinck’s researches that Ascomycetes, the
group of fungi from which the hyphae of most lichens are derived, are what
of nutrition.
A. Nutrition of Algae
a. Character of Algal Cells. Gonidia are chlorophyll-containing bodies
and assimilate carbon-dioxide from the atmosphere by photosynthesis as do
the chlorophyll cells of other plants. They also require water and mineral
salts which, in a free condition, they absorb from their immediate
surroundings, but which, in the lichen thallus, they must obtain from the
fungal hyphae. If the nutriment supplied to them in their inclosed position
be greater or even equal to what the cells could procure as free-living algae,
then they undoubtedly gain rather than lose by their association with the
fungus, and are not to be considered merely as victims of parasitism.
b. Supply of Nitrogen. Important contributions on the subject of algal
nutrition have been made by Beyerinck[235] and Artari[236]. The former
conducted a series of culture experiments with green algae, including the
gonidia of Physcia (Xanthoria) parietina. He successfully isolated the
lichen gonidia and, at first, attempted to grow them on gelatine with an
infusion of the Elm bark from which he had taken the lichen. Growth was
very slow and very feeble until he added to the culture-medium a solution
of malt-extract which contains peptones and sugar. Very soon he obtained
an active development of the gonidia, and they multiplied rapidly by
division[237] as in the lichen thallus. This proved to him conclusively the
great advantage to the algae of an abundant supply of nitrogen.
Artari in his work has demonstrated that there are two different
physiological races of green algae: (1) those that absorb peptones—which
he designates peptone-algae—and (2) those that do not so absorb peptones.
He tested the cells of Cystococcus humicola taken from the thallus of
Physcia parietina, and found that they belonged to the peptone group and
were therefore dependent on a sufficiency of nitrogenous material to attain
their normal vigorous growth. It was also discovered by Artari that the one
race can be made by cultivation to pass over to the other: that ordinary
algae can be educated to live on peptones, and peptone-algae to do without.
We learn further from Beyerinck’s researches that Ascomycetes, the
group of fungi from which the hyphae of most lichens are derived, are what
Page 88
he terms ammonia-sugar fungi; that is to say, the hyphae can abstract
nitrogen from ammonia salts and, with the addition of sugar, can form
peptones. The lichen peptone-algae are thus evidently, by their contact with
such fungi, in a favourable position for securing the nitrogenous food
supply most suited to their requirements. In their deep-seated layers, they
are to a large extent deprived of light, but it has been proved by Artari[238]
in a series of culture experiments extending over a long period, that the
gonidia of Xanthoria parietina remain green in the dark under very varied
conditions of nutriment, though the colour is distinctly fainter.
Recently Treboux[239] has revised the work done by Artari and Beyerinck
in reference to Cystococcus humicola. He denies that two physiological
races are represented in this alga, the lichen gonidia, in regard to the
nitrogen that they absorb, behaving exactly as do the free-living forms of
the species. He finds that the gonidium is not a peptone-carbohydrate
organism in the sense that it requires nitrogen in the form of peptones,
inorganic ammonia salts being a more acceptable food supply. Treboux
concludes that his results favour the view that the gonidia are in an
unfavourable situation for receiving the kind of nitrogenous compound
most advantageous to them, that they are therefore in a sense “victims” of
parasitism, though he qualifies the condition as being a lichen-parasitism or
helotism. This view does not accord with Chodat’s[240] results: in his
cultures of gonidia he observed that with glycocoll or peptone, which are
nearly equivalent, they developed four times better than with potassium
nitrate as their nitrogenous food, and he concluded that they assimilated
nitrogen better from bodies allied to peptides.
c. Effect of Symbiosis on the Alga. Treboux’s observations however
convinced him that the alga leads but a meagre existence within the thallus.
Cell-division—the expression of active vitality—was, he held, of rare
occurrence in the slowly growing lichen-plant, and zoospore formation in
entire abeyance. He contrasts this sluggish increase[241] with the rapid
multiplication of the free-living algal cells which cover whole tree-trunks
with their descendants in a comparatively short time. These latter cells, he
finds, are indeed rather smaller, being generally the products of recent
division, but mixed with them are numbers of larger resting cells,
comparable in size with the lichen gonidia. He states further, that the
gonidia are less brightly green and, as he judges, less healthy, though in
nitrogen from ammonia salts and, with the addition of sugar, can form
peptones. The lichen peptone-algae are thus evidently, by their contact with
such fungi, in a favourable position for securing the nitrogenous food
supply most suited to their requirements. In their deep-seated layers, they
are to a large extent deprived of light, but it has been proved by Artari[238]
in a series of culture experiments extending over a long period, that the
gonidia of Xanthoria parietina remain green in the dark under very varied
conditions of nutriment, though the colour is distinctly fainter.
Recently Treboux[239] has revised the work done by Artari and Beyerinck
in reference to Cystococcus humicola. He denies that two physiological
races are represented in this alga, the lichen gonidia, in regard to the
nitrogen that they absorb, behaving exactly as do the free-living forms of
the species. He finds that the gonidium is not a peptone-carbohydrate
organism in the sense that it requires nitrogen in the form of peptones,
inorganic ammonia salts being a more acceptable food supply. Treboux
concludes that his results favour the view that the gonidia are in an
unfavourable situation for receiving the kind of nitrogenous compound
most advantageous to them, that they are therefore in a sense “victims” of
parasitism, though he qualifies the condition as being a lichen-parasitism or
helotism. This view does not accord with Chodat’s[240] results: in his
cultures of gonidia he observed that with glycocoll or peptone, which are
nearly equivalent, they developed four times better than with potassium
nitrate as their nitrogenous food, and he concluded that they assimilated
nitrogen better from bodies allied to peptides.
c. Effect of Symbiosis on the Alga. Treboux’s observations however
convinced him that the alga leads but a meagre existence within the thallus.
Cell-division—the expression of active vitality—was, he held, of rare
occurrence in the slowly growing lichen-plant, and zoospore formation in
entire abeyance. He contrasts this sluggish increase[241] with the rapid
multiplication of the free-living algal cells which cover whole tree-trunks
with their descendants in a comparatively short time. These latter cells, he
finds, are indeed rather smaller, being generally the products of recent
division, but mixed with them are numbers of larger resting cells,
comparable in size with the lichen gonidia. He states further, that the
gonidia are less brightly green and, as he judges, less healthy, though in
Page 89
soredial formation or in the open they at once regain both colour and power
of division. Treboux had entirely failed to observe the sporulation which is
so abundant at certain seasons.
Their quick recovery seems also a strong argument in favour of the
absolutely normal condition of metabolism within the gonidial cell; and the
paler appearance of the chlorophyll is doubtless associated with the
acquisition of carbohydrates from other sources than by photosynthesis.
There is a wide difference between any degree of unfavourable life-
conditions and parasitism however slight, even though the balance of gain
is on the side of the fungus. It is not too fanciful to conclude that the
demand for nitrogen on the part of the alga has influenced its peculiar
association with the fungus. In the thallus of hypophloeodal lichens it has
been proved indeed that the alga Trentepohlia with apical growth is an
active agent in the symbiotic union. Cystococcus and other green algal cells
are stationary, but they are doubtless equally ready for—as many of them
are equally benefited by—the association. Keeble[242] has pointed out in the
case of Convoluta roscoffensis that nitrogen-hunger induces the green algae
to combine forces with an animal organism, though the benefit to them is
only temporary and though they are finally sacrificed. The lichen gonidia,
on the contrary, persist for a long time, probably far beyond their normal
period of existence as free algae.
Examples of algal association with other plants might be cited here: of
Nostoc in the roots of Cycas and in the cells of Anthoceros, and of Anabæna
in the leaf-cells of Azolla, but in these instances it is generally held that the
alga secures only shelter. It was by comparing the lichen-association with
the harmless invasion of Gunnera cells by Nostoc that Reinke[243] arrived at
his conception of “consortism.”
d. Supply of Carbon. Carbon, the essential constituent of all organic life,
is partly drawn from the carbon-dioxide of the air, and assimilated by the
green cells; it is also partly contributed by the fungus as a product of its
metabolism. A proof of this is afforded by Dufrenoy[244]: he found a
Parmelia growing closely round pine needles and even sending suckers into
the stomata. He covered the lichen with a black cloth and after seven weeks
found that the gonidia had remained very green. That growth had not been
checked was evidenced by an unusual development of soredia and of
of division. Treboux had entirely failed to observe the sporulation which is
so abundant at certain seasons.
Their quick recovery seems also a strong argument in favour of the
absolutely normal condition of metabolism within the gonidial cell; and the
paler appearance of the chlorophyll is doubtless associated with the
acquisition of carbohydrates from other sources than by photosynthesis.
There is a wide difference between any degree of unfavourable life-
conditions and parasitism however slight, even though the balance of gain
is on the side of the fungus. It is not too fanciful to conclude that the
demand for nitrogen on the part of the alga has influenced its peculiar
association with the fungus. In the thallus of hypophloeodal lichens it has
been proved indeed that the alga Trentepohlia with apical growth is an
active agent in the symbiotic union. Cystococcus and other green algal cells
are stationary, but they are doubtless equally ready for—as many of them
are equally benefited by—the association. Keeble[242] has pointed out in the
case of Convoluta roscoffensis that nitrogen-hunger induces the green algae
to combine forces with an animal organism, though the benefit to them is
only temporary and though they are finally sacrificed. The lichen gonidia,
on the contrary, persist for a long time, probably far beyond their normal
period of existence as free algae.
Examples of algal association with other plants might be cited here: of
Nostoc in the roots of Cycas and in the cells of Anthoceros, and of Anabæna
in the leaf-cells of Azolla, but in these instances it is generally held that the
alga secures only shelter. It was by comparing the lichen-association with
the harmless invasion of Gunnera cells by Nostoc that Reinke[243] arrived at
his conception of “consortism.”
d. Supply of Carbon. Carbon, the essential constituent of all organic life,
is partly drawn from the carbon-dioxide of the air, and assimilated by the
green cells; it is also partly contributed by the fungus as a product of its
metabolism. A proof of this is afforded by Dufrenoy[244]: he found a
Parmelia growing closely round pine needles and even sending suckers into
the stomata. He covered the lichen with a black cloth and after seven weeks
found that the gonidia had remained very green. That growth had not been
checked was evidenced by an unusual development of soredia and of
Page 90
spermogonia. Dufrenoy describes the condition as a parasitism of the algae
on the fungus which in turn was drawing nourishment from the pine
needles.
Artari[245] has proved that lichen gonidia can obtain carbohydrates from
the substratum as well as by photosynthesis. He cultivated the gonidia of
Xanthoria parietina and Placodium murorum on media which contained
organic substances as well as mineral salts, while depriving them of
atmospheric carbon-dioxide and in some cases of light also. The gonidia not
only grew well but, even in the dark, they remained normally green, a
phenomenon coinciding with Etard and Bouilhac’s[246] experience in
growing Nostoc in the dark: with suitable culture media the alga retained its
colour. Nostoc also grows in the dark in the rhizome of Gunnera.
Radais’[247] experiments with Chlorella vulgaris confirmed these results.
On certain organic media growth and cell-division were as rapid in the dark
as in the light, and chlorophyll was formed. The colour was at first
yellowish and the full green arrived slowly, especially on sugar media, but
in ten days it was uniform and normal.
When making further experiments with the alga, Stichococcus bacillaris,
Artari[248] found that it also grew well on an organic medium and that grape
sugar was the most valuable carbonaceous food supply. Chodat[249] also
found that sugar or glucose was a desirable ingredient of culture media.
Treboux[250], in his work on organic acids, has also proved by
experimental cultures with a large series of algae, including the gonidia of
Peltigera, that these green plants in the absence of light and in pure cultures
would grow and form carbohydrates if the culture medium contained a
small percentage of organic acids. The acids he employed were combined
with potassium and were thus rendered neutral or slightly alkaline; acetate
of potash proved to be the most advantageous compound of any that was
tested. Amino-acids and ammonia salts were added to provide the necessary
nitrogen. Oxalic acid and other organic acids of varying composition are
peculiarly abundant in lichen tissues and may be a source of carbon supply.
Marshall Ward[251] has found calcium carbonate crystals in the lower air-
containing tissues of Strigula complanata.
Treboux finally concluded from his researches that just as fungi can
extract carbohydrates from many sources, so algae can secure their carbon
on the fungus which in turn was drawing nourishment from the pine
needles.
Artari[245] has proved that lichen gonidia can obtain carbohydrates from
the substratum as well as by photosynthesis. He cultivated the gonidia of
Xanthoria parietina and Placodium murorum on media which contained
organic substances as well as mineral salts, while depriving them of
atmospheric carbon-dioxide and in some cases of light also. The gonidia not
only grew well but, even in the dark, they remained normally green, a
phenomenon coinciding with Etard and Bouilhac’s[246] experience in
growing Nostoc in the dark: with suitable culture media the alga retained its
colour. Nostoc also grows in the dark in the rhizome of Gunnera.
Radais’[247] experiments with Chlorella vulgaris confirmed these results.
On certain organic media growth and cell-division were as rapid in the dark
as in the light, and chlorophyll was formed. The colour was at first
yellowish and the full green arrived slowly, especially on sugar media, but
in ten days it was uniform and normal.
When making further experiments with the alga, Stichococcus bacillaris,
Artari[248] found that it also grew well on an organic medium and that grape
sugar was the most valuable carbonaceous food supply. Chodat[249] also
found that sugar or glucose was a desirable ingredient of culture media.
Treboux[250], in his work on organic acids, has also proved by
experimental cultures with a large series of algae, including the gonidia of
Peltigera, that these green plants in the absence of light and in pure cultures
would grow and form carbohydrates if the culture medium contained a
small percentage of organic acids. The acids he employed were combined
with potassium and were thus rendered neutral or slightly alkaline; acetate
of potash proved to be the most advantageous compound of any that was
tested. Amino-acids and ammonia salts were added to provide the necessary
nitrogen. Oxalic acid and other organic acids of varying composition are
peculiarly abundant in lichen tissues and may be a source of carbon supply.
Marshall Ward[251] has found calcium carbonate crystals in the lower air-
containing tissues of Strigula complanata.
Treboux finally concluded from his researches that just as fungi can
extract carbohydrates from many sources, so algae can secure their carbon
Page 91
supply in a variety of ways. He affirms that the metabolic activity of the
alga in these cultural conditions is entirely normal, and the various cell-
contents are formed as in the light. Whether, in this case, starch is formed
directly from the acids or through a series of combinations has not been
determined. Uhlir[252], with electric lighting, made successful cultures of
Nostoc isolated from Collemaceae on silicic acid, proving thereby that these
gonidia do not require a rich nutriment. A certain definite humidity was
however essential, and bacteria were never eliminated as they are associated
with the gelatinous membranes of Nostocaceae.
e. Nutrition within the Symbiotic Plant. Culture experiments bearing
more directly on the nutrition of lichens as a whole were carried out by F.
Tobler[253]. He proved that the gonidia had undoubtedly drawn on the
calcium oxalate secreted by the hyphae for their supply of carbon. In a
culture medium of poplar-bark gelatine he grew hyphae of Xanthoria
parietina, and noted an abundant deposit of oxalate crystals on their cell-
walls. A piece of the lichen thallus including both symbionts and grown on
a similar medium formed no crystals, and microscopic examination showed
that crystals were likewise absent from the hyphae of the thallus that had
grown normally on the tree, the inference being that the gonidia used them
up as quickly as they were deposited. It must be remembered in this
connection, however, that Zopf[254] has stated that where lichen acids are
freely formed as, for instance, in Xanthoria parietina, there is always less
formation and deposit of calcium oxalate crystals, which may partly
account for their absence in the normal thallus so rich in parietin.
Tobler next introduced lichen gonidia into a culture medium in which the
isolated hyphal constituent of a thallus had been previously cultivated, and
placed the culture in the dark. In these circumstances he found that the
gonidia were able to thrive but formed no colour: they were obtaining their
carbohydrates, he decided, not from photosynthesis, but from the excretory
products such as calcium oxalate that had been deposited in the culture
medium by the lichen hyphae. We may conclude with more or less certainty
that the loss of carbohydrates, due to the partial deprivation of light and air
suffered by the alga owing to its position in the lichen thallus, is more than
compensated by a physiological symbiosis with the fungus[255]. It has
indeed been proved that in the absence of free carbon-dioxide, algae may
alga in these cultural conditions is entirely normal, and the various cell-
contents are formed as in the light. Whether, in this case, starch is formed
directly from the acids or through a series of combinations has not been
determined. Uhlir[252], with electric lighting, made successful cultures of
Nostoc isolated from Collemaceae on silicic acid, proving thereby that these
gonidia do not require a rich nutriment. A certain definite humidity was
however essential, and bacteria were never eliminated as they are associated
with the gelatinous membranes of Nostocaceae.
e. Nutrition within the Symbiotic Plant. Culture experiments bearing
more directly on the nutrition of lichens as a whole were carried out by F.
Tobler[253]. He proved that the gonidia had undoubtedly drawn on the
calcium oxalate secreted by the hyphae for their supply of carbon. In a
culture medium of poplar-bark gelatine he grew hyphae of Xanthoria
parietina, and noted an abundant deposit of oxalate crystals on their cell-
walls. A piece of the lichen thallus including both symbionts and grown on
a similar medium formed no crystals, and microscopic examination showed
that crystals were likewise absent from the hyphae of the thallus that had
grown normally on the tree, the inference being that the gonidia used them
up as quickly as they were deposited. It must be remembered in this
connection, however, that Zopf[254] has stated that where lichen acids are
freely formed as, for instance, in Xanthoria parietina, there is always less
formation and deposit of calcium oxalate crystals, which may partly
account for their absence in the normal thallus so rich in parietin.
Tobler next introduced lichen gonidia into a culture medium in which the
isolated hyphal constituent of a thallus had been previously cultivated, and
placed the culture in the dark. In these circumstances he found that the
gonidia were able to thrive but formed no colour: they were obtaining their
carbohydrates, he decided, not from photosynthesis, but from the excretory
products such as calcium oxalate that had been deposited in the culture
medium by the lichen hyphae. We may conclude with more or less certainty
that the loss of carbohydrates, due to the partial deprivation of light and air
suffered by the alga owing to its position in the lichen thallus, is more than
compensated by a physiological symbiosis with the fungus[255]. It has
indeed been proved that in the absence of free carbon-dioxide, algae may
Page 92
utilize the half-bound CO₂ of carbonates, chiefly those of calcium and
magnesium, dissolved in water.
f. Affinities of Lichen Gonidia. Chodat[256] has, in recent years, made
cultures of lichen gonidia with a view to discovering their relation to free-
living algae and to testing at the same time their source of carbon supply.
He has come to the conclusion that lichen gonidia are probably in no
instance the normal Protococcus viridis: they differ from that alga in the
possession of a pyrenoid and in their reproduction by zoospores when free.
Careful cultures were made of different Cladonia gonidia which were
morphologically indistinguishable, and which varied in size from 10 to 16µ
in diameter, though smaller ones were always present. He recognized them
to be species of Cystococcus: they have a pyrenoid[257] in the centre and a
disc-like chromatophore more or less starred at the edge. These gonidia
grew well on agar, still better on agar-glucose, but best of all with an
addition of peptone to the culture. There was invariably at first a slight
difference in form and colour in the mass between the gonidia of one
species and those of another, but as growth continued they became alike.
In testing for carbon supply, he found that gonidia grew slowly without
sugar (glucose), and that, as sources of carbon, organic acids could not
entirely replace glucose though, in the dark, the gonidia used them to some
extent; the colony supplied with potassium nitrate, and grown in the dark,
had reached a diameter of only 2 mm. in three months. With glucose, it
measured 5 mm. in three weeks, while in three months it formed large
culture patches.
A further experiment was made to test their absorption of peptones by
artificial cultures carried out both in the light and the dark. The gonidia
grew poorly in all combinations of organic nitrogen compounds. When
combined with glucose, growth was at once more vigorous though only half
as much in the dark as in the light, the difference in this respect being
especially noticeable in the gonidia from Cladonia pyxidata. He concludes
that as gonidia in these cultures are saprophytic, so in the lichen thallus also
they are probably more or less saprophytic, obtaining not only their
nitrogen in organic form but also, when possible, their carbon material as
glucose or galactose from the hyphal symbiont which in turn is saprophytic
on humus, etc.
magnesium, dissolved in water.
f. Affinities of Lichen Gonidia. Chodat[256] has, in recent years, made
cultures of lichen gonidia with a view to discovering their relation to free-
living algae and to testing at the same time their source of carbon supply.
He has come to the conclusion that lichen gonidia are probably in no
instance the normal Protococcus viridis: they differ from that alga in the
possession of a pyrenoid and in their reproduction by zoospores when free.
Careful cultures were made of different Cladonia gonidia which were
morphologically indistinguishable, and which varied in size from 10 to 16µ
in diameter, though smaller ones were always present. He recognized them
to be species of Cystococcus: they have a pyrenoid[257] in the centre and a
disc-like chromatophore more or less starred at the edge. These gonidia
grew well on agar, still better on agar-glucose, but best of all with an
addition of peptone to the culture. There was invariably at first a slight
difference in form and colour in the mass between the gonidia of one
species and those of another, but as growth continued they became alike.
In testing for carbon supply, he found that gonidia grew slowly without
sugar (glucose), and that, as sources of carbon, organic acids could not
entirely replace glucose though, in the dark, the gonidia used them to some
extent; the colony supplied with potassium nitrate, and grown in the dark,
had reached a diameter of only 2 mm. in three months. With glucose, it
measured 5 mm. in three weeks, while in three months it formed large
culture patches.
A further experiment was made to test their absorption of peptones by
artificial cultures carried out both in the light and the dark. The gonidia
grew poorly in all combinations of organic nitrogen compounds. When
combined with glucose, growth was at once more vigorous though only half
as much in the dark as in the light, the difference in this respect being
especially noticeable in the gonidia from Cladonia pyxidata. He concludes
that as gonidia in these cultures are saprophytic, so in the lichen thallus also
they are probably more or less saprophytic, obtaining not only their
nitrogen in organic form but also, when possible, their carbon material as
glucose or galactose from the hyphal symbiont which in turn is saprophytic
on humus, etc.
Page 93
B. Nutrition of Fungi
Fungi being without chlorophyll are always indebted to other organisms
for their supply of carbohydrates. There has never therefore been any
question as to the advantage accruing to the hyphal constituent in the
composite thallus. The gonidia, as various workers have proved, have also a
marked preference for organized nourishment, and, in addition, they obtain
carbon by photosynthesis. Chodat[258] considers that probably they are thus
able to assimilate carbon-dioxide in excess, a distinct advantage to the
hyphae. In some instances the living gonidium is invaded and the contents
used up by the fungus and any dead gonidia are likewise utilized for food
supply. It is also taken for granted that the fungus takes advantage of the
presence of humus whether in the substratum or in aerial dust. In such slow
growing organisms, there is not any large demand for nourishment on the
part of the hyphae: for many lichens it seems to be mere subsistence with a
minimum of growth from year to year.
C. Symbiosis of other Plants
The conception of an advantageous symbiosis of fungi with other plants
has become familiar to us in Orchids and in the mycorhizal formation on
the roots of trees, shrubs, etc. Fungal hyphae are also frequent inhabitants of
the rhizoids of hepatics though, according to Gargeaune[259], the benefit to
the hepatic host-plant is doubtful.
An association of fungus and green plant of great interest and bearing
directly on the question of mutual advantage has been described by
Servettaz[260]. In his study of mosses, he was able to confirm Bonnier’s[261]
account of lichen hyphae growing over such plants as Vaucheria and the
protonema of mosses, which is undoubtedly hurtful; but he also found an
association of a moss with one of the lower fungi, Streptothrix or Oospora,
which was distinctly advantageous. In separate cultivation the fungus
developed compact masses and grew well in peptone agar broth.
Cultures of the moss, Phascum cuspidatum, were also made from the
spores on a glucose medium. The specimens in association with the fungus
were fully grown in two months, while the control cultures, without any
admixture of the fungus, had not developed beyond the protonema stage.
Fungi being without chlorophyll are always indebted to other organisms
for their supply of carbohydrates. There has never therefore been any
question as to the advantage accruing to the hyphal constituent in the
composite thallus. The gonidia, as various workers have proved, have also a
marked preference for organized nourishment, and, in addition, they obtain
carbon by photosynthesis. Chodat[258] considers that probably they are thus
able to assimilate carbon-dioxide in excess, a distinct advantage to the
hyphae. In some instances the living gonidium is invaded and the contents
used up by the fungus and any dead gonidia are likewise utilized for food
supply. It is also taken for granted that the fungus takes advantage of the
presence of humus whether in the substratum or in aerial dust. In such slow
growing organisms, there is not any large demand for nourishment on the
part of the hyphae: for many lichens it seems to be mere subsistence with a
minimum of growth from year to year.
C. Symbiosis of other Plants
The conception of an advantageous symbiosis of fungi with other plants
has become familiar to us in Orchids and in the mycorhizal formation on
the roots of trees, shrubs, etc. Fungal hyphae are also frequent inhabitants of
the rhizoids of hepatics though, according to Gargeaune[259], the benefit to
the hepatic host-plant is doubtful.
An association of fungus and green plant of great interest and bearing
directly on the question of mutual advantage has been described by
Servettaz[260]. In his study of mosses, he was able to confirm Bonnier’s[261]
account of lichen hyphae growing over such plants as Vaucheria and the
protonema of mosses, which is undoubtedly hurtful; but he also found an
association of a moss with one of the lower fungi, Streptothrix or Oospora,
which was distinctly advantageous. In separate cultivation the fungus
developed compact masses and grew well in peptone agar broth.
Cultures of the moss, Phascum cuspidatum, were also made from the
spores on a glucose medium. The specimens in association with the fungus
were fully grown in two months, while the control cultures, without any
admixture of the fungus, had not developed beyond the protonema stage.
Page 94
Servettaz draws attention to the proved fact that, in certain instances, plants
benefit when provided with substances similar to their own decay products,
and he considers that the fungus, in addition to its normal gaseous products,
has elaborated such substances, as acid products, from the glucose medium
to the great advantage of the moss plant.
A symbiotic association of Nostoc with another alga, described by
Wettstein[262], is also of interest. The blue-green cells were lodged in the
pyriform outgrowths of the siphoneous alga, Botrydium pyriforme Kütz.,
which the author of the paper places in a new genus, Geosiphon. The
sheltering Nostoc symbioticum fills all of the host left vacant by the plasma,
and when the season of decay sets in, it forms resting spores which migrate
into the rhizoids of the host, so that both plants regenerate together.
Wettstein has compared this symbiotic association with that of lichens,
and finds the analogy all the more striking in that the membrane of his new
alga had become chitinous, which he thinks may be due to organic nutrition.
II. LICHEN HYPHAE
A. Origin of Hyphae
Lichen hyphae form the ground tissue of the thallus apart from the
gonidia or algal cells. They are septate branched filaments of single cell
rows and are colourless or may be tinged by pigments or lichen acids to
some shade of yellow, brown or black. They are of fungal nature, and are
produced by the mature lichen spore.
The germination of the spore was probably first observed by Meyer[263].
His account of the actual process is somewhat vague, and he misinterpreted
the subsequent development into thallus and fruit entirely for want of the
necessary magnification; but that he did succeed in germinating the spores
is unquestionable. He cultivated them on a smooth surface and they grew
into a “dendritic formation”—a true hypothallus. Many years later the
development of hyphae from lichen spores was observed by Holle[264] who
saw and figured the process unmistakably in Borrera (Physcia) ciliaris.
benefit when provided with substances similar to their own decay products,
and he considers that the fungus, in addition to its normal gaseous products,
has elaborated such substances, as acid products, from the glucose medium
to the great advantage of the moss plant.
A symbiotic association of Nostoc with another alga, described by
Wettstein[262], is also of interest. The blue-green cells were lodged in the
pyriform outgrowths of the siphoneous alga, Botrydium pyriforme Kütz.,
which the author of the paper places in a new genus, Geosiphon. The
sheltering Nostoc symbioticum fills all of the host left vacant by the plasma,
and when the season of decay sets in, it forms resting spores which migrate
into the rhizoids of the host, so that both plants regenerate together.
Wettstein has compared this symbiotic association with that of lichens,
and finds the analogy all the more striking in that the membrane of his new
alga had become chitinous, which he thinks may be due to organic nutrition.
II. LICHEN HYPHAE
A. Origin of Hyphae
Lichen hyphae form the ground tissue of the thallus apart from the
gonidia or algal cells. They are septate branched filaments of single cell
rows and are colourless or may be tinged by pigments or lichen acids to
some shade of yellow, brown or black. They are of fungal nature, and are
produced by the mature lichen spore.
The germination of the spore was probably first observed by Meyer[263].
His account of the actual process is somewhat vague, and he misinterpreted
the subsequent development into thallus and fruit entirely for want of the
necessary magnification; but that he did succeed in germinating the spores
is unquestionable. He cultivated them on a smooth surface and they grew
into a “dendritic formation”—a true hypothallus. Many years later the
development of hyphae from lichen spores was observed by Holle[264] who
saw and figured the process unmistakably in Borrera (Physcia) ciliaris.
Page 95
A series of spore cultures was undertaken by Tulasne[265] with the
twofold object of discovering the exact origin of hyphae and gonidia and of
their relationship to each other. The results of his classical experiment with
the spores of Verrucaria muralis—as interpreted by him—were accepted by
the lichenologists of that time as conclusive evidence of the genetic origin
of the gonidia within the thallus.
Fig. 14. Germinating spores of Verrucaria muralis Ach. after two
months’ culture × ca. 500 (after Tulasne).
The spores of the lichen in large numbers had been sown by Tulasne in
early spring on the smooth polished surface of a piece of limestone, and
were covered with a watch-glass to protect them from dust, etc. At irregular
intervals they were moistened with water, and from time to time a few
spores were abstracted from the culture and examined microscopically.
Tulasne observed that the spore did not increase or change in volume in the
process of germination, but that gradually the contents passed out into the
growing hyphae, till finally a thin membrane only was left and still
persisted after two months (Fig. 14). For a considerable time there was no
septation; at length cross-divisions were formed, at first close to the spore,
and then later in the branches. The hyphae meanwhile increased in
dimension, the cells becoming rounder and somewhat wider, though always
more slender than the spore which had given rise to them. In time a felted
tissue was formed with here and there certain cells, filled with green
colouring matter, similar to the gonidia of the lichen and thus the early
stages at least of a new thallus were observed. The green cells, we now
twofold object of discovering the exact origin of hyphae and gonidia and of
their relationship to each other. The results of his classical experiment with
the spores of Verrucaria muralis—as interpreted by him—were accepted by
the lichenologists of that time as conclusive evidence of the genetic origin
of the gonidia within the thallus.
Fig. 14. Germinating spores of Verrucaria muralis Ach. after two
months’ culture × ca. 500 (after Tulasne).
The spores of the lichen in large numbers had been sown by Tulasne in
early spring on the smooth polished surface of a piece of limestone, and
were covered with a watch-glass to protect them from dust, etc. At irregular
intervals they were moistened with water, and from time to time a few
spores were abstracted from the culture and examined microscopically.
Tulasne observed that the spore did not increase or change in volume in the
process of germination, but that gradually the contents passed out into the
growing hyphae, till finally a thin membrane only was left and still
persisted after two months (Fig. 14). For a considerable time there was no
septation; at length cross-divisions were formed, at first close to the spore,
and then later in the branches. The hyphae meanwhile increased in
dimension, the cells becoming rounder and somewhat wider, though always
more slender than the spore which had given rise to them. In time a felted
tissue was formed with here and there certain cells, filled with green
colouring matter, similar to the gonidia of the lichen and thus the early
stages at least of a new thallus were observed. The green cells, we now
Page 96
know, must have gained entrance to the culture from the air, or they may
have been introduced with the water.
B. Development of lichenoid Hyphae
Lichen hyphae are usually thick-walled, thus differing from those of
fungi generally, in which the membranes, as a rule, remain comparatively
thin. This character was adduced by the so-called “autonomous” school as a
proof of the fundamental distinction between the hyphal elements of the
two groups of plants. It can, however, easily be observed that, in the early
stages of germination, the lichen hyphae, as they issue from the spore, are
thin-walled and exactly comparable with those of fungi. Growth is apical,
and septation and branching arise exactly as in fungi, and, in certain
circumstances, anastomosis takes place between converging filaments. But
if algae are present in the culture the peculiar lichen characteristics very
soon appear.
Bonnier[266], who made a large series of synthetic cultures, distinguishes
three types of growth in lichenoid hyphae (Fig. 15):
1. Clasping filaments, repeatedly branched, which attach and surround
the algae.
2. Filaments with rather short swollen cells which ultimately form the
hyphal tissues of cortex and medulla.
3. Searching filaments which elongate towards the periphery and go to
the encounter of new algae.
In five days after germination of the spores, the clasping hyphae had laid
hold of the algae which meanwhile had increased by division; the swollen
cells had begun to branch out and ten days later a differentiation of tissue
was already apparent. The searching filaments had increased in number and
length, and anastomosis between them had taken place when no further
algae were encountered. The cell-walls of the swollen hyphae and their
branches had begun to thicken and to become united to form a kind of
cellular tissue or “paraplectenchyma[267].” At a later date, about a month
after the sowing of the spores, there was a definite cellular cortex formed
have been introduced with the water.
B. Development of lichenoid Hyphae
Lichen hyphae are usually thick-walled, thus differing from those of
fungi generally, in which the membranes, as a rule, remain comparatively
thin. This character was adduced by the so-called “autonomous” school as a
proof of the fundamental distinction between the hyphal elements of the
two groups of plants. It can, however, easily be observed that, in the early
stages of germination, the lichen hyphae, as they issue from the spore, are
thin-walled and exactly comparable with those of fungi. Growth is apical,
and septation and branching arise exactly as in fungi, and, in certain
circumstances, anastomosis takes place between converging filaments. But
if algae are present in the culture the peculiar lichen characteristics very
soon appear.
Bonnier[266], who made a large series of synthetic cultures, distinguishes
three types of growth in lichenoid hyphae (Fig. 15):
1. Clasping filaments, repeatedly branched, which attach and surround
the algae.
2. Filaments with rather short swollen cells which ultimately form the
hyphal tissues of cortex and medulla.
3. Searching filaments which elongate towards the periphery and go to
the encounter of new algae.
In five days after germination of the spores, the clasping hyphae had laid
hold of the algae which meanwhile had increased by division; the swollen
cells had begun to branch out and ten days later a differentiation of tissue
was already apparent. The searching filaments had increased in number and
length, and anastomosis between them had taken place when no further
algae were encountered. The cell-walls of the swollen hyphae and their
branches had begun to thicken and to become united to form a kind of
cellular tissue or “paraplectenchyma[267].” At a later date, about a month
after the sowing of the spores, there was a definite cellular cortex formed
Page 97
over the thallus. The hyphal cells are uninucleate, though in the medulla
they may be 1-2-nucleate.
Fig. 15. Synthetic culture of Physcia parietina spores and Protococcus viridis five
days after germination. s, lichen-spore; a, septate filaments; b, clasping filaments;
c, searching filaments. × 500 (after Bonnier).
The hyphae in close contact with the gonidia remain thin-walled, and
have been termed by Wainio[268] “meristematic.” They furnish the growing
elements of the lichen either apical or intercalary. In most genera the organs
of fructification take rise from them, or in their immediate neighbourhood,
and isidia and soredia also originate from these gonidial hyphae.
As the filaments pass from the gonidial zone to other layers, the cell-
walls become thicker with a consequent reduction of the cell-lumen, very
noticeable in the pith, but carried to its furthest extent in the “decomposed”
cortex where the cells in the degenerate tissue often become reduced to
disconnected streaks indicating the cell-lumen, and the outer cortical layer
is merely a continuous mass of mucilage.
All lichen tissues arise from the branching and septation of the hyphae,
the septa always forming at right angles to the long axis of the filaments.
There is no instance of longitudinal cell-division except in the spores of
they may be 1-2-nucleate.
Fig. 15. Synthetic culture of Physcia parietina spores and Protococcus viridis five
days after germination. s, lichen-spore; a, septate filaments; b, clasping filaments;
c, searching filaments. × 500 (after Bonnier).
The hyphae in close contact with the gonidia remain thin-walled, and
have been termed by Wainio[268] “meristematic.” They furnish the growing
elements of the lichen either apical or intercalary. In most genera the organs
of fructification take rise from them, or in their immediate neighbourhood,
and isidia and soredia also originate from these gonidial hyphae.
As the filaments pass from the gonidial zone to other layers, the cell-
walls become thicker with a consequent reduction of the cell-lumen, very
noticeable in the pith, but carried to its furthest extent in the “decomposed”
cortex where the cells in the degenerate tissue often become reduced to
disconnected streaks indicating the cell-lumen, and the outer cortical layer
is merely a continuous mass of mucilage.
All lichen tissues arise from the branching and septation of the hyphae,
the septa always forming at right angles to the long axis of the filaments.
There is no instance of longitudinal cell-division except in the spores of
Page 98
certain genera (Collema, Urceolaria, Polyblastia, etc.). The branching of
the hypha is dichotomous or lateral, and very irregular. Frequent septation
and coherent growth result in the formation of plectenchyma.
C. Culture of Hyphae without Gonidia
Artificial cultures had demonstrated the germination of lichen spores,
with the formation of hyphae, and from synthetic cultures of fungus and
alga complete lichen plants had been produced. To Möller[269] we owe the
first cultures of a thalline body from the fungus alone, both from spermatia
and from ascospores. The germination of the spermatia has a direct bearing
on their function as spores or as sexual organs and is described in a later
chapter.
The ascospores of Lecanora subfusca were caught in a drop of water on a
slide as they were ejaculated from the ascus, and, on the following day, a
very fine germinating tube was seen to have pierced the exospore. The
hypha became slightly thicker, and branching began on the third day. If in
water alone the culture soon died off, but in a nutrient solution growth
slowly continued. The hyphae branched out in all directions from the spore
as a centre and formed an orbicular expansion which in fourteen days had
reached a size of ·1 mm. in diameter. After three weeks’ growth it was large
enough to be visible without a lens; the mycelial threads were more
crowded, and certain terminal hyphae had branched upwards in an aerial
tuft, this development taking place from the centre outwards. Möller
marked this stage as the transition from a mere protothallus to a thallus
formation. In three months a diameter of 1·5-2 mm. was reached; a
transverse section gave a thickness of ·86 mm. and from the under side
loose hyphae branched downwards and attached the thallus, when it had
been transferred to a solid substratum such as cork. Above these rhizoidal
hyphae, a stratum of rather loose mycelium represented the medulla, and,
surmounting that, a cortical layer in which the hyphae were very closely
compacted. Delicate terminal branches rose into the air over the whole
surface, very similar in character to hypothallic hyphae at the margin of the
thallus.
Lecanora subfusca has a rather small simple spore; it emitted
germinating tubes from each end, and a septum across the middle of the
the hypha is dichotomous or lateral, and very irregular. Frequent septation
and coherent growth result in the formation of plectenchyma.
C. Culture of Hyphae without Gonidia
Artificial cultures had demonstrated the germination of lichen spores,
with the formation of hyphae, and from synthetic cultures of fungus and
alga complete lichen plants had been produced. To Möller[269] we owe the
first cultures of a thalline body from the fungus alone, both from spermatia
and from ascospores. The germination of the spermatia has a direct bearing
on their function as spores or as sexual organs and is described in a later
chapter.
The ascospores of Lecanora subfusca were caught in a drop of water on a
slide as they were ejaculated from the ascus, and, on the following day, a
very fine germinating tube was seen to have pierced the exospore. The
hypha became slightly thicker, and branching began on the third day. If in
water alone the culture soon died off, but in a nutrient solution growth
slowly continued. The hyphae branched out in all directions from the spore
as a centre and formed an orbicular expansion which in fourteen days had
reached a size of ·1 mm. in diameter. After three weeks’ growth it was large
enough to be visible without a lens; the mycelial threads were more
crowded, and certain terminal hyphae had branched upwards in an aerial
tuft, this development taking place from the centre outwards. Möller
marked this stage as the transition from a mere protothallus to a thallus
formation. In three months a diameter of 1·5-2 mm. was reached; a
transverse section gave a thickness of ·86 mm. and from the under side
loose hyphae branched downwards and attached the thallus, when it had
been transferred to a solid substratum such as cork. Above these rhizoidal
hyphae, a stratum of rather loose mycelium represented the medulla, and,
surmounting that, a cortical layer in which the hyphae were very closely
compacted. Delicate terminal branches rose into the air over the whole
surface, very similar in character to hypothallic hyphae at the margin of the
thallus.
Lecanora subfusca has a rather small simple spore; it emitted
germinating tubes from each end, and a septum across the middle of the
Page 99
spore appeared after germination had taken place. Another experiment was
with a much larger muriform spore measuring 80 µ in length and 20 µ in
thickness. On germination about 20 tubes were formed, some of them rising
into the air at once, the others encircling the spore, so that the thallus took
form immediately; growth in this case also was centrifugal. In three months
a diameter of 6 mm. was reached with a thickness of 1 to 2 mm. and
showing a differentiation into medulla and cortex. The hyphae did not
increase in width, but frequently globose or ovate swellings arose in or at
the ends, a character which recurs in the natural growth of hyphae both of
lichens and of Ascomycetes. These swellings depend on the nutrition.
Pertusaria communis possesses a very large simple spore, but it is
multinucleate and germinates with about 100 tubes which reach their
ultimate width of 3 to 4 µ before they emerge from the exospore. The
hyphae encircle the spore, and an opaque thalline growth is quickly formed
from which rise terminal hyphal branches. In ten weeks the differentiation
into medulla and cortex was reached, and in five months the hyphal thallus
measured 4 mm. in diameter and 1 to 2 mm. in thickness.
Möller instituted a comparison between the thalli he obtained from the
spores and those from the spermatia of another crustaceous lichen, Buellia
punctiformis (B. myriocarpa). After germination had taken place the hyphae
from the spermatia grew at first more quickly than those from the
ascospores, but as soon as thallus formation began the latter caught up and,
in eight weeks, both thalli were of equal size.
Another comparative culture with the spermatia and ascospores of
Opegrapha subsiderella gave similar results: the spores of that species are
elongate-fusiform and 6-to 8-septate; germination took place from the end
cells in two to three days after sowing. The germinating hyphae
corresponded exactly with those from the spermatia and growth was equally
slow in both. The middle cells of the spores may also produce germinating
tubes, but never more than about five were observed from any one spore. A
browning of the cortical layer was especially apparent in the hyphal culture
from another lichen, Graphis scripta: a clear brown colour gradually
changing to black appeared about the same period in all the cultures.
The hyphae from the spores of Arthonia developed quickest of all: the
hyphae were very slender, but in three to four months the growth had
with a much larger muriform spore measuring 80 µ in length and 20 µ in
thickness. On germination about 20 tubes were formed, some of them rising
into the air at once, the others encircling the spore, so that the thallus took
form immediately; growth in this case also was centrifugal. In three months
a diameter of 6 mm. was reached with a thickness of 1 to 2 mm. and
showing a differentiation into medulla and cortex. The hyphae did not
increase in width, but frequently globose or ovate swellings arose in or at
the ends, a character which recurs in the natural growth of hyphae both of
lichens and of Ascomycetes. These swellings depend on the nutrition.
Pertusaria communis possesses a very large simple spore, but it is
multinucleate and germinates with about 100 tubes which reach their
ultimate width of 3 to 4 µ before they emerge from the exospore. The
hyphae encircle the spore, and an opaque thalline growth is quickly formed
from which rise terminal hyphal branches. In ten weeks the differentiation
into medulla and cortex was reached, and in five months the hyphal thallus
measured 4 mm. in diameter and 1 to 2 mm. in thickness.
Möller instituted a comparison between the thalli he obtained from the
spores and those from the spermatia of another crustaceous lichen, Buellia
punctiformis (B. myriocarpa). After germination had taken place the hyphae
from the spermatia grew at first more quickly than those from the
ascospores, but as soon as thallus formation began the latter caught up and,
in eight weeks, both thalli were of equal size.
Another comparative culture with the spermatia and ascospores of
Opegrapha subsiderella gave similar results: the spores of that species are
elongate-fusiform and 6-to 8-septate; germination took place from the end
cells in two to three days after sowing. The germinating hyphae
corresponded exactly with those from the spermatia and growth was equally
slow in both. The middle cells of the spores may also produce germinating
tubes, but never more than about five were observed from any one spore. A
browning of the cortical layer was especially apparent in the hyphal culture
from another lichen, Graphis scripta: a clear brown colour gradually
changing to black appeared about the same period in all the cultures.
The hyphae from the spores of Arthonia developed quickest of all: the
hyphae were very slender, but in three to four months the growth had
Page 100
reached a diameter of 8 mm. In this plant there was the usual outgrowth of
delicate hyphae from the surface; no definite cortical layer appeared, but
only a very narrow line of more closely interwoven somewhat darker
hyphae. Frequently, from the surface of the original thallus, excrescences
arose which were the beginnings of further thalli.
Tobler[270] experimenting with Xanthoria parietina gained very similar
results. The spores were grown in malt extract for ten days, then transferred
to gelatine. In three to five weeks there was formed an orbicular mycelial
felt about 3 mm. in diameter and 2 mm. thick. The mycelium was
frequently brownish even in healthy cultures, but the aerial hyphae which,
at first, rose above the surface were always colourless. After these latter
disappeared a distinct brownish tinge of the thallus was visible. In seven
months it had increased in size to 15 mm. in length, 7 mm. in width and 3
mm. thick with a differentiation into three layers: a lower rather dense
tissue representing the pith, above that a layer of loose hyphae where the
gonidial zone would normally find place, and above that a second compact
tissue, or outer cortex, from which arose the aerial hyphae. The culture
could not be prolonged more than eight months.
D. Continuity of Protoplasm in Hyphal Cells
Wahrlich[271] demonstrated that continuity of protoplasm was as constant
between the cells of fungi as it has been proved to be between the cells of
the higher plants. His researches included the hyphae of the lichens,
Cladonia fimbriata and Physcia (Xanthoria) parietina.
Baur[272] and Darbishire[273] found independently that an open
connection existed between the cells of the carpogonial structures in the
lichens they examined. The subject as regards the thalline hyphae was again
taken up by Kienitz-Gerloff[274] who obtained his best results in the
hypothecial tissue of Peltigera canina and P. polydactyla. Most of the cross
septa showed one central protoplasmic strand traversing the wall from cell
to cell, but in some instances there were as many as four to six pits in the
walls. The thickening of the cell-walls is uneven and projects variously into
the cavity of the cell. Meyer’s[275] work was equally conclusive: all the cells
of an individual hypha, he found, are in protoplasmic connection; and in
delicate hyphae from the surface; no definite cortical layer appeared, but
only a very narrow line of more closely interwoven somewhat darker
hyphae. Frequently, from the surface of the original thallus, excrescences
arose which were the beginnings of further thalli.
Tobler[270] experimenting with Xanthoria parietina gained very similar
results. The spores were grown in malt extract for ten days, then transferred
to gelatine. In three to five weeks there was formed an orbicular mycelial
felt about 3 mm. in diameter and 2 mm. thick. The mycelium was
frequently brownish even in healthy cultures, but the aerial hyphae which,
at first, rose above the surface were always colourless. After these latter
disappeared a distinct brownish tinge of the thallus was visible. In seven
months it had increased in size to 15 mm. in length, 7 mm. in width and 3
mm. thick with a differentiation into three layers: a lower rather dense
tissue representing the pith, above that a layer of loose hyphae where the
gonidial zone would normally find place, and above that a second compact
tissue, or outer cortex, from which arose the aerial hyphae. The culture
could not be prolonged more than eight months.
D. Continuity of Protoplasm in Hyphal Cells
Wahrlich[271] demonstrated that continuity of protoplasm was as constant
between the cells of fungi as it has been proved to be between the cells of
the higher plants. His researches included the hyphae of the lichens,
Cladonia fimbriata and Physcia (Xanthoria) parietina.
Baur[272] and Darbishire[273] found independently that an open
connection existed between the cells of the carpogonial structures in the
lichens they examined. The subject as regards the thalline hyphae was again
taken up by Kienitz-Gerloff[274] who obtained his best results in the
hypothecial tissue of Peltigera canina and P. polydactyla. Most of the cross
septa showed one central protoplasmic strand traversing the wall from cell
to cell, but in some instances there were as many as four to six pits in the
walls. The thickening of the cell-walls is uneven and projects variously into
the cavity of the cell. Meyer’s[275] work was equally conclusive: all the cells
of an individual hypha, he found, are in protoplasmic connection; and in
Page 101
plectenchymatous tissue the side walls are frequently perforated. Cell-
fusions due to anastomosis are frequent in lichen hyphae, and the wall at or
near the point of fusion is also traversed by a thread of protoplasm, though
such connections are regarded as adventitious. Fusions with plasma
connections are numerous in the matted hairs on the upper surface of
Peltigera canina and they also occur between the hyphae forming the
rhizoids of that lichen. The work of Salter[276] may also be noted. He
claimed that his researches tended to show complete anatomical union
between all the tissues of the lichen plant, not only between the hyphae of
the various tissues but also between hyphae and gonidia.
III. LICHEN ALGAE
A. Types of Algae
The algal constituents of the lichen thallus belong to the two classes,
Myxophyceae, generally termed blue-green algae, and Chlorophyceae
which are coloured bright-green or yellow-green. Most of them are land
forms, and, in a free condition, they inhabit moist or shady situations, tree-
trunks, walls, etc. They multiply by division or by sporulation within the
thallus; zoospores are never formed except in open cultivation. The
determination of the genera and species to which the lichen algae severally
belong is often uncertain, but their distribution within the lichen kingdom is
as follows:
a. Myxophyceae associated with Phycolichens. The blue-green algae are
characterized by the colour of their pigments which persists in the gonidial
condition giving various tints to the component lichens, and by the
gelatinous sheath in which most of them are enclosed. This sheath, both in
the lichen gonidia[277] and in free-living forms, imbibes and retains
moisture to a remarkable extent and the thallus containing blue-green algae
profits by its power of storing moisture. Myxophyceae form the gonidia of
the gelatinous lichens as well as of some other non-gelatinous genera.
Several families are represented[278]:
Fam. Chroococcaceae. This family includes unicellular algae with thick
gelatinous sheaths. They increase normally by division, and colonies arise
fusions due to anastomosis are frequent in lichen hyphae, and the wall at or
near the point of fusion is also traversed by a thread of protoplasm, though
such connections are regarded as adventitious. Fusions with plasma
connections are numerous in the matted hairs on the upper surface of
Peltigera canina and they also occur between the hyphae forming the
rhizoids of that lichen. The work of Salter[276] may also be noted. He
claimed that his researches tended to show complete anatomical union
between all the tissues of the lichen plant, not only between the hyphae of
the various tissues but also between hyphae and gonidia.
III. LICHEN ALGAE
A. Types of Algae
The algal constituents of the lichen thallus belong to the two classes,
Myxophyceae, generally termed blue-green algae, and Chlorophyceae
which are coloured bright-green or yellow-green. Most of them are land
forms, and, in a free condition, they inhabit moist or shady situations, tree-
trunks, walls, etc. They multiply by division or by sporulation within the
thallus; zoospores are never formed except in open cultivation. The
determination of the genera and species to which the lichen algae severally
belong is often uncertain, but their distribution within the lichen kingdom is
as follows:
a. Myxophyceae associated with Phycolichens. The blue-green algae are
characterized by the colour of their pigments which persists in the gonidial
condition giving various tints to the component lichens, and by the
gelatinous sheath in which most of them are enclosed. This sheath, both in
the lichen gonidia[277] and in free-living forms, imbibes and retains
moisture to a remarkable extent and the thallus containing blue-green algae
profits by its power of storing moisture. Myxophyceae form the gonidia of
the gelatinous lichens as well as of some other non-gelatinous genera.
Several families are represented[278]:
Fam. Chroococcaceae. This family includes unicellular algae with thick
gelatinous sheaths. They increase normally by division, and colonies arise
Page 102
by the cohesion of the cells. Several genera form gonidia:
1. Chroococcus Naeg. Solitary or forming small colonies of 2-4-8 cells
(Fig. 16) generally surrounded by firm gelatinous colourless sheaths in
definite layers (lamellate). Chroococcus is considered by some
lichenologists to form the gonidium of Cora, a genus of Hymenolichens.
2. Microcystis Kütz. Globose or subglobose cells forming large colonies
surrounded by a common gelatinous layer (gonidia of Coriscium).
1. Chroococcus Naeg. Solitary or forming small colonies of 2-4-8 cells
(Fig. 16) generally surrounded by firm gelatinous colourless sheaths in
definite layers (lamellate). Chroococcus is considered by some
lichenologists to form the gonidium of Cora, a genus of Hymenolichens.
2. Microcystis Kütz. Globose or subglobose cells forming large colonies
surrounded by a common gelatinous layer (gonidia of Coriscium).
Page 103
Fig. 16. Examples of Chroococcus. A, Ch. giganteus West; B, Ch.
turgidus Naeg.; C and D, Ch. schizodermaticus West × 450 (after
West).
Fig. 17. Gloeocapsa magma
Kütz. × 450 (after West).
3. Gloeocapsa Kütz. (including Xanthocapsa). Globose cells with a
lamellate gelatinous wall, forming colonies enclosed in a common sheath
(Fig. 17); the inner integument is often coloured red or orange. These two
genera form the gonidia in the family Pyrenopsidaceae. Gloeocapsa
polydermatica Kütz. has been identified as a lichen gonidium.
turgidus Naeg.; C and D, Ch. schizodermaticus West × 450 (after
West).
Fig. 17. Gloeocapsa magma
Kütz. × 450 (after West).
3. Gloeocapsa Kütz. (including Xanthocapsa). Globose cells with a
lamellate gelatinous wall, forming colonies enclosed in a common sheath
(Fig. 17); the inner integument is often coloured red or orange. These two
genera form the gonidia in the family Pyrenopsidaceae. Gloeocapsa
polydermatica Kütz. has been identified as a lichen gonidium.
Page 104
Fam. nostocaceae. Filamentous algae unbranched and without base or
apex.
Nostoc Vauch. Composed of flexuous trichomes, with intercalary
heterocysts (colourless cells) (Fig. 18). Dense gelatinous colonies of
definite form are built up by cohesion. In some lichens the trichomes retain
their chain-like appearance, in others they are more or less broken up and
massed together, with disappearance of the gelatinous sheath (as in
Peltigera); colour mostly dark blue-green.
Fig. 18. Examples of Nostoc. N. Linckia Born. A, nat. size; B,
small portion × 340; C, N. coerulescens Lyngbye, nat. size (after
West).
apex.
Nostoc Vauch. Composed of flexuous trichomes, with intercalary
heterocysts (colourless cells) (Fig. 18). Dense gelatinous colonies of
definite form are built up by cohesion. In some lichens the trichomes retain
their chain-like appearance, in others they are more or less broken up and
massed together, with disappearance of the gelatinous sheath (as in
Peltigera); colour mostly dark blue-green.
Fig. 18. Examples of Nostoc. N. Linckia Born. A, nat. size; B,
small portion × 340; C, N. coerulescens Lyngbye, nat. size (after
West).
Page 105
Fig. 19. Example of Scytonema alga. S. mirabile Thur. C, apex of a branch; D,
organ of attachment at base of filament. × 440 (after West).
Nostoc occurs in a few or all of the genera of Pyrenidiaceae,
Collemaceae, Pannariaceae, Peltigeraceae and Stictaceae, and N.
sphaericum Vauch. (N. lichenoides Kütz.) has been determined as the lichen
gonidium. When the chains are broken up it has been wrongly classified as
another alga, Polycoccus punctiformis.
Fam. Scytonemaceae. Trichomes of single-cell rows, differentiated into
base and apex. Pseudo-branching arises at right angles to the main filament.
Scytonema Ag. Pseudo-branches piercing the sheath and passing out as
twin filaments (Fig. 19); colour, golden-brown. This alga occurs in genera
of Pyrenidiaceae, Ephebaceae, Pannariaceae, Heppiaceae, in Petractis a
genus of Gyalectaceae, and in Dictyonema one of the Hymenolichens.
Fam. Stigonemaceae. Trichomes of several-cell rows with base and apex;
colour, golden-brown.
Stigonema Ag. Stouter than Scytonema, with transverse and vertical
division of the cells, and generally copious branching (Fig. 20). This alga
occurs only in a few genera of Ephebaceae. S. panniforme Kirchn.
(Sirosiphon pulvinatus Bréb.) has been determined as forming the
gonidium.
Fam. Rivulariaceae. Trichomes with a heterocyst at the base and
tapering upwards, enclosed in mucilage (Fig. 21).
organ of attachment at base of filament. × 440 (after West).
Nostoc occurs in a few or all of the genera of Pyrenidiaceae,
Collemaceae, Pannariaceae, Peltigeraceae and Stictaceae, and N.
sphaericum Vauch. (N. lichenoides Kütz.) has been determined as the lichen
gonidium. When the chains are broken up it has been wrongly classified as
another alga, Polycoccus punctiformis.
Fam. Scytonemaceae. Trichomes of single-cell rows, differentiated into
base and apex. Pseudo-branching arises at right angles to the main filament.
Scytonema Ag. Pseudo-branches piercing the sheath and passing out as
twin filaments (Fig. 19); colour, golden-brown. This alga occurs in genera
of Pyrenidiaceae, Ephebaceae, Pannariaceae, Heppiaceae, in Petractis a
genus of Gyalectaceae, and in Dictyonema one of the Hymenolichens.
Fam. Stigonemaceae. Trichomes of several-cell rows with base and apex;
colour, golden-brown.
Stigonema Ag. Stouter than Scytonema, with transverse and vertical
division of the cells, and generally copious branching (Fig. 20). This alga
occurs only in a few genera of Ephebaceae. S. panniforme Kirchn.
(Sirosiphon pulvinatus Bréb.) has been determined as forming the
gonidium.
Fam. Rivulariaceae. Trichomes with a heterocyst at the base and
tapering upwards, enclosed in mucilage (Fig. 21).
Page 106
Fig. 20. Stigonema sp. × 200
(after Comère).
(after Comère).
Page 107
Fig. 21. Examples of Rivularia; A, B, C, R. Biasolettiana
Menegh.; D and E, R. minutula Born. and Fl. A and D nat.
size; B, C and E × 480 (after West).
Rivularia Thuret. In tufts fixed at the base and forming roundish
gelatinous colonies; colour, blue-green. The gonidium of Lichinaceae has
been identified as R. nitida Ag.
Algae belonging to one or other of these genera of Myxophyceae also
combine with the hyphae of Archilichens to form cephalodia[279] and
Krempelhuber[280] has recorded and figured a blue-green alga, probably
Gloeocapsa, in Baeomyces paeminosus from the South Sea Islands. They
also form the gonidia in a few species and genera of such families as
Stictaceae and Peltigeraceae.
Menegh.; D and E, R. minutula Born. and Fl. A and D nat.
size; B, C and E × 480 (after West).
Rivularia Thuret. In tufts fixed at the base and forming roundish
gelatinous colonies; colour, blue-green. The gonidium of Lichinaceae has
been identified as R. nitida Ag.
Algae belonging to one or other of these genera of Myxophyceae also
combine with the hyphae of Archilichens to form cephalodia[279] and
Krempelhuber[280] has recorded and figured a blue-green alga, probably
Gloeocapsa, in Baeomyces paeminosus from the South Sea Islands. They
also form the gonidia in a few species and genera of such families as
Stictaceae and Peltigeraceae.
Page 108
b. Chlorophyceae associated With Archilichens. The lichens of this
group are by far the most numerous both in genera and species, though
fewer algal families are represented.
Fam. Protococcaceae. Consisting of globular single cells, aggregated in
loose colonies, dividing variously.
1. Protococcus
viridis Ag.
(Pleurococcus vulgaris
Menegh.,
Cystococcushumicola
Naeg.). Cells dividing
into 2, 4 or 8 daughter-
cells and not separating
readily; in excessive
moisture forming short
filaments. The cells
contain parietal
chloroplasts, and,
according to Fig. 22. Pleurococcus vulgaris Menegh. (Protococcus viridis Ag.).
Chodat[281], are chl. chloroplast; p. protoderma stage; pa, palmelloid stage; py,
pyrenoid. × 520 (after West).
without a pyrenoid
(Fig. 22). This alga,
and allied species, forms the familiar green coating of tree-trunks, walls
etc., and, in lichenological literature, are quoted as the gonidia of most of
the crustaceous foliose and fruticose lichens. Chodat[281], who has recently
made comparative artificial cultures of algae, throws doubt on the identity
of many such gonidia. He lays great emphasis on the presence or absence of
a pyrenoid in algal cells. West, on the contrary, considers the pyrenoid as an
inconstant character. Chodat insists that the gonidia that contain pyrenoids
belong to another genus, Cystococcus Chod. (non Naeg.), a pyrenoid-
containing alga, which, in addition to multiplying by division of the cells,
also forms spores and zoospores when cultivated. He further records the
results of his cultures of gonidia, and finds that those taken from closely
related lichens, such as different species of Cladonia, though they are alike
morphologically, yet show constant variations in the culture colonies.
These, he holds, are sufficient to indicate difference of race if not of species
group are by far the most numerous both in genera and species, though
fewer algal families are represented.
Fam. Protococcaceae. Consisting of globular single cells, aggregated in
loose colonies, dividing variously.
1. Protococcus
viridis Ag.
(Pleurococcus vulgaris
Menegh.,
Cystococcushumicola
Naeg.). Cells dividing
into 2, 4 or 8 daughter-
cells and not separating
readily; in excessive
moisture forming short
filaments. The cells
contain parietal
chloroplasts, and,
according to Fig. 22. Pleurococcus vulgaris Menegh. (Protococcus viridis Ag.).
Chodat[281], are chl. chloroplast; p. protoderma stage; pa, palmelloid stage; py,
pyrenoid. × 520 (after West).
without a pyrenoid
(Fig. 22). This alga,
and allied species, forms the familiar green coating of tree-trunks, walls
etc., and, in lichenological literature, are quoted as the gonidia of most of
the crustaceous foliose and fruticose lichens. Chodat[281], who has recently
made comparative artificial cultures of algae, throws doubt on the identity
of many such gonidia. He lays great emphasis on the presence or absence of
a pyrenoid in algal cells. West, on the contrary, considers the pyrenoid as an
inconstant character. Chodat insists that the gonidia that contain pyrenoids
belong to another genus, Cystococcus Chod. (non Naeg.), a pyrenoid-
containing alga, which, in addition to multiplying by division of the cells,
also forms spores and zoospores when cultivated. He further records the
results of his cultures of gonidia, and finds that those taken from closely
related lichens, such as different species of Cladonia, though they are alike
morphologically, yet show constant variations in the culture colonies.
These, he holds, are sufficient to indicate difference of race if not of species
Page 109
and he designates the algae, according to the lichen in which they occur, as
Cystococcus Cladoniae pyxidatae, C. Cladoniae fimbriatae, etc.
Fig. 23. Cystococcus Cladoniae
pyxidatae Chod. from culture × 800
(after Chodat).
Meanwhile Paulson and Somerville Hastings[282] by their careful
research on the growing thallus have thrown considerable light on the
identity of the Protococcaceous lichen gonidium. They selected such well-
known lichens as Xanthoria parietina, Cladonia spp. and others, which they
collected during the spring months, February to April, the period of most
active growth. Many of the gonidia, they found, were in a stage of
reproduction, that showed a simultaneous rounding off of the gonidium
contents into globose bodies varying in number up to 32. Chodat had
figured this method of “sporulation” in his cultures of the lichen gonidium
both in Chlorella Beij. and in Cystococcus Chod. (Fig. 23). It has now been
abundantly proved that this form of increase is of frequent occurrence in the
thallus itself. Chlorella has been suggested as probably the alga forming
these gonidia and recently West has signified his acquiescence in this
view[283].
2. Chlorella Beij. Occurring frequently on damp ground, bark of trees,
etc., dividing into numerous daughter-cells, probably reduced zoogonidia
(Fig. 23).
Chodat distinguishes between Cystococcus and Chlorella in that
Cystococcus may form zoospores (though rarely), Chlorella only
aplanospores. He found three gonidial species, Chlorella lichina in
Cystococcus Cladoniae pyxidatae, C. Cladoniae fimbriatae, etc.
Fig. 23. Cystococcus Cladoniae
pyxidatae Chod. from culture × 800
(after Chodat).
Meanwhile Paulson and Somerville Hastings[282] by their careful
research on the growing thallus have thrown considerable light on the
identity of the Protococcaceous lichen gonidium. They selected such well-
known lichens as Xanthoria parietina, Cladonia spp. and others, which they
collected during the spring months, February to April, the period of most
active growth. Many of the gonidia, they found, were in a stage of
reproduction, that showed a simultaneous rounding off of the gonidium
contents into globose bodies varying in number up to 32. Chodat had
figured this method of “sporulation” in his cultures of the lichen gonidium
both in Chlorella Beij. and in Cystococcus Chod. (Fig. 23). It has now been
abundantly proved that this form of increase is of frequent occurrence in the
thallus itself. Chlorella has been suggested as probably the alga forming
these gonidia and recently West has signified his acquiescence in this
view[283].
2. Chlorella Beij. Occurring frequently on damp ground, bark of trees,
etc., dividing into numerous daughter-cells, probably reduced zoogonidia
(Fig. 23).
Chodat distinguishes between Cystococcus and Chlorella in that
Cystococcus may form zoospores (though rarely), Chlorella only
aplanospores. He found three gonidial species, Chlorella lichina in
Page 110
Cladonia rangiferina, Ch. viscosa and
Ch. Cladoniae in other Cladonia spp.
3. Coccobotrys Chod. The cells of
this new algal genus are smaller than
those of Cystococcus or Protococcus
and have no pyrenoid. They were
isolated by Chodat from the thallus of
Verrucaria nigrescens (Fig. 24), and,
as they have thick membranes, they
adhere in a continuous layer or thallus.
Chodat also claims to have isolated a
species of Coccobotrys from
Dermatocarpon miniatum, a foliose
Pyrenolichen.
4. Coccomyxa Schmidle. Cells
ellipsoid, also without a pyrenoid. Two
species were obtained by Chodat from
the thallus of Solorinae and are
recorded as Coccomyxa Solorinae
croceae and C. Solorinae saccatae.
Coccomyxa subellipsoidea is
[284]
given as the gonidium of the
Fig. 23 a. A, C, Chlorella vulgaris Beyer. B
and C, stages in division × about 800 (after primitive lichen Botrydina vulgaris
Chodat); E, Chl. faginea Wille × 520 (after (Fig. 25). The cells are surrounded by a
Gerneck); F-I Chl. miniata; F, vegetable cell; common gelatinous sheath.
G-I, formation and escape of gonidia × 1000
(after Chodat).
Ch. Cladoniae in other Cladonia spp.
3. Coccobotrys Chod. The cells of
this new algal genus are smaller than
those of Cystococcus or Protococcus
and have no pyrenoid. They were
isolated by Chodat from the thallus of
Verrucaria nigrescens (Fig. 24), and,
as they have thick membranes, they
adhere in a continuous layer or thallus.
Chodat also claims to have isolated a
species of Coccobotrys from
Dermatocarpon miniatum, a foliose
Pyrenolichen.
4. Coccomyxa Schmidle. Cells
ellipsoid, also without a pyrenoid. Two
species were obtained by Chodat from
the thallus of Solorinae and are
recorded as Coccomyxa Solorinae
croceae and C. Solorinae saccatae.
Coccomyxa subellipsoidea is
[284]
given as the gonidium of the
Fig. 23 a. A, C, Chlorella vulgaris Beyer. B
and C, stages in division × about 800 (after primitive lichen Botrydina vulgaris
Chodat); E, Chl. faginea Wille × 520 (after (Fig. 25). The cells are surrounded by a
Gerneck); F-I Chl. miniata; F, vegetable cell; common gelatinous sheath.
G-I, formation and escape of gonidia × 1000
(after Chodat).
Page 111
Fig. 24. Coccobotrys Verrucariae Chod. from
culture × 800 (after Chodat).
Fig. 25. Coccomyxa
subellipsoidea Acton. Actively
dividing cells, the dark portions
indicating the chloroplasts ×
1000 (after Acton).
5. Diplosphaera Bial.[285] D. Chodati was taken from the thallus of
Lecanora tartarea and successfully cultivated. It resembles Protococcus,
but has smaller cells and grows more rapidly; it is evidently closely allied to
that genus, if not merely a form of it.
6. Urococcus Kütz. Cells more or less globose, rather large, and coloured
with a red-brown pigment, with the cell-wall thick and lamellate, forming
elongate strands of cells (Fig. 26). Recorded by Hue[286] in the cephalodium
of Lepolichen coccophorus, a Chilian lichen.
Fam. Tetrasporaceae. Cells in groups of 2 or 4 surrounded by a
gelatinous sheath.
1. Palmella Lyngb. Cells globose, oblong or ellipsoid, grouped without
order in a formless mucilage (Fig. 27). Among lichens associated with
Palmella are the Epigloeaceae and Chrysothricaceae.
culture × 800 (after Chodat).
Fig. 25. Coccomyxa
subellipsoidea Acton. Actively
dividing cells, the dark portions
indicating the chloroplasts ×
1000 (after Acton).
5. Diplosphaera Bial.[285] D. Chodati was taken from the thallus of
Lecanora tartarea and successfully cultivated. It resembles Protococcus,
but has smaller cells and grows more rapidly; it is evidently closely allied to
that genus, if not merely a form of it.
6. Urococcus Kütz. Cells more or less globose, rather large, and coloured
with a red-brown pigment, with the cell-wall thick and lamellate, forming
elongate strands of cells (Fig. 26). Recorded by Hue[286] in the cephalodium
of Lepolichen coccophorus, a Chilian lichen.
Fam. Tetrasporaceae. Cells in groups of 2 or 4 surrounded by a
gelatinous sheath.
1. Palmella Lyngb. Cells globose, oblong or ellipsoid, grouped without
order in a formless mucilage (Fig. 27). Among lichens associated with
Palmella are the Epigloeaceae and Chrysothricaceae.
Page 112
Fig. 27. Palmella sp. × 400 (after
Fig. 26. Urococcus sp. Group of Comère).
cells much magnified (after
Hassall).
Fig. 28. Gloeocystis sp. × 400
(after Comère).
2. Gloeocystis Naeg. Cells oblong or globose with a lamellate sheath
forming small colonies; colour, red-brown (Fig. 28). This alga along with
Urococcus was found by Hue in the cephalodia of Lepolichen coccophora,
but whereas Gloeocystis frequently occupies the cephalodium alone,
Urococcus is always accompanied by Scytonema, the normal gonidium of
the cephalodium.
Fig. 26. Urococcus sp. Group of Comère).
cells much magnified (after
Hassall).
Fig. 28. Gloeocystis sp. × 400
(after Comère).
2. Gloeocystis Naeg. Cells oblong or globose with a lamellate sheath
forming small colonies; colour, red-brown (Fig. 28). This alga along with
Urococcus was found by Hue in the cephalodia of Lepolichen coccophora,
but whereas Gloeocystis frequently occupies the cephalodium alone,
Urococcus is always accompanied by Scytonema, the normal gonidium of
the cephalodium.
Page 113
Fig. 29. A, Trentepohlia umbrina Born.;
B, T. aurea Mart. × 300 (after Kütz.).
B, T. aurea Mart. × 300 (after Kütz.).
Page 114
Fig. 30. Example of Cladophora. Cl. glomerata
Kütz. A, nat. size; B, × 85 (after West).
Fam. Trentepohliaceae. Filamentous and branched, the filaments short
and creeping or long and forming tufts and felts or cushions; colour,
brownish-yellow or reddish-orange.
Trentepohlia Born. Branching alternate; cells filled with red or orange
oil; no pyrenoids (Fig. 29). A large number of lichens are associated with
this genus: Pyrenulaceae, Arthoniaceae, Graphidaceae, Roccellaceae,
Thelotremaceae, Gyalectaceae and Coenogoniaceae, etc., in whole or in
part. Two species have been determined, T. umbrina Born., the gonidium of
the Graphidaceae, and T. aurea which is associated with the only European
Coenogonium, C. ebeneum (Fig. 3). Deckenbach[287] claimed that he had
proved by cultures that T. umbrina was a growth stage of T. aurea.
Kütz. A, nat. size; B, × 85 (after West).
Fam. Trentepohliaceae. Filamentous and branched, the filaments short
and creeping or long and forming tufts and felts or cushions; colour,
brownish-yellow or reddish-orange.
Trentepohlia Born. Branching alternate; cells filled with red or orange
oil; no pyrenoids (Fig. 29). A large number of lichens are associated with
this genus: Pyrenulaceae, Arthoniaceae, Graphidaceae, Roccellaceae,
Thelotremaceae, Gyalectaceae and Coenogoniaceae, etc., in whole or in
part. Two species have been determined, T. umbrina Born., the gonidium of
the Graphidaceae, and T. aurea which is associated with the only European
Coenogonium, C. ebeneum (Fig. 3). Deckenbach[287] claimed that he had
proved by cultures that T. umbrina was a growth stage of T. aurea.
Page 115
Fam. Cladophoraceae. Filamentous, variously and copiously branched,
the cells rather large and multinucleate.
Cladophora Kütz. Filaments branching, of one-cell rows, attached at the
base; colour, bright or dark green; mostly aquatic and marine (Fig. 30).
Only one lichen, Racodium rupestre, a member of the Coenogoniaceae, is
associated with Cladophora. It is a British lichen, and is always sterile.
Fam. Mycoideaceae. Epiphytic algae consisting of thin discs which are
composed of radiating filaments.
1. Mycoidea Cunningh. (Cephaleuros Kunze). In Mycoidea parasitica
the filaments of the disc are partly erect and partly decumbent, reddish to
green (Fig. 31). It forms the gonidium of the parasitic lichen, Strigula
complanata, which was studied by Marshall Ward in Ceylon[288].
Zahlbruckner gives Phyllactidium as an alternative gonidium of
Strigulaceae.
2. Phycopeltis Millard. Disc a stratum one-cell thick, bearing seta, adnate
to the lower surface of the leaf, yellow-green in colour. Phycopeltis (Fig.
32) has been identified as the gonidium of Strigula complanata in New
Zealand and of Mazosia (Chiodectonaceae), a leaf lichen from tropical
America.
Fig. 31. Mycoidea parasitica Cunningh. much
magnified (after Marshall Ward).
There is some confusion as to the genera of algae that form the gonidia of
these epiphyllous lichens. Phyllactidium given by Zahlbruckner as the
gonidium of all the Strigulaceae (except Strigula in part) is classified by de
Toni[289] as probably synonymous with Phycopeltis Millard, and as
differing from Mycoidea parasitica in the mode of growth.
the cells rather large and multinucleate.
Cladophora Kütz. Filaments branching, of one-cell rows, attached at the
base; colour, bright or dark green; mostly aquatic and marine (Fig. 30).
Only one lichen, Racodium rupestre, a member of the Coenogoniaceae, is
associated with Cladophora. It is a British lichen, and is always sterile.
Fam. Mycoideaceae. Epiphytic algae consisting of thin discs which are
composed of radiating filaments.
1. Mycoidea Cunningh. (Cephaleuros Kunze). In Mycoidea parasitica
the filaments of the disc are partly erect and partly decumbent, reddish to
green (Fig. 31). It forms the gonidium of the parasitic lichen, Strigula
complanata, which was studied by Marshall Ward in Ceylon[288].
Zahlbruckner gives Phyllactidium as an alternative gonidium of
Strigulaceae.
2. Phycopeltis Millard. Disc a stratum one-cell thick, bearing seta, adnate
to the lower surface of the leaf, yellow-green in colour. Phycopeltis (Fig.
32) has been identified as the gonidium of Strigula complanata in New
Zealand and of Mazosia (Chiodectonaceae), a leaf lichen from tropical
America.
Fig. 31. Mycoidea parasitica Cunningh. much
magnified (after Marshall Ward).
There is some confusion as to the genera of algae that form the gonidia of
these epiphyllous lichens. Phyllactidium given by Zahlbruckner as the
gonidium of all the Strigulaceae (except Strigula in part) is classified by de
Toni[289] as probably synonymous with Phycopeltis Millard, and as
differing from Mycoidea parasitica in the mode of growth.
Page 116
Fam. Prasiolaceae. Thallus filamentous, often expanded into broad
sheets by the fusion of the filaments in one plane.
Prasiola Ag. Thallus filamentous, of one-to many-cell rows, or widely
expanded (Fig. 33). The gonidium of Mastoidiaceae (Pyrenocarpeae).
Fig. 32. Phycopeltis expansa Jenn. much
magnified (after Vaughan Jennings).
Fig. 33. Prasiola parietina Wille × 500 (after West).
B. Changes induced in the Alga
sheets by the fusion of the filaments in one plane.
Prasiola Ag. Thallus filamentous, of one-to many-cell rows, or widely
expanded (Fig. 33). The gonidium of Mastoidiaceae (Pyrenocarpeae).
Fig. 32. Phycopeltis expansa Jenn. much
magnified (after Vaughan Jennings).
Fig. 33. Prasiola parietina Wille × 500 (after West).
B. Changes induced in the Alga
Page 117
a. Myxophyceae. Though, as a general rule, the alga is less affected by its
altered life-conditions than the fungus, yet in many instances it becomes
considerably modified in appearance. In species of the genus Pyrenopsis—
small gelatinous lichens—the alga is a Gloeocapsa very similar to G.
magma. In the open it forms small colonies of blue-green cells surrounded
by a gelatinous sheath which is coloured red with gloeocapsin. As a
gonidium lying towards or on the outside of the granules composing the
thallus, the red sheath of the cells is practically unchanged, so that the
resemblance to Gloeocapsa is unmistakable. In the inner parts of the
thallus, the colonies are somewhat broken up by the hyphae and the sheaths
are not only less evident but much more faintly coloured. In Synalissa, a
minute shrubby lichen which has the same algal constituent, the tissue of
the thallus is more highly evolved, and in it the red colour can barely be
seen and then only towards the outside; at the centre it disappears entirely.
The long chaplets of Nostoc cells persist almost unchanged in the thallus of
the Collemaceae, but in heteromerous genera such as Pannaria and
Peltigera they are broken up, or they are coiled together and packed into
restricted areas or zones. The altered alga has been frequently described as
Polycoccus punctiformis. A similar modification occurs in many
cephalodia, so that the true affinity of the alga, in most instances, can only
be ascertained after free cultivation.
Bornet[290] has described in Coccocarpia molybdaea the change that the
alga Scytonema undergoes as the thallus develops: in very young fronds the
filaments of Scytonema are unchanged and are merely enclosed between
layers of hyphae. At a later stage, with increase of the thallus in thickness,
the algal filaments are broken up, their covering sheath disappears, and the
cells become rounded and isolated. Petractis (Gyalecta) exanthematica has
also a Scytonema as gonidium, and equally exact observations have been
made by Fünfstück[291] on the way it is transformed by symbiosis: with the
exception of a very thin superficial layer, the thallus is immersed in the rock
and is permeated by the alga to its lowest limits, 3 to 4 mm. below the
surface, Petractis being a homoiomerous lichen. The Scytonema trichomes
embedded in the rock become narrower, and the sheath, which in the
epilithic part of the thallus is 4µ wide, disappears almost entirely. The green
colour of the cells fades and septation is less frequent and less regular. The
filaments in that condition are very like oil-hyphae and can only be
altered life-conditions than the fungus, yet in many instances it becomes
considerably modified in appearance. In species of the genus Pyrenopsis—
small gelatinous lichens—the alga is a Gloeocapsa very similar to G.
magma. In the open it forms small colonies of blue-green cells surrounded
by a gelatinous sheath which is coloured red with gloeocapsin. As a
gonidium lying towards or on the outside of the granules composing the
thallus, the red sheath of the cells is practically unchanged, so that the
resemblance to Gloeocapsa is unmistakable. In the inner parts of the
thallus, the colonies are somewhat broken up by the hyphae and the sheaths
are not only less evident but much more faintly coloured. In Synalissa, a
minute shrubby lichen which has the same algal constituent, the tissue of
the thallus is more highly evolved, and in it the red colour can barely be
seen and then only towards the outside; at the centre it disappears entirely.
The long chaplets of Nostoc cells persist almost unchanged in the thallus of
the Collemaceae, but in heteromerous genera such as Pannaria and
Peltigera they are broken up, or they are coiled together and packed into
restricted areas or zones. The altered alga has been frequently described as
Polycoccus punctiformis. A similar modification occurs in many
cephalodia, so that the true affinity of the alga, in most instances, can only
be ascertained after free cultivation.
Bornet[290] has described in Coccocarpia molybdaea the change that the
alga Scytonema undergoes as the thallus develops: in very young fronds the
filaments of Scytonema are unchanged and are merely enclosed between
layers of hyphae. At a later stage, with increase of the thallus in thickness,
the algal filaments are broken up, their covering sheath disappears, and the
cells become rounded and isolated. Petractis (Gyalecta) exanthematica has
also a Scytonema as gonidium, and equally exact observations have been
made by Fünfstück[291] on the way it is transformed by symbiosis: with the
exception of a very thin superficial layer, the thallus is immersed in the rock
and is permeated by the alga to its lowest limits, 3 to 4 mm. below the
surface, Petractis being a homoiomerous lichen. The Scytonema trichomes
embedded in the rock become narrower, and the sheath, which in the
epilithic part of the thallus is 4µ wide, disappears almost entirely. The green
colour of the cells fades and septation is less frequent and less regular. The
filaments in that condition are very like oil-hyphae and can only be
Page 118
distinguished as algal by staining reagents such as alkanna. They never
seem to be in contact with the fungal elements: there is no visible
appearance of parasitism nor even of consortism.
b. Chlorophyceae. As a rule the green-celled gonidium such as
Protococcus is not changed in form though the colour may be less vivid, but
in certain lichens there do occur modifications in its appearance. In Micarea
(Biatorina) prasina, Hedlund[292] noted that the gonidium was a minute
alga possessing a gelatinous sheath similar to that of a Gloeocapsa. He
isolated the alga, made artificial cultures and found that, in the altered
conditions, it gradually increased in size, threw off the gelatinous sheath
and developed into normal Protococcus cells, measuring 7 to 10µ in
diameter. The gelatinous sheath was thus proved to be merely a biological
variation, probably of value to the lichen owing to its capacity to imbibe
and retain moisture. Zukal[293] also made cultures of this alga, but wrongly
concluded it was a Gloeocystis.
Moebius[294] has described the transformation from algae to lichen
gonidia in a species epiphytic on Orchids in Porto Rico. He had observed
that most of the leaves were inhabited by a membranaceous alga,
Phyllactidium, and that constantly associated with it were small scraps of a
lichen thallus containing isolated globose gonidia. The cells of the alga,
under the influence of the invading fungus, were, in this case, formed into
isolated round bodies which divided into four, each daughter-cell becoming
surrounded by a membrane and being capable, in turn, of further division.
Frank[295] followed the change from a free alga to a gonidium in
Chroolepus (Trentepohlia) umbrinum, as shown in the hypophloeodal thalli
of the Graphideae. The alga itself is frequent on beech bark, where it forms
wide-spreading brownish-red incrustations consisting of short chains
occasionally branched. The individual cells have thick laminated
membranes and vary in width from 20 µ to 37 µ. The free alga constantly
tends to penetrate below the cortical layers of the tree on which it grows,
and the immersed cells become not only longer and of a thinner texture, but
the characteristic red colour so entirely disappears, that the growing
penetrating apical cell may be light green or almost colourless. As a lichen
gonidium the alga undergoes even more drastic changes: the red oily
granules gradually vanish and the cells become chlorophyll-green or, if any
seem to be in contact with the fungal elements: there is no visible
appearance of parasitism nor even of consortism.
b. Chlorophyceae. As a rule the green-celled gonidium such as
Protococcus is not changed in form though the colour may be less vivid, but
in certain lichens there do occur modifications in its appearance. In Micarea
(Biatorina) prasina, Hedlund[292] noted that the gonidium was a minute
alga possessing a gelatinous sheath similar to that of a Gloeocapsa. He
isolated the alga, made artificial cultures and found that, in the altered
conditions, it gradually increased in size, threw off the gelatinous sheath
and developed into normal Protococcus cells, measuring 7 to 10µ in
diameter. The gelatinous sheath was thus proved to be merely a biological
variation, probably of value to the lichen owing to its capacity to imbibe
and retain moisture. Zukal[293] also made cultures of this alga, but wrongly
concluded it was a Gloeocystis.
Moebius[294] has described the transformation from algae to lichen
gonidia in a species epiphytic on Orchids in Porto Rico. He had observed
that most of the leaves were inhabited by a membranaceous alga,
Phyllactidium, and that constantly associated with it were small scraps of a
lichen thallus containing isolated globose gonidia. The cells of the alga,
under the influence of the invading fungus, were, in this case, formed into
isolated round bodies which divided into four, each daughter-cell becoming
surrounded by a membrane and being capable, in turn, of further division.
Frank[295] followed the change from a free alga to a gonidium in
Chroolepus (Trentepohlia) umbrinum, as shown in the hypophloeodal thalli
of the Graphideae. The alga itself is frequent on beech bark, where it forms
wide-spreading brownish-red incrustations consisting of short chains
occasionally branched. The individual cells have thick laminated
membranes and vary in width from 20 µ to 37 µ. The free alga constantly
tends to penetrate below the cortical layers of the tree on which it grows,
and the immersed cells become not only longer and of a thinner texture, but
the characteristic red colour so entirely disappears, that the growing
penetrating apical cell may be light green or almost colourless. As a lichen
gonidium the alga undergoes even more drastic changes: the red oily
granules gradually vanish and the cells become chlorophyll-green or, if any
Page 119
retain a bright colour, they are orange or yellow. The branching of the
chains is more regular, the cells more elongate and narrower; usually they
are about 13 to 21 µ long and 8 µ wide, or even less. Deeper down in the
periderm, the chains become disintegrated into separate units. Another
notable alteration takes place in the cell-membrane which becomes thin and
delicate. It has, however, been observed that if these algal cells reach the
surface, owing to peeling of the bark, etc., they resume the appearance of a
normal Trentepohlia.
In certain cases where two kinds of algae were supposed to be present in
some lichens, it has been proved that one species only is represented, the
difference in their form being caused by mechanical pressure of the
surrounding hyphae, as in Endocarpon and Staurothele where the hymenial
gonidia are cylindrical in form and much smaller than those of the thallus.
They were on this account classified by Stahl[296] under a separate algal
genus, Stichococcus, but they are now known to be growth forms of
Protococcus, the alga that is normally present in the thallus. Similar
variations were found by Neubner[297] in the gonidia of the Caliciaceae, but,
by culture experiments with the gonidia apart from the hyphae, he
succeeded in demonstrating transition forms in all stages between the
“Pleurococcus” cells and those of “Stichococcus,” though the characters
acquired by the latter are transmitted to following generations. The
transformation from spherical to cylindrical algal cells had been also noted
by Krabbe[298] in the young podetia of some species of Cladonia, the
change in form being due to the continued pressure in one direction of the
parallel hyphae.
Isolated algal cells have been observed within the cortex of various
lichens. They are carried thither by the hyphae from the gonidial zone in the
process of cortical formation, but they soon die off as in that position they
are deprived of a sufficiency of air and of moisture. Forssell[299] found
Xanthocapsa cells embedded in the hymenium of Omphalaria Heppii. They
were similar to those of the thallus, but they were not associated with
hyphae and had undergone less change than the thalline algae.
C. Constancy of Algal Constituents
chains is more regular, the cells more elongate and narrower; usually they
are about 13 to 21 µ long and 8 µ wide, or even less. Deeper down in the
periderm, the chains become disintegrated into separate units. Another
notable alteration takes place in the cell-membrane which becomes thin and
delicate. It has, however, been observed that if these algal cells reach the
surface, owing to peeling of the bark, etc., they resume the appearance of a
normal Trentepohlia.
In certain cases where two kinds of algae were supposed to be present in
some lichens, it has been proved that one species only is represented, the
difference in their form being caused by mechanical pressure of the
surrounding hyphae, as in Endocarpon and Staurothele where the hymenial
gonidia are cylindrical in form and much smaller than those of the thallus.
They were on this account classified by Stahl[296] under a separate algal
genus, Stichococcus, but they are now known to be growth forms of
Protococcus, the alga that is normally present in the thallus. Similar
variations were found by Neubner[297] in the gonidia of the Caliciaceae, but,
by culture experiments with the gonidia apart from the hyphae, he
succeeded in demonstrating transition forms in all stages between the
“Pleurococcus” cells and those of “Stichococcus,” though the characters
acquired by the latter are transmitted to following generations. The
transformation from spherical to cylindrical algal cells had been also noted
by Krabbe[298] in the young podetia of some species of Cladonia, the
change in form being due to the continued pressure in one direction of the
parallel hyphae.
Isolated algal cells have been observed within the cortex of various
lichens. They are carried thither by the hyphae from the gonidial zone in the
process of cortical formation, but they soon die off as in that position they
are deprived of a sufficiency of air and of moisture. Forssell[299] found
Xanthocapsa cells embedded in the hymenium of Omphalaria Heppii. They
were similar to those of the thallus, but they were not associated with
hyphae and had undergone less change than the thalline algae.
C. Constancy of Algal Constituents
Page 120
Lichen hyphae of one family or genus, as a rule, combine with the same
species of alga, and the continuity of genera and species is maintained.
There are, however, related lichens that differ chiefly or only in the
characters of the gonidia. Among such closely allied genera or sections of
genera may be cited Sticta with bright-green algae and the section Stictina
with blue-green; Peltidea similarly related to Peltigera and Nephroma to
Nephromium. In the genus Solorina, some of the species possess bright-
green, others blue-green algae, while in one, S. crocea[300], there is an upper
layer of small bright-green gonidia that project in irregular pyramids into
the upper cortex; while below these there stretches a more or less
interrupted band of blue-green Nostoc cells. The two layers are usually
separated by strands of hyphae, but occasionally they come into close
contact, and the hyphal filaments pass from one zone to the other. In this
genus cephalodia containing blue-green Nostoc are characteristic of all the
“bright-green” species. Harmand[301] has recorded the presence of two
different types of gonidia in Lecanora atra f. subgrumosa; one of them, the
normal Protococcus alga of the species, the other, pale-blue-green cells of
Nostoc affinity.
Forssell[302] states that in Lecanora (Psoroma) hypnorum, the normal
bright-green gonidia of some of the squamules may be replaced by Nostoc.
In that case they are regarded as cephalodia, though in structure they
exactly resemble the squamules of Pannaria pezizoides, and Forssell
considers that there is sufficient evidence of the identity of the hyphal
constituent in these two lichens, the alga alone being different.
It may be that in Archilichens with a marked capacity to form a second
symbiotic union with blue-green algae, a tendency to revert to a primitive
condition is evident—a condition which has persisted wholly in Peltigera
with its Nostoc zone, but is manifested only by cephalodia formation in the
Peltidea section of the genus. In this connection, however, we must bear in
mind Forssell’s view that it is the Archilichens that are the more
primitive[303].
The alien blue-green algae with their gelatinous sheaths are adapted to
the absorption and retention of moisture, and, in this way, they doubtless
render important service to the lichens that harbour them in cephalodia.
species of alga, and the continuity of genera and species is maintained.
There are, however, related lichens that differ chiefly or only in the
characters of the gonidia. Among such closely allied genera or sections of
genera may be cited Sticta with bright-green algae and the section Stictina
with blue-green; Peltidea similarly related to Peltigera and Nephroma to
Nephromium. In the genus Solorina, some of the species possess bright-
green, others blue-green algae, while in one, S. crocea[300], there is an upper
layer of small bright-green gonidia that project in irregular pyramids into
the upper cortex; while below these there stretches a more or less
interrupted band of blue-green Nostoc cells. The two layers are usually
separated by strands of hyphae, but occasionally they come into close
contact, and the hyphal filaments pass from one zone to the other. In this
genus cephalodia containing blue-green Nostoc are characteristic of all the
“bright-green” species. Harmand[301] has recorded the presence of two
different types of gonidia in Lecanora atra f. subgrumosa; one of them, the
normal Protococcus alga of the species, the other, pale-blue-green cells of
Nostoc affinity.
Forssell[302] states that in Lecanora (Psoroma) hypnorum, the normal
bright-green gonidia of some of the squamules may be replaced by Nostoc.
In that case they are regarded as cephalodia, though in structure they
exactly resemble the squamules of Pannaria pezizoides, and Forssell
considers that there is sufficient evidence of the identity of the hyphal
constituent in these two lichens, the alga alone being different.
It may be that in Archilichens with a marked capacity to form a second
symbiotic union with blue-green algae, a tendency to revert to a primitive
condition is evident—a condition which has persisted wholly in Peltigera
with its Nostoc zone, but is manifested only by cephalodia formation in the
Peltidea section of the genus. In this connection, however, we must bear in
mind Forssell’s view that it is the Archilichens that are the more
primitive[303].
The alien blue-green algae with their gelatinous sheaths are adapted to
the absorption and retention of moisture, and, in this way, they doubtless
render important service to the lichens that harbour them in cephalodia.
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D. Displacement of Algae within the Thallus
a. Normal displacement. Lindau[304] has contrasted the advancing apical
growth of the creeping alga Trentepohlia with the stationary condition of
the unicellular species that multiply by repeated division or by sporulation,
and thus form more or less dense zones and groups of gonidia in most
lichens. The fungus in the latter case pushes its way among the algae and
breaks up the compact masses by a shoving movement, thus letting in light
and air. The growing hypha usually applies itself closely round an algal cell,
and secondary branches arise which in time encircle it in a network of short
cells. In the thallus of Variolaria[305] the hyphae from the lower tissues,
termed push-hyphae by Nienburg[306], push their way into the algal groups
and filaments composed of short cells come to lie closely round the
individual gonidia. Continued growth is centrifugal, and the algae are
carried outward with the extension of the hyphae (Fig. 12). Cell-division is
more active at the periphery, that being the area of vigorous growth, and the
algal cells are, in consequence, generally smaller in that region than those
further back, the latter having entered more or less into a resting condition,
or, as is more probable, these smaller cells are aplanospores not fully
mature.
b. Local displacement. Specimens of Parmelia physodes were found
several times by Bitter, the grey-green surface of which was marbled with
whitish lines, caused by the absence of gonidia under these lighter-coloured
areas. The thallus was otherwise healthy as was manifested by the freely
fruiting condition: no explanation of the phenomenon was forthcoming.
Bitter compared the condition with the appearance of lighter areas on the
thallus of Parmelia obscurata.
Something of the same nature was observed on the thallus of a Peltigera
collected by F. T. Brooks near Cambridge. The marking took the form of a
series of concentric circles, starting from several centres. The darker lines
were found on examination to contain the normal blue-green algal zone,
while the colour had faded from the lighter parts. The cause of the
difference in colouration was not apparent.
E. Non-gonidial Organisms associated with Lichen Hyphae
a. Normal displacement. Lindau[304] has contrasted the advancing apical
growth of the creeping alga Trentepohlia with the stationary condition of
the unicellular species that multiply by repeated division or by sporulation,
and thus form more or less dense zones and groups of gonidia in most
lichens. The fungus in the latter case pushes its way among the algae and
breaks up the compact masses by a shoving movement, thus letting in light
and air. The growing hypha usually applies itself closely round an algal cell,
and secondary branches arise which in time encircle it in a network of short
cells. In the thallus of Variolaria[305] the hyphae from the lower tissues,
termed push-hyphae by Nienburg[306], push their way into the algal groups
and filaments composed of short cells come to lie closely round the
individual gonidia. Continued growth is centrifugal, and the algae are
carried outward with the extension of the hyphae (Fig. 12). Cell-division is
more active at the periphery, that being the area of vigorous growth, and the
algal cells are, in consequence, generally smaller in that region than those
further back, the latter having entered more or less into a resting condition,
or, as is more probable, these smaller cells are aplanospores not fully
mature.
b. Local displacement. Specimens of Parmelia physodes were found
several times by Bitter, the grey-green surface of which was marbled with
whitish lines, caused by the absence of gonidia under these lighter-coloured
areas. The thallus was otherwise healthy as was manifested by the freely
fruiting condition: no explanation of the phenomenon was forthcoming.
Bitter compared the condition with the appearance of lighter areas on the
thallus of Parmelia obscurata.
Something of the same nature was observed on the thallus of a Peltigera
collected by F. T. Brooks near Cambridge. The marking took the form of a
series of concentric circles, starting from several centres. The darker lines
were found on examination to contain the normal blue-green algal zone,
while the colour had faded from the lighter parts. The cause of the
difference in colouration was not apparent.
E. Non-gonidial Organisms associated with Lichen Hyphae
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Bonnier[307] made a series of cultures with lichen spores and green cells
other than those that form lichen gonidia. In one instance he substituted
Protococcus botryoides for the normal gonidia of Parmelia (Xanthoria)
parietina; in another of his cultures he replaced Protococcus viridis by the
filamentous alga Trentepohlia abietina. In both cases the hyphae attached
themselves to the green cells and a certain stage of thallus formation was
reached, though growth ceased fairly early. Another experiment made with
the large filaments of Vaucheria sessilis met with the same amount of
success (Fig. 34). The germinating hyphae attached themselves to the alga
and grew all round it, but there was no advance to tissue formation.
Cultures were also made with the protonema of mosses. Either spores of
mosses and lichens were germinated together, or lichen spores were sown in
close proximity to fully formed protonemata. The developing hyphae seized
on the moss cells and formed a network of branching anastomosing
filaments along the whole length of the protonema without, however,
penetrating the cells. If suitable algae were encountered, proper thallus
formation commenced, and Bonnier considers that the hyphae receive
stimulus and nourishment from the protonema sufficient to tide them over a
considerable period, perhaps until the algal symbiont is met. An interesting
variation was noted in connection with the cultures of Mnium hornum[308].
If the protonema were of the usual vigorous type, the whole length was
encased by the hyphal network; but if it were delicate and slender, the
protoplasm collected in the cell that was touched by hyphae and formed a
sort of swollen thick-walled bud (Fig. 35). This new body persisted when
the rest of the filament and the hyphae had disappeared, and, in favourable
conditions, grew again to form a moss plant.
other than those that form lichen gonidia. In one instance he substituted
Protococcus botryoides for the normal gonidia of Parmelia (Xanthoria)
parietina; in another of his cultures he replaced Protococcus viridis by the
filamentous alga Trentepohlia abietina. In both cases the hyphae attached
themselves to the green cells and a certain stage of thallus formation was
reached, though growth ceased fairly early. Another experiment made with
the large filaments of Vaucheria sessilis met with the same amount of
success (Fig. 34). The germinating hyphae attached themselves to the alga
and grew all round it, but there was no advance to tissue formation.
Cultures were also made with the protonema of mosses. Either spores of
mosses and lichens were germinated together, or lichen spores were sown in
close proximity to fully formed protonemata. The developing hyphae seized
on the moss cells and formed a network of branching anastomosing
filaments along the whole length of the protonema without, however,
penetrating the cells. If suitable algae were encountered, proper thallus
formation commenced, and Bonnier considers that the hyphae receive
stimulus and nourishment from the protonema sufficient to tide them over a
considerable period, perhaps until the algal symbiont is met. An interesting
variation was noted in connection with the cultures of Mnium hornum[308].
If the protonema were of the usual vigorous type, the whole length was
encased by the hyphal network; but if it were delicate and slender, the
protoplasm collected in the cell that was touched by hyphae and formed a
sort of swollen thick-walled bud (Fig. 35). This new body persisted when
the rest of the filament and the hyphae had disappeared, and, in favourable
conditions, grew again to form a moss plant.
Page 123
Fig. 34. Germinating hyphae of
Lecanora subfusca Ach., growing over
the alga Vaucheria sessilis DC., much
magnified (after Bonnier).
F. Parasitism of Algae on Lichens
A curious instance of undoubted parasitism by an alga, not as in Strigula on one of
the higher plants, but on a lichen thallus, is recorded by Forssell[309]. A group of
Protococcus-like cells established on the thallus of Peltigera had found their way into
the tissue, the underlying cortical cells having degenerated. The blue-green cells of the
normal gonidial layer had died off before their advance but no zone was formed by the
invading algae; they simply withdrew nourishment and gave seemingly no return. The
phenomenon is somewhat isolated and accidental but illustrates the capacity of the
alga to absorb food supply from lichen hyphae.
Lecanora subfusca Ach., growing over
the alga Vaucheria sessilis DC., much
magnified (after Bonnier).
F. Parasitism of Algae on Lichens
A curious instance of undoubted parasitism by an alga, not as in Strigula on one of
the higher plants, but on a lichen thallus, is recorded by Forssell[309]. A group of
Protococcus-like cells established on the thallus of Peltigera had found their way into
the tissue, the underlying cortical cells having degenerated. The blue-green cells of the
normal gonidial layer had died off before their advance but no zone was formed by the
invading algae; they simply withdrew nourishment and gave seemingly no return. The
phenomenon is somewhat isolated and accidental but illustrates the capacity of the
alga to absorb food supply from lichen hyphae.
Page 124
Fig. 35. Pure culture of protonema of Mnium hornum L. with spores and hyphae of
Lecidea vernalis Ach. a,a,a, buds forming × 150 (after Bonnier).
An instance of epiphytic growth has also been recorded by Zahlbruckner[310]. He
found an alga, Trentepohlia abietina, covering the thallus of a Brazilian lichen,
Parmelia isidiophora, and growing so profusely as to obscure the isidiose character
towards the centre of the thallus. There was no genetic connection of the alga with the
lichen as the former was not that of the lichen gonidium. Lichen thalli are indeed very
frequently the habitat of green algae, though their occurrence may be and probably is
accidental.
Lecidea vernalis Ach. a,a,a, buds forming × 150 (after Bonnier).
An instance of epiphytic growth has also been recorded by Zahlbruckner[310]. He
found an alga, Trentepohlia abietina, covering the thallus of a Brazilian lichen,
Parmelia isidiophora, and growing so profusely as to obscure the isidiose character
towards the centre of the thallus. There was no genetic connection of the alga with the
lichen as the former was not that of the lichen gonidium. Lichen thalli are indeed very
frequently the habitat of green algae, though their occurrence may be and probably is
accidental.
Page 125
CHAPTER III
MORPHOLOGY
GENERAL ACCOUNT OF LICHEN STRUCTURE
I. ORIGIN OF LICHEN STRUCTURES
The two organisms, fungus and alga, that enter into the composition of the lichen
plant are each characterized by the simplicity of their original structure in which there
is little or no differentiation into tissues. The gonidia-forming algae are many of them
unicellular, and increase mainly by division or by sporulation into daughter-cells
which become rounded off and repeat the life of the mother-cell; others, belonging to
different genera, are filaments, mostly of single cell-rows, with apical growth. The
hyphal elements of the lichen are derived from fungi in which the vegetative body is
composed of branching filaments, a character which persists in the lichen thallus.
The union of the two symbionts has stimulated both, but more especially the
fungus, to new developments of vegetative form, in which the fungus, as the
predominant partner, provides the framework of the lichen plant-body. Varied
structures have been evolved in order to secure life conditions favourable to both
constituents, though more especially to the alga; and as the close association of the
assimilating and growing tissues is maintained, the thallus thus formed is capable of
indefinite increase.
A. Forms of Cell-Structure
There is no true parenchyma or cellular structure in the lichen thallus such as forms
the ground tissue of the higher plants. The fungal hyphae are persistently filamentous
and either simple or branched. By frequent and regular cell-division—always at right
angles to the long axis—and by coherent growth, a pseudoparenchyma may however
be built up which functions either as a protective or strengthening tissue (Fig. 36).
MORPHOLOGY
GENERAL ACCOUNT OF LICHEN STRUCTURE
I. ORIGIN OF LICHEN STRUCTURES
The two organisms, fungus and alga, that enter into the composition of the lichen
plant are each characterized by the simplicity of their original structure in which there
is little or no differentiation into tissues. The gonidia-forming algae are many of them
unicellular, and increase mainly by division or by sporulation into daughter-cells
which become rounded off and repeat the life of the mother-cell; others, belonging to
different genera, are filaments, mostly of single cell-rows, with apical growth. The
hyphal elements of the lichen are derived from fungi in which the vegetative body is
composed of branching filaments, a character which persists in the lichen thallus.
The union of the two symbionts has stimulated both, but more especially the
fungus, to new developments of vegetative form, in which the fungus, as the
predominant partner, provides the framework of the lichen plant-body. Varied
structures have been evolved in order to secure life conditions favourable to both
constituents, though more especially to the alga; and as the close association of the
assimilating and growing tissues is maintained, the thallus thus formed is capable of
indefinite increase.
A. Forms of Cell-Structure
There is no true parenchyma or cellular structure in the lichen thallus such as forms
the ground tissue of the higher plants. The fungal hyphae are persistently filamentous
and either simple or branched. By frequent and regular cell-division—always at right
angles to the long axis—and by coherent growth, a pseudoparenchyma may however
be built up which functions either as a protective or strengthening tissue (Fig. 36).
Page 126
Fig. 36. Vertical section of
young stage of stratose thallus
(Xanthoria parietina Th. Fr.). a,
plectenchyma of cortex; b,
medullary hyphae; c, gonidial
zone. × 500 (after
Schwendener).
Lindau[311] proposed the name “plectenchyma” for the tangled weft of hyphae that
is the principal tissue system in fungi as well as lichens. The more elaborated
pseudoparenchyma he designates as “paraplectenchyma,” while the term
“prosoplectenchyma” he reserved for the fibrous or chondroid strands of compact
filaments that occur frequently in the thallus of the larger fruticose lichens, and are of
service in strengthening the fronds. The term plectenchyma is now generally used for
pseudoparenchyma.
B. Types of Thallus
Three factors, according to Reinke[312], have been of influence in determining the
thalline development. The first, and most important, is the necessity to provide for the
work of photosynthesis on the part of the alga. There is also the building up of a tissue
that should serve as a storage of reserve material, essential in a plant the existence of
which is prolonged far beyond the natural duration of either of the component
organisms; and, finally, there is the need of protecting the long-lived plant as a whole
though more particularly the alga.
Wallroth was the first to make a comparative study of the different lichen thalli. He
distinguished those lichens in which the green cells and the colourless filaments are
interspersed equally through the entire thallus as “homoiomerous” (Fig. 2), and those
in which there are distinct layers of cortex, gonidia, and medulla, as “heteromerous”
(Fig. 1), terms which, though now considered of less importance in classification, still
persist and are of service in describing the position of the alga with regard to the
general structure. A less evident definition of the different types of thallus has been
proposed by Zukal[313] who divides them into “endogenous” and “exogenous.”
young stage of stratose thallus
(Xanthoria parietina Th. Fr.). a,
plectenchyma of cortex; b,
medullary hyphae; c, gonidial
zone. × 500 (after
Schwendener).
Lindau[311] proposed the name “plectenchyma” for the tangled weft of hyphae that
is the principal tissue system in fungi as well as lichens. The more elaborated
pseudoparenchyma he designates as “paraplectenchyma,” while the term
“prosoplectenchyma” he reserved for the fibrous or chondroid strands of compact
filaments that occur frequently in the thallus of the larger fruticose lichens, and are of
service in strengthening the fronds. The term plectenchyma is now generally used for
pseudoparenchyma.
B. Types of Thallus
Three factors, according to Reinke[312], have been of influence in determining the
thalline development. The first, and most important, is the necessity to provide for the
work of photosynthesis on the part of the alga. There is also the building up of a tissue
that should serve as a storage of reserve material, essential in a plant the existence of
which is prolonged far beyond the natural duration of either of the component
organisms; and, finally, there is the need of protecting the long-lived plant as a whole
though more particularly the alga.
Wallroth was the first to make a comparative study of the different lichen thalli. He
distinguished those lichens in which the green cells and the colourless filaments are
interspersed equally through the entire thallus as “homoiomerous” (Fig. 2), and those
in which there are distinct layers of cortex, gonidia, and medulla, as “heteromerous”
(Fig. 1), terms which, though now considered of less importance in classification, still
persist and are of service in describing the position of the alga with regard to the
general structure. A less evident definition of the different types of thallus has been
proposed by Zukal[313] who divides them into “endogenous” and “exogenous.”
Page 127
a. Endogenous Thallus. The term has been applied to a comparatively small
number of homoiomerous lichens in which the alga predominates in the development,
and determines the form of the thallus. These algae, members of the Myxophyceae,
are extremely gelatinous, and the hyphae grow alongside or within the gelatinous
sheath. In the simpler forms the vegetative structure is of the most primitive type: the
alga retains its original character almost unchanged, and the ascomycetous fungus
grows along with and beside it (Fig. 4). Such are the minutely tufted thalli of
Thermutis and Spilonema and the longer strands of Ephebe, in which the associated
Scytonema or Stigonema, filamentous blue-green algae, though excited to excessive
growth, scarcely lose their normal appearance, making it difficult at times to
recognize the lichenoid character unless the fruits also are present.
Equally primitive in most cases is the structure of the thallus associated with
Gloeocapsa. The resulting lichens, Pyrenopsis, Psorotichia, etc. are simply gelatinous
crusts of the alga with a more or less scanty intermingling of fungal hyphae.
In the Collemaceae, the gonidial cells of which are species of Nostoc (Fig. 2), there
appears a more developed thallus; but in general, symbiosis in Collema has wrought
the minimum of change in the habit of the alga, hence the indecision of the earlier
botanists as to the identification and classification of Nostoc and Collema. Though in
many of the species of the genus Collema no definite tissue is formed, yet, under the
influence of symbiosis, the plants become moulded into variously shaped lobes which
are specifically constant. In some species there is an advance towards more
elaboration of form in the protective tissues of the apothecia, a layer of thin-walled
plectenchyma being occasionally formed beneath or around the fruit as in Collema
granuliferum.
In all these lichens, it is only the thallus that can be considered as primitive: the
fruit is a more or less open apothecium—more rarely a perithecium—with a fully
developed hymenium. Frequently it is provided with a protective thalline margin.
b. Exogenous Thallus. In this group, composed almost exclusively of
heteromerous lichens, Zukal includes all those in which the fungus takes the lead in
thalline development. He counts as such Leptogium, a genus closely allied to Collema
but with more membranous lobes, in which the short terminal cells of the hyphae have
united to form a continuous cortex. A higher development, therefore, becomes at once
apparent, though in some genera, as in Coenogonium, the alga still predominates,
while the simplest forms may be merely a scanty weft of filaments associated with
groups of algal cells. Such a thallus is characteristic of the Ectolechiaceae, and some
Gyalectaceae, etc., which have, indeed, been described by Zahlbruckner[314] as
homoiomerous though their gonidia belong to the non-gelatinous Chlorophyceae.
Heteromerous lichens have been arranged by Hue[315] according to their general
structure in three great series:
number of homoiomerous lichens in which the alga predominates in the development,
and determines the form of the thallus. These algae, members of the Myxophyceae,
are extremely gelatinous, and the hyphae grow alongside or within the gelatinous
sheath. In the simpler forms the vegetative structure is of the most primitive type: the
alga retains its original character almost unchanged, and the ascomycetous fungus
grows along with and beside it (Fig. 4). Such are the minutely tufted thalli of
Thermutis and Spilonema and the longer strands of Ephebe, in which the associated
Scytonema or Stigonema, filamentous blue-green algae, though excited to excessive
growth, scarcely lose their normal appearance, making it difficult at times to
recognize the lichenoid character unless the fruits also are present.
Equally primitive in most cases is the structure of the thallus associated with
Gloeocapsa. The resulting lichens, Pyrenopsis, Psorotichia, etc. are simply gelatinous
crusts of the alga with a more or less scanty intermingling of fungal hyphae.
In the Collemaceae, the gonidial cells of which are species of Nostoc (Fig. 2), there
appears a more developed thallus; but in general, symbiosis in Collema has wrought
the minimum of change in the habit of the alga, hence the indecision of the earlier
botanists as to the identification and classification of Nostoc and Collema. Though in
many of the species of the genus Collema no definite tissue is formed, yet, under the
influence of symbiosis, the plants become moulded into variously shaped lobes which
are specifically constant. In some species there is an advance towards more
elaboration of form in the protective tissues of the apothecia, a layer of thin-walled
plectenchyma being occasionally formed beneath or around the fruit as in Collema
granuliferum.
In all these lichens, it is only the thallus that can be considered as primitive: the
fruit is a more or less open apothecium—more rarely a perithecium—with a fully
developed hymenium. Frequently it is provided with a protective thalline margin.
b. Exogenous Thallus. In this group, composed almost exclusively of
heteromerous lichens, Zukal includes all those in which the fungus takes the lead in
thalline development. He counts as such Leptogium, a genus closely allied to Collema
but with more membranous lobes, in which the short terminal cells of the hyphae have
united to form a continuous cortex. A higher development, therefore, becomes at once
apparent, though in some genera, as in Coenogonium, the alga still predominates,
while the simplest forms may be merely a scanty weft of filaments associated with
groups of algal cells. Such a thallus is characteristic of the Ectolechiaceae, and some
Gyalectaceae, etc., which have, indeed, been described by Zahlbruckner[314] as
homoiomerous though their gonidia belong to the non-gelatinous Chlorophyceae.
Heteromerous lichens have been arranged by Hue[315] according to their general
structure in three great series:
Page 128
1. Stratosae. Crustaceous, squamulose and foliose lichens with a dorsiventral
thallus.
2. Radiatae. Fruticose, shrubby or filamentous lichens with a strap-shaped or
cylindrical thallus of radiate structure.
3. Stratosae-Radiatae. Primary dorsiventral thallus, either crustaceous or
squamulose, with a secondary upright thallus of radiate structure called the podetium
(Cladoniaceae).
II. STRATOSE THALLUS
1. CRUSTACEOUS LICHENS
A. General Structure
In the series “Stratosae,” the plant is dorsiventral, the tissues forming the thallus
being arranged more or less regularly in strata one above the other (Fig. 37). On the
upper surface there is a hyphal layer constituting a cortex, either rudimentary or
highly elaborated; beneath the cortex is situated the gonidial zone composed of algae
and hyphae in close association; and deeper down the medulla, generally a loose
tissue of branching hyphae. The lower cortex which abuts on the medulla may be as
fully developed as the upper or it may be absent.
Fig. 37. Vertical section of crustaceous lichen (Lecanora subfusca
var. chlarona Hue) on bark. a, lichen cortex; b, gonidia; c, cells of
the periderm. × 100.
The growing tissue is chiefly marginal; the hyphae on the outer edge remain
“meristematic”[316] and provide for horizontal as well as vertical extension; and there
is also continual increase of the algal cells. There is in addition a certain amount of
intercalary growth due to the activity of the gonidial tissue, both algal and fungal,
providing for the renewal of the cortex, and even interposing new tissue.
B. Saxicolous Lichens
a. Epilithic Lichens. The crustaceous lichens forming this group spread over the
rock surfaces. The support must be stable to allow the necessary time for the slowly
thallus.
2. Radiatae. Fruticose, shrubby or filamentous lichens with a strap-shaped or
cylindrical thallus of radiate structure.
3. Stratosae-Radiatae. Primary dorsiventral thallus, either crustaceous or
squamulose, with a secondary upright thallus of radiate structure called the podetium
(Cladoniaceae).
II. STRATOSE THALLUS
1. CRUSTACEOUS LICHENS
A. General Structure
In the series “Stratosae,” the plant is dorsiventral, the tissues forming the thallus
being arranged more or less regularly in strata one above the other (Fig. 37). On the
upper surface there is a hyphal layer constituting a cortex, either rudimentary or
highly elaborated; beneath the cortex is situated the gonidial zone composed of algae
and hyphae in close association; and deeper down the medulla, generally a loose
tissue of branching hyphae. The lower cortex which abuts on the medulla may be as
fully developed as the upper or it may be absent.
Fig. 37. Vertical section of crustaceous lichen (Lecanora subfusca
var. chlarona Hue) on bark. a, lichen cortex; b, gonidia; c, cells of
the periderm. × 100.
The growing tissue is chiefly marginal; the hyphae on the outer edge remain
“meristematic”[316] and provide for horizontal as well as vertical extension; and there
is also continual increase of the algal cells. There is in addition a certain amount of
intercalary growth due to the activity of the gonidial tissue, both algal and fungal,
providing for the renewal of the cortex, and even interposing new tissue.
B. Saxicolous Lichens
a. Epilithic Lichens. The crustaceous lichens forming this group spread over the
rock surfaces. The support must be stable to allow the necessary time for the slowly
Page 129
developing organism, and therefore rocks that are friable or subject to continual
weathering are bare of lichens.
aa. Hypothallus or Prothallus. The first stage of growth in the lichen thallus can
be most easily traced in epilithic crustaceous species, especially in those that inhabit a
smooth rock surface. The spore, on germination, produces a delicate branching septate
mycelium which radiates on all sides, as was so well observed and recorded by
Tulasne[317] in Verrucaria muralis (Fig. 14). Zukal[318] has called this first beginning
the prothallus. In time the cell-walls of the filaments become much thicker and
though, in some species, they remain colourless, in others they become dark-coloured,
all except the extreme tips, owing to the presence of lichen pigments—a provision,
Zukal[319] considers, to protect them against the ravages of insects, etc. The prothallic
filaments adhere closely to the substratum and the branching becomes gradually more
dendroid in form, though sometimes hyphae are united into strands, or even form a
kind of plectenchymatous tissue. This purely hyphal stage may persist for long periods
without much change. In time there may be a fortuitous encounter with the algae (Fig.
38 a) which become the gonidia of the plant. Either these have been already
established on the substratum as free-growing organisms, or, as accidentally
conveyed, they alight on the prothallus. The contact between alga and hypha excites
both to active growth and to cell-division; and the rapidly multiplying gonidia are as
speedily surrounded by the vigorously growing hyphal filaments.
weathering are bare of lichens.
aa. Hypothallus or Prothallus. The first stage of growth in the lichen thallus can
be most easily traced in epilithic crustaceous species, especially in those that inhabit a
smooth rock surface. The spore, on germination, produces a delicate branching septate
mycelium which radiates on all sides, as was so well observed and recorded by
Tulasne[317] in Verrucaria muralis (Fig. 14). Zukal[318] has called this first beginning
the prothallus. In time the cell-walls of the filaments become much thicker and
though, in some species, they remain colourless, in others they become dark-coloured,
all except the extreme tips, owing to the presence of lichen pigments—a provision,
Zukal[319] considers, to protect them against the ravages of insects, etc. The prothallic
filaments adhere closely to the substratum and the branching becomes gradually more
dendroid in form, though sometimes hyphae are united into strands, or even form a
kind of plectenchymatous tissue. This purely hyphal stage may persist for long periods
without much change. In time there may be a fortuitous encounter with the algae (Fig.
38 a) which become the gonidia of the plant. Either these have been already
established on the substratum as free-growing organisms, or, as accidentally
conveyed, they alight on the prothallus. The contact between alga and hypha excites
both to active growth and to cell-division; and the rapidly multiplying gonidia are as
speedily surrounded by the vigorously growing hyphal filaments.
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Fig. 38 A. Hypothallus of Rhizocarpon
confervoides DC., from the extreme edge, with
loose gonidia × 600.
Fig. 38 B. Young thallus of Rhizocarpon confervoides DC., with
various centres of gonidial growth on the hypothallus × 30.
confervoides DC., from the extreme edge, with
loose gonidia × 600.
Fig. 38 B. Young thallus of Rhizocarpon confervoides DC., with
various centres of gonidial growth on the hypothallus × 30.
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Schwendener[320] has thus described the origin and further development of
prothallus and gonidia: on the dark-coloured proto- or prothallus, he noted small
nestling groups of green cells which he, at that time, regarded as direct outgrowths
from the lichen hyphae. These gonidial cells, increasing by division, multiplied
gradually and gathered into a connected zone. He also observed that the hyphae in
contact with the gonidia became more thin-walled and produced many new branches.
Some of these newly formed branches grow upwards and form the cortex, others grow
downwards and build up the medulla or pith; the filaments at the circumference
continue to advance and may start new centres of gonidial activity (Fig. 38 b). In
many species, however, this prothallus or, as it is usually termed at this stage, the
hypothallus, becomes very soon overgrown and obscured by the vigorous increase of
the first formed symbiotic tissue and can barely be seen as a white or dark line
bordering the thallus (Fig. 39). Schwendener[321] has stated that probably only lichens
that develop from the spore are distinguished by a protothallus, and that those arising
from soredia do not form these first creeping filaments.
Fig. 39. Lecanora parella Ach. Determinate
thallus with white bordering hypothallus, reduced
(M. P., Photo.).
bb. Formation of crustaceous tissues. Some crustaceous lichens have a
persistently scanty furfuraceous crust, the vegetative development never advancing
much beyond the first rather loose association of gonidia and hyphae; but in those in
which a distinct crust or granules are formed, three different strata of tissue are
discernible:
prothallus and gonidia: on the dark-coloured proto- or prothallus, he noted small
nestling groups of green cells which he, at that time, regarded as direct outgrowths
from the lichen hyphae. These gonidial cells, increasing by division, multiplied
gradually and gathered into a connected zone. He also observed that the hyphae in
contact with the gonidia became more thin-walled and produced many new branches.
Some of these newly formed branches grow upwards and form the cortex, others grow
downwards and build up the medulla or pith; the filaments at the circumference
continue to advance and may start new centres of gonidial activity (Fig. 38 b). In
many species, however, this prothallus or, as it is usually termed at this stage, the
hypothallus, becomes very soon overgrown and obscured by the vigorous increase of
the first formed symbiotic tissue and can barely be seen as a white or dark line
bordering the thallus (Fig. 39). Schwendener[321] has stated that probably only lichens
that develop from the spore are distinguished by a protothallus, and that those arising
from soredia do not form these first creeping filaments.
Fig. 39. Lecanora parella Ach. Determinate
thallus with white bordering hypothallus, reduced
(M. P., Photo.).
bb. Formation of crustaceous tissues. Some crustaceous lichens have a
persistently scanty furfuraceous crust, the vegetative development never advancing
much beyond the first rather loose association of gonidia and hyphae; but in those in
which a distinct crust or granules are formed, three different strata of tissue are
discernible:
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1st. An upper cortical tissue of interlaced hyphae with frequent septation and with
swollen gelatinous walls, closely compacted and with the lumen of the cells almost
obliterated, not unfrequently a layer of mucilage serving as an outer cuticle. This type
of cortex has been called by Hue[322] “decomposed.” It is subject to constant surface
weathering, thin layers being continually peeled off, but it is as continually being
renewed endogenously by the upward growth of hyphae from the active gonidial zone.
Exceptions to this type of cortex in crustaceous lichens are found in some Pertusariae
where a secondary plectenchymatous cortex is formed, and in Dirina where it is
fastigiate[323] as in Roccella.
2nd. The gonidial zone—a somewhat irregular layer of algae and hyphae below the
cortex—which varies in thickness according to the species.
3rd. The medullary tissue of somewhat loosely intermingled branching hyphae,
with generally rather swollen walls and narrow lumen. It rests directly on the
substratum and follows every inequality and crack so closely, even where it does not
penetrate, that the thallus cannot be detached without breaking it away.
In Verrucaria mucosa, a smooth brown maritime lichen found on rocks between
tide-levels, the thallus is composed of tightly packed vertical rows of hyphae, slender,
rather thin-walled, and divided into short cells. The gonidia are chiefly massed
towards the upper surface, but they also occur in vertical rows in the medulla. One or
two of the upper cells are brown and form an even cortex. The same formation occurs
in some other sea-washed species; the arrangement of the tissue elements recalls that
of crustaceous Florideae such as Hildenbrandtia, Cruoria, etc.
cc. Formation of areolae. An “areolate” thallus is
seamed and scored by cracks of varying width and depth
which divide it into minute compartments. These cracks or
fissures or chinks originate in two ways depending on the
presence or absence of hypothallic hyphae. Where the
hypothallus is active, new areolae arise when the filaments
encounter new groups of algae. More vigorous growth
starts at once and proceeds on all sides from these algal
centres, until similarly formed areolae are met, a more or
Fig. 40. Young thallus of less pronounced fissure marking the limits of each. This
Rhizocarpon geographicum DC.,
with primary and subsequent primary areolation, termed rimose or rimulose, is well seen
(dotted lines) areolation × 5. in the thin smooth thallus of Rhizocarpon geographicum
(Fig. 40); but the first-formed areolae are also very
frequently slightly marked by subsequent cracks due to
unequal growth. The areolation caused by primary growth conditions tends to become
gradually less obvious or to disappear altogether.
Secondary areolation is due to unequal intercalary growth of the otherwise
continuous thallus[324]. A more active increase of any minute portions provokes a
swollen gelatinous walls, closely compacted and with the lumen of the cells almost
obliterated, not unfrequently a layer of mucilage serving as an outer cuticle. This type
of cortex has been called by Hue[322] “decomposed.” It is subject to constant surface
weathering, thin layers being continually peeled off, but it is as continually being
renewed endogenously by the upward growth of hyphae from the active gonidial zone.
Exceptions to this type of cortex in crustaceous lichens are found in some Pertusariae
where a secondary plectenchymatous cortex is formed, and in Dirina where it is
fastigiate[323] as in Roccella.
2nd. The gonidial zone—a somewhat irregular layer of algae and hyphae below the
cortex—which varies in thickness according to the species.
3rd. The medullary tissue of somewhat loosely intermingled branching hyphae,
with generally rather swollen walls and narrow lumen. It rests directly on the
substratum and follows every inequality and crack so closely, even where it does not
penetrate, that the thallus cannot be detached without breaking it away.
In Verrucaria mucosa, a smooth brown maritime lichen found on rocks between
tide-levels, the thallus is composed of tightly packed vertical rows of hyphae, slender,
rather thin-walled, and divided into short cells. The gonidia are chiefly massed
towards the upper surface, but they also occur in vertical rows in the medulla. One or
two of the upper cells are brown and form an even cortex. The same formation occurs
in some other sea-washed species; the arrangement of the tissue elements recalls that
of crustaceous Florideae such as Hildenbrandtia, Cruoria, etc.
cc. Formation of areolae. An “areolate” thallus is
seamed and scored by cracks of varying width and depth
which divide it into minute compartments. These cracks or
fissures or chinks originate in two ways depending on the
presence or absence of hypothallic hyphae. Where the
hypothallus is active, new areolae arise when the filaments
encounter new groups of algae. More vigorous growth
starts at once and proceeds on all sides from these algal
centres, until similarly formed areolae are met, a more or
Fig. 40. Young thallus of less pronounced fissure marking the limits of each. This
Rhizocarpon geographicum DC.,
with primary and subsequent primary areolation, termed rimose or rimulose, is well seen
(dotted lines) areolation × 5. in the thin smooth thallus of Rhizocarpon geographicum
(Fig. 40); but the first-formed areolae are also very
frequently slightly marked by subsequent cracks due to
unequal growth. The areolation caused by primary growth conditions tends to become
gradually less obvious or to disappear altogether.
Secondary areolation is due to unequal intercalary growth of the otherwise
continuous thallus[324]. A more active increase of any minute portions provokes a
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tension or straining of the cortex between the swollen areas and the surrounding more
sluggish tissues; the surface layers give way and chinks arise, a condition described by
older lichenologists as “rimose-diffract” or sometimes as “rhagadiose.” The thallus is
generally thicker, more broken and granular in the older central parts of the lichen.
Towards the circumference, where the tissue is thinner and growth more equal, the
chinks are less evident. Sometimes the more vigorously growing areolae may extend
over those immediately adjoining, in which case the covered portions become brown
and their gonidia gradually disappear.
Strongly marked intersecting lines, similar to those round the margin of the thallus,
are formed when hypothalli that have themselves started from different centres touch
each other. A large continuous patch of crustaceous thallus may thus be composed of
many individuals (Fig. 41).
Fig. 41. Rhizocarpon geographicum DC. on boulder, reduced (M.
P., Photo.).
b. Endolithic Lichens. In many species, only the lower hyphae penetrate the
substratum either of rock or soil. In a few, more especially those growing on
limestone, the greater part or even the whole of the vegetative thallus and sometimes
also the fruits are, to some extent, immersed in the rock. It has now been demonstrated
that a number of lichens, formerly described as athalline, possess a considerable
vegetative body which cannot be examined until the limestone in which they are
embedded is dissolved by acids. One such species, Petractis (Gyalecta)
exanthematica, studied by Steiner[325] and later by Fünfstück[326], is associated with
the blue-green filamentous alga, Scytonema, and is homoiomerous in structure, the
alga growing through and permeating the whole of the embedded thallus. A partly
homoiomerous thallus, associated with Trentepohlia, has been described by
Bachmann[327]. He found the bright-yellow filaments of the alga covering the surface
of a calcareous rock. By reason of their apical growth, they pierced the rock and
sluggish tissues; the surface layers give way and chinks arise, a condition described by
older lichenologists as “rimose-diffract” or sometimes as “rhagadiose.” The thallus is
generally thicker, more broken and granular in the older central parts of the lichen.
Towards the circumference, where the tissue is thinner and growth more equal, the
chinks are less evident. Sometimes the more vigorously growing areolae may extend
over those immediately adjoining, in which case the covered portions become brown
and their gonidia gradually disappear.
Strongly marked intersecting lines, similar to those round the margin of the thallus,
are formed when hypothalli that have themselves started from different centres touch
each other. A large continuous patch of crustaceous thallus may thus be composed of
many individuals (Fig. 41).
Fig. 41. Rhizocarpon geographicum DC. on boulder, reduced (M.
P., Photo.).
b. Endolithic Lichens. In many species, only the lower hyphae penetrate the
substratum either of rock or soil. In a few, more especially those growing on
limestone, the greater part or even the whole of the vegetative thallus and sometimes
also the fruits are, to some extent, immersed in the rock. It has now been demonstrated
that a number of lichens, formerly described as athalline, possess a considerable
vegetative body which cannot be examined until the limestone in which they are
embedded is dissolved by acids. One such species, Petractis (Gyalecta)
exanthematica, studied by Steiner[325] and later by Fünfstück[326], is associated with
the blue-green filamentous alga, Scytonema, and is homoiomerous in structure, the
alga growing through and permeating the whole of the embedded thallus. A partly
homoiomerous thallus, associated with Trentepohlia, has been described by
Bachmann[327]. He found the bright-yellow filaments of the alga covering the surface
of a calcareous rock. By reason of their apical growth, they pierced the rock and
Page 134
dissolved a way for themselves, not only among the loose particles, but right through
a clear calcium crystal reaching generally to a depth of about 200µ, though isolated
threads had gone 350µ below the surface. Near the outside the tendency was for the
algae to become stouter and to increase by intercalary growth and by budded yeast-
like outgrowths; lower down they were somewhat smaller. The hyphae that became
united with the algae were unusually slender and were characterized by frequent
anastomoses. They closely surrounded the gonidia and also filled the loose spaces of
the limestone with their fine thread-like strands. Though oil was undoubtedly present
in the lower hyphae there were no swollen nor sphaeroid cells[328]. Some interesting
experiments with moisture proved that the part of the rock permeated with the lichen
absorbed much more water and retained it longer than the part that was lichen-free.
Generally the embedded tissues follow the same order as in other crustaceous
lichens: an upper layer of cortical hyphae, next a gonidial zone, and beneath that an
interlaced tissue of medullary or rhizoidal hyphae which often form fat-cells[328].
Friedrich[329] has given measurements of the immersed thallus of Lecanora
(Biatorella) simplex: under a cortical layer of hyphae there was a gonidial zone 600-
700µ thick, while the lower hyphae reached a depth of 12 mm.; he has also recorded
an instance of a thallus reaching a depth of 30 mm.
On siliceous rocks such as granite, rhizoidal hyphae penetrate the rock chiefly
between the thin separable flakes of mica. Bachmann[330] has recognized in these
conditions three distinct series of cell-formations: (1) slender long-celled sparsely
branched hyphae which form a network by frequent anastomoses; (2) further down,
though only occasionally, hyphae with short thick-walled bead-like cells; and (3)
beneath these, but only in or near mica crystals, spherical cells containing oil or some
albuminous substance.
c. Chemical Nature of the Substratum. Lichens growing on calcareous rocks or
soils are more or less endolithic, those on siliceous rocks are largely epilithic, but
Bachmann[331] found that the mica crystals in granite were penetrated, much in the
same way as limestone, by the lichen hyphae. These travel through the mica in all
directions, though they tend to follow the line of cleavage, thus taking the direction of
least cohesion. He found that oil-hyphae were formed, and also certain peculiar
bristle-like terminal branches; in other cases there were thin layers of plectenchyma,
and gonidia were also present. If however felspar or quartz crystals, no matter how
thin, blocked the way, further growth was arrested, the hyphae being unable to pierce
through or even to leave any trace on the quartz[332]. On granite containing no mica
constituents the hyphae can only follow the cracks between the different impenetrable
crystals.
Stahlecker[333] has confirmed Bachmann’s observations, but he considers that the
difference in habit and structure between the endolithic and epilithic series of lichens
is due rather to the chemical than to the physical nature of the substratum. Thus in a
a clear calcium crystal reaching generally to a depth of about 200µ, though isolated
threads had gone 350µ below the surface. Near the outside the tendency was for the
algae to become stouter and to increase by intercalary growth and by budded yeast-
like outgrowths; lower down they were somewhat smaller. The hyphae that became
united with the algae were unusually slender and were characterized by frequent
anastomoses. They closely surrounded the gonidia and also filled the loose spaces of
the limestone with their fine thread-like strands. Though oil was undoubtedly present
in the lower hyphae there were no swollen nor sphaeroid cells[328]. Some interesting
experiments with moisture proved that the part of the rock permeated with the lichen
absorbed much more water and retained it longer than the part that was lichen-free.
Generally the embedded tissues follow the same order as in other crustaceous
lichens: an upper layer of cortical hyphae, next a gonidial zone, and beneath that an
interlaced tissue of medullary or rhizoidal hyphae which often form fat-cells[328].
Friedrich[329] has given measurements of the immersed thallus of Lecanora
(Biatorella) simplex: under a cortical layer of hyphae there was a gonidial zone 600-
700µ thick, while the lower hyphae reached a depth of 12 mm.; he has also recorded
an instance of a thallus reaching a depth of 30 mm.
On siliceous rocks such as granite, rhizoidal hyphae penetrate the rock chiefly
between the thin separable flakes of mica. Bachmann[330] has recognized in these
conditions three distinct series of cell-formations: (1) slender long-celled sparsely
branched hyphae which form a network by frequent anastomoses; (2) further down,
though only occasionally, hyphae with short thick-walled bead-like cells; and (3)
beneath these, but only in or near mica crystals, spherical cells containing oil or some
albuminous substance.
c. Chemical Nature of the Substratum. Lichens growing on calcareous rocks or
soils are more or less endolithic, those on siliceous rocks are largely epilithic, but
Bachmann[331] found that the mica crystals in granite were penetrated, much in the
same way as limestone, by the lichen hyphae. These travel through the mica in all
directions, though they tend to follow the line of cleavage, thus taking the direction of
least cohesion. He found that oil-hyphae were formed, and also certain peculiar
bristle-like terminal branches; in other cases there were thin layers of plectenchyma,
and gonidia were also present. If however felspar or quartz crystals, no matter how
thin, blocked the way, further growth was arrested, the hyphae being unable to pierce
through or even to leave any trace on the quartz[332]. On granite containing no mica
constituents the hyphae can only follow the cracks between the different impenetrable
crystals.
Stahlecker[333] has confirmed Bachmann’s observations, but he considers that the
difference in habit and structure between the endolithic and epilithic series of lichens
is due rather to the chemical than to the physical nature of the substratum. Thus in a
Page 135
rock of mixed composition such as granite, the more basic constituents are preferred
by the hyphae, and are the first to be surrounded: mica, when present, is at once
penetrated; particles of hornblende, which contain 40 to 50 per cent. only of silicic
acid, are laid hold of by the filaments of the lichen before the felspar, of which the
acid content is about 60 per cent.; quartz grains which are pure silica are attacked last
of all, though in the course of time they also become corroded.
The character of the substratum also affects to a great extent the comparative
development of the different thalline layers: the hyphal tissues in silicicolous lichens
are much thinner than in lichens on limestone, and the gonidial zone is
correspondingly wider. In a species of Staurothele on granite, Stahlecker[333]
estimated the gonidial zone to be about 600 µ thick, while the lower medullary
hyphae, partly burrowing into the rock, measured about 6 mm. Other measurements at
different parts of the thallus gave a rhizoidal depth of 3 mm., while on a more finely
granular substratum, with a gonidial zone of 350 µ, the rhizoidal hyphae measured
only 1-1/2 mm. On calcareous rocks, on the contrary, with a gonidial zone that is
certainly no larger, the hyphal elements penetrate the rock to varying depths down to
15 mm. or even more.
Lang[334] has recorded equally interesting measurements for Sarcogyne (Biatorella)
latericola: on slaty rock which contained no mixture of lime, the gonidial zone had a
thickness of 80 µ, a considerable proportion of the very thin thallus. Fünfstück[335] has
indeed suggested that this lichen on acid rocks is only a starved condition of
Sarcogyne (Biatorella) simplex, which on calcareous rocks, though with a broader
gonidial zone, has, as noted above, a correspondingly much larger hyphal tissue.
Stahlecker’s theory is that the hyphae require more energy to grow in the acid
conditions that prevail in siliceous rocks, and therefore they make larger demands on
the algal symbionts. It follows that the latter must be stimulated to more abundant
growth than in circumstances favourable to the fungus, such as are found in basic
(calcareous) rocks; he concludes that on the acid (siliceous) rocks, the epilithic or
superficial condition is not only a physical but a biological necessity, to enable the
algae to grow and multiply in a zone well exposed to light with full opportunity for
active photosynthesis and healthy increase.
C. Corticolous Lichens
The crustaceous lichens occurring on bark or on dead wood, like those on rocks, are
either partly or wholly immersed in the substratum (hypophloeodal), or they grow on
the surface (epiphloeodal); but even those with a superficial crust are anchored by the
lower hyphae which enter any crack or crevice of wood or bark and so securely attach
the thallus, that it can only be removed by cutting away the underlying substance.
by the hyphae, and are the first to be surrounded: mica, when present, is at once
penetrated; particles of hornblende, which contain 40 to 50 per cent. only of silicic
acid, are laid hold of by the filaments of the lichen before the felspar, of which the
acid content is about 60 per cent.; quartz grains which are pure silica are attacked last
of all, though in the course of time they also become corroded.
The character of the substratum also affects to a great extent the comparative
development of the different thalline layers: the hyphal tissues in silicicolous lichens
are much thinner than in lichens on limestone, and the gonidial zone is
correspondingly wider. In a species of Staurothele on granite, Stahlecker[333]
estimated the gonidial zone to be about 600 µ thick, while the lower medullary
hyphae, partly burrowing into the rock, measured about 6 mm. Other measurements at
different parts of the thallus gave a rhizoidal depth of 3 mm., while on a more finely
granular substratum, with a gonidial zone of 350 µ, the rhizoidal hyphae measured
only 1-1/2 mm. On calcareous rocks, on the contrary, with a gonidial zone that is
certainly no larger, the hyphal elements penetrate the rock to varying depths down to
15 mm. or even more.
Lang[334] has recorded equally interesting measurements for Sarcogyne (Biatorella)
latericola: on slaty rock which contained no mixture of lime, the gonidial zone had a
thickness of 80 µ, a considerable proportion of the very thin thallus. Fünfstück[335] has
indeed suggested that this lichen on acid rocks is only a starved condition of
Sarcogyne (Biatorella) simplex, which on calcareous rocks, though with a broader
gonidial zone, has, as noted above, a correspondingly much larger hyphal tissue.
Stahlecker’s theory is that the hyphae require more energy to grow in the acid
conditions that prevail in siliceous rocks, and therefore they make larger demands on
the algal symbionts. It follows that the latter must be stimulated to more abundant
growth than in circumstances favourable to the fungus, such as are found in basic
(calcareous) rocks; he concludes that on the acid (siliceous) rocks, the epilithic or
superficial condition is not only a physical but a biological necessity, to enable the
algae to grow and multiply in a zone well exposed to light with full opportunity for
active photosynthesis and healthy increase.
C. Corticolous Lichens
The crustaceous lichens occurring on bark or on dead wood, like those on rocks, are
either partly or wholly immersed in the substratum (hypophloeodal), or they grow on
the surface (epiphloeodal); but even those with a superficial crust are anchored by the
lower hyphae which enter any crack or crevice of wood or bark and so securely attach
the thallus, that it can only be removed by cutting away the underlying substance.
Page 136
a. Epiphloeodal Lichens. These lichens originate in the same way as the
corresponding epilithic series from soredia or from germinating spores, and follow the
same stages of growth; first a hypothallus with subsequent colonization of gonidia, the
formation of granules, areolae, etc. The small compartments are formed as primary or
secondary areolae; the larger spaces are marked out by the encounter of hypothalli
starting from different centres.
The thickness of the thallus varies considerably according to the species. In some
Pertusariae with a stoutish irregular crust there is a narrow amorphous cortical layer
of almost obliterated cells, a thin gonidial zone about 35 µ in width and a massive
rather dense medulla of colourless hyphae. Darbishire[336] has described and figured
in Varicellaria microsticta, one of the Pertusariaceae, single hyphae that extend like
beams across the wide medulla and connect the two cortices. In some Lecanorae and
Lecideae there is, on the contrary, an extremely thin thallus consisting of groups of
algae and loose fungal filaments, which grow over and between the dead cork cells of
the outer bark. On palings, there is often a fairly substantial granular crust present,
with a gonidial zone up to about 80 µ thick, while the underlying or medullary hyphae
burrow among the dead wood fibres.
b. Hypophloeodal Lichens. These immersed lichens are comparable with the
endolithic species of the rock formations, as their thallus is almost entirely developed
under the outer bark of the tree. They are recognizable, even in the absence of any
fructification, by the somewhat shining brownish, white or olive-green patches that
indicate the underlying lichen. This type of thallus occurs in widely separated families
and genera, Lecidea, Lecanora, etc., but it is most constant in Graphideae and in those
Pyrenolichens of which the algal symbiont belongs to the genus Trentepohlia. The
development of these lichens is of peculiar interest as it has been proved that though
both symbionts are embedded in the corky tissues, the hyphae arrive there first, and, at
some later stage, are followed by the gonidia. There is therefore no question of the
alga being a “captured slave” or “unwilling mate.”
Frank[337] made a thorough study of several subcortical forms. He found that in
Arthonia radiata, the first outwardly visible indication of the presence of the lichen on
ash bark was a greenish spot quite distinct from the normal dull-grey colour of the
periderm. Usually the spots are round in outline, but they tend to become ellipsoid in a
horizontal direction, being influenced by the growth in thickness of the tree. At this
early stage only hyphae are present; Bornet[338] as well as Frank described the outer
periderm cells as penetrated and crammed with the colourless slender filaments.
Lindau[339], in a more recent work, disputes that statement: he found that the hyphae
invariably grew between the dead cork cells, splitting them up and disintegrating the
bark, but never piercing the membranes. The purely prothallic condition, as a weft of
closely entangled hyphae, may last, Frank considers, for a long period in an almost
quiescent condition—possibly for several years—before the gonidia arrive.
corresponding epilithic series from soredia or from germinating spores, and follow the
same stages of growth; first a hypothallus with subsequent colonization of gonidia, the
formation of granules, areolae, etc. The small compartments are formed as primary or
secondary areolae; the larger spaces are marked out by the encounter of hypothalli
starting from different centres.
The thickness of the thallus varies considerably according to the species. In some
Pertusariae with a stoutish irregular crust there is a narrow amorphous cortical layer
of almost obliterated cells, a thin gonidial zone about 35 µ in width and a massive
rather dense medulla of colourless hyphae. Darbishire[336] has described and figured
in Varicellaria microsticta, one of the Pertusariaceae, single hyphae that extend like
beams across the wide medulla and connect the two cortices. In some Lecanorae and
Lecideae there is, on the contrary, an extremely thin thallus consisting of groups of
algae and loose fungal filaments, which grow over and between the dead cork cells of
the outer bark. On palings, there is often a fairly substantial granular crust present,
with a gonidial zone up to about 80 µ thick, while the underlying or medullary hyphae
burrow among the dead wood fibres.
b. Hypophloeodal Lichens. These immersed lichens are comparable with the
endolithic species of the rock formations, as their thallus is almost entirely developed
under the outer bark of the tree. They are recognizable, even in the absence of any
fructification, by the somewhat shining brownish, white or olive-green patches that
indicate the underlying lichen. This type of thallus occurs in widely separated families
and genera, Lecidea, Lecanora, etc., but it is most constant in Graphideae and in those
Pyrenolichens of which the algal symbiont belongs to the genus Trentepohlia. The
development of these lichens is of peculiar interest as it has been proved that though
both symbionts are embedded in the corky tissues, the hyphae arrive there first, and, at
some later stage, are followed by the gonidia. There is therefore no question of the
alga being a “captured slave” or “unwilling mate.”
Frank[337] made a thorough study of several subcortical forms. He found that in
Arthonia radiata, the first outwardly visible indication of the presence of the lichen on
ash bark was a greenish spot quite distinct from the normal dull-grey colour of the
periderm. Usually the spots are round in outline, but they tend to become ellipsoid in a
horizontal direction, being influenced by the growth in thickness of the tree. At this
early stage only hyphae are present; Bornet[338] as well as Frank described the outer
periderm cells as penetrated and crammed with the colourless slender filaments.
Lindau[339], in a more recent work, disputes that statement: he found that the hyphae
invariably grew between the dead cork cells, splitting them up and disintegrating the
bark, but never piercing the membranes. The purely prothallic condition, as a weft of
closely entangled hyphae, may last, Frank considers, for a long period in an almost
quiescent condition—possibly for several years—before the gonidia arrive.
Page 137
It is always difficult to observe the entrance of the gonidia but they seem to spread
first under the second or third layers of the periderm. With care it is possible to trace a
filament of Trentepohlia from the surface downwards, and to see that the foremost cell
is really the growing and advancing apex of the creeping alga. Both symbionts show
increased vigour when they encounter each other: the thallus at once develops in
extent and in depth, and, ultimately, reproductive bodies are formed. In some species
the apothecia or perithecia alone emerge above the bark, in others the outer peridermal
cells are thrown off, and the thallus thus becomes superficial to some extent as a white
scurfy or furfuraceous crust.
The change from a hypophloeodal to a partly epiphloeodal condition depends
largely on the nature of the bark. Frank[337] found that Lecanora pallida remained for
a long time immersed when growing on the thick rugged bark of oak trunks. When
well lighted, or on trees with a thin periderm, such as the ash, the lichen emerges
much earlier and becomes superficial.
Black (or occasionally white) lines intersect the thallus and mark, as in saxicolous
lichens (Fig. 41), the boundary lines between different individuals or different species.
The pioneer hyphae of certain lichens very frequently become dark-coloured, and
Bitter[340] has suggested as the reason for this that in damp weather the hypothallic
growth is exceptionally vigorous. When dry weather supervenes, with high winds or
strong sunshine, the outlying hyphae, unprotected by the thallus, become dark-
coloured. On the return of more normal conditions the blackened tips are thrown off.
Bitter further states that species of Graphideae do not form a permanent black limiting
line when they grow in an isolated position: it is only when their advance is checked
by some other thallus that the dark persistent edge appears, a characteristic also to be
seen in the crust of other lichens. The dark boundary is always more marked in sunny
exposed situations: in the shade, the line is reduced to a mere thread.
Bitter’s restriction of black boundary lines to cases of encountering thalli only,
would exclude the comparison one is tempted to make between the advancing hyphae
of lichens and those of many woody fungi where the extreme edge of the white
invaded woody tissue is marked by a dark line. In the latter case however it is the cells
of the host that are stained black by the fungus pigment.
2. SQUAMULOSE LICHENS
A. Development of the Squamule
The crustaceous thallus is more or less firmly adherent to, or confused with, the
substratum. Further advance to a new type of thallus is made when certain hyphal
cells of soredium or granule take the lead in an ascending direction both upwards and
outwards. As growth becomes definitely apical or one-sided, the structure rises free
first under the second or third layers of the periderm. With care it is possible to trace a
filament of Trentepohlia from the surface downwards, and to see that the foremost cell
is really the growing and advancing apex of the creeping alga. Both symbionts show
increased vigour when they encounter each other: the thallus at once develops in
extent and in depth, and, ultimately, reproductive bodies are formed. In some species
the apothecia or perithecia alone emerge above the bark, in others the outer peridermal
cells are thrown off, and the thallus thus becomes superficial to some extent as a white
scurfy or furfuraceous crust.
The change from a hypophloeodal to a partly epiphloeodal condition depends
largely on the nature of the bark. Frank[337] found that Lecanora pallida remained for
a long time immersed when growing on the thick rugged bark of oak trunks. When
well lighted, or on trees with a thin periderm, such as the ash, the lichen emerges
much earlier and becomes superficial.
Black (or occasionally white) lines intersect the thallus and mark, as in saxicolous
lichens (Fig. 41), the boundary lines between different individuals or different species.
The pioneer hyphae of certain lichens very frequently become dark-coloured, and
Bitter[340] has suggested as the reason for this that in damp weather the hypothallic
growth is exceptionally vigorous. When dry weather supervenes, with high winds or
strong sunshine, the outlying hyphae, unprotected by the thallus, become dark-
coloured. On the return of more normal conditions the blackened tips are thrown off.
Bitter further states that species of Graphideae do not form a permanent black limiting
line when they grow in an isolated position: it is only when their advance is checked
by some other thallus that the dark persistent edge appears, a characteristic also to be
seen in the crust of other lichens. The dark boundary is always more marked in sunny
exposed situations: in the shade, the line is reduced to a mere thread.
Bitter’s restriction of black boundary lines to cases of encountering thalli only,
would exclude the comparison one is tempted to make between the advancing hyphae
of lichens and those of many woody fungi where the extreme edge of the white
invaded woody tissue is marked by a dark line. In the latter case however it is the cells
of the host that are stained black by the fungus pigment.
2. SQUAMULOSE LICHENS
A. Development of the Squamule
The crustaceous thallus is more or less firmly adherent to, or confused with, the
substratum. Further advance to a new type of thallus is made when certain hyphal
cells of soredium or granule take the lead in an ascending direction both upwards and
outwards. As growth becomes definitely apical or one-sided, the structure rises free
Page 138
from the substratum, and small lobules or leaflet-like squamules are formed. Each
squamule in this type of thallus is distinct in origin and not merely the branch of a
larger whole.
In a few lichens the advance from the crustaceous to the squamulose structure is
very slight. The granules seem but to have been flattened out at one side, and raised
into minute rounded projections such as those that compose the thallus of Lecanora
badia generally described as “subsquamulose.” The squamulose formation is more
pronounced in Lecidea ostreata, and in some species of Pannaria; and the whole
thallus may finally consist of small separate lobes as in Lecidea lurida, Lecanora
crassa, L. saxicola, species of Dermatocarpon and the primary thallus of the
Cladoniae. Most of these squamules are of a firm texture and more or less round in
outline; in some species of Cladonia, etc., they are variously crenate, or cut into
pinnate-like leaflets. Squamulose lichens grow mostly on rocks or soil, occasionally
on dead wood, and are generally attached by single rhizoidal hyphae, either produced
at all points of the under surface, or from the base only, growth in the latter case being
one-sided. In a few instances, as in Heppia Guepini, there is a central hold-fast.
A frequent type of squamulose thallus is that termed “placodioid,” or “effigurate,”
in which the squamulose character is chiefly apparent at the circumference. The
thallus is more or less orbicular in outline; the centre may be squamulose or granular
and cracked into areolae; the outer edge is composed of radiating lobules closely
appressed to the substratum (Fig. 42).
Fig. 42. Placodium murorum
DC. Part of placodioid thallus
with apothecia × 2.
All lichens with this type of thallus were at one time included in the genus
Placodium, now restricted by some lichenologists to squamulose or crustaceous
species with polarilocular spores. Many of them rival Xanthoria parietina in their
brilliant yellow colouring.
squamule in this type of thallus is distinct in origin and not merely the branch of a
larger whole.
In a few lichens the advance from the crustaceous to the squamulose structure is
very slight. The granules seem but to have been flattened out at one side, and raised
into minute rounded projections such as those that compose the thallus of Lecanora
badia generally described as “subsquamulose.” The squamulose formation is more
pronounced in Lecidea ostreata, and in some species of Pannaria; and the whole
thallus may finally consist of small separate lobes as in Lecidea lurida, Lecanora
crassa, L. saxicola, species of Dermatocarpon and the primary thallus of the
Cladoniae. Most of these squamules are of a firm texture and more or less round in
outline; in some species of Cladonia, etc., they are variously crenate, or cut into
pinnate-like leaflets. Squamulose lichens grow mostly on rocks or soil, occasionally
on dead wood, and are generally attached by single rhizoidal hyphae, either produced
at all points of the under surface, or from the base only, growth in the latter case being
one-sided. In a few instances, as in Heppia Guepini, there is a central hold-fast.
A frequent type of squamulose thallus is that termed “placodioid,” or “effigurate,”
in which the squamulose character is chiefly apparent at the circumference. The
thallus is more or less orbicular in outline; the centre may be squamulose or granular
and cracked into areolae; the outer edge is composed of radiating lobules closely
appressed to the substratum (Fig. 42).
Fig. 42. Placodium murorum
DC. Part of placodioid thallus
with apothecia × 2.
All lichens with this type of thallus were at one time included in the genus
Placodium, now restricted by some lichenologists to squamulose or crustaceous
species with polarilocular spores. Many of them rival Xanthoria parietina in their
brilliant yellow colouring.
Page 139
Fig. 43. Lecania candicans A. Zahlbr., with placodioid thallus,
reduced (S. H., Photo.).
There are also greyish-white effigurate lichens such as Lecanora saxicola, Lecania
candicans (Fig. 43) and Buellia canescens, well-known British species.
B. Tissues of Squamulose Thallus
The anatomical structure of the squamules is in general somewhat similar to that of
the crustaceous thallus: an upper cortex, a gonidial zone, and below that a medullary
layer of loose hyphae with sometimes a lower cortex.
1. The upper cortex, as in crustaceous lichens, is generally of the “decomposed”[341]
or amorphous type: interlaced hyphae with thick gelatinous walls. A more highly
developed form is apparent in Parmeliella and Pannaria where the upper cortex is
formed of plectenchyma, while in the squamules of Heppia the whole structure is built
up of plectenchyma, with the exception of a narrow band of loose hyphae in the
central pith.
2. The gonidia are Myxophyceae or Chlorophyceae; the squamules in some
instances may be homoiomerous as in Lepidocollema, but generally they belong to the
heteromerous series, with the gonidia in a circumscribed zone, and either continuous
or in groups. Friedrich[342] held that, as in crustaceous lichens the development of the
gonidial as compared with the other tissues depended on the substratum. The
squamules of Pannaria microphylla on sandstone were 100 µ thick, and the gonidial
layer occupied 80 or 90 µ of the whole[343]. With that may be compared Placodium
Garovagli on lime-containing rock: the gonidial layer measured only 50 µ across, the
pith hyphae 280 µ and the rhizoidal hyphae that penetrated the rock 500 µ.
3. The medullary layer, as a rule, is of closely compacted hyphae which give
solidity to the squamules; in those of Heppia it is almost entirely formed of
reduced (S. H., Photo.).
There are also greyish-white effigurate lichens such as Lecanora saxicola, Lecania
candicans (Fig. 43) and Buellia canescens, well-known British species.
B. Tissues of Squamulose Thallus
The anatomical structure of the squamules is in general somewhat similar to that of
the crustaceous thallus: an upper cortex, a gonidial zone, and below that a medullary
layer of loose hyphae with sometimes a lower cortex.
1. The upper cortex, as in crustaceous lichens, is generally of the “decomposed”[341]
or amorphous type: interlaced hyphae with thick gelatinous walls. A more highly
developed form is apparent in Parmeliella and Pannaria where the upper cortex is
formed of plectenchyma, while in the squamules of Heppia the whole structure is built
up of plectenchyma, with the exception of a narrow band of loose hyphae in the
central pith.
2. The gonidia are Myxophyceae or Chlorophyceae; the squamules in some
instances may be homoiomerous as in Lepidocollema, but generally they belong to the
heteromerous series, with the gonidia in a circumscribed zone, and either continuous
or in groups. Friedrich[342] held that, as in crustaceous lichens the development of the
gonidial as compared with the other tissues depended on the substratum. The
squamules of Pannaria microphylla on sandstone were 100 µ thick, and the gonidial
layer occupied 80 or 90 µ of the whole[343]. With that may be compared Placodium
Garovagli on lime-containing rock: the gonidial layer measured only 50 µ across, the
pith hyphae 280 µ and the rhizoidal hyphae that penetrated the rock 500 µ.
3. The medullary layer, as a rule, is of closely compacted hyphae which give
solidity to the squamules; in those of Heppia it is almost entirely formed of
Page 140
plectenchyma.
4. The lower cortex is frequently little developed or absent, especially when the
squamules are closely applied to the support as in some species of Dermatocarpon. In
some of the squamulose Lecanorae (L. crassa and L. saxicola) the lowest hyphae are
somewhat more closely interwoven; they become brown in colour, and the lichen is
attached to the substratum by rhizoid-like branches. In Lecanora lentigera there is a
layer of parallel hyphae along the under surface. Further development is reached when
a plectenchyma of thick-walled cells is formed both above and below, as in Psoroma
hypnorum, though on the under surface the continuity is often broken. The squamules
of Cladoniae are described under the radiate-stratose series.
3. FOLIOSE LICHENS
A. Development of foliose Thallus
The larger leafy lichens are occasionally monophyllous and attached at a central
point as in Umbilicaria, but mostly they are broken up into lobes which are either
imbricate and crowded, or represent the dividing and branching of the expanding
thallus at the circumference. They are horizontal spreading structures, with marginal
and apical growth. The several tissues of the squamule are repeated in the foliose
thallus, but further provision is made to meet the requirements of the larger organism.
There is the greater development of cortical tissue, especially on the lower surface,
and the more abundant formation of rhizoidal organs to attach the large flat fronds to
the support. There are also various adaptations to secure the aeration of the internal
tissues[344].
B. Cortical Tissues
Schwendener[345] was the first who, with the improved microscope, made a
systematic study of the minute structure of lichens. He examined typical species in
genera of widely different groups and described their anatomy in detail. The most
variable and perhaps the most important of the tissues of lichens is the cortex, which
is most fully developed in the larger thalli, and as the same type of cortical structures
recurs in lichens widely different in affinity as well as in form, it seems well to group
together here the ascertained facts about these covering layers.
a. Types of Cortical Structure. Zukal[346], and more recently Hue[347], have made
independent studies in the comparative morphology of the thallus and have given
particular attention to the different varieties of cortex. They each find that the
variations come under a definite series of types. Zukal recognized five of these:
4. The lower cortex is frequently little developed or absent, especially when the
squamules are closely applied to the support as in some species of Dermatocarpon. In
some of the squamulose Lecanorae (L. crassa and L. saxicola) the lowest hyphae are
somewhat more closely interwoven; they become brown in colour, and the lichen is
attached to the substratum by rhizoid-like branches. In Lecanora lentigera there is a
layer of parallel hyphae along the under surface. Further development is reached when
a plectenchyma of thick-walled cells is formed both above and below, as in Psoroma
hypnorum, though on the under surface the continuity is often broken. The squamules
of Cladoniae are described under the radiate-stratose series.
3. FOLIOSE LICHENS
A. Development of foliose Thallus
The larger leafy lichens are occasionally monophyllous and attached at a central
point as in Umbilicaria, but mostly they are broken up into lobes which are either
imbricate and crowded, or represent the dividing and branching of the expanding
thallus at the circumference. They are horizontal spreading structures, with marginal
and apical growth. The several tissues of the squamule are repeated in the foliose
thallus, but further provision is made to meet the requirements of the larger organism.
There is the greater development of cortical tissue, especially on the lower surface,
and the more abundant formation of rhizoidal organs to attach the large flat fronds to
the support. There are also various adaptations to secure the aeration of the internal
tissues[344].
B. Cortical Tissues
Schwendener[345] was the first who, with the improved microscope, made a
systematic study of the minute structure of lichens. He examined typical species in
genera of widely different groups and described their anatomy in detail. The most
variable and perhaps the most important of the tissues of lichens is the cortex, which
is most fully developed in the larger thalli, and as the same type of cortical structures
recurs in lichens widely different in affinity as well as in form, it seems well to group
together here the ascertained facts about these covering layers.
a. Types of Cortical Structure. Zukal[346], and more recently Hue[347], have made
independent studies in the comparative morphology of the thallus and have given
particular attention to the different varieties of cortex. They each find that the
variations come under a definite series of types. Zukal recognized five of these:
Page 141
1. Pseudoparenchymatous (plectenchyma): by frequent septation of regularly
arranged hyphae and by coalescence a kind of continuous cell-structure is formed.
2. Palisade cells: the outer elongate ends of the hyphae lie close together in a
direction at right angles to the surface of the thallus and form a coherent row of
parallel cells.
3. Fibrous: the cortical hyphae lie in strands of fine filaments parallel with the
surface of the thallus.
4. Intricate: hyphae confusedly interwoven and becoming dark in colour form the
lower cortex of some foliose lichens.
These four types, Zukal finds, are practically without interstices in the tissue and
form a perfect protection against excessive transpiration. He adds yet another form:
5. A cortex formed of hyphae with dark-coloured swollen cells, which is not a
protection against transpiration. It occurs among lower crustaceous forms.
Hue has summed up the different varieties under four types, but as he has omitted
the “fibrous” cortex, we arrive again at five different kinds of cortical formation,
though they do not exactly correspond to those of Zukal. A definite name is given to
each type:
1. Intricate: an intricate dense layer of gelatinous-walled hyphae, branching in all
directions, but not coalescent (Fig. 44). This rather unusual type of cortex occurs in
Sphaerophorus and Stereocaulon, both of which have an upright rigid thallus
(fruticose).
arranged hyphae and by coalescence a kind of continuous cell-structure is formed.
2. Palisade cells: the outer elongate ends of the hyphae lie close together in a
direction at right angles to the surface of the thallus and form a coherent row of
parallel cells.
3. Fibrous: the cortical hyphae lie in strands of fine filaments parallel with the
surface of the thallus.
4. Intricate: hyphae confusedly interwoven and becoming dark in colour form the
lower cortex of some foliose lichens.
These four types, Zukal finds, are practically without interstices in the tissue and
form a perfect protection against excessive transpiration. He adds yet another form:
5. A cortex formed of hyphae with dark-coloured swollen cells, which is not a
protection against transpiration. It occurs among lower crustaceous forms.
Hue has summed up the different varieties under four types, but as he has omitted
the “fibrous” cortex, we arrive again at five different kinds of cortical formation,
though they do not exactly correspond to those of Zukal. A definite name is given to
each type:
1. Intricate: an intricate dense layer of gelatinous-walled hyphae, branching in all
directions, but not coalescent (Fig. 44). This rather unusual type of cortex occurs in
Sphaerophorus and Stereocaulon, both of which have an upright rigid thallus
(fruticose).
Page 142
Fig. 44. Sphaerophorus coralloides Pers. Transverse section of
cortex and gonidial layer near the growing point of a frond × 600.
Fig. 45. Roccella fuciformis DC. Transverse
section of cortex near the growing point of a
frond × 600.
2. Fastigiate: the hyphae bend outwards or upwards to form the cortex. A primary
filament can be distinguished with abundant branches, all tending in the same
direction; anastomosis may take place between the hyphae. The end branches are
densely packed, though there are occasional interstices (Fig. 45). Such a cortex occurs
in Thamnolia; in several genera of Roccellaceae—Roccellographa, Roccellina,
cortex and gonidial layer near the growing point of a frond × 600.
Fig. 45. Roccella fuciformis DC. Transverse
section of cortex near the growing point of a
frond × 600.
2. Fastigiate: the hyphae bend outwards or upwards to form the cortex. A primary
filament can be distinguished with abundant branches, all tending in the same
direction; anastomosis may take place between the hyphae. The end branches are
densely packed, though there are occasional interstices (Fig. 45). Such a cortex occurs
in Thamnolia; in several genera of Roccellaceae—Roccellographa, Roccellina,
Page 143
Reinkella, Pentagenella, Combea, Schizopelte and Roccella—and also in the
crustaceous genus Dirina. The fastigiate cortex corresponds with Zukal’s palisade
cells.
3. Decomposed: in this, the most frequent type of cortex, the hyphae that travel up
from the gonidial layer become irregularly branched and frequently septate. The cell-
walls of the terminal branches become swollen into a gelatinous mass, the
transformation being brought about by a change in the molecular constituents of the
cell-walls which permits the imbibition and storage of water. The tissue, owing to the
enormous increase of the wall, is so closely pressed together that the individual
hyphae become indistinct; the cell-lumen finally disappears altogether, or, at most, is
only to be detected in section as a narrow disconnected dark streak. The decomposed
cortex is characteristic of many lichens, crustaceous (Fig. 46) and squamulose, as well
as of such highly developed genera as Usnea, Letharia, Ramalina, Cetraria, Evernia
and certain Parmeliae.
Fig. 46. Lecanora glaucoma var.
corrugata Nyl. Vertical section of cortex
× 500 (after Hue).
Zukal took no note of the decomposed cortex but the omission is intentional and is
due to his regarding the structure of the youngest stages of the thallus near the
growing point as the most typical and as giving the best indication as to the true
arrangement of hyphae in the cortex. He thus describes palisade tissue as the
characteristic cortex of Evernia, since the formation near the growing point of the
fronds is somewhat palisade-like and he finds fibrous cortex at the tips of Usnea
filaments. In both these instances Hue has described the cortex as decomposed
because he takes account only of the fully formed thallus in which the tissues have
reached a permanent condition.
crustaceous genus Dirina. The fastigiate cortex corresponds with Zukal’s palisade
cells.
3. Decomposed: in this, the most frequent type of cortex, the hyphae that travel up
from the gonidial layer become irregularly branched and frequently septate. The cell-
walls of the terminal branches become swollen into a gelatinous mass, the
transformation being brought about by a change in the molecular constituents of the
cell-walls which permits the imbibition and storage of water. The tissue, owing to the
enormous increase of the wall, is so closely pressed together that the individual
hyphae become indistinct; the cell-lumen finally disappears altogether, or, at most, is
only to be detected in section as a narrow disconnected dark streak. The decomposed
cortex is characteristic of many lichens, crustaceous (Fig. 46) and squamulose, as well
as of such highly developed genera as Usnea, Letharia, Ramalina, Cetraria, Evernia
and certain Parmeliae.
Fig. 46. Lecanora glaucoma var.
corrugata Nyl. Vertical section of cortex
× 500 (after Hue).
Zukal took no note of the decomposed cortex but the omission is intentional and is
due to his regarding the structure of the youngest stages of the thallus near the
growing point as the most typical and as giving the best indication as to the true
arrangement of hyphae in the cortex. He thus describes palisade tissue as the
characteristic cortex of Evernia, since the formation near the growing point of the
fronds is somewhat palisade-like and he finds fibrous cortex at the tips of Usnea
filaments. In both these instances Hue has described the cortex as decomposed
because he takes account only of the fully formed thallus in which the tissues have
reached a permanent condition.
Page 144
Fig. 47. Peltigera canina DC. Vertical section of cortex and
gonidial zone × 600.
4. Plectenchymatous: the last of Hue’s types corresponds with the first described
by Zukal. It is the result of the lateral coherence and frequent septation of the hyphae
into short almost square or rounded cells (Fig. 47). The simplest type of such a cortex
can be studied in Leptogium, a genus of gelatinous lichens in which the tips of the
hyphae are cut off at the surface by one or more septa. The resulting cells are wider
than the hyphae and they cohere together to form, in some species, disconnected
patches of cells; in others, a continuous cortical covering one or more cells thick,
while in the margin of the apothecium they form a deep cellular layer. The cellular
type of cortex is found also, as already stated, in some crustaceous Pertusariae, and in
a few squamulose genera or species. It forms the uppermost layer of the Peltigera
thallus and both cortices of many of the larger foliose lichens such as Sticta, Parmelia,
etc.
5. The “fibrous” cortex must be added to this series, as was pointed out by Heber
Howe[348] who gave the less appropriate designation of “simple” to the type. It
consists of long rather sparingly branched slender hyphae that grow in a direction
parallel with the surface of the thallus (Fig. 48). It is characteristic of several fruticose
and foliose lichens with more or less upright growth, such as we find in several of the
Physciae, and in the allied genus Teloschistes, in Alectoria, several genera of
Roccellaceae, in Usnea longissima and in Parmelia pubescens, etc. Zukal would have
included all the Usneae as the tips are fibrous.
gonidial zone × 600.
4. Plectenchymatous: the last of Hue’s types corresponds with the first described
by Zukal. It is the result of the lateral coherence and frequent septation of the hyphae
into short almost square or rounded cells (Fig. 47). The simplest type of such a cortex
can be studied in Leptogium, a genus of gelatinous lichens in which the tips of the
hyphae are cut off at the surface by one or more septa. The resulting cells are wider
than the hyphae and they cohere together to form, in some species, disconnected
patches of cells; in others, a continuous cortical covering one or more cells thick,
while in the margin of the apothecium they form a deep cellular layer. The cellular
type of cortex is found also, as already stated, in some crustaceous Pertusariae, and in
a few squamulose genera or species. It forms the uppermost layer of the Peltigera
thallus and both cortices of many of the larger foliose lichens such as Sticta, Parmelia,
etc.
5. The “fibrous” cortex must be added to this series, as was pointed out by Heber
Howe[348] who gave the less appropriate designation of “simple” to the type. It
consists of long rather sparingly branched slender hyphae that grow in a direction
parallel with the surface of the thallus (Fig. 48). It is characteristic of several fruticose
and foliose lichens with more or less upright growth, such as we find in several of the
Physciae, and in the allied genus Teloschistes, in Alectoria, several genera of
Roccellaceae, in Usnea longissima and in Parmelia pubescens, etc. Zukal would have
included all the Usneae as the tips are fibrous.
Page 145
Fig. 48. Physcia ciliaris DC. Vertical section of thallus. a, cortex; b, gonidial zone;
c, medulla. × 100.
More than one type of cortex, as already stated, may appear in a genus: a striking
instance of variability occurs in Solorina where, as Hue[349] has pointed out, the
cortex of S. octospora is fastigiate, that of all the other species being
plectenchymatous. Cortical development is a specific rather than a generic
characteristic.
b. Origin of Variation in Cortical Structure. The immediate causes making for
differentiation in cortical development are: the prevailing direction of growth of the
hyphae as they rise from the gonidial zone; the amount of branching and the crowding
of the filaments; the frequency of septation; and the thickening or degeneration of the
cell-walls which may become almost or entirely mucilaginous. In the
plectenchymatous cortex, the walls may remain quite thin and the cells small as in
Xanthoria parietina, or the walls may be much thickened as in both cortices of Sticta.
As a result of stretching the cell may increase enormously in size: in some instances
where the internal hyphae are about 3 µ to 4 µ in width, the cortical cells formed from
these hyphae may have a cell cavity 15 µ to 16 µ in diameter.
c. Loss and Renewal of Cortex. Very frequently the cortex is covered over by a
layer of homogeneous mucilage which forms an outer cuticle. It arises from the
continual degeneration of the outer cell-walls and it is liable to friction and removal
by atmospheric agency as was first described by Schwendener[350] in the weather-
beaten cortex of Umbilicaria pustulata. He had noted the irregular jagged outline of
the cross section of the thallus, and he then suggested, as the probable reason, the
decay of the outer rind with the constant renewal of it by the hyphae from the
underlying gonidial zone, though he was unable definitely to prove his theory. The
peeling of the dead outer layer (with its replacement by new tissue) has however been
observed many times since his day. It has been described by Darbishire[351] in
Pertusaria: in that genus there is at first a primary cortex formed of hyphae that grow
c, medulla. × 100.
More than one type of cortex, as already stated, may appear in a genus: a striking
instance of variability occurs in Solorina where, as Hue[349] has pointed out, the
cortex of S. octospora is fastigiate, that of all the other species being
plectenchymatous. Cortical development is a specific rather than a generic
characteristic.
b. Origin of Variation in Cortical Structure. The immediate causes making for
differentiation in cortical development are: the prevailing direction of growth of the
hyphae as they rise from the gonidial zone; the amount of branching and the crowding
of the filaments; the frequency of septation; and the thickening or degeneration of the
cell-walls which may become almost or entirely mucilaginous. In the
plectenchymatous cortex, the walls may remain quite thin and the cells small as in
Xanthoria parietina, or the walls may be much thickened as in both cortices of Sticta.
As a result of stretching the cell may increase enormously in size: in some instances
where the internal hyphae are about 3 µ to 4 µ in width, the cortical cells formed from
these hyphae may have a cell cavity 15 µ to 16 µ in diameter.
c. Loss and Renewal of Cortex. Very frequently the cortex is covered over by a
layer of homogeneous mucilage which forms an outer cuticle. It arises from the
continual degeneration of the outer cell-walls and it is liable to friction and removal
by atmospheric agency as was first described by Schwendener[350] in the weather-
beaten cortex of Umbilicaria pustulata. He had noted the irregular jagged outline of
the cross section of the thallus, and he then suggested, as the probable reason, the
decay of the outer rind with the constant renewal of it by the hyphae from the
underlying gonidial zone, though he was unable definitely to prove his theory. The
peeling of the dead outer layer (with its replacement by new tissue) has however been
observed many times since his day. It has been described by Darbishire[351] in
Pertusaria: in that genus there is at first a primary cortex formed of hyphae that grow
Page 146
in a radial direction, parallel to the surface of the thallus. The walls of these hyphae
become gradually more and more mucilaginous till the cells are obliterated.
Meanwhile short-celled filaments grow up in serried ranks from the gonidial layer and
finally push off the dead “fibrous” cortex. The new tissue takes on a plectenchymatous
character, and the outer cells in time become decomposed and provide a mucilaginous
cuticle which in turn is also subject to wasting.
The same process of peeling was noted by Rosendahl[352] in some species of brown
Parmeliae, where the dead tissues were thrown off in shreds, though only in isolated
patches. But whether in patches or as a continuous sheath, there is constant
degeneration, with continual renewal of the dead material from the internal tissues.
The cortex is the most highly developed of all the lichen structures and is of
immense importance to the plant as may be judged from the various adaptations to
different needs[353]. The cortical cell-walls are frequently impregnated with some
dark-coloured substance which, in exposed situations, must counteract the influence
of too direct sunlight and be of service in sheltering the gonidia. Lichen acids—
sometimes very brightly coloured—and oxalic acid are deposited in the cortical
tissues in great abundance and aid in retaining moisture; but the two chief functions to
which the cortex is specially adapted are the checking of transpiration and the
strengthening of the thallus against external strains.
d. Cortical Hairs or Trichomes. Though somewhat rare, cortical hairs are present
on the upper surface of several foliose lichens. They take rise, in all the instances
noted, as a prolongation of one of the cell-rows forming a plectenchymatous cortex.
In Peltidea (Peltigera) aphthosa they are especially evident near the growing edges
of the thallus; and they take part in the development of the superficial cephalodia[354]
which are a constant feature of the lichen. They tend to disappear with age and leave
the central older parts of the thallus smooth and shining. In several other species of
Peltigera (P. canina, etc.) they are present and persist during the life of the cortex. In
these lichens the cells of the cortical tissue are thin-walled, all except the outer layer,
the membranes of which are much thicker. The hairs rising from them are also thick-
walled and septate. Generally they branch in all directions and anastomose with
neighbouring hairs so that a confused felted tangle is formed; they vary in size but are,
as a rule, about double the width of the medullary hyphae as are the cortical cells from
which they rise. They disappear from the thallus, frequently in patches, probably by
weathering, but over large surfaces, and especially where any inequality affords a
shelter, they persist as a soft down.
Hairs are also present on the upper surface of some Parmeliae. Rosendahl[355] has
described and figured them in P. glabra and P. verruculifera—short pointed
unbranched hyphae, two or more septate and with thickened walls. They are most
easily seen near the edge of the thallus, though they persist more or less over the
become gradually more and more mucilaginous till the cells are obliterated.
Meanwhile short-celled filaments grow up in serried ranks from the gonidial layer and
finally push off the dead “fibrous” cortex. The new tissue takes on a plectenchymatous
character, and the outer cells in time become decomposed and provide a mucilaginous
cuticle which in turn is also subject to wasting.
The same process of peeling was noted by Rosendahl[352] in some species of brown
Parmeliae, where the dead tissues were thrown off in shreds, though only in isolated
patches. But whether in patches or as a continuous sheath, there is constant
degeneration, with continual renewal of the dead material from the internal tissues.
The cortex is the most highly developed of all the lichen structures and is of
immense importance to the plant as may be judged from the various adaptations to
different needs[353]. The cortical cell-walls are frequently impregnated with some
dark-coloured substance which, in exposed situations, must counteract the influence
of too direct sunlight and be of service in sheltering the gonidia. Lichen acids—
sometimes very brightly coloured—and oxalic acid are deposited in the cortical
tissues in great abundance and aid in retaining moisture; but the two chief functions to
which the cortex is specially adapted are the checking of transpiration and the
strengthening of the thallus against external strains.
d. Cortical Hairs or Trichomes. Though somewhat rare, cortical hairs are present
on the upper surface of several foliose lichens. They take rise, in all the instances
noted, as a prolongation of one of the cell-rows forming a plectenchymatous cortex.
In Peltidea (Peltigera) aphthosa they are especially evident near the growing edges
of the thallus; and they take part in the development of the superficial cephalodia[354]
which are a constant feature of the lichen. They tend to disappear with age and leave
the central older parts of the thallus smooth and shining. In several other species of
Peltigera (P. canina, etc.) they are present and persist during the life of the cortex. In
these lichens the cells of the cortical tissue are thin-walled, all except the outer layer,
the membranes of which are much thicker. The hairs rising from them are also thick-
walled and septate. Generally they branch in all directions and anastomose with
neighbouring hairs so that a confused felted tangle is formed; they vary in size but are,
as a rule, about double the width of the medullary hyphae as are the cortical cells from
which they rise. They disappear from the thallus, frequently in patches, probably by
weathering, but over large surfaces, and especially where any inequality affords a
shelter, they persist as a soft down.
Hairs are also present on the upper surface of some Parmeliae. Rosendahl[355] has
described and figured them in P. glabra and P. verruculifera—short pointed
unbranched hyphae, two or more septate and with thickened walls. They are most
easily seen near the edge of the thallus, though they persist more or less over the
Page 147
surface; they also grow on the margins of the apothecia. In P. verruculifera they arise
from the soredia; in P. glabra a few isolated hairs are present on the under surface.
In Nephromium tomentosum there is a scanty formation of hairs on the upper
surface. They are abundant on the lower surface, and function as attaching organs. A
thick tomentum of hairs is similarly present on the lower surface of many of the
Stictaceae either as an almost unbroken covering or in scattered patches. In several
species of Leptogium they grow out from the lower cortical cells and attach the thin
horizontal fronds; and very occasionally they are present in Collema.
C. Gonidial Tissues
With the exception of some species of Collema and Leptogium lichens included
under the term foliose, are heteromerous in structure, and the algae that form the
gonidial zone are situated below the upper cortex and, therefore, in the most
favourable position for photosynthesis. Whether belonging to the Myxophyceae or the
Chlorophyceae, they form a green band, straight and continuous in some forms, in
others somewhat broken up into groups. In certain species they push up at intervals
among the cortical cells, as in Gyrophora and in Parmelia tristis. In Solorina crocea a
regular series of gonidial pyramids rises towards the upper surface. The green cells are
frequently more dense at some points than at others, and they may penetrate in groups
well into the medulla.
The fungal tissue of the gonidial zone is composed of hyphae which have thinner
walls, and are generally somewhat loosely interlacing. In Peltigera[356] the gonidial
hyphae are so connected by frequent branching and by anastomosis that a net-like
structure is formed, in the meshes of which the algae—a species of Nostoc—are
massed more or less in groups. In lichens with a plectenchymatous cortex, the cellular
tissue may extend downwards into the gonidial zone and the gonidia thus become
enmeshed among the cells, a type of formation well seen in the squamulose species,
Dermatocarpon lachneum and Heppia Guepini, where the massive plectenchyma of
both the upper and lower cortices encroaches on the pith. In Endocarpon and in
Psoroma the gonidia are also surrounded by short cells.
A similar type of structure occurs in Cora Pavonia, one of the Hymenolichenes: the
gonidial hyphae in that species form a cellular tissue in which are embedded the blue-
green Chroococcus cells[357].
D. Medulla and Lower Cortex
a. Medulla. The hyphal tissue of the dorsiventral thallus that lies between the
gonidial zone and the lower cortex or base of the plant is always referred to as the
medulla or pith. It is, as a rule, by far the most considerable portion of the thallus. In
Parmelia caperata (Fig. 49), for instance, the lobes of which are about 300 µ thick,
from the soredia; in P. glabra a few isolated hairs are present on the under surface.
In Nephromium tomentosum there is a scanty formation of hairs on the upper
surface. They are abundant on the lower surface, and function as attaching organs. A
thick tomentum of hairs is similarly present on the lower surface of many of the
Stictaceae either as an almost unbroken covering or in scattered patches. In several
species of Leptogium they grow out from the lower cortical cells and attach the thin
horizontal fronds; and very occasionally they are present in Collema.
C. Gonidial Tissues
With the exception of some species of Collema and Leptogium lichens included
under the term foliose, are heteromerous in structure, and the algae that form the
gonidial zone are situated below the upper cortex and, therefore, in the most
favourable position for photosynthesis. Whether belonging to the Myxophyceae or the
Chlorophyceae, they form a green band, straight and continuous in some forms, in
others somewhat broken up into groups. In certain species they push up at intervals
among the cortical cells, as in Gyrophora and in Parmelia tristis. In Solorina crocea a
regular series of gonidial pyramids rises towards the upper surface. The green cells are
frequently more dense at some points than at others, and they may penetrate in groups
well into the medulla.
The fungal tissue of the gonidial zone is composed of hyphae which have thinner
walls, and are generally somewhat loosely interlacing. In Peltigera[356] the gonidial
hyphae are so connected by frequent branching and by anastomosis that a net-like
structure is formed, in the meshes of which the algae—a species of Nostoc—are
massed more or less in groups. In lichens with a plectenchymatous cortex, the cellular
tissue may extend downwards into the gonidial zone and the gonidia thus become
enmeshed among the cells, a type of formation well seen in the squamulose species,
Dermatocarpon lachneum and Heppia Guepini, where the massive plectenchyma of
both the upper and lower cortices encroaches on the pith. In Endocarpon and in
Psoroma the gonidia are also surrounded by short cells.
A similar type of structure occurs in Cora Pavonia, one of the Hymenolichenes: the
gonidial hyphae in that species form a cellular tissue in which are embedded the blue-
green Chroococcus cells[357].
D. Medulla and Lower Cortex
a. Medulla. The hyphal tissue of the dorsiventral thallus that lies between the
gonidial zone and the lower cortex or base of the plant is always referred to as the
medulla or pith. It is, as a rule, by far the most considerable portion of the thallus. In
Parmelia caperata (Fig. 49), for instance, the lobes of which are about 300 µ thick,
Page 148
over 200 µ of the space is occupied by this layer. It varies however very largely in
extent in different lichens according to species, and also according to the substratum.
In another Parmelia with a very thin thallus, P. alpicola growing on quartzite, the
medulla measures scarcely twice the width of the gonidial zone. It forms a fairly
massive tissue in some of the crustaceous lichens—in some Pertusariae and
Lecanorae—attaining a width of about 600 µ.
Nylander[358] distinguished three types of medullary tissue in lichens:
(1) felted, which includes all those of a purely filamentous structure;
(2) cretaceous or tartareous, more compact than the felted, and containing granular
or crystalline substances as in some Pertusariae; and lastly
(3) the cellular medulla in which the closely packed hyphae are divided into short
cells and a kind of plectenchyma is formed, as in Lecanora (Psoroma) hypnorum, in
Endocarpon, etc.
Fig. 49. Parmelia caperata Ach. (S. H., Photo.).
The felted medulla is characteristic of most lichens and is formed of loose slender
branching septate hyphae with thickish walls. This interwoven hyphal texture provides
abundant air-spaces.
Hue[359] has noted that the walls of the medullary hyphae in Parmeliae are smooth,
unless they have been exposed to great extremes of heat or cold, when they become
wrinkled or scaly. They are very thick-walled in Peltigera (Fig. 50).
extent in different lichens according to species, and also according to the substratum.
In another Parmelia with a very thin thallus, P. alpicola growing on quartzite, the
medulla measures scarcely twice the width of the gonidial zone. It forms a fairly
massive tissue in some of the crustaceous lichens—in some Pertusariae and
Lecanorae—attaining a width of about 600 µ.
Nylander[358] distinguished three types of medullary tissue in lichens:
(1) felted, which includes all those of a purely filamentous structure;
(2) cretaceous or tartareous, more compact than the felted, and containing granular
or crystalline substances as in some Pertusariae; and lastly
(3) the cellular medulla in which the closely packed hyphae are divided into short
cells and a kind of plectenchyma is formed, as in Lecanora (Psoroma) hypnorum, in
Endocarpon, etc.
Fig. 49. Parmelia caperata Ach. (S. H., Photo.).
The felted medulla is characteristic of most lichens and is formed of loose slender
branching septate hyphae with thickish walls. This interwoven hyphal texture provides
abundant air-spaces.
Hue[359] has noted that the walls of the medullary hyphae in Parmeliae are smooth,
unless they have been exposed to great extremes of heat or cold, when they become
wrinkled or scaly. They are very thick-walled in Peltigera (Fig. 50).
Page 149
Fig. 50. Hyphae from lower medulla of Peltigera canina DC. ×
600.
b. Lower Cortex. In some foliose lichens such as Peltigera there is no special
tissue developed on the under surface. In Lobaria pulmonaria large patches of the
under surface are bare, and the medulla is exposed to the outer atmosphere, sheltered
only by its position. In some other lichens the lowermost hyphae lie closer together
and a kind of felt of almost parallel filaments is formed, generally darker in colour, as
in Lecanora lentigera, and in some species of Physcia.
Most frequently however the tissues of the upper cortex are repeated on the lower
surface, though differing somewhat in detail. In all of the brown Parmeliae, according
to Rosendahl[360], the structure is identical for both cortices, though the upper
develops now hairs, now isidia, breathing pores, etc., while the lower produces
rhizinae. The amorphous mucilaginous cuticle so often present on the upper surface is
absent from the lower, the walls of the latter being often charged instead with dark-
brown pigments.
c. Hypothallic Structures. An unusual development of hyphae from the lower
cortex occurs in the genera Anzia and Pannoparmelia—both closely related to
Parmelia—whereby a loose sponge-like hypothallus of anastomosing reticulate
strands is formed. In one of the simpler types, Anzia colpodes, a North American
species, the hyphae passing out from the lower medulla become abruptly dark-brown
in colour, and are divided into short thick-walled cells. Frequent branching and
anastomosis of these hyphae result in the formation of a cushion-like structure about
twice the bulk of the thallus. In another species from Australia (A. Japonica) there is a
lower cortex, distinct from the medulla, consisting of septate colourless hyphae with
thick walls. From these branch out free filaments, similar in structure but dark in
colour, which branch and anastomose as in the previous species.
600.
b. Lower Cortex. In some foliose lichens such as Peltigera there is no special
tissue developed on the under surface. In Lobaria pulmonaria large patches of the
under surface are bare, and the medulla is exposed to the outer atmosphere, sheltered
only by its position. In some other lichens the lowermost hyphae lie closer together
and a kind of felt of almost parallel filaments is formed, generally darker in colour, as
in Lecanora lentigera, and in some species of Physcia.
Most frequently however the tissues of the upper cortex are repeated on the lower
surface, though differing somewhat in detail. In all of the brown Parmeliae, according
to Rosendahl[360], the structure is identical for both cortices, though the upper
develops now hairs, now isidia, breathing pores, etc., while the lower produces
rhizinae. The amorphous mucilaginous cuticle so often present on the upper surface is
absent from the lower, the walls of the latter being often charged instead with dark-
brown pigments.
c. Hypothallic Structures. An unusual development of hyphae from the lower
cortex occurs in the genera Anzia and Pannoparmelia—both closely related to
Parmelia—whereby a loose sponge-like hypothallus of anastomosing reticulate
strands is formed. In one of the simpler types, Anzia colpodes, a North American
species, the hyphae passing out from the lower medulla become abruptly dark-brown
in colour, and are divided into short thick-walled cells. Frequent branching and
anastomosis of these hyphae result in the formation of a cushion-like structure about
twice the bulk of the thallus. In another species from Australia (A. Japonica) there is a
lower cortex, distinct from the medulla, consisting of septate colourless hyphae with
thick walls. From these branch out free filaments, similar in structure but dark in
colour, which branch and anastomose as in the previous species.
Page 150
Fig. 51. Pannoparmelia anzioides Darb.
Vertical section of thallus and hypothallus. a,
cortex; b, gonidial zone; c, medulla; d, lower
cortex; e, hypothallus. × ca. 450 (after
Darbishire).
In Pannoparmelia the lower cortex and the outgrowths from it are several cells
thick; they may be thick-walled as in Anzia, or they may be thin-walled as described
and figured by Darbishire[361] in Pannoparmelia anzioides, a species from Tierra del
Fuego (Fig. 51). A somewhat dense interwoven felt of hyphae occurs also in certain
parts of the under surface of Parmelia physodes[362].
This peculiar structure, regarded as a hypothallus, is probably of service in the
retention of moisture. The thick cell-walls in most of the forms suggest some such
function.
E. Structures for Protection and Attachment
Such structures are almost wholly confined to the larger foliose and fruticose
lichens and are all of the same simple type; they are fungal in origin and very rarely
are gonidia associated with them.
Vertical section of thallus and hypothallus. a,
cortex; b, gonidial zone; c, medulla; d, lower
cortex; e, hypothallus. × ca. 450 (after
Darbishire).
In Pannoparmelia the lower cortex and the outgrowths from it are several cells
thick; they may be thick-walled as in Anzia, or they may be thin-walled as described
and figured by Darbishire[361] in Pannoparmelia anzioides, a species from Tierra del
Fuego (Fig. 51). A somewhat dense interwoven felt of hyphae occurs also in certain
parts of the under surface of Parmelia physodes[362].
This peculiar structure, regarded as a hypothallus, is probably of service in the
retention of moisture. The thick cell-walls in most of the forms suggest some such
function.
E. Structures for Protection and Attachment
Such structures are almost wholly confined to the larger foliose and fruticose
lichens and are all of the same simple type; they are fungal in origin and very rarely
are gonidia associated with them.
Page 151
Fig. 52. Usnea florida Web. Ciliate apothecia (S.
H., Photo.).
a. Cilia. In a few widely separated lichens stoutish cilia are borne, mostly on the
margins of the thallus lobes, or on the margins of the apothecia (Fig. 52). They arise
from the cortical cells or hyphae, several of which grow out in a compact strand which
tapers gradually to a point. Cilia vary in length up to about 1 cm. or even longer. In
some lichens they retain the colour of the cortex and are greyish or whitish-grey, as in
Physcia ciliaris or in Physcia hispida (Fig. 110). They provide a yellow fringe to the
apothecia of Physcia chrysophthalma and a green fringe to those of Usnea florida.
They are dark-brown or almost black in Parmelia perlata var. ciliata and in P. cetrata,
etc. as also in Gyrophora cylindrica. The fronds of Cetraria islandica and other
species of the genus are bordered with short spinulose brown hairs whose main
function seems to be the bearing of “pycnidia” though in many cases they are barren
(Fig. 128).
Superficial cilia are more rarely formed than marginal ones, but they are
characteristic of one not uncommon British species, Parmelia proboscidea (P.
pilosella Hue). Scattered over the surface of that lichen are numerous crowded groups
of isidia which, frequently, are prolonged upwards as dark-brown or blackish cilia.
Nearly every isidium bears a small brown spot on the apex at an early stage of growth.
Similar cilia are sparsely scattered over the thallus, but their base is always a rather
stouter grey structure, which suggests an isidial origin. Cilia also occur on the margin
of the lobes.
H., Photo.).
a. Cilia. In a few widely separated lichens stoutish cilia are borne, mostly on the
margins of the thallus lobes, or on the margins of the apothecia (Fig. 52). They arise
from the cortical cells or hyphae, several of which grow out in a compact strand which
tapers gradually to a point. Cilia vary in length up to about 1 cm. or even longer. In
some lichens they retain the colour of the cortex and are greyish or whitish-grey, as in
Physcia ciliaris or in Physcia hispida (Fig. 110). They provide a yellow fringe to the
apothecia of Physcia chrysophthalma and a green fringe to those of Usnea florida.
They are dark-brown or almost black in Parmelia perlata var. ciliata and in P. cetrata,
etc. as also in Gyrophora cylindrica. The fronds of Cetraria islandica and other
species of the genus are bordered with short spinulose brown hairs whose main
function seems to be the bearing of “pycnidia” though in many cases they are barren
(Fig. 128).
Superficial cilia are more rarely formed than marginal ones, but they are
characteristic of one not uncommon British species, Parmelia proboscidea (P.
pilosella Hue). Scattered over the surface of that lichen are numerous crowded groups
of isidia which, frequently, are prolonged upwards as dark-brown or blackish cilia.
Nearly every isidium bears a small brown spot on the apex at an early stage of growth.
Similar cilia are sparsely scattered over the thallus, but their base is always a rather
stouter grey structure, which suggests an isidial origin. Cilia also occur on the margin
of the lobes.
Page 152
As lichens are a favourite food of snails, insects, etc., it is considered that these
structures are protective in function, and that they impede, if they do not entirely
prevent, the larger marauders in their work of destruction.
Fig. 53. Rhizoid of Parmelia exasperata Carroll (P. aspidota Rosend.). A, hyphae
growing out from lower cortex × 450. B, tip of rhizoid with gelatinous sheath ×
335 (after Rosendahl).
b. Rhizinae. Lichen rootlets are mainly for the purpose of attachment and have little
significance as organs of absorption. They have been noted in only one crustaceous
lichen, Varicellaria microsticta[363], an alpine species that spreads over bark or soil,
and which is further distinguished by being provided with a lower cortex of
plectenchyma. In foliose lichens they are frequently abundant, though by no means
universal, and attach the spreading fronds to the support. They originate, as
Schwendener[364] pointed out, from the outer cortical cells, exactly as do the cilia, and
are scattered over the under surface or are confined to special areas. Rosendahl[365]
has described their development in the brown species of Parmeliae: the under cortex
in these lichens is formed of a cellular plectenchyma with thickish walls; the rootlets
arise by the outgrowth of several neighbouring cells from some slight elevation near
the edge of the thallus. Branching and interlacing of these growing rhizinal hyphae
follow, the outermost frequently spreading outwards at right angles to the axis, and
forming a cellular cortex. The apex of the rhizoid is generally an enlarged tuft of loose
hyphae involved in mucilage (Fig. 53), a provision for securing firmer cohesion to the
support; or the tips spread out as a kind of sucker. Not unfrequently neighbouring
“rootlets” are connected by mucilage at the tips, or by outgrowths of their hyphae, and
a rather large hold-fast sheath is formed.
structures are protective in function, and that they impede, if they do not entirely
prevent, the larger marauders in their work of destruction.
Fig. 53. Rhizoid of Parmelia exasperata Carroll (P. aspidota Rosend.). A, hyphae
growing out from lower cortex × 450. B, tip of rhizoid with gelatinous sheath ×
335 (after Rosendahl).
b. Rhizinae. Lichen rootlets are mainly for the purpose of attachment and have little
significance as organs of absorption. They have been noted in only one crustaceous
lichen, Varicellaria microsticta[363], an alpine species that spreads over bark or soil,
and which is further distinguished by being provided with a lower cortex of
plectenchyma. In foliose lichens they are frequently abundant, though by no means
universal, and attach the spreading fronds to the support. They originate, as
Schwendener[364] pointed out, from the outer cortical cells, exactly as do the cilia, and
are scattered over the under surface or are confined to special areas. Rosendahl[365]
has described their development in the brown species of Parmeliae: the under cortex
in these lichens is formed of a cellular plectenchyma with thickish walls; the rootlets
arise by the outgrowth of several neighbouring cells from some slight elevation near
the edge of the thallus. Branching and interlacing of these growing rhizinal hyphae
follow, the outermost frequently spreading outwards at right angles to the axis, and
forming a cellular cortex. The apex of the rhizoid is generally an enlarged tuft of loose
hyphae involved in mucilage (Fig. 53), a provision for securing firmer cohesion to the
support; or the tips spread out as a kind of sucker. Not unfrequently neighbouring
“rootlets” are connected by mucilage at the tips, or by outgrowths of their hyphae, and
a rather large hold-fast sheath is formed.
Page 153
Fig. 55. Peltigera canina DC.
Under surface with veins and
rhizoids (after Reinke).
Fig. 54. Peltigera canina DC. (S. H., Photo.).
In species of Peltigera (Fig. 54) the rhizinae are confined to the veins or ridges
(Fig. 55); they are thickish at the base, and are generally rather long and straggling.
Meyer[366] states that the central hyphae are stoutish and much entangled owing to the
branching and frequent anastomosis of one hypha with another; the peripheral
terminal branches are thinner-walled and free. These rhizinae vary in colour from
white in Peltigera canina to brown or black in other species. Most species of
Peltigera spread over grass or mosses, to which they cling by these long loose
“rootlets.”
Lichen rhizinae, distinguished by Reinke[367] as “aerial rhizinae,” are more or less
characteristic of all the species of Parmelia with the exception of those belonging to
the subgenus Hypogymnia in which they are of very rare occurrence, arising,
according to Bitter[368], only in response to some external friction. They are invariably
dark-coloured, rather short, about one to a few millimetres in length, and are simple or
branched. The branches may go off at any angle and are sometimes curved back at the
ends in anchor-like fashion. The Parmeliae grow on firm substances, trees, rocks, etc.,
and the irregularities of their attaching structures are conditioned by the obstacles
encountered on the substratum. Not unfrequently the lobes are attached by the rhizinae
to underlying portions of the thallus.
In the genus Gyrophora, the rhizinae are simple strands of hyphae (G. polyrhiza) or
they are corticate structures (G. murina, G. spodochroa and G. vellea). They are also
Under surface with veins and
rhizoids (after Reinke).
Fig. 54. Peltigera canina DC. (S. H., Photo.).
In species of Peltigera (Fig. 54) the rhizinae are confined to the veins or ridges
(Fig. 55); they are thickish at the base, and are generally rather long and straggling.
Meyer[366] states that the central hyphae are stoutish and much entangled owing to the
branching and frequent anastomosis of one hypha with another; the peripheral
terminal branches are thinner-walled and free. These rhizinae vary in colour from
white in Peltigera canina to brown or black in other species. Most species of
Peltigera spread over grass or mosses, to which they cling by these long loose
“rootlets.”
Lichen rhizinae, distinguished by Reinke[367] as “aerial rhizinae,” are more or less
characteristic of all the species of Parmelia with the exception of those belonging to
the subgenus Hypogymnia in which they are of very rare occurrence, arising,
according to Bitter[368], only in response to some external friction. They are invariably
dark-coloured, rather short, about one to a few millimetres in length, and are simple or
branched. The branches may go off at any angle and are sometimes curved back at the
ends in anchor-like fashion. The Parmeliae grow on firm substances, trees, rocks, etc.,
and the irregularities of their attaching structures are conditioned by the obstacles
encountered on the substratum. Not unfrequently the lobes are attached by the rhizinae
to underlying portions of the thallus.
In the genus Gyrophora, the rhizinae are simple strands of hyphae (G. polyrhiza) or
they are corticate structures (G. murina, G. spodochroa and G. vellea). They are also
Page 154
present in species of Solorina, Ricasolia, Sticta and Physcia and very sparingly in
Cetraria (Platysma).
c. Haptera. Sernander[369] has grouped all the more distinctively aerial organs of
attachment, apart from rhizinae, under the term “hapteron” and he has described a
number of instances in which cilia and even the growing points of the thallus may
become transformed to haptera or sucker-like sheaths.
The long cilia of Physcia ciliaris occasionally form haptera at their tips where the
hyphae are loose and in active growing condition. Contact with some substance
induces branching by which a spreading sheath arises; a plug-like process may also be
developed which pierces the substance encountered—not unfrequently another lobe of
its own thallus. The long flaccid fronds of Evernia furfuracea are frequently
connected together by bridge-like haptera which rise at any angle of the thallus or
from any part of the surface.
The spinous hairs that border the thalline margins in Cetraria may also, in contact
with some body—often another frond of the lichen—form a hapteron, either while the
spermogonium, which occupies the tip of the spine, is still in a rudimentary stage, or
after it has discharged its spermatia. The small sucker sheath may in that case arise
either from the apex of the cilium, from the wall of the spermogonium or from its
base. By means of these haptera, not only different individuals become united
together, but instances are given by Sernander in which Cetraria islandica, normally a
ground lichen, had become epiphytic by attaching itself in this way to the trunk of a
tree (Pinus sylvestris).
In Alectoria, haptera are formed at the tip of the thallus filament as an apical cone-
like growth from which hyphae may branch out and penetrate any convenient object.
A species of this genus was thus found clinging to stems of Betula nana. Apical
haptera are very frequent in Cladonia rangiferina and Cl. sylvatica, induced here also
by contact. These two plants, as well as several species of Cetraria, tend, indeed, to
become entirely epiphytic on the heaths of the Calluna formations. Haptera similar to
those of Alectoria occur in Usnea, Evernia, Ramalina and Cornicularia (Cetraria). In
Evernia prunastri var. stictoceros, a heath form, the fronds become attached to the
stems and branches of Erica tetralix by hapteroid strands of slender glutinous hyphae
which persist on the frond of the lichen after it is detached as small very dark
tubercles surmounted, as Parfitt[370] pointed out, by a dark-brown grumous mass of
cells. Plug-like haptera may be formed at the base of Cladoniae which attach them to
each other and to the substratum. The brightly coloured fronds of Letharia vulpina are
attached to each other in somewhat tangled fashion by lateral bridges or by fascicles
of hyphae dark-brown at the base but colourless at the apices, exactly like aerial
adventitious rhizinae. They grow out from the fronds generally at or near the tips and
lay hold of a neighbouring frond by means of mucilage. These haptera are evidently
formed in response to friction. Haptera along with other lichen attachments have
Cetraria (Platysma).
c. Haptera. Sernander[369] has grouped all the more distinctively aerial organs of
attachment, apart from rhizinae, under the term “hapteron” and he has described a
number of instances in which cilia and even the growing points of the thallus may
become transformed to haptera or sucker-like sheaths.
The long cilia of Physcia ciliaris occasionally form haptera at their tips where the
hyphae are loose and in active growing condition. Contact with some substance
induces branching by which a spreading sheath arises; a plug-like process may also be
developed which pierces the substance encountered—not unfrequently another lobe of
its own thallus. The long flaccid fronds of Evernia furfuracea are frequently
connected together by bridge-like haptera which rise at any angle of the thallus or
from any part of the surface.
The spinous hairs that border the thalline margins in Cetraria may also, in contact
with some body—often another frond of the lichen—form a hapteron, either while the
spermogonium, which occupies the tip of the spine, is still in a rudimentary stage, or
after it has discharged its spermatia. The small sucker sheath may in that case arise
either from the apex of the cilium, from the wall of the spermogonium or from its
base. By means of these haptera, not only different individuals become united
together, but instances are given by Sernander in which Cetraria islandica, normally a
ground lichen, had become epiphytic by attaching itself in this way to the trunk of a
tree (Pinus sylvestris).
In Alectoria, haptera are formed at the tip of the thallus filament as an apical cone-
like growth from which hyphae may branch out and penetrate any convenient object.
A species of this genus was thus found clinging to stems of Betula nana. Apical
haptera are very frequent in Cladonia rangiferina and Cl. sylvatica, induced here also
by contact. These two plants, as well as several species of Cetraria, tend, indeed, to
become entirely epiphytic on the heaths of the Calluna formations. Haptera similar to
those of Alectoria occur in Usnea, Evernia, Ramalina and Cornicularia (Cetraria). In
Evernia prunastri var. stictoceros, a heath form, the fronds become attached to the
stems and branches of Erica tetralix by hapteroid strands of slender glutinous hyphae
which persist on the frond of the lichen after it is detached as small very dark
tubercles surmounted, as Parfitt[370] pointed out, by a dark-brown grumous mass of
cells. Plug-like haptera may be formed at the base of Cladoniae which attach them to
each other and to the substratum. The brightly coloured fronds of Letharia vulpina are
attached to each other in somewhat tangled fashion by lateral bridges or by fascicles
of hyphae dark-brown at the base but colourless at the apices, exactly like aerial
adventitious rhizinae. They grow out from the fronds generally at or near the tips and
lay hold of a neighbouring frond by means of mucilage. These haptera are evidently
formed in response to friction. Haptera along with other lichen attachments have
Page 155
received considerable attention from Galløe[371]. He finds them arising on various
positions of the lichen fronds and has classified them accordingly.
After the haptera have become attached, they increase in size and strength and
supply a strong anchorage for the plant; the point of contact frequently forms a basis
for renewed growth while the part beneath the hapteron may gradually die off.
Haptera are more especially characteristic of fruticose lichens, but Sernander
considers that the rhizinae of foliose species may function as haptera. They are
important organs of tundra and heath formations as they enable the lichens to get a
foothold in well-lighted positions, and by their aid the fronds are more able to resist
the extreme tearing strains to which they are subjected in high and unsheltered
moorlands.
F. Strengthening Tissues of Stratose Lichens
Squamulose and foliose lichens grow mostly in close relation with the support, and
the flat expanding thallus, as in the Parmeliae, is attached at many points to the
substance—tree, rock, etc.—over which the plants spread. Special provision for
support is therefore not required, and the lobes remain thin and flaccid. Yet, in a
number of widely different genera the attachment to the substratum is very slight, and
in these we find an adaptation of existing tissues fitted to resist tearing strains,
resistance being almost invariably secured by the strengthening of the cortical layers.
a. By development of the Cortex. Such a transformation of tissue is well illustrated
in Heppia Guepini. The thallus consists of rigid squamules which are attached at one
point only; the cortex of both surfaces is plectenchymatous and very thick and even
the medulla is largely cellular.
The much larger but equally rigid coriaceous thallus of Dermatocarpon miniatum
(Fig. 56) has also a single central attachment or umbilicus, and both cortices consist of
a compact many-layered plectenchyma. The same structure occurs in Umbilicaria
pustulata and in some species of Gyrophora, which, having only a single central hold-
fast, gain the necessary stiffening through the increase of the cortical layers.
positions of the lichen fronds and has classified them accordingly.
After the haptera have become attached, they increase in size and strength and
supply a strong anchorage for the plant; the point of contact frequently forms a basis
for renewed growth while the part beneath the hapteron may gradually die off.
Haptera are more especially characteristic of fruticose lichens, but Sernander
considers that the rhizinae of foliose species may function as haptera. They are
important organs of tundra and heath formations as they enable the lichens to get a
foothold in well-lighted positions, and by their aid the fronds are more able to resist
the extreme tearing strains to which they are subjected in high and unsheltered
moorlands.
F. Strengthening Tissues of Stratose Lichens
Squamulose and foliose lichens grow mostly in close relation with the support, and
the flat expanding thallus, as in the Parmeliae, is attached at many points to the
substance—tree, rock, etc.—over which the plants spread. Special provision for
support is therefore not required, and the lobes remain thin and flaccid. Yet, in a
number of widely different genera the attachment to the substratum is very slight, and
in these we find an adaptation of existing tissues fitted to resist tearing strains,
resistance being almost invariably secured by the strengthening of the cortical layers.
a. By development of the Cortex. Such a transformation of tissue is well illustrated
in Heppia Guepini. The thallus consists of rigid squamules which are attached at one
point only; the cortex of both surfaces is plectenchymatous and very thick and even
the medulla is largely cellular.
The much larger but equally rigid coriaceous thallus of Dermatocarpon miniatum
(Fig. 56) has also a single central attachment or umbilicus, and both cortices consist of
a compact many-layered plectenchyma. The same structure occurs in Umbilicaria
pustulata and in some species of Gyrophora, which, having only a single central hold-
fast, gain the necessary stiffening through the increase of the cortical layers.
Page 156
Fig. 56. Dermatocarpon miniatum Th. Fr. (S. H., Photo.).
In the Stictaceae there are a large number of widely-expanded forms, and as the
attachment depends mostly on a somewhat short tomentum, strength is obtained here
also by the thick plectenchymatous cortex of both surfaces. When areas denuded of
tomentum and cortex occur, as in Lobaria pulmonaria, the under surface is not
sensibly weakened, since the cortical tissue remains connected in a stout and firm
reticulation.
b. By development of Veins or Nerves. Certain ground lichens belonging to the
Peltigeraceae have a wide spreading thallus often with very large lobes. The upper
cortex is a many-layered plectenchyma, but the under surface is covered only by a
loose felt of hyphae which branch out into a more or less dense tomentum. As the firm
upper cortex continues to increase by intercalary growth from the branching upwards
of hyphae from the meristematic gonidial zone, there occurs an extension of the upper
thallus with which the lower cannot keep pace[372]. A little way back from the edge,
the result of the stretching is seen in the splitting asunder of the felted hyphae of the
under surface, and in the consequent formation of a reticulate series of ridges known
as the veins or nerves; they represent the original tomentose covering, and are white,
black or brown, according to the colour of the tomentum itself. The naked ellipsoid
interstices show the white medulla, and, if the veins are wide, the colourless areas are
correspondingly small. Rhizinae are formed on the nerves in several of the species,
and anchor the thallus to the support. In Peltigera canina, the under surface is almost
wholly colourless, the veins are very prominent (Fig. 55), and are further strengthened
by the growth and branching of the parallel hyphae of which they are composed. They
serve to strengthen the large and flabby thallus and form a rigid base for the long
rhizinae by which the lichen clings to the grass or moss over which it grows.
The most perfect development of strengthening nerves is to be found in
Hydrothyria venosa[373], a rather rare water lichen that occurs in the streams of North
In the Stictaceae there are a large number of widely-expanded forms, and as the
attachment depends mostly on a somewhat short tomentum, strength is obtained here
also by the thick plectenchymatous cortex of both surfaces. When areas denuded of
tomentum and cortex occur, as in Lobaria pulmonaria, the under surface is not
sensibly weakened, since the cortical tissue remains connected in a stout and firm
reticulation.
b. By development of Veins or Nerves. Certain ground lichens belonging to the
Peltigeraceae have a wide spreading thallus often with very large lobes. The upper
cortex is a many-layered plectenchyma, but the under surface is covered only by a
loose felt of hyphae which branch out into a more or less dense tomentum. As the firm
upper cortex continues to increase by intercalary growth from the branching upwards
of hyphae from the meristematic gonidial zone, there occurs an extension of the upper
thallus with which the lower cannot keep pace[372]. A little way back from the edge,
the result of the stretching is seen in the splitting asunder of the felted hyphae of the
under surface, and in the consequent formation of a reticulate series of ridges known
as the veins or nerves; they represent the original tomentose covering, and are white,
black or brown, according to the colour of the tomentum itself. The naked ellipsoid
interstices show the white medulla, and, if the veins are wide, the colourless areas are
correspondingly small. Rhizinae are formed on the nerves in several of the species,
and anchor the thallus to the support. In Peltigera canina, the under surface is almost
wholly colourless, the veins are very prominent (Fig. 55), and are further strengthened
by the growth and branching of the parallel hyphae of which they are composed. They
serve to strengthen the large and flabby thallus and form a rigid base for the long
rhizinae by which the lichen clings to the grass or moss over which it grows.
The most perfect development of strengthening nerves is to be found in
Hydrothyria venosa[373], a rather rare water lichen that occurs in the streams of North
Page 157
America. It consists of fan-like lobes of thin structure, the cortex being only about one
cell thick. The fronds are about 3 cm. wide and they are contracted below into a stalk
which serves to attach the plant to the substratum. Several fronds may grow together
in a dense tuft, the expanded upper portion floating freely in the water. Frequently the
plants form a dense growth over the rocky beds of the stream.
At the point where the stalk expands into the free erect frond, there arise a series of
stout veins which spread upwards and outwards. They are definitely formed structures
and not adaptations of pre-existing tissues: certain hyphae arise from the medulla at
the contracted base of the frond, take a radial direction and, by increase, become
developed into firm strands. The individual hyphae also increase in size, and the
swelling of the nerve gives rise to a ridge prominent on both surfaces. They seldom
anastomose at first but towards the tips they become smaller and spread out in delicate
ramifications which unite at various points. There is no doubt, as Bitter[372] points out,
that the nerves function as strengthening tissues and preserve the frond from the strain
of the water currents which would, otherwise, tear apart the delicate texture.
III. RADIATE THALLUS
1. CHARACTERS OF RADIATE THALLUS
In the stratose dorsiventral thallus, there is a widely extended growing area situated
round the free margins of the thallus. In the radiate thallus of the fruticose or
filamentous lichens, growth is confined to an apical region. Attachment to the
substratum is at one point only—the base of the plant—thus securing the exposure of
all sides equally to light. The cortex surrounds the fronds, and the gonidia (mostly
Protococcaceae) lie in a zone or in groups between the cortex and the medulla. It is the
highest type of vegetative development in the lichen kingdom, since it secures the
widest room for the gonidial layer, and the largest opportunity for photosynthesis.
cell thick. The fronds are about 3 cm. wide and they are contracted below into a stalk
which serves to attach the plant to the substratum. Several fronds may grow together
in a dense tuft, the expanded upper portion floating freely in the water. Frequently the
plants form a dense growth over the rocky beds of the stream.
At the point where the stalk expands into the free erect frond, there arise a series of
stout veins which spread upwards and outwards. They are definitely formed structures
and not adaptations of pre-existing tissues: certain hyphae arise from the medulla at
the contracted base of the frond, take a radial direction and, by increase, become
developed into firm strands. The individual hyphae also increase in size, and the
swelling of the nerve gives rise to a ridge prominent on both surfaces. They seldom
anastomose at first but towards the tips they become smaller and spread out in delicate
ramifications which unite at various points. There is no doubt, as Bitter[372] points out,
that the nerves function as strengthening tissues and preserve the frond from the strain
of the water currents which would, otherwise, tear apart the delicate texture.
III. RADIATE THALLUS
1. CHARACTERS OF RADIATE THALLUS
In the stratose dorsiventral thallus, there is a widely extended growing area situated
round the free margins of the thallus. In the radiate thallus of the fruticose or
filamentous lichens, growth is confined to an apical region. Attachment to the
substratum is at one point only—the base of the plant—thus securing the exposure of
all sides equally to light. The cortex surrounds the fronds, and the gonidia (mostly
Protococcaceae) lie in a zone or in groups between the cortex and the medulla. It is the
highest type of vegetative development in the lichen kingdom, since it secures the
widest room for the gonidial layer, and the largest opportunity for photosynthesis.
Page 158
Fig. 57. Roccella fuciformis DC.
Shrubby upright lichens consist mostly of strap-shaped fronds, either simple or
branched, which may be broadened to thin bands (Fig. 57) or may be narrowed and
thickened till they are almost cylindrical. The fronds vary in length according to the
species from a few millimetres upwards: those of Roccella have been found
measuring 30 cm. in length; those of Ramalina reticulata, the largest of all the
American lichens, extend to considerably more.
Lichens of filamentous growth are more or less cylindrical (Fig. 58). They are in
some species upright and of moderate length, but in a few pendulous forms they grow
to a great length: specimens of Usnea longissima have been recorded that measured 6
to 8 metres from base to tip.
Shrubby upright lichens consist mostly of strap-shaped fronds, either simple or
branched, which may be broadened to thin bands (Fig. 57) or may be narrowed and
thickened till they are almost cylindrical. The fronds vary in length according to the
species from a few millimetres upwards: those of Roccella have been found
measuring 30 cm. in length; those of Ramalina reticulata, the largest of all the
American lichens, extend to considerably more.
Lichens of filamentous growth are more or less cylindrical (Fig. 58). They are in
some species upright and of moderate length, but in a few pendulous forms they grow
to a great length: specimens of Usnea longissima have been recorded that measured 6
to 8 metres from base to tip.
Page 159
Fig. 58. Usnea barbata Web. (S. H., Photo.).
The radiate type of thallus occurs in most of the lichen groups but most frequently
in the Gymnocarpeae. In gelatinous Discolichens it is represented in the Lichinaceae.
It is rare among Pyrenocarpeae: there is one very minute British lichen in that series,
Pyrenidium actinellum, and one from N. America, Pyrenothamnia, that are of
fruticose habit.
2. INTERMEDIATE TYPES OF THALLUS
Between the foliose and the fruticose types, there are intermediate forms that might
be, and often are, classified now in one group and now in the other. These are chiefly:
Physcia (Anaptychia) ciliaris, Ph. leucomelas and the species of Evernia.
In the two former the habit is more or less fruticose as the plants are affixed to the
substratum at a basal point, but the fronds are decumbent and the internal structure is
of the dorsiventral type: there is an upper “fibrous” cortex of closely compacted
parallel hyphae, a gonidial zone—the gonidia lying partly in the cortex and partly
among the loose hyphae of the medulla—and a lower cortex formed of a weft of
hyphae which also run somewhat parallel to the surface. Both species are
distinguished by the numerous marginal cilia, either pale or dark in colour. These two
lichens are greyish-coloured on the upper surface and greyish or whitish below.
Evernia furfuracea with a basal attachment[374], and with a partly horizontal and
partly upright growth, has a dorsiventral thallus, dark greyish-green above and black
The radiate type of thallus occurs in most of the lichen groups but most frequently
in the Gymnocarpeae. In gelatinous Discolichens it is represented in the Lichinaceae.
It is rare among Pyrenocarpeae: there is one very minute British lichen in that series,
Pyrenidium actinellum, and one from N. America, Pyrenothamnia, that are of
fruticose habit.
2. INTERMEDIATE TYPES OF THALLUS
Between the foliose and the fruticose types, there are intermediate forms that might
be, and often are, classified now in one group and now in the other. These are chiefly:
Physcia (Anaptychia) ciliaris, Ph. leucomelas and the species of Evernia.
In the two former the habit is more or less fruticose as the plants are affixed to the
substratum at a basal point, but the fronds are decumbent and the internal structure is
of the dorsiventral type: there is an upper “fibrous” cortex of closely compacted
parallel hyphae, a gonidial zone—the gonidia lying partly in the cortex and partly
among the loose hyphae of the medulla—and a lower cortex formed of a weft of
hyphae which also run somewhat parallel to the surface. Both species are
distinguished by the numerous marginal cilia, either pale or dark in colour. These two
lichens are greyish-coloured on the upper surface and greyish or whitish below.
Evernia furfuracea with a basal attachment[374], and with a partly horizontal and
partly upright growth, has a dorsiventral thallus, dark greyish-green above and black
Page 160
beneath, with occasional rhizinae towards the base. The cortex of both surfaces
belongs to the “decomposed” type; the gonidial zone lies below the upper surface, and
the medullary tissue is of loose hyphae. In certain forms of the species isidia are
abundant on the upper surface, a character of foliose rather than of fruticose lichens.
E. furfuracea grows on trees and very frequently on palings.
Fig. 59. Evernia prunastri Ach. (M. P., Photo.).
E. prunastri, the second species of the genus, is more distinctly upright in habit,
with a penetrating basal hold-fast and upright strap-shaped branching fronds, light-
greyish green on the “upper” surface and white on the other (Fig. 59). The internal
structure is sub-radiate; both cortices are “decomposed”; the gonidial zone consists of
somewhat loose groups of algae, very constant below the “upper” surface, with an
occasional group in the pith near to the lower cortex in positions that are more
exposed to light. There is also a tendency for the gonidial zone to pass round the
margin and spread some way along the under side. The medulla is of loose arachnoid
texture and the whole plant is very limp when moist. It grows on trees, often in dense
clusters.
3. FRUTICOSE AND FILAMENTOUS
A. General Structure of Thallus
The conditions of strain and tension in the upright plant are entirely different from
those in the decumbent thallus, and to meet the new requirements, new adaptations of
belongs to the “decomposed” type; the gonidial zone lies below the upper surface, and
the medullary tissue is of loose hyphae. In certain forms of the species isidia are
abundant on the upper surface, a character of foliose rather than of fruticose lichens.
E. furfuracea grows on trees and very frequently on palings.
Fig. 59. Evernia prunastri Ach. (M. P., Photo.).
E. prunastri, the second species of the genus, is more distinctly upright in habit,
with a penetrating basal hold-fast and upright strap-shaped branching fronds, light-
greyish green on the “upper” surface and white on the other (Fig. 59). The internal
structure is sub-radiate; both cortices are “decomposed”; the gonidial zone consists of
somewhat loose groups of algae, very constant below the “upper” surface, with an
occasional group in the pith near to the lower cortex in positions that are more
exposed to light. There is also a tendency for the gonidial zone to pass round the
margin and spread some way along the under side. The medulla is of loose arachnoid
texture and the whole plant is very limp when moist. It grows on trees, often in dense
clusters.
3. FRUTICOSE AND FILAMENTOUS
A. General Structure of Thallus
The conditions of strain and tension in the upright plant are entirely different from
those in the decumbent thallus, and to meet the new requirements, new adaptations of
Page 161
structure are provided either in the cortex or in the medulla.
Cortical Structures. With the exception of the distinctly plectenchymatous cortex,
all the other types already described recur in fruticose lichens; in various ways they
have been modified to provide not only covering but support to the fronds.
a. The fastigiate cortex. This reaches its highest development in Roccella in which
the branched hyphal tips, slightly clavate and thick-walled, lie closely packed in
palisade formation at right angles to the main axis (Fig. 45). They afford not only
bending power, but give great consistency to the fronds. The cortex is further
strengthened in R. fuciformis[375] by the compact arrangement of the medullary
hyphae that run parallel with the surface, and among which occur single thick-walled
filaments. The plant grows on maritime rocks in very exposed situations; and the
narrow strap-shaped fronds, as stated above, may attain a length of 30 cm., though
usually they are from 10 to 18 cm. in height. The same type of cortex, but less highly
differentiated, affords a certain amount of stiffness to the cylindrical much weaker
fronds of Thamnolia.
b. The fibrous cortex. This type is found in a number of lichens with long
filamentous hanging fronds. It consists of parallel hyphae, rarely septate and rarely
branched, but frequently anastomosing and with strongly thickened “sclerotic” walls.
Such a cortex is the only strengthening element in Alectoria, and it affords great
toughness and flexibility to the thong-like thallus. It is also present in Ramalina
(Alectoria) thrausta, a species with slender fronds (Fig. 60).
Cortical Structures. With the exception of the distinctly plectenchymatous cortex,
all the other types already described recur in fruticose lichens; in various ways they
have been modified to provide not only covering but support to the fronds.
a. The fastigiate cortex. This reaches its highest development in Roccella in which
the branched hyphal tips, slightly clavate and thick-walled, lie closely packed in
palisade formation at right angles to the main axis (Fig. 45). They afford not only
bending power, but give great consistency to the fronds. The cortex is further
strengthened in R. fuciformis[375] by the compact arrangement of the medullary
hyphae that run parallel with the surface, and among which occur single thick-walled
filaments. The plant grows on maritime rocks in very exposed situations; and the
narrow strap-shaped fronds, as stated above, may attain a length of 30 cm., though
usually they are from 10 to 18 cm. in height. The same type of cortex, but less highly
differentiated, affords a certain amount of stiffness to the cylindrical much weaker
fronds of Thamnolia.
b. The fibrous cortex. This type is found in a number of lichens with long
filamentous hanging fronds. It consists of parallel hyphae, rarely septate and rarely
branched, but frequently anastomosing and with strongly thickened “sclerotic” walls.
Such a cortex is the only strengthening element in Alectoria, and it affords great
toughness and flexibility to the thong-like thallus. It is also present in Ramalina
(Alectoria) thrausta, a species with slender fronds (Fig. 60).
Page 162
Fig. 60. Alectoria thrausta Ach. A, transverse section of frond; a,
cortex; b, gonidia; c, arachnoid medulla × 37. B, fibrous hyphae
from longitudinal section of cortex. × 430 (after Brandt).
In Usnea longissima the cortex both of the fibrillose branchlets and of the main axis
is fibrous, and is composed of narrow thick-walled hyphae which grow in a long
spiral round the central strand. The hyphae become more frequently septate further
back from the apex (Fig. 61). Such a type of cortex provides an exceedingly elastic
and efficient protection for the long slender thallus.
cortex; b, gonidia; c, arachnoid medulla × 37. B, fibrous hyphae
from longitudinal section of cortex. × 430 (after Brandt).
In Usnea longissima the cortex both of the fibrillose branchlets and of the main axis
is fibrous, and is composed of narrow thick-walled hyphae which grow in a long
spiral round the central strand. The hyphae become more frequently septate further
back from the apex (Fig. 61). Such a type of cortex provides an exceedingly elastic
and efficient protection for the long slender thallus.
Page 163
Fig. 61. Usnea longissima Ach. Longitudinal sections of outer
cortex. A, near the apex; B, the middle portion of a fibril. × 525
(after Schulte).
The same type of cortex forms the strengthening element in the fruticose or partly
fruticose members of the family Physciaceae. One of these, Teloschistes flavicans, is a
bright yellow filamentous lichen with a somewhat straggling habit. The fronds are
very slender and are either cylindrical or slightly flattened. The hyphae of the outer
cortex are compactly fibrous; added toughness is given by the presence of some
longitudinal strands of hyphae in the central pith.
Another still more familiar grey lichen, Physcia ciliaris, has long flat branching
fronds which, though dorsiventral in structure, are partly upright in habit. Strength is
secured as in Teloschistes by the fibrous upper cortex. Other species of Physciae are
somewhat similar in habit and in structure.
In Dendrographa leucophaea, a slender strap-shaped rock lichen, Darbishire[376]
has described the outer cortex as composed of closely compacted parallel hyphae
resembling the strengthening cortex of Alectoria and very different from the fastigiate
cortex of the Roccellae with which it is usually classified.
B. Special strengthening Structures
a. Sclerotic strands. This form of strengthening tissue is characteristic of
Ramalina. With the exception of R. thrausta (more truly an Alectoria) all the species
have a rather weak cortical layer of branching intricate thick-walled hyphae, regarded
cortex. A, near the apex; B, the middle portion of a fibril. × 525
(after Schulte).
The same type of cortex forms the strengthening element in the fruticose or partly
fruticose members of the family Physciaceae. One of these, Teloschistes flavicans, is a
bright yellow filamentous lichen with a somewhat straggling habit. The fronds are
very slender and are either cylindrical or slightly flattened. The hyphae of the outer
cortex are compactly fibrous; added toughness is given by the presence of some
longitudinal strands of hyphae in the central pith.
Another still more familiar grey lichen, Physcia ciliaris, has long flat branching
fronds which, though dorsiventral in structure, are partly upright in habit. Strength is
secured as in Teloschistes by the fibrous upper cortex. Other species of Physciae are
somewhat similar in habit and in structure.
In Dendrographa leucophaea, a slender strap-shaped rock lichen, Darbishire[376]
has described the outer cortex as composed of closely compacted parallel hyphae
resembling the strengthening cortex of Alectoria and very different from the fastigiate
cortex of the Roccellae with which it is usually classified.
B. Special strengthening Structures
a. Sclerotic strands. This form of strengthening tissue is characteristic of
Ramalina. With the exception of R. thrausta (more truly an Alectoria) all the species
have a rather weak cortical layer of branching intricate thick-walled hyphae, regarded
Page 164
by Brandt[377] as plectenchymatous, but more correctly by Hue[378] as “decomposed”
on account of the gelatinous walls and diminishing lumen of the irregularly arranged
cells.
Fig. 62. Ramalina minuscula Nyl. A, transverse section of frond ×
37; B, longitudinal strengthening hyphae of inner cortex × 430
(after Brandt).
In R. evernioides, a plant with very wide flat almost decumbent fronds of soft
texture, in R. ceruchis and in R. homalea there is a somewhat compact medulla which
gives a slight stiffness to the thallus. The other species of the genus are provided with
strengthening mechanical tissue within the cortex formed of closely united sclerotic
hyphae that run parallel to the surface (Fig. 62). In a transverse section of the thallus,
this tissue appears sometimes as a continuous ring which may project irregularly into
the pith (R. calicaris); more frequently it is in the form of strands or bundles which
alternate with the groups of gonidia (R. siliquosa, R. Curnowii, etc.). In R. fraxinea
these strands may be scarcely discernible in young fronds, though sometimes already
well developed near the tips. Occasionally isolated strands of fibres appear in the pith
(R. Curnowii), or the sclerotic projections may even stretch across the pith to the other
side (R. strepsilis) (Fig. 75 b).
In the Cladoniae support along with flexibility is secured to the upright podetium
by the parallel closely packed hyphae that form round the hollow cylinder a band
called the “chondroid” layer from its cartilage-like consistency.
b. Chondroid axis. The central medullary tissue in Ramalina is, with few
exceptions, a loose arachnoid structure; often the fronds are almost hollow. In one
species of Usnea, U. Taylori, found in polar regions, there is a similar loose though
on account of the gelatinous walls and diminishing lumen of the irregularly arranged
cells.
Fig. 62. Ramalina minuscula Nyl. A, transverse section of frond ×
37; B, longitudinal strengthening hyphae of inner cortex × 430
(after Brandt).
In R. evernioides, a plant with very wide flat almost decumbent fronds of soft
texture, in R. ceruchis and in R. homalea there is a somewhat compact medulla which
gives a slight stiffness to the thallus. The other species of the genus are provided with
strengthening mechanical tissue within the cortex formed of closely united sclerotic
hyphae that run parallel to the surface (Fig. 62). In a transverse section of the thallus,
this tissue appears sometimes as a continuous ring which may project irregularly into
the pith (R. calicaris); more frequently it is in the form of strands or bundles which
alternate with the groups of gonidia (R. siliquosa, R. Curnowii, etc.). In R. fraxinea
these strands may be scarcely discernible in young fronds, though sometimes already
well developed near the tips. Occasionally isolated strands of fibres appear in the pith
(R. Curnowii), or the sclerotic projections may even stretch across the pith to the other
side (R. strepsilis) (Fig. 75 b).
In the Cladoniae support along with flexibility is secured to the upright podetium
by the parallel closely packed hyphae that form round the hollow cylinder a band
called the “chondroid” layer from its cartilage-like consistency.
b. Chondroid axis. The central medullary tissue in Ramalina is, with few
exceptions, a loose arachnoid structure; often the fronds are almost hollow. In one
species of Usnea, U. Taylori, found in polar regions, there is a similar loose though
Page 165
very circumscribed medullary and gonidial tissue in the centre of the somewhat
cylindrical thallus, and a wide band of sclerotic fibres towards the cortex.
Fig. 63 a. A, Usnea barbata Web. Longitudinal section of filament with young
adventitious branch. a, chondroid axis; b, gonidial tissue; c, cortex. × 100 (after
Schwendener). B, U. longissima Ach. Hyphae from central axis × 525 (after
Schulte).
In all other species of Usnea the medulla itself is transformed into a strong central
strand of long-celled thick-walled hyphae closely knit together by frequent
anastomoses (Fig. 63 a). This central strand of the Usneas is known as the “chondroid
axis.” A narrow band of loose air-containing hyphae and a gonidial zone lie round the
central axis between it and the outer cortex (Fig. 63 a, b). At the extreme apex, the
external cortical hyphae grow in a direction parallel with the long axis of the plant, but
further back, they branch out at right angles and become swollen and mostly
“decomposed” as in the cortex of Ramalina.
In Letharia (L. vulpina, etc.) the structure is midway between Ramalina and Usnea:
the central axis is either a solid strand of chondroid hyphae or several separate strands.
cylindrical thallus, and a wide band of sclerotic fibres towards the cortex.
Fig. 63 a. A, Usnea barbata Web. Longitudinal section of filament with young
adventitious branch. a, chondroid axis; b, gonidial tissue; c, cortex. × 100 (after
Schwendener). B, U. longissima Ach. Hyphae from central axis × 525 (after
Schulte).
In all other species of Usnea the medulla itself is transformed into a strong central
strand of long-celled thick-walled hyphae closely knit together by frequent
anastomoses (Fig. 63 a). This central strand of the Usneas is known as the “chondroid
axis.” A narrow band of loose air-containing hyphae and a gonidial zone lie round the
central axis between it and the outer cortex (Fig. 63 a, b). At the extreme apex, the
external cortical hyphae grow in a direction parallel with the long axis of the plant, but
further back, they branch out at right angles and become swollen and mostly
“decomposed” as in the cortex of Ramalina.
In Letharia (L. vulpina, etc.) the structure is midway between Ramalina and Usnea:
the central axis is either a solid strand of chondroid hyphae or several separate strands.
Page 166
Fig. 63 b. Usnea longissima Ach. A, transverse section of fibril × 85. B, a,
chondroid axis; b, gonidial tissue; c, cortex × 525 (after Schulte).
In three other genera with upright fruticose thalli, Sphaerophorus, Argopsis and
Stereocaulon, rigidity is maintained by a medulla approaching the chondroid type. In
Sphaerophorus the species may have either flattened or cylindrical branching stalks,
but in all of them, the centre is occupied by longitudinal strands of hyphae. Argopsis, a
monotypic genus from Kerguelen, has a cylindrical branching thallus with a strong
solid axis; it is closely allied to Stereocaulon, a genus of familiar moorland lichens.
The central tissue of the stalks in Stereocaulon is also composed of elongate, thick-
walled conglutinate hyphae, formed into a strand which is, however, not entirely solid.
C. Survey of Mechanical Tissues
Mechanical tissues scarcely appear among fungi, except perhaps as stoutish
cartilaginous hyphae in the stalks of some Agarics (Collybiae, etc.), or as a ring of
more compact consistency round the central hyphae of rhizomorphic strands. It is
practically a new adaptation of hyphal structure confined to lichens of the fruticose
group, where there is the same requirement as in the higher plants for rigidity, flexure
and tenacity.
Rigidity is attained as in other plants by groups or strands of mechanical tissue
situated close to the periphery, as they are so arranged in Ramalina and Cladonia; or
the same end is achieved by a strongly developed fastigiate cortex as in Roccella.
Bending strains to which the same lichens are subjected, are equally well met by the
peripheral disposition of the mechanical elements.
Tenacity and elasticity are provided for in the pendulous forms either by a fibrous
cortex as in Alectoria, or by the chondroid axis in Usnea. Haberlandt[379] has recorded
some interesting results of tests made by him as to the stretching capacity of a freshly
chondroid axis; b, gonidial tissue; c, cortex × 525 (after Schulte).
In three other genera with upright fruticose thalli, Sphaerophorus, Argopsis and
Stereocaulon, rigidity is maintained by a medulla approaching the chondroid type. In
Sphaerophorus the species may have either flattened or cylindrical branching stalks,
but in all of them, the centre is occupied by longitudinal strands of hyphae. Argopsis, a
monotypic genus from Kerguelen, has a cylindrical branching thallus with a strong
solid axis; it is closely allied to Stereocaulon, a genus of familiar moorland lichens.
The central tissue of the stalks in Stereocaulon is also composed of elongate, thick-
walled conglutinate hyphae, formed into a strand which is, however, not entirely solid.
C. Survey of Mechanical Tissues
Mechanical tissues scarcely appear among fungi, except perhaps as stoutish
cartilaginous hyphae in the stalks of some Agarics (Collybiae, etc.), or as a ring of
more compact consistency round the central hyphae of rhizomorphic strands. It is
practically a new adaptation of hyphal structure confined to lichens of the fruticose
group, where there is the same requirement as in the higher plants for rigidity, flexure
and tenacity.
Rigidity is attained as in other plants by groups or strands of mechanical tissue
situated close to the periphery, as they are so arranged in Ramalina and Cladonia; or
the same end is achieved by a strongly developed fastigiate cortex as in Roccella.
Bending strains to which the same lichens are subjected, are equally well met by the
peripheral disposition of the mechanical elements.
Tenacity and elasticity are provided for in the pendulous forms either by a fibrous
cortex as in Alectoria, or by the chondroid axis in Usnea. Haberlandt[379] has recorded
some interesting results of tests made by him as to the stretching capacity of a freshly
Page 167
gathered pendulous species in which the central strand was from ·5 to 1 mm. thick. He
found he could draw it out 100 to 110 per cent. of its normal length before it gave
way. In an upright species the frond broke when stretched 60 to 70 per cent. In both of
the plants tested, the central strand retained its elasticity up to 20 per cent. of
stretching. The outer cortical tissue was cracked and broken in the experiments.
Schulte[380] calculated somewhat roughly the tenacity of Usnea longissima and found
that a piece of the main axis 8 cm. long carried up to 300 grms. without breaking.
D. Reticulate Fronds
In the upright radiate thallus, more especially among the Ramalinae, though also
among Cladoniae[381], there has appeared a reticulate thallus resulting from the
elongate splitting of the tissues, and due to unequal growth tension and straining of
the gelatinous cortex when swollen with moisture. In several species of Ramalina, the
strap-shaped frond is hollow in the centre; and strands of strengthening fibres give rise
to a series of cortical ridges. The thinner tissue between is frequently torn apart and
ellipsoid openings appear which do not however pierce beyond the central hollow.
Such breaks are irregular and accidental though occurring constantly in Ramalina
fraxinea, R. dilacerata, etc.
A more complete type of reticulation is always present in a Californian lichen,
Ramalina reticulata, in which the large flat frond is a delicate open network from tip
to base (Fig. 64). It grows on the branches of deciduous trees and hangs in crowded
tufts up to 30 cm. or more in length. Usually it is so torn, that the real size attainable
can only be guessed at. It is attached at the base by a spreading discoid hold-fast, and,
in mature plants, consists of a stoutish main axis from which side branches are
irregularly given off. These latter are firm at the base like the parent stalk, but soon
they broaden out into very wide fronds. Splitting begins at the tips of the branches
while still young; they are then spathulate in form with a slightly narrower recurved
tip, below which the first perforations are visible, small at first, but gradually
enlarging with the growth of the frond.
found he could draw it out 100 to 110 per cent. of its normal length before it gave
way. In an upright species the frond broke when stretched 60 to 70 per cent. In both of
the plants tested, the central strand retained its elasticity up to 20 per cent. of
stretching. The outer cortical tissue was cracked and broken in the experiments.
Schulte[380] calculated somewhat roughly the tenacity of Usnea longissima and found
that a piece of the main axis 8 cm. long carried up to 300 grms. without breaking.
D. Reticulate Fronds
In the upright radiate thallus, more especially among the Ramalinae, though also
among Cladoniae[381], there has appeared a reticulate thallus resulting from the
elongate splitting of the tissues, and due to unequal growth tension and straining of
the gelatinous cortex when swollen with moisture. In several species of Ramalina, the
strap-shaped frond is hollow in the centre; and strands of strengthening fibres give rise
to a series of cortical ridges. The thinner tissue between is frequently torn apart and
ellipsoid openings appear which do not however pierce beyond the central hollow.
Such breaks are irregular and accidental though occurring constantly in Ramalina
fraxinea, R. dilacerata, etc.
A more complete type of reticulation is always present in a Californian lichen,
Ramalina reticulata, in which the large flat frond is a delicate open network from tip
to base (Fig. 64). It grows on the branches of deciduous trees and hangs in crowded
tufts up to 30 cm. or more in length. Usually it is so torn, that the real size attainable
can only be guessed at. It is attached at the base by a spreading discoid hold-fast, and,
in mature plants, consists of a stoutish main axis from which side branches are
irregularly given off. These latter are firm at the base like the parent stalk, but soon
they broaden out into very wide fronds. Splitting begins at the tips of the branches
while still young; they are then spathulate in form with a slightly narrower recurved
tip, below which the first perforations are visible, small at first, but gradually
enlarging with the growth of the frond.
Page 168
Fig. 64. Ramalina reticulata Krempelh. Portion of frond (after Cramer).
Ramalina reticulata is an extremely gelatinous lichen and the formation of the
network was supposed by Lutz[382] to be entirely due to the swelling of the tissues, or
the imbibition of water, causing tension and splitting. A more exact explanation of the
phenomenon is given by Peirce[383]: he found that it was due to the thickened incurved
tip, which, on the addition of moisture, swells in length, breadth and thickness,
causing it to bend slightly upwards and then curve backwards over the thallus, thus
straining the part immediately behind. These various movements result in the splitting
of the frond while it is young and the cortices are thin and weak.
Peirce made a series of experiments to test the capacity of the tissues to support
tensile strains. In a dry state, a piece of the lichen held a weight up to 150 grms.; when
wet it broke with a weight of 30 grms. It was also observed that the thickness of the
frond doubled on wetting.
E. Rooting Base in Fruticose Lichens
Fruticose and filamentous lichens are distinguished by their mode of attachment to
the substratum: instead of a system of rhizinae or of hairs spread over a large area,
there is usually one definite rooting base by which the plant maintains its hold on the
support.
Intermediate between the foliose and fruticose types of thallus are several species
which are decumbent in habit, but which are attached at one (or sometimes more)
definite points, with but little penetration of the underlying substance. One such
lichen, Evernia furfuracea, has been classified now as foliose, and again as fruticose.
The earliest stage of the thallus is in the form of a rosette-like sheath which bears
rhizinae on the under surface, very numerous at the centre of the sheath, but entirely
wanting towards the periphery. A secondary thallus of strap-shaped rather narrow
fronds rises from the sheath and increases by irregular dichotomous branching. These
branches, which are considered by Zopf[384] as adventitious, may also come into
contact with the substratum and produce a few rhizinae at that point; or if the frond is
more closely applied, the irritation thus produced causes a still greater outgrowth of
rhizinae and the formation of a new base from which other fronds originate. These
renewed centres of growth are not of very frequent occurrence; they were first
observed and described by Lindau[385] in another species, Evernia prunastri, and were
aptly compared by him to the creeping stolons of flowering plants.
Evernia furfuracea grows frequently on dead wood, palings, etc., as well as on
trees. E. prunastri grows invariably on trees, and has a more constantly upright
fruticose habit; in this species also, a basal sheath is present, and the attachment is
secured by means of rhizoidal hyphae which penetrate deeply into the periderm of the
tree, taking advantage of the openings afforded by the lenticels. The sheath hyphae are
Ramalina reticulata is an extremely gelatinous lichen and the formation of the
network was supposed by Lutz[382] to be entirely due to the swelling of the tissues, or
the imbibition of water, causing tension and splitting. A more exact explanation of the
phenomenon is given by Peirce[383]: he found that it was due to the thickened incurved
tip, which, on the addition of moisture, swells in length, breadth and thickness,
causing it to bend slightly upwards and then curve backwards over the thallus, thus
straining the part immediately behind. These various movements result in the splitting
of the frond while it is young and the cortices are thin and weak.
Peirce made a series of experiments to test the capacity of the tissues to support
tensile strains. In a dry state, a piece of the lichen held a weight up to 150 grms.; when
wet it broke with a weight of 30 grms. It was also observed that the thickness of the
frond doubled on wetting.
E. Rooting Base in Fruticose Lichens
Fruticose and filamentous lichens are distinguished by their mode of attachment to
the substratum: instead of a system of rhizinae or of hairs spread over a large area,
there is usually one definite rooting base by which the plant maintains its hold on the
support.
Intermediate between the foliose and fruticose types of thallus are several species
which are decumbent in habit, but which are attached at one (or sometimes more)
definite points, with but little penetration of the underlying substance. One such
lichen, Evernia furfuracea, has been classified now as foliose, and again as fruticose.
The earliest stage of the thallus is in the form of a rosette-like sheath which bears
rhizinae on the under surface, very numerous at the centre of the sheath, but entirely
wanting towards the periphery. A secondary thallus of strap-shaped rather narrow
fronds rises from the sheath and increases by irregular dichotomous branching. These
branches, which are considered by Zopf[384] as adventitious, may also come into
contact with the substratum and produce a few rhizinae at that point; or if the frond is
more closely applied, the irritation thus produced causes a still greater outgrowth of
rhizinae and the formation of a new base from which other fronds originate. These
renewed centres of growth are not of very frequent occurrence; they were first
observed and described by Lindau[385] in another species, Evernia prunastri, and were
aptly compared by him to the creeping stolons of flowering plants.
Evernia furfuracea grows frequently on dead wood, palings, etc., as well as on
trees. E. prunastri grows invariably on trees, and has a more constantly upright
fruticose habit; in this species also, a basal sheath is present, and the attachment is
secured by means of rhizoidal hyphae which penetrate deeply into the periderm of the
tree, taking advantage of the openings afforded by the lenticels. The sheath hyphae are
Page 169
continuous with the medullary hyphae of the frond, and gonidia are frequently
enclosed in the tissues; the sheath spreads to some extent over the surface of the bark,
and round the base of the fronds, thus rendering the attachment of the lichen to the
tree doubly secure.
Among Ramalinae, the development of the base was followed by Brandt[386] in one
species, R. Landroensis, an arboreal lichen from S. Tyrol. A rosette-like sheath was
formed consisting solely of strands of thick-walled hyphae which spread over the
bark. There were no gonidia included in the tissue.
A different type of attachment was found by Lilian Porter[387] in corticolous
Ramalinae—R. fraxinea, R. fastigiata, and R. pollinaria. The lichens were anchored
to the tree by strands of closely compacted hyphae longitudinally arranged and
continuous with the cortical hyphae. These enter the periderm of the tree by cracks or
lenticels, and by wedge action cause extensive splitting. The strands may also spread
horizontally and give rise to new plants. The living tissues of the tree were thus
penetrated and injured, and there was evidence that hypertrophied tissue was formed
and caused erosion of the wood.
Fig. 65. Ramalina siliquosa A. L. Sm., on rocks, reduced (M. P.,
Photo.).
Several Ramalinae—R. siliquosa, R. Curnowii, etc.—grow on rocks, often in
extremely exposed situations, in isolated tufts or in crowded swards (Fig. 65). The
separate tufts are not unfrequently connected at the base by a crustaceous thallus. It is
possible also to see on the rock, here and there, small areas of compact thalline
granules that have scarcely begun to put out the upright fronds. These granules are
corticate on the upper surface and contain gonidia; from the lower surface, slender
branching hyphae in rhizoid-like strands penetrate down between the inequalities and
separable particles of the rock, if the formation is granitic. They frequently have
groups of gonidia associated with them, and they continue to ramify and spread, the
enclosed in the tissues; the sheath spreads to some extent over the surface of the bark,
and round the base of the fronds, thus rendering the attachment of the lichen to the
tree doubly secure.
Among Ramalinae, the development of the base was followed by Brandt[386] in one
species, R. Landroensis, an arboreal lichen from S. Tyrol. A rosette-like sheath was
formed consisting solely of strands of thick-walled hyphae which spread over the
bark. There were no gonidia included in the tissue.
A different type of attachment was found by Lilian Porter[387] in corticolous
Ramalinae—R. fraxinea, R. fastigiata, and R. pollinaria. The lichens were anchored
to the tree by strands of closely compacted hyphae longitudinally arranged and
continuous with the cortical hyphae. These enter the periderm of the tree by cracks or
lenticels, and by wedge action cause extensive splitting. The strands may also spread
horizontally and give rise to new plants. The living tissues of the tree were thus
penetrated and injured, and there was evidence that hypertrophied tissue was formed
and caused erosion of the wood.
Fig. 65. Ramalina siliquosa A. L. Sm., on rocks, reduced (M. P.,
Photo.).
Several Ramalinae—R. siliquosa, R. Curnowii, etc.—grow on rocks, often in
extremely exposed situations, in isolated tufts or in crowded swards (Fig. 65). The
separate tufts are not unfrequently connected at the base by a crustaceous thallus. It is
possible also to see on the rock, here and there, small areas of compact thalline
granules that have scarcely begun to put out the upright fronds. These granules are
corticate on the upper surface and contain gonidia; from the lower surface, slender
branching hyphae in rhizoid-like strands penetrate down between the inequalities and
separable particles of the rock, if the formation is granitic. They frequently have
groups of gonidia associated with them, and they continue to ramify and spread, the
Page 170
pure white filaments often enough enclosing morsels of the rock. The upright fronds
are continuous with the base and are thus securely anchored to the substratum.
On a smooth rock surface such as quartzite a continuous sward of Ramalina growth
is impossible. The basal hyphae being unable to penetrate the even surface of the rock,
the attachment is slight and the plants are easily dislodged. They do however succeed,
sometimes, in taking hold, and small groups of fronds arise from a crustaceous base
which varies in depth from ·5 to 1 mm. The tissues of this base are very irregularly
arranged: towards the upper surface loose hyphae with scattered groups of algae are
traversed by strands of gelatinized sclerotic hyphae similar to the strengthening tissues
of the upright fronds, while down below there are to be found not only slender
hyphae, but a layer of gonidia visible as a white and green film on the rock when the
overlying particles are scaled off.
Darbishire[388] found that attachment to the substratum by means of a basal sheath
was characteristic of all the genera of Roccellaceae. He looks on this sheath, which is
the first stage in the development of the plant, as a primary or proto-thallus, analogous
to the primary squamules of the Cladoniae, and he carries the analogy still further by
treating the upright fronds as podetia. The sheath of the Roccellaceae varies in size but
it is always of very limited extent; it is mainly composed of medullary hyphae, and
gonidia may or may not be present. The whole structure is permanent and important,
and is generally protected by a well-developed upper cortex similar in structure to that
of the upright thallus, i.e. of a fastigiate type. There is no lower cortex.
The two British species of Roccella—R. fuciformis and R. phycopsis—grow on
maritime rocks, the latter also occasionally on trees. In R. fuciformis, the attaching
sheath is a flat structure which slopes up a little round the base of the upright frond. It
is about 2 mm. thick, the cortex occupying about 40 µ of that space; a few scattered
gonidia are present immediately below. The remaining tissue of the sheath is
composed of firmly wefted slender filaments. Towards the lower surface, there is a
more closely compacted dark brown layer from which pass out the hyphae that
penetrate the rock.
The sheath of R. phycopsis is a small structure about 3 to 4 mm. in width and 1·5
mm. thick. A few gonidia may be found below the dense cortical layer, but they tend
to disappear as the upright fronds become larger and the shade, in consequence, more
dense. Lower down the hyphae take an intensely yellow hue; mixed with them are
also some brown filaments. A somewhat larger sheath 7 to 8 mm. wide forms the base
of R. tinctoria. In structure it corresponds—as do those of the other species—with the
ones already described.
In purely filamentous species such as Usnea there is also primary sheath formation:
the medullary hyphae spread out in radiating strands which force their way wherever
possible into the underlying substance; on trees they enter into any chink or crevice of
the outer bark like wedges; or they ramify between the cork cells which are split up by
are continuous with the base and are thus securely anchored to the substratum.
On a smooth rock surface such as quartzite a continuous sward of Ramalina growth
is impossible. The basal hyphae being unable to penetrate the even surface of the rock,
the attachment is slight and the plants are easily dislodged. They do however succeed,
sometimes, in taking hold, and small groups of fronds arise from a crustaceous base
which varies in depth from ·5 to 1 mm. The tissues of this base are very irregularly
arranged: towards the upper surface loose hyphae with scattered groups of algae are
traversed by strands of gelatinized sclerotic hyphae similar to the strengthening tissues
of the upright fronds, while down below there are to be found not only slender
hyphae, but a layer of gonidia visible as a white and green film on the rock when the
overlying particles are scaled off.
Darbishire[388] found that attachment to the substratum by means of a basal sheath
was characteristic of all the genera of Roccellaceae. He looks on this sheath, which is
the first stage in the development of the plant, as a primary or proto-thallus, analogous
to the primary squamules of the Cladoniae, and he carries the analogy still further by
treating the upright fronds as podetia. The sheath of the Roccellaceae varies in size but
it is always of very limited extent; it is mainly composed of medullary hyphae, and
gonidia may or may not be present. The whole structure is permanent and important,
and is generally protected by a well-developed upper cortex similar in structure to that
of the upright thallus, i.e. of a fastigiate type. There is no lower cortex.
The two British species of Roccella—R. fuciformis and R. phycopsis—grow on
maritime rocks, the latter also occasionally on trees. In R. fuciformis, the attaching
sheath is a flat structure which slopes up a little round the base of the upright frond. It
is about 2 mm. thick, the cortex occupying about 40 µ of that space; a few scattered
gonidia are present immediately below. The remaining tissue of the sheath is
composed of firmly wefted slender filaments. Towards the lower surface, there is a
more closely compacted dark brown layer from which pass out the hyphae that
penetrate the rock.
The sheath of R. phycopsis is a small structure about 3 to 4 mm. in width and 1·5
mm. thick. A few gonidia may be found below the dense cortical layer, but they tend
to disappear as the upright fronds become larger and the shade, in consequence, more
dense. Lower down the hyphae take an intensely yellow hue; mixed with them are
also some brown filaments. A somewhat larger sheath 7 to 8 mm. wide forms the base
of R. tinctoria. In structure it corresponds—as do those of the other species—with the
ones already described.
In purely filamentous species such as Usnea there is also primary sheath formation:
the medullary hyphae spread out in radiating strands which force their way wherever
possible into the underlying substance; on trees they enter into any chink or crevice of
the outer bark like wedges; or they ramify between the cork cells which are split up by
Page 171
the mere growth pressure. By the vertical increase of the base, the fronds may be
hoisted up and an intercalary basal portion may arise lacking both gonidia and cortical
layer. Very frequently several bases are united and the lichen appears to be of tufted
habit.
A basal sheath provides a similar firm attachment for Alectoria jubata and allied
species: these are slender mostly dark brown lichens which hang in tangled filaments
from the branches of trees, rocks, etc.
These attaching sheaths differ in function as well as in structure from the horizontal
thallus of the Cladoniaceae. They may be more truly compared with the primary
thallus of the red algae Dumontia and Phyllophora which are similarly affixed to the
substratum, while upright fronds of subsequent formation bear the fructifications.
IV. STRATOSE-RADIATE THALLUS
1. STRATOSE OR PRIMARY THALLUS
A. General Characteristics
This series includes the lichens of one family only, the
Cladoniaceae, the genera of which are characterized by the
twofold thallus, one portion being primary, horizontal and
stratose, the other secondary and radiate, the latter an
upright simple or branching structure termed a “podetium”
which narrows above, or widens to form a trumpet-shaped
cup or “scyphus” (Fig. 66). The apothecia are terminal on
the podetium or on the margins of the scyphi; in a few
species they are developed on the primary thallus. Some
degree of primary thallus-formation has been
demonstrated in all the genera, if not in all the species of
the family. The genus Cladina was established to include
those species of Cladonia in which, it was believed, only a Fig. 66. Cladonia pyxidata
[389] Hoffm. Basal squamule and
secondary podetial thallus was present, but Wainio podetium. a, apothecia; s,
found in Cladonia sylvatica a granular basal crust and, in spermogonia (after Krabbe).
Cladonia uncialis, minute round scales with crenate
margins measuring from ·5 to 1 mm. in width. In some
species (subgenus Cladina) the primary thallus is quickly evanescent, in others it is
granular or squamulose and persistent. Where the basal thallus is so much reduced as
to be practically non-existent, apothecia are rarely developed and soredia are absent.
Renewal of growth in these lichens is secured by the dispersal of fragments of the
podetial thallus; they are torn off and scattered by the wind or by animals, and, if
suitable conditions are met, a new plant arises.
hoisted up and an intercalary basal portion may arise lacking both gonidia and cortical
layer. Very frequently several bases are united and the lichen appears to be of tufted
habit.
A basal sheath provides a similar firm attachment for Alectoria jubata and allied
species: these are slender mostly dark brown lichens which hang in tangled filaments
from the branches of trees, rocks, etc.
These attaching sheaths differ in function as well as in structure from the horizontal
thallus of the Cladoniaceae. They may be more truly compared with the primary
thallus of the red algae Dumontia and Phyllophora which are similarly affixed to the
substratum, while upright fronds of subsequent formation bear the fructifications.
IV. STRATOSE-RADIATE THALLUS
1. STRATOSE OR PRIMARY THALLUS
A. General Characteristics
This series includes the lichens of one family only, the
Cladoniaceae, the genera of which are characterized by the
twofold thallus, one portion being primary, horizontal and
stratose, the other secondary and radiate, the latter an
upright simple or branching structure termed a “podetium”
which narrows above, or widens to form a trumpet-shaped
cup or “scyphus” (Fig. 66). The apothecia are terminal on
the podetium or on the margins of the scyphi; in a few
species they are developed on the primary thallus. Some
degree of primary thallus-formation has been
demonstrated in all the genera, if not in all the species of
the family. The genus Cladina was established to include
those species of Cladonia in which, it was believed, only a Fig. 66. Cladonia pyxidata
[389] Hoffm. Basal squamule and
secondary podetial thallus was present, but Wainio podetium. a, apothecia; s,
found in Cladonia sylvatica a granular basal crust and, in spermogonia (after Krabbe).
Cladonia uncialis, minute round scales with crenate
margins measuring from ·5 to 1 mm. in width. In some
species (subgenus Cladina) the primary thallus is quickly evanescent, in others it is
granular or squamulose and persistent. Where the basal thallus is so much reduced as
to be practically non-existent, apothecia are rarely developed and soredia are absent.
Renewal of growth in these lichens is secured by the dispersal of fragments of the
podetial thallus; they are torn off and scattered by the wind or by animals, and, if
suitable conditions are met, a new plant arises.
Page 172
Cladonia squamules vary in size from very small scales as in Cl. uncialis to the
fairly large foliose fronds of Cl. foliacea which extend to 5 cm. in length and about 1
cm. or more in width. It is interesting to note that when the primary thallus is well
developed, the podetia are relatively unimportant and frequently are not formed. As a
rule the squamules are rounded or somewhat elongate in form with entire or variously
cut and crenate margins. They may be very insignificant and sparsely scattered over
the substratum, or massed in crowded swards of leaflets which are frequently almost
upright. In colour they are bluish-grey, yellowish or brownish above, and white
beneath (red in Cl. miniata), frequently becoming very dark-coloured towards the
rooting base. These several characteristics are specific and are often of considerable
value in diagnosis. In certain conditions of shade or moisture, squamules are formed
on the podetium; they repeat the characters of the basal squamules of the species.
B. Tissues of the Primary Thallus
The stratose layers of tissue in the squamules of Cladonia are arranged as in other
horizontal thalli.
a. Cortical tissue. In nearly all these squamules the cortex is of the “decomposed”
type. In a few species there is a plectenchymatous formation—in Cl. nana, a Brazilian
ground species, and in two New Zealand species, Cl. enantia f. dilatata and Cl. Neo-
Zelandica. The principal growing area is situated all round the margins though
generally there is more activity at the apex. Frequently there is a gradual perishing of
the squamule at the base which counterbalances the forward increase.
The upper surface in some species is cracked into minute areolae; the cracks, seen
in section, penetrate almost to the base of the decomposed gelatinous cortex. They are
largely due to alternate swelling and contraction of the gelatinous surface, or to
extension caused, though rarely, by intercalary growth from the hyphae below. The
surface is subject to weathering and peeling as in other lichens; but the loss is
constantly repaired by the upward growth of the meristematic hyphae from the
gonidial zone; they push up between the older cortical filaments and so provide for the
expansion as well as for the renewal of the cortical tissue.
b. Gonidial tissue. The gonidia consisting of Protococcaceous algae form a layer
immediately below the cortex. Isolated green cells are not unfrequently carried up by
the growing hyphae into the cortical region, but they do not long survive in this
compact non-aerated tissue. Their empty membranes can however be picked out by
the blue stain they take with iodine and sulphuric acid.
Krabbe[390] has described the phases of development in the growing region: he
finds that differentiation into pith, gonidial zone and cortex takes place some little
way back from the edge. At the extreme apex the hyphae lie fairly parallel to each
other; further back, they branch upwards to form the cortex, and to separate the
fairly large foliose fronds of Cl. foliacea which extend to 5 cm. in length and about 1
cm. or more in width. It is interesting to note that when the primary thallus is well
developed, the podetia are relatively unimportant and frequently are not formed. As a
rule the squamules are rounded or somewhat elongate in form with entire or variously
cut and crenate margins. They may be very insignificant and sparsely scattered over
the substratum, or massed in crowded swards of leaflets which are frequently almost
upright. In colour they are bluish-grey, yellowish or brownish above, and white
beneath (red in Cl. miniata), frequently becoming very dark-coloured towards the
rooting base. These several characteristics are specific and are often of considerable
value in diagnosis. In certain conditions of shade or moisture, squamules are formed
on the podetium; they repeat the characters of the basal squamules of the species.
B. Tissues of the Primary Thallus
The stratose layers of tissue in the squamules of Cladonia are arranged as in other
horizontal thalli.
a. Cortical tissue. In nearly all these squamules the cortex is of the “decomposed”
type. In a few species there is a plectenchymatous formation—in Cl. nana, a Brazilian
ground species, and in two New Zealand species, Cl. enantia f. dilatata and Cl. Neo-
Zelandica. The principal growing area is situated all round the margins though
generally there is more activity at the apex. Frequently there is a gradual perishing of
the squamule at the base which counterbalances the forward increase.
The upper surface in some species is cracked into minute areolae; the cracks, seen
in section, penetrate almost to the base of the decomposed gelatinous cortex. They are
largely due to alternate swelling and contraction of the gelatinous surface, or to
extension caused, though rarely, by intercalary growth from the hyphae below. The
surface is subject to weathering and peeling as in other lichens; but the loss is
constantly repaired by the upward growth of the meristematic hyphae from the
gonidial zone; they push up between the older cortical filaments and so provide for the
expansion as well as for the renewal of the cortical tissue.
b. Gonidial tissue. The gonidia consisting of Protococcaceous algae form a layer
immediately below the cortex. Isolated green cells are not unfrequently carried up by
the growing hyphae into the cortical region, but they do not long survive in this
compact non-aerated tissue. Their empty membranes can however be picked out by
the blue stain they take with iodine and sulphuric acid.
Krabbe[390] has described the phases of development in the growing region: he
finds that differentiation into pith, gonidial zone and cortex takes place some little
way back from the edge. At the extreme apex the hyphae lie fairly parallel to each
other; further back, they branch upwards to form the cortex, and to separate the
Page 173
masses of multiplying gonidia, by pushing between them and so spreading them
through the whole apical tissue. The gonidia immediately below the upper cortex,
where they are well-lighted, continue to increase and gradually form into the gonidial
zone; those that lie deeper among the medullary hyphae remain quiescent, and before
long disappear altogether.
Where the squamules assume the upright position (as in Cladonia cervicornis),
there is a tendency for the gonidia to pass round to the lower surface, and soredia are
occasionally formed.
c. Medullary tissue. The hyphae of the medulla are described by Wainio as having
long cells with narrow lumen, and as being encrusted with granulations that may
coalesce into more or less detachable granules; in colour they are mostly white, but
pale-yellow in Cl. foliacea and blood-red in Cl. miniata, a subtropical species. They
are connected at the base of the squamules with a filamentous hypothallus which
penetrates the substratum and attaches the plant. In a few species rhizinae are formed,
while in others the hyphae of the podetium grow downwards, towards and into the
substratum as a short stout rhizoid.
d. Soredia. Though frequent on the podetia, soredia are rare on the squamules, and,
according to Wainio[391], always originate at the growing region, from which they
spread over the under surface—rather sparsely in Cl. cariosa, Cl. squamosa, etc., but
abundantly in Cl. digitata and a few others. In some instances, they develop further
into small corticate areolae on the under surface (Cl. coccifera, Cl. pyxidata and Cl.
squamosa).
2. RADIATE OR SECONDARY THALLUS
A. Origin of the Podetium
The upright podetium, as described by Wainio[392] and by Krabbe[393], is a
secondary product of the basal granule or squamule. It is developed from the hyphae
of the gonidial zone, generally where a crack has occurred in the cortex and rather
close to the base or more rarely on or near the edge of the squamule (Cl. verticillata,
etc.). At these areas, certain meristematic gonidial hyphae increase and unite to form a
strand of filaments below the upper cortex but above the gonidial layer, the latter
remaining for a time undisturbed as to the arrangement of the algal cells.
This initial tissue—the primordium of the podetium—continues to grow not only in
width but in length: the basal portion grows downwards and at length displaces the
gonidial zone, while the upper part as a compact cylinder forces its way through the
cortex above, the cortical tissue, however, taking no part in its formation; as it
advances, the edges of the gonidial and cortical zones bend upwards and form a sheath
distinguishable for some time round the base of the emerging podetium.
through the whole apical tissue. The gonidia immediately below the upper cortex,
where they are well-lighted, continue to increase and gradually form into the gonidial
zone; those that lie deeper among the medullary hyphae remain quiescent, and before
long disappear altogether.
Where the squamules assume the upright position (as in Cladonia cervicornis),
there is a tendency for the gonidia to pass round to the lower surface, and soredia are
occasionally formed.
c. Medullary tissue. The hyphae of the medulla are described by Wainio as having
long cells with narrow lumen, and as being encrusted with granulations that may
coalesce into more or less detachable granules; in colour they are mostly white, but
pale-yellow in Cl. foliacea and blood-red in Cl. miniata, a subtropical species. They
are connected at the base of the squamules with a filamentous hypothallus which
penetrates the substratum and attaches the plant. In a few species rhizinae are formed,
while in others the hyphae of the podetium grow downwards, towards and into the
substratum as a short stout rhizoid.
d. Soredia. Though frequent on the podetia, soredia are rare on the squamules, and,
according to Wainio[391], always originate at the growing region, from which they
spread over the under surface—rather sparsely in Cl. cariosa, Cl. squamosa, etc., but
abundantly in Cl. digitata and a few others. In some instances, they develop further
into small corticate areolae on the under surface (Cl. coccifera, Cl. pyxidata and Cl.
squamosa).
2. RADIATE OR SECONDARY THALLUS
A. Origin of the Podetium
The upright podetium, as described by Wainio[392] and by Krabbe[393], is a
secondary product of the basal granule or squamule. It is developed from the hyphae
of the gonidial zone, generally where a crack has occurred in the cortex and rather
close to the base or more rarely on or near the edge of the squamule (Cl. verticillata,
etc.). At these areas, certain meristematic gonidial hyphae increase and unite to form a
strand of filaments below the upper cortex but above the gonidial layer, the latter
remaining for a time undisturbed as to the arrangement of the algal cells.
This initial tissue—the primordium of the podetium—continues to grow not only in
width but in length: the basal portion grows downwards and at length displaces the
gonidial zone, while the upper part as a compact cylinder forces its way through the
cortex above, the cortical tissue, however, taking no part in its formation; as it
advances, the edges of the gonidial and cortical zones bend upwards and form a sheath
distinguishable for some time round the base of the emerging podetium.
Page 174
Even when the primary horizontal thallus is merely crustaceous, the podetia take
origin similarly from a subcortical weft of hyphae in an areola or granule.
B. Structure of the Podetium
a. General structure. In the early stages of development the podetium is solid
throughout, two layers of tissue being discernible—the hyphae forming the centre of
the cylinder being thick-walled and closely compacted, and the hyphae on the exterior
loosely branching with numerous air-spaces between the filaments.
In all species, with the exception of Cl. solida, which remains solid during the life
of the plant, a central cavity arises while the podetium is still quite short (about 1 to
1·5 mm. in Cl. pyxidata and Cl. degenerans). The first indication of the opening is a
narrow split in the internal cylinder, due to the difference in growth tension between
the more free and rapid increase of the external medullary layer and the slower
elongation of the chondroid tissue at the centre. The cavity gradually widens and
becomes more completely tubular with the upward growth of the podetium; it is lined
by the chondroid sclerotic band which supports the whole structure (Fig. 67).
b. Gonidial tissue. In most species of Cladoniaceae, a layer of gonidial tissue forms
a more or less continuous outer covering of the podetium, thus distinguishing it from
the purely hyphal stalks of the apothecia in Caliciaceae. Even in the genus Baeomyces,
while the podetia of some of the species are without gonidia, neighbouring species are
provided with green cells on the upright stalks clearly showing their true affinity with
the Cladoniae. In one British species of Cladonia (Cl. caespiticia) the short podetium
consists only of the fibrous chondroid cylinder, and thus resembles the apothecial
stalk of Baeomyces rufus, but in that species also there are occasional surface gonidia
that may give rise to squamules.
origin similarly from a subcortical weft of hyphae in an areola or granule.
B. Structure of the Podetium
a. General structure. In the early stages of development the podetium is solid
throughout, two layers of tissue being discernible—the hyphae forming the centre of
the cylinder being thick-walled and closely compacted, and the hyphae on the exterior
loosely branching with numerous air-spaces between the filaments.
In all species, with the exception of Cl. solida, which remains solid during the life
of the plant, a central cavity arises while the podetium is still quite short (about 1 to
1·5 mm. in Cl. pyxidata and Cl. degenerans). The first indication of the opening is a
narrow split in the internal cylinder, due to the difference in growth tension between
the more free and rapid increase of the external medullary layer and the slower
elongation of the chondroid tissue at the centre. The cavity gradually widens and
becomes more completely tubular with the upward growth of the podetium; it is lined
by the chondroid sclerotic band which supports the whole structure (Fig. 67).
b. Gonidial tissue. In most species of Cladoniaceae, a layer of gonidial tissue forms
a more or less continuous outer covering of the podetium, thus distinguishing it from
the purely hyphal stalks of the apothecia in Caliciaceae. Even in the genus Baeomyces,
while the podetia of some of the species are without gonidia, neighbouring species are
provided with green cells on the upright stalks clearly showing their true affinity with
the Cladoniae. In one British species of Cladonia (Cl. caespiticia) the short podetium
consists only of the fibrous chondroid cylinder, and thus resembles the apothecial
stalk of Baeomyces rufus, but in that species also there are occasional surface gonidia
that may give rise to squamules.
Page 175
Fig. 67. Cladonia squamosa Hoffm.
Vertical section of podetium with early
stage of central tube and of podetial
squamules × 100 (after Krabbe).
Krabbe[394] concluded from his observations that the podetial gonidia of Cladonia
arrived from the open, conveyed by wind, water or insects from the loose soredia that
are generally so plentiful in any Cladonia colony. They alighted, he held, on the
growing stalks and, being secured by the free-growing ends of the exterior hyphae,
they increased and became an integral part of the podetium. In more recent times
Baur[395] has recalled and supported Krabbe’s view, but Wainio[396], on the contrary,
claims to have proved that in the earliest stages of the podetium the gonidia were
already present, having been carried up from the gonidial zone of the primary thallus
by the primordial hyphae. Increase of these green cells follows normally by cell-
division or sporulation.
Algal cells have been found to be common to different lichens, but in Cladoniae
Chodat[397] claims to have proved by cultures that each species tested has a special
gonidium, determined by him as a species of Cystococcus, which would render
colonization by algae from the open much less probable. In addition, the fungal
hyphae are specific, and any soredia (with their combined symbionts) that alighted on
the podetium could only be utilized if they originated from the same species; or, if
they were incorporated, the hyphae belonging to any other species would of necessity
die off and be replaced by those of the podetium.
Vertical section of podetium with early
stage of central tube and of podetial
squamules × 100 (after Krabbe).
Krabbe[394] concluded from his observations that the podetial gonidia of Cladonia
arrived from the open, conveyed by wind, water or insects from the loose soredia that
are generally so plentiful in any Cladonia colony. They alighted, he held, on the
growing stalks and, being secured by the free-growing ends of the exterior hyphae,
they increased and became an integral part of the podetium. In more recent times
Baur[395] has recalled and supported Krabbe’s view, but Wainio[396], on the contrary,
claims to have proved that in the earliest stages of the podetium the gonidia were
already present, having been carried up from the gonidial zone of the primary thallus
by the primordial hyphae. Increase of these green cells follows normally by cell-
division or sporulation.
Algal cells have been found to be common to different lichens, but in Cladoniae
Chodat[397] claims to have proved by cultures that each species tested has a special
gonidium, determined by him as a species of Cystococcus, which would render
colonization by algae from the open much less probable. In addition, the fungal
hyphae are specific, and any soredia (with their combined symbionts) that alighted on
the podetium could only be utilized if they originated from the same species; or, if
they were incorporated, the hyphae belonging to any other species would of necessity
die off and be replaced by those of the podetium.
Page 176
c. Cortical tissue. In some species a cortex of the decomposed type of thick-walled
conglutinate hyphae is present, either continuous over the whole surface of the
podetium, as in Cl. gracilis (Fig. 68), or in interrupted areas or granules as in Cl.
pyxidata (Fig. 69) and others. In Cl. degenerans, the spaces between the corticated
areolae are filled in by loose filaments without any green cells. Cl. rangiferina, Cl.
sylvatica, etc. are non-corticate, being covered all over with a loose felt of intricate
hyphae.
conglutinate hyphae is present, either continuous over the whole surface of the
podetium, as in Cl. gracilis (Fig. 68), or in interrupted areas or granules as in Cl.
pyxidata (Fig. 69) and others. In Cl. degenerans, the spaces between the corticated
areolae are filled in by loose filaments without any green cells. Cl. rangiferina, Cl.
sylvatica, etc. are non-corticate, being covered all over with a loose felt of intricate
hyphae.
Page 177
Fig. 68. Cladonia gracilis Hoffm. (S. H., Photo.).
Fig. 69. Cladonia pyxidata Hoffm. (S. H., Photo.).
In the section Clathrinae (Cl. retepora, etc.) the cortex is formed of
longitudinal hyphae with thick gelatinous walls.
Fig. 69. Cladonia pyxidata Hoffm. (S. H., Photo.).
In the section Clathrinae (Cl. retepora, etc.) the cortex is formed of
longitudinal hyphae with thick gelatinous walls.
Page 178
d. Soredia. Frequently the podetium is coated in whole or in part by
granules of a sorediate character—coarsely granular in Cl. pyxidata, finely
pulverulent in Cl. fimbriata. Though fairly constant to type in the different
species, they are subject to climatic influences, and, when there is abundant
moisture, both soredia and areolae develop into squamules on the podetium.
A considerable number of species have thus a more or less densely
squamulose “form” or “variety.”
C. Development of the Scyphus
Two types of podetia occur in Cladonia: those that end abruptly and are
crowned when fertile by the apothecia or spermogonia (pycnidia), or if
sterile grow indefinitely tapering gradually to a point (Fig. 70); and those
that widen out into the trumpet-shaped or cup-like expansion called the
scyphus (Fig. 69). Species may be constantly scyphiferous or as constantly
ascyphous; in a few species, and even in individual tufts, both types of
podetium may be present.
Fig. 70. Cladonia furcata Schrad. Sterile thallus (S.H., Photo.).
Wainio[398], who has studied every stage of development in the
Cladoniae, has described the scyphus as originating in several different
ways:
granules of a sorediate character—coarsely granular in Cl. pyxidata, finely
pulverulent in Cl. fimbriata. Though fairly constant to type in the different
species, they are subject to climatic influences, and, when there is abundant
moisture, both soredia and areolae develop into squamules on the podetium.
A considerable number of species have thus a more or less densely
squamulose “form” or “variety.”
C. Development of the Scyphus
Two types of podetia occur in Cladonia: those that end abruptly and are
crowned when fertile by the apothecia or spermogonia (pycnidia), or if
sterile grow indefinitely tapering gradually to a point (Fig. 70); and those
that widen out into the trumpet-shaped or cup-like expansion called the
scyphus (Fig. 69). Species may be constantly scyphiferous or as constantly
ascyphous; in a few species, and even in individual tufts, both types of
podetium may be present.
Fig. 70. Cladonia furcata Schrad. Sterile thallus (S.H., Photo.).
Wainio[398], who has studied every stage of development in the
Cladoniae, has described the scyphus as originating in several different
ways:
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a. From abortive Apothecia. In certain species the apothecium appears at
a very early stage in the development of the podetium of which it occupies
the apical region. Owing to the subsequent formation of the tubular cavity
in the centre of the stalk, the base of the apothecium may eventually lie
directly over the hollow space and, therefore, out of touch with the growing
assimilating tissues; or even before the appearance of the tube, the wide
separation between the primordium of the apothecium and the gonidia,
entailing deficient nutrition, may have produced a similar effect. In either
case central degeneration of the apothecium sets in, and the hypothecial
filaments, having begun to grow radially, continue to travel in the same
direction both outwards and upwards so that gradually a cup-shaped
structure is evolved—the amphithecium of the fruit without the thecium.
The whole or only a part of the apothecium may be abortive, and the
scyphus may therefore be entirely sterile or the fruits may survive at the
edges. The apothecia may even be entirely abortive after a fertile
commencement, but in that case also the primordial hyphae retain the
primitive impulse not only to radial direction, but also to the more copious
branching, and a scyphus is formed as in the previous case. It must also be
borne in mind that the tendency in many Cladonia species to scyphiform
has become hereditary.
Baur[399], in his study of Cl. pyxidata, has taken the view that the origin
of the scyphus was due to a stronger apical growth of the hyphae at the
circumference than over the central tubular portion of the podetium, and
that considerable intercalary growth added to the expanding sides of the
cup.
Scyphi originating from an abortive apothecium are characteristic of
species in which the base is closed (Wainio’s Section Clausae), the tissue in
that case being continuous over the inside of the cup as in Cl. pyxidata, Cl.
coccifera and many others.
b. From polytomous Branching. Another method of scyphus formation
occurs in Cl. amaurocrea and a few other species in which the branching is
polytomous (several members rising from about the same level).
Concrescence of the tissues at the base of these branches produces a
scyphus; it is normally closed by a diaphragm that has spread out from the
a very early stage in the development of the podetium of which it occupies
the apical region. Owing to the subsequent formation of the tubular cavity
in the centre of the stalk, the base of the apothecium may eventually lie
directly over the hollow space and, therefore, out of touch with the growing
assimilating tissues; or even before the appearance of the tube, the wide
separation between the primordium of the apothecium and the gonidia,
entailing deficient nutrition, may have produced a similar effect. In either
case central degeneration of the apothecium sets in, and the hypothecial
filaments, having begun to grow radially, continue to travel in the same
direction both outwards and upwards so that gradually a cup-shaped
structure is evolved—the amphithecium of the fruit without the thecium.
The whole or only a part of the apothecium may be abortive, and the
scyphus may therefore be entirely sterile or the fruits may survive at the
edges. The apothecia may even be entirely abortive after a fertile
commencement, but in that case also the primordial hyphae retain the
primitive impulse not only to radial direction, but also to the more copious
branching, and a scyphus is formed as in the previous case. It must also be
borne in mind that the tendency in many Cladonia species to scyphiform
has become hereditary.
Baur[399], in his study of Cl. pyxidata, has taken the view that the origin
of the scyphus was due to a stronger apical growth of the hyphae at the
circumference than over the central tubular portion of the podetium, and
that considerable intercalary growth added to the expanding sides of the
cup.
Scyphi originating from an abortive apothecium are characteristic of
species in which the base is closed (Wainio’s Section Clausae), the tissue in
that case being continuous over the inside of the cup as in Cl. pyxidata, Cl.
coccifera and many others.
b. From polytomous Branching. Another method of scyphus formation
occurs in Cl. amaurocrea and a few other species in which the branching is
polytomous (several members rising from about the same level).
Concrescence of the tissues at the base of these branches produces a
scyphus; it is normally closed by a diaphragm that has spread out from the
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different bases, but frequently there is a perforation due to stretching. These
species belong to the Section Perviae.
c. From arrested Growth. In most cases however where the scyphus is
open as in Cl. furcata, Cl. squamosa, etc., development of the cup follows
on cessation of growth, or on perforation at the summit of the podetium.
Round this quiescent portion there rises a circle of minute prominences
which carry on the apical development. As they increase in size, the spaces
between them are bridged over by lateral growth, and the scyphus thus
formed is large or small according to the number of these outgrowths.
Apothecia or spermogonia may be produced at their tips, or the vegetative
development may continue. Scyphi formed in this manner are also open or
“pervious.”
d. Gonidia of the Scyphus. Gonidia are absent in the early stages of
scyphus formation when it arises from degeneration of the apical tissues,
either fertile or vegetative; but gradually they migrate from the podetium,
from the base of young outgrowths, or by furrows at the edge, and so spread
over the surface of the cup. Soredia may possibly alight, as Krabbe insists
that they do, and may aid in colonizing the naked area. Their presence,
however, would only be accidental; they are not essential, and scyphi are
formed in many non-sorediate species such as Cl. verticillata. The cortex of
the scyphus becomes in the end continuous with that of the podetium and is
always similar in type.
e. Species without Scyphi. In species where the whole summit of the
podetium is occupied by an apothecium, as in Cl. bellidiflora, no scyphus is
formed. There is also an absence of scyphi in podetia that taper to a point.
In those podetia the hyphae are parallel to the long axis and remain in
connection with the external gonidial layer so that they are unaffected by
the central cavity. Instances of tapering growth are also to be found in
species that are normally scyphiferous such as Cl. fimbriata subsp. fibula,
and Cl. cornuta, as well as in species like Cl. rangiferina that are constantly
ascyphous.
The scyphus is considered by Wainio[400] to represent an advanced stage
of development in the species or in the individual, and any conditions that
act unfavourably on growth, such as excessive dryness, would also hinder
the formation of this peculiar lichen structure.
species belong to the Section Perviae.
c. From arrested Growth. In most cases however where the scyphus is
open as in Cl. furcata, Cl. squamosa, etc., development of the cup follows
on cessation of growth, or on perforation at the summit of the podetium.
Round this quiescent portion there rises a circle of minute prominences
which carry on the apical development. As they increase in size, the spaces
between them are bridged over by lateral growth, and the scyphus thus
formed is large or small according to the number of these outgrowths.
Apothecia or spermogonia may be produced at their tips, or the vegetative
development may continue. Scyphi formed in this manner are also open or
“pervious.”
d. Gonidia of the Scyphus. Gonidia are absent in the early stages of
scyphus formation when it arises from degeneration of the apical tissues,
either fertile or vegetative; but gradually they migrate from the podetium,
from the base of young outgrowths, or by furrows at the edge, and so spread
over the surface of the cup. Soredia may possibly alight, as Krabbe insists
that they do, and may aid in colonizing the naked area. Their presence,
however, would only be accidental; they are not essential, and scyphi are
formed in many non-sorediate species such as Cl. verticillata. The cortex of
the scyphus becomes in the end continuous with that of the podetium and is
always similar in type.
e. Species without Scyphi. In species where the whole summit of the
podetium is occupied by an apothecium, as in Cl. bellidiflora, no scyphus is
formed. There is also an absence of scyphi in podetia that taper to a point.
In those podetia the hyphae are parallel to the long axis and remain in
connection with the external gonidial layer so that they are unaffected by
the central cavity. Instances of tapering growth are also to be found in
species that are normally scyphiferous such as Cl. fimbriata subsp. fibula,
and Cl. cornuta, as well as in species like Cl. rangiferina that are constantly
ascyphous.
The scyphus is considered by Wainio[400] to represent an advanced stage
of development in the species or in the individual, and any conditions that
act unfavourably on growth, such as excessive dryness, would also hinder
the formation of this peculiar lichen structure.
Page 181
D. Branching of the Podetium
Though branching is a constant feature in many species, regular
dichotomy is rare: more often there is an irregular form of polytomy in
which one of the members grows more vigorously than the others and
branches again, so that a kind of sympodium arises, as in Cl. rangiferina,
Cl. sylvatica, etc.
Adventitious branches may also arise from the podetium, owing to some
disturbance of the normal growth, some undue exposure to wind or to too
great light, or owing to some external injury. They originate from the
gonidial tissue in the same way as does the podetium from the primary
thallus; the parallel hyphae of the main axis take no part in their
development.
In a number of species secondary podetia arise from the centre of the
scyphus—constantly in Cl. verticillata and Cl. cervicornis, etc.,
accidentally or rarely in Cl. foliacea, Cl. pyxidata, Cl. fimbriata, etc.
Wainio[401] has stated that they arise when the scyphus is already at an
advanced stage of growth and that they are to be regarded as adventitious
branches.
The proliferations from the borders of the scyphus are in a different
category. They represent the continuity of apical growth, as the edges of the
scyphus are but an enlarged apex. These marginal proliferations thus
correspond to polytomous branching. In many instances their advance is
soon stopped by the formation of an apothecium and they figure more as
fruit stalks than as podetial branches.
E. Perforations and Reticulation of the Podetium
Perforations in the podetial wall at the axils of the branches are constant
in certain species such as Cl. rangiferina, Cl. uncialis, etc. They are caused
by the tension of the branches as they emerge from the main stalk. A tearing
of the tissue may also arise in the base of the scyphus, due to its increase in
size, which causes the splitting of the diaphragm at the bottom of the cup.
Among the Cladoniae the reticulate condition recurs now and again. In
our native Cladonia cariosa the splitting of the podetial wall is a constant
Though branching is a constant feature in many species, regular
dichotomy is rare: more often there is an irregular form of polytomy in
which one of the members grows more vigorously than the others and
branches again, so that a kind of sympodium arises, as in Cl. rangiferina,
Cl. sylvatica, etc.
Adventitious branches may also arise from the podetium, owing to some
disturbance of the normal growth, some undue exposure to wind or to too
great light, or owing to some external injury. They originate from the
gonidial tissue in the same way as does the podetium from the primary
thallus; the parallel hyphae of the main axis take no part in their
development.
In a number of species secondary podetia arise from the centre of the
scyphus—constantly in Cl. verticillata and Cl. cervicornis, etc.,
accidentally or rarely in Cl. foliacea, Cl. pyxidata, Cl. fimbriata, etc.
Wainio[401] has stated that they arise when the scyphus is already at an
advanced stage of growth and that they are to be regarded as adventitious
branches.
The proliferations from the borders of the scyphus are in a different
category. They represent the continuity of apical growth, as the edges of the
scyphus are but an enlarged apex. These marginal proliferations thus
correspond to polytomous branching. In many instances their advance is
soon stopped by the formation of an apothecium and they figure more as
fruit stalks than as podetial branches.
E. Perforations and Reticulation of the Podetium
Perforations in the podetial wall at the axils of the branches are constant
in certain species such as Cl. rangiferina, Cl. uncialis, etc. They are caused
by the tension of the branches as they emerge from the main stalk. A tearing
of the tissue may also arise in the base of the scyphus, due to its increase in
size, which causes the splitting of the diaphragm at the bottom of the cup.
Among the Cladoniae the reticulate condition recurs now and again. In
our native Cladonia cariosa the splitting of the podetial wall is a constant
Page 182
character of the species, the carious condition being caused by unequal
growth which tears apart the longitudinal fibres that surround the central
hollow.
A more advanced type of reticulation arises in the group of the
Clathrinae in which there is no inner chondroid cylinder. In Cladonia
aggregata, in which the perforations are somewhat irregular, two types of
podetia have been described by Lindsay[402] from Falkland Island
specimens: those bearing apothecia are short and broad, fastigiately
branched upwards and with reticulate perforations, while podetia bearing
spermogonia are slender, elongate and branched, with fewer reticulations.
An imperfect network is also characteristic of Cl. Sullivani, a Brazilian
species. But the most marvellous and regular form of reticulation occurs in
Cl. retepora, an Australian lichen (Fig. 71): towards the tips of the podetia
the ellipsoid meshes are small, but they gradually become larger towards
the base. In this species the outer tissue, though of parallel hyphae, is
closely interwoven and forms a continuous growth at the edges of the
perforations, giving an unbroken smooth surface and checking any irregular
tearing. The enlargement of the walls is solely due to intercalary growth.
The origin of the reticulate structure in the Clathrinae is unknown, though it
is doubtless associated with wide podetia and rendered possible by the
absence of an internal chondroid layer. The reticulate structure is
marvellously adapted for the absorption of water: Cl. retepora, more
especially, imbibes and holds moisture like a sponge.
growth which tears apart the longitudinal fibres that surround the central
hollow.
A more advanced type of reticulation arises in the group of the
Clathrinae in which there is no inner chondroid cylinder. In Cladonia
aggregata, in which the perforations are somewhat irregular, two types of
podetia have been described by Lindsay[402] from Falkland Island
specimens: those bearing apothecia are short and broad, fastigiately
branched upwards and with reticulate perforations, while podetia bearing
spermogonia are slender, elongate and branched, with fewer reticulations.
An imperfect network is also characteristic of Cl. Sullivani, a Brazilian
species. But the most marvellous and regular form of reticulation occurs in
Cl. retepora, an Australian lichen (Fig. 71): towards the tips of the podetia
the ellipsoid meshes are small, but they gradually become larger towards
the base. In this species the outer tissue, though of parallel hyphae, is
closely interwoven and forms a continuous growth at the edges of the
perforations, giving an unbroken smooth surface and checking any irregular
tearing. The enlargement of the walls is solely due to intercalary growth.
The origin of the reticulate structure in the Clathrinae is unknown, though it
is doubtless associated with wide podetia and rendered possible by the
absence of an internal chondroid layer. The reticulate structure is
marvellously adapted for the absorption of water: Cl. retepora, more
especially, imbibes and holds moisture like a sponge.
Page 183
Fig. 71. Cladonia retepora Fr. From Tasmania.
F. Rooting Structures of Cladoniae
The squamules of the primary thallus are attached, as are most
squamules, to the supporting substance by strands of hyphae which may be
combined into simple or branching rhizinae and penetrate the soil or the
wood on which the lichen grows. There is frequently but one of these
rooting structures and it branches repeatedly until the ultimate branchlets
end in delicate mycelium. Generally they are grey or brown and are not
easily traced, but when they are orange-coloured, as according to
Wainio[403] they frequently are in Cladonia miniata and Cl. digitata, they
are more readily observed, especially if the habitat be a mossy one.
In Cl. alpicola it has been found that the rooting structure is frequently as
thick as the podetium itself. If the podetium originates from the basal
portion of the squamule, the hyphae from the chondroid layer, surrounding
the hollow centre, take a downward direction and become continuous with
the rhizoid. Should the point of insertion be near the apex of the squamule,
these hyphae form a nerve within the squamule or along the under surface,
and finally also unite with the rhizoid at the base, a form of rooting
characteristic of Cl. cartilaginea, Cl. digitata and several other species.
Mycelium may spread from the rhizinae along the surface of the
substratum and give rise to new squamules and new tufts of podetia, a
method of reproduction that is of considerable importance in species that
are generally sterile and that form no soredia.
Many species, especially those of the section Cladina, soon lose all
connection with the substratum, there being a continual decay of the lower
part of the podetia. As apical growth may continue for centuries, the
perishing of the base is not to be wondered at.
G. Haptera
The presence of haptera in Cladoniae has already been alluded to. They
occur usually in the form of cilia or rhizinae[404], but differ from the latter in
their more simple regular growth being composed of conglutinate parallel
hyphae. They arise on the edges of the squamules or of the scyphus, but in
F. Rooting Structures of Cladoniae
The squamules of the primary thallus are attached, as are most
squamules, to the supporting substance by strands of hyphae which may be
combined into simple or branching rhizinae and penetrate the soil or the
wood on which the lichen grows. There is frequently but one of these
rooting structures and it branches repeatedly until the ultimate branchlets
end in delicate mycelium. Generally they are grey or brown and are not
easily traced, but when they are orange-coloured, as according to
Wainio[403] they frequently are in Cladonia miniata and Cl. digitata, they
are more readily observed, especially if the habitat be a mossy one.
In Cl. alpicola it has been found that the rooting structure is frequently as
thick as the podetium itself. If the podetium originates from the basal
portion of the squamule, the hyphae from the chondroid layer, surrounding
the hollow centre, take a downward direction and become continuous with
the rhizoid. Should the point of insertion be near the apex of the squamule,
these hyphae form a nerve within the squamule or along the under surface,
and finally also unite with the rhizoid at the base, a form of rooting
characteristic of Cl. cartilaginea, Cl. digitata and several other species.
Mycelium may spread from the rhizinae along the surface of the
substratum and give rise to new squamules and new tufts of podetia, a
method of reproduction that is of considerable importance in species that
are generally sterile and that form no soredia.
Many species, especially those of the section Cladina, soon lose all
connection with the substratum, there being a continual decay of the lower
part of the podetia. As apical growth may continue for centuries, the
perishing of the base is not to be wondered at.
G. Haptera
The presence of haptera in Cladoniae has already been alluded to. They
occur usually in the form of cilia or rhizinae[404], but differ from the latter in
their more simple regular growth being composed of conglutinate parallel
hyphae. They arise on the edges of the squamules or of the scyphus, but in
Page 184
Cl. foliacea and Cl. ceratophylla they are formed at the points of the
podetial branches (more rarely in Cl. cervicornis and Cl. gracilis). By the
aid of these rhizinose haptera the squamule or branch becomes attached to
any substance within reach. They also aid in the production of new
individuals by anchoring some fragment of the thallus to a support until it
has grown to independent existence and has produced new rhizinae or hold-
fasts. They are a very prominent feature of Cl. verticillaris f. penicillata in
which they form a thick fringe on the edges of the squamules, or frequently
grow out as branched cilia from the proliferations on the margins of the
scyphus.
H. Morphology of the Podetium
In the above account, the podetia have been treated as part of the
vegetative thallus, seeing that, partly or entirely, they are assimilative and
absorptive organs. This view does not, however, take into account their
origin and development, in consideration of which Wainio[405] and later
Krabbe[406] considered them as part of the sporiferous organ. This view was
also held by some of the earliest lichenologists: Necker[407], for instance,
constantly referred to the upright structure as “stipes”; Persoon[408] included
it, under the term “pedunculus,” as part of the “inflorescence” of the lichen,
and Acharius[409] established the name “podetium” to describe the stalk of
the apothecium in Baeomyces.
Later lichenologists, such as Wallroth[410], looked on the podetia as
advanced stages of the thallus, or as forming a supplementary thallus.
Tulasne[411] described them as branching upright processes from the
horizontal form, and Koerber[412] considered them as the true thallus, the
primary squamule being merely a protothallus. By them and by succeeding
students of lichens the twofold character of the thallus was accepted until
Wainio and Krabbe by their more exact researches discovered the
endogenous origin of the podetium, which they considered was conclusive
evidence of its apothecial character: they claimed that the primordium of
the podetium was homologous with the primordium of the apothecium.
Reinke[413] and Wainio are in accord with Krabbe as to the probable
morphological significance of the podetium, but they both insist on its
modified thalline character. Wainio sums up that: “the podetium is an
podetial branches (more rarely in Cl. cervicornis and Cl. gracilis). By the
aid of these rhizinose haptera the squamule or branch becomes attached to
any substance within reach. They also aid in the production of new
individuals by anchoring some fragment of the thallus to a support until it
has grown to independent existence and has produced new rhizinae or hold-
fasts. They are a very prominent feature of Cl. verticillaris f. penicillata in
which they form a thick fringe on the edges of the squamules, or frequently
grow out as branched cilia from the proliferations on the margins of the
scyphus.
H. Morphology of the Podetium
In the above account, the podetia have been treated as part of the
vegetative thallus, seeing that, partly or entirely, they are assimilative and
absorptive organs. This view does not, however, take into account their
origin and development, in consideration of which Wainio[405] and later
Krabbe[406] considered them as part of the sporiferous organ. This view was
also held by some of the earliest lichenologists: Necker[407], for instance,
constantly referred to the upright structure as “stipes”; Persoon[408] included
it, under the term “pedunculus,” as part of the “inflorescence” of the lichen,
and Acharius[409] established the name “podetium” to describe the stalk of
the apothecium in Baeomyces.
Later lichenologists, such as Wallroth[410], looked on the podetia as
advanced stages of the thallus, or as forming a supplementary thallus.
Tulasne[411] described them as branching upright processes from the
horizontal form, and Koerber[412] considered them as the true thallus, the
primary squamule being merely a protothallus. By them and by succeeding
students of lichens the twofold character of the thallus was accepted until
Wainio and Krabbe by their more exact researches discovered the
endogenous origin of the podetium, which they considered was conclusive
evidence of its apothecial character: they claimed that the primordium of
the podetium was homologous with the primordium of the apothecium.
Reinke[413] and Wainio are in accord with Krabbe as to the probable
morphological significance of the podetium, but they both insist on its
modified thalline character. Wainio sums up that: “the podetium is an
Page 185
apothecial stalk, that is to say an elongation of the conceptacle most
frequently transformed by metamorphosis to a vertical thallus, though
visibly retaining its stalk character.” Sättler[414], one of the most recent
students of Cladonia, regards the podetium as evolved with reference to
spore-dissemination, and therefore of apothecial character. His views are
described and discussed in the chapter on phylogeny.
Reinke and others sought for a solution of the problem in Baeomyces,
one of the more primitive genera of the Cladoniaceae. The thallus, except in
a few mostly exotic species, scarcely advances beyond the crustaceous
condition; the podetia are short and so varied in character that species have
been assigned by systematists to several different genera. In one of them,
Baeomyces roseus, the podetium or stalk originates according to
Nienburg[415] deep down in the medulla of a fertile granule as a specialized
weft of tissue; there is no carpogonium nor trichogyne formed; the hyphae
that grow upward and form the podetium are generative filaments and give
rise to asci and paraphyses. In a second species, B. rufus (Sphyridium), the
gonidial zone and outer cortex of a thalline granule swell out to form a
thalline protuberance; the carpogonium arises close to the apex, and from it
branch the generative filaments. Nienburg regards the stalk of B. roseus as
apothecial and as representing an extension of the proper margin[416]
(excipulum proprium), that of B. rufus as a typical vegetative podetium.
In the genus Cladonia, differentiation of the generative hyphae may take
place at a very early stage. Wainio[417] observed, in Cl. caespiticia, a
trichogyne in a still solid podetium only 90µ in height; usually they appear
later, and, where scyphi are formed, the carpogonium often arises at the
edge of the scyphus. Baur[418] and Wolff[419] have furnished conclusive
evidence of the late appearance of the carpogonium in Cl. pyxidata, Cl.
degenerans, Cl. furcata and Cl. gracilis: in all of these species carpogonia
with trichogynes were observed on the edge of well-developed scyphi. Baur
draws the conclusion that the podetium is merely a vertical thallus, citing as
additional evidence that it also bears the spermogonia (or pycnidia), though
at the same time he allows that the apothecium may have played an
important part in its phylogenetic development. He agrees also with the
account of the first appearance of the podetium as described by Krabbe,
who found that it began with the hyphae of the gonidial zone branching
upwards in a quite normal manner, only that there were more of them, and
frequently transformed by metamorphosis to a vertical thallus, though
visibly retaining its stalk character.” Sättler[414], one of the most recent
students of Cladonia, regards the podetium as evolved with reference to
spore-dissemination, and therefore of apothecial character. His views are
described and discussed in the chapter on phylogeny.
Reinke and others sought for a solution of the problem in Baeomyces,
one of the more primitive genera of the Cladoniaceae. The thallus, except in
a few mostly exotic species, scarcely advances beyond the crustaceous
condition; the podetia are short and so varied in character that species have
been assigned by systematists to several different genera. In one of them,
Baeomyces roseus, the podetium or stalk originates according to
Nienburg[415] deep down in the medulla of a fertile granule as a specialized
weft of tissue; there is no carpogonium nor trichogyne formed; the hyphae
that grow upward and form the podetium are generative filaments and give
rise to asci and paraphyses. In a second species, B. rufus (Sphyridium), the
gonidial zone and outer cortex of a thalline granule swell out to form a
thalline protuberance; the carpogonium arises close to the apex, and from it
branch the generative filaments. Nienburg regards the stalk of B. roseus as
apothecial and as representing an extension of the proper margin[416]
(excipulum proprium), that of B. rufus as a typical vegetative podetium.
In the genus Cladonia, differentiation of the generative hyphae may take
place at a very early stage. Wainio[417] observed, in Cl. caespiticia, a
trichogyne in a still solid podetium only 90µ in height; usually they appear
later, and, where scyphi are formed, the carpogonium often arises at the
edge of the scyphus. Baur[418] and Wolff[419] have furnished conclusive
evidence of the late appearance of the carpogonium in Cl. pyxidata, Cl.
degenerans, Cl. furcata and Cl. gracilis: in all of these species carpogonia
with trichogynes were observed on the edge of well-developed scyphi. Baur
draws the conclusion that the podetium is merely a vertical thallus, citing as
additional evidence that it also bears the spermogonia (or pycnidia), though
at the same time he allows that the apothecium may have played an
important part in its phylogenetic development. He agrees also with the
account of the first appearance of the podetium as described by Krabbe,
who found that it began with the hyphae of the gonidial zone branching
upwards in a quite normal manner, only that there were more of them, and
Page 186
that they finally pierced the cortex. Krabbe also asserted that in the early
stages the podetia were without gonidia and that these arrived later from the
open as colonists, in this contradicting Wainio’s statement that gonidia were
carried up from the primary thallus.
It seems probable that the podetium—as Wainio and Baur both have
stated—is homologous with the apothecial stalk, though in most cases it is
completely transformed into a vertical thallus. If the view of their formation
from the gonidial zone is accepted, then they differ widely in origin from
normal branches in which the tissues of the main axis are repeated in the
secondary structures, whereas in this vertical thallus, hyphae from the
gonidial zone alone take part in the development. It must be admitted that
Baur’s view of the podetium as essentially thalline seems to be strengthened
by the formation of podetia at the centre of the scyphus, as in Cl.
verticillata, which are new structures and are not an elongation of the
original conceptacular tissue. It can however equally be argued that the
acquired thalline character is complete and, therefore, includes the
possibility of giving rise to new podetia.
The relegation of the carpogonium to a position far removed from the
base or primordium of the apothecium need not necessarily interfere with
the conception of the primordial tissue as homologous with the conceptacle;
but more research is needed, as Baur dealt only with one species, Cl.
pyxidata, and Gertrude Wolff confined her attention to the carpogonial
stages at the edge of the scyphus.
The Cladoniae require light, and inhabit by preference open moorlands,
naked clay walls, borders of ditches, exposed sand-dunes, etc. Those with
large and persistent squamules can live in arid situations, probably because
the primary thallus is able to retain moisture for a long time[420]. When the
primary thallus is small and feeble the podetia are generally much branched
and live in close colonies which retain moisture. Sterile podetia are long-
lived and grow indefinitely at the apex though the base as continually
perishes and changes into humus. Wainio[421] cites an instance in which the
bases of a tuft of Cl. alpestris had formed a gelatinous mass more than a
decimetre in thickness.
I. Pilophorus and Stereocaulon
stages the podetia were without gonidia and that these arrived later from the
open as colonists, in this contradicting Wainio’s statement that gonidia were
carried up from the primary thallus.
It seems probable that the podetium—as Wainio and Baur both have
stated—is homologous with the apothecial stalk, though in most cases it is
completely transformed into a vertical thallus. If the view of their formation
from the gonidial zone is accepted, then they differ widely in origin from
normal branches in which the tissues of the main axis are repeated in the
secondary structures, whereas in this vertical thallus, hyphae from the
gonidial zone alone take part in the development. It must be admitted that
Baur’s view of the podetium as essentially thalline seems to be strengthened
by the formation of podetia at the centre of the scyphus, as in Cl.
verticillata, which are new structures and are not an elongation of the
original conceptacular tissue. It can however equally be argued that the
acquired thalline character is complete and, therefore, includes the
possibility of giving rise to new podetia.
The relegation of the carpogonium to a position far removed from the
base or primordium of the apothecium need not necessarily interfere with
the conception of the primordial tissue as homologous with the conceptacle;
but more research is needed, as Baur dealt only with one species, Cl.
pyxidata, and Gertrude Wolff confined her attention to the carpogonial
stages at the edge of the scyphus.
The Cladoniae require light, and inhabit by preference open moorlands,
naked clay walls, borders of ditches, exposed sand-dunes, etc. Those with
large and persistent squamules can live in arid situations, probably because
the primary thallus is able to retain moisture for a long time[420]. When the
primary thallus is small and feeble the podetia are generally much branched
and live in close colonies which retain moisture. Sterile podetia are long-
lived and grow indefinitely at the apex though the base as continually
perishes and changes into humus. Wainio[421] cites an instance in which the
bases of a tuft of Cl. alpestris had formed a gelatinous mass more than a
decimetre in thickness.
I. Pilophorus and Stereocaulon
Page 187
These two genera are usually included in Cladoniaceae on account of
their twofold thallus and their somewhat similar fruit formation. They differ
from Cladonia in the development of the podetia which are not endogenous
in origin as in that genus, but are formed by the growth upwards of a
primary granule or squamule and correspond more nearly to Tulasne’s
conception of the podetium as a process from the horizontal thallus. In
Pilophorus the primary granular thallus persists during the life of the plants;
the short podetium is unbranched, and consists of a somewhat compact
medulla of parallel hyphae surrounded by a looser cortical tissue, such as
that of the basal granule, in which are embedded the algal cells. The black
colour of the apothecium is due to the thick dark hypothecium.
Stereocaulon is also a direct growth from a short-lived primary
squamule[422]. The podetia, called “pseudopodetia” by Wainio, are usually
very much branched. They possess a central strand of hyphae not entirely
solid, and an outer layer of loose felted hyphae in which the gonidia find
place. A coating of mucilage on the outside gives a glabrous shiny surface,
or, if that is absent, the surface is tomentose as in St. tomentosum. In all the
species the podetia are more or less thickly beset with small variously
divided squamules similar in form to the primary evanescent thallus. Gall-
like cephalodia are associated with most of the species and aid in the work
of assimilation.
Stereocaulon cannot depend on the evanescent primary thallus for
attachment to the soil. The podetia of the different species have developed
various rooting bases: in St. ramulosum there is a basal sheath formed, in St.
coralloides a well-developed system of rhizoids[423].
V. STRUCTURES PECULIAR TO LICHENS
1. AERATION STRUCTURES
A. Cyphellae and Pseudocyphellae
The thallus of Stictaceae has been regarded by Nylander[424] and others
as one of the most highly organized, not only on account of the size attained
by the spreading lobes, but also because in that family are chiefly found
those very definite cup-like structures which were named “cyphellae” by
their twofold thallus and their somewhat similar fruit formation. They differ
from Cladonia in the development of the podetia which are not endogenous
in origin as in that genus, but are formed by the growth upwards of a
primary granule or squamule and correspond more nearly to Tulasne’s
conception of the podetium as a process from the horizontal thallus. In
Pilophorus the primary granular thallus persists during the life of the plants;
the short podetium is unbranched, and consists of a somewhat compact
medulla of parallel hyphae surrounded by a looser cortical tissue, such as
that of the basal granule, in which are embedded the algal cells. The black
colour of the apothecium is due to the thick dark hypothecium.
Stereocaulon is also a direct growth from a short-lived primary
squamule[422]. The podetia, called “pseudopodetia” by Wainio, are usually
very much branched. They possess a central strand of hyphae not entirely
solid, and an outer layer of loose felted hyphae in which the gonidia find
place. A coating of mucilage on the outside gives a glabrous shiny surface,
or, if that is absent, the surface is tomentose as in St. tomentosum. In all the
species the podetia are more or less thickly beset with small variously
divided squamules similar in form to the primary evanescent thallus. Gall-
like cephalodia are associated with most of the species and aid in the work
of assimilation.
Stereocaulon cannot depend on the evanescent primary thallus for
attachment to the soil. The podetia of the different species have developed
various rooting bases: in St. ramulosum there is a basal sheath formed, in St.
coralloides a well-developed system of rhizoids[423].
V. STRUCTURES PECULIAR TO LICHENS
1. AERATION STRUCTURES
A. Cyphellae and Pseudocyphellae
The thallus of Stictaceae has been regarded by Nylander[424] and others
as one of the most highly organized, not only on account of the size attained
by the spreading lobes, but also because in that family are chiefly found
those very definite cup-like structures which were named “cyphellae” by
Page 188
Acharius[425]. They are small hollow depressions about 1/2 mm. or more in
width scattered irregularly over the under surface of the thallus.
a. Historical. Cyphellae were first pointed out by the Swiss botanist,
Haller[426]. In his description of a lichen referable to Sticta fuliginosa he
describes certain white circular depressions “to be found among the short
brown hairs of the under surface.” At a later date Schreber[427] made these
“white excavated points” the leading character of his lichen genus Sticta.
In urceolate or proper cyphellae, the base of the depression rests on the
medulla; the margin is formed from the ruptured cortex and projects slightly
inwards over the edge of the cup. Contrasted with these are the
pseudocyphellae, somewhat roundish openings of a simpler structure which
replace the others in many of the species. They have no definite margin; the
internal hyphae have forced their way to the exterior and form a protruding
tuft slightly above the surface. Meyer[428] reckoned them all among soredia;
but he distinguished between those in which the medullary hyphae became
conglutinated to form a margin (true cyphellae) and those in which there
was a granular outburst of filaments (pseudocyphellae). He also included a
third type, represented in Lobaria pulmonaria on the under surface of
which there are numerous non-corticate, angular patches where the pith is
laid bare (Fig. 72). Delise[429], writing about the same time on the Sticteae,
gives due attention to their occurrence, classifying the various species of
Sticta as cyphellate or non-cyphellate.
Acharius had limited the name “cyphella” to the hollow urceolate bodies
that had a well-defined margin. Nylander[430] at first included under that
term both types of structure, but later[431] he classified the pulverulent
“soredia-like” forms in another group, the pseudocyphellae. As a rule they
bear no relation to soredia, and algae are rarely associated with the
protruding filaments. Schwendener[432], and later Wainio[433], in describing
Sticta aurata from Brazil, state, as exceptional, that the citrine-yellow
pseudocyphellae of that species are sparingly sorediate.
width scattered irregularly over the under surface of the thallus.
a. Historical. Cyphellae were first pointed out by the Swiss botanist,
Haller[426]. In his description of a lichen referable to Sticta fuliginosa he
describes certain white circular depressions “to be found among the short
brown hairs of the under surface.” At a later date Schreber[427] made these
“white excavated points” the leading character of his lichen genus Sticta.
In urceolate or proper cyphellae, the base of the depression rests on the
medulla; the margin is formed from the ruptured cortex and projects slightly
inwards over the edge of the cup. Contrasted with these are the
pseudocyphellae, somewhat roundish openings of a simpler structure which
replace the others in many of the species. They have no definite margin; the
internal hyphae have forced their way to the exterior and form a protruding
tuft slightly above the surface. Meyer[428] reckoned them all among soredia;
but he distinguished between those in which the medullary hyphae became
conglutinated to form a margin (true cyphellae) and those in which there
was a granular outburst of filaments (pseudocyphellae). He also included a
third type, represented in Lobaria pulmonaria on the under surface of
which there are numerous non-corticate, angular patches where the pith is
laid bare (Fig. 72). Delise[429], writing about the same time on the Sticteae,
gives due attention to their occurrence, classifying the various species of
Sticta as cyphellate or non-cyphellate.
Acharius had limited the name “cyphella” to the hollow urceolate bodies
that had a well-defined margin. Nylander[430] at first included under that
term both types of structure, but later[431] he classified the pulverulent
“soredia-like” forms in another group, the pseudocyphellae. As a rule they
bear no relation to soredia, and algae are rarely associated with the
protruding filaments. Schwendener[432], and later Wainio[433], in describing
Sticta aurata from Brazil, state, as exceptional, that the citrine-yellow
pseudocyphellae of that species are sparingly sorediate.
Page 189
Fig. 72. Lobaria pulmonaria Hoffm. Showing pitted surface. a,
under surface. Reduced (S. H., Photo.).
Fig. 73. Sticta damaecornis Nyl. Transverse section of thallus
with cyphella × 100.
b. Development of Cyphellae. The cortex of both surfaces in the thallus
of Sticta is a several-layered plectenchyma of thick-walled closely packed
cells, the outer layer growing out into hairs on the under surface of most of
the species. Where either cyphellae or pseudocyphellae occur, a more or
less open channel is formed between the exterior and the internal tissues of
the lichen. In the case of the cyphellae, the medullary hyphae which line the
cup are divided into short roundish cells with comparatively thin walls (Fig.
under surface. Reduced (S. H., Photo.).
Fig. 73. Sticta damaecornis Nyl. Transverse section of thallus
with cyphella × 100.
b. Development of Cyphellae. The cortex of both surfaces in the thallus
of Sticta is a several-layered plectenchyma of thick-walled closely packed
cells, the outer layer growing out into hairs on the under surface of most of
the species. Where either cyphellae or pseudocyphellae occur, a more or
less open channel is formed between the exterior and the internal tissues of
the lichen. In the case of the cyphellae, the medullary hyphae which line the
cup are divided into short roundish cells with comparatively thin walls (Fig.
Page 190
73). They form a tissue sharply differentiated from the loose hyphae that
occupy the medulla. The rounded cells tend to lie in vertical rows, though
the arrangement in fully formed cyphellae is generally somewhat irregular.
The terminal empty cells are loosely attached and as they are eventually
abstricted and strewn over the inside of the cup they give to it the
characteristic white powdery appearance.
According to Schwendener[434] development begins by an exuberant
growth of the medulla which raises and finally bursts the cortex; prominent
cyphellae have been thus formed in Sticta damaecornis (Fig. 73). In other
species the swelling is less noticeable or entirely absent. The opening of the
cup measures usually about 1/2 mm. across, but it may stretch to a greater
width.
c. Pseudocyphellae. In these no margin is formed, the cortex is simply
burst by the protruding filaments which are of the same colour—yellow or
white—as the medullary hyphae. They vary in size, from a minute point up
to 4 mm. in diameter.
d. Occurrence and Distribution. The genus Sticta is divided into two
sections: (1) Eusticta in which the gonidia are bright-green algae, and (2)
Stictina in which they are blue-green. Cyphellae and pseudocyphellae are
fairly evenly distributed between the sections; they never occur together.
Stizenberger[435] found that 36 species of the section Eusticta were
cyphellate, while in 43 species pseudocyphellae were formed. In the section
Stictina there were 38 of the former and only 31 of the latter type. Both
sections of the genus are widely distributed in all countries, but they are
most abundant south of the equator, reaching their highest development in
Australia and New Zealand.
In the British Isles Sticta is rather poorly represented as follows:
§ Eusticta (with bright-green gonidia).
Cyphellate: S. damaecornis.
Pseudocyphellate: S. aurata.
§ Stictina (with blue-green gonidia).
occupy the medulla. The rounded cells tend to lie in vertical rows, though
the arrangement in fully formed cyphellae is generally somewhat irregular.
The terminal empty cells are loosely attached and as they are eventually
abstricted and strewn over the inside of the cup they give to it the
characteristic white powdery appearance.
According to Schwendener[434] development begins by an exuberant
growth of the medulla which raises and finally bursts the cortex; prominent
cyphellae have been thus formed in Sticta damaecornis (Fig. 73). In other
species the swelling is less noticeable or entirely absent. The opening of the
cup measures usually about 1/2 mm. across, but it may stretch to a greater
width.
c. Pseudocyphellae. In these no margin is formed, the cortex is simply
burst by the protruding filaments which are of the same colour—yellow or
white—as the medullary hyphae. They vary in size, from a minute point up
to 4 mm. in diameter.
d. Occurrence and Distribution. The genus Sticta is divided into two
sections: (1) Eusticta in which the gonidia are bright-green algae, and (2)
Stictina in which they are blue-green. Cyphellae and pseudocyphellae are
fairly evenly distributed between the sections; they never occur together.
Stizenberger[435] found that 36 species of the section Eusticta were
cyphellate, while in 43 species pseudocyphellae were formed. In the section
Stictina there were 38 of the former and only 31 of the latter type. Both
sections of the genus are widely distributed in all countries, but they are
most abundant south of the equator, reaching their highest development in
Australia and New Zealand.
In the British Isles Sticta is rather poorly represented as follows:
§ Eusticta (with bright-green gonidia).
Cyphellate: S. damaecornis.
Pseudocyphellate: S. aurata.
§ Stictina (with blue-green gonidia).
Page 191
Cyphellate: S. fuliginosa, S. limbata, S. sylvatica, S.
Dufourei.
Pseudocyphellate: S. intricata var. Thouarsii, S. crocata.
Structures resembling cyphellae, with an overarching rim, are sprinkled
over the brown under surface of the Australian lichen, Heterodea Mülleri;
the thallus is without a lower cortex, the medulla being protected by thickly
woven hyphae. Heterodea was at one time included among Stictaceae,
though now it is classified under Parmeliaceae. Pseudocyphellae are also
present on the non-corticate under surface of Nephromium tomentosum,
where they occur as little white pustules among the brown hairs; and the
white impressed spots on the under surface of Cetraria islandica and allied
species, first determined as air pores by Zukal[436], have also been described
by Wainio[437] as pseudocyphellae.
There seems no doubt that the chief function of these various structures
is, as Schwendener[438] suggested, to allow a free passage of air to the
assimilating gonidial zone. Jatta[439] considers them to be analogous to the
lenticels of higher plants and of service in the interchange of gases—
expelling carbonic acid and receiving oxygen from the outer atmosphere. It
is remarkable that such serviceable organs should have been evolved in so
few lichens.
B. Breathing-Pores
Dufourei.
Pseudocyphellate: S. intricata var. Thouarsii, S. crocata.
Structures resembling cyphellae, with an overarching rim, are sprinkled
over the brown under surface of the Australian lichen, Heterodea Mülleri;
the thallus is without a lower cortex, the medulla being protected by thickly
woven hyphae. Heterodea was at one time included among Stictaceae,
though now it is classified under Parmeliaceae. Pseudocyphellae are also
present on the non-corticate under surface of Nephromium tomentosum,
where they occur as little white pustules among the brown hairs; and the
white impressed spots on the under surface of Cetraria islandica and allied
species, first determined as air pores by Zukal[436], have also been described
by Wainio[437] as pseudocyphellae.
There seems no doubt that the chief function of these various structures
is, as Schwendener[438] suggested, to allow a free passage of air to the
assimilating gonidial zone. Jatta[439] considers them to be analogous to the
lenticels of higher plants and of service in the interchange of gases—
expelling carbonic acid and receiving oxygen from the outer atmosphere. It
is remarkable that such serviceable organs should have been evolved in so
few lichens.
B. Breathing-Pores
Page 192
Fig. 74. Parmelia exasperata Carroll. Vertical section of thallus.
a, breathing-pores; b, rhizoid. × 60 (after Rosendahl).
a. Definite Breathing-Pores. The cyphellae and pseudocyphellae
described above are confined to the under surface of the thallus in those
lichens where they occur. Distinct breathing-pores of a totally different
structure are present on the upper surface of the tree-lichen, Parmelia
aspidota (P. exasperata), one of the brown-coloured species. They are
somewhat thickly scattered as isidia- or cone-like warts over the lichen
thallus (Fig. 74) and give it the characteristically rough or “exasperate”
character. They are direct outgrowths from the thallus, and Zukal[440], who
discovered their peculiar nature and function, describes them as being filled
with a hyphal tissue, with abundant air-spaces, and in direct communication
with the medulla; gonidia, if present, are confined to the basal part. The
cortex covering these minute cones, he further states, is very thin on the top,
or often wanting, so that a true pore is formed which, however, is only
opened after the cortex elsewhere has become thick and horny.
Rosendahl[441], who has re-examined these “breathing-pores,” finds that in
the early stage of their growth, near the margin or younger portion of the
thallus, they are entirely covered by the cortex. Later, the hyphae at the top
become looser and more frequently septate, and a fine network of
anastomosing and intricate filaments takes the place of the closely cohering
cortical cells. These hyphae are divided into shorter cells, but do not
otherwise differ from those of the medulla. Rosendahl was unable to detect
an open pore at any stage, though he entirely agrees with Zukal as to the
breathing function of these structures. The gonidia of the immediately
underlying zone are sparsely arranged and a few of them are found in the
lower half of the cone; the hyphae of the medulla can be traced up to the
apex. Zukal[442] claims to have found breathing-pores in Cornicularia
(Parmelia) tristis and in several other Parmeliae, notably in Parmelia
stygia. The thallus of the latter species has minute holes or openings in the
upper cortex, but they are without any definite form and may be only
fortuitous.
a, breathing-pores; b, rhizoid. × 60 (after Rosendahl).
a. Definite Breathing-Pores. The cyphellae and pseudocyphellae
described above are confined to the under surface of the thallus in those
lichens where they occur. Distinct breathing-pores of a totally different
structure are present on the upper surface of the tree-lichen, Parmelia
aspidota (P. exasperata), one of the brown-coloured species. They are
somewhat thickly scattered as isidia- or cone-like warts over the lichen
thallus (Fig. 74) and give it the characteristically rough or “exasperate”
character. They are direct outgrowths from the thallus, and Zukal[440], who
discovered their peculiar nature and function, describes them as being filled
with a hyphal tissue, with abundant air-spaces, and in direct communication
with the medulla; gonidia, if present, are confined to the basal part. The
cortex covering these minute cones, he further states, is very thin on the top,
or often wanting, so that a true pore is formed which, however, is only
opened after the cortex elsewhere has become thick and horny.
Rosendahl[441], who has re-examined these “breathing-pores,” finds that in
the early stage of their growth, near the margin or younger portion of the
thallus, they are entirely covered by the cortex. Later, the hyphae at the top
become looser and more frequently septate, and a fine network of
anastomosing and intricate filaments takes the place of the closely cohering
cortical cells. These hyphae are divided into shorter cells, but do not
otherwise differ from those of the medulla. Rosendahl was unable to detect
an open pore at any stage, though he entirely agrees with Zukal as to the
breathing function of these structures. The gonidia of the immediately
underlying zone are sparsely arranged and a few of them are found in the
lower half of the cone; the hyphae of the medulla can be traced up to the
apex. Zukal[442] claims to have found breathing-pores in Cornicularia
(Parmelia) tristis and in several other Parmeliae, notably in Parmelia
stygia. The thallus of the latter species has minute holes or openings in the
upper cortex, but they are without any definite form and may be only
fortuitous.
Page 193
Fig. 75 a. Ramalina fraxinea Ach. A, surface
view of frond. a, air-pores; b, young apothecia. ×
12. B, transverse section of part of frond. a,
breathing-pore; f, strengthening fibres. × 37 (after
Brandt).
Fig. 75 b. Ramalina strepsilis Zahlbr. Transverse section of part of
frond showing distribution of: a, air-pores, and f, strengthening
fibres. × 37 (after Brandt).
view of frond. a, air-pores; b, young apothecia. ×
12. B, transverse section of part of frond. a,
breathing-pore; f, strengthening fibres. × 37 (after
Brandt).
Fig. 75 b. Ramalina strepsilis Zahlbr. Transverse section of part of
frond showing distribution of: a, air-pores, and f, strengthening
fibres. × 37 (after Brandt).
Page 194
Zukal[442] published drawings of channels of looser tissue between the
exterior and the pith in Oropogon Loxensis and in Usnea barbata. He
considered them to be of definite service in aeration. The fronds of
Ramalina dilacerata by stretching develop a series of elongate holes.
Reinke[443] found openings in Ramalina Eckloni which pierced to the centre
of the thallus, and Darbishire[444] has figured a break in the frond of another
species, R. fraxinea (Fig. 75 a), which he has designated as a breathing-
pore. Finally Brandt[445], in his careful study of the anatomy of Ramalinae,
has described as breathing-pores certain open areas usually of ellipsoid
form in the compact cortex of several species: in R. strepsilis (Fig. 75 b)
and R. Landroensis, and in the British species, R. siliquosa and R. fraxinea.
These openings are however mostly rare and difficult to find or to
distinguish from holes that may be due to any accident in the life of the
lichen. It is noteworthy that Rosendahl found no further examples of
breathing-pores in the brown Parmeliae that he examined in such detail. No
other organs specially adapted for aeration of the thallus have been
discovered.
b. Other openings in the Thallus. Lobaria is the only genus of
Stictaceae in which neither cyphellae nor pseudocyphellae are formed; but
in two species, L. scrobiculata and L. pulmonaria, the lower surface is
marked with oblong or angular bare convex patches, much larger than
cyphellae. They are exposed portions of the medulla, which at these spots
has been denuded of the covering cortex. Corresponding with these bare
spots there is a pitting of the upper surface.
A somewhat similar but reversed structure characterizes Umbilicaria
pustulata, which as the name implies is distinguished by the presence of
pustules, ellipsoid swellings above, with a reticulation of cavities below.
Bitter[446] in this instance has proved that they are due to disconnected
centres of intercalary growth which are more vigorous on the upper surface
and give rise to cracks in the less active tissue beneath. These cracks
gradually become enlarged; they are, as it were, accidental in origin but are
doubtless of considerable service in aeration.
In some Parmeliae there are constantly formed minute round holes,
either right through the apothecia (P. cetrata, etc.), or through the thallus (P.
pertusa). Minute holes are also present in the under cortex of Parmelia
exterior and the pith in Oropogon Loxensis and in Usnea barbata. He
considered them to be of definite service in aeration. The fronds of
Ramalina dilacerata by stretching develop a series of elongate holes.
Reinke[443] found openings in Ramalina Eckloni which pierced to the centre
of the thallus, and Darbishire[444] has figured a break in the frond of another
species, R. fraxinea (Fig. 75 a), which he has designated as a breathing-
pore. Finally Brandt[445], in his careful study of the anatomy of Ramalinae,
has described as breathing-pores certain open areas usually of ellipsoid
form in the compact cortex of several species: in R. strepsilis (Fig. 75 b)
and R. Landroensis, and in the British species, R. siliquosa and R. fraxinea.
These openings are however mostly rare and difficult to find or to
distinguish from holes that may be due to any accident in the life of the
lichen. It is noteworthy that Rosendahl found no further examples of
breathing-pores in the brown Parmeliae that he examined in such detail. No
other organs specially adapted for aeration of the thallus have been
discovered.
b. Other openings in the Thallus. Lobaria is the only genus of
Stictaceae in which neither cyphellae nor pseudocyphellae are formed; but
in two species, L. scrobiculata and L. pulmonaria, the lower surface is
marked with oblong or angular bare convex patches, much larger than
cyphellae. They are exposed portions of the medulla, which at these spots
has been denuded of the covering cortex. Corresponding with these bare
spots there is a pitting of the upper surface.
A somewhat similar but reversed structure characterizes Umbilicaria
pustulata, which as the name implies is distinguished by the presence of
pustules, ellipsoid swellings above, with a reticulation of cavities below.
Bitter[446] in this instance has proved that they are due to disconnected
centres of intercalary growth which are more vigorous on the upper surface
and give rise to cracks in the less active tissue beneath. These cracks
gradually become enlarged; they are, as it were, accidental in origin but are
doubtless of considerable service in aeration.
In some Parmeliae there are constantly formed minute round holes,
either right through the apothecia (P. cetrata, etc.), or through the thallus (P.
pertusa). Minute holes are also present in the under cortex of Parmelia
Page 195
vittata and of P. enteromorpha, species of the subgenus Hypogymnia.
Nylander[447], who first drew attention to these holes of the lower cortex,
described them as arising at the forking of two lobes; but though they do
occur in that position, they as frequently bear no relation to the branching.
Bitter’s[448] opinion is that they arise by the decay of the cortical tissues in
very limited areas, from some unknown cause, and that the holes that pierce
right through the thallus in other species may be similarly explained.
Still other minute openings into the thallus occur in Parmelia vittata, P.
obscurata and P. farinacea var. obscurascens. In the two latter the openings
like pin-holes are terminal on the lobes and are situated exactly on the apex,
between the pith and the gonidial zone; sometimes several holes can be
detected on the end of one lobe. Further growth in length is checked by
these holes. They appear more frequently on the darker, better illuminated
plants. In Parmelia vittata the terminal holes are at the end of excessively
minute adventitious branches which arise below the gonidial zone on the
margin of the primary lobes. All these terminal holes are directed upwards
and are visible from above.
Bitter does not attribute any physiological significance to these very
definite openings in the thallus. It has been generally assumed that they aid
in the aeration of the thallus; it is also possible that they may be of service
in absorption, and they might even be regarded as open water conductors.
C. General Aeration of the Thallus
Definite structures adapted to secure the aeration of the thallus in a
limited number of lichens have been described above. These are the
breathing-pores of Parmelia exasperata and the cyphellae and
pseudocyphellae of the Stictaceae, with which also may be perhaps
included the circumscribed breaks in the under cortex in some members of
that family.
Though lichens are composed of two actively growing organisms, the
symbiotic plant increases very slowly. The absorption of water and mineral
salts must in many instances be of the scantiest and the formation of
carbohydrates by the deep-seated chlorophyll cells of correspondingly small
amount. Active aeration seems therefore uncalled for though by no means
Nylander[447], who first drew attention to these holes of the lower cortex,
described them as arising at the forking of two lobes; but though they do
occur in that position, they as frequently bear no relation to the branching.
Bitter’s[448] opinion is that they arise by the decay of the cortical tissues in
very limited areas, from some unknown cause, and that the holes that pierce
right through the thallus in other species may be similarly explained.
Still other minute openings into the thallus occur in Parmelia vittata, P.
obscurata and P. farinacea var. obscurascens. In the two latter the openings
like pin-holes are terminal on the lobes and are situated exactly on the apex,
between the pith and the gonidial zone; sometimes several holes can be
detected on the end of one lobe. Further growth in length is checked by
these holes. They appear more frequently on the darker, better illuminated
plants. In Parmelia vittata the terminal holes are at the end of excessively
minute adventitious branches which arise below the gonidial zone on the
margin of the primary lobes. All these terminal holes are directed upwards
and are visible from above.
Bitter does not attribute any physiological significance to these very
definite openings in the thallus. It has been generally assumed that they aid
in the aeration of the thallus; it is also possible that they may be of service
in absorption, and they might even be regarded as open water conductors.
C. General Aeration of the Thallus
Definite structures adapted to secure the aeration of the thallus in a
limited number of lichens have been described above. These are the
breathing-pores of Parmelia exasperata and the cyphellae and
pseudocyphellae of the Stictaceae, with which also may be perhaps
included the circumscribed breaks in the under cortex in some members of
that family.
Though lichens are composed of two actively growing organisms, the
symbiotic plant increases very slowly. The absorption of water and mineral
salts must in many instances be of the scantiest and the formation of
carbohydrates by the deep-seated chlorophyll cells of correspondingly small
amount. Active aeration seems therefore uncalled for though by no means
Page 196
excluded, and there are many indirect channels by which air can penetrate
to the deeper tissues.
In crustaceous forms, whether corticate or not, the thallus is often deeply
seamed and cracked into areolae, and thus is easily pervious to water and
air. The growing edges and growing points are also everywhere more or less
loose and open to the atmosphere. In the larger foliose and fruticose lichens,
the soredia that burst an opening in the thallus, and the cracks that are so
frequent a feature of the upper cortex, all permit of gaseous interchange.
The apical growing point of fruticose lichens is thin and porous, and in
many of them the ribs and veins of their channelled surfaces entail a
straining of the cortical tissue that results in the formation of thinner
permeable areas. Zukal[449] devoted special attention to the question of
aeration, and he finds evidence of air-passages through empty spermogonia
and through the small round holes that are constant in the upper surface of
certain foliose species. He claims also to have proved a system of air-canals
right through the thallus of the gelatinous Collemaceae. Though his proof in
this instance is somewhat unconvincing, he establishes the abundant
presence of air in the massively developed hypothecium of Collema fruits.
He found that the carpogonial complex of hyphae was always well supplied
with air, and that caused him to view with favour the suggestion that the
function of the trichogyne is to provide an air-passage. In foliose lichens,
the under surface is frequently non-corticate, in whole or in part; or the
cortex becomes seamed and scarred with increasing expansion, the growth
in the lower layers failing to keep pace with that of the overlying tissues, as
in Umbilicaria pustulata.
It is unquestionable that the interior of the thallus of most lichens
contains abundant empty spaces between the loose-lying hyphae, and that
these spaces are filled with air.
2. CEPHALODIA
A. Historical and Descriptive
The term “cephalodium” was first used by Acharius[450] to designate
certain globose apothecia (pycnidia). At a later date he applied it to the
peculiar outgrowths that grow on the thallus of Peltigera aphthosa, already
to the deeper tissues.
In crustaceous forms, whether corticate or not, the thallus is often deeply
seamed and cracked into areolae, and thus is easily pervious to water and
air. The growing edges and growing points are also everywhere more or less
loose and open to the atmosphere. In the larger foliose and fruticose lichens,
the soredia that burst an opening in the thallus, and the cracks that are so
frequent a feature of the upper cortex, all permit of gaseous interchange.
The apical growing point of fruticose lichens is thin and porous, and in
many of them the ribs and veins of their channelled surfaces entail a
straining of the cortical tissue that results in the formation of thinner
permeable areas. Zukal[449] devoted special attention to the question of
aeration, and he finds evidence of air-passages through empty spermogonia
and through the small round holes that are constant in the upper surface of
certain foliose species. He claims also to have proved a system of air-canals
right through the thallus of the gelatinous Collemaceae. Though his proof in
this instance is somewhat unconvincing, he establishes the abundant
presence of air in the massively developed hypothecium of Collema fruits.
He found that the carpogonial complex of hyphae was always well supplied
with air, and that caused him to view with favour the suggestion that the
function of the trichogyne is to provide an air-passage. In foliose lichens,
the under surface is frequently non-corticate, in whole or in part; or the
cortex becomes seamed and scarred with increasing expansion, the growth
in the lower layers failing to keep pace with that of the overlying tissues, as
in Umbilicaria pustulata.
It is unquestionable that the interior of the thallus of most lichens
contains abundant empty spaces between the loose-lying hyphae, and that
these spaces are filled with air.
2. CEPHALODIA
A. Historical and Descriptive
The term “cephalodium” was first used by Acharius[450] to designate
certain globose apothecia (pycnidia). At a later date he applied it to the
peculiar outgrowths that grow on the thallus of Peltigera aphthosa, already
Page 197
described by earlier writers, along with other similar structures, as
“corpuscula,” “maculae,” etc. The term is now restricted to those purely
vegetative gall-like growths which are in organic connection with the
thallus of the lichen, but which contain one or more algae of a different type
from the one present in the gonidial zone. They are mostly rather small
structures, and they take various forms according to the lichen species on
which they occur. They are only found on thalli in which the gonidia are
bright-green algae (Chlorophyceae) and, with a few exceptions, they
contain only blue-green (Myxophyceae). Cephalodia with bright-green
algae were found by Hue[451] on two Parmeliae from Chili, in addition to
the usual blue-green forms; the one contained Urococcus, the other
Gloeocystis. Several with both types of algae were detected also by Hue[451]
within the thallus of Aspicilia spp.
Flörke[452] in his account of German lichens described the cephalodia
that grow on the podetia of Stereocaulon as fungoid bodies, “corpuscula
fungosa.” Wallroth[453], who had made a special study of lichen gonidia,
finally established that the distinguishing feature of the cephalodia was their
gonidia which differed in colour from those of the normal gonidial zone. He
considered that the outgrowths were a result of changes that had arisen in
the epidermal tissues of the lichens, and, to avoid using a name of mixed
import such as “cephalodia,” he proposed a new designation, calling them
“phymata” or warts.
Further descriptions of cephalodia were given by Th. M. Fries[454] in his
Monograph of Stereocaulon and Pilophorus; but the greatest advance in the
exact knowledge of these bodies is due to Forssell[455] who made a
comprehensive examination of the various types, examples of which
occurred, he found, in connection with about 100 different lichens. Though
fairly constant for the different species, they are not universally so, and are
sometimes very rare even when present, and then difficult to find. A striking
instance of variability in their occurrence is recorded for Ricasolia
amplissima (Lobaria laciniata) (Fig. 76). The cephalodia of that species are
prominent upright branching structures which grow in crowded tufts
irregularly scattered over the surface. They are an unfailing and
conspicuous specific character of the lichens in Europe, but are entirely
wanting in North American specimens.
“corpuscula,” “maculae,” etc. The term is now restricted to those purely
vegetative gall-like growths which are in organic connection with the
thallus of the lichen, but which contain one or more algae of a different type
from the one present in the gonidial zone. They are mostly rather small
structures, and they take various forms according to the lichen species on
which they occur. They are only found on thalli in which the gonidia are
bright-green algae (Chlorophyceae) and, with a few exceptions, they
contain only blue-green (Myxophyceae). Cephalodia with bright-green
algae were found by Hue[451] on two Parmeliae from Chili, in addition to
the usual blue-green forms; the one contained Urococcus, the other
Gloeocystis. Several with both types of algae were detected also by Hue[451]
within the thallus of Aspicilia spp.
Flörke[452] in his account of German lichens described the cephalodia
that grow on the podetia of Stereocaulon as fungoid bodies, “corpuscula
fungosa.” Wallroth[453], who had made a special study of lichen gonidia,
finally established that the distinguishing feature of the cephalodia was their
gonidia which differed in colour from those of the normal gonidial zone. He
considered that the outgrowths were a result of changes that had arisen in
the epidermal tissues of the lichens, and, to avoid using a name of mixed
import such as “cephalodia,” he proposed a new designation, calling them
“phymata” or warts.
Further descriptions of cephalodia were given by Th. M. Fries[454] in his
Monograph of Stereocaulon and Pilophorus; but the greatest advance in the
exact knowledge of these bodies is due to Forssell[455] who made a
comprehensive examination of the various types, examples of which
occurred, he found, in connection with about 100 different lichens. Though
fairly constant for the different species, they are not universally so, and are
sometimes very rare even when present, and then difficult to find. A striking
instance of variability in their occurrence is recorded for Ricasolia
amplissima (Lobaria laciniata) (Fig. 76). The cephalodia of that species are
prominent upright branching structures which grow in crowded tufts
irregularly scattered over the surface. They are an unfailing and
conspicuous specific character of the lichens in Europe, but are entirely
wanting in North American specimens.
Page 198
Fig. 76. Ricasolia amplissima de Not. (Lobaria laciniata Wain.)
on oak, reduced. The dark patches are tufts of branching
cephalodia (A. Wilson, Photo.).
As cephalodia contain rather dark-coloured, blue-green algae, they are
nearly always noticeably darker than the thalli on which they grow, varying
from yellowish-red or brown in those of Lecanora gelida to pale-coloured
in Lecidea consentiens[456], a darker red in Lecidea panaeola and various
shades of green, grey or brown in Stereocaulon, Lobaria (Ricasolia), etc.
They form either flat expansions of varying size on the upper surface of the
thallus, rounded or wrinkled wart-like growths, or upright branching
structures. On the lower surface, where they are not unfrequent, they take
the form of small brown nodules or swellings. In a number of species
packets of blue-green algae surrounded by hyphae are found embedded in
the thallus, either in the pith or immediately under the cortex. They are of
the same nature as the superficial excrescences and are also regarded as
cephalodia.
B. Classification
Forssell has drawn up a classification of these structures, as follows:
I. Cephalodia vera.
on oak, reduced. The dark patches are tufts of branching
cephalodia (A. Wilson, Photo.).
As cephalodia contain rather dark-coloured, blue-green algae, they are
nearly always noticeably darker than the thalli on which they grow, varying
from yellowish-red or brown in those of Lecanora gelida to pale-coloured
in Lecidea consentiens[456], a darker red in Lecidea panaeola and various
shades of green, grey or brown in Stereocaulon, Lobaria (Ricasolia), etc.
They form either flat expansions of varying size on the upper surface of the
thallus, rounded or wrinkled wart-like growths, or upright branching
structures. On the lower surface, where they are not unfrequent, they take
the form of small brown nodules or swellings. In a number of species
packets of blue-green algae surrounded by hyphae are found embedded in
the thallus, either in the pith or immediately under the cortex. They are of
the same nature as the superficial excrescences and are also regarded as
cephalodia.
B. Classification
Forssell has drawn up a classification of these structures, as follows:
I. Cephalodia vera.
Page 199
1. Cephalodia epigena (including perigena) developed on the upper
outer surface of the thallus, which are tuberculose, lobulate, clavate or
branched in form. These are generally corticate structures.
2. Cephalodia hypogena which are developed on the under surface of
the thallus; they are termed “thalloid” if they are entirely superficial, and
“immersed” when they are enclosed within the tissues. They are non-
corticate though surrounded by a weft of hyphae. Forssell further includes
here certain placodioid (lobate), granuliform and fruticose forms which
develop on the hypothallus of the lichen, and gradually push their way up
either through the host thallus, or, as in Lecidea panaeola, between the
thalline granules.
Nylander[457] arranged the cephalodia known to him in three groups: (1)
Ceph. epigena, (2) Ceph. hypogena and (3) Ceph. endogena. Schneider[458]
still more simply and practically describes them as Ectotrophic (external),
and Endotrophic (internal).
II. Pseudocephalodia.
These are a small and doubtful group of cephalodia which are apparently
in very slight connection with the host thallus, and show a tendency to
independent growth. They occur as small scales on Solorina bispora[459]
and S. spongiosa and also on Lecidea pallida. Forssell has suggested that
the cephalodia of Psoroma hypnorum and of Lecidea panaeola might also
be included under this head.
Forssell and others have found and described cephalodia in the following
families and genera:
Sphaerophoraceae.
Sphaerophorus (S. stereocauloides).
Lecideaceae.
Lecidea (L. panaeola, L. consentiens, L. pelobotrya, etc.).
outer surface of the thallus, which are tuberculose, lobulate, clavate or
branched in form. These are generally corticate structures.
2. Cephalodia hypogena which are developed on the under surface of
the thallus; they are termed “thalloid” if they are entirely superficial, and
“immersed” when they are enclosed within the tissues. They are non-
corticate though surrounded by a weft of hyphae. Forssell further includes
here certain placodioid (lobate), granuliform and fruticose forms which
develop on the hypothallus of the lichen, and gradually push their way up
either through the host thallus, or, as in Lecidea panaeola, between the
thalline granules.
Nylander[457] arranged the cephalodia known to him in three groups: (1)
Ceph. epigena, (2) Ceph. hypogena and (3) Ceph. endogena. Schneider[458]
still more simply and practically describes them as Ectotrophic (external),
and Endotrophic (internal).
II. Pseudocephalodia.
These are a small and doubtful group of cephalodia which are apparently
in very slight connection with the host thallus, and show a tendency to
independent growth. They occur as small scales on Solorina bispora[459]
and S. spongiosa and also on Lecidea pallida. Forssell has suggested that
the cephalodia of Psoroma hypnorum and of Lecidea panaeola might also
be included under this head.
Forssell and others have found and described cephalodia in the following
families and genera:
Sphaerophoraceae.
Sphaerophorus (S. stereocauloides).
Lecideaceae.
Lecidea (L. panaeola, L. consentiens, L. pelobotrya, etc.).
Page 200
Cladoniaceae.
Stereocaulon, Pilophorus and Argopsis.
Pannariaceae.
Psoroma (P. hypnorum).
Peltigeraceae.
Peltigera (Peltidea), Nephroma and Solorina.
Stictaceae.
Lobaria, Sticta.
Lecanoraceae.
Lecania (L. lecanorina), Aspicilia[460].
Physciaceae.
Placodium bicolor[461].
C. Algae that form Cephalodia
The algae of the cephalodia belong mostly to genera that form the normal
gonidia of other lichens. They are:
Stigonema,—in Lecanora gelida, Stereocaulon, Pilophorus robustus, and
Lecidea pelobotrya.
Scytonema,—a rare constituent of cephalodia.
Stereocaulon, Pilophorus and Argopsis.
Pannariaceae.
Psoroma (P. hypnorum).
Peltigeraceae.
Peltigera (Peltidea), Nephroma and Solorina.
Stictaceae.
Lobaria, Sticta.
Lecanoraceae.
Lecania (L. lecanorina), Aspicilia[460].
Physciaceae.
Placodium bicolor[461].
C. Algae that form Cephalodia
The algae of the cephalodia belong mostly to genera that form the normal
gonidia of other lichens. They are:
Stigonema,—in Lecanora gelida, Stereocaulon, Pilophorus robustus, and
Lecidea pelobotrya.
Scytonema,—a rare constituent of cephalodia.
Page 201
Nostoc,—the most frequent gonidium of cephalodia. It occurs in those of
the genera Sticta, Lobaria, Peltigera, Nephroma, Solorina and Psoroma;
occasionally in Stereocaulon and in Lecidea pallida.
Lyngbya and Rivularia,—rarely present, the latter in Sticta oregana[462].
Chroococcus and Gloeocapsa,—also very rare.
Scytonema, Chroococcus, Gloeocapsa and Lyngbya are generally found
in combination with some other cephalodia-building alga, though
Nylander[463] found Scytonema alone in the lobulate cephalodia of
Sphaerophorus stereocauloides, a New Zealand lichen, and the only species
of that genus in which cephalodia are developed; and Hue[460] records
Gloeocapsa as forming internal cephalodia in two species of Aspicilia.
Bornet[464] found Lyngbya associated with Scytonema in the cephalodia of
Stereocaulon ramulosum, and, in the same lichen, Forssell[465] found, in the
several cephalodia of one specimen, Nostoc, Scytonema, and Lyngbya,
while, in those of another, Scytonema and Stigonema were present. In the
latter instance these algae were living free on the podetium. Forssell[465]
also determined two different algae, Gloeocapsa magma and Chroococcus
turgidus, present in a cephalodium on Lecidea panaeola var. elegans.
As a general rule only one kind of alga enters into the formation of the
cephalodia of any species or genus. A form of Nostoc, for instance, is
invariably the gonidial constituent of these bodies in the genera, Lobaria,
Sticta, etc. In other lichens different blue-green algae, as noted above, may
occupy the cephalodia even on the same specimen. Forssell finds alternative
algae occurring in the cephalodia of:
Lecanora gelida and Lecidea illita contain either Stigonema or Nostoc;
Lecidea panaeola, with Gloeocapsa, Stigonema or Chroococcus;
Lecidea pelobotrya, with Stigonema or Nostoc;
Pilophorus robustus, with Gloeocapsa, Stigonema, or Nostoc.
the genera Sticta, Lobaria, Peltigera, Nephroma, Solorina and Psoroma;
occasionally in Stereocaulon and in Lecidea pallida.
Lyngbya and Rivularia,—rarely present, the latter in Sticta oregana[462].
Chroococcus and Gloeocapsa,—also very rare.
Scytonema, Chroococcus, Gloeocapsa and Lyngbya are generally found
in combination with some other cephalodia-building alga, though
Nylander[463] found Scytonema alone in the lobulate cephalodia of
Sphaerophorus stereocauloides, a New Zealand lichen, and the only species
of that genus in which cephalodia are developed; and Hue[460] records
Gloeocapsa as forming internal cephalodia in two species of Aspicilia.
Bornet[464] found Lyngbya associated with Scytonema in the cephalodia of
Stereocaulon ramulosum, and, in the same lichen, Forssell[465] found, in the
several cephalodia of one specimen, Nostoc, Scytonema, and Lyngbya,
while, in those of another, Scytonema and Stigonema were present. In the
latter instance these algae were living free on the podetium. Forssell[465]
also determined two different algae, Gloeocapsa magma and Chroococcus
turgidus, present in a cephalodium on Lecidea panaeola var. elegans.
As a general rule only one kind of alga enters into the formation of the
cephalodia of any species or genus. A form of Nostoc, for instance, is
invariably the gonidial constituent of these bodies in the genera, Lobaria,
Sticta, etc. In other lichens different blue-green algae, as noted above, may
occupy the cephalodia even on the same specimen. Forssell finds alternative
algae occurring in the cephalodia of:
Lecanora gelida and Lecidea illita contain either Stigonema or Nostoc;
Lecidea panaeola, with Gloeocapsa, Stigonema or Chroococcus;
Lecidea pelobotrya, with Stigonema or Nostoc;
Pilophorus robustus, with Gloeocapsa, Stigonema, or Nostoc.
Page 202
Fig. 77. Lecanora gelida Ach. a, lobate cephalodia × 12 (after
Zopf).
Riddle[466] has employed cephalodia with their enclosed algae as
diagnostic characters in the genus Stereocaulon. When the alga is
Stigonema, as in S. paschale, etc., the cephalodia are generally very
conspicuous, grey in colour, spherical, wrinkled or folded, though
sometimes black and fibrillose (S. denudatum). Those containing Nostoc
are, on the contrary, minute and are coloured verdigris-green (S.
tomentosum and S. alpinum).
Instances are recorded of algal colonies adhering to, and even
penetrating, the thallus of lichens, but as they never enter into relationship
with the lichen hyphae, they are antagonistic rather than symbiotic and have
no relation to cephalodia.
D. Development of Cephalodia
Zopf).
Riddle[466] has employed cephalodia with their enclosed algae as
diagnostic characters in the genus Stereocaulon. When the alga is
Stigonema, as in S. paschale, etc., the cephalodia are generally very
conspicuous, grey in colour, spherical, wrinkled or folded, though
sometimes black and fibrillose (S. denudatum). Those containing Nostoc
are, on the contrary, minute and are coloured verdigris-green (S.
tomentosum and S. alpinum).
Instances are recorded of algal colonies adhering to, and even
penetrating, the thallus of lichens, but as they never enter into relationship
with the lichen hyphae, they are antagonistic rather than symbiotic and have
no relation to cephalodia.
D. Development of Cephalodia
Page 203
a. Ectotrophic. Among the most familiar examples of external
cephalodia are the small rather dark-coloured warts or swellings that are
scattered irregularly over the surface of Peltigera (Peltidea) aphthosa. This
lichen has a grey foliose thallus of rather large sparingly divided lobes; it
spreads about a hand-breadth or more over the surface of the ground in
moist upland localities. The specific name “aphthosa” was given by
Linnaeus to the plant on account of the supposed resemblance of the dotted
thallus to the infantile ailment of “thrush.” Babikoff[467] has published an
account of the formation and development of these Peltidea cephalodia. He
determined the algae contained in them to be Nostoc by isolating and
growing them on moist sterilized soil. He observed that the smaller, and
presumably younger, excrescences were near the edges of the lobes. The
cortical cells in that position grow out into fine septate hairs that are really
the ends of growing hyphae. Among the hairs were scattered minute
colonies of Nostoc cells lying loose or so closely adhering to the hairs as to
be undetachable (Fig. 78 a). In older stages the hairs, evidently stimulated
by contact with the Nostoc, had increased in size and sent out branches,
some of which penetrated the gelatinous algal colony; others, spreading
over its surface, gradually formed a cortex continuous with that of the
thallus. The alga also increased, and the structure assumed a rounded or
lentiform shape. The thalline cortex immediately below broke down, and
the underlying gonidial zone almost wholly died off and became absorbed.
The hyphae of the cephalodium had meanwhile penetrated downwards as
root-like filaments, those of the thallus growing upwards into the new
overlying tissue (Fig. 78 b). The foreign alga has been described as
parasitic, as it draws from the lichen hyphae the necessary inorganic food
material; but it might equally well be considered as a captive pressed into
the service of the lichen to aid in the work of assimilation or as a willing
associate giving and receiving mutual benefit.
cephalodia are the small rather dark-coloured warts or swellings that are
scattered irregularly over the surface of Peltigera (Peltidea) aphthosa. This
lichen has a grey foliose thallus of rather large sparingly divided lobes; it
spreads about a hand-breadth or more over the surface of the ground in
moist upland localities. The specific name “aphthosa” was given by
Linnaeus to the plant on account of the supposed resemblance of the dotted
thallus to the infantile ailment of “thrush.” Babikoff[467] has published an
account of the formation and development of these Peltidea cephalodia. He
determined the algae contained in them to be Nostoc by isolating and
growing them on moist sterilized soil. He observed that the smaller, and
presumably younger, excrescences were near the edges of the lobes. The
cortical cells in that position grow out into fine septate hairs that are really
the ends of growing hyphae. Among the hairs were scattered minute
colonies of Nostoc cells lying loose or so closely adhering to the hairs as to
be undetachable (Fig. 78 a). In older stages the hairs, evidently stimulated
by contact with the Nostoc, had increased in size and sent out branches,
some of which penetrated the gelatinous algal colony; others, spreading
over its surface, gradually formed a cortex continuous with that of the
thallus. The alga also increased, and the structure assumed a rounded or
lentiform shape. The thalline cortex immediately below broke down, and
the underlying gonidial zone almost wholly died off and became absorbed.
The hyphae of the cephalodium had meanwhile penetrated downwards as
root-like filaments, those of the thallus growing upwards into the new
overlying tissue (Fig. 78 b). The foreign alga has been described as
parasitic, as it draws from the lichen hyphae the necessary inorganic food
material; but it might equally well be considered as a captive pressed into
the service of the lichen to aid in the work of assimilation or as a willing
associate giving and receiving mutual benefit.
Page 204
Fig. 78 a. Hairs of Peltigera aphthosa Willd.
associated with Nostoc colony much magnified
(after Babikoff).
Fig. 78 b. Peltigera aphthosa Willd. Vertical section of thallus and cephalodium ×
480 (after Babikoff).
Th. M. Fries[468] had previously described the development of the
cephalodia in Stereocaulon but failed to find the earliest stages. He
concluded from his observations that parasitic algae were common in the
associated with Nostoc colony much magnified
(after Babikoff).
Fig. 78 b. Peltigera aphthosa Willd. Vertical section of thallus and cephalodium ×
480 (after Babikoff).
Th. M. Fries[468] had previously described the development of the
cephalodia in Stereocaulon but failed to find the earliest stages. He
concluded from his observations that parasitic algae were common in the
Page 205
cortical layer of the lichens, but only rarely formed the “monstrous
growths” called cephalodia.
b. Endotrophic. Winter[469] examined the later stages of internal
cephalodine formation in a species of Sticta. The alga, probably a species of
Rivularia, which gives origin to the cephalodia, may be situated
immediately below the upper cortex, in the medullary layer close to the
gonidial zone, or between the pith and the under cortex. The protuberance
caused by the increasing tissue, which also contains the invading alga,
arises accordingly either on the upper or the lower surface. In some cases it
was found that the normal gonidial layer had been pushed up by the
protruding cephalodium and lay like a cap over the top. The cephalodia
described by Winter are endogenous in origin, though the mature body
finally emerges from the interior and becomes either epigenous or
hypogenous. Schneider[470] has followed the development of a somewhat
similar endotrophic or endogenous type in Sticta oregana due also to the
presence of a species of Rivularia. How the alga attained its position in the
medulla of the thallus was not observed.
Fig. 79. Nephroma expallidum Nyl. Vertical section of thallus. a,
endotrophic cephalodium × 100 (after Forssell).
Both the algal cells of internal cephalodia and the hyphae in contact with
them increase vigorously, and the newly formed tissue curving upwards or
downwards appears on the outside as a swelling or nodule varying in size
from that of a pin-head to a pea. On the upper surface the gonidial zone
partly encroaches on the nodule, but the foreign alga remains in the centre
of the structure well separated from the thalline gonidia by a layer of
hyphae. The group is internally divided into small nests of dark-green algae
surrounded by strands of hyphae (Fig. 79). The swellings, when they occur
growths” called cephalodia.
b. Endotrophic. Winter[469] examined the later stages of internal
cephalodine formation in a species of Sticta. The alga, probably a species of
Rivularia, which gives origin to the cephalodia, may be situated
immediately below the upper cortex, in the medullary layer close to the
gonidial zone, or between the pith and the under cortex. The protuberance
caused by the increasing tissue, which also contains the invading alga,
arises accordingly either on the upper or the lower surface. In some cases it
was found that the normal gonidial layer had been pushed up by the
protruding cephalodium and lay like a cap over the top. The cephalodia
described by Winter are endogenous in origin, though the mature body
finally emerges from the interior and becomes either epigenous or
hypogenous. Schneider[470] has followed the development of a somewhat
similar endotrophic or endogenous type in Sticta oregana due also to the
presence of a species of Rivularia. How the alga attained its position in the
medulla of the thallus was not observed.
Fig. 79. Nephroma expallidum Nyl. Vertical section of thallus. a,
endotrophic cephalodium × 100 (after Forssell).
Both the algal cells of internal cephalodia and the hyphae in contact with
them increase vigorously, and the newly formed tissue curving upwards or
downwards appears on the outside as a swelling or nodule varying in size
from that of a pin-head to a pea. On the upper surface the gonidial zone
partly encroaches on the nodule, but the foreign alga remains in the centre
of the structure well separated from the thalline gonidia by a layer of
hyphae. The group is internally divided into small nests of dark-green algae
surrounded by strands of hyphae (Fig. 79). The swellings, when they occur
Page 206
on the lower surface of the lichen, correspond to those of the upper in
general structure, but there is no intermixture of thalline gonidia. That
Nostoc cells can grow and retain the power to form chlorophyll in adverse
conditions was proved by Etard and Bouilhac[471] who made a culture of the
alga on artificial media in the dark, when there was formed a green pigment
of chlorophyll nature.
Endotrophic cephalodia occur in many groups of lichens. Hue[472] states
that he found them in twelve species of Aspicilia. As packets of blue-green
algae they are a constant feature in the thallus of Solorinae. The species of
that genus grow on mossy soil in damp places, and must come frequently in
contact with Nostoc colonies. In Solorina crocea an interrupted band of
blue-green algae lies below the normal gonidial zone and sometimes
replaces it—a connecting structure between cephalodia and a true gonidial
zone.
c. Pseudocephalodia. Under this section have been classified those
cephalodia that are almost independent of the lichen thallus though to some
extent organically connected with it, as for instance that of Lecidea
panaeola which originate on the hypothallus of the lichen and maintain
their position between the crustaceous granules.
The cephalodia of Lecanora gelida, as described by Sernander[473], might
also be included here. He watched their development in their native habitat,
an exposed rock-surface which was richly covered with the lichen in all
stages of growth. Two kinds of thallus, the one containing blue-green algae
(Chroococcus), the other bright-green, were observed on the rock in close
proximity. At the point of contact, growth ceased, but the thallus with
bright-green algae, being the more vigorous, was able to spread round and
underneath the other and so gradually to transform it to a superficial flat
cephalodium. All such thalli encountered by the dominant lichen were
successively surrounded in the same way. The cephalodium, growing more
slowly, sent root-like hyphae into the tissue of the underlying lichen, and
the two organisms thus became organically connected. Sernander considers
that the two algae are antagonistic to each other, but that the hyphae can
combine with either.
The pseudocephalodia of Usnea species are abortive apothecia; they are
surrounded at the base by the gonidial zone and cortex of the thallus, and
general structure, but there is no intermixture of thalline gonidia. That
Nostoc cells can grow and retain the power to form chlorophyll in adverse
conditions was proved by Etard and Bouilhac[471] who made a culture of the
alga on artificial media in the dark, when there was formed a green pigment
of chlorophyll nature.
Endotrophic cephalodia occur in many groups of lichens. Hue[472] states
that he found them in twelve species of Aspicilia. As packets of blue-green
algae they are a constant feature in the thallus of Solorinae. The species of
that genus grow on mossy soil in damp places, and must come frequently in
contact with Nostoc colonies. In Solorina crocea an interrupted band of
blue-green algae lies below the normal gonidial zone and sometimes
replaces it—a connecting structure between cephalodia and a true gonidial
zone.
c. Pseudocephalodia. Under this section have been classified those
cephalodia that are almost independent of the lichen thallus though to some
extent organically connected with it, as for instance that of Lecidea
panaeola which originate on the hypothallus of the lichen and maintain
their position between the crustaceous granules.
The cephalodia of Lecanora gelida, as described by Sernander[473], might
also be included here. He watched their development in their native habitat,
an exposed rock-surface which was richly covered with the lichen in all
stages of growth. Two kinds of thallus, the one containing blue-green algae
(Chroococcus), the other bright-green, were observed on the rock in close
proximity. At the point of contact, growth ceased, but the thallus with
bright-green algae, being the more vigorous, was able to spread round and
underneath the other and so gradually to transform it to a superficial flat
cephalodium. All such thalli encountered by the dominant lichen were
successively surrounded in the same way. The cephalodium, growing more
slowly, sent root-like hyphae into the tissue of the underlying lichen, and
the two organisms thus became organically connected. Sernander considers
that the two algae are antagonistic to each other, but that the hyphae can
combine with either.
The pseudocephalodia of Usnea species are abortive apothecia; they are
surrounded at the base by the gonidial zone and cortex of the thallus, and
Page 207
they contain no foreign gonidia.
E. Autosymbiotic Cephalodia
Bitter[474] has thus designated small scales, like miniature thalli, that
develop constantly on the upper cortex of Peltigera lepidophora, a small
lichen not uncommon in Finland, and first recorded by Wainio as a variety
of Peltigera canina. The alga contained in the scales is a blue-green Nostoc
similar to the gonidia of the thallus. Bitter[475] described the development as
similar to that of the cephalodia of Peltigera aphthosa, but the outgrowths,
being lobate in form, are less firmly attached and thus easily become
separated and dispersed; as the gonidia are identical with those of the parent
thallus they act as vegetative organs of reproduction.
Bitter’s work has been criticized by Linkola[476] who claims to have
discovered by means of very thin microtome sections that there is a genetic
connection between the scales and the underlying thallus, not only with the
hyphae, as in true cephalodia, but with the algae as well, so that these
outgrowths should be regarded as isidia.
In the earliest stages, according to Linkola, a small group of algae may be
observed in the cortical tissue of the Peltigera apart from the gonidial zone
and near the upper surface. Gradually a protruding head is formed which is
at first covered over with a brown cortical layer one cell thick. The head
increases and becomes more lobate in form, being attached to the thallus at
the base by a very narrow neck and more loosely at other parts of the scale.
In older scales, the gonidia are entirely separated from those of the thallus,
and a dark-brown cortex several cells in thickness covers over the top and
sides; there is a colourless layer of plectenchyma beneath. At this advanced
stage the scales are almost completely superficial and correspond with the
cephaloidal rather than with the isidial type of formation. The algae even in
the very early stages are distinct from the gonidial zone and the whole
development, if isidial, must be considered as somewhat abnormal.
3. SOREDIA
A. Structure and Origin of Soredia
E. Autosymbiotic Cephalodia
Bitter[474] has thus designated small scales, like miniature thalli, that
develop constantly on the upper cortex of Peltigera lepidophora, a small
lichen not uncommon in Finland, and first recorded by Wainio as a variety
of Peltigera canina. The alga contained in the scales is a blue-green Nostoc
similar to the gonidia of the thallus. Bitter[475] described the development as
similar to that of the cephalodia of Peltigera aphthosa, but the outgrowths,
being lobate in form, are less firmly attached and thus easily become
separated and dispersed; as the gonidia are identical with those of the parent
thallus they act as vegetative organs of reproduction.
Bitter’s work has been criticized by Linkola[476] who claims to have
discovered by means of very thin microtome sections that there is a genetic
connection between the scales and the underlying thallus, not only with the
hyphae, as in true cephalodia, but with the algae as well, so that these
outgrowths should be regarded as isidia.
In the earliest stages, according to Linkola, a small group of algae may be
observed in the cortical tissue of the Peltigera apart from the gonidial zone
and near the upper surface. Gradually a protruding head is formed which is
at first covered over with a brown cortical layer one cell thick. The head
increases and becomes more lobate in form, being attached to the thallus at
the base by a very narrow neck and more loosely at other parts of the scale.
In older scales, the gonidia are entirely separated from those of the thallus,
and a dark-brown cortex several cells in thickness covers over the top and
sides; there is a colourless layer of plectenchyma beneath. At this advanced
stage the scales are almost completely superficial and correspond with the
cephaloidal rather than with the isidial type of formation. The algae even in
the very early stages are distinct from the gonidial zone and the whole
development, if isidial, must be considered as somewhat abnormal.
3. SOREDIA
A. Structure and Origin of Soredia
Page 208
Soredia are minute separable parts of the lichen thallus, and are
composed of one or more gonidia which are clasped and surrounded by the
lichen hyphae (Fig. 80). They occur on the surface or margins of the thallus
of a fairly large number of lichens either in a powdery excrescence or in a
pustule-like body comprehensively termed a “soralium” (Fig. 81). The
soralia vary in form and dimensions according to the species. Each
individual soredium is capable of developing into a new plant; it is a form
of vegetative reproduction characteristic of lichens.
Acharius[477] gave the name “soredia” to the
powdery bodies with reference to their
propagating function; he also interpreted the
soredium as an “apothecium of the second
order.” But long before his time they had been
observed and commented on by succeeding
Fig. 80. Soredia. a, of Physcia
pulverulenta Nyl.; b, of botanists: first by Malpighi[478] who judged
Ramalina farinacea Ach. × 600. them to be seeds, he having seen them develop
new plants; by Micheli[479] who however
distinguished between the true fruit and those
[480]
seeds; and by Linnaeus who considered them to be the female organs of
the plant, the apothecia being, as he then thought, the male organs.
Hedwig[481], on the other hand, regarded the apothecia as the seed
receptacles and the soredia as male bodies. Sprengel’s[482] statement that
they were “a subtile germinating powder mixed with delicate hair-like
threads which take the place of seeds” established finally their true
function. Wallroth[483], who was the first really to investigate their structure
and their relation to the parent plant, recognized them as of the same type as
the “brood-cells” or gonidia; and as the latter, he found, could become free
from the thallus and form a green layer on trees, walls, etc., in shady
situations, so the soredia also could become free, though for a time they
remained attached to the lichen and were covered by a veil, i.e. by the
surrounding hyphal filaments. Koerber[484] also gave much careful study to
soredia, their nature and function. As propagating organs he found they
were of more importance than spores, especially in the larger lichens.
composed of one or more gonidia which are clasped and surrounded by the
lichen hyphae (Fig. 80). They occur on the surface or margins of the thallus
of a fairly large number of lichens either in a powdery excrescence or in a
pustule-like body comprehensively termed a “soralium” (Fig. 81). The
soralia vary in form and dimensions according to the species. Each
individual soredium is capable of developing into a new plant; it is a form
of vegetative reproduction characteristic of lichens.
Acharius[477] gave the name “soredia” to the
powdery bodies with reference to their
propagating function; he also interpreted the
soredium as an “apothecium of the second
order.” But long before his time they had been
observed and commented on by succeeding
Fig. 80. Soredia. a, of Physcia
pulverulenta Nyl.; b, of botanists: first by Malpighi[478] who judged
Ramalina farinacea Ach. × 600. them to be seeds, he having seen them develop
new plants; by Micheli[479] who however
distinguished between the true fruit and those
[480]
seeds; and by Linnaeus who considered them to be the female organs of
the plant, the apothecia being, as he then thought, the male organs.
Hedwig[481], on the other hand, regarded the apothecia as the seed
receptacles and the soredia as male bodies. Sprengel’s[482] statement that
they were “a subtile germinating powder mixed with delicate hair-like
threads which take the place of seeds” established finally their true
function. Wallroth[483], who was the first really to investigate their structure
and their relation to the parent plant, recognized them as of the same type as
the “brood-cells” or gonidia; and as the latter, he found, could become free
from the thallus and form a green layer on trees, walls, etc., in shady
situations, so the soredia also could become free, though for a time they
remained attached to the lichen and were covered by a veil, i.e. by the
surrounding hyphal filaments. Koerber[484] also gave much careful study to
soredia, their nature and function. As propagating organs he found they
were of more importance than spores, especially in the larger lichens.
Page 209
Fig. 81. Vertical section of young soralium of Evernia furfuracea var. soralifera
Bitter × 60 (after Bitter).
According to Schwendener[485], the formation of soredia is due to
increased and almost abnormal activity of division in the gonidial cell; the
hyphal filament attached to it also becomes active and sends out branches
from the cell immediately below the point of contact which force their way
between the newly divided gonidia and finally surround them. A soredial
“head” of smaller or larger size is thus gradually built up on the stalk
filament or filaments, and is ultimately detached by the breaking down of
the slender support.
a. Scattered Soredia. The simplest example of soredial formation may
be seen on the bark of trees or on palings when the green coating of algal
cells is gradually assuming a greyish hue caused by the invasion of hyphal
lichenoid growth. This condition is generally referred to as “leprose” and
has even been classified as a distinct genus, Lepra or Lepraria. Somewhat
similar soredial growth is also associated with many species of Cladonia,
the turfy soil in the neighbourhood of the upright podetia being often
powdered with white granules. Such soredia are especially abundant in that
genus, so much so, that Meyer[486], Krabbe[487] and others have maintained
Bitter × 60 (after Bitter).
According to Schwendener[485], the formation of soredia is due to
increased and almost abnormal activity of division in the gonidial cell; the
hyphal filament attached to it also becomes active and sends out branches
from the cell immediately below the point of contact which force their way
between the newly divided gonidia and finally surround them. A soredial
“head” of smaller or larger size is thus gradually built up on the stalk
filament or filaments, and is ultimately detached by the breaking down of
the slender support.
a. Scattered Soredia. The simplest example of soredial formation may
be seen on the bark of trees or on palings when the green coating of algal
cells is gradually assuming a greyish hue caused by the invasion of hyphal
lichenoid growth. This condition is generally referred to as “leprose” and
has even been classified as a distinct genus, Lepra or Lepraria. Somewhat
similar soredial growth is also associated with many species of Cladonia,
the turfy soil in the neighbourhood of the upright podetia being often
powdered with white granules. Such soredia are especially abundant in that
genus, so much so, that Meyer[486], Krabbe[487] and others have maintained
Page 210
that the spores take little part in the propagation of species. The under side
of the primary thallus, but more frequently the upright podetia, are often
covered with a coating of soredia, either finely furfuraceous, or of larger
growth and coarsely granular, the size of the soredia depending on the
number of gonidia enclosed in each “head.”
Soredia are only occasionally present on the apothecial margins: the
rather swollen rims in Lobaria scrobiculata are sometimes powdery-grey,
and Bitter[488] has observed soredia, or rather soralia, on the apothecial
margins of Parmelia vittata; they are very rare, however, and are probably
to be explained by excess of moisture in the surroundings.
b. Isidial Soredia. In a few lichens soredia arise by the breaking down of
the cortex at the tips of the thalline outgrowths termed “isidia.” In Parmelia
verruculifera, for instance, where the coralloid isidia grow in closely
packed groups or warts, the upper part of the isidium frequently becomes
soredial. In that lichen the younger parts of the upper cortex bear hairs or
trichomes, and the individual soredia are also adorned with hairs. The
somewhat short warted isidia of P. subaurifera may become entirely
sorediose, and in P. farinacea the whole thallus is covered with isidia
transformed into soralia. The transformation is constant and is a distinct
specific character. Bitter[488] considers that it proves that no sharp
distinction exists between isidia and soralia, at least in their initial stages.
c. Soredia as Buds.
[489]
Schwendener has described
soredia in the genus Usnea which
give rise to new branches. Many of
the species in that genus are
plentifully sprinkled with the white
powdery bodies. A short way back
from the apex of the filament the
separate soredia show a tendency to
apical growth and might be
regarded as groups of young plants
still attached to the parent branch. Fig. 82. Usnea barbata Web. Longitudinal
section of filament and base of “soredial” branch
One of these developing more × 40 (after Schwendener).
quickly pushes the others aside and
of the primary thallus, but more frequently the upright podetia, are often
covered with a coating of soredia, either finely furfuraceous, or of larger
growth and coarsely granular, the size of the soredia depending on the
number of gonidia enclosed in each “head.”
Soredia are only occasionally present on the apothecial margins: the
rather swollen rims in Lobaria scrobiculata are sometimes powdery-grey,
and Bitter[488] has observed soredia, or rather soralia, on the apothecial
margins of Parmelia vittata; they are very rare, however, and are probably
to be explained by excess of moisture in the surroundings.
b. Isidial Soredia. In a few lichens soredia arise by the breaking down of
the cortex at the tips of the thalline outgrowths termed “isidia.” In Parmelia
verruculifera, for instance, where the coralloid isidia grow in closely
packed groups or warts, the upper part of the isidium frequently becomes
soredial. In that lichen the younger parts of the upper cortex bear hairs or
trichomes, and the individual soredia are also adorned with hairs. The
somewhat short warted isidia of P. subaurifera may become entirely
sorediose, and in P. farinacea the whole thallus is covered with isidia
transformed into soralia. The transformation is constant and is a distinct
specific character. Bitter[488] considers that it proves that no sharp
distinction exists between isidia and soralia, at least in their initial stages.
c. Soredia as Buds.
[489]
Schwendener has described
soredia in the genus Usnea which
give rise to new branches. Many of
the species in that genus are
plentifully sprinkled with the white
powdery bodies. A short way back
from the apex of the filament the
separate soredia show a tendency to
apical growth and might be
regarded as groups of young plants
still attached to the parent branch. Fig. 82. Usnea barbata Web. Longitudinal
section of filament and base of “soredial” branch
One of these developing more × 40 (after Schwendener).
quickly pushes the others aside and
Page 211
by continued growth fills up the soredial opening in the cortex with a plug
of tissue; finally it forms a complete lateral branch. Schwendener calls them
“soredial” branches (Fig. 82) to distinguish them from the others formed in
the course of the normal development.
B. Soralia
In lichens of foliose and fruticose structure, and in a few crustaceous
forms, the soredia are massed together into the compact bodies called
soralia, and thus are confined to certain areas of the plant surface. The
simpler soralia arise from the gonidial zone below the cortex by the active
division of some of the algal cells. The hyphae, interlaced with the green
cells, are thin-walled and are, as stated by Wainio[490], still in a
meristematic condition; they are thus able readily to branch and to form
new filaments which clasp the continually multiplying gonidia. This growth
is in an upward or outward direction away from the medulla, and strong
mechanical pressure is exerted by the increasing tissue on the overlying
cortical layers. Finally the soredia force their way through to the surface at
definite points. The cortex is thrown back and forms a margin round the
soralium, though shreds of epidermal tissue remain for a time mixed with
the powdery granules.
a. Form and Occurrence of Soralia. The term “soralium” was first
applied only to the highly developed soredial structures considered by
Acharius to be secondary apothecia; it is now employed for any
circumscribed group of soredia.[491] The soralia vary in size and form and in
position, according to the species on which they occur; these characters are
constant enough to be of considerable diagnostic value. Within the single
genus Parmelia, they are to be found as small round dots sprinkled over the
surface of P. dubia; as elongate furrows irregularly placed on P. sulcata; as
pearly excrescences at or near the margins of P. perlata, and as swollen
tubercles at the tips of the lobes of P. physodes (Fig. 83). Their development
is strongly influenced and furthered by shade and moisture, and, given such
conditions in excess, they may coalesce and cover large patches of the
thallus with a powdery coating, though only in those species that would
have borne soredia in fairly normal conditions.
of tissue; finally it forms a complete lateral branch. Schwendener calls them
“soredial” branches (Fig. 82) to distinguish them from the others formed in
the course of the normal development.
B. Soralia
In lichens of foliose and fruticose structure, and in a few crustaceous
forms, the soredia are massed together into the compact bodies called
soralia, and thus are confined to certain areas of the plant surface. The
simpler soralia arise from the gonidial zone below the cortex by the active
division of some of the algal cells. The hyphae, interlaced with the green
cells, are thin-walled and are, as stated by Wainio[490], still in a
meristematic condition; they are thus able readily to branch and to form
new filaments which clasp the continually multiplying gonidia. This growth
is in an upward or outward direction away from the medulla, and strong
mechanical pressure is exerted by the increasing tissue on the overlying
cortical layers. Finally the soredia force their way through to the surface at
definite points. The cortex is thrown back and forms a margin round the
soralium, though shreds of epidermal tissue remain for a time mixed with
the powdery granules.
a. Form and Occurrence of Soralia. The term “soralium” was first
applied only to the highly developed soredial structures considered by
Acharius to be secondary apothecia; it is now employed for any
circumscribed group of soredia.[491] The soralia vary in size and form and in
position, according to the species on which they occur; these characters are
constant enough to be of considerable diagnostic value. Within the single
genus Parmelia, they are to be found as small round dots sprinkled over the
surface of P. dubia; as elongate furrows irregularly placed on P. sulcata; as
pearly excrescences at or near the margins of P. perlata, and as swollen
tubercles at the tips of the lobes of P. physodes (Fig. 83). Their development
is strongly influenced and furthered by shade and moisture, and, given such
conditions in excess, they may coalesce and cover large patches of the
thallus with a powdery coating, though only in those species that would
have borne soredia in fairly normal conditions.
Page 212
Soralia of definite form are of rather rare occurrence in crustaceous
lichens, with the exception of the Pertusariaceae, where they are frequent,
and some species of Lecanora and Placodium. They are known in only two
hypophloeodal (subcortical) lichens, Arthonia pruinosa and Xylographa
spilomatica. Among squamulose thalli they are typical of some Cladoniae,
and also of Lecidea (Psora) ostreata, where they are produced on the upper
surface towards the apex of the squamule.
Fig. 83. Parmelia physodes Ach. Thallus growing horizontally;
soredia on the ends of the lobes (S. H., Photo.).
b. Position of soraliferous Lobes. According to observations made by
Bitter[492], the occurrence of soralia on one lobe or another may depend to a
considerable extent on the orientation of the thallus. He cites the variability
in habit of the familiar lichen, Parmelia physodes and its various forms,
which grow on trees or on soil. In the horizontal thalli there is much less
tendency to soredial formation, and the soredia that arise are generally
confined to branching lobes on the older parts of the thallus.
That type of growth is in marked contrast with the thallus obliged to take
a vertical direction as on a tree. In such a case the lobes, growing downward
from the point of origin, form soralia at their tips at an early stage (Fig. 84).
The lateral lobes, and especially those that lie close to the substratum, are
the next to become soraliate. Similar observations have been made on the
soraliferous lobes of Cetraria pinastri. The cause is probably due to the
lichens, with the exception of the Pertusariaceae, where they are frequent,
and some species of Lecanora and Placodium. They are known in only two
hypophloeodal (subcortical) lichens, Arthonia pruinosa and Xylographa
spilomatica. Among squamulose thalli they are typical of some Cladoniae,
and also of Lecidea (Psora) ostreata, where they are produced on the upper
surface towards the apex of the squamule.
Fig. 83. Parmelia physodes Ach. Thallus growing horizontally;
soredia on the ends of the lobes (S. H., Photo.).
b. Position of soraliferous Lobes. According to observations made by
Bitter[492], the occurrence of soralia on one lobe or another may depend to a
considerable extent on the orientation of the thallus. He cites the variability
in habit of the familiar lichen, Parmelia physodes and its various forms,
which grow on trees or on soil. In the horizontal thalli there is much less
tendency to soredial formation, and the soredia that arise are generally
confined to branching lobes on the older parts of the thallus.
That type of growth is in marked contrast with the thallus obliged to take
a vertical direction as on a tree. In such a case the lobes, growing downward
from the point of origin, form soralia at their tips at an early stage (Fig. 84).
The lateral lobes, and especially those that lie close to the substratum, are
the next to become soraliate. Similar observations have been made on the
soraliferous lobes of Cetraria pinastri. The cause is probably due to the
Page 213
greater excess of moisture draining downwards to the lower parts of the
thallus. The lobes that bear the soralia are generally narrower than the
others and are very frequently raised from contact with the substratum.
They tend to grow out from the thallus in an upright direction and then to
turn backwards at the tip, so that the opening of the soralium is directed
downwards. Bitter says that the cause of this change in direction is not
clear, though possibly on teleological reasoning it is of advantage that the
opening of the soralium should be protected from direct rainfall. The
opening lies midway between the upper and lower cortex, and the upper
tissue in these capitate soralia continues to grow and to form an arched
helmet or hood-covering which serves further to protect the soralium.
Fig. 84. Parmelia physodes Ach. Thallus growing
vertically; soredia chiefly on the lobes directed
downwards, reduced (M. P., Photo.).
Similar soralia are characteristic of Physcia hispida (Ph. stellaris subsp.
tenella), the apical helmet being a specially pronounced feature of that
species, though, as Lesdain[493] has pointed out, the hooded structures are
primarily the work of insects. In vertical substrata they occur on the lower
lobes of the plant.
thallus. The lobes that bear the soralia are generally narrower than the
others and are very frequently raised from contact with the substratum.
They tend to grow out from the thallus in an upright direction and then to
turn backwards at the tip, so that the opening of the soralium is directed
downwards. Bitter says that the cause of this change in direction is not
clear, though possibly on teleological reasoning it is of advantage that the
opening of the soralium should be protected from direct rainfall. The
opening lies midway between the upper and lower cortex, and the upper
tissue in these capitate soralia continues to grow and to form an arched
helmet or hood-covering which serves further to protect the soralium.
Fig. 84. Parmelia physodes Ach. Thallus growing
vertically; soredia chiefly on the lobes directed
downwards, reduced (M. P., Photo.).
Similar soralia are characteristic of Physcia hispida (Ph. stellaris subsp.
tenella), the apical helmet being a specially pronounced feature of that
species, though, as Lesdain[493] has pointed out, the hooded structures are
primarily the work of insects. In vertical substrata they occur on the lower
lobes of the plant.
Page 214
Apical soralia are rare in fruticose lichens, but in an Alpine variety of
Ramalina minuscula they are formed at the tips of the fronds and are
protected by an extension of the upper cortical tissues. Another instance
occurs in a Ramalina from New Granada referred by Nylander to R.
calicaris var. farinacea: it presents a striking example of the helmet tip.
c. Deep-seated Soralia. In the cases already described Schwendener[494]
and Nilson[495] held that the algae gave the first impulse to the formation of
the soredia; but in the Pertusariaceae[496], a family of crustaceous lichens,
there has been evolved a type of endogenous soralium which originates
with the medullary hyphae. In these, special hyphae rise from a weft of
filaments situated just above the lowest layer of the thallus at the base of the
medulla, the weft being distinguished from the surrounding tissue by
staining blue with iodine. A loose strand of hyphae staining the usual yellow
colour rises from the surface of the “blue” weft and, traversing the
medullary tissue, surrounds the gonidia on the under side of the gonidial
zone. The hyphae continue to grow upward, pushing aside both the upper
gonidial zone and the cortex, and carrying with them the algal cells first
encountered. When the summit is reached, there follows a very active
growth of both gonidia and hyphae. Each separate soredium so produced
consists finally of five to ten algal cells surrounded by hyphae and measures
8 µ to 13 µ in diameter. The cortex forms a well-defined wall or margin
round the mass of soredia.
A slightly different development is found in Lecanora tartarea, one of
the “crottle” lichens, which has been placed by Darbishire in
Pertusariaceae. The hyphae destined to form soredia also start from the weft
of tissue at the base of the thallus, but they simply grow through the
gonidial zone instead of pushing it aside.
In his examination of Pertusariaceae Darbishire found that the apothecia
also originated from a similar deeply seated blue-staining tissue, and he
concluded that the soralia represented abortive apothecia and really
corresponded to Acharius’s “apothecia of the second order.” His conclusion
as to the homology of these two organs is disputed by Bitter[497], who
considers that the common point of origin is explained by the equal demand
of the hyphae in both cases for special nutrition, and by the need of
mechanical support at the base to enable the hyphae to reach the surface and
Ramalina minuscula they are formed at the tips of the fronds and are
protected by an extension of the upper cortical tissues. Another instance
occurs in a Ramalina from New Granada referred by Nylander to R.
calicaris var. farinacea: it presents a striking example of the helmet tip.
c. Deep-seated Soralia. In the cases already described Schwendener[494]
and Nilson[495] held that the algae gave the first impulse to the formation of
the soredia; but in the Pertusariaceae[496], a family of crustaceous lichens,
there has been evolved a type of endogenous soralium which originates
with the medullary hyphae. In these, special hyphae rise from a weft of
filaments situated just above the lowest layer of the thallus at the base of the
medulla, the weft being distinguished from the surrounding tissue by
staining blue with iodine. A loose strand of hyphae staining the usual yellow
colour rises from the surface of the “blue” weft and, traversing the
medullary tissue, surrounds the gonidia on the under side of the gonidial
zone. The hyphae continue to grow upward, pushing aside both the upper
gonidial zone and the cortex, and carrying with them the algal cells first
encountered. When the summit is reached, there follows a very active
growth of both gonidia and hyphae. Each separate soredium so produced
consists finally of five to ten algal cells surrounded by hyphae and measures
8 µ to 13 µ in diameter. The cortex forms a well-defined wall or margin
round the mass of soredia.
A slightly different development is found in Lecanora tartarea, one of
the “crottle” lichens, which has been placed by Darbishire in
Pertusariaceae. The hyphae destined to form soredia also start from the weft
of tissue at the base of the thallus, but they simply grow through the
gonidial zone instead of pushing it aside.
In his examination of Pertusariaceae Darbishire found that the apothecia
also originated from a similar deeply seated blue-staining tissue, and he
concluded that the soralia represented abortive apothecia and really
corresponded to Acharius’s “apothecia of the second order.” His conclusion
as to the homology of these two organs is disputed by Bitter[497], who
considers that the common point of origin is explained by the equal demand
of the hyphae in both cases for special nutrition, and by the need of
mechanical support at the base to enable the hyphae to reach the surface and
Page 215
to thrust back the cortex without deviating from their upward course
through the tissues.
C. Dispersal and Germination of Soredia
Soredia become free by the breaking down of the hyphal stalks at the
septa or otherwise. They are widely dispersed by wind or water and soon
make their appearance on any suitable exposed soil. Krabbe[498] has stated
that, in many cases, the loosely attached soredia coating some of the
Cladonia podetia are of external origin, carried thither by the air-currents.
Insects too aid in the work of dissemination: Darbishire[499] has told us how
he watched small mites and other insects moving about over the soralia of
Pertusaria amara and becoming completely powdered by the white
granules.
Darbishire[499] also gives an account of his experiments in the culture of
soredia. He sowed them on poplar wood about the beginning of February in
suitable conditions of moisture, etc. Long hyphal threads were at once
produced from the filaments surrounding the gonidia, and gonidia that had
become free were seen to divide repeatedly. Towards the end of August of
the same year a few soredia had increased in size to about 450µ in diameter,
and were transferred to elm bark. By September they had further increased
to a diameter of 520µ, and the gonidia showed a tendency towards
aggregation. No further differentiation or growth was noted.
More success attended Tobler’s[500] attempt to cultivate the soredia of
Cladonia sp. He sowed them on soil kept suitably moist in a pot and after
about nine months he obtained fully formed squamules, at first only an
isolated one or two, but later a plentiful crop all over the surface of the soil.
Tobler also adds that soredia taken from a Cladonia, that had been kept for
about half a year in a dry room, grew when sown on a damp substratum.
The algae however had suffered more or less from the prolonged
desiccation, and some of them failed to develop.
A suggestion has been made by Bitter[501] that a hybrid plant might result
from the intermingling of soredia from the thallus of allied lichens. He
proposed the theory to explain the great similarity between plants of
through the tissues.
C. Dispersal and Germination of Soredia
Soredia become free by the breaking down of the hyphal stalks at the
septa or otherwise. They are widely dispersed by wind or water and soon
make their appearance on any suitable exposed soil. Krabbe[498] has stated
that, in many cases, the loosely attached soredia coating some of the
Cladonia podetia are of external origin, carried thither by the air-currents.
Insects too aid in the work of dissemination: Darbishire[499] has told us how
he watched small mites and other insects moving about over the soralia of
Pertusaria amara and becoming completely powdered by the white
granules.
Darbishire[499] also gives an account of his experiments in the culture of
soredia. He sowed them on poplar wood about the beginning of February in
suitable conditions of moisture, etc. Long hyphal threads were at once
produced from the filaments surrounding the gonidia, and gonidia that had
become free were seen to divide repeatedly. Towards the end of August of
the same year a few soredia had increased in size to about 450µ in diameter,
and were transferred to elm bark. By September they had further increased
to a diameter of 520µ, and the gonidia showed a tendency towards
aggregation. No further differentiation or growth was noted.
More success attended Tobler’s[500] attempt to cultivate the soredia of
Cladonia sp. He sowed them on soil kept suitably moist in a pot and after
about nine months he obtained fully formed squamules, at first only an
isolated one or two, but later a plentiful crop all over the surface of the soil.
Tobler also adds that soredia taken from a Cladonia, that had been kept for
about half a year in a dry room, grew when sown on a damp substratum.
The algae however had suffered more or less from the prolonged
desiccation, and some of them failed to develop.
A suggestion has been made by Bitter[501] that a hybrid plant might result
from the intermingling of soredia from the thallus of allied lichens. He
proposed the theory to explain the great similarity between plants of
Page 216
Parmelia physodes and P. tubulosa growing in close proximity. There is no
proof that such mingling of the fungal elements ever takes place.
D. Evolution of Soredia
Soredia have been compared to the gemmae of the Bryophytes and also
to the slips and cuttings of the higher plants. There is a certain analogy
between all forms of vegetative reproduction, but soredia are peculiar in
that they include two dissimilar organisms. In the lichen kingdom there has
been evolved this new form of propagation in order to secure the
continuance of the composite life, and, in a number of species, it has almost
entirely superseded the somewhat uncertain method of spore germination
inherited from the fungal ancestor, but which leaves more or less to chance
the encounter with the algal symbiont.
From a phylogenetic point of view we should regard the sorediate lichens
as the more highly evolved, and those which have no soredia as
phylogenetically young, though, as Lindau[502] has pointed out, soredia are
all comparatively recent. They probably did not appear until lichens had
reached a more or less advanced stage of development, and, considering the
polyphyletic origin of lichens, they must have arisen at more than one point,
and probably at first in circumstances where the formation of apothecia was
hindered by prolonged conditions of shade and moisture.
That soredia are ontogenetic in character, and not, as Nilson[503] has
asserted, accidental products of excessively moist conditions is further
proved by the non-sorediate character of those species of crustaceous
lichens belonging to Lecanora, Verrucaria, etc. that are frequently
immersed in water. Bitter[504] found that the soredia occurring on Peltigera
spuria were not formed on the lobes which were more constantly moist, nor
at the edges where the cortex was thinnest: they always emerged on young
parts of the thallus a short way back from the edge.
Bitter[504] points out that in extremely unfavourable circumstances—in
the polluted atmosphere near towns, or in persistent shade—lichens, that
would otherwise form a normal thallus, remain in a backward sorediose
state. He considers, however, that many of these formless crusts are
autonomous growths with specific morphological and chemical
proof that such mingling of the fungal elements ever takes place.
D. Evolution of Soredia
Soredia have been compared to the gemmae of the Bryophytes and also
to the slips and cuttings of the higher plants. There is a certain analogy
between all forms of vegetative reproduction, but soredia are peculiar in
that they include two dissimilar organisms. In the lichen kingdom there has
been evolved this new form of propagation in order to secure the
continuance of the composite life, and, in a number of species, it has almost
entirely superseded the somewhat uncertain method of spore germination
inherited from the fungal ancestor, but which leaves more or less to chance
the encounter with the algal symbiont.
From a phylogenetic point of view we should regard the sorediate lichens
as the more highly evolved, and those which have no soredia as
phylogenetically young, though, as Lindau[502] has pointed out, soredia are
all comparatively recent. They probably did not appear until lichens had
reached a more or less advanced stage of development, and, considering the
polyphyletic origin of lichens, they must have arisen at more than one point,
and probably at first in circumstances where the formation of apothecia was
hindered by prolonged conditions of shade and moisture.
That soredia are ontogenetic in character, and not, as Nilson[503] has
asserted, accidental products of excessively moist conditions is further
proved by the non-sorediate character of those species of crustaceous
lichens belonging to Lecanora, Verrucaria, etc. that are frequently
immersed in water. Bitter[504] found that the soredia occurring on Peltigera
spuria were not formed on the lobes which were more constantly moist, nor
at the edges where the cortex was thinnest: they always emerged on young
parts of the thallus a short way back from the edge.
Bitter[504] points out that in extremely unfavourable circumstances—in
the polluted atmosphere near towns, or in persistent shade—lichens, that
would otherwise form a normal thallus, remain in a backward sorediose
state. He considers, however, that many of these formless crusts are
autonomous growths with specific morphological and chemical
Page 217
peculiarities. They hold these outposts of lichen vegetation and are not
found growing in any other localities. The proof would be to transport them
to more favourable conditions, and watch development.
4. ISIDIA
A. Form and Structure of Isidia
Many lichens are rough and scabrous on the surface, with minute simple
or divided coral-like outgrowths of the same texture as the underlying
thallus, though sometimes they are darker in colour as in Evernia
furfuracea. They always contain gonidia and are covered by a cortex
continuous with that of the thallus.
This very marked condition was considered by Acharius[505] as of generic
importance and the genus, Isidium, was established by him, with the
diagnostic characters: “branchlets produced on the surface, or coralloid,
simple and branched.” In the genus were included the more densely isidioid
states of various crustaceous species such as Isidium corallinum and I.
Westringii, both of which are varieties of Pertusariae. Fries[506], with his
accustomed insight, recognized them as only growth forms. The genus was
however still accepted in English Floras[507] as late as 1833, though we find
it dropped by Taylor[508] in the Flora Hibernica a few years later.
The development of the isidial outgrowth has been described by
Rosendahl[509] in several species of Parmelia. In one of them, P. papulosa,
which has a cortical layer one cell thick, the isidium begins as a small
swelling or wart on the upper surface of the thallus. At that stage the cells of
the cortex have already lost their normal arrangement and show irregular
division. They divide still further, as gonidia and hyphae push their way up.
The full-grown isidia in this species are cylindrical or clavate, simple or
branched. They are peculiar in that they bear laterally here and there minute
rhizoids, a development not recorded in any other isidia. The inner tissue
accords with that of the normal thallus and there is a clearly marked cortex,
gonidial zone and pith. A somewhat analogous development takes place in
the isidia of Parmelia proboscidea; in that lichen they are mostly prolonged
into a dark-coloured cilium.
found growing in any other localities. The proof would be to transport them
to more favourable conditions, and watch development.
4. ISIDIA
A. Form and Structure of Isidia
Many lichens are rough and scabrous on the surface, with minute simple
or divided coral-like outgrowths of the same texture as the underlying
thallus, though sometimes they are darker in colour as in Evernia
furfuracea. They always contain gonidia and are covered by a cortex
continuous with that of the thallus.
This very marked condition was considered by Acharius[505] as of generic
importance and the genus, Isidium, was established by him, with the
diagnostic characters: “branchlets produced on the surface, or coralloid,
simple and branched.” In the genus were included the more densely isidioid
states of various crustaceous species such as Isidium corallinum and I.
Westringii, both of which are varieties of Pertusariae. Fries[506], with his
accustomed insight, recognized them as only growth forms. The genus was
however still accepted in English Floras[507] as late as 1833, though we find
it dropped by Taylor[508] in the Flora Hibernica a few years later.
The development of the isidial outgrowth has been described by
Rosendahl[509] in several species of Parmelia. In one of them, P. papulosa,
which has a cortical layer one cell thick, the isidium begins as a small
swelling or wart on the upper surface of the thallus. At that stage the cells of
the cortex have already lost their normal arrangement and show irregular
division. They divide still further, as gonidia and hyphae push their way up.
The full-grown isidia in this species are cylindrical or clavate, simple or
branched. They are peculiar in that they bear laterally here and there minute
rhizoids, a development not recorded in any other isidia. The inner tissue
accords with that of the normal thallus and there is a clearly marked cortex,
gonidial zone and pith. A somewhat analogous development takes place in
the isidia of Parmelia proboscidea; in that lichen they are mostly prolonged
into a dark-coloured cilium.
Page 218
In Parmelia scortea the cortex is several cells thick, and the outermost
rows are compressed and dead in the older parts of the thallus; but here also
the first appearance of the isidium is in the form of a minute wart. The
lower layers (4 to 6) of living cortical cells divide actively; the gonidia also
share in the new growth, and the protuberance thus formed pushes off the
outer dead cortex and emerges as an isidium (Fig. 85). They are always
rather stouter in form than those of P. papulosa and may be simple or
branched. The gonidia in this case do not form a definite zone, but are
scattered through the pith of the isidium.
Here also should be included the coralloid branching isidia that adorn the
upper surface and margins of the thallus of Umbilicaria pustulata. They
begin as small tufts of somewhat cylindrical bodies, but they sometimes
broaden out to almost leafy expansions with crisp edges. Most frequently
they are situated on the bulging pustules where intercalary growth is active.
Owing to their continued development on these areas, the tissue becomes
slack, and the centre of the isidial tuft may fall out, leaving a hole in the
thallus which becomes still more open by the tension of thalline expansion.
New isidia sprout from the edges of the wound and the process may again
be repeated. It has been asserted that these structures are only formed on
injured parts of the thallus—something like gall-formations—but Bitter[510]
has proved that the wound is first occasioned by the isidial growth
weakening the thallus.
rows are compressed and dead in the older parts of the thallus; but here also
the first appearance of the isidium is in the form of a minute wart. The
lower layers (4 to 6) of living cortical cells divide actively; the gonidia also
share in the new growth, and the protuberance thus formed pushes off the
outer dead cortex and emerges as an isidium (Fig. 85). They are always
rather stouter in form than those of P. papulosa and may be simple or
branched. The gonidia in this case do not form a definite zone, but are
scattered through the pith of the isidium.
Here also should be included the coralloid branching isidia that adorn the
upper surface and margins of the thallus of Umbilicaria pustulata. They
begin as small tufts of somewhat cylindrical bodies, but they sometimes
broaden out to almost leafy expansions with crisp edges. Most frequently
they are situated on the bulging pustules where intercalary growth is active.
Owing to their continued development on these areas, the tissue becomes
slack, and the centre of the isidial tuft may fall out, leaving a hole in the
thallus which becomes still more open by the tension of thalline expansion.
New isidia sprout from the edges of the wound and the process may again
be repeated. It has been asserted that these structures are only formed on
injured parts of the thallus—something like gall-formations—but Bitter[510]
has proved that the wound is first occasioned by the isidial growth
weakening the thallus.
Page 219
Fig. 85. Vertical section of isidia of
Parmelia scortea Ach. A, early stage; B.
later stage. × 60 (after Rosendahl).
B. Origin and Function of Isidia
Nilson[511] (later Kajanus[512]) insists that isidia and soredia are both
products of excessive moisture. He argues that lichen species, in the course
of their development, have become adapted to a certain degree of humidity,
and, if the optimum is passed, the new conditions entail a change in the
growth of the plant. The gonidia are stimulated to increased growth, and the
mechanical pressure exerted by the multiplying cells either results in the
emergence of isidial structures where the cortex is unbroken, or, if the
cortex is weaker and easily bursts, in the formation of soralia.
This view can hardly be accepted; isidia as well as soredia are typical of
certain species and are produced regularly and normally in ordinary
conditions; both of them are often present on the same thallus. It is not
denied, however, that their development in certain instances is furthered by
Parmelia scortea Ach. A, early stage; B.
later stage. × 60 (after Rosendahl).
B. Origin and Function of Isidia
Nilson[511] (later Kajanus[512]) insists that isidia and soredia are both
products of excessive moisture. He argues that lichen species, in the course
of their development, have become adapted to a certain degree of humidity,
and, if the optimum is passed, the new conditions entail a change in the
growth of the plant. The gonidia are stimulated to increased growth, and the
mechanical pressure exerted by the multiplying cells either results in the
emergence of isidial structures where the cortex is unbroken, or, if the
cortex is weaker and easily bursts, in the formation of soralia.
This view can hardly be accepted; isidia as well as soredia are typical of
certain species and are produced regularly and normally in ordinary
conditions; both of them are often present on the same thallus. It is not
denied, however, that their development in certain instances is furthered by
Page 220
increased shade or moisture. In Evernia furfuracea isidia are more freely
produced on the older more shaded parts of the thallus. Zopf[513] has
described such an instance in Evernia olivetorina (E. furfuracea), which
grew in the high Alps on pine trees, and which was much more isidiose
when it grew on the outer ends of the branches, where dew, rain or snow
had more direct influence. He[514] quotes other examples occurring in forms
of E. furfuracea which grew on the branches of pines, larches, etc. in a
damp locality in S. Tyrol. The thalli hung in great abundance on each side
of the branches, and were invariably more isidiose near the tips, because
evidently the water or snow trickled down and was retained longer there
than at the base.
Bitter[515] has given a striking instance of shade influence in Umbilicaria.
He found that some boulders on which the lichen grew freely had become
covered over with fallen pine needles. The result was at first an enormous
increase of the coralline isidia, though finally the lichen was killed by the
want of light.
Isidia are primarily of service to the plant in increasing the assimilating
surface. Occasionally they grow out into new thallus lobes. The more
slender are easily rubbed off, and, when scattered, become efficient organs
of propagation. This view of their function is emphasized by Bitter who
points out that both in Evernia furfuracea and in Umbilicaria pustulata
other organs of reproduction are rare or absent. Zopf[513] found new plants
of Evernia furfuracea beginning to grow on the trunk of a tree lower down
than an old isidiose specimen. They had developed from isidia which had
been detached and washed down by rain.
VI. HYMENOLICHENS
A. Supposed Affinity with other Plants
Lichens in which the fungal elements belong to the Hymenomycetes are
confined to three tropical genera. They are associated with blue-green algae
and are most nearly related to the Thelephoraceae among fungi. The spores
are borne, as in that family, on basidia.
produced on the older more shaded parts of the thallus. Zopf[513] has
described such an instance in Evernia olivetorina (E. furfuracea), which
grew in the high Alps on pine trees, and which was much more isidiose
when it grew on the outer ends of the branches, where dew, rain or snow
had more direct influence. He[514] quotes other examples occurring in forms
of E. furfuracea which grew on the branches of pines, larches, etc. in a
damp locality in S. Tyrol. The thalli hung in great abundance on each side
of the branches, and were invariably more isidiose near the tips, because
evidently the water or snow trickled down and was retained longer there
than at the base.
Bitter[515] has given a striking instance of shade influence in Umbilicaria.
He found that some boulders on which the lichen grew freely had become
covered over with fallen pine needles. The result was at first an enormous
increase of the coralline isidia, though finally the lichen was killed by the
want of light.
Isidia are primarily of service to the plant in increasing the assimilating
surface. Occasionally they grow out into new thallus lobes. The more
slender are easily rubbed off, and, when scattered, become efficient organs
of propagation. This view of their function is emphasized by Bitter who
points out that both in Evernia furfuracea and in Umbilicaria pustulata
other organs of reproduction are rare or absent. Zopf[513] found new plants
of Evernia furfuracea beginning to grow on the trunk of a tree lower down
than an old isidiose specimen. They had developed from isidia which had
been detached and washed down by rain.
VI. HYMENOLICHENS
A. Supposed Affinity with other Plants
Lichens in which the fungal elements belong to the Hymenomycetes are
confined to three tropical genera. They are associated with blue-green algae
and are most nearly related to the Thelephoraceae among fungi. The spores
are borne, as in that family, on basidia.
Page 221
Fig. 86. Cora Pavonia Fr. (after Mattirolo).
The best known Hymenolichen, Cora Pavonia (Fig. 86), was discovered
by Swartz[516] during his travels in the W. Indies (1785-87) growing on
trees in the mountains of Jamaica, and the new plant was recorded by him
as Ulva montana. Gmelin[517] also included it in Ulva in close association
with Ulva (Padina) Pavonia, but that classification was shortly after
disputed by Woodward[518] who thought its affinity was more nearly with
the fungi and suggested that it should be made the type of a new genus near
to Boletus (Polystictus) versicolor. Fries[519] in due time made the new
genus Cora, though he included it among algae; finally Nylander[520]
established the lichenoid character of the thallus and transferred it to the
Lecanorei.
The best known Hymenolichen, Cora Pavonia (Fig. 86), was discovered
by Swartz[516] during his travels in the W. Indies (1785-87) growing on
trees in the mountains of Jamaica, and the new plant was recorded by him
as Ulva montana. Gmelin[517] also included it in Ulva in close association
with Ulva (Padina) Pavonia, but that classification was shortly after
disputed by Woodward[518] who thought its affinity was more nearly with
the fungi and suggested that it should be made the type of a new genus near
to Boletus (Polystictus) versicolor. Fries[519] in due time made the new
genus Cora, though he included it among algae; finally Nylander[520]
established the lichenoid character of the thallus and transferred it to the
Lecanorei.
Page 222
It was made the subject of more exact investigation by Mattirolo[521] who
recognized its affinity with Thelephora, a genus of Hymenomycetes. Later
Johow[522] went to the West Indies and studied the Hymenolichens in their
native home. The genera and species described by Johow have been
reduced to Cora and Dictyonema; a new genus Corella has since been
added by Wainio[523].
Johow found that Cora grew on the mountains usually from 1000 to 2000
ft. above sea-level. As it requires for its development a cool damp climate
with strong though indirect illumination, it is found neither in sunny
situations nor in the depths of dark woods. It grows most freely in diffuse
light, on the lower trunks and branches of trees in open situations, but high
up on the stem where the vegetation is more dense. It stands out from the
tree like a small thin bracket fungus, one specimen placed above another,
with a dimidiate growth similar to that of Polystictus versicolor. Both
surfaces are marked by concentric zones which give it an appearance
somewhat like Padina Pavonia. These zones indicate unequal intercalary
growth both above and below. The whole plant is blue-green when wet,
greyish-white when dry, and of a thin membranaceous consistency.
B. Structure of Thallus
There is no proper cortex in any of the genera, but in Cora there is a
fastigiate branching of the hyphae in parallel lines towards the upper
surface; just at the outside they turn and lie in a horizontal direction, and, as
the branching becomes more profuse, a rather compact cover is formed. The
gonidia, which consist of blue-green Chroococcus cells, lie at the base of
the upward branches and they are surrounded with thin-walled short-celled
hyphae closely interwoven into a kind of cellular tissue. The medulla of
loose hyphae passes over to the lower cortex, also of more or less loose
filaments. The outermost cells of the latter very frequently grow out into
short jagged or crenate processes (Fig. 87).
recognized its affinity with Thelephora, a genus of Hymenomycetes. Later
Johow[522] went to the West Indies and studied the Hymenolichens in their
native home. The genera and species described by Johow have been
reduced to Cora and Dictyonema; a new genus Corella has since been
added by Wainio[523].
Johow found that Cora grew on the mountains usually from 1000 to 2000
ft. above sea-level. As it requires for its development a cool damp climate
with strong though indirect illumination, it is found neither in sunny
situations nor in the depths of dark woods. It grows most freely in diffuse
light, on the lower trunks and branches of trees in open situations, but high
up on the stem where the vegetation is more dense. It stands out from the
tree like a small thin bracket fungus, one specimen placed above another,
with a dimidiate growth similar to that of Polystictus versicolor. Both
surfaces are marked by concentric zones which give it an appearance
somewhat like Padina Pavonia. These zones indicate unequal intercalary
growth both above and below. The whole plant is blue-green when wet,
greyish-white when dry, and of a thin membranaceous consistency.
B. Structure of Thallus
There is no proper cortex in any of the genera, but in Cora there is a
fastigiate branching of the hyphae in parallel lines towards the upper
surface; just at the outside they turn and lie in a horizontal direction, and, as
the branching becomes more profuse, a rather compact cover is formed. The
gonidia, which consist of blue-green Chroococcus cells, lie at the base of
the upward branches and they are surrounded with thin-walled short-celled
hyphae closely interwoven into a kind of cellular tissue. The medulla of
loose hyphae passes over to the lower cortex, also of more or less loose
filaments. The outermost cells of the latter very frequently grow out into
short jagged or crenate processes (Fig. 87).
Page 223
Fig. 87. Cora Pavonia Fr. Vertical
section of thallus. a, upper cortex; b,
gonidial layer; c, medulla and lower
cortex of crenate cells; d, tuft of fertile
hyphae. × 160. e, basidia and spores ×
1000 (after Johow).
In Corella, the mature lichen is squamulose or consists of small lobes; in
Dictyonema there is a rather flat dimidiate expansion; in both the alga is
Scytonema, the trichomes of which largely retain their form and are
surrounded by parallel growths of branching hyphae. The whole tissue is
loose and spongy.
section of thallus. a, upper cortex; b,
gonidial layer; c, medulla and lower
cortex of crenate cells; d, tuft of fertile
hyphae. × 160. e, basidia and spores ×
1000 (after Johow).
In Corella, the mature lichen is squamulose or consists of small lobes; in
Dictyonema there is a rather flat dimidiate expansion; in both the alga is
Scytonema, the trichomes of which largely retain their form and are
surrounded by parallel growths of branching hyphae. The whole tissue is
loose and spongy.
Page 224
Corella spreads over soil on a white hypothallus without rhizinae. In the
other two genera which live on soil, or more frequently on trees, there is a
rather extensive formation of hold-fast tissue. When the dimidiate thallus
grows on a rough bark, rhizoidal strands of hyphae travel over it and
penetrate between the cracks; if the bark is smooth, there is a more
continuous weft of hyphae. In both cases a spongy cushion of filamentous
tissue develops at the base of the lichen between the tree and the bracket
thallus. There is also in both genera an encrusting form which Johow
regarded as representing a distinct genus Laudatea, but which Möller found
to be merely a growth stage. Möller[524] judged from that and from other
characteristics that the same fungus enters into the composition of both
Cora and Dictyonema and that only the algal constituents are different.
C. Sporiferous Tissues
As in Hymenomycetes, the spores of Hymenolichens are exogenous, and
are borne at the tips of basidia which in these lichens are produced on the
under surface of the thallus. In Cora the fertile filaments may form a
continuous series of basidia over the surface, but generally they grow out in
separate though crowded tufts. As these tufts broaden outwards, they tend to
unite at the free edges, and may finally present a continuous hymenial layer.
Each basidium bears four sterigmata and spores (Fig. 87 e); paraphyses
exactly similar to the basidia are abundant in the hymenium. In Dictyonema
the hymenium is less regular, but otherwise it resembles that of Cora. No
hymenium has as yet been observed in Corella; it includes, so far as known,
one species, C. brasiliensis, which spreads over soil or rocks.
other two genera which live on soil, or more frequently on trees, there is a
rather extensive formation of hold-fast tissue. When the dimidiate thallus
grows on a rough bark, rhizoidal strands of hyphae travel over it and
penetrate between the cracks; if the bark is smooth, there is a more
continuous weft of hyphae. In both cases a spongy cushion of filamentous
tissue develops at the base of the lichen between the tree and the bracket
thallus. There is also in both genera an encrusting form which Johow
regarded as representing a distinct genus Laudatea, but which Möller found
to be merely a growth stage. Möller[524] judged from that and from other
characteristics that the same fungus enters into the composition of both
Cora and Dictyonema and that only the algal constituents are different.
C. Sporiferous Tissues
As in Hymenomycetes, the spores of Hymenolichens are exogenous, and
are borne at the tips of basidia which in these lichens are produced on the
under surface of the thallus. In Cora the fertile filaments may form a
continuous series of basidia over the surface, but generally they grow out in
separate though crowded tufts. As these tufts broaden outwards, they tend to
unite at the free edges, and may finally present a continuous hymenial layer.
Each basidium bears four sterigmata and spores (Fig. 87 e); paraphyses
exactly similar to the basidia are abundant in the hymenium. In Dictyonema
the hymenium is less regular, but otherwise it resembles that of Cora. No
hymenium has as yet been observed in Corella; it includes, so far as known,
one species, C. brasiliensis, which spreads over soil or rocks.
Page 225
CHAPTER IV
REPRODUCTION
1. REPRODUCTION BY ASCOSPORES
A. Historical Survey
The earliest observations as to the propagation of lichens were made by
Malpighi[525] who recorded the presence of soredia on the lichen plant and
noted their function as reproductive bodies. He was followed after a
considerable interval by Tournefort[526] who placed lichens in a class apart
owing to the form of the fruit: “This fruit,” he writes, “is a species of bason
or cup which seems to take the place of seeds in these kinds of plants.” He
figures Ramalina fraxinea and Physcia ciliaris, both well fruited specimens,
and he represents the “minute dust” contained in the fruits as subrotund in
form. The spores of Physcia ciliaris are of a large size and dark in colour
and were undoubtedly seen by Tournefort. Morison[527], in his History of
Oxford Plants, published very shortly after, dismissed Tournefort’s “seeds”
as being too minute to be of any practical interest.
Micheli[528], with truer scientific insight, made the fruiting organs the
subject of special study. He decided that the apothecia were floral
receptacles, receptacula florum, and that the spores were the “flowers” of
the lichen. He has figured them in a vertical series in situ, in a section of the
disc of Solorina saccata[529] and also in a species of Pertusaria[529], in both
of which plants the ascospores are unusually large. He adds that he had not
so far seen the “semina.”
Micheli’s views were not shared by his immediate successors.
Dillenius[530] scarcely believed that the spores could be “flowers” and, in
any case, he concluded that they were too minute to be of any real
significance in the life of the plant.
REPRODUCTION
1. REPRODUCTION BY ASCOSPORES
A. Historical Survey
The earliest observations as to the propagation of lichens were made by
Malpighi[525] who recorded the presence of soredia on the lichen plant and
noted their function as reproductive bodies. He was followed after a
considerable interval by Tournefort[526] who placed lichens in a class apart
owing to the form of the fruit: “This fruit,” he writes, “is a species of bason
or cup which seems to take the place of seeds in these kinds of plants.” He
figures Ramalina fraxinea and Physcia ciliaris, both well fruited specimens,
and he represents the “minute dust” contained in the fruits as subrotund in
form. The spores of Physcia ciliaris are of a large size and dark in colour
and were undoubtedly seen by Tournefort. Morison[527], in his History of
Oxford Plants, published very shortly after, dismissed Tournefort’s “seeds”
as being too minute to be of any practical interest.
Micheli[528], with truer scientific insight, made the fruiting organs the
subject of special study. He decided that the apothecia were floral
receptacles, receptacula florum, and that the spores were the “flowers” of
the lichen. He has figured them in a vertical series in situ, in a section of the
disc of Solorina saccata[529] and also in a species of Pertusaria[529], in both
of which plants the ascospores are unusually large. He adds that he had not
so far seen the “semina.”
Micheli’s views were not shared by his immediate successors.
Dillenius[530] scarcely believed that the spores could be “flowers” and, in
any case, he concluded that they were too minute to be of any real
significance in the life of the plant.
Page 226
Linnaeus[531], and after him Necker[532], Scopoli[533] and others describe
the apothecia as the male, the soredia as the female organs of lichens. These
old time botanists worked with very low powers of magnification, and
easily went astray in the interpretation of imperfectly seen phenomena.
Koelreuter[534], a Professor of Natural History in Carlsruhe, who
published a work on The discovered Secret of Cryptogams, next hazarded
the opinion that the seeds of lichens originated from the substance of the
pith, and that the overlying cortical layer supplied the fertilizing sap.
Hoffmann[535] devoted a great deal of attention to lichen fructification and
he also thought that fertilization must take place within the tissue of the
lichens. He regarded the soredia as the true seeds, while allowing that a
second series of seeds might be contained in the scutellae (apothecia).
A distinct advance was made by Hedwig[536], a Professor of Botany in
Leipzig, towards the end of the eighteenth century. He followed Tournefort
in selecting Physcia ciliaris for research, and in that plant he describes and
figures not only the apothecia with the dark-coloured septate spores, but
also the pycnidia or spermogonia which he regarded as male organs. The
soredia, typically represented and figured by him on Parmelia physodes, he
judged to be “male flowers of a different type.”
Acharius[537] did not add much to the knowledge of reproduction in
lichens, though he takes ample note of the various fruiting structures for
which he invented the terms apothecia, perithecia and soredia. Under still
another term gongyli he included not only spores, but the spore guttulae as
well as the gonidia or cells forming the soredia.
Hornschuch[538] of Greifswald described the propagation of the lower
lichens as being solely by means of a germinating “powder”; the more
highly organized forms were provided with receptacles or apothecia
containing spores which he considered as analogous to flowers rather than
to fruits. The important contributions to Lichenology of Wallroth[539] and
Meyer[540] close this period of uncertainty: the former deals almost
exclusively with the form and character of the vegetative thallus and the
function of the “reproductive gonidia.” Meyer, a less prolix writer, very
clearly states that the method of reproduction is twofold: by spores
produced in fruits, or by the germinating granules of the soredia.
the apothecia as the male, the soredia as the female organs of lichens. These
old time botanists worked with very low powers of magnification, and
easily went astray in the interpretation of imperfectly seen phenomena.
Koelreuter[534], a Professor of Natural History in Carlsruhe, who
published a work on The discovered Secret of Cryptogams, next hazarded
the opinion that the seeds of lichens originated from the substance of the
pith, and that the overlying cortical layer supplied the fertilizing sap.
Hoffmann[535] devoted a great deal of attention to lichen fructification and
he also thought that fertilization must take place within the tissue of the
lichens. He regarded the soredia as the true seeds, while allowing that a
second series of seeds might be contained in the scutellae (apothecia).
A distinct advance was made by Hedwig[536], a Professor of Botany in
Leipzig, towards the end of the eighteenth century. He followed Tournefort
in selecting Physcia ciliaris for research, and in that plant he describes and
figures not only the apothecia with the dark-coloured septate spores, but
also the pycnidia or spermogonia which he regarded as male organs. The
soredia, typically represented and figured by him on Parmelia physodes, he
judged to be “male flowers of a different type.”
Acharius[537] did not add much to the knowledge of reproduction in
lichens, though he takes ample note of the various fruiting structures for
which he invented the terms apothecia, perithecia and soredia. Under still
another term gongyli he included not only spores, but the spore guttulae as
well as the gonidia or cells forming the soredia.
Hornschuch[538] of Greifswald described the propagation of the lower
lichens as being solely by means of a germinating “powder”; the more
highly organized forms were provided with receptacles or apothecia
containing spores which he considered as analogous to flowers rather than
to fruits. The important contributions to Lichenology of Wallroth[539] and
Meyer[540] close this period of uncertainty: the former deals almost
exclusively with the form and character of the vegetative thallus and the
function of the “reproductive gonidia.” Meyer, a less prolix writer, very
clearly states that the method of reproduction is twofold: by spores
produced in fruits, or by the germinating granules of the soredia.
Page 227
B. Forms of Reproductive Organs
From the time of Tournefort, considerable attention had been given to the
various forms of scutellae, tuberculae, etc., as characters of diagnostic
importance. Sprengel[541] grouped these bodies finally into nine different
types with appropriate names which have now been mostly superseded by
the comprehensive terms, apothecia and perithecia. A general classification
on the lines of fruit development was established by Luyken[542], who,
following Persoon’s[543] classification of fungi, and thus recognizing their
affinity, summed up all known lichens as Gymnocarpeae with open fruits,
and Angiocarpeae with closed fruits.
a. Apothecia. As in discomycetous fungi, the lichen apothecium is in the
form of an open concave or convex disc, but generally of rather small size,
rarely more than 1 cm. in diameter (Fig. 88); there is no development in
lichen fruits equal to the cup-like ascomata of the larger Pezizae. In most
cases the lichen apothecium retains its vitality as a spore-bearing organ for a
considerable period, sometimes for several years, and it is strengthened and
protected by one or more external margins of sterile tissue. Immediately
surrounding the fertile disc there is a compact wall of interwoven hyphae.
In some of the shorter-lived soft fruits, as in Biatora, this hyphal margin
may be thin, and may gradually be pushed aside as the disc develops and
becomes convex, but generally it forms a prominent rim round the disc and
may be tough or even horny, and often hard and carbonaceous. This wall,
which is present, to some extent, in nearly all lichens, is described as the
“proper margin.” A second “thalline margin” containing gonidia is present
in many genera[544]: it is a structure peculiar to the lichen apothecium and
forms the amphithecium.
From the time of Tournefort, considerable attention had been given to the
various forms of scutellae, tuberculae, etc., as characters of diagnostic
importance. Sprengel[541] grouped these bodies finally into nine different
types with appropriate names which have now been mostly superseded by
the comprehensive terms, apothecia and perithecia. A general classification
on the lines of fruit development was established by Luyken[542], who,
following Persoon’s[543] classification of fungi, and thus recognizing their
affinity, summed up all known lichens as Gymnocarpeae with open fruits,
and Angiocarpeae with closed fruits.
a. Apothecia. As in discomycetous fungi, the lichen apothecium is in the
form of an open concave or convex disc, but generally of rather small size,
rarely more than 1 cm. in diameter (Fig. 88); there is no development in
lichen fruits equal to the cup-like ascomata of the larger Pezizae. In most
cases the lichen apothecium retains its vitality as a spore-bearing organ for a
considerable period, sometimes for several years, and it is strengthened and
protected by one or more external margins of sterile tissue. Immediately
surrounding the fertile disc there is a compact wall of interwoven hyphae.
In some of the shorter-lived soft fruits, as in Biatora, this hyphal margin
may be thin, and may gradually be pushed aside as the disc develops and
becomes convex, but generally it forms a prominent rim round the disc and
may be tough or even horny, and often hard and carbonaceous. This wall,
which is present, to some extent, in nearly all lichens, is described as the
“proper margin.” A second “thalline margin” containing gonidia is present
in many genera[544]: it is a structure peculiar to the lichen apothecium and
forms the amphithecium.
Page 228
Fig. 88. Lecanora subfusca Ach. A, thallus and apothecia × 3; B,
vertical section of apothecium. a, hymenium; b, hypothecium; c,
thalline margin or amphithecium; d, gonidia. × 60 (after Reinke).
At the base of the apothecium there is a weft of light- or dark-coloured
hyphae called the hypothecium, which is continued up and round the sides
as the parathecium merging into the “proper margin.” It forms the lining of
a cup-shaped hollow which is filled by the paraphyses, which are upright
closely packed thread-like hyphae, and by the spore-containing asci or
thecae, these together constituting the thecium or hymenium. The
paraphyses are very numerous as compared with the asci; they are simple or
branched, frequently septate, especially towards the apex, and mostly
slender, varying in width from 1-4µ, though Hue describes paraphyses in
Aspicilia atroviolacea as 8-12µ thick. They may be thread-like throughout
their length, or they may widen towards the tips which are not infrequently
coloured. Small apical cells are often abstricted and lie loose on the
epithecium, giving at times a pruinose or powdered character to the disc. In
some genera there is a profuse branching of the paraphyses to form a dense
vertical section of apothecium. a, hymenium; b, hypothecium; c,
thalline margin or amphithecium; d, gonidia. × 60 (after Reinke).
At the base of the apothecium there is a weft of light- or dark-coloured
hyphae called the hypothecium, which is continued up and round the sides
as the parathecium merging into the “proper margin.” It forms the lining of
a cup-shaped hollow which is filled by the paraphyses, which are upright
closely packed thread-like hyphae, and by the spore-containing asci or
thecae, these together constituting the thecium or hymenium. The
paraphyses are very numerous as compared with the asci; they are simple or
branched, frequently septate, especially towards the apex, and mostly
slender, varying in width from 1-4µ, though Hue describes paraphyses in
Aspicilia atroviolacea as 8-12µ thick. They may be thread-like throughout
their length, or they may widen towards the tips which are not infrequently
coloured. Small apical cells are often abstricted and lie loose on the
epithecium, giving at times a pruinose or powdered character to the disc. In
some genera there is a profuse branching of the paraphyses to form a dense
Page 229
protective epithecium over the surface of the hymenium as in the genus
Arthonia.
The apothecia may be sessile and closely adnate to or even sunk in the
thallus, or they may be shortly stalked. The thalline margin shares generally
the characters of the thallus; the disc is mostly of a firm consistency and is
light or dark in colour according to genus or species; most frequently it is
some shade of brown. Marginate apothecia, i.e. those with a thalline
margin, are often referred to as “lecanorine,” that being a distinctive feature
of the genus Lecanora. In the immarginate series, with a proper margin
only, the texture may be soft and waxy, termed “biatorine” as in Biatora; or
hard and carbonaceous as in the genus Lecidea, and is then described as
“lecideine.”
In the subseries Graphidineae, the apothecium has the form of a very flat,
roundish or irregular body entirely without a margin, called an “ardella” as
in Arthonia; or more generally it is an elongate narrow “lirella,” in which
the disc is a mere slit between two dark-coloured proper margins. The
hypothecium of the lirellae is sometimes much reduced and in that case the
hymenium rests directly on a thin layer above the thalline tissue as in
Graphis elegans (Fig. 89).
Lichen fruits require abundant light,
and plants growing in the shade are
mostly sterile. Naturally, therefore, the
reproductive bodies are to be found on the
best illuminated parts of the thallus. In
crustaceous and in most foliose forms,
they are variously situated on the upper
surface, wherever the light falls most
directly. In the genera Nephromium and
Nephromopsis, on the contrary, they arise
on the under surface, though at the
extreme margin, but as the fertile lobes
eventually turn upwards the apothecia as
Fig. 89. Graphis elegans Ach. A, thallus they mature become fully exposed. In
and lirellae; B, vertical section of shrubby or fruticose lichens their position
furrowed lirella. × ca. 50.
is lateral on the fronds, or more frequently
at or near the tips.
Arthonia.
The apothecia may be sessile and closely adnate to or even sunk in the
thallus, or they may be shortly stalked. The thalline margin shares generally
the characters of the thallus; the disc is mostly of a firm consistency and is
light or dark in colour according to genus or species; most frequently it is
some shade of brown. Marginate apothecia, i.e. those with a thalline
margin, are often referred to as “lecanorine,” that being a distinctive feature
of the genus Lecanora. In the immarginate series, with a proper margin
only, the texture may be soft and waxy, termed “biatorine” as in Biatora; or
hard and carbonaceous as in the genus Lecidea, and is then described as
“lecideine.”
In the subseries Graphidineae, the apothecium has the form of a very flat,
roundish or irregular body entirely without a margin, called an “ardella” as
in Arthonia; or more generally it is an elongate narrow “lirella,” in which
the disc is a mere slit between two dark-coloured proper margins. The
hypothecium of the lirellae is sometimes much reduced and in that case the
hymenium rests directly on a thin layer above the thalline tissue as in
Graphis elegans (Fig. 89).
Lichen fruits require abundant light,
and plants growing in the shade are
mostly sterile. Naturally, therefore, the
reproductive bodies are to be found on the
best illuminated parts of the thallus. In
crustaceous and in most foliose forms,
they are variously situated on the upper
surface, wherever the light falls most
directly. In the genera Nephromium and
Nephromopsis, on the contrary, they arise
on the under surface, though at the
extreme margin, but as the fertile lobes
eventually turn upwards the apothecia as
Fig. 89. Graphis elegans Ach. A, thallus they mature become fully exposed. In
and lirellae; B, vertical section of shrubby or fruticose lichens their position
furrowed lirella. × ca. 50.
is lateral on the fronds, or more frequently
at or near the tips.
Page 230
b. Perithecia. The small closed perithecium is characteristic of the
Pyrenocarpeae which correspond with the Pyrenomycetes among fungi. It is
partially or entirely immersed in the thallus or in the substratum on which
the lichen grows, and is either a globose or conical body wholly surrounded
by a hyphal wall, when it is described as “entire” (Fig. 90), or it is
somewhat hemispherical in form and the outer wall is developed only on
the upper exposed part: a type of perithecium usually designated by the
term “dimidiate.” As the perithecial wall gives sufficient protection to the
asci, the paraphyses are of less importance and are frequently very
sparingly produced, or they may even be dissolved and used up at an early
stage. The thallus of the Pyrenocarpeae is often extremely reduced, and the
perithecia are then the only visible portion of the lichen.
A few lichens among Graphidineae and Pyrenocarpeae grow in a united
body generally looked on as a stroma; but Wainio[545] has demonstrated that
as the fruiting bodies give rise to this structure by agglomeration—by the
cohesion of their margins—it can only be regarded as a pseudostroma. Two
British genera of Pyrenolichens, Mycoporum and Mycoporellum, exhibit
this pseudo-stromatoid formation.
Fig. 90. A, entire perithecium of
Porina olivacea A. L. Sm. × ca.
40; B, dimidiate perithecium of
Acrocordia gemmata Koerb. ×
ca. 20.
C. Development of Reproductive Organs
Pyrenocarpeae which correspond with the Pyrenomycetes among fungi. It is
partially or entirely immersed in the thallus or in the substratum on which
the lichen grows, and is either a globose or conical body wholly surrounded
by a hyphal wall, when it is described as “entire” (Fig. 90), or it is
somewhat hemispherical in form and the outer wall is developed only on
the upper exposed part: a type of perithecium usually designated by the
term “dimidiate.” As the perithecial wall gives sufficient protection to the
asci, the paraphyses are of less importance and are frequently very
sparingly produced, or they may even be dissolved and used up at an early
stage. The thallus of the Pyrenocarpeae is often extremely reduced, and the
perithecia are then the only visible portion of the lichen.
A few lichens among Graphidineae and Pyrenocarpeae grow in a united
body generally looked on as a stroma; but Wainio[545] has demonstrated that
as the fruiting bodies give rise to this structure by agglomeration—by the
cohesion of their margins—it can only be regarded as a pseudostroma. Two
British genera of Pyrenolichens, Mycoporum and Mycoporellum, exhibit
this pseudo-stromatoid formation.
Fig. 90. A, entire perithecium of
Porina olivacea A. L. Sm. × ca.
40; B, dimidiate perithecium of
Acrocordia gemmata Koerb. ×
ca. 20.
C. Development of Reproductive Organs
Page 231
As most known lichens belong to the Ascolichens, the study of
development has been concentrated on that group. Tulasne[546] was the first
to make a microscopic study of lichen tissues and he described in
considerable detail the general anatomical structure of apothecia and
perithecia. Later, Fuisting[547] traced the development of a number of
perithecia through their different stages of growth, but his most interesting
discovery was made in Lecidea fumosa, a crustaceous Discolichen with an
areolate thallus in which the apothecia are seated on the fungal hyphae
between the areolae. In the very early stages represented by a complex of
slender hyphae, he observed an unbranched septate filament with short
cuboid cells, richer in contents than the surrounding filaments and
somewhat similar to the structure known to mycologists as “Woronin’s
hypha,” which is an ascogonial structure. These specialized cells
disappeared as the hymenium began to form.
1. DISCOLICHENS
Fig. 91. Collema microphyllum Ach. Vertical section of thallus. a,
carpogonium; b, trichogyne. × 350 (after Stahl).
a. Carpogonia of Gelatinous Lichens. Stahl’s[548] work on various
Collemaceae followed on the same lines as that of Fuisting. The first
species selected by him for examination, Collema (Leptogium)
development has been concentrated on that group. Tulasne[546] was the first
to make a microscopic study of lichen tissues and he described in
considerable detail the general anatomical structure of apothecia and
perithecia. Later, Fuisting[547] traced the development of a number of
perithecia through their different stages of growth, but his most interesting
discovery was made in Lecidea fumosa, a crustaceous Discolichen with an
areolate thallus in which the apothecia are seated on the fungal hyphae
between the areolae. In the very early stages represented by a complex of
slender hyphae, he observed an unbranched septate filament with short
cuboid cells, richer in contents than the surrounding filaments and
somewhat similar to the structure known to mycologists as “Woronin’s
hypha,” which is an ascogonial structure. These specialized cells
disappeared as the hymenium began to form.
1. DISCOLICHENS
Fig. 91. Collema microphyllum Ach. Vertical section of thallus. a,
carpogonium; b, trichogyne. × 350 (after Stahl).
a. Carpogonia of Gelatinous Lichens. Stahl’s[548] work on various
Collemaceae followed on the same lines as that of Fuisting. The first
species selected by him for examination, Collema (Leptogium)
Page 232
microphyllum’ is a gelatinous lichen which grows on old trunks of poplars
and willows. It has a small olive-green thallus which, in autumn, is crowded
with apothecia; the spermogones or pycnidia appear as minute reddish
points on the edge of the thallus. Within the thallus, and midway between
the upper and lower surface, there arises, as a branch from a vegetative
hypha, a many-septate filament coiled in spiral form at the base, with the
free end growing upwards and projecting a short distance above the surface
and occasionally forked (Fig. 91). The tip-cell is slightly swollen and
covered with a mucilaginous coat continuous with the mucilage of the
thallus. The whole structure, characterized by the larger size and by the
richer contents of its cells, was regarded by Stahl as a carpogonium, the
coiled base representing the ascogonium, the upright hypha functioning as
the receptive organ or trichogyne, comparable to that of the Florideae. The
spermatia, which mature at this early stage of carpogonial development, are
expelled from a neighbouring spermogonium on the addition of moisture
and easily reach the protruding trichogyne. They adhere to the mucilaginous
wall of the end-cell, and, in two or three instances, Stahl found that
copulation had taken place. As the affixed spermatium was empty, he
concluded that the contents had passed over into the trichogyne, and that the
nucleus had travelled down to the ascogonium. Certain degenerative
changes that followed seemed to confirm the view that there had been
fertilization: the cells of the trichogyne had lost their turgidity and at the
same time the cross-walls had swollen considerably and stood out like knots
in the hypha (Fig. 92). The ascogonial cells had also increased not only in
size but in number by intercalary division, so that the spiral arrangement
became obscured. Ascogenous hyphae arose from the ascogonial cells, and
asci cut off by a basal septum were finally formed from these hyphae.
Lateral branches from below the septum also formed asci.
Stahl’s observations were repeated and extended by Borzi[549] on another
of the Collemaceae, Collema nigrescens. In that plant the foliaceous thallus
is of thin texture and has a distinct cellular cortex. The carpogonia were
found at varying depths near to the cortical region; the ascogonium, of two
and a half to four spirals, consisted of ten to fifteen cells with very thin
walls, the trichogyne of five to ten cells, the terminal cell projecting above
the thallus. Borzi also found spermatia fused with the tip-cell.
and willows. It has a small olive-green thallus which, in autumn, is crowded
with apothecia; the spermogones or pycnidia appear as minute reddish
points on the edge of the thallus. Within the thallus, and midway between
the upper and lower surface, there arises, as a branch from a vegetative
hypha, a many-septate filament coiled in spiral form at the base, with the
free end growing upwards and projecting a short distance above the surface
and occasionally forked (Fig. 91). The tip-cell is slightly swollen and
covered with a mucilaginous coat continuous with the mucilage of the
thallus. The whole structure, characterized by the larger size and by the
richer contents of its cells, was regarded by Stahl as a carpogonium, the
coiled base representing the ascogonium, the upright hypha functioning as
the receptive organ or trichogyne, comparable to that of the Florideae. The
spermatia, which mature at this early stage of carpogonial development, are
expelled from a neighbouring spermogonium on the addition of moisture
and easily reach the protruding trichogyne. They adhere to the mucilaginous
wall of the end-cell, and, in two or three instances, Stahl found that
copulation had taken place. As the affixed spermatium was empty, he
concluded that the contents had passed over into the trichogyne, and that the
nucleus had travelled down to the ascogonium. Certain degenerative
changes that followed seemed to confirm the view that there had been
fertilization: the cells of the trichogyne had lost their turgidity and at the
same time the cross-walls had swollen considerably and stood out like knots
in the hypha (Fig. 92). The ascogonial cells had also increased not only in
size but in number by intercalary division, so that the spiral arrangement
became obscured. Ascogenous hyphae arose from the ascogonial cells, and
asci cut off by a basal septum were finally formed from these hyphae.
Lateral branches from below the septum also formed asci.
Stahl’s observations were repeated and extended by Borzi[549] on another
of the Collemaceae, Collema nigrescens. In that plant the foliaceous thallus
is of thin texture and has a distinct cellular cortex. The carpogonia were
found at varying depths near to the cortical region; the ascogonium, of two
and a half to four spirals, consisted of ten to fifteen cells with very thin
walls, the trichogyne of five to ten cells, the terminal cell projecting above
the thallus. Borzi also found spermatia fused with the tip-cell.
Page 233
A further important contribution was made
by Baur[550] in his study of Collema
crispum[551]. There occur in nature two forms
of this lichen, one of them crowded with
apothecia and spermogonia, the other with a
more luxuriant thallus, but with few
apothecia and no spermogonia. On the latter
almost sterile form Baur found in spring and
again in autumn immense numbers of
carpogonia—about one thousand in a
medium sized thallus—which nearly all
gradually lost the characteristics of
reproductive organs, and, anastomising with
other hyphae, became part of the vegetative
system. In a few cases in which, presumably,
a spermatium had fused with a trichogyne,
very large apothecia had developed.
As the first-mentioned form was always
crowded with apothecia in every stage of Fig. 92. Collema microphyllum Ach.
development, as well as with carpogonia and Carpogonium and trichogyne after
copulation × 500 (after Stahl).
spermogonia, it seemed natural to conclude
that the difference was entirely due to the
presence or absence of spermatia in sufficient numbers to ensure
fertilization. The period during which copulation is possible passes very
rapidly, though subsequent development is slow, occupying about half-a-
year from the time of fertilization to the formation of the first ascus.
Baur confirmed Stahl’s observations on the various developmental
changes. In several instances he found a spermatium fused with the
trichogyne, though he could not see continuity between the lumina of the
fusing cells. After copulation with the spermatium the trichogyne nucleus,
which occupied the lower third of the terminal cell, had disappeared, and
the plasma contents had acquired a deeper tint; the other trichogyne cells,
which had also lost their nuclei, were partly collapsed owing to the pressure
of the surrounding tissue, and openings were plainly visible through some
of the swollen septa, especially of the lower cells. In addition the ascogonial
cells, all of which were uninucleate, had increased in number by intercalary
by Baur[550] in his study of Collema
crispum[551]. There occur in nature two forms
of this lichen, one of them crowded with
apothecia and spermogonia, the other with a
more luxuriant thallus, but with few
apothecia and no spermogonia. On the latter
almost sterile form Baur found in spring and
again in autumn immense numbers of
carpogonia—about one thousand in a
medium sized thallus—which nearly all
gradually lost the characteristics of
reproductive organs, and, anastomising with
other hyphae, became part of the vegetative
system. In a few cases in which, presumably,
a spermatium had fused with a trichogyne,
very large apothecia had developed.
As the first-mentioned form was always
crowded with apothecia in every stage of Fig. 92. Collema microphyllum Ach.
development, as well as with carpogonia and Carpogonium and trichogyne after
copulation × 500 (after Stahl).
spermogonia, it seemed natural to conclude
that the difference was entirely due to the
presence or absence of spermatia in sufficient numbers to ensure
fertilization. The period during which copulation is possible passes very
rapidly, though subsequent development is slow, occupying about half-a-
year from the time of fertilization to the formation of the first ascus.
Baur confirmed Stahl’s observations on the various developmental
changes. In several instances he found a spermatium fused with the
trichogyne, though he could not see continuity between the lumina of the
fusing cells. After copulation with the spermatium the trichogyne nucleus,
which occupied the lower third of the terminal cell, had disappeared, and
the plasma contents had acquired a deeper tint; the other trichogyne cells,
which had also lost their nuclei, were partly collapsed owing to the pressure
of the surrounding tissue, and openings were plainly visible through some
of the swollen septa, especially of the lower cells. In addition the ascogonial
cells, all of which were uninucleate, had increased in number by intercalary
Page 234
division. Plasma connections were opened from cell to cell, but only in the
primary septa, the later formed cell-membranes being continuous.
Ascogenous hyphae had branched out from the ascogonium as a series of
uninucleate cell rows from which the asci finally arose.
Baur’s interpretation was that the first cell of the ascogonium reached by
the male nucleus after its passage down through the cells of the trichogyne
represented the egg-cell, and that, after fusion, the resultant nucleus
divided, and a daughter nucleus passed on to the other auxiliary-cells. No
male nucleus nor fusion of nuclei was, however, observed by him, and his
deductions rest on conjecture.
Krabbe[552] and after him Mäule[553] found in Collema pulposum
reproductive organs similar to those described by Stahl, but in a recent
paper on an American form of that species a peculiar condition has been
described by Freda Bachmann[554]. She[555] found that the spermatia
originated, not in spermogonia, but as groups of cells budded off from
vegetative hyphae within the tissue of the lichen and occupying the same
position as spermogonia, i.e. the region close below the upper surface. The
trichogynes, therefore, never emerged into the open, but travelled towards
these internal spermatia, and fusion with them was effected. The changes
that afterwards took place in the carpogonial cells were similar to those that
had been recognized by Stahl and Baur as consequent on fertilization.
Additional cytological details have been published in a subsequent
paper[556]: after fusion with the spermatium the terminal cell of the
trichogyne collapsed, its nucleus became disintegrated and the cross septa
of the lower trichogyne cells became perforated, these perforations being
closed again at a later stage by a gelatinous plug. The nuclear history is
more doubtful: the disappearance of the nuclei from the spermatium and
from the terminal cell of the trichogyne was noted; two nuclei were seen to
be present in the penultimate cell, and these the author interpreted as
division products of the original cell nucleus. In the same cell, lying close
against the lower septum and partly within the opening, there was a mass of
chromatin material which might be the male nucleus migrating downwards.
The next point of interest was observed in the twelfth cell from the tip in
which there were two nuclei, a larger and a smaller, the latter judged to be
the male cell, the small size being due to probable division of the
primary septa, the later formed cell-membranes being continuous.
Ascogenous hyphae had branched out from the ascogonium as a series of
uninucleate cell rows from which the asci finally arose.
Baur’s interpretation was that the first cell of the ascogonium reached by
the male nucleus after its passage down through the cells of the trichogyne
represented the egg-cell, and that, after fusion, the resultant nucleus
divided, and a daughter nucleus passed on to the other auxiliary-cells. No
male nucleus nor fusion of nuclei was, however, observed by him, and his
deductions rest on conjecture.
Krabbe[552] and after him Mäule[553] found in Collema pulposum
reproductive organs similar to those described by Stahl, but in a recent
paper on an American form of that species a peculiar condition has been
described by Freda Bachmann[554]. She[555] found that the spermatia
originated, not in spermogonia, but as groups of cells budded off from
vegetative hyphae within the tissue of the lichen and occupying the same
position as spermogonia, i.e. the region close below the upper surface. The
trichogynes, therefore, never emerged into the open, but travelled towards
these internal spermatia, and fusion with them was effected. The changes
that afterwards took place in the carpogonial cells were similar to those that
had been recognized by Stahl and Baur as consequent on fertilization.
Additional cytological details have been published in a subsequent
paper[556]: after fusion with the spermatium the terminal cell of the
trichogyne collapsed, its nucleus became disintegrated and the cross septa
of the lower trichogyne cells became perforated, these perforations being
closed again at a later stage by a gelatinous plug. The nuclear history is
more doubtful: the disappearance of the nuclei from the spermatium and
from the terminal cell of the trichogyne was noted; two nuclei were seen to
be present in the penultimate cell, and these the author interpreted as
division products of the original cell nucleus. In the same cell, lying close
against the lower septum and partly within the opening, there was a mass of
chromatin material which might be the male nucleus migrating downwards.
The next point of interest was observed in the twelfth cell from the tip in
which there were two nuclei, a larger and a smaller, the latter judged to be
the male cell, the small size being due to probable division of the
Page 235
spermatium nucleus either before or after leaving the spermatium. It is
stated however that the spermatium was always uninucleate. Meanwhile the
cells of the ascogonium had increased in size, the perforations of the septa
between the cells became more evident, and their nuclei persisted. In one
cell at this stage two nuclei were present, one of the two presumably a male
nucleus; no fusion of nuclei was observed in the ascogonial cells. Later the
cross walls between the cells were seen to have disappeared more
completely and migration of nuclei had taken place, so that some of the
cells appeared to be empty while others were multinucleate. Considerable
multiplication of the nuclei occurred before the ascogenous hyphae were
formed: twelve nuclei were observed in a part of the ascogonium which was
just beginning to give off a branch. Several branches might arise from one
cell, and their cells were either uni- or binucleate, the nuclei being larger
than those of the vegetative hyphae. The formation of the asci was not
distinctly seen, but young binucleate asci were not uncommon. The fusion
of the two nuclei was followed by the enlargement of the ascus and the
subsequent nuclear division for spore formation. In the first heterotypic
division twelve chromosomes, double the number observed in the
vegetative nucleus, were counted on the equatorial plate. In the third
division they were reduced to the normal number of six, from which F.
Bachmann concludes that a twofold fusion must have taken place—in the
ascogonium and again in the ascus.
Spiral or coiled ascogonia were observed by Wainio[557] in the gelatinous
crustaceous genus Pyrenopsis, but the trichogynes did not reach the surface.
In Lichina[558], a maritime gelatinous lichen where the carpogonia occur in
groups, trichogynes have not been demonstrated.
A peculiarity of some gelatinous lichens noted by Stahl[559] and others in
species of Physma, and by Forssell[560] in Pyrenopsis and Psorotichia, is the
development of carpogonia at the base of, and within the perithecial walls
of old spermogonia. No special significance is however attached to this
phenomenon, and it is interesting to note that a similar growth was observed
by Zukal[561] in a pyrenomycetous fungus, Pleospora collematum, a
harmless parasite on Physma compactum and other Collemaceae. The
structures invaded were true pycnidia of the fungus as the minute spores
were seen to germinate. A “Woronin’s hypha” at the base of several of these
pycnidia developed asci which pushed up among the spent sporophores.
stated however that the spermatium was always uninucleate. Meanwhile the
cells of the ascogonium had increased in size, the perforations of the septa
between the cells became more evident, and their nuclei persisted. In one
cell at this stage two nuclei were present, one of the two presumably a male
nucleus; no fusion of nuclei was observed in the ascogonial cells. Later the
cross walls between the cells were seen to have disappeared more
completely and migration of nuclei had taken place, so that some of the
cells appeared to be empty while others were multinucleate. Considerable
multiplication of the nuclei occurred before the ascogenous hyphae were
formed: twelve nuclei were observed in a part of the ascogonium which was
just beginning to give off a branch. Several branches might arise from one
cell, and their cells were either uni- or binucleate, the nuclei being larger
than those of the vegetative hyphae. The formation of the asci was not
distinctly seen, but young binucleate asci were not uncommon. The fusion
of the two nuclei was followed by the enlargement of the ascus and the
subsequent nuclear division for spore formation. In the first heterotypic
division twelve chromosomes, double the number observed in the
vegetative nucleus, were counted on the equatorial plate. In the third
division they were reduced to the normal number of six, from which F.
Bachmann concludes that a twofold fusion must have taken place—in the
ascogonium and again in the ascus.
Spiral or coiled ascogonia were observed by Wainio[557] in the gelatinous
crustaceous genus Pyrenopsis, but the trichogynes did not reach the surface.
In Lichina[558], a maritime gelatinous lichen where the carpogonia occur in
groups, trichogynes have not been demonstrated.
A peculiarity of some gelatinous lichens noted by Stahl[559] and others in
species of Physma, and by Forssell[560] in Pyrenopsis and Psorotichia, is the
development of carpogonia at the base of, and within the perithecial walls
of old spermogonia. No special significance is however attached to this
phenomenon, and it is interesting to note that a similar growth was observed
by Zukal[561] in a pyrenomycetous fungus, Pleospora collematum, a
harmless parasite on Physma compactum and other Collemaceae. The
structures invaded were true pycnidia of the fungus as the minute spores
were seen to germinate. A “Woronin’s hypha” at the base of several of these
pycnidia developed asci which pushed up among the spent sporophores.
Page 236
b. Carpogonia of non-gelatinous Lichens. The soft loose tissue of the
gelatinous lichens is more favourable for the minute study of apothecial
development than the closely interwoven hyphae of non-gelatinous forms,
but Borzi[562] had already extended the study to species of Parmelia,
Anaptychia, Sticta, Ricasolia and Lecanora, and in all of them he succeeded
in establishing the presence of ascogonia and trichogynes. After him a
constant succession of students have worked at the problem of reproduction
in lichens.
Lindau[563] published results of the examination of a considerable series
of lichens. In Anaptychia (Physcia) ciliaris, Physcia stellaris, Ph.
pulverulenta, Ramalina fraxinea, Placodium (Lecanora) saxicolum,
Lecanora subfusca and Lecidea enteroleuca he demonstrated the presence
of ascogonia with trichogynes. In Parmelia tiliacea and in Xanthoria
parietina he found ascogonia but failed to see trichogynes. In none of the
species examined by him did he observe any fusion between the trichogyne
and a spermatium.
In Anaptychia ciliaris he was able to pick out extremely early stages by
staining with a solution of chlor-zinc-iodine. Mäule[564] applied the same
test to Physcia pulverulenta, but found that to be successful the reaction
required some time. Certain cells of the hyphae—mostly terminal cells—in
the lower area of the gonidial zone and even occasionally in the pith
(according to Lindau) coloured a deep brown, while the ordinary thalline
hyphae were tinted yellow. He assumed that these were initial ascogonial
cells on account of the richer plasma contents, and also because of the
somewhat larger size of the cells. In the same region of the thallus young
carpogonia were observed as outgrowths from vegetative hyphae, though
the trichogynes had not yet reached the surface.
gelatinous lichens is more favourable for the minute study of apothecial
development than the closely interwoven hyphae of non-gelatinous forms,
but Borzi[562] had already extended the study to species of Parmelia,
Anaptychia, Sticta, Ricasolia and Lecanora, and in all of them he succeeded
in establishing the presence of ascogonia and trichogynes. After him a
constant succession of students have worked at the problem of reproduction
in lichens.
Lindau[563] published results of the examination of a considerable series
of lichens. In Anaptychia (Physcia) ciliaris, Physcia stellaris, Ph.
pulverulenta, Ramalina fraxinea, Placodium (Lecanora) saxicolum,
Lecanora subfusca and Lecidea enteroleuca he demonstrated the presence
of ascogonia with trichogynes. In Parmelia tiliacea and in Xanthoria
parietina he found ascogonia but failed to see trichogynes. In none of the
species examined by him did he observe any fusion between the trichogyne
and a spermatium.
In Anaptychia ciliaris he was able to pick out extremely early stages by
staining with a solution of chlor-zinc-iodine. Mäule[564] applied the same
test to Physcia pulverulenta, but found that to be successful the reaction
required some time. Certain cells of the hyphae—mostly terminal cells—in
the lower area of the gonidial zone and even occasionally in the pith
(according to Lindau) coloured a deep brown, while the ordinary thalline
hyphae were tinted yellow. He assumed that these were initial ascogonial
cells on account of the richer plasma contents, and also because of the
somewhat larger size of the cells. In the same region of the thallus young
carpogonia were observed as outgrowths from vegetative hyphae, though
the trichogynes had not yet reached the surface.
Page 237
Fig. 93. Physcia pulverulenta Fig. 94. Physcia (Anaptychia) ciliaris DC. Vertical
Nyl. Vertical section of thallus section of developing ascogonium. a, paraphyses; b,
and carpogonium before ascogonial hyphae; c, ascogonial cells. × 800 (after
fertilization. a, outer cortex; b, Baur).
inner cortex; c, gonidial layer; d,
medulla. × ca. 540 (after
Darbishire).
At a more advanced stage the carpogonia were seen to be embedded in
the gonidial zone and occurred in groups. The cells of the ascogonium,
easily recognized by the darker stain, were short and stout, measuring about
6-8µ in length and 4·4µ in width. They were arranged in somewhat
indistinct spirals; but the crowding of the groups resulted in a confused
intermingling of the various generative filaments. The trichogynes
composed of longer narrower cells rose above the hyphae of the cortex;
they also stained a deep brown and the projecting cell was always thin-
walled. Lindau frequently observed spermatia very firmly attached to the
trichogyne cell but without any plasma connection between the two. The
changes in the trichogyne described by Stahl and Baur in Collemaceae were
not seen in Anaptychia; the peculiar swelling of the septa seems to be a
phenomenon confined to gelatinous lichens. During the trichogyne stage in
Nyl. Vertical section of thallus section of developing ascogonium. a, paraphyses; b,
and carpogonium before ascogonial hyphae; c, ascogonial cells. × 800 (after
fertilization. a, outer cortex; b, Baur).
inner cortex; c, gonidial layer; d,
medulla. × ca. 540 (after
Darbishire).
At a more advanced stage the carpogonia were seen to be embedded in
the gonidial zone and occurred in groups. The cells of the ascogonium,
easily recognized by the darker stain, were short and stout, measuring about
6-8µ in length and 4·4µ in width. They were arranged in somewhat
indistinct spirals; but the crowding of the groups resulted in a confused
intermingling of the various generative filaments. The trichogynes
composed of longer narrower cells rose above the hyphae of the cortex;
they also stained a deep brown and the projecting cell was always thin-
walled. Lindau frequently observed spermatia very firmly attached to the
trichogyne cell but without any plasma connection between the two. The
changes in the trichogyne described by Stahl and Baur in Collemaceae were
not seen in Anaptychia; the peculiar swelling of the septa seems to be a
phenomenon confined to gelatinous lichens. During the trichogyne stage in
Page 238
this lichen the vegetative hyphae from the medulla grow up and surround
the young carpogonia, and, at the same time, very slender hyphae begin to
branch upwards to form the paraphyses. Darbishire’s[565] examination of
Physcia pulverulenta demonstrated the presence of the coiled ascogonium
and the trichogyne in that species (Fig. 93).
Baur[566] has also given the results of an examination of Anaptychia. He
frequently observed copulation between the spermatium and the tip of the
trichogyne, but not any passage of nucleus or contents. After copulation the
ascogonial cells increased in size and became irregular in form, and open
communication was established between them (Fig. 94). There was no
increase in their number by intercalary division as in Collema. After
producing ascogenous hyphae the cells were seen to have lost their contents
and then to have gradually disappeared. The fertile hyphae, which now took
a blue colouration with chlor-zinc-iodine, gradually spread out and formed
a wide-stretching hymenium. Several carpogonia took part in the formation
of one apothecium.
The tissue below the ascogonium meanwhile developed vigorously,
forming a weft of encircling hyphae, while the upper branches grew
vertically towards the cortex. Gonidia in contact with the developing fruit
also increased, and, with the hyphae, formed the exciple or thalline margin.
The growth upward of the paraphyses raises the overlying cortex which in
Anaptychia is “fibrous”; it gradually dies off and allows the exposure of the
disc, though small shreds of dead tissue are frequently left. In species such
as those of Xanthoria where the cortex is of vertical cell-rows, the
apothecial hyphae simply push their way between the cell-rows and so
through to the open.
Baur found the development of the apothecium somewhat similar in the
crustaceous corticolous lichen, Lecanora subfusca. After a long period of
sterile growth, spermogonia appeared in great abundance, and, a little later,
carpogonia in groups of five to ten; the trichogynes emerged very slightly
above the cortex; they were now branched. The ascogonia were frequently a
confused clump of cells, though sometimes they showed distinct spirals.
The surrounding hyphae had taken a vertical direction towards the cortex at
a still earlier stage, and the brown tips were visible on the exterior before
the trichogynes were formed. The whole growth was extremely slow.
the young carpogonia, and, at the same time, very slender hyphae begin to
branch upwards to form the paraphyses. Darbishire’s[565] examination of
Physcia pulverulenta demonstrated the presence of the coiled ascogonium
and the trichogyne in that species (Fig. 93).
Baur[566] has also given the results of an examination of Anaptychia. He
frequently observed copulation between the spermatium and the tip of the
trichogyne, but not any passage of nucleus or contents. After copulation the
ascogonial cells increased in size and became irregular in form, and open
communication was established between them (Fig. 94). There was no
increase in their number by intercalary division as in Collema. After
producing ascogenous hyphae the cells were seen to have lost their contents
and then to have gradually disappeared. The fertile hyphae, which now took
a blue colouration with chlor-zinc-iodine, gradually spread out and formed
a wide-stretching hymenium. Several carpogonia took part in the formation
of one apothecium.
The tissue below the ascogonium meanwhile developed vigorously,
forming a weft of encircling hyphae, while the upper branches grew
vertically towards the cortex. Gonidia in contact with the developing fruit
also increased, and, with the hyphae, formed the exciple or thalline margin.
The growth upward of the paraphyses raises the overlying cortex which in
Anaptychia is “fibrous”; it gradually dies off and allows the exposure of the
disc, though small shreds of dead tissue are frequently left. In species such
as those of Xanthoria where the cortex is of vertical cell-rows, the
apothecial hyphae simply push their way between the cell-rows and so
through to the open.
Baur found the development of the apothecium somewhat similar in the
crustaceous corticolous lichen, Lecanora subfusca. After a long period of
sterile growth, spermogonia appeared in great abundance, and, a little later,
carpogonia in groups of five to ten; the trichogynes emerged very slightly
above the cortex; they were now branched. The ascogonia were frequently a
confused clump of cells, though sometimes they showed distinct spirals.
The surrounding hyphae had taken a vertical direction towards the cortex at
a still earlier stage, and the brown tips were visible on the exterior before
the trichogynes were formed. The whole growth was extremely slow.
Page 239
In Physcia stellaris the carpogonia occurred in groups also, though
Lindau[567] thinks that, unlike Anaptychia (Physcia) ciliaris, only one is left
to form the fruit. Only one, according to Darbishire[568], entered into the
apothecium in the allied species, Physcia pulverulenta. In the latter plasma
connections were visible from cell to cell of the trichogyne, and, after
copulation with the spermatium, the ascogonial cells increased in size—
though not in number—and the plasma connections between them became
so wide that the ascogonium had the appearance of an almost continuous
multinucleate cell or coenogamete[569]. As in gelatinous lichens, each of
these cells gave rise to ascogenous hyphae.
c. General Summary. The main features of development described above
recur in most of the species that have been examined.
(1) The carpogonia arise in a complex of hyphae situated on the under
side of, or immediately below the gonidial zone. Usually they vary in
number from five to twenty for each apothecium, though as many as
seventy-two have been computed for Icmadophila ericetorum[570], and
Wainio[571] describes them as so numerous in Coccocarpia pellita var., that
their trichogynes covered some of the young apothecia with a hairy pile
perceptible with a hand lens, though at the same time other apothecia on the
same specimens were absolutely smooth.
(2) The trichogynes, when present, travel up through the gonidial and
cortical regions of the thallus; Darbishire[572] observes that in Physcia
pulverulenta, they may diverge to the side to secure an easier course
between the groups of algae. They emerge above the surface to a distance of
about 15µ or less; after an interval they collapse and disappear. Their cells,
which are longer and narrower than those of the ascogonium, are
uninucleate and vary in number according to species or to individual
lichens. Baur[573] thought that possibly several trichogynes in succession
might arise from one ascogonium.
(3) How many carpogonia share in the development of the apothecium is
still a debated question. In Collema only one is functional. Baur[574] was
unable to decide if one or more were fertilized in Parmelia acetabulum, and
in Usnea Nienburg[575] found that, out of several, one alone survived (Fig.
95). But in Anaptychia ciliaris and in Lecanora subfusca Baur[574]
Lindau[567] thinks that, unlike Anaptychia (Physcia) ciliaris, only one is left
to form the fruit. Only one, according to Darbishire[568], entered into the
apothecium in the allied species, Physcia pulverulenta. In the latter plasma
connections were visible from cell to cell of the trichogyne, and, after
copulation with the spermatium, the ascogonial cells increased in size—
though not in number—and the plasma connections between them became
so wide that the ascogonium had the appearance of an almost continuous
multinucleate cell or coenogamete[569]. As in gelatinous lichens, each of
these cells gave rise to ascogenous hyphae.
c. General Summary. The main features of development described above
recur in most of the species that have been examined.
(1) The carpogonia arise in a complex of hyphae situated on the under
side of, or immediately below the gonidial zone. Usually they vary in
number from five to twenty for each apothecium, though as many as
seventy-two have been computed for Icmadophila ericetorum[570], and
Wainio[571] describes them as so numerous in Coccocarpia pellita var., that
their trichogynes covered some of the young apothecia with a hairy pile
perceptible with a hand lens, though at the same time other apothecia on the
same specimens were absolutely smooth.
(2) The trichogynes, when present, travel up through the gonidial and
cortical regions of the thallus; Darbishire[572] observes that in Physcia
pulverulenta, they may diverge to the side to secure an easier course
between the groups of algae. They emerge above the surface to a distance of
about 15µ or less; after an interval they collapse and disappear. Their cells,
which are longer and narrower than those of the ascogonium, are
uninucleate and vary in number according to species or to individual
lichens. Baur[573] thought that possibly several trichogynes in succession
might arise from one ascogonium.
(3) How many carpogonia share in the development of the apothecium is
still a debated question. In Collema only one is functional. Baur[574] was
unable to decide if one or more were fertilized in Parmelia acetabulum, and
in Usnea Nienburg[575] found that, out of several, one alone survived (Fig.
95). But in Anaptychia ciliaris and in Lecanora subfusca Baur[574]
Page 240
considers it proved that several share in the formation of the apothecium. In
this connection it is interesting to note that, according to Harper[576] and
others, several ascogonia enter into one Pyronema fruit.
(4) The ascogonial cells, before and after
fertilization, are distinguished from the
surrounding hyphae by a reaction to various
stains, which is different from that of the
vegetative hyphae, and also by the shortness and
width of their cells. The whole of the apothecial
primordium is generally recognizable by the
clear shining appearance of the cells.
(5) The ascogonia do not always form a
distinct spiral; frequently they lie in irregular
groups. Each cell is uninucleate and may
ultimately produce ascogenous hyphae, though
in Anaptychia Baur[574] noted that some of the
cells failed to develop.
(6) The hyphae from the ascogonial cells
Fig. 95. Usnea barbata Web.
spread out in a complex layer at the base of the
Carpogonium with trichogyne × hymenium, and send up branches which form
1100 (after Nienburg). the asci, either, as in most Ascomycetes, from
the penultimate cell of the fertile branch, or
from the last cell, as in Sphyridium (Baeomyces
rufus)[575] and in Baeomyces roseus. The same variation has been observed
in fungi—in a species of Peziza[577], in which it is the end-cell of the branch
that becomes the mother-cell of the ascus; but this deviation from the
normal is evidently of rare occurrence either in lichens or fungi.
d. Hypothecium and Paraphyses. The hypothecium is the layer of hyphae
that subtends the hymenium, and is formed from the complex of hyphae
that envelope the first stages of the carpogonia. It is vegetative in origin and
distinct from the generative system.
In lichens belonging to the Collemaceae, the paraphyses rise from the
branching of the carpogonial stalk-cell immediately below the
this connection it is interesting to note that, according to Harper[576] and
others, several ascogonia enter into one Pyronema fruit.
(4) The ascogonial cells, before and after
fertilization, are distinguished from the
surrounding hyphae by a reaction to various
stains, which is different from that of the
vegetative hyphae, and also by the shortness and
width of their cells. The whole of the apothecial
primordium is generally recognizable by the
clear shining appearance of the cells.
(5) The ascogonia do not always form a
distinct spiral; frequently they lie in irregular
groups. Each cell is uninucleate and may
ultimately produce ascogenous hyphae, though
in Anaptychia Baur[574] noted that some of the
cells failed to develop.
(6) The hyphae from the ascogonial cells
Fig. 95. Usnea barbata Web.
spread out in a complex layer at the base of the
Carpogonium with trichogyne × hymenium, and send up branches which form
1100 (after Nienburg). the asci, either, as in most Ascomycetes, from
the penultimate cell of the fertile branch, or
from the last cell, as in Sphyridium (Baeomyces
rufus)[575] and in Baeomyces roseus. The same variation has been observed
in fungi—in a species of Peziza[577], in which it is the end-cell of the branch
that becomes the mother-cell of the ascus; but this deviation from the
normal is evidently of rare occurrence either in lichens or fungi.
d. Hypothecium and Paraphyses. The hypothecium is the layer of hyphae
that subtends the hymenium, and is formed from the complex of hyphae
that envelope the first stages of the carpogonia. It is vegetative in origin and
distinct from the generative system.
In lichens belonging to the Collemaceae, the paraphyses rise from the
branching of the carpogonial stalk-cell immediately below the
Page 241
ascogonium[578], but have no plasma connection with it. They are thus
comparable in origin with the paraphyses of many Discomycetes.
In several genera in which the algal constituents are blue-green, such as
Stictina, Pannaria, Nephroma, Ricasolia and Peltigera, Sturgis[579] found
that reproduction was apogamous and also that asci and paraphyses
originated from the same cell-system: a tuft of paraphyses arose from the
basal cell of the ascus, or an ascus from the basal cell of a paraphysis. These
results are at variance with those of most other workers, but the figures
drawn by Sturgis seem to be clear and convincing.
Again in Usnea barbata, as described by Nienburg[580], the ascogonial
cells, after the disappearance of the trichogyne, branch profusely not only
upwards towards the cortex but also downwards and to each side. The
upward branches give rise normally to the asci, the lower branches produce
the subhymenium and later the paraphyses, and the two systems are thus
genetically connected, though they remain distinct from each other, and asci
are never formed from the lower cells.
In most heteromerous lichens, however, the origin of the paraphyses is
exclusively vegetative: they arise as branches from the primordial complex
that forms the covering hyphae of the ascogonium both above and below.
Schwendener[581] had already pointed out the difference in origin between
the two constituents of the hymenium in one of his earlier studies on the
development of the apothecium, and this view has been repeatedly
confirmed by recent workers, except by Wahlberg[582] who has insisted that
they rise from the same cells as the asci, a statement disproved by Baur[583].
The paraphyses originate not only from the covering hyphae, but from
vegetative cells in close connection with the primordium. In this mode of
development, lichens diverge from fungi, but even in these a vegetative
origin for the paraphyses has been pointed out in Lachnea scutellata[584]
where they branch from the hyphae lying round the ascogonium.
There is no general rule for the order of development. In Lecanora
subfusca Baur[583] found that vertical filaments had reached the surface by
the time the trichogyne was formed, and their pointed brown tips gave a
ready clue to the position of the carpogonia. In Lecidea enteroleuca[585]
they show their characteristic form and arrangement before there is any
comparable in origin with the paraphyses of many Discomycetes.
In several genera in which the algal constituents are blue-green, such as
Stictina, Pannaria, Nephroma, Ricasolia and Peltigera, Sturgis[579] found
that reproduction was apogamous and also that asci and paraphyses
originated from the same cell-system: a tuft of paraphyses arose from the
basal cell of the ascus, or an ascus from the basal cell of a paraphysis. These
results are at variance with those of most other workers, but the figures
drawn by Sturgis seem to be clear and convincing.
Again in Usnea barbata, as described by Nienburg[580], the ascogonial
cells, after the disappearance of the trichogyne, branch profusely not only
upwards towards the cortex but also downwards and to each side. The
upward branches give rise normally to the asci, the lower branches produce
the subhymenium and later the paraphyses, and the two systems are thus
genetically connected, though they remain distinct from each other, and asci
are never formed from the lower cells.
In most heteromerous lichens, however, the origin of the paraphyses is
exclusively vegetative: they arise as branches from the primordial complex
that forms the covering hyphae of the ascogonium both above and below.
Schwendener[581] had already pointed out the difference in origin between
the two constituents of the hymenium in one of his earlier studies on the
development of the apothecium, and this view has been repeatedly
confirmed by recent workers, except by Wahlberg[582] who has insisted that
they rise from the same cells as the asci, a statement disproved by Baur[583].
The paraphyses originate not only from the covering hyphae, but from
vegetative cells in close connection with the primordium. In this mode of
development, lichens diverge from fungi, but even in these a vegetative
origin for the paraphyses has been pointed out in Lachnea scutellata[584]
where they branch from the hyphae lying round the ascogonium.
There is no general rule for the order of development. In Lecanora
subfusca Baur[583] found that vertical filaments had reached the surface by
the time the trichogyne was formed, and their pointed brown tips gave a
ready clue to the position of the carpogonia. In Lecidea enteroleuca[585]
they show their characteristic form and arrangement before there is any
Page 242
trace of ascus formation. In Solorina[585] they are well formed before the
ascogenous hyphae appear. In other lichens such as Placodium
saxicolum[586], Peltigera rufescens[587] and P. malacea[587] the two systems
—paraphyses and ascogonium—grow simultaneously, though in P.
horizontalis the ascogonium has disappeared by the time the paraphyses are
formed. In the genus Nephroma, in Physcia stellaris and in Xanthorina
parietina the paraphyses are also late in making their appearance.
In most instances, the paraphyses push their way up between the cortical
cells which gradually become absorbed, or they may stop short of the
surface as in Nephromium tomentosum[587]. The overlying layer of cortical
cells in that case dies off gradually and in time disappears. Such an
apothecium is said to be “at first veiled.” Later formed paraphyses at the
circumference of the apothecium form the parathecium, which is thus
continuous with the hypothecium.
e. Variations in apothecial Development. Lichens are among the least
stereotyped of plants: instances of variation have been noted in several
genera.
aa. Parmeliae. A somewhat complicated course of development has been
traced by Baur[588] in Parmelia acetabulum. In that lichen the group of
three to six carpogonia do not lie free in the gonidial tissue, but originate
nearer the surface (Fig. 96) and are surrounded from the first by a tissue
connected with, and resembling the tissue of the cortex. In the several
ascogonia, there are more cells and more spirals than in Collema or in
Physcia, and all of them are somewhat confusedly intertwined. The
trichogynes are composed of three to five cells and project 10 to 15µ above
the surface. When further development begins, the ascogonial cells branch
out and form a primary darker layer or hypothecium above which extends
the subhymenium, a light-coloured band of loosely woven hyphae.
Branches from the ascogonial hyphae at a later stage push their way up
through this tissue and form above it a second plexus of hyphae—the base
of the hymenium. Baur considers this a very advanced type of apothecium;
he found it also present in Parmelia saxatilis, though, in that species, the
further growth of the first ascogonial layer was more rapid and the
secondary plexus and hymenium were formed earlier in the life of the
apothecium. He has also stated that a similar development occurs in other
ascogenous hyphae appear. In other lichens such as Placodium
saxicolum[586], Peltigera rufescens[587] and P. malacea[587] the two systems
—paraphyses and ascogonium—grow simultaneously, though in P.
horizontalis the ascogonium has disappeared by the time the paraphyses are
formed. In the genus Nephroma, in Physcia stellaris and in Xanthorina
parietina the paraphyses are also late in making their appearance.
In most instances, the paraphyses push their way up between the cortical
cells which gradually become absorbed, or they may stop short of the
surface as in Nephromium tomentosum[587]. The overlying layer of cortical
cells in that case dies off gradually and in time disappears. Such an
apothecium is said to be “at first veiled.” Later formed paraphyses at the
circumference of the apothecium form the parathecium, which is thus
continuous with the hypothecium.
e. Variations in apothecial Development. Lichens are among the least
stereotyped of plants: instances of variation have been noted in several
genera.
aa. Parmeliae. A somewhat complicated course of development has been
traced by Baur[588] in Parmelia acetabulum. In that lichen the group of
three to six carpogonia do not lie free in the gonidial tissue, but originate
nearer the surface (Fig. 96) and are surrounded from the first by a tissue
connected with, and resembling the tissue of the cortex. In the several
ascogonia, there are more cells and more spirals than in Collema or in
Physcia, and all of them are somewhat confusedly intertwined. The
trichogynes are composed of three to five cells and project 10 to 15µ above
the surface. When further development begins, the ascogonial cells branch
out and form a primary darker layer or hypothecium above which extends
the subhymenium, a light-coloured band of loosely woven hyphae.
Branches from the ascogonial hyphae at a later stage push their way up
through this tissue and form above it a second plexus of hyphae—the base
of the hymenium. Baur considers this a very advanced type of apothecium;
he found it also present in Parmelia saxatilis, though, in that species, the
further growth of the first ascogonial layer was more rapid and the
secondary plexus and hymenium were formed earlier in the life of the
apothecium. He has also stated that a similar development occurs in other
Page 243
genera such as Usnea, though Nienburg’s[589] work scarcely confirms that
view.
Fig. 96. Parmelia acetabulum Dub. Vertical section of thallus and
carpogonial group × 550 (after Baur).
In the brown Parmeliae, Rosendahl[590] found the same series of
apothecial tissues, but he interprets the course of development somewhat
differently: the basal dark layer or hypothecium he found to be of purely
vegetative origin; above it extended the lighter-coloured subhymenium; the
ascogenous hyphae were present only in the second layer of dark tissue
immediately under the hymenium.
In most lichens the primordium of the apothecium arises towards the
lower side of the gonidial zone, the hyphae of which retain the meristematic
character. In Parmeliae, as was noted by Lindau[591] in P. tiliacea, and by
Baur[592] and Rosendahl[590] in other species, the carpogonial groups are
formed above the gonidial zone, either immediately below the cortex as in
P. glabratula, or in a swelling of the cortex itself as in P. aspidota, in which
species the external enlargement is visible by the time the trichogynes reach
the surface. In P. glabra, with a development entirely similar to that of P.
aspidota, no trichogynes were seen at any stage. The position of the
view.
Fig. 96. Parmelia acetabulum Dub. Vertical section of thallus and
carpogonial group × 550 (after Baur).
In the brown Parmeliae, Rosendahl[590] found the same series of
apothecial tissues, but he interprets the course of development somewhat
differently: the basal dark layer or hypothecium he found to be of purely
vegetative origin; above it extended the lighter-coloured subhymenium; the
ascogenous hyphae were present only in the second layer of dark tissue
immediately under the hymenium.
In most lichens the primordium of the apothecium arises towards the
lower side of the gonidial zone, the hyphae of which retain the meristematic
character. In Parmeliae, as was noted by Lindau[591] in P. tiliacea, and by
Baur[592] and Rosendahl[590] in other species, the carpogonial groups are
formed above the gonidial zone, either immediately below the cortex as in
P. glabratula, or in a swelling of the cortex itself as in P. aspidota, in which
species the external enlargement is visible by the time the trichogynes reach
the surface. In P. glabra, with a development entirely similar to that of P.
aspidota, no trichogynes were seen at any stage. The position of the
Page 244
primordium close under the cortex is also a feature of Ramalina fraxinea as
described by G. Wolff[593]. The trichogynes in that species are fairly
numerous.
A further peculiarity in Parmelia acetabulum attracted Baur’s[592]
attention. Carpogonia with trichogynes are extremely numerous in that
species as are the spermogonia, the open pores of which are to be found
everywhere between the trichogynes, and yet fertilization can occur but
rarely, as disintegrating carpogonia are abundant and very few apothecia are
formed. Baur makes the suggestion that possibly cross-fertilization may be
necessary, or that the spermatia, in this instance, do not fertilize and that
development must therefore be apogamous, in which case the small number
of fruits formed is due to some unknown cause. Fünfstück[594] thought that
degeneration of the carpogonia had not gone so far, but that a few had
acquired the power to develop apogamously. In Parmelia saxatilis only a
small percentage of carpogonia attain to apothecia, although spermogonia
are abundant and in close proximity, but in that species, unlike P.
acetabulum, a large number reach the earlier stages of fruit formation; the
more vigorous apothecia seem to inhibit the growth of those that lag behind.
bb. Pertusariae. In Pertusaria, the apothecial primordium is situated
immediately below the gonidial zone; the cells have a somewhat larger
lumen and thinner walls than those of the vegetative hyphae. In the
ascogonium there are more cells than in Parmelia acetabulum; the
trichogynes are short-lived, and several carpogonia probably enter into the
formation of each apothecium; the paraphyses arise from the covering
hyphae. So far the course of development presents nothing unusual. The
peculiar pertusarian feature as described by Krabbe[595], and after him by
Baur[596], does not appear till a later stage. By continual growth in thickness
of the overlying thallus, the apothecia gradually become submerged and
tend to degenerate; meanwhile, however, a branch from the ascogonial
hyphae at the base of the hymenium pushes up along one side and forms a
secondary ascogonial cell-plexus over the top of the first-formed disc. A
new apothecium thus arises and remains sporiferous until it also comes to
lie in too deep a position, when the process is repeated. Sometimes the
regenerating hypha travels to the right or left away from the original
apothecium, it may be to a distance of 2 mm. or according to Fünfstück
even considerably farther. Fünfstück[597] has gathered indeed from his own
described by G. Wolff[593]. The trichogynes in that species are fairly
numerous.
A further peculiarity in Parmelia acetabulum attracted Baur’s[592]
attention. Carpogonia with trichogynes are extremely numerous in that
species as are the spermogonia, the open pores of which are to be found
everywhere between the trichogynes, and yet fertilization can occur but
rarely, as disintegrating carpogonia are abundant and very few apothecia are
formed. Baur makes the suggestion that possibly cross-fertilization may be
necessary, or that the spermatia, in this instance, do not fertilize and that
development must therefore be apogamous, in which case the small number
of fruits formed is due to some unknown cause. Fünfstück[594] thought that
degeneration of the carpogonia had not gone so far, but that a few had
acquired the power to develop apogamously. In Parmelia saxatilis only a
small percentage of carpogonia attain to apothecia, although spermogonia
are abundant and in close proximity, but in that species, unlike P.
acetabulum, a large number reach the earlier stages of fruit formation; the
more vigorous apothecia seem to inhibit the growth of those that lag behind.
bb. Pertusariae. In Pertusaria, the apothecial primordium is situated
immediately below the gonidial zone; the cells have a somewhat larger
lumen and thinner walls than those of the vegetative hyphae. In the
ascogonium there are more cells than in Parmelia acetabulum; the
trichogynes are short-lived, and several carpogonia probably enter into the
formation of each apothecium; the paraphyses arise from the covering
hyphae. So far the course of development presents nothing unusual. The
peculiar pertusarian feature as described by Krabbe[595], and after him by
Baur[596], does not appear till a later stage. By continual growth in thickness
of the overlying thallus, the apothecia gradually become submerged and
tend to degenerate; meanwhile, however, a branch from the ascogonial
hyphae at the base of the hymenium pushes up along one side and forms a
secondary ascogonial cell-plexus over the top of the first-formed disc. A
new apothecium thus arises and remains sporiferous until it also comes to
lie in too deep a position, when the process is repeated. Sometimes the
regenerating hypha travels to the right or left away from the original
apothecium, it may be to a distance of 2 mm. or according to Fünfstück
even considerably farther. Fünfstück[597] has gathered indeed from his own
Page 245
investigations that such cases of regeneration are by no means rare:
ascogenous hyphae, several centimetres long, destined to give rise to new
apothecia are not unusual, and their activity can be recognized
macroscopically by the linear arrangement of the apothecia in such lichens
as Rhizocarpon (petraeum) concentricum (Fig. 97).
Fig. 97. Rhizocarpon petraeum Massal. Concentrically arranged
apothecia, reduced (J. Adams, Photo.).
In Variolaria, a genus closely allied to or generally included in
Pertusaria, Darbishire[598] has described the primordial tissue as taking rise
almost at the base of the crustaceous thallus: strands of delicate hyphae,
staining blue with iodine, mount upwards from that region through the
medulla and gonidial zone[599]. The ascogonium does not appear till the
surface is almost reached.
cc. Graphideae. Several members of the Graphidaceae were studied by
G. Wolff[600]: she demonstrated the presence of carpogonia with emerging
trichogynes in Graphis elegans, a species which is distinguished by the
deeply furrowed margins of the lirellae (Fig. 89). Before the carpogonia
appeared it was possible to distinguish the cushion-like primordial tissue of
the apothecium in the thallus which is almost wholly immersed in the
periderm layers of the bark on which it grows. The trichogynes were very
sparingly septate, and a rather large nucleus occupied a position near the tip
of the terminal cell. The dark carbonaceous outer wall makes its appearance
ascogenous hyphae, several centimetres long, destined to give rise to new
apothecia are not unusual, and their activity can be recognized
macroscopically by the linear arrangement of the apothecia in such lichens
as Rhizocarpon (petraeum) concentricum (Fig. 97).
Fig. 97. Rhizocarpon petraeum Massal. Concentrically arranged
apothecia, reduced (J. Adams, Photo.).
In Variolaria, a genus closely allied to or generally included in
Pertusaria, Darbishire[598] has described the primordial tissue as taking rise
almost at the base of the crustaceous thallus: strands of delicate hyphae,
staining blue with iodine, mount upwards from that region through the
medulla and gonidial zone[599]. The ascogonium does not appear till the
surface is almost reached.
cc. Graphideae. Several members of the Graphidaceae were studied by
G. Wolff[600]: she demonstrated the presence of carpogonia with emerging
trichogynes in Graphis elegans, a species which is distinguished by the
deeply furrowed margins of the lirellae (Fig. 89). Before the carpogonia
appeared it was possible to distinguish the cushion-like primordial tissue of
the apothecium in the thallus which is almost wholly immersed in the
periderm layers of the bark on which it grows. The trichogynes were very
sparingly septate, and a rather large nucleus occupied a position near the tip
of the terminal cell. The dark carbonaceous outer wall makes its appearance
Page 246
in this species at an early stage of development along the sides of the
lirellae, but never below, as there is always a layer of living cells at the
base. After the first-formed hymenium is exhausted, these basal cells
develop a new apothecium with a new carbonaceous wall that pushes back
the first-formed, leaving a cleft between the old and the new. This
regenerating process, somewhat analogous to the formation of new
apothecia in Pertusaria, may be repeated in Graphis elegans as many as
five times, the traces of the older discs being clearly seen in the channelled
margins of the lirellae.
dd. Cladoniae. The chief points of
interest in the Cladoniae are the position
of the apothecial primordia and the
function of the podetium, which are
discussed later[601]. Krabbe[602]
determined not only the endogenous
origin of the podetium but also the
appearance of fertile cells in the
primordium (Fig. 98). Both frequently
take rise where a crack occurs in the
cortex of the primary squamule, the cells Fig. 98. Cladonia decorticata Spreng.
Vertical section of squamule and
of the gonidial tissue being especially primordium of podetium. a, developing
active at these somewhat exposed places. podetium; b, probably fertile hyphae; c,
The fertile hyphae elongate and branch cortical tissue; d, gonidial cells. 1 × 600
(after Krabbe).
within the stalk of the developing
podetium, sometimes very early, or not
until there is a pause in growth, when carpogonia are formed. As a rule
trichogynes emerge in great numbers[600], generally close to, or rather
below, the spermogonia. In Cl. pyxidata[603] the carpogonia are
characterized by the large diameter of the cells—three to five times that of
the vegetative hyphae. Though most of the trichogynes disappear at an early
stage, some of them may persist for a considerable period. As development
proceeds, the vegetative hyphae interspersed among the ascogonial cells
grow upwards, slender branches push up between them and gradually a
compact sheath of paraphyses is built up. The ascogenous hyphae
meanwhile spread radially at the base of the paraphyses and the asci begin
to form. The apothecia may be further enlarged by intercalary growth, and
lirellae, but never below, as there is always a layer of living cells at the
base. After the first-formed hymenium is exhausted, these basal cells
develop a new apothecium with a new carbonaceous wall that pushes back
the first-formed, leaving a cleft between the old and the new. This
regenerating process, somewhat analogous to the formation of new
apothecia in Pertusaria, may be repeated in Graphis elegans as many as
five times, the traces of the older discs being clearly seen in the channelled
margins of the lirellae.
dd. Cladoniae. The chief points of
interest in the Cladoniae are the position
of the apothecial primordia and the
function of the podetium, which are
discussed later[601]. Krabbe[602]
determined not only the endogenous
origin of the podetium but also the
appearance of fertile cells in the
primordium (Fig. 98). Both frequently
take rise where a crack occurs in the
cortex of the primary squamule, the cells Fig. 98. Cladonia decorticata Spreng.
Vertical section of squamule and
of the gonidial tissue being especially primordium of podetium. a, developing
active at these somewhat exposed places. podetium; b, probably fertile hyphae; c,
The fertile hyphae elongate and branch cortical tissue; d, gonidial cells. 1 × 600
(after Krabbe).
within the stalk of the developing
podetium, sometimes very early, or not
until there is a pause in growth, when carpogonia are formed. As a rule
trichogynes emerge in great numbers[600], generally close to, or rather
below, the spermogonia. In Cl. pyxidata[603] the carpogonia are
characterized by the large diameter of the cells—three to five times that of
the vegetative hyphae. Though most of the trichogynes disappear at an early
stage, some of them may persist for a considerable period. As development
proceeds, the vegetative hyphae interspersed among the ascogonial cells
grow upwards, slender branches push up between them and gradually a
compact sheath of paraphyses is built up. The ascogenous hyphae
meanwhile spread radially at the base of the paraphyses and the asci begin
to form. The apothecia may be further enlarged by intercalary growth, and
Page 247
this vigorous development of vegetative tissue immediately underneath
raises the whole fruit structure well above the surface level.
Sättler[604] in his paper on Cladoniae[605] cites as an argument in favour
of fertilization the relative positions of carpogonia and spermogonia on the
podetia. The carpogonia with their emerging trichogynes being situated
rather below the spermogonia. Both organs, he states, have been
demonstrated in eleven species; he himself observed them in the primordial
podetia of Cladonia botrytes and of Cl. Floerkeana.
2. PYRENOLICHENS
a. Development of the Perithecium. It is to Fuisting[606] that we owe the
first account of development in the lichen perithecium. Though he failed to
see the earlier stages (in Verrucaria Dufourii), he recognized the primordial
complex of hyphae in the gonidial zone of the thallus, from which
originated a vertical strand of hyphae destined to form the tubular neck of
the perithecium. Growth in the lower part is in abeyance for a time, and it is
only after the neck is formed, and the fruiting body is widened by the
ingrowth of external hyphae, that the asci begin to branch up from the tissue
at the base.
b. Formation of Carpogonia. Stahl[607] had indicated that not only in
gymnocarpous but also in angiocarpous lichens, it would be found that
carpogonia were formed as in Collema. Baur[608] justified this surmise, and
demonstrated the presence of ascogonia in groups of three to eight, with
trichogynes that reached the surface in Endocarpon (Dermatocarpon)
miniatum (Fig. 99). It is one of the few foliaceous Pyrenolichens, and the
leathery thallus is attached to the substratum by a central point, thus
allowing in the thallus not only peripheral but also intercalary growth, the
latter specially active round the point of basal attachment; carpogonia may
be found in any region where the tissue is newly formed, and at any season.
The upper cortex is composed of short-celled thick-walled hyphae, with
branching vertical to the surface, and so closely packed that there is an
appearance of plectenchyma; the medullary hyphae are also thick-walled
but with longer cells. The carpogonia of this species arise as a branch from
the vegetative hyphae and are without special covering hyphae, so frequent
a feature in other lichens. The trichogynes bore their way through the
raises the whole fruit structure well above the surface level.
Sättler[604] in his paper on Cladoniae[605] cites as an argument in favour
of fertilization the relative positions of carpogonia and spermogonia on the
podetia. The carpogonia with their emerging trichogynes being situated
rather below the spermogonia. Both organs, he states, have been
demonstrated in eleven species; he himself observed them in the primordial
podetia of Cladonia botrytes and of Cl. Floerkeana.
2. PYRENOLICHENS
a. Development of the Perithecium. It is to Fuisting[606] that we owe the
first account of development in the lichen perithecium. Though he failed to
see the earlier stages (in Verrucaria Dufourii), he recognized the primordial
complex of hyphae in the gonidial zone of the thallus, from which
originated a vertical strand of hyphae destined to form the tubular neck of
the perithecium. Growth in the lower part is in abeyance for a time, and it is
only after the neck is formed, and the fruiting body is widened by the
ingrowth of external hyphae, that the asci begin to branch up from the tissue
at the base.
b. Formation of Carpogonia. Stahl[607] had indicated that not only in
gymnocarpous but also in angiocarpous lichens, it would be found that
carpogonia were formed as in Collema. Baur[608] justified this surmise, and
demonstrated the presence of ascogonia in groups of three to eight, with
trichogynes that reached the surface in Endocarpon (Dermatocarpon)
miniatum (Fig. 99). It is one of the few foliaceous Pyrenolichens, and the
leathery thallus is attached to the substratum by a central point, thus
allowing in the thallus not only peripheral but also intercalary growth, the
latter specially active round the point of basal attachment; carpogonia may
be found in any region where the tissue is newly formed, and at any season.
The upper cortex is composed of short-celled thick-walled hyphae, with
branching vertical to the surface, and so closely packed that there is an
appearance of plectenchyma; the medullary hyphae are also thick-walled
but with longer cells. The carpogonia of this species arise as a branch from
the vegetative hyphae and are without special covering hyphae, so frequent
a feature in other lichens. The trichogynes bore their way through the
Page 248
compact cortex and rise well above
the surface. After they have
disappeared—presumably after
fertilization—the vegetative hyphae
round and between the ascogonia
become active and travel upwards
slightly converging to a central
point. The asci begin to grow out
from the ascogenous hyphae of the
base before the vertical filaments
have quite pierced the cortex.
Pyrenula nitida has also been
studied by Baur[609]. It is a very
common species on smooth bark,
with a thin crustaceous thallus
immersed among the outer
periderm cells. Unlike most other
lichens, it forms carpogonia in
spring only, from February to April. Fig. 99. Dermatocarpon miniatum Th. Fr.
A primordial coil of hyphae lies at Vertical section of thallus and carpogonial group
× 600 (after Baur).
the base of the gonidial layer, and,
before there is any appearance of
carpogonia, a thick strand of hyphae is seen to be directed upwards, so that
a definite form and direction is given to the perithecium at a very early
stage. The ascogonial cells which are differentiated are extremely small,
and, like those of all other species examined, are uninucleate. There are five
to ten carpogonia in each primordium; the trichogynes grow up through the
hyphal strand and emerge 5-10 µ above the surface. After their
disappearance, a weft of ascogenous tissue is formed at the base, and, at the
same time, the surrounding vegetative tissue takes part in the building up of
a plectenchymatous wall of minute dark-coloured cells. Further
development is rapid and occupies probably only a few weeks.
In many of the pyrenocarpous lichens—Verrucariae and others—the
walls of the paraphyses dissolve in mucilage as the spores become mature, a
character associated with spore ejection and dispersal. In some genera and
species, as in Pyrenula, they remain intact.
the surface. After they have
disappeared—presumably after
fertilization—the vegetative hyphae
round and between the ascogonia
become active and travel upwards
slightly converging to a central
point. The asci begin to grow out
from the ascogenous hyphae of the
base before the vertical filaments
have quite pierced the cortex.
Pyrenula nitida has also been
studied by Baur[609]. It is a very
common species on smooth bark,
with a thin crustaceous thallus
immersed among the outer
periderm cells. Unlike most other
lichens, it forms carpogonia in
spring only, from February to April. Fig. 99. Dermatocarpon miniatum Th. Fr.
A primordial coil of hyphae lies at Vertical section of thallus and carpogonial group
× 600 (after Baur).
the base of the gonidial layer, and,
before there is any appearance of
carpogonia, a thick strand of hyphae is seen to be directed upwards, so that
a definite form and direction is given to the perithecium at a very early
stage. The ascogonial cells which are differentiated are extremely small,
and, like those of all other species examined, are uninucleate. There are five
to ten carpogonia in each primordium; the trichogynes grow up through the
hyphal strand and emerge 5-10 µ above the surface. After their
disappearance, a weft of ascogenous tissue is formed at the base, and, at the
same time, the surrounding vegetative tissue takes part in the building up of
a plectenchymatous wall of minute dark-coloured cells. Further
development is rapid and occupies probably only a few weeks.
In many of the pyrenocarpous lichens—Verrucariae and others—the
walls of the paraphyses dissolve in mucilage as the spores become mature, a
character associated with spore ejection and dispersal. In some genera and
species, as in Pyrenula, they remain intact.
Page 249
D. Apogamous Reproduction
Though fertilization by an externally produced male nucleus has not been
definitely proved there is probability that, in some instances, the fruit may
be the product of sexual fusion. There are however a number of genera and
species in which the development is apogamous so far as any external
copulation is possible and the sporiferous tissue seems to be a purely
vegetative product up to the stage of ascus formation.
In Phlyctis agelaea Krabbe[610] found abundant apothecia developing
normally and not accompanied by spermogonia; in Phialopsis rubra studied
also by him the primordium arises among the cells of the periderm on
which the lichen grows, and he failed to find any trace of a sexual act. In his
elaborate study of Gloeolichens Forssell[611] established the presence of
carpogonia with trichogynes in two species—Pyrenopsis phaeococca and P.
impolita, but without any appearance of fertilization; in all the others
examined, the origin of the fruit was vegetative. Wainio[612] records a
similar observation in a species of Pyrenopsis in which there was formed a
spiral ascogonium and a trichogyne, but the latter never reached the surface.
Neubner[613] claimed to have proved a vegetative origin for the asci in
the Caliciaceae; but he overlooked the presence of spermogonia and his
conclusions are doubtful.
Fünfstück[614] found apogamous development in Peltigera (including
Peltidea) and his results have never been disputed. The ascogonial cells are
surrounded at an early stage by a weft of vegetative hyphae. No trichogynes
are formed and spermogonia are absent or very rare in the genus, though
pycnidia with macrospores occur occasionally.
Some recent work by Darbishire[615] on the genus supplies additional
details. The apothecial primordium always originated near the growing
margin of the thallus, where certain medullary hyphae were seen to swell up
and stain more deeply than others. These at first were uninucleate, but the
nuclei increased by division as the cells became larger, and in time there
was formed a mass of closely interwoven cells full of cytoplasm. “No
coiled carpogonia can be made out, but these darkly stained cells form part
of a connected system of branching hyphae coming from the medulla
Though fertilization by an externally produced male nucleus has not been
definitely proved there is probability that, in some instances, the fruit may
be the product of sexual fusion. There are however a number of genera and
species in which the development is apogamous so far as any external
copulation is possible and the sporiferous tissue seems to be a purely
vegetative product up to the stage of ascus formation.
In Phlyctis agelaea Krabbe[610] found abundant apothecia developing
normally and not accompanied by spermogonia; in Phialopsis rubra studied
also by him the primordium arises among the cells of the periderm on
which the lichen grows, and he failed to find any trace of a sexual act. In his
elaborate study of Gloeolichens Forssell[611] established the presence of
carpogonia with trichogynes in two species—Pyrenopsis phaeococca and P.
impolita, but without any appearance of fertilization; in all the others
examined, the origin of the fruit was vegetative. Wainio[612] records a
similar observation in a species of Pyrenopsis in which there was formed a
spiral ascogonium and a trichogyne, but the latter never reached the surface.
Neubner[613] claimed to have proved a vegetative origin for the asci in
the Caliciaceae; but he overlooked the presence of spermogonia and his
conclusions are doubtful.
Fünfstück[614] found apogamous development in Peltigera (including
Peltidea) and his results have never been disputed. The ascogonial cells are
surrounded at an early stage by a weft of vegetative hyphae. No trichogynes
are formed and spermogonia are absent or very rare in the genus, though
pycnidia with macrospores occur occasionally.
Some recent work by Darbishire[615] on the genus supplies additional
details. The apothecial primordium always originated near the growing
margin of the thallus, where certain medullary hyphae were seen to swell up
and stain more deeply than others. These at first were uninucleate, but the
nuclei increased by division as the cells became larger, and in time there
was formed a mass of closely interwoven cells full of cytoplasm. “No
coiled carpogonia can be made out, but these darkly stained cells form part
of a connected system of branching hyphae coming from the medulla
Page 250
further back.” Long unbranched multi-septate hyphae—evidently
functionless trichogynes—travelled towards the cortex but gradually died
off. Certain of the larger cells—the “ascogonia”—grew out as ascogenous
hyphae into which the nuclei passed in pairs and finally gave rise to the
asci.
These results tally well with those obtained by M. and Mme Moreau[616],
though they make no mention of any trichogyne. They found that the
terminal cells of the ascogenous hyphae were transformed into asci, and the
two nuclei in these cells fused—the only fusion that took place. In
Nephromium, one of the same family, the case for apogamy is not so clear;
but Fünfstück found no trichogynes, and though spermogonia were present
on the thallus, they were always somewhat imperfectly developed.
Sturgis[617] supplemented these results in his study of other lichens
containing blue-green algae. In species of Heppia, Pannaria, Hydrothyria,
Stictina and Ricasolia, he failed to find any evidence of fertilization by
spermatia.
Solorina, also a member of Peltigeraceae, was added to the list of
apogamous genera by Metzger[618] and his work was confirmed and
amplified by Baur[619]: certain hyphae of the gonidial zone branch out into
larger ascogonial cells which increase by active intercalary growth, by
division and by branching, and so gradually give rise to the ascogenous
hyphae and finally to the asci. Baur looked on this and other similar
formations as instances of degeneration from the normal carpogonial type
of development. Moreau[620] (Fernand and Mme) have also examined
Solorina with much the same results: the paraphyses rise first from cells
that have been produced by the gonidial hyphae; later, ascogenous hyphae
are formed and spread horizontally at the base of the paraphyses, finally
giving rise at their tips to the asci. Metzger[618] had further discovered that
spermogonia were absent and trichogynes undeveloped in two very
different crustaceous lichens, Acarospora (Lecanora) glaucocarpa and
Verrucaria calciseda, the latter a pyrenocarpous species and, as the name
implies, found only on limestone.
Krabbe[621] had noted the absence of any fertilization process in
Gyrophora vellea. At a later date, Gyrophora cylindrica was made the
functionless trichogynes—travelled towards the cortex but gradually died
off. Certain of the larger cells—the “ascogonia”—grew out as ascogenous
hyphae into which the nuclei passed in pairs and finally gave rise to the
asci.
These results tally well with those obtained by M. and Mme Moreau[616],
though they make no mention of any trichogyne. They found that the
terminal cells of the ascogenous hyphae were transformed into asci, and the
two nuclei in these cells fused—the only fusion that took place. In
Nephromium, one of the same family, the case for apogamy is not so clear;
but Fünfstück found no trichogynes, and though spermogonia were present
on the thallus, they were always somewhat imperfectly developed.
Sturgis[617] supplemented these results in his study of other lichens
containing blue-green algae. In species of Heppia, Pannaria, Hydrothyria,
Stictina and Ricasolia, he failed to find any evidence of fertilization by
spermatia.
Solorina, also a member of Peltigeraceae, was added to the list of
apogamous genera by Metzger[618] and his work was confirmed and
amplified by Baur[619]: certain hyphae of the gonidial zone branch out into
larger ascogonial cells which increase by active intercalary growth, by
division and by branching, and so gradually give rise to the ascogenous
hyphae and finally to the asci. Baur looked on this and other similar
formations as instances of degeneration from the normal carpogonial type
of development. Moreau[620] (Fernand and Mme) have also examined
Solorina with much the same results: the paraphyses rise first from cells
that have been produced by the gonidial hyphae; later, ascogenous hyphae
are formed and spread horizontally at the base of the paraphyses, finally
giving rise at their tips to the asci. Metzger[618] had further discovered that
spermogonia were absent and trichogynes undeveloped in two very
different crustaceous lichens, Acarospora (Lecanora) glaucocarpa and
Verrucaria calciseda, the latter a pyrenocarpous species and, as the name
implies, found only on limestone.
Krabbe[621] had noted the absence of any fertilization process in
Gyrophora vellea. At a later date, Gyrophora cylindrica was made the
Page 251
subject of exact research by Lindau[622]. In that species the spermogonia (or
pycnidia) are situated on the outer edge of the thallus lobes; a few
millimetres nearer the centre appear the primordia of the apothecia, at first
without any external indication of their presence. The initial coil which
arises on the lower side of the gonidial zone consists of thickly wefted
hyphae with short cells, slightly thicker than those of the thallus. It was
difficult to establish their connection with the underlying medullary hyphae
since these very soon change to a brown plectenchyma. From about the
middle of the ascogonial coil there rises a bundle of parallel stoutish hyphae
which traverse the gonidial zone and the cortex and slightly overtop the
surface. They are genetically connected at the base with the more or less
spirally coiled hyphae, and are similar to the trichogynes described in other
lichens. Lindau did not find that they had any sexual significance, and
ascribed to them the mechanical function of terebrators or borers. The
correctness of his deductions has been disputed by various workers:
Baur[619] looks on these “trichogynes” as the first paraphyses. The
reproductive organs in Stereocaulon were examined by G. Wolff[623], and
the absence of trichogynes was proved, though spermogonia were not
wanting. She also failed to find any evidence of fertilization in Xanthoria
parietina, in which lichen the ascogenous hyphae branch out from an
ascogonium that does not form a trichogyne.
Rosendahl[624], as already stated, could find no trichogynes in Parmelia
glabra. In Parmelia obscurata, on the contrary, Bitter[625] found that
carpogonia with trichogynes were abundant and spermogonia very rare. In
other species of the subgenus, Hypogymnia, he has pointed out that
apothecia are either absent or occur but seldom, while spermogonia are
numerous, and he concludes that the spermatia must function as spores or
conidia. Baur[626] however does not accept that conclusion; he suggests as
probable that the male organs persist longer in a functionless condition than
do the apothecia.
Still more recently Nienburg[627] has described the ascogonium of
Baeomyces sp. and also of Sphyridium byssoides (Baeomyces rufus) as
reduced and probably degenerate. His results do not disprove those obtained
by Krabbe[628] on the same lichen (Sphyridium fungiforme). The apothecia
are terminal on short stalks in that species. When the stalk is about ·5mm. in
pycnidia) are situated on the outer edge of the thallus lobes; a few
millimetres nearer the centre appear the primordia of the apothecia, at first
without any external indication of their presence. The initial coil which
arises on the lower side of the gonidial zone consists of thickly wefted
hyphae with short cells, slightly thicker than those of the thallus. It was
difficult to establish their connection with the underlying medullary hyphae
since these very soon change to a brown plectenchyma. From about the
middle of the ascogonial coil there rises a bundle of parallel stoutish hyphae
which traverse the gonidial zone and the cortex and slightly overtop the
surface. They are genetically connected at the base with the more or less
spirally coiled hyphae, and are similar to the trichogynes described in other
lichens. Lindau did not find that they had any sexual significance, and
ascribed to them the mechanical function of terebrators or borers. The
correctness of his deductions has been disputed by various workers:
Baur[619] looks on these “trichogynes” as the first paraphyses. The
reproductive organs in Stereocaulon were examined by G. Wolff[623], and
the absence of trichogynes was proved, though spermogonia were not
wanting. She also failed to find any evidence of fertilization in Xanthoria
parietina, in which lichen the ascogenous hyphae branch out from an
ascogonium that does not form a trichogyne.
Rosendahl[624], as already stated, could find no trichogynes in Parmelia
glabra. In Parmelia obscurata, on the contrary, Bitter[625] found that
carpogonia with trichogynes were abundant and spermogonia very rare. In
other species of the subgenus, Hypogymnia, he has pointed out that
apothecia are either absent or occur but seldom, while spermogonia are
numerous, and he concludes that the spermatia must function as spores or
conidia. Baur[626] however does not accept that conclusion; he suggests as
probable that the male organs persist longer in a functionless condition than
do the apothecia.
Still more recently Nienburg[627] has described the ascogonium of
Baeomyces sp. and also of Sphyridium byssoides (Baeomyces rufus) as
reduced and probably degenerate. His results do not disprove those obtained
by Krabbe[628] on the same lichen (Sphyridium fungiforme). The apothecia
are terminal on short stalks in that species. When the stalk is about ·5mm. in
Page 252
height, sections through the tip show numerous primordia (12 to 15) ranged
below the outer cortex, though only one, or at most three, develop further.
These ascogonial groups are connected with each other by delicate
filaments, and Nienburg concluded that they were secondary products from
a primary group lower down in the tissue. Spirals were occasionally seen in
what he considered to be the secondary ascogonia, but usually the fertile
cells lie in loose uncoiled masses; isolated hyphae were observed to travel
upwards from these cells, but they never emerged above the surface.
Usnea macrocarpa—if Schulte’s[629] work may be accepted—is also
apogamous, though in Usnea barbata Nienburg[627] found trichogynes (Fig.
95) and the various developments that are taken as evidence of fertilization.
Wainio[630] had demonstrated emergent straight trichogynes in Usnea laevis
but without any sign of fertilization.
E. Discussion of Lichen Reproduction
In Ascolichens fertilization by the fusion of nuclei in the ascogonium is
still a debated question. The female organ or carpogonium, as outlined
above, comprises a twisted or spirally coiled multi-septate hypha, with a
terminal branch regarded as a trichogyne which is also multi-septate, and
through which the nucleus of the spermatium must travel to reach the
female cell. It is instructive to compare the lichen carpogonium with that of
other plants.
a. The Trichogyne. In the Florideae, or red seaweeds, in which the
trichogyne was first described, that organ is merely a hair-like prolongation
of the egg-cell and acts as a receptive tube. It contains granular protoplasm
but no nucleus and terminates in a shiny tip covered with mucilage. The
spermatium, unlike that of lichens, is a naked cell, and being non-motile is
conveyed by water to the tip of the trichogyne to which it adheres; the
intervening wall then breaks down and the male nucleus passes over. After
this process of fertilization a plug of mucilage cuts off the trichogyne, and it
withers away.
In Coleochaete, a genus of small freshwater green algae, a trichogyne is
also present in some of the species: it is again a prolongation of an oogonial
cell.
below the outer cortex, though only one, or at most three, develop further.
These ascogonial groups are connected with each other by delicate
filaments, and Nienburg concluded that they were secondary products from
a primary group lower down in the tissue. Spirals were occasionally seen in
what he considered to be the secondary ascogonia, but usually the fertile
cells lie in loose uncoiled masses; isolated hyphae were observed to travel
upwards from these cells, but they never emerged above the surface.
Usnea macrocarpa—if Schulte’s[629] work may be accepted—is also
apogamous, though in Usnea barbata Nienburg[627] found trichogynes (Fig.
95) and the various developments that are taken as evidence of fertilization.
Wainio[630] had demonstrated emergent straight trichogynes in Usnea laevis
but without any sign of fertilization.
E. Discussion of Lichen Reproduction
In Ascolichens fertilization by the fusion of nuclei in the ascogonium is
still a debated question. The female organ or carpogonium, as outlined
above, comprises a twisted or spirally coiled multi-septate hypha, with a
terminal branch regarded as a trichogyne which is also multi-septate, and
through which the nucleus of the spermatium must travel to reach the
female cell. It is instructive to compare the lichen carpogonium with that of
other plants.
a. The Trichogyne. In the Florideae, or red seaweeds, in which the
trichogyne was first described, that organ is merely a hair-like prolongation
of the egg-cell and acts as a receptive tube. It contains granular protoplasm
but no nucleus and terminates in a shiny tip covered with mucilage. The
spermatium, unlike that of lichens, is a naked cell, and being non-motile is
conveyed by water to the tip of the trichogyne to which it adheres; the
intervening wall then breaks down and the male nucleus passes over. After
this process of fertilization a plug of mucilage cuts off the trichogyne, and it
withers away.
In Coleochaete, a genus of small freshwater green algae, a trichogyne is
also present in some of the species: it is again a prolongation of an oogonial
cell.
Page 253
In the Ascomycetes, certain cells or cell-processes associated with the
ascogonium have been described as trichogynes or receptive cells. In one of
the simpler types, Monascus[631], the “trichogyne” is a cell cut off from the
ascogonial cell. When fertilization takes place, the wall between the two
cells breaks down to allow the passage of the male nucleus, but closes up
when the process is effected. In Pyronema confluens[632] it is represented by
a process from the ascogonial cell which fuses directly with the male cell. A
more elaborate “trichogyne” has been evolved in Lachnea stercorea[633],
another Discomycete: in that fungus it takes the form of a 3-5-septate hypha
with a longer terminal cell; it rises from some part of the ascogonial cell but
has no connection with any process of fertilization, so that the greater
elaboration of form is in this case concomitant with loss of function.
In the Laboulbeniaceae, a numerous and very peculiar series of
Ascomycetes that live on insects, there are, in nearly all of the reproductive
bodies, a carpogonial cell, a trichophoric cell and a trichogyne. The last-
named organ is in some genera a simple continuous cell, in others it is
septate and branched, occasionally it is absent[634]. The male cells are
spermatia of two kinds, exogenous or endogenous, and the plants are
monoecious or dioecious. Laboulbeniaceae have no connection with
lichens. Faull[635], a recent worker on the group, states that though he
observed spermatia attached to the trichogynes, he was not able to
demonstrate copulation (possibly owing to over-staining), nor could he
trace any migration of the nucleus through the trichophoric cell down to the
carpogonial cell. In two species of Laboulbenia that he examined there
were no antheridia, and the egg-cell acquired its second nucleus from the
neighbouring trichophoric cell. These conjugate nuclei divided
simultaneously and the two daughter nuclei passed on to the ascus and
fused, as in other Ascomycetes, to form the definitive nucleus.
Convincing evidence as to the importance of the trichogyne in fungi was
supposed, until lately, to be afforded by the presence and functional activity
of that organ associated with spermogonia in a few Pyrenomycetes—in
Poronia, Gnomonia and Polystigma. Poronia was examined by M.
Dawson[636] who found that a trichogyne-like filament distinct from the
vegetative hyphae rose from the neighbourhood of the ascogonial cells. It
took an upward course towards the exterior, but there was no indication that
it was ever receptive. In Gnomonia erythrostoma and in Polystigma rubrum
ascogonium have been described as trichogynes or receptive cells. In one of
the simpler types, Monascus[631], the “trichogyne” is a cell cut off from the
ascogonial cell. When fertilization takes place, the wall between the two
cells breaks down to allow the passage of the male nucleus, but closes up
when the process is effected. In Pyronema confluens[632] it is represented by
a process from the ascogonial cell which fuses directly with the male cell. A
more elaborate “trichogyne” has been evolved in Lachnea stercorea[633],
another Discomycete: in that fungus it takes the form of a 3-5-septate hypha
with a longer terminal cell; it rises from some part of the ascogonial cell but
has no connection with any process of fertilization, so that the greater
elaboration of form is in this case concomitant with loss of function.
In the Laboulbeniaceae, a numerous and very peculiar series of
Ascomycetes that live on insects, there are, in nearly all of the reproductive
bodies, a carpogonial cell, a trichophoric cell and a trichogyne. The last-
named organ is in some genera a simple continuous cell, in others it is
septate and branched, occasionally it is absent[634]. The male cells are
spermatia of two kinds, exogenous or endogenous, and the plants are
monoecious or dioecious. Laboulbeniaceae have no connection with
lichens. Faull[635], a recent worker on the group, states that though he
observed spermatia attached to the trichogynes, he was not able to
demonstrate copulation (possibly owing to over-staining), nor could he
trace any migration of the nucleus through the trichophoric cell down to the
carpogonial cell. In two species of Laboulbenia that he examined there
were no antheridia, and the egg-cell acquired its second nucleus from the
neighbouring trichophoric cell. These conjugate nuclei divided
simultaneously and the two daughter nuclei passed on to the ascus and
fused, as in other Ascomycetes, to form the definitive nucleus.
Convincing evidence as to the importance of the trichogyne in fungi was
supposed, until lately, to be afforded by the presence and functional activity
of that organ associated with spermogonia in a few Pyrenomycetes—in
Poronia, Gnomonia and Polystigma. Poronia was examined by M.
Dawson[636] who found that a trichogyne-like filament distinct from the
vegetative hyphae rose from the neighbourhood of the ascogonial cells. It
took an upward course towards the exterior, but there was no indication that
it was ever receptive. In Gnomonia erythrostoma and in Polystigma rubrum
Page 254
spermogonia with spermatia—presumably male organs—are produced in
abundance shortly before the ascosporous fruit is developed. The spermatia
in both cases exhibit the characters of male cells, i.e. very little cytoplasm
and a comparatively large nucleus that occupies most of the cell cavity,
along with complete incapacity to germinate. Brooks[637] found in
Gnomonia that tufts of the so-called trichogynes originated near the
ascogonial cells, but they were “mere continuations of ordinary vegetative
hyphae belonging to the coil.” They are septate and reach the surface, and
the tip-cell is longer than the others as in the lichen trichogyne.
A somewhat similar arrangement is present in Polystigma, in which
Blackman and Welsford[638] have proved that the filaments, considered as
trichogynes by previous workers, are merely vegetative hyphae. A
trichogyne-like structure is also present in Capnodium, one of the more
primitive Pyrenomycetes, but it has no sexual significance.
Lindau[639] in his paper on Gyrophora suggested that the trichogyne in
lichens acted as a “terebrator” or boring apparatus, of service to the deeply
immersed carpogonium in enabling it to reach the surface. Van Tieghem[640]
explained its presence on physiological grounds as necessary for
respiration, a view also favoured by Zukal[641], while Wainio[642] and
Steiner[643] see in it only an “end-hypha,” the vigorous growth of which is
due to its connection with the well-nourished cells of the ascogonium.
Lindau’s view has been rejected by succeeding writers: as has been
already stated, it is the paraphyses that usually open the way outward for
the apothecium. Van Tieghem’s theory has been considered more worthy of
attention and both Dawson and Brooks incline to think that the projecting
filaments described above may perform some service in respiration, even
though primarily they may have functioned as sexual receptive organs.
There is very little support to be drawn from fungi for the theory that the
presence of a trichogyne necessarily entails fertilization by spermatia.
Lichens in this connection must be judged as a class apart.
It has perhaps been too lightly assumed that the trichogyne in lichens
indicates some relationship with the Florideae[644]. Such a view might be
possible if we could regard lichens and Florideae as derived from some
common remote ancestor, though even then the difference in spore
abundance shortly before the ascosporous fruit is developed. The spermatia
in both cases exhibit the characters of male cells, i.e. very little cytoplasm
and a comparatively large nucleus that occupies most of the cell cavity,
along with complete incapacity to germinate. Brooks[637] found in
Gnomonia that tufts of the so-called trichogynes originated near the
ascogonial cells, but they were “mere continuations of ordinary vegetative
hyphae belonging to the coil.” They are septate and reach the surface, and
the tip-cell is longer than the others as in the lichen trichogyne.
A somewhat similar arrangement is present in Polystigma, in which
Blackman and Welsford[638] have proved that the filaments, considered as
trichogynes by previous workers, are merely vegetative hyphae. A
trichogyne-like structure is also present in Capnodium, one of the more
primitive Pyrenomycetes, but it has no sexual significance.
Lindau[639] in his paper on Gyrophora suggested that the trichogyne in
lichens acted as a “terebrator” or boring apparatus, of service to the deeply
immersed carpogonium in enabling it to reach the surface. Van Tieghem[640]
explained its presence on physiological grounds as necessary for
respiration, a view also favoured by Zukal[641], while Wainio[642] and
Steiner[643] see in it only an “end-hypha,” the vigorous growth of which is
due to its connection with the well-nourished cells of the ascogonium.
Lindau’s view has been rejected by succeeding writers: as has been
already stated, it is the paraphyses that usually open the way outward for
the apothecium. Van Tieghem’s theory has been considered more worthy of
attention and both Dawson and Brooks incline to think that the projecting
filaments described above may perform some service in respiration, even
though primarily they may have functioned as sexual receptive organs.
There is very little support to be drawn from fungi for the theory that the
presence of a trichogyne necessarily entails fertilization by spermatia.
Lichens in this connection must be judged as a class apart.
It has perhaps been too lightly assumed that the trichogyne in lichens
indicates some relationship with the Florideae[644]. Such a view might be
possible if we could regard lichens and Florideae as derived from some
common remote ancestor, though even then the difference in spore
Page 255
production—in one case exogenous, and in the other in asci and therefore
endogenous—would be a strong argument against their affinity. But all the
evidence goes to prove that lichens are late derivatives of fungi and have
originated from them at different points. Fungi are interposed between
lichens and any other ancestors, and inherited characters must have been
transmitted through them. F. Bachmann’s suggestion[645] that Collema
pulposum should be regarded “as a link between aquatic red algae and
terrestrial ascomycetes such as Pyronema and the mildews” cannot
therefore be accepted. It seems more probable that the lichen trichogyne is a
new structure evolved in response to some physiological requirement—
either sexual or metabolic—of the deeply embedded fruit primordium.
b. The Ascogonium. In fungi there is usually one cell forming the
ascogonium, a coenogamete, which after fertilization produces ascogenous
hyphae. There are exceptions, such as Cutting[646] found in Ascophanus
carneus, in which it is composed of several cells in open contact by the
formation of wide secondary pores in the cell-walls. In lichens the
ascogonium is divided into a varying number of uninucleate cells.
Darbishire[647] (in Physcia) and Baur[648] (in Anaptychia) have described an
opening between the different cells, after presumed fertilization, that might
perhaps constitute a coenogamete. Ascogenous hyphae arise from all, or
nearly all the cells, whether fertilized by spermatia or not, and asci continue
to be formed over a long period of time. There may even be regeneration of
the entire fruiting body as described in Graphis elegans and in Pertusaria,
apparently without renewed fertilization.
Spermogonia (or pycnidia) and the ascosporous fruits generally grow on
the same thallus, though not unfrequently only one of the two kinds is
present. As the spermogonia appear first, while the apothecia or perithecia
are still in the initial stages, that sequence of development seems to add
support to the view that their function is primarily sexual; but it is equally
valid as a proof of their pycnidial nature since the corresponding bodies in
fungi precede the more perfect ascosporous fruits in the life-cycle.
The differences in fertility between the two kinds of thallus in Collema
crispum may be recalled[649]. Baur considered that development of the
carpogonia was dependant on the presence of spermatia: a strong argument
for the necessity of fertilization by these. The conditions in Parmelia
endogenous—would be a strong argument against their affinity. But all the
evidence goes to prove that lichens are late derivatives of fungi and have
originated from them at different points. Fungi are interposed between
lichens and any other ancestors, and inherited characters must have been
transmitted through them. F. Bachmann’s suggestion[645] that Collema
pulposum should be regarded “as a link between aquatic red algae and
terrestrial ascomycetes such as Pyronema and the mildews” cannot
therefore be accepted. It seems more probable that the lichen trichogyne is a
new structure evolved in response to some physiological requirement—
either sexual or metabolic—of the deeply embedded fruit primordium.
b. The Ascogonium. In fungi there is usually one cell forming the
ascogonium, a coenogamete, which after fertilization produces ascogenous
hyphae. There are exceptions, such as Cutting[646] found in Ascophanus
carneus, in which it is composed of several cells in open contact by the
formation of wide secondary pores in the cell-walls. In lichens the
ascogonium is divided into a varying number of uninucleate cells.
Darbishire[647] (in Physcia) and Baur[648] (in Anaptychia) have described an
opening between the different cells, after presumed fertilization, that might
perhaps constitute a coenogamete. Ascogenous hyphae arise from all, or
nearly all the cells, whether fertilized by spermatia or not, and asci continue
to be formed over a long period of time. There may even be regeneration of
the entire fruiting body as described in Graphis elegans and in Pertusaria,
apparently without renewed fertilization.
Spermogonia (or pycnidia) and the ascosporous fruits generally grow on
the same thallus, though not unfrequently only one of the two kinds is
present. As the spermogonia appear first, while the apothecia or perithecia
are still in the initial stages, that sequence of development seems to add
support to the view that their function is primarily sexual; but it is equally
valid as a proof of their pycnidial nature since the corresponding bodies in
fungi precede the more perfect ascosporous fruits in the life-cycle.
The differences in fertility between the two kinds of thallus in Collema
crispum may be recalled[649]. Baur considered that development of the
carpogonia was dependant on the presence of spermatia: a strong argument
for the necessity of fertilization by these. The conditions in Parmelia
Page 256
acetabulum, also recorded by Baur, lend themselves less easily to any
conclusion. On the thallus of that species the spermogonia and carpogonia
present are out of all proportion to the very few apothecia that are
ultimately formed. Though Baur suggested that cross-fertilization might be
necessary, he admits that the development may be vegetative and so
uninfluenced by the presence or absence of spermatia.
It is the very frequent occurrence of the trichogyne as an integral part of
the carpogonium that constitutes the strongest argument for fertilization by
spermatia. There is a possibility that such an organ may have been universal
at one time both in fungi and in lichens, and that it has mostly degenerated
through loss of function in the former, as it has disappeared in many
instances in lichens. Again, there is but a scanty and vestigial record of
spermogonia in Ascomycetes. They may have died out, or they may have
developed into the asexual pycnidia which are associated with so many
species. If we take that view we may trace the same tendency in lichens, as
for instance in the capacity of various spermatia to germinate, though in
lichen spermogonia there has been apparently less change from the more
primitive condition. It is also possible that some process of nuclear fusion,
or more probably of conjugation, takes place in the ascogonial cells, and
that in the latter case the only fusion, as in some (or most) fungi, is between
the two nuclei in the ascus.
If it be conceded that fully developed carpogonia with emergent
trichogynes, accompanied by spermogonia and spermatia, represent
fertilization, or the probability of fertilization, then the process may be
assumed to take place in a fairly large and widely distributed series of
lichens. Copulation between the spermatium and the trichogyne has been
seen by Stahl[650], Baur[651] and by F. Bachmann[652] in Collema. In Physcia
pulverulenta Darbishire[653] could not prove copulation in the earlier stages,
but he found what he took to be the remains of emptied spermatia adhering
to the tips of old trichogynes. Changes in the trichogyne following on
presumed copulation have been demonstrated by several workers in the
Collemaceae, and open communication as a result of fertilization between
the cells of the ascogonium has been described in two species. This
coenocytic condition of the ascogonium (or archicarp), considered by
Darbishire and others as an evidence of fertilization, has been demonstrated
by Fitzpatrick[654] in the fungus Rhizina undulata. The walls between the
conclusion. On the thallus of that species the spermogonia and carpogonia
present are out of all proportion to the very few apothecia that are
ultimately formed. Though Baur suggested that cross-fertilization might be
necessary, he admits that the development may be vegetative and so
uninfluenced by the presence or absence of spermatia.
It is the very frequent occurrence of the trichogyne as an integral part of
the carpogonium that constitutes the strongest argument for fertilization by
spermatia. There is a possibility that such an organ may have been universal
at one time both in fungi and in lichens, and that it has mostly degenerated
through loss of function in the former, as it has disappeared in many
instances in lichens. Again, there is but a scanty and vestigial record of
spermogonia in Ascomycetes. They may have died out, or they may have
developed into the asexual pycnidia which are associated with so many
species. If we take that view we may trace the same tendency in lichens, as
for instance in the capacity of various spermatia to germinate, though in
lichen spermogonia there has been apparently less change from the more
primitive condition. It is also possible that some process of nuclear fusion,
or more probably of conjugation, takes place in the ascogonial cells, and
that in the latter case the only fusion, as in some (or most) fungi, is between
the two nuclei in the ascus.
If it be conceded that fully developed carpogonia with emergent
trichogynes, accompanied by spermogonia and spermatia, represent
fertilization, or the probability of fertilization, then the process may be
assumed to take place in a fairly large and widely distributed series of
lichens. Copulation between the spermatium and the trichogyne has been
seen by Stahl[650], Baur[651] and by F. Bachmann[652] in Collema. In Physcia
pulverulenta Darbishire[653] could not prove copulation in the earlier stages,
but he found what he took to be the remains of emptied spermatia adhering
to the tips of old trichogynes. Changes in the trichogyne following on
presumed copulation have been demonstrated by several workers in the
Collemaceae, and open communication as a result of fertilization between
the cells of the ascogonium has been described in two species. This
coenocytic condition of the ascogonium (or archicarp), considered by
Darbishire and others as an evidence of fertilization, has been demonstrated
by Fitzpatrick[654] in the fungus Rhizina undulata. The walls between the
Page 257
cells of the archicarp in that Ascomycete became more or less open, so that
the ascogenous hyphae growing from the central cells were able easily to
draw nutrition from the whole coenocyte, but no process of fertilization in
Rhizina preceded the breaking down of the septa and no fusion of nuclei
was observed until the stage of ascus formation.
The real distinction between fertile and vegetative hyphae lies, according
to Harper[655], in the relative size of the nuclei. F. Bachmann speaks of one
large nucleus in the spermatium of Collema pulposum which would indicate
sexual function. There is however very little nuclear history of lichens
known at any stage until the beginning of ascus formation, when fusion of
two nuclei certainly take place as in fungi to form the definitive nucleus of
the ascus.
The whole matter may be summed up in Fünfstück’s[656] statement that:
“though research has proved as very probable that fertilization takes place,
it is an undoubted fact that no one has observed any such process.”
F. Final Stages of Apothecial Development
The emergence of the lichen apothecium from the thallus, and the form it
takes, are of special interest, as, though it is essentially fungal in structure, it
is subject to various modifications entailed by symbiosis.
a. Open or closed Apothecia. Schwendener[657] drew attention to two
types of apothecia directly influenced by the thallus: those that are closed at
first and only open gradually, and those which are, as he says, open from
the first. The former occur in genera and species in which the thallus has a
stoutish cortex, as, for instance, in Lobaria where the young fructification
has all the appearance of an opening perithecium. The open apothecia
(primitus aperta) are found in non-corticate lichens, in which case the
pioneer paraphyses arrive at the surface easily and without any converging
growth. Similar apothecia are borne directly on the hypothallus at the
periphery, or between the thalline areolae, and they are also characteristic of
thin or slender thalli as in Coenogonium.
In both types of apothecium, the paraphyses pierce the cortex (Fig. 100)
and secure the emergence of the developing ascomata.
the ascogenous hyphae growing from the central cells were able easily to
draw nutrition from the whole coenocyte, but no process of fertilization in
Rhizina preceded the breaking down of the septa and no fusion of nuclei
was observed until the stage of ascus formation.
The real distinction between fertile and vegetative hyphae lies, according
to Harper[655], in the relative size of the nuclei. F. Bachmann speaks of one
large nucleus in the spermatium of Collema pulposum which would indicate
sexual function. There is however very little nuclear history of lichens
known at any stage until the beginning of ascus formation, when fusion of
two nuclei certainly take place as in fungi to form the definitive nucleus of
the ascus.
The whole matter may be summed up in Fünfstück’s[656] statement that:
“though research has proved as very probable that fertilization takes place,
it is an undoubted fact that no one has observed any such process.”
F. Final Stages of Apothecial Development
The emergence of the lichen apothecium from the thallus, and the form it
takes, are of special interest, as, though it is essentially fungal in structure, it
is subject to various modifications entailed by symbiosis.
a. Open or closed Apothecia. Schwendener[657] drew attention to two
types of apothecia directly influenced by the thallus: those that are closed at
first and only open gradually, and those which are, as he says, open from
the first. The former occur in genera and species in which the thallus has a
stoutish cortex, as, for instance, in Lobaria where the young fructification
has all the appearance of an opening perithecium. The open apothecia
(primitus aperta) are found in non-corticate lichens, in which case the
pioneer paraphyses arrive at the surface easily and without any converging
growth. Similar apothecia are borne directly on the hypothallus at the
periphery, or between the thalline areolae, and they are also characteristic of
thin or slender thalli as in Coenogonium.
In both types of apothecium, the paraphyses pierce the cortex (Fig. 100)
and secure the emergence of the developing ascomata.
Page 258
Fig. 100. Physcia ciliaris DC. Vertical section of apothecium still
covered by the cortex. a, paraphyses; b, hypothecium; c, gonidia
of thallus and amphithecium. × 150 (after Baur).
b. Emergence of the Ascocarp. Hue[658] has taken up this subject in
recent years and has described the process by which the vegetative hyphae
surrounding the fruit primordium, excited to active growth by contact with
the generative system, take part in the later stages of fruit formation. The
primordium generally occupies a position near to, or just within, the upper
medulla, and the hyphae in contact with it soon begin to branch freely in a
vertical direction, surrounding the developing fruit and carrying it upwards
generally to a superficial position. The different methods of the final
emergence give two very distinct types of mature apothecium: the lecideine
in which the gonidial zone takes no part in the upward growth, and the
lecanorine into which the gonidia enter as an integral part.
In the lecideine series (Fig. 101) the encircling hyphae from the upper
medulla rise as a compact column through the gonidial zone to the surface
of the thallus; they then spread radially before curving up to form the outer
wall or “proper margin” round the spore-bearing disc. The branching of the
hyphae is fastigiate with compact shorter branches at the exterior. In such
an apothecium gonidia are absent both below the hypothecium and in the
margins.
covered by the cortex. a, paraphyses; b, hypothecium; c, gonidia
of thallus and amphithecium. × 150 (after Baur).
b. Emergence of the Ascocarp. Hue[658] has taken up this subject in
recent years and has described the process by which the vegetative hyphae
surrounding the fruit primordium, excited to active growth by contact with
the generative system, take part in the later stages of fruit formation. The
primordium generally occupies a position near to, or just within, the upper
medulla, and the hyphae in contact with it soon begin to branch freely in a
vertical direction, surrounding the developing fruit and carrying it upwards
generally to a superficial position. The different methods of the final
emergence give two very distinct types of mature apothecium: the lecideine
in which the gonidial zone takes no part in the upward growth, and the
lecanorine into which the gonidia enter as an integral part.
In the lecideine series (Fig. 101) the encircling hyphae from the upper
medulla rise as a compact column through the gonidial zone to the surface
of the thallus; they then spread radially before curving up to form the outer
wall or “proper margin” round the spore-bearing disc. The branching of the
hyphae is fastigiate with compact shorter branches at the exterior. In such
an apothecium gonidia are absent both below the hypothecium and in the
margins.
Page 259
Fig. 101. Lecidea parasema Ach. Vertical section
of thallus and apothecium with proper margin
only × ca. 50.
In lecanorine development the ascending hyphae from the medulla, in
some cases, carry with them algal cells which multiply and spread as a
second gonidial layer under the hypothecium (Fig. 102). These hyphae may
also spread in a radial direction while still within the thallus and give rise to
an “immersed” apothecium which is lecanorine as it encloses gonidia
within its special tissues, for example, in Acarospora and Solorina. But in
most cases the lecanorine fruit is superficial and not unfrequently it is raised
on a short stalk (Usnea, etc.); both the primary gonidial zone of the thallus
and the outer cortex are associated with the medullary column of hyphae
from the first and grow up along with it, thus providing the outer part of the
apothecium, an additional “thalline margin” continuous with the thallus
itself. It is an advanced type of development peculiar to lichens, and it
provides for fertility of long continuance which is in striking contrast with
the fugitive ascocarps of the Discomycetes.
of thallus and apothecium with proper margin
only × ca. 50.
In lecanorine development the ascending hyphae from the medulla, in
some cases, carry with them algal cells which multiply and spread as a
second gonidial layer under the hypothecium (Fig. 102). These hyphae may
also spread in a radial direction while still within the thallus and give rise to
an “immersed” apothecium which is lecanorine as it encloses gonidia
within its special tissues, for example, in Acarospora and Solorina. But in
most cases the lecanorine fruit is superficial and not unfrequently it is raised
on a short stalk (Usnea, etc.); both the primary gonidial zone of the thallus
and the outer cortex are associated with the medullary column of hyphae
from the first and grow up along with it, thus providing the outer part of the
apothecium, an additional “thalline margin” continuous with the thallus
itself. It is an advanced type of development peculiar to lichens, and it
provides for fertility of long continuance which is in striking contrast with
the fugitive ascocarps of the Discomycetes.
Page 260
Fig. 102. Lecanora tartarea Ach. Vertical section of apothecium. a, hymenium; b,
proper margin or parathecium; c, thalline margin or amphithecium. × 30 (after
Reinke).
The distinction between lecideine and lecanorine apothecia is of great
value in classification, but it is not always easily demonstrable; it is
occasionally necessary to examine the early stages, as in the more advanced
the thalline margin may be pushed aside by the turgid disc and become
practically obliterated.
The “proper margin” reaches its highest development in the lecideine and
graphideine types. It is less prominent or often almost entirely replaced
when the thalline margin is superadded, except in genera such as
Thelotrema and Diploschistes which have distinct “double margins.”
There is an unusual type of apothecium in the genus Gyrophora. The fruit
is lecideine, the thalline gonidia taking no part in the development. The
growth of the initial ascogenous tissue, according to Lindau[659], is
constantly towards the periphery of the disc so that a weak spot arises in the
centre which is promptly filled by a vigorous sterile growth of paraphyses.
This process is repeated from new centres again and again, resulting in the
irregularly concentric lines of sterile and fertile areas of the “gyrose” fruit
(Fig. 103). The paraphyses soon become black at the tips. Asci are not
proper margin or parathecium; c, thalline margin or amphithecium. × 30 (after
Reinke).
The distinction between lecideine and lecanorine apothecia is of great
value in classification, but it is not always easily demonstrable; it is
occasionally necessary to examine the early stages, as in the more advanced
the thalline margin may be pushed aside by the turgid disc and become
practically obliterated.
The “proper margin” reaches its highest development in the lecideine and
graphideine types. It is less prominent or often almost entirely replaced
when the thalline margin is superadded, except in genera such as
Thelotrema and Diploschistes which have distinct “double margins.”
There is an unusual type of apothecium in the genus Gyrophora. The fruit
is lecideine, the thalline gonidia taking no part in the development. The
growth of the initial ascogenous tissue, according to Lindau[659], is
constantly towards the periphery of the disc so that a weak spot arises in the
centre which is promptly filled by a vigorous sterile growth of paraphyses.
This process is repeated from new centres again and again, resulting in the
irregularly concentric lines of sterile and fertile areas of the “gyrose” fruit
(Fig. 103). The paraphyses soon become black at the tips. Asci are not
Page 261
formed until the ascogenous layer has acquired a certain degree of stability,
and spores are accordingly present only in advanced stages of growth.
Fig. 103. Apothecial gyrose discs
of Gyrophora cylindrica Ach. ×
12 (after Lindau).
G. Lichen Asci and Spores
a. Historical. The presence of spores, as such, in the lichen fruit was first
established by Hedwig[660] in Anaptychia (Physcia) ciliaris. He rightly
judged the minute bodies to be the “semina” of the plant. In that species
they are fairly large, measuring about 50µ, long and 24µ thick, and as they
are very dark in colour when mature, they stand out conspicuously from the
surrounding colourless tissue of the hymenium. Acharius[661] also took note
of these “semina” and happily replaced the term by that of “spores.” They
may be produced, he states, in a compact nucleus (Sphaerophoron), in a
naked disc (Calicium), or they may be embedded in the disc (Opegrapha
and Lecidea). Sprengel[662] opined that the spores—which he figures—were
true seeds, though he allows that there had been no record of their
development into new plants. Luyken[663] made a further contribution to the
subject by dividing lichens into gymnocarpous and angiocarpous forms,
according as the spores, enclosed in cells or vesicles (thecae), were borne in
an open disc or in a closed perithecium.
In his Systema of lichen genera Eschweiler[664], some years later,
described and figured the spores as “thecae” enclosed in cylindrical asci.
Fée[665] in contemporary works gave special prominence to the colour and
form of the spores in all the lichens dealt with.
b. Development of the Ascus. The first attempt to trace the origin and
development of lichen asci and spores was made by Mohl[666]. He describes
and spores are accordingly present only in advanced stages of growth.
Fig. 103. Apothecial gyrose discs
of Gyrophora cylindrica Ach. ×
12 (after Lindau).
G. Lichen Asci and Spores
a. Historical. The presence of spores, as such, in the lichen fruit was first
established by Hedwig[660] in Anaptychia (Physcia) ciliaris. He rightly
judged the minute bodies to be the “semina” of the plant. In that species
they are fairly large, measuring about 50µ, long and 24µ thick, and as they
are very dark in colour when mature, they stand out conspicuously from the
surrounding colourless tissue of the hymenium. Acharius[661] also took note
of these “semina” and happily replaced the term by that of “spores.” They
may be produced, he states, in a compact nucleus (Sphaerophoron), in a
naked disc (Calicium), or they may be embedded in the disc (Opegrapha
and Lecidea). Sprengel[662] opined that the spores—which he figures—were
true seeds, though he allows that there had been no record of their
development into new plants. Luyken[663] made a further contribution to the
subject by dividing lichens into gymnocarpous and angiocarpous forms,
according as the spores, enclosed in cells or vesicles (thecae), were borne in
an open disc or in a closed perithecium.
In his Systema of lichen genera Eschweiler[664], some years later,
described and figured the spores as “thecae” enclosed in cylindrical asci.
Fée[665] in contemporary works gave special prominence to the colour and
form of the spores in all the lichens dealt with.
b. Development of the Ascus. The first attempt to trace the origin and
development of lichen asci and spores was made by Mohl[666]. He describes
Page 262
the mother-cell (the ascus) as filled at first with a clouded granular
substance changing later into a definite number—usually eight—of simple
or septate spores. Dangeard[667] included the lichens Borrera (Physcia)
ciliaris and Endocarpon (Dermatocarpon) miniatam among the plants that
he studied for ascus and spore development. He found that in lichens, as in
fungi, the ascus arose usually from the penultimate cell of a crooked hypha
(Fig. 104) and that it contained at first two nuclei derived from adjoining
cells. These nuclei are similar in size to those of the vegetative hyphae, and
in each there is a large nucleolus with chromatin material massed on one
side. Fusion takes place, as in fungi, between the two nuclei, and the
secondary or definitive nucleus thus formed divides successively to form
the eight spore-nuclei. Baur[668] and Nienburg[669] have confirmed
Dangeard’s results as regards lichens, and René Maire[670] has also
contributed important cytological details on the development of the spores.
In Anaptychia (Physcia) ciliaris he found that the fused nucleus became
larger and that a synapsis stage supervened during which the long slender
chromatin filaments became paired, and at the same time shorter and
thicker. The nuclear membrane disappeared as the chromatin filaments were
united in masses joined together by linin threads which also disappeared
later. At the most advanced stage observed by Maire there was visible a
nucleolus embedded in a condensed plasma and surrounded by eight
medianly constricted filaments destined to form the equatorial plate. A few
isolated observations were also made on the cytology of the ascus in
Peltigera canina, in which lichen the preceding ascogonial development is
wholly vegetative. The secondary nucleus was seen to contain a chromatin
mass and a large nucleolus; in addition two angular bodies of uncertain
signification were associated with the nucleolus, each with a central
vacuole. The nucleolus disappeared in the prophase of the first division and
four double chromosomes were then plainly visible. The succeeding phases
of the first and the second nuclear division were not seen, but in the
prophase of the third it was possible to distinguish four chromatin masses
outside the nucleolus. The slow growth of the lichen plant renders
continuous observation extremely difficult.
F. Bachmann[671] was able to make important cytological observations in
her study of Collema pulposum. As regards the vegetative and ascogonial
nuclei, five or perhaps six chromosomes appeared on the spindle when the
substance changing later into a definite number—usually eight—of simple
or septate spores. Dangeard[667] included the lichens Borrera (Physcia)
ciliaris and Endocarpon (Dermatocarpon) miniatam among the plants that
he studied for ascus and spore development. He found that in lichens, as in
fungi, the ascus arose usually from the penultimate cell of a crooked hypha
(Fig. 104) and that it contained at first two nuclei derived from adjoining
cells. These nuclei are similar in size to those of the vegetative hyphae, and
in each there is a large nucleolus with chromatin material massed on one
side. Fusion takes place, as in fungi, between the two nuclei, and the
secondary or definitive nucleus thus formed divides successively to form
the eight spore-nuclei. Baur[668] and Nienburg[669] have confirmed
Dangeard’s results as regards lichens, and René Maire[670] has also
contributed important cytological details on the development of the spores.
In Anaptychia (Physcia) ciliaris he found that the fused nucleus became
larger and that a synapsis stage supervened during which the long slender
chromatin filaments became paired, and at the same time shorter and
thicker. The nuclear membrane disappeared as the chromatin filaments were
united in masses joined together by linin threads which also disappeared
later. At the most advanced stage observed by Maire there was visible a
nucleolus embedded in a condensed plasma and surrounded by eight
medianly constricted filaments destined to form the equatorial plate. A few
isolated observations were also made on the cytology of the ascus in
Peltigera canina, in which lichen the preceding ascogonial development is
wholly vegetative. The secondary nucleus was seen to contain a chromatin
mass and a large nucleolus; in addition two angular bodies of uncertain
signification were associated with the nucleolus, each with a central
vacuole. The nucleolus disappeared in the prophase of the first division and
four double chromosomes were then plainly visible. The succeeding phases
of the first and the second nuclear division were not seen, but in the
prophase of the third it was possible to distinguish four chromatin masses
outside the nucleolus. The slow growth of the lichen plant renders
continuous observation extremely difficult.
F. Bachmann[671] was able to make important cytological observations in
her study of Collema pulposum. As regards the vegetative and ascogonial
nuclei, five or perhaps six chromosomes appeared on the spindle when the
Page 263
nucleus divided. In the asci, the
usual paired nuclei were present in
the early stages and did not fuse
until the ascus had elongated
considerably. After fusion the
definitive nucleus enlarged with the
growth of the ascus and did not
divide until the ascus had attained
full size. The nucleolus was large,
and usually excentric, and there
were at first a number of chromatin
masses on an irregular spirem. In
synapsis the spirem was drawn into
a compact mass, but after synapsis,
“the chromatin is again in the form
of a knotty spirem.” In late
prophases the chromosomes, small
ovoid bodies, were scattered on the
spindle; later they were aggregated
Fig. 104. Developing asci of Physcia ciliaris DC.
× 800 (after Baur).
in the centre, and, in the early
metaphase, about twelve were
counted now split longitudinally.
There were thus twice as many chromosomes in the first division in the
ascus as in nuclear divisions of the vegetative hyphae. F. Bachmann failed
to see the second division; there were at least five chromosomes in the third
division.
Considerable importance is given to the number of the chromosomes in
the successive divisions in the ascus since they are considered to be proof of
a previous double fusion—in the ascogonium and again in the ascus—
necessitating, therefore, a double reduction division to arrive at the
gametophytic or vegetative number of five or six chromosomes in the third
division in the ascus. There have been too few observations to draw any
general conclusions.
c. Development of Spores. The spore wall begins to form, as in
Ascomycetes, at the apex of the nucleus with the curving over of the astral
threads, the nucleus at that stage presenting the figure of a flask the neck of
usual paired nuclei were present in
the early stages and did not fuse
until the ascus had elongated
considerably. After fusion the
definitive nucleus enlarged with the
growth of the ascus and did not
divide until the ascus had attained
full size. The nucleolus was large,
and usually excentric, and there
were at first a number of chromatin
masses on an irregular spirem. In
synapsis the spirem was drawn into
a compact mass, but after synapsis,
“the chromatin is again in the form
of a knotty spirem.” In late
prophases the chromosomes, small
ovoid bodies, were scattered on the
spindle; later they were aggregated
Fig. 104. Developing asci of Physcia ciliaris DC.
× 800 (after Baur).
in the centre, and, in the early
metaphase, about twelve were
counted now split longitudinally.
There were thus twice as many chromosomes in the first division in the
ascus as in nuclear divisions of the vegetative hyphae. F. Bachmann failed
to see the second division; there were at least five chromosomes in the third
division.
Considerable importance is given to the number of the chromosomes in
the successive divisions in the ascus since they are considered to be proof of
a previous double fusion—in the ascogonium and again in the ascus—
necessitating, therefore, a double reduction division to arrive at the
gametophytic or vegetative number of five or six chromosomes in the third
division in the ascus. There have been too few observations to draw any
general conclusions.
c. Development of Spores. The spore wall begins to form, as in
Ascomycetes, at the apex of the nucleus with the curving over of the astral
threads, the nucleus at that stage presenting the figure of a flask the neck of
Page 264
which is occupied by the centrosome. The final spore-nucleus, as observed
by Maire, divides once again in Anaptychia and division is followed by the
formation of a median septum, the mature spore being two-celled. In
Peltigera the spore is at first ovoid, but both nucleus and spore gradually
elongate. The fully formed spore is narrowly fusiform and by repeated
nuclear division and subsequent cross-septation it becomes 4- or even 5-6-
celled.
The spores of lichens are wholly fungoid, and, in many cases, form a
parallel series with the spores of the Ascomycetes. Markings of the
epispore, such as reticulations, spines, etc., are rarely present (Solorina
spongiosa), though thickening of the wall occurs in many species
(Pertusariae, etc.), a peculiarity which was first pointed out by Mohl[672]
who contrasted the spore walls with the delicate membranes of other lichen
cells. Some spores, described as “halonate,” have an outer gelatinous
covering which probably prevents the spore from drying up and thus
prolongs the period of possible germination. Both asci and spores are, as a
rule, more sparingly produced than in fungi; in many instances some or all
of the spores in the ascus are imperfectly formed, and the full complement
is frequently lacking, possibly owing to some occurrence of adverse
conditions during the long slow development of the apothecium. In the
larger number of genera and species the spores are small bodies, but in
some, as for instance in the Pertusariae and in some Pyrenocarpeae, they
exceed in size all known fungus spores. In Varicellaria microsticta, a rare
crustaceous lichen of high mountains, the solitary 1-septate spore measures
up to 350 µ, in length and 115 µ in width. Most spores contain reserve
material in the form of fat, etc., many are dark-coloured; Zukal[673] has
suggested that the colour may be protective.
Their ejection from the ascus at maturity is caused by the twofold
pressure of the paraphyses and the marginal hyphae on the addition of
moisture. The spores may be shot up at least 1 cm. from the disc[674].
d. Spore Germination. Meyer[675] was the first who cultivated lichen
spores and the dendritic formation which he obtained by growing them on a
smooth surface was undoubtedly the prothallus (or hypothallus) of the
lichen. Actual germination was however not observed till Holle[676] in 1846
watched and figured the process as it occurs in Physcia ciliaris.
by Maire, divides once again in Anaptychia and division is followed by the
formation of a median septum, the mature spore being two-celled. In
Peltigera the spore is at first ovoid, but both nucleus and spore gradually
elongate. The fully formed spore is narrowly fusiform and by repeated
nuclear division and subsequent cross-septation it becomes 4- or even 5-6-
celled.
The spores of lichens are wholly fungoid, and, in many cases, form a
parallel series with the spores of the Ascomycetes. Markings of the
epispore, such as reticulations, spines, etc., are rarely present (Solorina
spongiosa), though thickening of the wall occurs in many species
(Pertusariae, etc.), a peculiarity which was first pointed out by Mohl[672]
who contrasted the spore walls with the delicate membranes of other lichen
cells. Some spores, described as “halonate,” have an outer gelatinous
covering which probably prevents the spore from drying up and thus
prolongs the period of possible germination. Both asci and spores are, as a
rule, more sparingly produced than in fungi; in many instances some or all
of the spores in the ascus are imperfectly formed, and the full complement
is frequently lacking, possibly owing to some occurrence of adverse
conditions during the long slow development of the apothecium. In the
larger number of genera and species the spores are small bodies, but in
some, as for instance in the Pertusariae and in some Pyrenocarpeae, they
exceed in size all known fungus spores. In Varicellaria microsticta, a rare
crustaceous lichen of high mountains, the solitary 1-septate spore measures
up to 350 µ, in length and 115 µ in width. Most spores contain reserve
material in the form of fat, etc., many are dark-coloured; Zukal[673] has
suggested that the colour may be protective.
Their ejection from the ascus at maturity is caused by the twofold
pressure of the paraphyses and the marginal hyphae on the addition of
moisture. The spores may be shot up at least 1 cm. from the disc[674].
d. Spore Germination. Meyer[675] was the first who cultivated lichen
spores and the dendritic formation which he obtained by growing them on a
smooth surface was undoubtedly the prothallus (or hypothallus) of the
lichen. Actual germination was however not observed till Holle[676] in 1846
watched and figured the process as it occurs in Physcia ciliaris.
Page 265
Spores divided by transverse septa into two or more cells, as well as
those that have become “muriform” by transverse and longitudinal
septation, may germinate from each cell.
Fig. 105. Multinucleate spore of Lecidea
(Mycoblastus) sanguinaria Ach. × 540
Fig. 106. Germination of
(after Zopf).
multinucleate spore of
Ochrolechia pallescens Koerb. ×
390 (after de Bary).
e. Multinucleate Spores. These spores, which are all very large, occur in
several genera or subgenera: in Lecidea subg. Mycoblastus (Fig. 105),
Lecanora subg. Ochrolechia and in Pertusariaceae. Tulasne[677] in his
experiments with germinating spores found that in Lecanora parella
(Ochrolechia pallescens?) germinating tubes were produced all over the
surface of the spore (Fig. 106). De Bary[678] verified his observations in that
and other species and added considerable detail: about twenty-four hours
after sowing spores of Ochrolechia pallescens, numerous little warts arose
on the surface of the spore which gradually grew out into delicate hyphae.
All these spores contain fat globules and finely granular protoplasm with a
very large number of minute nuclei; the presence of the latter has been
demonstrated by Haberlandt[679] and later by Zopf[680] who reckoned about
200 to 300 in the spore of Mycoblastus sanguinarius. These nuclei had
continued to multiply during the ripening of the spore while it was still
contained in the ascus[680]. Owing to the presence of the large fat globules
the plasma is confined to an external layer close to the spore wall; the
those that have become “muriform” by transverse and longitudinal
septation, may germinate from each cell.
Fig. 105. Multinucleate spore of Lecidea
(Mycoblastus) sanguinaria Ach. × 540
Fig. 106. Germination of
(after Zopf).
multinucleate spore of
Ochrolechia pallescens Koerb. ×
390 (after de Bary).
e. Multinucleate Spores. These spores, which are all very large, occur in
several genera or subgenera: in Lecidea subg. Mycoblastus (Fig. 105),
Lecanora subg. Ochrolechia and in Pertusariaceae. Tulasne[677] in his
experiments with germinating spores found that in Lecanora parella
(Ochrolechia pallescens?) germinating tubes were produced all over the
surface of the spore (Fig. 106). De Bary[678] verified his observations in that
and other species and added considerable detail: about twenty-four hours
after sowing spores of Ochrolechia pallescens, numerous little warts arose
on the surface of the spore which gradually grew out into delicate hyphae.
All these spores contain fat globules and finely granular protoplasm with a
very large number of minute nuclei; the presence of the latter has been
demonstrated by Haberlandt[679] and later by Zopf[680] who reckoned about
200 to 300 in the spore of Mycoblastus sanguinarius. These nuclei had
continued to multiply during the ripening of the spore while it was still
contained in the ascus[680]. Owing to the presence of the large fat globules
the plasma is confined to an external layer close to the spore wall; the
Page 266
nuclei are embedded in the plasma and are connected by strands of
protoplasm. The epispore in some of these large spores is extremely
developed: in some Pertusariae it measures 4-5 µ in thickness.
f. Polaribilocular Spores. The most peculiar of all lichen spores are
those termed polaribilocular—signifying a two-celled spore of which the
median septum has become so thickened that the cell-cavities with their
contents are relegated to the two poles of the spore, an open canal
frequently connecting the two cell-spaces (Fig. 107). Other terms have been
suggested and used by various writers to describe this unusual character
such as blasteniospore[681], orculiform[682] and placodiomorph[683] or more
simply polarilocular.
The polarilocular colourless spore is found in a connected series of
lichens—crustaceous, foliose and fruticose (Placodium, Xanthoria,
Teloschistes). In another series with a darker thallus (Rinodina and Physcia)
the spore is brown-coloured, and the median septum cuts across the plasma-
connection. In other respects the brown spore is similar to the colourless
one and possesses a thickened wall with reduced cell-cavities.
The method of cell-division in these spores
resembles that known as “cleavage by
constriction,” in which the cross wall arises by
an ingrowth from all sides of the cell; in time
the centre is reached and the wall is complete, or
an open pore is left between the divided cells.
Cell “cleavage” occurs frequently among
Thallophytes, though it is unknown among the
higher plants. Among Algae it is the normal
form of cell-division in Cladophora and also in
Spirogyra, though in the latter the wall passes Fig. 107. Polarilocular spores. a,
right across and cuts through the connecting Xanthoria parietina Th. Fr.; b,
Rinodina roboris Th. Fr.; c,
plasma threads. Harper[684] found “cleavage by Physcia pulverulenta Nyl.; d,
constriction” in two instances among fungi: the Physcia ciliaris DC. × 600.
conidia of Erysiphe and the gametes of
Sporodinia are cut off by a septum which
originates as a circular ingrowth of the outer wall, comparable, he
considers, with the cell-division of Cladophora.
protoplasm. The epispore in some of these large spores is extremely
developed: in some Pertusariae it measures 4-5 µ in thickness.
f. Polaribilocular Spores. The most peculiar of all lichen spores are
those termed polaribilocular—signifying a two-celled spore of which the
median septum has become so thickened that the cell-cavities with their
contents are relegated to the two poles of the spore, an open canal
frequently connecting the two cell-spaces (Fig. 107). Other terms have been
suggested and used by various writers to describe this unusual character
such as blasteniospore[681], orculiform[682] and placodiomorph[683] or more
simply polarilocular.
The polarilocular colourless spore is found in a connected series of
lichens—crustaceous, foliose and fruticose (Placodium, Xanthoria,
Teloschistes). In another series with a darker thallus (Rinodina and Physcia)
the spore is brown-coloured, and the median septum cuts across the plasma-
connection. In other respects the brown spore is similar to the colourless
one and possesses a thickened wall with reduced cell-cavities.
The method of cell-division in these spores
resembles that known as “cleavage by
constriction,” in which the cross wall arises by
an ingrowth from all sides of the cell; in time
the centre is reached and the wall is complete, or
an open pore is left between the divided cells.
Cell “cleavage” occurs frequently among
Thallophytes, though it is unknown among the
higher plants. Among Algae it is the normal
form of cell-division in Cladophora and also in
Spirogyra, though in the latter the wall passes Fig. 107. Polarilocular spores. a,
right across and cuts through the connecting Xanthoria parietina Th. Fr.; b,
Rinodina roboris Th. Fr.; c,
plasma threads. Harper[684] found “cleavage by Physcia pulverulenta Nyl.; d,
constriction” in two instances among fungi: the Physcia ciliaris DC. × 600.
conidia of Erysiphe and the gametes of
Sporodinia are cut off by a septum which
originates as a circular ingrowth of the outer wall, comparable, he
considers, with the cell-division of Cladophora.
Page 267
The development of the thickened wall of polarilocular spores has been
studied by Hue[685], who contends however that there is no true septation in
the colourless spores so long as the central canal remains open. According
to his observations the wall of the young spore is formed of a thin tegument,
everywhere equal in thickness, and consisting of concentric layers. This
tegument becomes continually thicker at the equator of the spore by the
addition of new layers from the interior, and the protoplasmic contents are
compressed into a gradually diminishing space. In the end the wall almost
touches at the centre, and the spore consists of two polar cell-cavities with a
narrow open passage between. A median line pierced by the canal is
frequently seen. In a few species there is a second constriction cleavage and
the spore becomes quadrilocular.
Hue insists that this spore should be regarded as only one-celled; for
though the walls may touch at the centre, he says they never coalesce. He
has unfortunately given no cytological observations as to whether the spore
is uni- or binucleate.
In Xanthoria parietina, one of the species with characteristic
polaribilocular spores, germination, it would seem, takes place mostly at
one end only of the spore, though a germinating tube issues at both ends
frequently enough to suggest that the spore is binucleate and two-celled.
The absence of germination from one or other of the cells only may
probably be due to the drain on their small resources. Hue has cited the
rarity of such instances of double germination in support of his view of the
one-celled nature of the spore. He instances that out of fifteen spores,
Tulasne[686] has figured only three that have germinated at each end;
Bornet[687] figures one in seven with the double germination and
Bonnier[688] one in sixteen spores.
Further evidence is wanted as to the nuclear history of these hyaline
spores. In the case of the brown spores, which show the same thickening of
the wall and restricted cell-cavity, though with a distinct median septum,
nuclear division was observed by René Maire[689] before septation in one
such species, Anaptychia ciliaris.
II. SECONDARY SPORES
studied by Hue[685], who contends however that there is no true septation in
the colourless spores so long as the central canal remains open. According
to his observations the wall of the young spore is formed of a thin tegument,
everywhere equal in thickness, and consisting of concentric layers. This
tegument becomes continually thicker at the equator of the spore by the
addition of new layers from the interior, and the protoplasmic contents are
compressed into a gradually diminishing space. In the end the wall almost
touches at the centre, and the spore consists of two polar cell-cavities with a
narrow open passage between. A median line pierced by the canal is
frequently seen. In a few species there is a second constriction cleavage and
the spore becomes quadrilocular.
Hue insists that this spore should be regarded as only one-celled; for
though the walls may touch at the centre, he says they never coalesce. He
has unfortunately given no cytological observations as to whether the spore
is uni- or binucleate.
In Xanthoria parietina, one of the species with characteristic
polaribilocular spores, germination, it would seem, takes place mostly at
one end only of the spore, though a germinating tube issues at both ends
frequently enough to suggest that the spore is binucleate and two-celled.
The absence of germination from one or other of the cells only may
probably be due to the drain on their small resources. Hue has cited the
rarity of such instances of double germination in support of his view of the
one-celled nature of the spore. He instances that out of fifteen spores,
Tulasne[686] has figured only three that have germinated at each end;
Bornet[687] figures one in seven with the double germination and
Bonnier[688] one in sixteen spores.
Further evidence is wanted as to the nuclear history of these hyaline
spores. In the case of the brown spores, which show the same thickening of
the wall and restricted cell-cavity, though with a distinct median septum,
nuclear division was observed by René Maire[689] before septation in one
such species, Anaptychia ciliaris.
II. SECONDARY SPORES
Page 268
A. Reproduction by Oidia
In certain conditions of nutrition, fungal hyphae break up into separate
cells, each of which functions as a reproductive conidium or oidium, which
on germination forms new hyphae. Neubner[690] has demonstrated a similar
process in the hyphae of the Caliciaceae and compares it with the oidial
formation described by Brefeld[691] in the Basidiomycetes.
The thallus of this family of lichens is granular or furfuraceous; it never
goes beyond the Lepra stage of development[692]. In some species it is
scanty, in others it is abundant and spreads over large areas of the trunks of
old trees. It is only when growth is especially luxuriant that oidia are
formed. Neubner was able to recognize the oidial condition by the more
opaque appearance of the granules, and under the microscope he observed
the hyphae surrounding the gonidia gradually fall away and break up into
minute cylindrical cells somewhat like spermatia in size and form. There
was no question of abnormal or unhealthy conditions, as the oidia were
formed in a freely fruiting thallus.
The gonidia associated with the oidial hyphae also showed unusual
vitality and active division took place as they were set free by the breaking
up of the encircling hyphae. The germination of the oidia provides an
abundance of hyphal filaments for the rapidly increasing algal cells, and
there follows a wide-spread development of the lichen thallus.
Oidial formation has not been observed in any other family of lichens.
B. Reproduction by Conidia
a. Instances of Conidial Formation. It is remarkable that the type of
asexual reproduction so abundantly represented in fungi by the large and
varied group of the Hyphomycetes is practically absent in lichens. An
exception is to be found in a minute gelatinous lichen that grows on soil. It
was discovered by Bornet[693] and called by him Arnoldia (Physma)
minutula. From the thallus rise up simple or sparingly branched colourless
conidiophores which bear at the tips globose brown conidia (Fig. 108).
Bornet[694] obtained these conidia by keeping very thin sections of the
thallus in a drop of water[693].
In certain conditions of nutrition, fungal hyphae break up into separate
cells, each of which functions as a reproductive conidium or oidium, which
on germination forms new hyphae. Neubner[690] has demonstrated a similar
process in the hyphae of the Caliciaceae and compares it with the oidial
formation described by Brefeld[691] in the Basidiomycetes.
The thallus of this family of lichens is granular or furfuraceous; it never
goes beyond the Lepra stage of development[692]. In some species it is
scanty, in others it is abundant and spreads over large areas of the trunks of
old trees. It is only when growth is especially luxuriant that oidia are
formed. Neubner was able to recognize the oidial condition by the more
opaque appearance of the granules, and under the microscope he observed
the hyphae surrounding the gonidia gradually fall away and break up into
minute cylindrical cells somewhat like spermatia in size and form. There
was no question of abnormal or unhealthy conditions, as the oidia were
formed in a freely fruiting thallus.
The gonidia associated with the oidial hyphae also showed unusual
vitality and active division took place as they were set free by the breaking
up of the encircling hyphae. The germination of the oidia provides an
abundance of hyphal filaments for the rapidly increasing algal cells, and
there follows a wide-spread development of the lichen thallus.
Oidial formation has not been observed in any other family of lichens.
B. Reproduction by Conidia
a. Instances of Conidial Formation. It is remarkable that the type of
asexual reproduction so abundantly represented in fungi by the large and
varied group of the Hyphomycetes is practically absent in lichens. An
exception is to be found in a minute gelatinous lichen that grows on soil. It
was discovered by Bornet[693] and called by him Arnoldia (Physma)
minutula. From the thallus rise up simple or sparingly branched colourless
conidiophores which bear at the tips globose brown conidia (Fig. 108).
Bornet[694] obtained these conidia by keeping very thin sections of the
thallus in a drop of water[693].
Page 269
Fig. 108. Conidia developed
from thallus of Arnoldia
minutula Born. × 950 (after
Bornet).
Yet another instance of conidial growth is given by Steiner[695]. He had
observed that the apothecia on plants of Caloplaca aurantia var. callopisma
Stein. differed from those of normal appearance in the warted unevenness
of the disc and also in being more swollen and convex, the thalline margin
being almost obliterated. He found, on microscopical examination, that the
hymenium was occupied by paraphyses and by occasional asci, the latter
seldom containing spores, and being usually more or less collapsed. The
component parts of the apothecium were entirely normal and healthy, but
the paraphyses and the few asci were crushed aside by the intrusion of
numerous slender unbranched septate conidiophores. Several of these might
spring from one base and the hypha from which they originated could be
from thallus of Arnoldia
minutula Born. × 950 (after
Bornet).
Yet another instance of conidial growth is given by Steiner[695]. He had
observed that the apothecia on plants of Caloplaca aurantia var. callopisma
Stein. differed from those of normal appearance in the warted unevenness
of the disc and also in being more swollen and convex, the thalline margin
being almost obliterated. He found, on microscopical examination, that the
hymenium was occupied by paraphyses and by occasional asci, the latter
seldom containing spores, and being usually more or less collapsed. The
component parts of the apothecium were entirely normal and healthy, but
the paraphyses and the few asci were crushed aside by the intrusion of
numerous slender unbranched septate conidiophores. Several of these might
spring from one base and the hypha from which they originated could be
Page 270
traced some distance into the ascogenous layer, though a connection with
that cell-system could not be demonstrated. While still embedded in the
hymenium, an ellipsoid or obovate swelling began to form at the apex of
the conidiophore; it became separated from the stalk by a septum and later
divided into a two-celled conidium. The conidiophore increased in length
by intercalary growth and finally emerged above the disc; the mature
conidium was pyriform and measured 15-20 µ × 9-11 µ.
Steiner regarded these conidia as entirely abnormal; pycnidia with
stylospores are unknown in the genus and they were not, he alleges, the
product of any parasitic growth.
b. Comparison With Hyphomycetes. The conidial form of fructification in
fungi, known as a Hyphomycete, is generally a stage in the life-cycle of
some Ascomycete; it represents the rapid summer form of asexual
reproduction. The ascospore of the resting fruit-form in many species
germinates on any suitable matrix and may at once produce conidiophores
and conidia, which in turn germinate, and either continue the conidial
generation or proceed to the formation of the perfect fruiting form with asci
and ascospores.
Such a form of transient reproduction is almost impossible in lichens, as
the hypha produced by the germinating lichen ascospore has little vitality
without the algal symbiont. In natural conditions development practically
ceases in the absence of symbiosis. When union between the symbionts
takes place, and growth becomes active, thallus construction at once
commences. But in certain conditions of shade and moisture, only the
rudiments of a lichen thallus are formed, known as a leprose or sorediose
condition. Soredia also arise in the normal life of many lichens. As the
individual granules or soredia may each give rise to a complete lichen plant,
they may well be considered as replacing the lost conidial fructification.
C. Campylidium and Orthidium
Müller[696] has described under the name Campylidium a supposed new
type of asexual fructification which he found on the thallus of tropical
species of Gyalecta, Lopadium, etc., and which he considered analogous to
pycnidia and spermogonia. Wainio[697] has however recognized the cup-like
that cell-system could not be demonstrated. While still embedded in the
hymenium, an ellipsoid or obovate swelling began to form at the apex of
the conidiophore; it became separated from the stalk by a septum and later
divided into a two-celled conidium. The conidiophore increased in length
by intercalary growth and finally emerged above the disc; the mature
conidium was pyriform and measured 15-20 µ × 9-11 µ.
Steiner regarded these conidia as entirely abnormal; pycnidia with
stylospores are unknown in the genus and they were not, he alleges, the
product of any parasitic growth.
b. Comparison With Hyphomycetes. The conidial form of fructification in
fungi, known as a Hyphomycete, is generally a stage in the life-cycle of
some Ascomycete; it represents the rapid summer form of asexual
reproduction. The ascospore of the resting fruit-form in many species
germinates on any suitable matrix and may at once produce conidiophores
and conidia, which in turn germinate, and either continue the conidial
generation or proceed to the formation of the perfect fruiting form with asci
and ascospores.
Such a form of transient reproduction is almost impossible in lichens, as
the hypha produced by the germinating lichen ascospore has little vitality
without the algal symbiont. In natural conditions development practically
ceases in the absence of symbiosis. When union between the symbionts
takes place, and growth becomes active, thallus construction at once
commences. But in certain conditions of shade and moisture, only the
rudiments of a lichen thallus are formed, known as a leprose or sorediose
condition. Soredia also arise in the normal life of many lichens. As the
individual granules or soredia may each give rise to a complete lichen plant,
they may well be considered as replacing the lost conidial fructification.
C. Campylidium and Orthidium
Müller[696] has described under the name Campylidium a supposed new
type of asexual fructification which he found on the thallus of tropical
species of Gyalecta, Lopadium, etc., and which he considered analogous to
pycnidia and spermogonia. Wainio[697] has however recognized the cup-like
Page 271
structure as a fungus, Cyphella aeruginascens Karst., which grows on the
bark of trees and occasionally is parasitic on the crustaceous thallus of
lichens. Wainio has also identified the plant, Lecidea irregularis, first
described by Fée[698], as also synonymous with the fungus.
Another name Orthidium was proposed by Müller[699] for a type of
fructification he found in Brazil which he contrasts or associates with
Campylidium. It has an open marginate disc with sporophores bearing
acrogenous spores. He found it growing in connection with a thin lichen
thallus on leaves and considered it to be a form of lichen reproduction.
Possibly Orthidium is also a Cyphella.
III. SPERMOGONIA OR PYCNIDIA
A. Historical Account of Spermogonia
The name spermogonium was given by Tulasne[700] to the “punctiform
conceptacles” that are so plentifully produced on many lichen thalli, on the
assumption that they were the male organs of the plant, and that the spore-
like bodies borne in them were non-motile male cells or spermatia.
The first record of their association with lichens was made by
Dillenius[701], who indicates the presence of black tubercles on the thallus
of Physcia ciliaris. He figures them also on several species of Cladonia, on
Ramalina and on Dermatocarpon, but without any suggestion as to their
function. Hedwig’s[702] study of the reproductive organs of the Linnaean
Cryptogams included lichens. He examined Physcia ciliaris, a species that
not only is quite common but is generally found in a fruiting condition and
with very prominent spermogonia, and has been therefore a favourite lichen
for purposes of examination and study. Hedwig describes and figures not
only the apothecia but also those other bodies which he designates as
“punctula mascula,” or again as “puncta floris masculi.” In his later work he
gives a drawing of Lichen (Gyrophora) proboscideus, with two of the
spermogonia in section.
Acharius[703] included them among the lichen structures which he called
“cephalodia”: he described them as very minute tubercles rising up from the
substance of the thallus and projecting somewhat above it. He also figures a
bark of trees and occasionally is parasitic on the crustaceous thallus of
lichens. Wainio has also identified the plant, Lecidea irregularis, first
described by Fée[698], as also synonymous with the fungus.
Another name Orthidium was proposed by Müller[699] for a type of
fructification he found in Brazil which he contrasts or associates with
Campylidium. It has an open marginate disc with sporophores bearing
acrogenous spores. He found it growing in connection with a thin lichen
thallus on leaves and considered it to be a form of lichen reproduction.
Possibly Orthidium is also a Cyphella.
III. SPERMOGONIA OR PYCNIDIA
A. Historical Account of Spermogonia
The name spermogonium was given by Tulasne[700] to the “punctiform
conceptacles” that are so plentifully produced on many lichen thalli, on the
assumption that they were the male organs of the plant, and that the spore-
like bodies borne in them were non-motile male cells or spermatia.
The first record of their association with lichens was made by
Dillenius[701], who indicates the presence of black tubercles on the thallus
of Physcia ciliaris. He figures them also on several species of Cladonia, on
Ramalina and on Dermatocarpon, but without any suggestion as to their
function. Hedwig’s[702] study of the reproductive organs of the Linnaean
Cryptogams included lichens. He examined Physcia ciliaris, a species that
not only is quite common but is generally found in a fruiting condition and
with very prominent spermogonia, and has been therefore a favourite lichen
for purposes of examination and study. Hedwig describes and figures not
only the apothecia but also those other bodies which he designates as
“punctula mascula,” or again as “puncta floris masculi.” In his later work he
gives a drawing of Lichen (Gyrophora) proboscideus, with two of the
spermogonia in section.
Acharius[703] included them among the lichen structures which he called
“cephalodia”: he described them as very minute tubercles rising up from the
substance of the thallus and projecting somewhat above it. He also figures a
Page 272
section through two “cephalodia” of Physcia ciliaris. Fries[704] looked on
them as being mostly “anamorphoses of apothecia, the presence of abortive
fruits transforming the angiocarpous lichen to the appearance of a
gymnocarpous form.” Wallroth[705] assigned the small black fruits to the
comprehensive fungus genus Sphaeria or classified lichens bearing
spermogonia only as distinct genera and species (Pyrenothea and
Thrombium). Later students of lichens—Schaerer[706], Flotow[707], and
others—accepted Wallroth’s interpretation of their relation to the thallus, or
they ignored them altogether in their descriptions of species.
B. Spermogonia as Male Organs
Interest in these minute “tubercles” and their enclosed “corpuscles” was
revived by Itzigsohn[708] who examined them with an improved
microscope. He macerated in water during a few days that part of the
thallus on which they were developed, and, at the end of the time,
discovered that the solution contained large numbers of motile bodies which
he naturally took to be the corpuscles from the broken down tubercles. He
claimed to have established their function as male motile cells or
spermatozoa. The discovery seemed not only to prove their sexual nature,
but to link up the reproduction of lichens with that of the higher
cryptogams. The tubercles in which the “spermatozoa” were produced he
designated as antheridia. More prolonged maceration of the tissue to the
very verge of decay yielded still larger numbers of the “spermatozoa” which
we now recognize to have been motile bacilli.
Tulasne[709] next took up the subject, and failing to find the motile cells,
he wrongly insisted that Itzigsohn had been misled by mere Brownian
movement, but at the same time he accepted the theory that the minute
conceptacles were spermogonia or male organs of lichens. He also pointed
out that their constant occurrence on the thallus of practically every species
of lichen, and their definite form, though with considerable variation,
rendered it impossible to regard them as accidental or of no importance to
the life of the plant. He compared them with fungal pycnidia such as
Phyllosticta or Septoria which outwardly they resembled, but whereas the
pycnidial spores germinated freely, the spermatia of the spermogonia, as far
as his experience went, were incapable of germination.
them as being mostly “anamorphoses of apothecia, the presence of abortive
fruits transforming the angiocarpous lichen to the appearance of a
gymnocarpous form.” Wallroth[705] assigned the small black fruits to the
comprehensive fungus genus Sphaeria or classified lichens bearing
spermogonia only as distinct genera and species (Pyrenothea and
Thrombium). Later students of lichens—Schaerer[706], Flotow[707], and
others—accepted Wallroth’s interpretation of their relation to the thallus, or
they ignored them altogether in their descriptions of species.
B. Spermogonia as Male Organs
Interest in these minute “tubercles” and their enclosed “corpuscles” was
revived by Itzigsohn[708] who examined them with an improved
microscope. He macerated in water during a few days that part of the
thallus on which they were developed, and, at the end of the time,
discovered that the solution contained large numbers of motile bodies which
he naturally took to be the corpuscles from the broken down tubercles. He
claimed to have established their function as male motile cells or
spermatozoa. The discovery seemed not only to prove their sexual nature,
but to link up the reproduction of lichens with that of the higher
cryptogams. The tubercles in which the “spermatozoa” were produced he
designated as antheridia. More prolonged maceration of the tissue to the
very verge of decay yielded still larger numbers of the “spermatozoa” which
we now recognize to have been motile bacilli.
Tulasne[709] next took up the subject, and failing to find the motile cells,
he wrongly insisted that Itzigsohn had been misled by mere Brownian
movement, but at the same time he accepted the theory that the minute
conceptacles were spermogonia or male organs of lichens. He also pointed
out that their constant occurrence on the thallus of practically every species
of lichen, and their definite form, though with considerable variation,
rendered it impossible to regard them as accidental or of no importance to
the life of the plant. He compared them with fungal pycnidia such as
Phyllosticta or Septoria which outwardly they resembled, but whereas the
pycnidial spores germinated freely, the spermatia of the spermogonia, as far
as his experience went, were incapable of germination.
Page 273
C. Occurrence and Distribution
a. Relation to Thallus and Apothecia. We owe to Tulasne[710] the first
comparative study of lichen spermogonia. He described not only their
outward form, but their minute structure, in a considerable number of
representative species. A few years later Lindsay[711] published a memoir
dealing with the spermogonia of the larger foliose and fruticose lichens,
and, in a second paper, he embodied the results of his study of an equally
extensive selection of crustaceous species. Lindsay’s work is unfortunately
somewhat damaged by faulty determination of the lichens he examined, and
by lack of the necessary discrimination between one thallus and another of
associated and intermingled species. Both memoirs contain, however, much
valuable information as to the forms of spermogonia, with their
spermatiophores and spermatia, and as to their distribution over the lichen
thallus.
Though spermogonia are mostly found associated with apothecia, yet in
some lichens, such as Cerania (Thamnolia) vermicularis, they are the only
sporiferous organs known. Not unfrequently crustaceous thalli bear
spermogonia only, and in some Cladoniae, more especially in ascyphous
species, spermogonia are produced abundantly at the tips of the podetial
branches (Fig. 109), while apothecia are exceedingly rare. Usually they
occur in scattered or crowded groups, more rarely they are solitary. Very
often they are developed and the contents dispersed before the apothecia
reach the surface of the thallus; hence the difficulty in relating these
organisms, since the mature apothecium is mostly of extreme importance in
determining the species.
a. Relation to Thallus and Apothecia. We owe to Tulasne[710] the first
comparative study of lichen spermogonia. He described not only their
outward form, but their minute structure, in a considerable number of
representative species. A few years later Lindsay[711] published a memoir
dealing with the spermogonia of the larger foliose and fruticose lichens,
and, in a second paper, he embodied the results of his study of an equally
extensive selection of crustaceous species. Lindsay’s work is unfortunately
somewhat damaged by faulty determination of the lichens he examined, and
by lack of the necessary discrimination between one thallus and another of
associated and intermingled species. Both memoirs contain, however, much
valuable information as to the forms of spermogonia, with their
spermatiophores and spermatia, and as to their distribution over the lichen
thallus.
Though spermogonia are mostly found associated with apothecia, yet in
some lichens, such as Cerania (Thamnolia) vermicularis, they are the only
sporiferous organs known. Not unfrequently crustaceous thalli bear
spermogonia only, and in some Cladoniae, more especially in ascyphous
species, spermogonia are produced abundantly at the tips of the podetial
branches (Fig. 109), while apothecia are exceedingly rare. Usually they
occur in scattered or crowded groups, more rarely they are solitary. Very
often they are developed and the contents dispersed before the apothecia
reach the surface of the thallus; hence the difficulty in relating these
organisms, since the mature apothecium is mostly of extreme importance in
determining the species.
Page 274
Fig. 109. Cladonia furcata Schrad.
Branched podetium with spermogonia at
the tips (after Krabbe).
Branched podetium with spermogonia at
the tips (after Krabbe).
Page 275
Fig. 110. Physcia hispida Tuckerm. Ciliate frond.
a, spermogonia; b, apothecia. × ca. 5 (after
Lindsay).
In a very large number of lichens, both crustaceous and foliose, the
spermogonia are scattered over the entire thallus (Fig. 110), covering it
more or less thickly with minute black dots, as in Parmelia conspersa. In
other instances, they are to some extent confined to the peripheral areas as
in Parmelia physodes; or they occur on the extreme edge of the thallus as in
the crustaceous species Lecanora glaucoma (sordida). In Pyrenula nitida
they grow on the marginal hypothallus, usually on the dark line of
demarcation between two thalli.
They tend to congregate on, and indeed are practically restricted to the
better lighted portions of the thallus. On the fronds of foliose forms, they
appear, for instance, on the swollen pustules of Umbilicaria pustulata,
while in Lobaria pulmonaria, they are mostly lodged in the ridges that
surround the depressions in the thallus. In Parmelia conspersa, Urceolaria
(Diploschistes) scruposa and some others, they occasionally invade the
margins of the apothecium or even the apothecial disc as in Lichina.
Forssell[712] found that a spermogonium had developed among cells of
Gloeocapsa that covered the disc of a spent apothecium of Pyrenopsis
haematopis.
In fruticose lichens such as Usnea, Ramalina, etc. they occur near the
apex of the fronds, and in Cladonia they occupy the tips of the ascyphous
podetia or the margins of the scyphi. In some Cladoniae, however,
a, spermogonia; b, apothecia. × ca. 5 (after
Lindsay).
In a very large number of lichens, both crustaceous and foliose, the
spermogonia are scattered over the entire thallus (Fig. 110), covering it
more or less thickly with minute black dots, as in Parmelia conspersa. In
other instances, they are to some extent confined to the peripheral areas as
in Parmelia physodes; or they occur on the extreme edge of the thallus as in
the crustaceous species Lecanora glaucoma (sordida). In Pyrenula nitida
they grow on the marginal hypothallus, usually on the dark line of
demarcation between two thalli.
They tend to congregate on, and indeed are practically restricted to the
better lighted portions of the thallus. On the fronds of foliose forms, they
appear, for instance, on the swollen pustules of Umbilicaria pustulata,
while in Lobaria pulmonaria, they are mostly lodged in the ridges that
surround the depressions in the thallus. In Parmelia conspersa, Urceolaria
(Diploschistes) scruposa and some others, they occasionally invade the
margins of the apothecium or even the apothecial disc as in Lichina.
Forssell[712] found that a spermogonium had developed among cells of
Gloeocapsa that covered the disc of a spent apothecium of Pyrenopsis
haematopis.
In fruticose lichens such as Usnea, Ramalina, etc. they occur near the
apex of the fronds, and in Cladonia they occupy the tips of the ascyphous
podetia or the margins of the scyphi. In some Cladoniae, however,
Page 276
spermogonia are produced on the basal squamules, more rarely on the
squamules that clothe the podetia.
b. Form and Size. Spermogonia are specifically constant in form, the
same type being found on the same lichen species all over the globe. The
larger number are entirely immersed and are ovoid or roundish (Fig. 111 A)
or occasionally somewhat flattened bodies (Nephromium laevigatum), or
again, but more rarely, they are irregular in outline with an infolding of the
walls that gives the interior a chambered form (Fig. 111 B) (Lichina
pygmaea); but all of these are only visible as minute points on the thallus.
Fig. 111. Immersed spermogonia. A, globose in Parmelia
acetabulum Dub. × 600; B, with infolded walls in Lecidea (Psora)
testacea Ach. × 144 (after Glück).
A second series, also immersed, are borne in small protuberances of the
thallus. These very prominent forms are rarely found in crustaceous lichens,
but they are characteristic of such well-known species as Ramalina
fraxinea, Xanthoria parietina, Ricasolia amplissima, Baeomyces roseus,
etc. Other spermogonia project slightly above the level of the thallus, as in
Cladonia papillaria and Lecidea lurida; while in a few instances they are
practically free, these last strikingly exemplified in Cetraria islandica
where they occupy the small projections or cilia (Fig. 112) that fringe the
margins of the lobes; they are free also in most species of Cladonia.
In size they vary from such minute bodies as those in Parmelia
exasperata which measure 25-35 µ in diam., up to nearly 1 mm. in Lobaria
laetevirens. As a rule, they range from about 150 µ to 400 µ across the
widest part, and are generally rather longer than broad. They open above by
a small slit or pore called the ostiole about 20 µ to 100 µ wide which is
frequently dark in colour. In one instance, in Icmadophila aeruginosa,
squamules that clothe the podetia.
b. Form and Size. Spermogonia are specifically constant in form, the
same type being found on the same lichen species all over the globe. The
larger number are entirely immersed and are ovoid or roundish (Fig. 111 A)
or occasionally somewhat flattened bodies (Nephromium laevigatum), or
again, but more rarely, they are irregular in outline with an infolding of the
walls that gives the interior a chambered form (Fig. 111 B) (Lichina
pygmaea); but all of these are only visible as minute points on the thallus.
Fig. 111. Immersed spermogonia. A, globose in Parmelia
acetabulum Dub. × 600; B, with infolded walls in Lecidea (Psora)
testacea Ach. × 144 (after Glück).
A second series, also immersed, are borne in small protuberances of the
thallus. These very prominent forms are rarely found in crustaceous lichens,
but they are characteristic of such well-known species as Ramalina
fraxinea, Xanthoria parietina, Ricasolia amplissima, Baeomyces roseus,
etc. Other spermogonia project slightly above the level of the thallus, as in
Cladonia papillaria and Lecidea lurida; while in a few instances they are
practically free, these last strikingly exemplified in Cetraria islandica
where they occupy the small projections or cilia (Fig. 112) that fringe the
margins of the lobes; they are free also in most species of Cladonia.
In size they vary from such minute bodies as those in Parmelia
exasperata which measure 25-35 µ in diam., up to nearly 1 mm. in Lobaria
laetevirens. As a rule, they range from about 150 µ to 400 µ across the
widest part, and are generally rather longer than broad. They open above by
a small slit or pore called the ostiole about 20 µ to 100 µ wide which is
frequently dark in colour. In one instance, in Icmadophila aeruginosa,
Page 277
Nienburg[713] has described a spermogonium with a wide opening, the
spermatiophores being massed in palisade formation along the bottom of a
cup-like structure.
c. Colour of Spermogonia. Though usually the ostiole is visible as a
darker point than the surrounding tissue, spermogonia are often difficult to
locate unless the thallus is first wetted, when they become visible to slight
magnification. They appear as black points in many Parmeliae, Physciae,
Roccellae, etc., though even in these cases they are often brown when
moistened. They are distinctly brown in some Cladoniae, in Nephromium,
and in some Physciae; orange-red or yellow in Placodium and concolorous
with the thallus in Usnea, Ramalina, Stereocaulon, etc.
Fig. 112. Free spermogonia in spinous cilia of
Cetraria islandica Ach. A, part of frond; B, cilia.
× 10.
D. Structure
a. Origin and Growth. The spermogonia (or pycnidia) of lichens when
mature are more or less hollow structures provided with a distinct wall or
“perithecium,” sometimes only one cell thick and then not easily
demonstrable, as in Physcia speciosa, Opegrapha vulgata, Pyrenula nitida,
etc. More generally the “perithecium” is composed of a layer of several
spermatiophores being massed in palisade formation along the bottom of a
cup-like structure.
c. Colour of Spermogonia. Though usually the ostiole is visible as a
darker point than the surrounding tissue, spermogonia are often difficult to
locate unless the thallus is first wetted, when they become visible to slight
magnification. They appear as black points in many Parmeliae, Physciae,
Roccellae, etc., though even in these cases they are often brown when
moistened. They are distinctly brown in some Cladoniae, in Nephromium,
and in some Physciae; orange-red or yellow in Placodium and concolorous
with the thallus in Usnea, Ramalina, Stereocaulon, etc.
Fig. 112. Free spermogonia in spinous cilia of
Cetraria islandica Ach. A, part of frond; B, cilia.
× 10.
D. Structure
a. Origin and Growth. The spermogonia (or pycnidia) of lichens when
mature are more or less hollow structures provided with a distinct wall or
“perithecium,” sometimes only one cell thick and then not easily
demonstrable, as in Physcia speciosa, Opegrapha vulgata, Pyrenula nitida,
etc. More generally the “perithecium” is composed of a layer of several
Page 278
cells with stoutish walls which are sometimes colourless, but usually some
shade of yellow to dark-brown, with a darker ostiole. The latter, a small slit
or pore, arises by the breaking down of some of the cells at the apex. After
the expulsion of the spermatia, a new tissue is formed which completely
blocks up the empty spermogonium. In filamentous lichens such as Usnea a
dangerous local weakening of the thallus is thus avoided.
Spermogonia originate from hyphae in or near the gonidial zone. The
earliest stages have not been seen, but Möller[714] noted as the first
recognizable appearance or primordium of the “pycnidia” in cultures of
Calicium trachelinum a ball or coil of delicate yellowish-coloured hyphae.
At a more advanced stage the sporophores (or spermatiophores) could be
traced as outgrowths from the peripheral hyphae, directed in palisade
formation towards the centre of the hyphal coil about 20-30 µ long and very
slender and colourless. They begin to bud off spermatia almost
immediately, as it has been found that these are present in abundance while
the developing spermogonium is still wholly immersed in the thallus.
Meanwhile there is gradually formed on the outside a layer of plectenchyma
which forms the wall. Additional spermatiophores arise from the wall tissue
and push their way inwards between the ranks of the first formed series.
The spermogonium slowly enlarges and stretches and as the
spermatiophores do not grow any longer a central hollow arises which
becomes packed with spermatia (or spores) before the ostiole is open.
A somewhat similar process of development is described by Sturgis[715]
in the spermogonia of Ricasolia amplissima, in which species the
primordium arises by a profuse branching of the medullary hyphae in
certain areas close to the gonidial zone. The cells of these branching hyphae
are filled with oily matter and gradually they build up a dense, somewhat
cylindrical body which narrows above to a neck-like form. The growth is
upwards through the gonidial layer, and the structure widens to a more
spherical outline. It finally reaches the outer cortex when some of the apical
cell membranes are absorbed and a minute pore is formed. The central part
becomes hollow, also by absorption, and the space thus left is lined and
almost filled with multicellular branches of the hyphae forming the wall;
from the cells of this new tissue the spermatia are abstricted.
shade of yellow to dark-brown, with a darker ostiole. The latter, a small slit
or pore, arises by the breaking down of some of the cells at the apex. After
the expulsion of the spermatia, a new tissue is formed which completely
blocks up the empty spermogonium. In filamentous lichens such as Usnea a
dangerous local weakening of the thallus is thus avoided.
Spermogonia originate from hyphae in or near the gonidial zone. The
earliest stages have not been seen, but Möller[714] noted as the first
recognizable appearance or primordium of the “pycnidia” in cultures of
Calicium trachelinum a ball or coil of delicate yellowish-coloured hyphae.
At a more advanced stage the sporophores (or spermatiophores) could be
traced as outgrowths from the peripheral hyphae, directed in palisade
formation towards the centre of the hyphal coil about 20-30 µ long and very
slender and colourless. They begin to bud off spermatia almost
immediately, as it has been found that these are present in abundance while
the developing spermogonium is still wholly immersed in the thallus.
Meanwhile there is gradually formed on the outside a layer of plectenchyma
which forms the wall. Additional spermatiophores arise from the wall tissue
and push their way inwards between the ranks of the first formed series.
The spermogonium slowly enlarges and stretches and as the
spermatiophores do not grow any longer a central hollow arises which
becomes packed with spermatia (or spores) before the ostiole is open.
A somewhat similar process of development is described by Sturgis[715]
in the spermogonia of Ricasolia amplissima, in which species the
primordium arises by a profuse branching of the medullary hyphae in
certain areas close to the gonidial zone. The cells of these branching hyphae
are filled with oily matter and gradually they build up a dense, somewhat
cylindrical body which narrows above to a neck-like form. The growth is
upwards through the gonidial layer, and the structure widens to a more
spherical outline. It finally reaches the outer cortex when some of the apical
cell membranes are absorbed and a minute pore is formed. The central part
becomes hollow, also by absorption, and the space thus left is lined and
almost filled with multicellular branches of the hyphae forming the wall;
from the cells of this new tissue the spermatia are abstricted.
Page 279
b. Forms and types of Spermatiophores. The variations in form of the
fertile hyphae in the spermogonium were first pointed out by Nylander[716]
who described them as sterigmata[717]. He considered the differences in
branching, etc. as of high diagnostic value, dividing them into two groups:
simple “sterigmata” (or spermatiophores), with non-septate hyphae, and
arthrosterigmata, with jointed or septate hyphae.
Simple “sterigmata” comprise those in which the spore or spermatium is
borne at the end of a secondary branch or sterigma, the latter having arisen
from a cell of the upright spermatiophore or from a simple basal cell. The
arthrosterigmata consist of “short cells almost as broad as they are long,
much pressed together, and appearing almost agglutinate especially toward
the base; they fill almost the whole cavity of the spermogonium.” The
arthrosterigmata may grow out into the centre of the cavity as a single cell-
row, as a loose branching network, or, as in Endocarpon, they may form a
tissue filling the whole interior. Each cell of this tissue that borders on a
cavity may bud off a spermatium either directly or from the end of a short
process.
fertile hyphae in the spermogonium were first pointed out by Nylander[716]
who described them as sterigmata[717]. He considered the differences in
branching, etc. as of high diagnostic value, dividing them into two groups:
simple “sterigmata” (or spermatiophores), with non-septate hyphae, and
arthrosterigmata, with jointed or septate hyphae.
Simple “sterigmata” comprise those in which the spore or spermatium is
borne at the end of a secondary branch or sterigma, the latter having arisen
from a cell of the upright spermatiophore or from a simple basal cell. The
arthrosterigmata consist of “short cells almost as broad as they are long,
much pressed together, and appearing almost agglutinate especially toward
the base; they fill almost the whole cavity of the spermogonium.” The
arthrosterigmata may grow out into the centre of the cavity as a single cell-
row, as a loose branching network, or, as in Endocarpon, they may form a
tissue filling the whole interior. Each cell of this tissue that borders on a
cavity may bud off a spermatium either directly or from the end of a short
process.
Page 280
Fig. 113 a. Types of lichen “sporophores” and
pycnidiospores. 1, Peltigera rufescens Hoffm. × 910;
2,Lecidea (Psora) testacea Ach. × 1200; 3,Cladonia
cariosa Spreng. × 1000; 4, Pyrenula nitida Ach. × 1130;
5, Parmelia tristis Nyl. × 700; 6, Lobaria pulmonaria
Hoffm. × 1000 (after Glück).
The most important contributions on the subject of spermogonia in recent
years are those of Glück[718] and Steiner[719]. Glück, who insisted on the
“pycnidial” non-sexual character of the organs, recognized eight types of
“sporophores” differing in the complexity of their branching or in the form
of the “spores” (Fig. 113 a):
pycnidiospores. 1, Peltigera rufescens Hoffm. × 910;
2,Lecidea (Psora) testacea Ach. × 1200; 3,Cladonia
cariosa Spreng. × 1000; 4, Pyrenula nitida Ach. × 1130;
5, Parmelia tristis Nyl. × 700; 6, Lobaria pulmonaria
Hoffm. × 1000 (after Glück).
The most important contributions on the subject of spermogonia in recent
years are those of Glück[718] and Steiner[719]. Glück, who insisted on the
“pycnidial” non-sexual character of the organs, recognized eight types of
“sporophores” differing in the complexity of their branching or in the form
of the “spores” (Fig. 113 a):
Page 281
1. The Peltigera type: the sporophores consist of a basal cell bearing one
or more long sterigmata and rather stoutish ellipsoid spores. (These are true
pycnidia.)
2. The Psora type: a more elongate simple sporophore with sterigmata
and oblong spores.
3. The Cladonia type: a branching sporophore, each branch with
sterigmata and oblong spores.
4. The Squamaria type (called by Glück Placodium): also a branching
sporophore but with long sickle-like bent spores.
5. The Parmelia type: a more complicated system of branching and
anastomosing of the sporophores, with oblong spores.
6, and 7. The Sticta and Physcia types: in both of these the sporophores
are multi-septate; they consist of a series of radiately arranged hyphae rising
from a basal tissue all round the pycnidium. They anastomose to form a
network and bud off “spermatia” from the free cells or rather from minute
sterigmata. In the Physcia type there is more general anastomosis of the
sporophores and frequently masses of sterile cells along with the fertile
members occupy the centre of the pycnidium. The spermatia of these and
the following Endocarpon type are short cylindrical bodies (Fig. 113 b).
Fig. 113 b. 7, Physcia ciliaris DC. × 600; 8, Endocarpon sp. × 600
(after Glück).
or more long sterigmata and rather stoutish ellipsoid spores. (These are true
pycnidia.)
2. The Psora type: a more elongate simple sporophore with sterigmata
and oblong spores.
3. The Cladonia type: a branching sporophore, each branch with
sterigmata and oblong spores.
4. The Squamaria type (called by Glück Placodium): also a branching
sporophore but with long sickle-like bent spores.
5. The Parmelia type: a more complicated system of branching and
anastomosing of the sporophores, with oblong spores.
6, and 7. The Sticta and Physcia types: in both of these the sporophores
are multi-septate; they consist of a series of radiately arranged hyphae rising
from a basal tissue all round the pycnidium. They anastomose to form a
network and bud off “spermatia” from the free cells or rather from minute
sterigmata. In the Physcia type there is more general anastomosis of the
sporophores and frequently masses of sterile cells along with the fertile
members occupy the centre of the pycnidium. The spermatia of these and
the following Endocarpon type are short cylindrical bodies (Fig. 113 b).
Fig. 113 b. 7, Physcia ciliaris DC. × 600; 8, Endocarpon sp. × 600
(after Glück).
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8. Endocarpon type: the pycnidium is filled by a tissue of short broad
cells, with irregular hollow spaces lined by fertile cells similar to those of
the Sticta and Physcia types.
The three last named types of sporophores represent Nylander’s section
of arthrosterigmata. Steiner has followed Nylander in also arranging the
various forms into two leading groups. The first, characterized by the
secondary branch or “sterigma,” he designates “exobasidial”; the second,
comprising the three last types in which the spores are borne directly on the
cells of the sporophore or on very short processes, he describes as
“endobasidial.” Steiner also introduces a new term, fulcrum, for the
sporophore.
The pycnidia in which these different sporophores occur are not, as a
rule, characteristic of one family. Peltigera type is found only in one family
and the Cladonia type is fairly constant in Cladoniae, but “Psora” pycnidia
are found on very varying lichens among the Lecideaceae, Verrucariaceae
and others. The Squamaria type with long bent spores is found not only in
Squamaria (Glück’s Placodium) but also in Lecidea, Roccella, Pyrenula,
etc. Parmelia type is characteristic of many Parmeliae and also of species
of Evernia, Alectoria, Platysma and Cetraria. The Sticta type occurs in
Gyrophora, Umbilicaria, Nephromium and Lecanora as well as in Sticta
and in one species at least of Collema. To the Physcia type belong the
pycnidia of most Physciaceae and of various Parmeliae, and to the closely
related Endocarpon type the pycnidia of Endocarpon and of Xanthoria
parietina.
c. Periphyses and Sterile Filaments. In a few
species, Roccella tinctoria, Pertusaria
globulifera, etc., short one-celled sterile hyphae
are formed within the spermogonium near the
ostiole, towards which they converge. They
correspond to the periphyses in the perithecia of
some Pyrenolichens, Verrucaria, etc. (described
by Gibelli[720] as spermatiophores); they are also
present in some of the Pyrenomycetes
(Sordaria, etc.), and in many cases replace the
Fig. 114. Sterile filaments in paraphyses in function when these have broken
spermogonia of Lecidea
down. Sterile hyphae also occur, towards the
cells, with irregular hollow spaces lined by fertile cells similar to those of
the Sticta and Physcia types.
The three last named types of sporophores represent Nylander’s section
of arthrosterigmata. Steiner has followed Nylander in also arranging the
various forms into two leading groups. The first, characterized by the
secondary branch or “sterigma,” he designates “exobasidial”; the second,
comprising the three last types in which the spores are borne directly on the
cells of the sporophore or on very short processes, he describes as
“endobasidial.” Steiner also introduces a new term, fulcrum, for the
sporophore.
The pycnidia in which these different sporophores occur are not, as a
rule, characteristic of one family. Peltigera type is found only in one family
and the Cladonia type is fairly constant in Cladoniae, but “Psora” pycnidia
are found on very varying lichens among the Lecideaceae, Verrucariaceae
and others. The Squamaria type with long bent spores is found not only in
Squamaria (Glück’s Placodium) but also in Lecidea, Roccella, Pyrenula,
etc. Parmelia type is characteristic of many Parmeliae and also of species
of Evernia, Alectoria, Platysma and Cetraria. The Sticta type occurs in
Gyrophora, Umbilicaria, Nephromium and Lecanora as well as in Sticta
and in one species at least of Collema. To the Physcia type belong the
pycnidia of most Physciaceae and of various Parmeliae, and to the closely
related Endocarpon type the pycnidia of Endocarpon and of Xanthoria
parietina.
c. Periphyses and Sterile Filaments. In a few
species, Roccella tinctoria, Pertusaria
globulifera, etc., short one-celled sterile hyphae
are formed within the spermogonium near the
ostiole, towards which they converge. They
correspond to the periphyses in the perithecia of
some Pyrenolichens, Verrucaria, etc. (described
by Gibelli[720] as spermatiophores); they are also
present in some of the Pyrenomycetes
(Sordaria, etc.), and in many cases replace the
Fig. 114. Sterile filaments in paraphyses in function when these have broken
spermogonia of Lecidea
down. Sterile hyphae also occur, towards the
Page 283
fuscoatra Ach. much magnified
base, mingled with the fertile spermatiophores
(after Lindsay).
(Fig. 114). These latter were first described and
figured by Tulasne[721] in the spermogonia of
Ramalina fraxinea as stoutish branching filaments, rising from the same
base as the spermatiophores but much longer, and frequently anastomosing
with each other. They have been noted also in Usnea barbata and in several
species of Parmelia, and have been compared by Nylander[722] to
paraphyses. They are usually colourless, but, in the Parmeliae, are often
brownish and thus easily distinguished from the spermatiophores. It has
been stated that these filaments are sometimes fertile. Similar sterile hyphae
have been recorded in the pycnidia of fungi, in Sporocladus (Hendersonia)
lichenicola (Sphaeropsideae) by Corda[723] who described them as
paraphyses, and also in Steganosporium cellulosum (Melanconieae). These
observations have been confirmed by Allescher[724] in his recent work on
Fungi Imperfecti. Keiszler[725] has described a Phoma-like, pycnidium
parasitic on the leprose thallus of Haematomma elatinum. It contains short
slender sporophores and, mixed with these, long branched sterile hyphae
which reach to the ostiole and evidently function as paraphyses, though
Keiszler suggests that they may be a second form of sporophore that has
become sterile. On account of their presence he placed the fungus in a new
genus Lichenophoma.
E. Spermatia or Pycnidiospores
a. Origin and Form of Spermatia. Lichen spermatia arise at the tips of the
sterigmata either through simple abstriction or by budding. In the former
case—as in the Squamaria type—a delicate cross-wall is formed by which
the spermatium is separated off. When they arise by budding, there is first a
small clavate sac-like swelling of the end of the short process or sterigma
which gradually grows out into a spermatium on a very narrow base. This
latter formation occurs in the Sticta, Physcia and Endocarpon types.
Nylander[726] has distinguished the following forms of spermatia:
1. Ob-clavate, the broad end attached to the sterigma as in Usneae,
Cetraria glauca and C. juniperina.
base, mingled with the fertile spermatiophores
(after Lindsay).
(Fig. 114). These latter were first described and
figured by Tulasne[721] in the spermogonia of
Ramalina fraxinea as stoutish branching filaments, rising from the same
base as the spermatiophores but much longer, and frequently anastomosing
with each other. They have been noted also in Usnea barbata and in several
species of Parmelia, and have been compared by Nylander[722] to
paraphyses. They are usually colourless, but, in the Parmeliae, are often
brownish and thus easily distinguished from the spermatiophores. It has
been stated that these filaments are sometimes fertile. Similar sterile hyphae
have been recorded in the pycnidia of fungi, in Sporocladus (Hendersonia)
lichenicola (Sphaeropsideae) by Corda[723] who described them as
paraphyses, and also in Steganosporium cellulosum (Melanconieae). These
observations have been confirmed by Allescher[724] in his recent work on
Fungi Imperfecti. Keiszler[725] has described a Phoma-like, pycnidium
parasitic on the leprose thallus of Haematomma elatinum. It contains short
slender sporophores and, mixed with these, long branched sterile hyphae
which reach to the ostiole and evidently function as paraphyses, though
Keiszler suggests that they may be a second form of sporophore that has
become sterile. On account of their presence he placed the fungus in a new
genus Lichenophoma.
E. Spermatia or Pycnidiospores
a. Origin and Form of Spermatia. Lichen spermatia arise at the tips of the
sterigmata either through simple abstriction or by budding. In the former
case—as in the Squamaria type—a delicate cross-wall is formed by which
the spermatium is separated off. When they arise by budding, there is first a
small clavate sac-like swelling of the end of the short process or sterigma
which gradually grows out into a spermatium on a very narrow base. This
latter formation occurs in the Sticta, Physcia and Endocarpon types.
Nylander[726] has distinguished the following forms of spermatia:
1. Ob-clavate, the broad end attached to the sterigma as in Usneae,
Cetraria glauca and C. juniperina.
Page 284
2. Acicular and minute but slightly swollen at each end, somewhat dumb-
bell like, in Cetraria nivalis, C. cucullata, Alectoria, Evernia and some
Parmeliae, frequently borne on “arthrosterigmata.”
3. Acicular, cylindrical and straight, the most common form; these occur
in most of the Lecanorae, Cladoniae, Lecideae, Graphideae, Pyrenocarpeae
and occasionally they are budded off from arthrosterigmata.
4. Acicular, cylindrical, bent; sometimes these are very long, measuring
up to 40 µ; they are found in various Lecideae, Lecanorae, Graphideae,
Pyrenocarpeae, and also in Roccella, Pilophorus and species of
Stereocaulon.
5. Ellipsoid or oblong and generally very minute; they are borne on
simple sterigmata and are characteristic of the genera Calicium,
Chaenotheca, Lichina, Ephebe, of the small genus Glypholecia and of a few
species of Lecanora and Lecidea.
In many instances there is more or less variation of form and of size in
the species or even in the individual. There are no spherical spermatia.
b. Size and Structure. The shortest spermatia in any of our British
lichens are those of Lichina pygmaea which are about 1·4 µ in length and
the longest are those of Lecanora crassa which measure up to 39 µ. In
width they vary from about 0·5 µ to 2 µ. The mature spermogonium is
filled with spermatia and, generally, with a mass of mucilage that swells
with moisture and secures their expulsion.
The spermatia of lichens are colourless and are provided with a cell-wall
and a nucleus. The presence of a nucleus was demonstrated by Möller[727]
in the spermatia of Calicium parietinum, Opegrapha atra, Collema
microphyllum, C. pulposum and C. Hildenbrandii, and by Istvanffi[728] in
those of Buellia punctiformis (B. myriocarpa), Opegrapha subsiderella,
Collema Hildenbrandii, Calicium trachelinum, Pertusaria communis and
Arthonia communis (A. astroidea). Istvanffi made use of fresh material,
fixing the spermatia with osmic acid, and in all of these very minute bodies
he demonstrated the presence of a nucleus which stained readily with
haematoxylin and which he has figured in the spermatia of Buellia
punctiformis as an extremely small dot-like structure in the centre of the
cell. On germination, as in the cell-multiplication of other plants, the
bell like, in Cetraria nivalis, C. cucullata, Alectoria, Evernia and some
Parmeliae, frequently borne on “arthrosterigmata.”
3. Acicular, cylindrical and straight, the most common form; these occur
in most of the Lecanorae, Cladoniae, Lecideae, Graphideae, Pyrenocarpeae
and occasionally they are budded off from arthrosterigmata.
4. Acicular, cylindrical, bent; sometimes these are very long, measuring
up to 40 µ; they are found in various Lecideae, Lecanorae, Graphideae,
Pyrenocarpeae, and also in Roccella, Pilophorus and species of
Stereocaulon.
5. Ellipsoid or oblong and generally very minute; they are borne on
simple sterigmata and are characteristic of the genera Calicium,
Chaenotheca, Lichina, Ephebe, of the small genus Glypholecia and of a few
species of Lecanora and Lecidea.
In many instances there is more or less variation of form and of size in
the species or even in the individual. There are no spherical spermatia.
b. Size and Structure. The shortest spermatia in any of our British
lichens are those of Lichina pygmaea which are about 1·4 µ in length and
the longest are those of Lecanora crassa which measure up to 39 µ. In
width they vary from about 0·5 µ to 2 µ. The mature spermogonium is
filled with spermatia and, generally, with a mass of mucilage that swells
with moisture and secures their expulsion.
The spermatia of lichens are colourless and are provided with a cell-wall
and a nucleus. The presence of a nucleus was demonstrated by Möller[727]
in the spermatia of Calicium parietinum, Opegrapha atra, Collema
microphyllum, C. pulposum and C. Hildenbrandii, and by Istvanffi[728] in
those of Buellia punctiformis (B. myriocarpa), Opegrapha subsiderella,
Collema Hildenbrandii, Calicium trachelinum, Pertusaria communis and
Arthonia communis (A. astroidea). Istvanffi made use of fresh material,
fixing the spermatia with osmic acid, and in all of these very minute bodies
he demonstrated the presence of a nucleus which stained readily with
haematoxylin and which he has figured in the spermatia of Buellia
punctiformis as an extremely small dot-like structure in the centre of the
cell. On germination, as in the cell-multiplication of other plants, the
Page 285
nucleus leads the way. Germination is preceded by nuclear division, and
each new hyphal cell of the growing mycelium receives a nucleus.
c. Germination of Spermatia (pycnidiospores). The strongest argument in
favour of regarding the spermatia of lichens as male cells had always been
the impossibility of inducing their germination. That difficulty had at length
been overcome by Möller[727] who cultivated them in artificial solutions,
and by that means obtained germination in nine different lichen species. He
therefore rejected the commonly employed terms spermatia and
spermogonia and substituted pycnoconidium and pycnidia. Pycnidiospore
has been however preferred as more in accordance with modern fungal
terminology. His first experiment was with the “spermatia” of Buellia
punctiformis (B. myriocarpa) which measure about 8-10 µ in length and
about 3 µ in width, and are borne directly on the septate spermatiophores
(arthrosterigmata). In a culture drop, the spore had swelled to about double
its size by the second or third day, and germination had taken place at both
ends, the membrane of the spore being continuous with that of the
germinating tube. In a short time cross septa were formed in the hyphae
which at first were very close to each other. While apical growth advanced
these first formed cells increased in width to twice the original size and, in
consequence, became slightly constricted at the septa. In fourteen days a
circular patch of mycelium had been formed about 280 µ in diameter. The
development exactly resembled that obtained from the ascospores of the
same species grown in the absence of gonidia. The largest thallus obtained
in either case was about 2 mm. in diameter after three months’ growth. The
older hyphae had a tendency to become brownish in colour; those at the
periphery remained colourless. In Opegrapha subsiderella the development,
though equally successful, was very much slower. The pycnidiospores (or
spermatia) have the form of minute bent rods measuring 5·7 µ × 1·5 µ.
Each end of the spore produced slender hyphae about the fifth or sixth day
after sowing. In four weeks, the whole length of the filament with the spore
in the middle was 300 µ. In four months a patch of mycelium was formed 2
mm. in diameter. Growth was even more sluggish with the pycnidiospores
of Opegrapha atra. In that species they are rod-shaped and 5-6 µ long.
Germination took place on the fifth or sixth day and in fourteen days a
germination tube was produced about five times the length of the spore. In
four weeks the first branching was noticed and was followed by a second
each new hyphal cell of the growing mycelium receives a nucleus.
c. Germination of Spermatia (pycnidiospores). The strongest argument in
favour of regarding the spermatia of lichens as male cells had always been
the impossibility of inducing their germination. That difficulty had at length
been overcome by Möller[727] who cultivated them in artificial solutions,
and by that means obtained germination in nine different lichen species. He
therefore rejected the commonly employed terms spermatia and
spermogonia and substituted pycnoconidium and pycnidia. Pycnidiospore
has been however preferred as more in accordance with modern fungal
terminology. His first experiment was with the “spermatia” of Buellia
punctiformis (B. myriocarpa) which measure about 8-10 µ in length and
about 3 µ in width, and are borne directly on the septate spermatiophores
(arthrosterigmata). In a culture drop, the spore had swelled to about double
its size by the second or third day, and germination had taken place at both
ends, the membrane of the spore being continuous with that of the
germinating tube. In a short time cross septa were formed in the hyphae
which at first were very close to each other. While apical growth advanced
these first formed cells increased in width to twice the original size and, in
consequence, became slightly constricted at the septa. In fourteen days a
circular patch of mycelium had been formed about 280 µ in diameter. The
development exactly resembled that obtained from the ascospores of the
same species grown in the absence of gonidia. The largest thallus obtained
in either case was about 2 mm. in diameter after three months’ growth. The
older hyphae had a tendency to become brownish in colour; those at the
periphery remained colourless. In Opegrapha subsiderella the development,
though equally successful, was very much slower. The pycnidiospores (or
spermatia) have the form of minute bent rods measuring 5·7 µ × 1·5 µ.
Each end of the spore produced slender hyphae about the fifth or sixth day
after sowing. In four weeks, the whole length of the filament with the spore
in the middle was 300 µ. In four months a patch of mycelium was formed 2
mm. in diameter. Growth was even more sluggish with the pycnidiospores
of Opegrapha atra. In that species they are rod-shaped and 5-6 µ long.
Germination took place on the fifth or sixth day and in fourteen days a
germination tube was produced about five times the length of the spore. In
four weeks the first branching was noticed and was followed by a second
Page 286
branching in the seventh week. In three months the mycelial growth
measured 200-300 µ across.
Germination was also observed in a species of Arthonia, the spores of
which had begun to grow while still in the pycnidium. The most complete
results were obtained in species of Calicium: in C. parietinum the spores,
which are ovoid, slightly bent, and brownish in colour, swelled to an almost
globose shape and then germinated by a minute point at the junction of
spore and sterigma, and also at the opposite end; very rarely a third
germinating tube was formed. Growth was fairly rapid, so that in four
weeks there was a loose felt of mycelium measuring about 2 cm. × 1 cm.
and 1 mm. in depth. Parallel cultures were carried out with the ascospores
and the results in both cases were the same; in five or six weeks small black
points appeared, which gradually developed to pycnidia with mature
pycnidiospores from which further cultures were obtained.
On C. trachelinum, which has a thin greyish-white thallus spreading over
old trunks of trees, the pycnidia are usually abundant. Lindsay had noted
two different kinds and his observation was confirmed by Möller. The
spores in one pycnidium are ovoid, measuring 2·5-3 µ × 1·5-2 µ; in the
other rarer form, they are rod-shaped and 5-7 µ long. In the artificial
cultures they both swelled, the rod-like spores to double their width before
germination, and sometimes several tubes were put forth. Growth was slow,
but of exactly the same kind from these two types of spores as from the
ascospores. At the end of the second month pycnidia appeared on all the
cultures, in each case producing the ovoid type of spore.
In a second paper Möller[729] recorded the partially successful
germination of the “spermatia” of Collema (Leptogium) microphyllum, the
species in which Stahl had demonstrated sexual reproduction. Growth was
extraordinarily slow: after a month in the culture solution the first swelling
of the spermatium prior to germination took place, and some time later
small processes were formed in two or three directions. In the fourth month
a branched filament was formed.
Möller’s experiments with ascospores and pycnidiospores were primarily
undertaken to prove that the lichen hyphae were purely fungal and parasitic
on the algae. A series of cultures were made by Hedlund[730] in order to
demonstrate that the pycnidiospores were asexual reproductive bodies; they
measured 200-300 µ across.
Germination was also observed in a species of Arthonia, the spores of
which had begun to grow while still in the pycnidium. The most complete
results were obtained in species of Calicium: in C. parietinum the spores,
which are ovoid, slightly bent, and brownish in colour, swelled to an almost
globose shape and then germinated by a minute point at the junction of
spore and sterigma, and also at the opposite end; very rarely a third
germinating tube was formed. Growth was fairly rapid, so that in four
weeks there was a loose felt of mycelium measuring about 2 cm. × 1 cm.
and 1 mm. in depth. Parallel cultures were carried out with the ascospores
and the results in both cases were the same; in five or six weeks small black
points appeared, which gradually developed to pycnidia with mature
pycnidiospores from which further cultures were obtained.
On C. trachelinum, which has a thin greyish-white thallus spreading over
old trunks of trees, the pycnidia are usually abundant. Lindsay had noted
two different kinds and his observation was confirmed by Möller. The
spores in one pycnidium are ovoid, measuring 2·5-3 µ × 1·5-2 µ; in the
other rarer form, they are rod-shaped and 5-7 µ long. In the artificial
cultures they both swelled, the rod-like spores to double their width before
germination, and sometimes several tubes were put forth. Growth was slow,
but of exactly the same kind from these two types of spores as from the
ascospores. At the end of the second month pycnidia appeared on all the
cultures, in each case producing the ovoid type of spore.
In a second paper Möller[729] recorded the partially successful
germination of the “spermatia” of Collema (Leptogium) microphyllum, the
species in which Stahl had demonstrated sexual reproduction. Growth was
extraordinarily slow: after a month in the culture solution the first swelling
of the spermatium prior to germination took place, and some time later
small processes were formed in two or three directions. In the fourth month
a branched filament was formed.
Möller’s experiments with ascospores and pycnidiospores were primarily
undertaken to prove that the lichen hyphae were purely fungal and parasitic
on the algae. A series of cultures were made by Hedlund[730] in order to
demonstrate that the pycnidiospores were asexual reproductive bodies; they
Page 287
were grown in association with the lichen alga and their germination was
followed up to the subsequent formation of a lichen thallus.
d. Variation in Pycnidia. On the thallus of Catillaria denigrata
(Biatorina synothea) Hedlund found that there were constantly present two
types of pycnidia: the one with short slightly bent spores 4-8 µ × 1·5 µ, the
other with much longer bent spores 10-20 µ × 1·5 µ; there were numerous
transition forms between the two kinds of spores. Germination took place
by the prolongation of the spore; the hypha produced became septate and
branches were soon formed. Hedlund found that frequently germination had
already begun in the spores expelled from the spermogonium. In newly
formed thalline areolae it was possible to trace back the mycelium to
innumerable germinating spores of both types, long and short.
Lindsay had recorded more than one form of spermogonium on the same
lichen thallus, the spermatia varying considerably in size; but he was most
probably dealing with the mixed growth of more than one species. The
observations of Möller and Hedlund on this point are more exact, but the
limits of variation would very well include the two forms found by Möller
in Calicium trachelinum; and in the different pycnidia of Catillaria
denigrata Hedlund not only observed transition stages between the two
kinds of spores, but the longer pycnidiospores, as he himself allows,
indicated the elongation prior to germination: there is no good evidence of
more than one form in any species.
F. Pycnidia with Macrospores
Tulasne[731] records the presence on the lichen thallus of “pycnidia” as
well as of “spermogonia”; the former producing stylospores, larger bodies
than spermatia, occasionally septate and containing oil-drops or guttulae.
These spores are pyriform or ovoid in shape and are always borne at the tips
of simple sporophores. He compared the pycnidia with the fungus genera
Cytospora, Septoria, etc. As a rule they occur on lichens with a poorly
developed thallus, on some species of Lecanora, Lecanactis, Calicium,
Porina, in the family Strigulaceae and in Peltigera.
There is no morphological difference between pycnidia and spermogonia
except that the spermatia of the latter are narrower; but the difference is so
followed up to the subsequent formation of a lichen thallus.
d. Variation in Pycnidia. On the thallus of Catillaria denigrata
(Biatorina synothea) Hedlund found that there were constantly present two
types of pycnidia: the one with short slightly bent spores 4-8 µ × 1·5 µ, the
other with much longer bent spores 10-20 µ × 1·5 µ; there were numerous
transition forms between the two kinds of spores. Germination took place
by the prolongation of the spore; the hypha produced became septate and
branches were soon formed. Hedlund found that frequently germination had
already begun in the spores expelled from the spermogonium. In newly
formed thalline areolae it was possible to trace back the mycelium to
innumerable germinating spores of both types, long and short.
Lindsay had recorded more than one form of spermogonium on the same
lichen thallus, the spermatia varying considerably in size; but he was most
probably dealing with the mixed growth of more than one species. The
observations of Möller and Hedlund on this point are more exact, but the
limits of variation would very well include the two forms found by Möller
in Calicium trachelinum; and in the different pycnidia of Catillaria
denigrata Hedlund not only observed transition stages between the two
kinds of spores, but the longer pycnidiospores, as he himself allows,
indicated the elongation prior to germination: there is no good evidence of
more than one form in any species.
F. Pycnidia with Macrospores
Tulasne[731] records the presence on the lichen thallus of “pycnidia” as
well as of “spermogonia”; the former producing stylospores, larger bodies
than spermatia, occasionally septate and containing oil-drops or guttulae.
These spores are pyriform or ovoid in shape and are always borne at the tips
of simple sporophores. He compared the pycnidia with the fungus genera
Cytospora, Septoria, etc. As a rule they occur on lichens with a poorly
developed thallus, on some species of Lecanora, Lecanactis, Calicium,
Porina, in the family Strigulaceae and in Peltigera.
There is no morphological difference between pycnidia and spermogonia
except that the spermatia of the latter are narrower; but the difference is so
Page 288
slight that, as Steiner has pointed out, these organs found on Lecanora
piniperda, L. Sambuci and L. effusa have been described at one time as
containing microconidia (spermatia), at another macroconidia (stylospores).
He also regards as macrospores those of the pycnidia of Calicium
trachelinum which Möller was able to germinate so successfully, and all the
more so as they were brownish in colour, true microspores or spermatia
being colourless.
Müller[732] has recorded some observations on the pycnidia and
stylospores of the Strigulaceae, a family of tropical lichens inhabiting the
leaves of the higher plants. On the thallus of Strigula elegans var. tremula
from Madagascar and from India, he found pycnidia with stylospores of
abnormal dimensions measuring 18-26 µ in length and 3 µ in width, and
with 1 to 7 cross septa. In Strigula complanata var. genuina the stylospores
were 2-8-septate and varied from 7-65 µ, in length, some of the spores
being thus ten times longer than others, while the width remained the same.
Müller considers that in these cases the stylospore has already grown to a
septate hypha while in the pycnidium. As in the pycnidiospores, described
later by Hedlund, the spores had germinated by increase in length followed
by septation.
The spermogonia of Strigula, which are exactly similar to the pycnidia in
size and structure, produce spermatia, measuring about 3 µ × 2 µ, and it is
suggested by Müller that the stylospores may represent merely an advanced
stage of development of these spermatia. Both organs were constantly
associated on the same thallus; but whereas the spermogonia were abundant
on the younger part of the thallus at the periphery, they were almost entirely
replaced by pycnidia on the older portions near the centre, only a very few
spermogonia (presumably younger pycnidial stages) being found in that
region.
Lindsay[733] has described a great many different lichen pycnidia, but in
many instances he must have been dealing with species of the “Fungi
imperfecti” that were growing in association with the scattered granules of
crustaceous lichens. There are many fungi—Discomycetes and
Pyrenomycetes—parasitic on lichen thalli, and he has, in some cases,
undoubtedly been describing their secondary pycnidial form of fruit, which
indeed may appear far more frequently than the more perfect ascigerous
piniperda, L. Sambuci and L. effusa have been described at one time as
containing microconidia (spermatia), at another macroconidia (stylospores).
He also regards as macrospores those of the pycnidia of Calicium
trachelinum which Möller was able to germinate so successfully, and all the
more so as they were brownish in colour, true microspores or spermatia
being colourless.
Müller[732] has recorded some observations on the pycnidia and
stylospores of the Strigulaceae, a family of tropical lichens inhabiting the
leaves of the higher plants. On the thallus of Strigula elegans var. tremula
from Madagascar and from India, he found pycnidia with stylospores of
abnormal dimensions measuring 18-26 µ in length and 3 µ in width, and
with 1 to 7 cross septa. In Strigula complanata var. genuina the stylospores
were 2-8-septate and varied from 7-65 µ, in length, some of the spores
being thus ten times longer than others, while the width remained the same.
Müller considers that in these cases the stylospore has already grown to a
septate hypha while in the pycnidium. As in the pycnidiospores, described
later by Hedlund, the spores had germinated by increase in length followed
by septation.
The spermogonia of Strigula, which are exactly similar to the pycnidia in
size and structure, produce spermatia, measuring about 3 µ × 2 µ, and it is
suggested by Müller that the stylospores may represent merely an advanced
stage of development of these spermatia. Both organs were constantly
associated on the same thallus; but whereas the spermogonia were abundant
on the younger part of the thallus at the periphery, they were almost entirely
replaced by pycnidia on the older portions near the centre, only a very few
spermogonia (presumably younger pycnidial stages) being found in that
region.
Lindsay[733] has described a great many different lichen pycnidia, but in
many instances he must have been dealing with species of the “Fungi
imperfecti” that were growing in association with the scattered granules of
crustaceous lichens. There are many fungi—Discomycetes and
Pyrenomycetes—parasitic on lichen thalli, and he has, in some cases,
undoubtedly been describing their secondary pycnidial form of fruit, which
indeed may appear far more frequently than the more perfect ascigerous
Page 289
form, and might easily be mistaken for the pycnidial fructification of the
lichen.
G. General Survey
a. Sexual or Asexual. It has been necessary to give the preceding
detailed account of these various structures—pycnidia or spermogonia—in
view of the extreme importance attached to them as the possible male
organs of the lichen plant, and, in giving the results obtained by different
workers, the terminology employed by each one has been adopted as far as
possible: those who consider them to be sexual structures call them
spermogonia; those who refuse to accept that view write of them as
pycnidia.
Tulasne, Nylander and others unhesitatingly accepted them as male
organs without any knowledge of the female cell or of any method of
fertilization. Stahl’s discovery of the trichogyne seemed to settle the whole
question; but though he had evidence of copulation between the spermatium
and the receptive cell or trichogyne he had no real record of any sexual
process.
Many modern lichenologists reject the view that they are sexual; they
regard them as secondary organs of fructification analogous to the pycnidia
so abundant in the related groups of fungi. One would naturally expect
these pycnidia to reappear in lichens, and it might be considered somewhat
arbitrary to classify pycnidia in Sphaeropsideae as asexual reproductive
organs, and then to regard the very similar structures in lichens as sexual
spermogonia. It has also been pointed out that when undoubted pycnidia do
occur on the lichen thallus, as in Calicium, Strigula, Peltigera, etc., they in
no way differ from structures regarded as spermogonia except in the size of
the pycnidiospores—and, even among these, there are transition forms. The
different types of spermatia can be paralleled among the fungal
pycnidiospores and the same is also true as regards the sporophores
generally. Those described as arthrosterigmata by Nylander—as
endosporous by Steiner—were supposed to be peculiar to lichens; but
recently Laubert[734] has described a fungal pycnidium which grew on the
trunk of an apple tree and in which the spores are not borne on upright
sporophores but are budded off from the cells of the plectenchyma lining
lichen.
G. General Survey
a. Sexual or Asexual. It has been necessary to give the preceding
detailed account of these various structures—pycnidia or spermogonia—in
view of the extreme importance attached to them as the possible male
organs of the lichen plant, and, in giving the results obtained by different
workers, the terminology employed by each one has been adopted as far as
possible: those who consider them to be sexual structures call them
spermogonia; those who refuse to accept that view write of them as
pycnidia.
Tulasne, Nylander and others unhesitatingly accepted them as male
organs without any knowledge of the female cell or of any method of
fertilization. Stahl’s discovery of the trichogyne seemed to settle the whole
question; but though he had evidence of copulation between the spermatium
and the receptive cell or trichogyne he had no real record of any sexual
process.
Many modern lichenologists reject the view that they are sexual; they
regard them as secondary organs of fructification analogous to the pycnidia
so abundant in the related groups of fungi. One would naturally expect
these pycnidia to reappear in lichens, and it might be considered somewhat
arbitrary to classify pycnidia in Sphaeropsideae as asexual reproductive
organs, and then to regard the very similar structures in lichens as sexual
spermogonia. It has also been pointed out that when undoubted pycnidia do
occur on the lichen thallus, as in Calicium, Strigula, Peltigera, etc., they in
no way differ from structures regarded as spermogonia except in the size of
the pycnidiospores—and, even among these, there are transition forms. The
different types of spermatia can be paralleled among the fungal
pycnidiospores and the same is also true as regards the sporophores
generally. Those described as arthrosterigmata by Nylander—as
endosporous by Steiner—were supposed to be peculiar to lichens; but
recently Laubert[734] has described a fungal pycnidium which grew on the
trunk of an apple tree and in which the spores are not borne on upright
sporophores but are budded off from the cells of the plectenchyma lining
Page 290
the pycnidium. It may be that future research will discover other such
instances, though that type of sporophore is evidently of very rare
occurrence among fungi.
b. Comparison with Fungi. The most obvious spermogonia among fungi
with which to compare those of lichens occur in the Uredineae where they
are associated with the life-cycle of a large number of rust species. They are
small flask-shaped structures very much like the simpler forms of pycnidia
and they produce innumerable spermatia which are budded off from the tips
of simple spermatiophores. The mature spermatium has a delicate cell-wall
and contains a thin layer of cytoplasm with a dense nucleus which occupies
almost the whole cavity, cytological characters which, as Blackman[735] has
pointed out, are characteristic of male cells and are not found in any asexual
reproductive spores. If we accept Istvanffi’s[736] description and figures of
the lichen spermatia as correct, their structure is wholly different: there
being a very small nucleus in the centre of the cell comparable in size with
those of the vegetative hyphae (Fig. 115).
instances, though that type of sporophore is evidently of very rare
occurrence among fungi.
b. Comparison with Fungi. The most obvious spermogonia among fungi
with which to compare those of lichens occur in the Uredineae where they
are associated with the life-cycle of a large number of rust species. They are
small flask-shaped structures very much like the simpler forms of pycnidia
and they produce innumerable spermatia which are budded off from the tips
of simple spermatiophores. The mature spermatium has a delicate cell-wall
and contains a thin layer of cytoplasm with a dense nucleus which occupies
almost the whole cavity, cytological characters which, as Blackman[735] has
pointed out, are characteristic of male cells and are not found in any asexual
reproductive spores. If we accept Istvanffi’s[736] description and figures of
the lichen spermatia as correct, their structure is wholly different: there
being a very small nucleus in the centre of the cell comparable in size with
those of the vegetative hyphae (Fig. 115).
Page 291
Fig. 115. a, spermatia; b, hypha produced from spermatium of
Buellia punctiformis Th. Fr. × 950 (after Istvanffi).
Lichen “spermatia” also differ very strikingly from the male cells of any given group of plants
in their very great diversity of form and size; but the chief argument adduced by the opponents of
the sexual theory is the capacity of germination that has been proved to exist in a fair number of
species. It is true that germination has been induced in the spermatia of the Uredines by several
research workers—by Plowright[737], Sappin-Trouffy[738] and by Brefeld[739]—who employed
artificial nutritive solutions (sugar or honey), but the results obtained were not much more than the
budding process of yeast cells. Brefeld also succeeded in germinating the “spermatia” of a
pyrenomycetous fungus, Polystigma rubrum, one of the germinating tubes reaching a length four
times that of the spore; but it is now known that all of these fungal spermatia are non-functional,
either sexually or asexually, and degenerate soon after their expulsion, or even while still in the
spermogonium.
c. Influence of Symbiosis. In any consideration of lichens it is constantly necessary to hark back
to their origin as symbiotic organisms, and to bear in mind the influence of the composite life on
their development. After germination from the spore, the lichen hypha is so dependant on its
association with the alga, that, in natural conditions, though it persists without the gonidia for a
time, it attains to only a rather feeble growth of mycelial filaments. In nutritive cultures, as Möller
has proved, the absence of the alga is partly compensated by the artificial food supply, and a
scanty thalline growth is formed up to the stage of pycnidial fruits. Not only in pycnidia but in all
the fruiting bodies of lichens, symbiosis has entailed a distinct retrogression in the reproductive
importance of the spores, as compared with fungi.
In Ascomycetes, the asci constitute the overwhelming bulk of the hymenium; in most lichens,
there are serried ranks of paraphyses with comparatively few asci, and the spores are often
imperfectly developed. It would not therefore be surprising if the bodies claimed by Möller and
others as pycnidiospores had also lost even to a considerable extent their reproductive capacity.
d. Value in Diagnosis. Lichen spermogonia have once and again been found of value in
deciding the affinity of related plants, and though there are a number of lichens in which we have
no record of their occurrence, they are so constant in others, that they cannot be ignored in any
true estimation of species. Nylander laid undue stress on spermogonial characters, considering
them of almost higher diagnostic value than the much more important ascosporous fruit. They are,
after all, subsidiary organs, and often—especially in crustaceous species—they are absent, or their
relation to the species under examination is doubtful.
Buellia punctiformis Th. Fr. × 950 (after Istvanffi).
Lichen “spermatia” also differ very strikingly from the male cells of any given group of plants
in their very great diversity of form and size; but the chief argument adduced by the opponents of
the sexual theory is the capacity of germination that has been proved to exist in a fair number of
species. It is true that germination has been induced in the spermatia of the Uredines by several
research workers—by Plowright[737], Sappin-Trouffy[738] and by Brefeld[739]—who employed
artificial nutritive solutions (sugar or honey), but the results obtained were not much more than the
budding process of yeast cells. Brefeld also succeeded in germinating the “spermatia” of a
pyrenomycetous fungus, Polystigma rubrum, one of the germinating tubes reaching a length four
times that of the spore; but it is now known that all of these fungal spermatia are non-functional,
either sexually or asexually, and degenerate soon after their expulsion, or even while still in the
spermogonium.
c. Influence of Symbiosis. In any consideration of lichens it is constantly necessary to hark back
to their origin as symbiotic organisms, and to bear in mind the influence of the composite life on
their development. After germination from the spore, the lichen hypha is so dependant on its
association with the alga, that, in natural conditions, though it persists without the gonidia for a
time, it attains to only a rather feeble growth of mycelial filaments. In nutritive cultures, as Möller
has proved, the absence of the alga is partly compensated by the artificial food supply, and a
scanty thalline growth is formed up to the stage of pycnidial fruits. Not only in pycnidia but in all
the fruiting bodies of lichens, symbiosis has entailed a distinct retrogression in the reproductive
importance of the spores, as compared with fungi.
In Ascomycetes, the asci constitute the overwhelming bulk of the hymenium; in most lichens,
there are serried ranks of paraphyses with comparatively few asci, and the spores are often
imperfectly developed. It would not therefore be surprising if the bodies claimed by Möller and
others as pycnidiospores had also lost even to a considerable extent their reproductive capacity.
d. Value in Diagnosis. Lichen spermogonia have once and again been found of value in
deciding the affinity of related plants, and though there are a number of lichens in which we have
no record of their occurrence, they are so constant in others, that they cannot be ignored in any
true estimation of species. Nylander laid undue stress on spermogonial characters, considering
them of almost higher diagnostic value than the much more important ascosporous fruit. They are,
after all, subsidiary organs, and often—especially in crustaceous species—they are absent, or their
relation to the species under examination is doubtful.
Page 292
CHAPTER V
PHYSIOLOGY
I. CELLS AND CELL PRODUCTS
Any study of cells or cell-membranes in lichens should naturally include those of both
symbionts, but the algae though modified have not been profoundly changed, and their response to
the influences of the symbiotic environment has been already described in the discussion of lichen
gonidia. The description of cells and their contents refers therefore mainly to the fungal tissues
which form the framework of the plant; they have been transformed by symbiosis to lichenoid
hyphae in some respects differing from, in others resembling, the fungal hyphae from which they
are derived.
A. Cell-Membranes
a. Chitin. It was recognized by workers in the early years of the nineteenth century that the
substance forming the cell-walls of fungal hyphae differed very markedly from the cellulose of the
membranes in other groups of plants, the blue colouration with iodine and sulphuric acid so
characteristic of cellulose being absent in most fungi. Various explanations were suggested; but it
was always held that the doubtful substance was a cellulose containing something peculiar to
fungi, this view being strengthened by the fact that, after long treatment with potash, a blue
reaction was obtained. It was called fungus-cellulose by De Bary[740] in order to distinguish it
from true cellulose.
It was not till a much later date that any exact work was done on the fungal cell, and that
Gilson[741] by his researches was able to prove that the membranes of fungi contained probably no
cellulose, or, “if cellulose were present, it was in a different condition from the cellulose of other
plants.” Winterstein[742] followed with the results of his examination of fungus-cellulose: he found
that it contained nitrogen and therefore differed very considerably from typical plant cellulose.
Gilson[743] published a second paper dealing entirely with fungal tissues in which he also
established the presence of nitrogen, and added that this nitrogenous compound resembled in
various ways the chitin[744] of animal cells. He further discovered that by heating it with potash a
substance was obtained that took a reddish-violet stain when treated with iodine and weak
sulphuric acid. This substance, called by him mycosin, was proved later to be similar to
chitosan[744], a product of chitin.
Escombe[745] analysed the hyphal membranes of Cetraria and found that they consisted mainly
of a body called by him lichenin and of a paragalactan. From Peltigera he extracted a substance
with physical properties agreeing fairly well with those of chitosan, though analysis did not give
percentages reconcilable with that substance; the yield however was very small. No lichenin was
detected.
Van Wisselingh[746] examined the hyphae of lichens as well as of fungi and experimented with a
considerable number of both types of plants. He succeeded in proving the presence of chitin in the
higher fungi (Basidiomycetes and Ascomycetes) and in lichens with one or two exceptions
PHYSIOLOGY
I. CELLS AND CELL PRODUCTS
Any study of cells or cell-membranes in lichens should naturally include those of both
symbionts, but the algae though modified have not been profoundly changed, and their response to
the influences of the symbiotic environment has been already described in the discussion of lichen
gonidia. The description of cells and their contents refers therefore mainly to the fungal tissues
which form the framework of the plant; they have been transformed by symbiosis to lichenoid
hyphae in some respects differing from, in others resembling, the fungal hyphae from which they
are derived.
A. Cell-Membranes
a. Chitin. It was recognized by workers in the early years of the nineteenth century that the
substance forming the cell-walls of fungal hyphae differed very markedly from the cellulose of the
membranes in other groups of plants, the blue colouration with iodine and sulphuric acid so
characteristic of cellulose being absent in most fungi. Various explanations were suggested; but it
was always held that the doubtful substance was a cellulose containing something peculiar to
fungi, this view being strengthened by the fact that, after long treatment with potash, a blue
reaction was obtained. It was called fungus-cellulose by De Bary[740] in order to distinguish it
from true cellulose.
It was not till a much later date that any exact work was done on the fungal cell, and that
Gilson[741] by his researches was able to prove that the membranes of fungi contained probably no
cellulose, or, “if cellulose were present, it was in a different condition from the cellulose of other
plants.” Winterstein[742] followed with the results of his examination of fungus-cellulose: he found
that it contained nitrogen and therefore differed very considerably from typical plant cellulose.
Gilson[743] published a second paper dealing entirely with fungal tissues in which he also
established the presence of nitrogen, and added that this nitrogenous compound resembled in
various ways the chitin[744] of animal cells. He further discovered that by heating it with potash a
substance was obtained that took a reddish-violet stain when treated with iodine and weak
sulphuric acid. This substance, called by him mycosin, was proved later to be similar to
chitosan[744], a product of chitin.
Escombe[745] analysed the hyphal membranes of Cetraria and found that they consisted mainly
of a body called by him lichenin and of a paragalactan. From Peltigera he extracted a substance
with physical properties agreeing fairly well with those of chitosan, though analysis did not give
percentages reconcilable with that substance; the yield however was very small. No lichenin was
detected.
Van Wisselingh[746] examined the hyphae of lichens as well as of fungi and experimented with a
considerable number of both types of plants. He succeeded in proving the presence of chitin in the
higher fungi (Basidiomycetes and Ascomycetes) and in lichens with one or two exceptions
Page 293
(Cladonia and Cetraria). Though in some the quantity found was exceedingly small, in others,
such as Peltigera, the walls of the hyphae were extremely chitinous. More recently Wester[747] has
gone into the question as regards lichens, and he has practically confirmed all the results
previously obtained by Wisselingh. In some species, as for instance in Cladonia rangiferina, Cl.
squamosa, Cl. gracilis, Ramalina calicaris, Solorina crocea and others, he found that chitin
existed in large quantities, while in Evernia prunastri, Usnea florida, U. articulata, Sticta
damaecornis and Parmelia saxatilis very little was present. The variation in the amount present
may be very great even in the species of one genus: none for instance has been detected in
Cetraria islandica nor in C. nivalis while it is abundant in other Cetrariae. There is also
considerable variation in quantity in different individuals of the same species, and even in different
parts of the thallus of one lichen. Factors such as habitat, age of the plant, etc., may, however,
account to a considerable extent for the differences in the results obtained.
b. Lichenin and Allied Carbohydrates. It has been proved, as already stated, that chitin is
present in the hyphal cell-walls of all the lichens examined except in those of Cetraria islandica
(Iceland Moss), C. nivalis and, according to Wester[747], in those of Bryopogon (Alectoriae). In
these lichens another substance of purely carbohydrate nature is the chief constituent of the cell-
walls which swell up when soaked in water to a colourless gelatinous substance.
Berzelius[748] first drew attention to the peculiar qualities of this lichen product, and,
recognizing its resemblance in many respects to ordinary starch, he called it “lichen-starch” or
“moss-starch.” More exact observations were made later by Guérin-Varry[749] who described its
properties and showed by his experiments that it contained no admixture of either starch or gum.
He adopted the name lichenin for this organic soluble part of Iceland Moss. An analysis of lichenin
was made by Mulder[750] who detected in addition to lichenin, which coloured yellow with iodine,
small quantities of a blue-colouring substance which could be dissolved out from the lichenin and
which he considered to be true starch. Berg[751] also demonstrated the compound nature of
lichenin: he isolated two isomerous substances with the formula C₆H₁₀O₅. The name “isolichenin”
was given to the second blue-colouring substance by Beilstein[752] in 1881.
More recently Escombe[753] has chemically analysed the cell-wall of Cetraria islandica: after
the elimination of fat, oil, colouring matter and bitter constituents he found that there remained the
compound lichenin, an anhydride of galactose with the formula C₆H₁₀O₅, which, as stated above,
consists of two substances lichenin and isolichenin[754]; the latter is soluble in cold water and gives
a blue reaction with iodine, lichenin is only soluble in hot water and is not coloured blue. Both are
derivatives of galactose, a sugar found in a great number of organic tissues and substances, among
others in gums.
Lichenin has also been obtained by Lacour[755] from Lecanora esculenta, an edible desert lichen
supposed to be the manna of the Israelites. Wisselingh[756] tested the hymenium of thirteen
different lichens for lichenin. He found it in the walls of the ascus of all those he examined except
Graphis. Everniin, a constituent of Evernia prunastri, was isolated and described by Stüde[757]. It
is soluble in water and, though considered by Czapek[758] to be identical with lichenin, it differs,
according to Ulander[759], in being dextro-rotatory to polarized light; lichenin on the contrary is
optically inactive. Escombe[753] also obtained a substance from Evernia which he considered to be
comparable with chitosan. Usnein which has been extracted[756] from Usnea barbata may also be
identical with lichenin, but that has not yet been established. Ulander[759] examined chemically the
cell-walls of a fairly large number of lichens. Cetraria islandica, C. aculeata and Usnea barbata,
such as Peltigera, the walls of the hyphae were extremely chitinous. More recently Wester[747] has
gone into the question as regards lichens, and he has practically confirmed all the results
previously obtained by Wisselingh. In some species, as for instance in Cladonia rangiferina, Cl.
squamosa, Cl. gracilis, Ramalina calicaris, Solorina crocea and others, he found that chitin
existed in large quantities, while in Evernia prunastri, Usnea florida, U. articulata, Sticta
damaecornis and Parmelia saxatilis very little was present. The variation in the amount present
may be very great even in the species of one genus: none for instance has been detected in
Cetraria islandica nor in C. nivalis while it is abundant in other Cetrariae. There is also
considerable variation in quantity in different individuals of the same species, and even in different
parts of the thallus of one lichen. Factors such as habitat, age of the plant, etc., may, however,
account to a considerable extent for the differences in the results obtained.
b. Lichenin and Allied Carbohydrates. It has been proved, as already stated, that chitin is
present in the hyphal cell-walls of all the lichens examined except in those of Cetraria islandica
(Iceland Moss), C. nivalis and, according to Wester[747], in those of Bryopogon (Alectoriae). In
these lichens another substance of purely carbohydrate nature is the chief constituent of the cell-
walls which swell up when soaked in water to a colourless gelatinous substance.
Berzelius[748] first drew attention to the peculiar qualities of this lichen product, and,
recognizing its resemblance in many respects to ordinary starch, he called it “lichen-starch” or
“moss-starch.” More exact observations were made later by Guérin-Varry[749] who described its
properties and showed by his experiments that it contained no admixture of either starch or gum.
He adopted the name lichenin for this organic soluble part of Iceland Moss. An analysis of lichenin
was made by Mulder[750] who detected in addition to lichenin, which coloured yellow with iodine,
small quantities of a blue-colouring substance which could be dissolved out from the lichenin and
which he considered to be true starch. Berg[751] also demonstrated the compound nature of
lichenin: he isolated two isomerous substances with the formula C₆H₁₀O₅. The name “isolichenin”
was given to the second blue-colouring substance by Beilstein[752] in 1881.
More recently Escombe[753] has chemically analysed the cell-wall of Cetraria islandica: after
the elimination of fat, oil, colouring matter and bitter constituents he found that there remained the
compound lichenin, an anhydride of galactose with the formula C₆H₁₀O₅, which, as stated above,
consists of two substances lichenin and isolichenin[754]; the latter is soluble in cold water and gives
a blue reaction with iodine, lichenin is only soluble in hot water and is not coloured blue. Both are
derivatives of galactose, a sugar found in a great number of organic tissues and substances, among
others in gums.
Lichenin has also been obtained by Lacour[755] from Lecanora esculenta, an edible desert lichen
supposed to be the manna of the Israelites. Wisselingh[756] tested the hymenium of thirteen
different lichens for lichenin. He found it in the walls of the ascus of all those he examined except
Graphis. Everniin, a constituent of Evernia prunastri, was isolated and described by Stüde[757]. It
is soluble in water and, though considered by Czapek[758] to be identical with lichenin, it differs,
according to Ulander[759], in being dextro-rotatory to polarized light; lichenin on the contrary is
optically inactive. Escombe[753] also obtained a substance from Evernia which he considered to be
comparable with chitosan. Usnein which has been extracted[756] from Usnea barbata may also be
identical with lichenin, but that has not yet been established. Ulander[759] examined chemically the
cell-walls of a fairly large number of lichens. Cetraria islandica, C. aculeata and Usnea barbata,
Page 294
designated as the “Cetraria group,” contained soluble mucilage-forming substances similar to
lichenin. A second “Cladonia group” which included Cl. rangiferina with the variety alpestris,
Stereocaulon paschale and Peltigera aphthosa yielded almost none. After the soluble
carbohydrates were removed by hot water, the insoluble substances were hydrolysed and the
“Cetraria group” was found to contain abundant d-glucose with small quantities of d-mannose and
d-galactose; the “Cladonia group,” abundant d-mannose and d-galactose with but little d-glucose.
Hydrolysis was easier and quicker with the former group than with the latter.
Besides these, which rank as hexosans, Ulander found small quantities of pentosans and methyl
pentosans. All these substances which are such important constituents of the hyphal membranes of
lichens are classed by Ulander as hemicelluloses of the same nature as mannan, galactan and
dextran, or as substances between hemicellulose and the glucoses represented by lichenin,
everniin, etc. They are doubtless reserve stores of food material, and they are chiefly located in the
cell-walls of the medullary hyphae which are often so thick as almost to obliterate the lumen of the
cells. Ulander made no test for chitin in his researches.
Ulander’s results have been confirmed by those obtained by K. Müller[760]. In Cladonia
rangiferina, Müller found that the cell-membranes of the hyphae contained, as hemicelluloses,
pentosans in small quantities and galactan, but no lichenin and very little chitin. In Evernia
prunastri hemicelluloses formed the chief constituents of the thallus, and from it he was able to
isolate galactan soluble in weak hot acid, and everniin soluble in hot water, the latter with the
formula C₇H₁₅O₆, a result differing from that obtained by Stüde[761] who has given it as C₉H₁₄O₇;
chitin was also present in small quantities. In Ramalina fraxinea, the soluble part of the thallus (in
hot water) differed from everniin and might probably be lichenin. Cetraria islandica was also
analysed and yielded various hemicelluloses, chiefly dextran and galactan, with less pentosan. No
chitin has ever been found in this lichen. In testing minute quantities of material for chitin,
Wisselingh[762] heated the tissue in potash to 160° C. The potash was then gradually replaced by
glycerine and distilled water; the precipitate was placed on a slide and the preparation stained
under the microscope by potassium-iodide-iodine and weak sulphuric acid. Chitin, if present,
would have been changed by the potash to mycosin which gives a violet colour with the staining
solution.
It has been stated by Schellenberg[763] that these lichen membranes may become lignified. He
obtained a red reaction with phloroglucine test for lignin in Cetraria islandica and Cladonia
furcata. Further research is required.
c. Cellulose. Several workers claim to have found true cellulose in the cell-walls of the hyphal
tissues of a few lichens; but the more careful analyses of Escombe[764], Wisselingh[762] and
Wester[765] have disproved their results. The cell-walls of all the gonidia, however, are formed of
cellulose, or according to Escombe of glauco-cellulose, except those of Peltigera in which Wester
found neither cellulose nor chitin. Czapek[766] suggests that the blue reaction with iodine
characteristic of the cell-walls in some apothecia, of the asci and of the hyphae in cortex or
medulla in a few instances, may be due to the presence of carbohydrates of the nature of galactose.
Moreau[767] in a recent paper terms the substance that gives a blue reaction with iodine at the tips
of the asci “amyloid.” In Peltigera the ascus tip is occupied by such a plug of amyloid which at
maturity is projected like a cork from the ascus and may be found on the surface of the hymenium.
B. Contents and Products of the Fungal Cells
lichenin. A second “Cladonia group” which included Cl. rangiferina with the variety alpestris,
Stereocaulon paschale and Peltigera aphthosa yielded almost none. After the soluble
carbohydrates were removed by hot water, the insoluble substances were hydrolysed and the
“Cetraria group” was found to contain abundant d-glucose with small quantities of d-mannose and
d-galactose; the “Cladonia group,” abundant d-mannose and d-galactose with but little d-glucose.
Hydrolysis was easier and quicker with the former group than with the latter.
Besides these, which rank as hexosans, Ulander found small quantities of pentosans and methyl
pentosans. All these substances which are such important constituents of the hyphal membranes of
lichens are classed by Ulander as hemicelluloses of the same nature as mannan, galactan and
dextran, or as substances between hemicellulose and the glucoses represented by lichenin,
everniin, etc. They are doubtless reserve stores of food material, and they are chiefly located in the
cell-walls of the medullary hyphae which are often so thick as almost to obliterate the lumen of the
cells. Ulander made no test for chitin in his researches.
Ulander’s results have been confirmed by those obtained by K. Müller[760]. In Cladonia
rangiferina, Müller found that the cell-membranes of the hyphae contained, as hemicelluloses,
pentosans in small quantities and galactan, but no lichenin and very little chitin. In Evernia
prunastri hemicelluloses formed the chief constituents of the thallus, and from it he was able to
isolate galactan soluble in weak hot acid, and everniin soluble in hot water, the latter with the
formula C₇H₁₅O₆, a result differing from that obtained by Stüde[761] who has given it as C₉H₁₄O₇;
chitin was also present in small quantities. In Ramalina fraxinea, the soluble part of the thallus (in
hot water) differed from everniin and might probably be lichenin. Cetraria islandica was also
analysed and yielded various hemicelluloses, chiefly dextran and galactan, with less pentosan. No
chitin has ever been found in this lichen. In testing minute quantities of material for chitin,
Wisselingh[762] heated the tissue in potash to 160° C. The potash was then gradually replaced by
glycerine and distilled water; the precipitate was placed on a slide and the preparation stained
under the microscope by potassium-iodide-iodine and weak sulphuric acid. Chitin, if present,
would have been changed by the potash to mycosin which gives a violet colour with the staining
solution.
It has been stated by Schellenberg[763] that these lichen membranes may become lignified. He
obtained a red reaction with phloroglucine test for lignin in Cetraria islandica and Cladonia
furcata. Further research is required.
c. Cellulose. Several workers claim to have found true cellulose in the cell-walls of the hyphal
tissues of a few lichens; but the more careful analyses of Escombe[764], Wisselingh[762] and
Wester[765] have disproved their results. The cell-walls of all the gonidia, however, are formed of
cellulose, or according to Escombe of glauco-cellulose, except those of Peltigera in which Wester
found neither cellulose nor chitin. Czapek[766] suggests that the blue reaction with iodine
characteristic of the cell-walls in some apothecia, of the asci and of the hyphae in cortex or
medulla in a few instances, may be due to the presence of carbohydrates of the nature of galactose.
Moreau[767] in a recent paper terms the substance that gives a blue reaction with iodine at the tips
of the asci “amyloid.” In Peltigera the ascus tip is occupied by such a plug of amyloid which at
maturity is projected like a cork from the ascus and may be found on the surface of the hymenium.
B. Contents and Products of the Fungal Cells
Page 295
a. Cell-substances. The cells of lichen hyphae contain protoplasm and nucleus with glucoses. It
is doubtful if starch has been found in fungal hyphae; it is replaced, in some of the tissues at least,
by glycogen, a carbohydrate (C₆H₁₀O₅) very close to, if not identical with, animal glycogen, a
substance which is soluble in water and colours reddish-brown (wine-red) with iodine. Errera[768]
first detected its presence in Ascomycetes where it is associated with the epiplasm of the cells,
more especially of the asci, and he considered it to be physiologically homologous with starch. He
included lichens, as Ascomycetes, in his survey of fungi and quotes, in support of his view that
lichen hyphae also contain glycogen, a statement made by Schwendener[769] that “the contents of
the ascogenous hyphae of Coenogonium Linkii stain a deep-brown with iodine.” Errera also
instances the red-brown reaction with iodine, described by de Bary[770], as characteristic of the
large spores of Ochrolechia (Lecanora) pallescens, while the germinating tubes of these spores
become yellow with iodine like ordinary protoplasm. Glycogen has been, so far, found only in the
cells of the reproductive system.
Iodine was found by Gautier[771] in the gonidia of Parmelia and Peltigera, i.e. both in bright-
green and blue-green algae. The amount was scarcely calculable.
Herissey[772] claims to have established the presence of emulsin in a large series of lichens
belonging to such widely separated genera as Cladonia, Cetraria, Evernia, Peltigera, Pertusaria,
Parmelia, Ramalina, and Usnea. It is a ferment which acts upon amygdalin, though its presence
has been proved in plants such as lichens where no amygdalin has been found[773]. Diastase was
demonstrated in the cells of Roccella tinctoria, R. Montagnei and of Dendrographa leucophaea by
Ronceray[774] who states that, in conjunction with air and ammonia, it forms orchil, the well-
known colouring substance of these lichens. Diastatic ferments have also been determined[775] in
Usnea florida, Physcia parietina, Parmelia perlata and Peltigera canina.
b. Calcium Oxalate. Oxalic acid (C₂H₂O₄) is an oxidation product of alcohol and of most
carbohydrates and in combination is a frequent constituent of plant cells. Knop[776] held that it was
formed in lichens by the reduction and splitting of lichen acids, though, as Zopf[777] has pointed
out, these are generally insoluble. Hamlet and Plowright[778] demonstrated the presence of free
oxalic acid in many families of fungi including Pezizae and Sphaeriae. The acid combines with
calcium to form the oxalate (CaC₂0₄), which in the crystalline form is very common in lichens. In
the higher plants the crystals are formed within the cell, but in lichens they are always deposited
on the outer surface of the hyphal membranes, mainly of the medulla and the cortex.
Calcium oxalate was first detected in lichens by Henri Braconnot[779], who extracted it by
treating the powdered thallus of a number of species (Pertusaria communis, Diploschistes
scruposus, etc.) with different reagents. The quantity present varies greatly in lichens: Zopf[780]
found that it was abundant in all the species inhabiting limestone, and states that in such plants the
more purely lichenic acids are relatively scarce. Errera[781] has calculated the amount of calcium
oxalate in Lecanora esculenta, a desert lime-loving lichen, to be about 60 per cent. of the whole
substance of the thallus. Euler[782] gives for the same lichen even a larger proportion, 66 per cent.
of the dry weight. In Pertusaria communis, a corticolous species, the oxalate occurs as irregular
crystalline masses in the medulla (Fig. 116) and has been calculated as 47 per cent. of the whole
substance. Other crustaceous species such as Diploschistes scruposus, Haematomma coccineum,
H. ventosum, Lecanora saxicola, Lecanora tartarea, etc., contain large amounts either in the form
of octahedral crystals or as small granules.
is doubtful if starch has been found in fungal hyphae; it is replaced, in some of the tissues at least,
by glycogen, a carbohydrate (C₆H₁₀O₅) very close to, if not identical with, animal glycogen, a
substance which is soluble in water and colours reddish-brown (wine-red) with iodine. Errera[768]
first detected its presence in Ascomycetes where it is associated with the epiplasm of the cells,
more especially of the asci, and he considered it to be physiologically homologous with starch. He
included lichens, as Ascomycetes, in his survey of fungi and quotes, in support of his view that
lichen hyphae also contain glycogen, a statement made by Schwendener[769] that “the contents of
the ascogenous hyphae of Coenogonium Linkii stain a deep-brown with iodine.” Errera also
instances the red-brown reaction with iodine, described by de Bary[770], as characteristic of the
large spores of Ochrolechia (Lecanora) pallescens, while the germinating tubes of these spores
become yellow with iodine like ordinary protoplasm. Glycogen has been, so far, found only in the
cells of the reproductive system.
Iodine was found by Gautier[771] in the gonidia of Parmelia and Peltigera, i.e. both in bright-
green and blue-green algae. The amount was scarcely calculable.
Herissey[772] claims to have established the presence of emulsin in a large series of lichens
belonging to such widely separated genera as Cladonia, Cetraria, Evernia, Peltigera, Pertusaria,
Parmelia, Ramalina, and Usnea. It is a ferment which acts upon amygdalin, though its presence
has been proved in plants such as lichens where no amygdalin has been found[773]. Diastase was
demonstrated in the cells of Roccella tinctoria, R. Montagnei and of Dendrographa leucophaea by
Ronceray[774] who states that, in conjunction with air and ammonia, it forms orchil, the well-
known colouring substance of these lichens. Diastatic ferments have also been determined[775] in
Usnea florida, Physcia parietina, Parmelia perlata and Peltigera canina.
b. Calcium Oxalate. Oxalic acid (C₂H₂O₄) is an oxidation product of alcohol and of most
carbohydrates and in combination is a frequent constituent of plant cells. Knop[776] held that it was
formed in lichens by the reduction and splitting of lichen acids, though, as Zopf[777] has pointed
out, these are generally insoluble. Hamlet and Plowright[778] demonstrated the presence of free
oxalic acid in many families of fungi including Pezizae and Sphaeriae. The acid combines with
calcium to form the oxalate (CaC₂0₄), which in the crystalline form is very common in lichens. In
the higher plants the crystals are formed within the cell, but in lichens they are always deposited
on the outer surface of the hyphal membranes, mainly of the medulla and the cortex.
Calcium oxalate was first detected in lichens by Henri Braconnot[779], who extracted it by
treating the powdered thallus of a number of species (Pertusaria communis, Diploschistes
scruposus, etc.) with different reagents. The quantity present varies greatly in lichens: Zopf[780]
found that it was abundant in all the species inhabiting limestone, and states that in such plants the
more purely lichenic acids are relatively scarce. Errera[781] has calculated the amount of calcium
oxalate in Lecanora esculenta, a desert lime-loving lichen, to be about 60 per cent. of the whole
substance of the thallus. Euler[782] gives for the same lichen even a larger proportion, 66 per cent.
of the dry weight. In Pertusaria communis, a corticolous species, the oxalate occurs as irregular
crystalline masses in the medulla (Fig. 116) and has been calculated as 47 per cent. of the whole
substance. Other crustaceous species such as Diploschistes scruposus, Haematomma coccineum,
H. ventosum, Lecanora saxicola, Lecanora tartarea, etc., contain large amounts either in the form
of octahedral crystals or as small granules.
Page 296
Fig. 116. Pertusaria communis DC. Vertical
section of thallus. a, cortex; b, gonidia; c,
medulla; d, crystal of calcium oxalate. × ca. 100.
Rosendahl[783] has recently made observations as to the presence of the oxalate in the thallus of
the brown Parmeliae. Of the fourteen species examined by him, eleven contained calcium oxalate
as octahedral crystals or as small prisms, often piled up in thick irregular masses. Usually the
crystals were located in the medullary part of the thallus, but in two species, Parmelia
verruculifera and P. papulosa, they were abundant on the surface cells of the upper cortex.
c. Importance of Calcium Oxalate to the Lichen Plant. It is natural to conclude that a
substance of frequent occurrence in any group of plants is of some biological significance, and
suggestions have not been lacking as to the value of oxalic acid or of calcium oxalate in the
economy of the lichen thallus. Oxalic acid is known to be one of the most efficient solvents of
argillaceous earth and of iron oxides likely to be in the soil. These materials are also conveyed to
the thallus as air-borne dust, and would thus, with the aid of the acid, be easily dissolved and
absorbed. As a direct proof of this, Knop[784] has stated that lichen-ash always contains
argillaceous earth. According to Kratzmann[785], aluminium, a product of clay, is stored up in
various lichens. He proved the amount in the ash of Umbilicaria pustulata to be 4·46 per cent., in
Usnea barbata 1·79 per cent., in U. longissima considerable quantities while in Roccella tinctoria
it occurred in great abundance. It was also abundant in Diploschistes scruposus, 28·17 per cent.; it
declined in Variolaria (Pertusaria) dealbata to 7·77 per cent., in Cladonia rangiferina to 1·76-
2·12 per cent. and in Ramalina fraxinea to 1·8 per cent.
Calcium oxalate is directly advantageous to the thallus by virtue of the capacity of the crystals
to reduce or prevent evaporation, as has been pointed out by Zukal[786]. A like service afforded by
crystals to the leaves of the higher plants in desert lands has been described by Kerner[787]. These
are frequently encrusted with lime crystals which allow the copious night dews to soak underneath
them to the underlying cells, while during the day they impede, if they do not altogether check,
evaporation.
Calcium oxalate crystals are insoluble in acetic acid, soluble in hydrochloric acid without
evolution of gas; they deposit gypsum crystals in a solution of sulphuric acid.
C. Oil-Cells
a. Oil-Cells of Endolithic Lichens. Calcicolous immersed lichens are able to dissolve the lime
of the substratum, and their hyphae penetrate more or less deeply into the rock. In some forms the
entire thallus may thus be immersed, the fruits alone being visible on the surface of the stone. In
two such species, Verrucaria calciseda and Petractis (Gyalecta) exanthematica, Steiner[788]
detected peculiar sphaeroid or barrel-shaped cells that differed from the other hyphal cells of the
thallus, not only in their form, but in their greenish-coloured contents. Similar cells were found by
section of thallus. a, cortex; b, gonidia; c,
medulla; d, crystal of calcium oxalate. × ca. 100.
Rosendahl[783] has recently made observations as to the presence of the oxalate in the thallus of
the brown Parmeliae. Of the fourteen species examined by him, eleven contained calcium oxalate
as octahedral crystals or as small prisms, often piled up in thick irregular masses. Usually the
crystals were located in the medullary part of the thallus, but in two species, Parmelia
verruculifera and P. papulosa, they were abundant on the surface cells of the upper cortex.
c. Importance of Calcium Oxalate to the Lichen Plant. It is natural to conclude that a
substance of frequent occurrence in any group of plants is of some biological significance, and
suggestions have not been lacking as to the value of oxalic acid or of calcium oxalate in the
economy of the lichen thallus. Oxalic acid is known to be one of the most efficient solvents of
argillaceous earth and of iron oxides likely to be in the soil. These materials are also conveyed to
the thallus as air-borne dust, and would thus, with the aid of the acid, be easily dissolved and
absorbed. As a direct proof of this, Knop[784] has stated that lichen-ash always contains
argillaceous earth. According to Kratzmann[785], aluminium, a product of clay, is stored up in
various lichens. He proved the amount in the ash of Umbilicaria pustulata to be 4·46 per cent., in
Usnea barbata 1·79 per cent., in U. longissima considerable quantities while in Roccella tinctoria
it occurred in great abundance. It was also abundant in Diploschistes scruposus, 28·17 per cent.; it
declined in Variolaria (Pertusaria) dealbata to 7·77 per cent., in Cladonia rangiferina to 1·76-
2·12 per cent. and in Ramalina fraxinea to 1·8 per cent.
Calcium oxalate is directly advantageous to the thallus by virtue of the capacity of the crystals
to reduce or prevent evaporation, as has been pointed out by Zukal[786]. A like service afforded by
crystals to the leaves of the higher plants in desert lands has been described by Kerner[787]. These
are frequently encrusted with lime crystals which allow the copious night dews to soak underneath
them to the underlying cells, while during the day they impede, if they do not altogether check,
evaporation.
Calcium oxalate crystals are insoluble in acetic acid, soluble in hydrochloric acid without
evolution of gas; they deposit gypsum crystals in a solution of sulphuric acid.
C. Oil-Cells
a. Oil-Cells of Endolithic Lichens. Calcicolous immersed lichens are able to dissolve the lime
of the substratum, and their hyphae penetrate more or less deeply into the rock. In some forms the
entire thallus may thus be immersed, the fruits alone being visible on the surface of the stone. In
two such species, Verrucaria calciseda and Petractis (Gyalecta) exanthematica, Steiner[788]
detected peculiar sphaeroid or barrel-shaped cells that differed from the other hyphal cells of the
thallus, not only in their form, but in their greenish-coloured contents. Similar cells were found by
Page 297
Zukal[789] in another immersed (endolithic) lichen, Verrucaria rupestris f. rosea. He describes
them as roundish organs crowded on the hyphae and filled with a greenish shimmering
protoplasm. He[790] found the same types of sphaeroid and other swollen cells in the immersed
thallus of several calcicolous lichens and he finally determined the contents as fat in the form of
oil. He found also that these fat-cells, though very frequent, were not constantly present even in
the same species. His observations were confirmed by Hulth[791] for a number of allied
crustaceous lichens that grow not only on limestone but on volcanic rocks. In them he found a like
variety of fat-cells—intercalary or torulose cells, terminal sphaeroid cells and hyphae containing
scattered oil-drops. Bachmann[792] followed with a study of the thallus of purely calcicolous
lichens. The specialized oil-cells were fairly constant in the species he examined, and, as a rule,
they were formed either in the tissues immediately below, or at some distance from, the gonidial
zone. Fünfstück[793] has also published an account of various oil-cells in a large series of
calcicolous lichens (Fig. 117).
Fig. 117. Lecidea immersa Ach. A, sphaeroid fat-cells from
about 8 mm. below the surface × 550. B, oil-hyphae in
process of emptying: a, sphaeroid cells containing oil; b, cells
with oil-globules × 600 (after Fünfstück).
them as roundish organs crowded on the hyphae and filled with a greenish shimmering
protoplasm. He[790] found the same types of sphaeroid and other swollen cells in the immersed
thallus of several calcicolous lichens and he finally determined the contents as fat in the form of
oil. He found also that these fat-cells, though very frequent, were not constantly present even in
the same species. His observations were confirmed by Hulth[791] for a number of allied
crustaceous lichens that grow not only on limestone but on volcanic rocks. In them he found a like
variety of fat-cells—intercalary or torulose cells, terminal sphaeroid cells and hyphae containing
scattered oil-drops. Bachmann[792] followed with a study of the thallus of purely calcicolous
lichens. The specialized oil-cells were fairly constant in the species he examined, and, as a rule,
they were formed either in the tissues immediately below, or at some distance from, the gonidial
zone. Fünfstück[793] has also published an account of various oil-cells in a large series of
calcicolous lichens (Fig. 117).
Fig. 117. Lecidea immersa Ach. A, sphaeroid fat-cells from
about 8 mm. below the surface × 550. B, oil-hyphae in
process of emptying: a, sphaeroid cells containing oil; b, cells
with oil-globules × 600 (after Fünfstück).
Page 298
The occurrence of oil-(or fat-)cells is not dependent on the presence of any particular alga as the
gonidium of the lichen. Fünfstück[794] has described the immersed thallus of Opegrapha saxicola
as one of those richest in fat-cells. The gonidia belong to the filamentous alga Trentepohlia
umbrina and form a comparatively thin layer about 160µ thick near the upper surface; isolated
algal branches may grow down to 350µ into the rock, while the fungal elements descend to 11·5
mm., and though the very lowest hyphae were without oil—as were those immediately beneath the
gonidia—the interlying filaments, he found, were crowded with oil-cells. Sphaeroid terminal cells
were not present.
Fünfstück[794] has re-examined the thallus of Petractis exanthematica, an almost wholly
immersed lichen with a gelatinous gonidium, a species of Scytonema. The thallus is
homoiomerous: the alga forms no special zone, it intermingles with the hyphae down to the very
base of the thallus; the hyphae are extremely slender and at the base they measure only about 1µ in
width. Oil-cells are abundant in the form of intercalary cells about 3-5µ in thickness. Nearer the
surface sphaeroid cells are formed on short lateral outgrowths; they measure 14-16µ in diameter
and occur in groups of 15 to 20. The superficial part of the thallus is a mere film; the hyphae
composing it are slightly stouter and more thickly interwoven.
Bachmann[795] and Lang[796] have further described the anatomy of endolithic thalli especially
with reference to oil-cells, and have supplemented the researches of previous workers. New
methods of cutting the rock in thin slices and of dissolving away the lime enabled them to see the
tissues in their relative positions. In these immersed lichens, as described by them and by previous
writers, and more especially in calcicolous species, the gonidial zone of Protococcaceous algae lies
near the surface of the rock, and is mingled with delicate, thin-walled hyphae which usually do not
contain oil. The more deeply immersed layer is formed of a weft of equally thin-walled hyphae,
some of the cells of which are swollen and filled with fat globules. These oil-cells may occur at
intervals along the hyphae or they may form an almost continuous row. In addition, strands or
bundles of hyphae (Fig. 118) containing few or many oil globules traverse the tissue, and true
sphaeroid cells are generally present. These latter arise in great numbers on short lateral
branchlets, usually near the tip of a filament and the groups of cells are not unlike bunches of
grapes. Sometimes the oil-cells are massed together into a complex tissue. Hyphae from this layer
pierce still deeper into the rock and constitute the rhizoidal portion of the thallus. They also
produce sphaeroid oil-cells in great abundance (Fig. 119). In the immersed thallus of Sarcogyne
(Biatorella) pruinosa Lang[797] estimated the gonidial zone as 175-200µ in thickness, while the
colourless hyphae penetrated the rock to a depth of quite 15 mm.
gonidium of the lichen. Fünfstück[794] has described the immersed thallus of Opegrapha saxicola
as one of those richest in fat-cells. The gonidia belong to the filamentous alga Trentepohlia
umbrina and form a comparatively thin layer about 160µ thick near the upper surface; isolated
algal branches may grow down to 350µ into the rock, while the fungal elements descend to 11·5
mm., and though the very lowest hyphae were without oil—as were those immediately beneath the
gonidia—the interlying filaments, he found, were crowded with oil-cells. Sphaeroid terminal cells
were not present.
Fünfstück[794] has re-examined the thallus of Petractis exanthematica, an almost wholly
immersed lichen with a gelatinous gonidium, a species of Scytonema. The thallus is
homoiomerous: the alga forms no special zone, it intermingles with the hyphae down to the very
base of the thallus; the hyphae are extremely slender and at the base they measure only about 1µ in
width. Oil-cells are abundant in the form of intercalary cells about 3-5µ in thickness. Nearer the
surface sphaeroid cells are formed on short lateral outgrowths; they measure 14-16µ in diameter
and occur in groups of 15 to 20. The superficial part of the thallus is a mere film; the hyphae
composing it are slightly stouter and more thickly interwoven.
Bachmann[795] and Lang[796] have further described the anatomy of endolithic thalli especially
with reference to oil-cells, and have supplemented the researches of previous workers. New
methods of cutting the rock in thin slices and of dissolving away the lime enabled them to see the
tissues in their relative positions. In these immersed lichens, as described by them and by previous
writers, and more especially in calcicolous species, the gonidial zone of Protococcaceous algae lies
near the surface of the rock, and is mingled with delicate, thin-walled hyphae which usually do not
contain oil. The more deeply immersed layer is formed of a weft of equally thin-walled hyphae,
some of the cells of which are swollen and filled with fat globules. These oil-cells may occur at
intervals along the hyphae or they may form an almost continuous row. In addition, strands or
bundles of hyphae (Fig. 118) containing few or many oil globules traverse the tissue, and true
sphaeroid cells are generally present. These latter arise in great numbers on short lateral
branchlets, usually near the tip of a filament and the groups of cells are not unlike bunches of
grapes. Sometimes the oil-cells are massed together into a complex tissue. Hyphae from this layer
pierce still deeper into the rock and constitute the rhizoidal portion of the thallus. They also
produce sphaeroid oil-cells in great abundance (Fig. 119). In the immersed thallus of Sarcogyne
(Biatorella) pruinosa Lang[797] estimated the gonidial zone as 175-200µ in thickness, while the
colourless hyphae penetrated the rock to a depth of quite 15 mm.
Page 299
Fig. 118. Biatorella (Sarcogyne) simplex Br. and
Rostr. a, sphaeroid oil-cells; b, strand of oil-
hyphae from 10-15 mm. below the surface. × 585
(after Lang). Fig. 119. Biatorella pruinosa Mudd. a, complex of sphaeroid oil-
cells from 10 mm. below the surface; b, hypha of sphaeroid cells
also from inner part of the thallus. × 585 (after Lang).
b. Oil-cells of Epilithic Lichens. The general arrangement of the tissues and the occurrence and
form of the oil-cells vary in the different species according to the nature of the substratum. This
has been clearly demonstrated by Bachmann[798] in Aspicilia (Lecanora) calcarea, an almost
exclusively calcareous lichen as the name implies. On limestone, he found sphaeroid cells formed
in great abundance on the deeply penetrating rhizoidal hyphae (Fig. 120). On a non-calcareous
brick substratum[799], a specimen had grown which of necessity was epilithic. The cortex and
gonidial zone together were 40µ thick; immediately below there were hyphae with irregular cells
free from oil; lower still there was formed a compact tissue of globose fat-cells. In this case the
calcareous lichen still retained the capacity to form oil-cells on the non-calcareous impenetrable
substance.
Very little oil is formed, as a rule, in the cells of siliceous
crustaceous lichens which are almost wholly epilithic, but Bachmann
found a tissue of oil-cells in the thallus of Lecanora caesiocinerea,
from Labrador, on a granite composed of quartz, orthoclase and traces
of mica. A thallus of the same species collected in the Tyrol, though of
a thicker texture, contained no oil. Bachmann[799] suggests no
explanation of the variation.
On granite, rhizoidal hyphae penetrate the rock to a slight extent
between the different crystals, but only in connection with the mica[800]
are typical sphaeroid cells formed. Fig. 120. Lecanora (Aspicilia)
calcarea Sommerf. Early stage
More or less specialized oil-cells have been demonstrated by of sphaeroid cell formation ×
Fünfstück[801] in several superficial (epilithic) lichens which grow on a 175 (after Bachmann).
calcareous substratum, as for instance Lecanora (Placodium)
decipiens, Lecanora crassa and other similar species. The oil in these
lichens is usually restricted to more or less swollen or globose cells; but it may also be present in
the ordinary hyphae as globules. Zukal[802] found that the smooth little round granules sprinkled
over the thallus of the soil-lichens, Baeomyces roseus and B. rufus, contained in the hyphae typical
sphaeroid oil-cells and that they were specially well developed in specimens from Alpine
situations. In still another soil-lichen, Lecidea granulosa, shimmering green oil was found in
short-celled torulose hyphae.
Rostr. a, sphaeroid oil-cells; b, strand of oil-
hyphae from 10-15 mm. below the surface. × 585
(after Lang). Fig. 119. Biatorella pruinosa Mudd. a, complex of sphaeroid oil-
cells from 10 mm. below the surface; b, hypha of sphaeroid cells
also from inner part of the thallus. × 585 (after Lang).
b. Oil-cells of Epilithic Lichens. The general arrangement of the tissues and the occurrence and
form of the oil-cells vary in the different species according to the nature of the substratum. This
has been clearly demonstrated by Bachmann[798] in Aspicilia (Lecanora) calcarea, an almost
exclusively calcareous lichen as the name implies. On limestone, he found sphaeroid cells formed
in great abundance on the deeply penetrating rhizoidal hyphae (Fig. 120). On a non-calcareous
brick substratum[799], a specimen had grown which of necessity was epilithic. The cortex and
gonidial zone together were 40µ thick; immediately below there were hyphae with irregular cells
free from oil; lower still there was formed a compact tissue of globose fat-cells. In this case the
calcareous lichen still retained the capacity to form oil-cells on the non-calcareous impenetrable
substance.
Very little oil is formed, as a rule, in the cells of siliceous
crustaceous lichens which are almost wholly epilithic, but Bachmann
found a tissue of oil-cells in the thallus of Lecanora caesiocinerea,
from Labrador, on a granite composed of quartz, orthoclase and traces
of mica. A thallus of the same species collected in the Tyrol, though of
a thicker texture, contained no oil. Bachmann[799] suggests no
explanation of the variation.
On granite, rhizoidal hyphae penetrate the rock to a slight extent
between the different crystals, but only in connection with the mica[800]
are typical sphaeroid cells formed. Fig. 120. Lecanora (Aspicilia)
calcarea Sommerf. Early stage
More or less specialized oil-cells have been demonstrated by of sphaeroid cell formation ×
Fünfstück[801] in several superficial (epilithic) lichens which grow on a 175 (after Bachmann).
calcareous substratum, as for instance Lecanora (Placodium)
decipiens, Lecanora crassa and other similar species. The oil in these
lichens is usually restricted to more or less swollen or globose cells; but it may also be present in
the ordinary hyphae as globules. Zukal[802] found that the smooth little round granules sprinkled
over the thallus of the soil-lichens, Baeomyces roseus and B. rufus, contained in the hyphae typical
sphaeroid oil-cells and that they were specially well developed in specimens from Alpine
situations. In still another soil-lichen, Lecidea granulosa, shimmering green oil was found in
short-celled torulose hyphae.
Page 300
Rosendahl’s[803] researches on the brown Parmeliae resulted in the unexpected discovery of
specialized oil-cells situated in the cortices—upper and lower—of five species out of fourteen
which he examined. In one of the species, P. papulosa, they also occurred in the cortex of the
rhizoids. The oil-cells were thinner-walled and larger than the neighbouring cortical cells; they
were clavate or ovate in form and sometimes formed irregular external processes. They were more
or less completely filled with oil which coloured brown with osmic acid, left a fat stain on paper
and, when extracted, burned with a shining reddish flame. These oil-cells were never formed in the
medulla nor in the gonidial region.
c. Significance of Oil-formation. Zukal[804] regarded the oil stored in these specialized cells as
a reserve product of service to the plant in the strain of fruit-formation, or in times of prolonged
drought or deprivation of light. According to his observations fat was most freely formed in
lichens when periods of luxuriant growth alternated with periods of starvation. He cites, as proof
of his view, the frequent presence of empty sphaeroid cells, and the varying production of oil
affected by the condition, habitat, etc. of the plant. Fünfstück[805], on the other hand, considers the
oil of the sphaeroid and swollen cells as an excretion, representing the waste products of
metabolism in the active tissue, but due chiefly to the presence of an excess of carbonic acid
which, being set free by the action of the lichen acids on the carbonate of lime, forms the basis of
fat-formation. He points out that the development of fat-cells is always greater in endolithic
species in which the gonidial layer—the assimilating tissue—is extremely reduced. In epilithic
lichens with a wide gonidial zone, the formation of oil is insignificant. He states further that if the
oil were a direct product of assimilation, the cells in which it is stored would be found in contact
with the gonidia, and that is rarely the case, the maximum of fat production being always at some
distance.
Fünfstück tested the correctness of his views by a prolonged series of growth experiments: he
removed the gonidial layer in an endolithic lichen, and found that fat storage continued for some
time afterwards, its production being apparently independent of assimilative activity. The
correctness of his deductions was further proved by observations on lichens from glacier stones. In
such unfavourable conditions the gonidia were scanty or absent, having died off, but the hyphae
persisted and formed oil. He[806] also placed in the dark two quick-growing calcicolous lichens,
Verrucaria calciseda and Opegrapha saxicola. At the end of the experiment, he found that they
had increased in size without using up the fat. Lang[807] also is inclined to reject Zukal’s theory,
seeing that the fat is formed at a distance from the tissues—reproductive and others—in need of
food supply. He agrees with Fünfstück that the oil is an excretion and represents a waste-product
of the plant.
Considerable light is thrown on the subject of oil-formation by the results of recent researches
on the nutrition of algae and fungi. Beijerinck[808] made comparative cultures of diatoms taken
from the soil, and he found that so long as culture conditions were favourable, any fat that might
be formed was at once assimilated. If, however, some adverse influence checked the growth of the
organism while carbonic acid assimilation was in full vigour, fat was at once accumulated. The
adverse influence in this case was the lack of nitrogen, and Beijerinck considers it an almost
universal rule in plants and animals, that where there is absence of nitrogen, in a culture otherwise
suitable, fat-oils will be massed in those cells which are capable of forming oil. He observed that
in two of the cultures of diatoms the one which alone was supplied with nitrogen grew normally,
while the other, deprived of nitrogen, formed quantities of oil-drops. Wehmer[809] records the same
experience in his cultural study of Aspergillus. Sphaeroid fat-cells, similar to those described by
Zukal in calcicolous lichens, were formed in the hyphae of a culture containing an overplus of
specialized oil-cells situated in the cortices—upper and lower—of five species out of fourteen
which he examined. In one of the species, P. papulosa, they also occurred in the cortex of the
rhizoids. The oil-cells were thinner-walled and larger than the neighbouring cortical cells; they
were clavate or ovate in form and sometimes formed irregular external processes. They were more
or less completely filled with oil which coloured brown with osmic acid, left a fat stain on paper
and, when extracted, burned with a shining reddish flame. These oil-cells were never formed in the
medulla nor in the gonidial region.
c. Significance of Oil-formation. Zukal[804] regarded the oil stored in these specialized cells as
a reserve product of service to the plant in the strain of fruit-formation, or in times of prolonged
drought or deprivation of light. According to his observations fat was most freely formed in
lichens when periods of luxuriant growth alternated with periods of starvation. He cites, as proof
of his view, the frequent presence of empty sphaeroid cells, and the varying production of oil
affected by the condition, habitat, etc. of the plant. Fünfstück[805], on the other hand, considers the
oil of the sphaeroid and swollen cells as an excretion, representing the waste products of
metabolism in the active tissue, but due chiefly to the presence of an excess of carbonic acid
which, being set free by the action of the lichen acids on the carbonate of lime, forms the basis of
fat-formation. He points out that the development of fat-cells is always greater in endolithic
species in which the gonidial layer—the assimilating tissue—is extremely reduced. In epilithic
lichens with a wide gonidial zone, the formation of oil is insignificant. He states further that if the
oil were a direct product of assimilation, the cells in which it is stored would be found in contact
with the gonidia, and that is rarely the case, the maximum of fat production being always at some
distance.
Fünfstück tested the correctness of his views by a prolonged series of growth experiments: he
removed the gonidial layer in an endolithic lichen, and found that fat storage continued for some
time afterwards, its production being apparently independent of assimilative activity. The
correctness of his deductions was further proved by observations on lichens from glacier stones. In
such unfavourable conditions the gonidia were scanty or absent, having died off, but the hyphae
persisted and formed oil. He[806] also placed in the dark two quick-growing calcicolous lichens,
Verrucaria calciseda and Opegrapha saxicola. At the end of the experiment, he found that they
had increased in size without using up the fat. Lang[807] also is inclined to reject Zukal’s theory,
seeing that the fat is formed at a distance from the tissues—reproductive and others—in need of
food supply. He agrees with Fünfstück that the oil is an excretion and represents a waste-product
of the plant.
Considerable light is thrown on the subject of oil-formation by the results of recent researches
on the nutrition of algae and fungi. Beijerinck[808] made comparative cultures of diatoms taken
from the soil, and he found that so long as culture conditions were favourable, any fat that might
be formed was at once assimilated. If, however, some adverse influence checked the growth of the
organism while carbonic acid assimilation was in full vigour, fat was at once accumulated. The
adverse influence in this case was the lack of nitrogen, and Beijerinck considers it an almost
universal rule in plants and animals, that where there is absence of nitrogen, in a culture otherwise
suitable, fat-oils will be massed in those cells which are capable of forming oil. He observed that
in two of the cultures of diatoms the one which alone was supplied with nitrogen grew normally,
while the other, deprived of nitrogen, formed quantities of oil-drops. Wehmer[809] records the same
experience in his cultural study of Aspergillus. Sphaeroid fat-cells, similar to those described by
Zukal in calcicolous lichens, were formed in the hyphae of a culture containing an overplus of
Page 301
calcium carbonate, and he judged, entirely on morphological grounds, that these were not of the
nature of reserve-storage cells.
Stahel[810] has definitely established the same results in cultures of other filamentous fungi. In
an artificial culture medium in which nitrogen was almost wholly absent, the cells of the mycelium
seemed to be entirely occupied by oil-drops, and this fatty condition he considered to be a
symptom of degeneration due to the lack of nitrogen. These experiments enable us to understand
how the hyphae of calcicolous lichens, buried deep in the substratum, deprived of nitrogen and
overweighted with carbonic acid, may suffer from fatty degeneration as shown by the formation of
“sphaeroid-cells.” The connection between cause and effect is more obscure in the case of lichens
growing on the surface of the soil, such as Baeomyces roseus, or of tree lichens such as the brown
Parmeliae, but the same influence—lack of sufficient nitrogenous food—may be at work in those
as well as in the endolithic species, though to a less marked extent.
It seems probable that the capacity to form oil- or fat-cells has become part of the inherited
development of certain lichen species and persists through changes of habitat as exemplified in
Lecanora calcarea[811].
In considering the question of the formation and the function of fat in plant cells, it must be
remembered that the service rendered to the life of the organism by this substance is a very
variable one. In the higher plants (in seeds, etc.) fat undoubtedly functions in the same way as
starch and other carbohydrates as a reserve food. It is evidently not so in lichens, and in one of his
early researches, Pfeffer[812] proved that similarly oil was only an excretion in the cells of hepatics.
He grew various species in which oil-cells occurred in the dark and then tested the cell contents.
He found that after three months of conditions in which the formation of new carbohydrates was
excluded, the oil in the cells, instead of having served as reserve material, was entirely unchanged
and must in that instance be regarded as an excretion.
D. Lichen-Acids
a. Historical. The most distinctive and most universal of lichen products are the so-called
lichen-acids, peculiar substances found so far only in lichens. They occur in the form of crystals or
minute granules deposited in greater or less abundance as excretory bodies on the outer surface of
the hyphal cells. Though usually so minute as scarcely to be recognized as crystals, yet in a fairly
large series their form can be clearly seen with a high magnification. Many of them are colourless;
others are a bright yellow, orange or red, and give the clear pure tone of colour characteristic of
some of our most familiar lichens.
The first definite discovery of a lichen-acid was made towards the beginning of the nineteenth
century and is due to the researches of C. H. Pfaff[813]. He was engaged in an examination of
Cetraria islandica, the Iceland Moss, which in his time was held in high repute, not only as a food
but as a tonic. He wished to determine the chemical properties of the bitter principle contained in
it, which was so much prized by the Medical Faculty of the period, though the bitterness had to be
removed to render palatable the nutritious substance of the thallus. He succeeded in isolating an
acid which he tested and compared with other organic acids and found that it was a new substance,
nearest in chemical properties to succinic acid. In a final note, he states that the new “lichen-acid,”
as he named it, approached still nearer to boletic acid, a constituent of a fungus, though it was
distinct from that substance also in several particulars. The name “cetrarin” was proposed, at a
later date, by Herberger[814] who described it as a “subalkaloidal substance, slightly soluble in cold
nature of reserve-storage cells.
Stahel[810] has definitely established the same results in cultures of other filamentous fungi. In
an artificial culture medium in which nitrogen was almost wholly absent, the cells of the mycelium
seemed to be entirely occupied by oil-drops, and this fatty condition he considered to be a
symptom of degeneration due to the lack of nitrogen. These experiments enable us to understand
how the hyphae of calcicolous lichens, buried deep in the substratum, deprived of nitrogen and
overweighted with carbonic acid, may suffer from fatty degeneration as shown by the formation of
“sphaeroid-cells.” The connection between cause and effect is more obscure in the case of lichens
growing on the surface of the soil, such as Baeomyces roseus, or of tree lichens such as the brown
Parmeliae, but the same influence—lack of sufficient nitrogenous food—may be at work in those
as well as in the endolithic species, though to a less marked extent.
It seems probable that the capacity to form oil- or fat-cells has become part of the inherited
development of certain lichen species and persists through changes of habitat as exemplified in
Lecanora calcarea[811].
In considering the question of the formation and the function of fat in plant cells, it must be
remembered that the service rendered to the life of the organism by this substance is a very
variable one. In the higher plants (in seeds, etc.) fat undoubtedly functions in the same way as
starch and other carbohydrates as a reserve food. It is evidently not so in lichens, and in one of his
early researches, Pfeffer[812] proved that similarly oil was only an excretion in the cells of hepatics.
He grew various species in which oil-cells occurred in the dark and then tested the cell contents.
He found that after three months of conditions in which the formation of new carbohydrates was
excluded, the oil in the cells, instead of having served as reserve material, was entirely unchanged
and must in that instance be regarded as an excretion.
D. Lichen-Acids
a. Historical. The most distinctive and most universal of lichen products are the so-called
lichen-acids, peculiar substances found so far only in lichens. They occur in the form of crystals or
minute granules deposited in greater or less abundance as excretory bodies on the outer surface of
the hyphal cells. Though usually so minute as scarcely to be recognized as crystals, yet in a fairly
large series their form can be clearly seen with a high magnification. Many of them are colourless;
others are a bright yellow, orange or red, and give the clear pure tone of colour characteristic of
some of our most familiar lichens.
The first definite discovery of a lichen-acid was made towards the beginning of the nineteenth
century and is due to the researches of C. H. Pfaff[813]. He was engaged in an examination of
Cetraria islandica, the Iceland Moss, which in his time was held in high repute, not only as a food
but as a tonic. He wished to determine the chemical properties of the bitter principle contained in
it, which was so much prized by the Medical Faculty of the period, though the bitterness had to be
removed to render palatable the nutritious substance of the thallus. He succeeded in isolating an
acid which he tested and compared with other organic acids and found that it was a new substance,
nearest in chemical properties to succinic acid. In a final note, he states that the new “lichen-acid,”
as he named it, approached still nearer to boletic acid, a constituent of a fungus, though it was
distinct from that substance also in several particulars. The name “cetrarin” was proposed, at a
later date, by Herberger[814] who described it as a “subalkaloidal substance, slightly soluble in cold
Page 302
water to which it gives a bitter taste; soluble in hot water, but, on continued boiling, throwing
down a brown powder which is slightly soluble in alcohol and readily soluble in ether.” Knop and
Schnederman[815] found that Herberger’s “cetrarin” was a compound substance and contained
besides other substances “cetraric acid” and lichesterinic acid. It has now been determined by
Hesse[816] as fumarprotocetraric acid (C₆₂H₅₀O₃₅), a derivative of which is cetraric acid or
triaethylprotocetraric acid with the formula C₅₄H₃₉O₂₄(OC₂H₅)₃ and not C₂₀H₁₈O₉ as had been
supposed. Cetraric acid has not yet been isolated with certainty from any lichen[817].
After this first isolation of a definite chemical substance, further research was undertaken, and
gradually a number of these peculiar acids were recognized, the lichens examined being chiefly
those that were of real or supposed economic value either in medicine or in the arts. In late years a
wider chemical study of lichen products has been vigorously carried on, and the results gained
have been recently arranged and published in book form by Zopf[818]. Many of the statements on
the subject included here are taken from that work. Zopf gives a description of all the acids that
had been discovered up to the date of publication, and the methods employed for extracting each
substance. The structural formulae, the various affinities, derivatives and properties of the acids,
with their crystalline form, are set forth along with a list of the lichens examined and the acids
peculiar to each species. In many instances outline figures of the crystals obtained by extraction
are given. For a fuller treatment of the subject, the student is referred to the book itself, as only a
general account can be attempted here.
b. Occurrence and Examination of Lichen-Acids. Acids have been found, with few exceptions,
in all the lichens examined. They are sometimes brightly coloured and are then easily visible under
the microscope. Generally their presence can only be determined by reagents. Over 140 different
kinds have been recognized and their formulae determined, though many are still imperfectly
known. As a rule related lichen species contain the same acids, though in not a few cases one
species may contain several different kinds. In growing lichens, they form 1 to 8 per cent. of the
dry weight, and as they are practically, while unchanged, insoluble in water, they are not liable to
be washed out by rain, snow or floods. Their production seems to depend largely on the presence
of oxygen, as they are always found in greatest abundance on the more freely aerated parts of the
thallus, such as the soredial hyphae, the outer rind or the loose medullary filaments. They are also
often deposited on the exposed disc of the apothecium, on the tips of the paraphyses, and on the
wall lining the pycnidia. They are absent from the thallus of the Collemaceae, these being
extremely gelatinous lichens in which there can be little contact of the hyphae with the
atmosphere. No free acids, so far as is known, are contained in Sticta fuliginosa, but a compound
substance, trimethylamin, is present in the thallus of that lichen. It has also been affirmed that
acids do not occur in any Peltigera nor in two species of Nephromium, but Zopf[818] has extracted
a substance peltigerin both from species of Peltigera and from the section Peltidea.
For purposes of careful examination freshly gathered lichens are most serviceable, as the acids
alter in herbarium or stored specimens. It is well, when possible, to use a fairly large bulk of
material, as the acids are often present in small quantities. The lichens should be dried at a
temperature not above 40°C. for fear of changing the character of the contained substances, and
they should then be finely powdered. When only a small quantity of material is available, it has
been recommended that reagents should be applied and the effect watched under the microscope
with a low power magnification. This method is also of great service in determining the exact
position of the acids in the thallus.
In micro-chemical examination, Senft[819] deprecates the use of chloroform, ether, etc., seeing
that their too rapid evaporation leaves either an amorphous or crystalline mass of material which
down a brown powder which is slightly soluble in alcohol and readily soluble in ether.” Knop and
Schnederman[815] found that Herberger’s “cetrarin” was a compound substance and contained
besides other substances “cetraric acid” and lichesterinic acid. It has now been determined by
Hesse[816] as fumarprotocetraric acid (C₆₂H₅₀O₃₅), a derivative of which is cetraric acid or
triaethylprotocetraric acid with the formula C₅₄H₃₉O₂₄(OC₂H₅)₃ and not C₂₀H₁₈O₉ as had been
supposed. Cetraric acid has not yet been isolated with certainty from any lichen[817].
After this first isolation of a definite chemical substance, further research was undertaken, and
gradually a number of these peculiar acids were recognized, the lichens examined being chiefly
those that were of real or supposed economic value either in medicine or in the arts. In late years a
wider chemical study of lichen products has been vigorously carried on, and the results gained
have been recently arranged and published in book form by Zopf[818]. Many of the statements on
the subject included here are taken from that work. Zopf gives a description of all the acids that
had been discovered up to the date of publication, and the methods employed for extracting each
substance. The structural formulae, the various affinities, derivatives and properties of the acids,
with their crystalline form, are set forth along with a list of the lichens examined and the acids
peculiar to each species. In many instances outline figures of the crystals obtained by extraction
are given. For a fuller treatment of the subject, the student is referred to the book itself, as only a
general account can be attempted here.
b. Occurrence and Examination of Lichen-Acids. Acids have been found, with few exceptions,
in all the lichens examined. They are sometimes brightly coloured and are then easily visible under
the microscope. Generally their presence can only be determined by reagents. Over 140 different
kinds have been recognized and their formulae determined, though many are still imperfectly
known. As a rule related lichen species contain the same acids, though in not a few cases one
species may contain several different kinds. In growing lichens, they form 1 to 8 per cent. of the
dry weight, and as they are practically, while unchanged, insoluble in water, they are not liable to
be washed out by rain, snow or floods. Their production seems to depend largely on the presence
of oxygen, as they are always found in greatest abundance on the more freely aerated parts of the
thallus, such as the soredial hyphae, the outer rind or the loose medullary filaments. They are also
often deposited on the exposed disc of the apothecium, on the tips of the paraphyses, and on the
wall lining the pycnidia. They are absent from the thallus of the Collemaceae, these being
extremely gelatinous lichens in which there can be little contact of the hyphae with the
atmosphere. No free acids, so far as is known, are contained in Sticta fuliginosa, but a compound
substance, trimethylamin, is present in the thallus of that lichen. It has also been affirmed that
acids do not occur in any Peltigera nor in two species of Nephromium, but Zopf[818] has extracted
a substance peltigerin both from species of Peltigera and from the section Peltidea.
For purposes of careful examination freshly gathered lichens are most serviceable, as the acids
alter in herbarium or stored specimens. It is well, when possible, to use a fairly large bulk of
material, as the acids are often present in small quantities. The lichens should be dried at a
temperature not above 40°C. for fear of changing the character of the contained substances, and
they should then be finely powdered. When only a small quantity of material is available, it has
been recommended that reagents should be applied and the effect watched under the microscope
with a low power magnification. This method is also of great service in determining the exact
position of the acids in the thallus.
In micro-chemical examination, Senft[819] deprecates the use of chloroform, ether, etc., seeing
that their too rapid evaporation leaves either an amorphous or crystalline mass of material which
Page 303
does not lend itself to further examination. He recommends as more serviceable some oil solution,
preferably “bone oil” (neat’s-foot oil), in which a section of the thallus should be broken up under
a cover-glass and subjected to a process of slow heating; some days must elapse before the
extraction is complete. The surplus oil is then to be drained off, the section further bruised and the
substance examined.
Acids in bulk should be extracted by ether, acetone, chloroform, benzole, petrol-ether and
lignoin or by carbon bisulphide. Such solvents as alcohols, acetates and alkali solutions should not
be used as they tend to split up or to alter the constitution of the acids. For the same reason, the use
of chloroform is to a certain extent undesirable as it contains a percentage of alcohol. Ether and
acetone, or a mixture of both, are the most efficient solvents, and all acids can be extracted by their
use, if the material is left to soak a sufficient length of time, either in the cold or warmed. It is
however advisable to follow with a second solvent in case any other acid should be present in the
tissues. Concentrated sulphuric acid dissolves out all acids but often induces colour changes in the
process.
All known lichen-acids form crystals, though the crystalline form may alter with the solution
used. After filtering and distilling, the residue will be found to contain a mixture of these crystals
along with other substances, which may be removed by washing, etc.
c. Character of Acids. Many lichen-acids are more or less bitter to the taste; they are usually of
an acid nature though certain of the substances are neutral, such as zeorin, a constituent of various
Lecanoraceae, Physciaceae and Cladoniaceae, stictaurin, originally obtained from Sticta aurata,
leiphemin, from Haematomma coccineum, and others.
A large proportion are esters or alkyl salts formed by the union of an alcohol and an acid; these
are insoluble in alkaline carbonates. It is considered probable that the fungus generates the acid,
while the alcohol arises in the metabolic processes in the alga. It has indeed been proved that the
alcohol, erythrit, is formed in at least two algae, Protococcus vulgaris and Trentepohlia jolithus;
and the lichen-acid, erythrin (C₂₀H₂₂O₁₀), obtained from species of Roccella in which the alga is
Trentepohlia, is, according to Hesse, the erythrit ester of lecanoric acid (C₁₆H₁₄O₇), a very
frequent constituent of lichen thalli. It is certain that the interaction of both symbionts is necessary
for acid production. This was strikingly demonstrated by Tobler[820] in his cultural study of the
lichen thallus. He succeeded in growing, to a limited extent, the hyphal part of the thallus of
Xanthoria parietina on artificial media; but the filaments remained persistently colourless until he
added green algal cells to the culture. Almost immediately thereafter the characteristic yellow
colour appeared, proving the presence of parietin, formerly known as chrysophanic acid. Tobler’s
observation may easily be verified in plants from natural habitats. A depauperate form of
Placodium citrinum consisting mainly of a hypothallus of felted hyphae, with minute scattered
granules containing algae, was tested with potash, and only the hyphae immediately covering the
algal granules took the stain; the hypothallus gave no reaction.
It has been suggested[821] that when a decrease of albumenoids takes place, the quantity of
lichen-acid increases, so that the excreted substance should be regarded as a sort of waste product
of the living plant, “rather than as a product of deassimilation.” The subject is not yet wholly
understood.
d. Causes of Variation in Quantity and Quality of Lichen-Acids. Though it has been proved
that lichen-acids are formed freely all the year round on any soil or in any region, it happens
occasionally that they are almost or entirely lacking in growing plants. Schwarz[822] found this to
be the case in certain plants of Lecanora tartarea, and he suggests that the gyrophoric acid
preferably “bone oil” (neat’s-foot oil), in which a section of the thallus should be broken up under
a cover-glass and subjected to a process of slow heating; some days must elapse before the
extraction is complete. The surplus oil is then to be drained off, the section further bruised and the
substance examined.
Acids in bulk should be extracted by ether, acetone, chloroform, benzole, petrol-ether and
lignoin or by carbon bisulphide. Such solvents as alcohols, acetates and alkali solutions should not
be used as they tend to split up or to alter the constitution of the acids. For the same reason, the use
of chloroform is to a certain extent undesirable as it contains a percentage of alcohol. Ether and
acetone, or a mixture of both, are the most efficient solvents, and all acids can be extracted by their
use, if the material is left to soak a sufficient length of time, either in the cold or warmed. It is
however advisable to follow with a second solvent in case any other acid should be present in the
tissues. Concentrated sulphuric acid dissolves out all acids but often induces colour changes in the
process.
All known lichen-acids form crystals, though the crystalline form may alter with the solution
used. After filtering and distilling, the residue will be found to contain a mixture of these crystals
along with other substances, which may be removed by washing, etc.
c. Character of Acids. Many lichen-acids are more or less bitter to the taste; they are usually of
an acid nature though certain of the substances are neutral, such as zeorin, a constituent of various
Lecanoraceae, Physciaceae and Cladoniaceae, stictaurin, originally obtained from Sticta aurata,
leiphemin, from Haematomma coccineum, and others.
A large proportion are esters or alkyl salts formed by the union of an alcohol and an acid; these
are insoluble in alkaline carbonates. It is considered probable that the fungus generates the acid,
while the alcohol arises in the metabolic processes in the alga. It has indeed been proved that the
alcohol, erythrit, is formed in at least two algae, Protococcus vulgaris and Trentepohlia jolithus;
and the lichen-acid, erythrin (C₂₀H₂₂O₁₀), obtained from species of Roccella in which the alga is
Trentepohlia, is, according to Hesse, the erythrit ester of lecanoric acid (C₁₆H₁₄O₇), a very
frequent constituent of lichen thalli. It is certain that the interaction of both symbionts is necessary
for acid production. This was strikingly demonstrated by Tobler[820] in his cultural study of the
lichen thallus. He succeeded in growing, to a limited extent, the hyphal part of the thallus of
Xanthoria parietina on artificial media; but the filaments remained persistently colourless until he
added green algal cells to the culture. Almost immediately thereafter the characteristic yellow
colour appeared, proving the presence of parietin, formerly known as chrysophanic acid. Tobler’s
observation may easily be verified in plants from natural habitats. A depauperate form of
Placodium citrinum consisting mainly of a hypothallus of felted hyphae, with minute scattered
granules containing algae, was tested with potash, and only the hyphae immediately covering the
algal granules took the stain; the hypothallus gave no reaction.
It has been suggested[821] that when a decrease of albumenoids takes place, the quantity of
lichen-acid increases, so that the excreted substance should be regarded as a sort of waste product
of the living plant, “rather than as a product of deassimilation.” The subject is not yet wholly
understood.
d. Causes of Variation in Quantity and Quality of Lichen-Acids. Though it has been proved
that lichen-acids are formed freely all the year round on any soil or in any region, it happens
occasionally that they are almost or entirely lacking in growing plants. Schwarz[822] found this to
be the case in certain plants of Lecanora tartarea, and he suggests that the gyrophoric acid
Page 304
contained in the outer cortex of that lichen had been broken up by the ammonia of the atmosphere
into carbonic acid and orcin which is soluble in water, and would thus be washed away by rain. It
has also been shown by Schwendener[823] and others that the outer layers of the older thallus in
many lichens slowly perish, first breaking up and then peeling off; the denuded areas would
therefore have lost, for some time at least, their particular acids. Fünfstück[824] considers that the
difference in the presence and amount of acid in the same species of lichen may be due very often
to variation in the chemical character of the substratum, and this view tallies with the results noted
by Heber Howe[825] in his study of American Ramalinae. He observed that, though all showed a
pale-yellow reaction with potash, those growing on mineral substrata gave a more pronouncedly
yellow colour.
M. C. Knowles[826] found that in Ramalina scopulorum the colour reaction to potash varied
extremely, being more rapid and more intense, the more the plants were subject to the influence of
the sea-spray.
Lichen-acids are peculiarly abundant in soredia, and as, in some species, the thallus forms these
outgrowths, or even becomes leprose more freely in damp weather, the amount of acids produced
may depend on the amount of moisture in the atmosphere.
Their formation is also strongly influenced by light, as is well shown by the varying intensity of
colour in some yellow thalli. Placodium elegans, always a brightly coloured lichen, changes from
yellow to sealing-wax red in situations exposed to the full blaze of the sun. Haematomma
ventosum,though greenish-yellow in lowland situations is intensely yellow in the high Alps. The
same variation of colour is characteristic of Rhizocarpon geographicum which is a bright citron-
yellow at high altitudes, and becomes more greenish in hue as it nears the plains. The familiar
foliose lichen Xanthoria parietina is a brilliant orange-yellow in sunny situations, but grey-green
in the shade, and then yielding only minute quantities of parietin. West[827] and others have noted
its more luxuriant growth and brighter colour when it grows in positions where nitrogenous food is
plentiful, such as the roofs of farm-buildings, which are supplied with manure-laden dust, and
boulders by the sea-shore frequented by birds.
e. Distribution of Acids. Some acids, so far as is known, are only to be found in one or at most
in very few lichens, as for instance cuspidatic acid which is present in Ramalina cuspidata, and
scopuloric acid, a constituent of Ramalina scopulorum, the acids having been held to distinguish
by their reactions the one plant from the other.
Others of these peculiar products are abundant and widely distributed. Usninic acid, one of the
commonest, has been determined in some 70 species belonging to widely diverse genera, and
atranorin, a substance first discovered in Lecanora atra, has been found again many times; Zopf
gives a list of about 73 species or varieties from which it has been extracted. Another widely
distributed acid is salazinic acid which has been found by Lettau[828] in a very large number of
lichens.
E. Chemical Grouping of Lichen-Acids
Most of these acids have been provisionally arranged by Zopf in groups under the two great
organic series: I. The Fat series; and II. The Benzole or Aromatic series.
I. LICHEN-ACIDS OF THE FAT SERIES
into carbonic acid and orcin which is soluble in water, and would thus be washed away by rain. It
has also been shown by Schwendener[823] and others that the outer layers of the older thallus in
many lichens slowly perish, first breaking up and then peeling off; the denuded areas would
therefore have lost, for some time at least, their particular acids. Fünfstück[824] considers that the
difference in the presence and amount of acid in the same species of lichen may be due very often
to variation in the chemical character of the substratum, and this view tallies with the results noted
by Heber Howe[825] in his study of American Ramalinae. He observed that, though all showed a
pale-yellow reaction with potash, those growing on mineral substrata gave a more pronouncedly
yellow colour.
M. C. Knowles[826] found that in Ramalina scopulorum the colour reaction to potash varied
extremely, being more rapid and more intense, the more the plants were subject to the influence of
the sea-spray.
Lichen-acids are peculiarly abundant in soredia, and as, in some species, the thallus forms these
outgrowths, or even becomes leprose more freely in damp weather, the amount of acids produced
may depend on the amount of moisture in the atmosphere.
Their formation is also strongly influenced by light, as is well shown by the varying intensity of
colour in some yellow thalli. Placodium elegans, always a brightly coloured lichen, changes from
yellow to sealing-wax red in situations exposed to the full blaze of the sun. Haematomma
ventosum,though greenish-yellow in lowland situations is intensely yellow in the high Alps. The
same variation of colour is characteristic of Rhizocarpon geographicum which is a bright citron-
yellow at high altitudes, and becomes more greenish in hue as it nears the plains. The familiar
foliose lichen Xanthoria parietina is a brilliant orange-yellow in sunny situations, but grey-green
in the shade, and then yielding only minute quantities of parietin. West[827] and others have noted
its more luxuriant growth and brighter colour when it grows in positions where nitrogenous food is
plentiful, such as the roofs of farm-buildings, which are supplied with manure-laden dust, and
boulders by the sea-shore frequented by birds.
e. Distribution of Acids. Some acids, so far as is known, are only to be found in one or at most
in very few lichens, as for instance cuspidatic acid which is present in Ramalina cuspidata, and
scopuloric acid, a constituent of Ramalina scopulorum, the acids having been held to distinguish
by their reactions the one plant from the other.
Others of these peculiar products are abundant and widely distributed. Usninic acid, one of the
commonest, has been determined in some 70 species belonging to widely diverse genera, and
atranorin, a substance first discovered in Lecanora atra, has been found again many times; Zopf
gives a list of about 73 species or varieties from which it has been extracted. Another widely
distributed acid is salazinic acid which has been found by Lettau[828] in a very large number of
lichens.
E. Chemical Grouping of Lichen-Acids
Most of these acids have been provisionally arranged by Zopf in groups under the two great
organic series: I. The Fat series; and II. The Benzole or Aromatic series.
I. LICHEN-ACIDS OF THE FAT SERIES
Page 305
Group 1. Colourless substances soluble in alkali, the solution not coloured by iron chloride.
Exs. protolichesterinic acid (C₁₉H₃₄O₄) obtained from species of Cetraria, and roccellic acid
(C₁₇H₃₂O₄) from species of Roccella, from Lecanora tartarea, etc.
Group 2. Neutral colourless substances insoluble in alkalies, but soluble in alcohol, the solution
not coloured by iron chloride. Exs. zeorin (C₅₂H₈₈O₄), a product of widely diverse lichens, such as
Lecanora (Zeora) sulphurea, Haematomma coccineum, Physcia caesia, Cladonia deformis, etc.
and barbatin (C₉H₁₄O), a product of Usnea barbata.
Group 3. Brightly coloured acids, yellow, orange or red, all derivatives of pulvinic acid
(C₁₈H₁₂O₅), a laboratory compound which has not been found in nature. The group includes
among others vulpinic acid (C₁₉H₁₄O₅) from the brilliant yellow Evernia (Letharia) vulpina,
stictaurin (C₃₆H₂₂O₉) deposited in orange-red crystals on the hyphae of Sticta aurata, and
rhizocarpic acid (C₂₆H₂₀O₆) chiefly obtained from Rhizocarpon geographicum: it crystallizes out
in slender citron-yellow prisms.
Group 4. Only one acid, usninic (C₁₈H₁₆O₇), a derivative of acetylacetic acid, is placed in this
group. It is of very wide-spread occurrence, having been found in at least 70 species belonging to
very different genera and families of crustaceous shrubby and leafy lichens. Zopf himself isolated
it from 48 species.
Group 5. The thiophaninic acid (C₁₂H₆O₉) group representing only a small number. They are all
sulphur-yellow in colour and soluble in alcohol, the solution becoming blackish-green or dirty
blue on the addition of iron chloride, with one exception, that of subauriferin obtained from the
yellow-coloured medulla of Parmelia subaurifera which stains faintly wine-red in an iron
solution. Thiophaninic acid, which gives its name to this group, occurs in Pertusaria lutescens and
P. Wulfenii, both of which are yellowish crustaceous lichens growing mostly on the trunks of trees.
II. LICHEN-ACIDS OF THE BENZOLE SERIES
The larger number of lichen-acids belong to this series, of which 94 at least are already known.
They are divided into two subseries: I. Orcine derivatives, and II. Anthracene derivatives.
Subseries I. Orcine Derivatives
Zopf specially insists that the grouping of this series must be regarded as only a provisional
arrangement of the many lichen-acids that are included therein. All of them are split up into orcine
and carbonic acid by ammonia and other alkalies. On exposure to air, the ammoniacal or alkaline
solution changes gradually into orceine, the colouring principle and chief constituent of
commercial orchil. Orcine is not found free in nature. The orcine subseries includes five groups:
Group 1. The substances in this group form, with hypochlorite of lime (“CaCl”), red-coloured
compounds which yield, on splitting, orsellinic acid. Zopf enumerates seven acids as belonging to
this group, among which is lecanoric acid (C₁₆H₁₄O₇), found in many different lichens, e.g.
Roccella tinctoria, Lecanora tartarea, etc.: whenever there is a differentiated pith and cortex it
occurs in the pith alone. Erythrin (C₂₀H₂₂O₁₀), a constituent of the British marine lichen Roccella
fuciformis, also belongs to this orsellinic group.
Group 2. Substances which also form red products with CaCl, but do not break up into
orsellinic acid. Among the most noteworthy are olivetoric acid (C₂₁H₂₆O₇), a constituent of
Evernia furfuracea, perlatic acid (C₂₈H₃₀O₁₀) and glabratic acid (C₂₄H₂₆O₁₁), which are obtained
from species of Parmelia.
Exs. protolichesterinic acid (C₁₉H₃₄O₄) obtained from species of Cetraria, and roccellic acid
(C₁₇H₃₂O₄) from species of Roccella, from Lecanora tartarea, etc.
Group 2. Neutral colourless substances insoluble in alkalies, but soluble in alcohol, the solution
not coloured by iron chloride. Exs. zeorin (C₅₂H₈₈O₄), a product of widely diverse lichens, such as
Lecanora (Zeora) sulphurea, Haematomma coccineum, Physcia caesia, Cladonia deformis, etc.
and barbatin (C₉H₁₄O), a product of Usnea barbata.
Group 3. Brightly coloured acids, yellow, orange or red, all derivatives of pulvinic acid
(C₁₈H₁₂O₅), a laboratory compound which has not been found in nature. The group includes
among others vulpinic acid (C₁₉H₁₄O₅) from the brilliant yellow Evernia (Letharia) vulpina,
stictaurin (C₃₆H₂₂O₉) deposited in orange-red crystals on the hyphae of Sticta aurata, and
rhizocarpic acid (C₂₆H₂₀O₆) chiefly obtained from Rhizocarpon geographicum: it crystallizes out
in slender citron-yellow prisms.
Group 4. Only one acid, usninic (C₁₈H₁₆O₇), a derivative of acetylacetic acid, is placed in this
group. It is of very wide-spread occurrence, having been found in at least 70 species belonging to
very different genera and families of crustaceous shrubby and leafy lichens. Zopf himself isolated
it from 48 species.
Group 5. The thiophaninic acid (C₁₂H₆O₉) group representing only a small number. They are all
sulphur-yellow in colour and soluble in alcohol, the solution becoming blackish-green or dirty
blue on the addition of iron chloride, with one exception, that of subauriferin obtained from the
yellow-coloured medulla of Parmelia subaurifera which stains faintly wine-red in an iron
solution. Thiophaninic acid, which gives its name to this group, occurs in Pertusaria lutescens and
P. Wulfenii, both of which are yellowish crustaceous lichens growing mostly on the trunks of trees.
II. LICHEN-ACIDS OF THE BENZOLE SERIES
The larger number of lichen-acids belong to this series, of which 94 at least are already known.
They are divided into two subseries: I. Orcine derivatives, and II. Anthracene derivatives.
Subseries I. Orcine Derivatives
Zopf specially insists that the grouping of this series must be regarded as only a provisional
arrangement of the many lichen-acids that are included therein. All of them are split up into orcine
and carbonic acid by ammonia and other alkalies. On exposure to air, the ammoniacal or alkaline
solution changes gradually into orceine, the colouring principle and chief constituent of
commercial orchil. Orcine is not found free in nature. The orcine subseries includes five groups:
Group 1. The substances in this group form, with hypochlorite of lime (“CaCl”), red-coloured
compounds which yield, on splitting, orsellinic acid. Zopf enumerates seven acids as belonging to
this group, among which is lecanoric acid (C₁₆H₁₄O₇), found in many different lichens, e.g.
Roccella tinctoria, Lecanora tartarea, etc.: whenever there is a differentiated pith and cortex it
occurs in the pith alone. Erythrin (C₂₀H₂₂O₁₀), a constituent of the British marine lichen Roccella
fuciformis, also belongs to this orsellinic group.
Group 2. Substances which also form red products with CaCl, but do not break up into
orsellinic acid. Among the most noteworthy are olivetoric acid (C₂₁H₂₆O₇), a constituent of
Evernia furfuracea, perlatic acid (C₂₈H₃₀O₁₀) and glabratic acid (C₂₄H₂₆O₁₁), which are obtained
from species of Parmelia.
Page 306
Group 3. Contains three acids of somewhat restricted occurrence. They do not form red
products with CaCl, and they yield on splitting everninic acid. They are: evernic acid (C₁₇H₁₆O₇),
found in Evernia prunastri var. vulgaris, ramalic acid (C₁₇H₁₆O₇) in Ramalina pollinaria, and
umbilicaric acid (C₂₅H₂₂O₁₁) in species of Gyrophora.
Group 4. The numerous acids of this group are not easily soluble and have a very bitter taste.
They are not coloured by CaCl; when extracted with concentrated sulphuric acid, the solution
obtained is reddish-yellow or deep red. Among the most frequent are fumarprotocetraric acid
(C₆₂H₅₀O₃₅), the bitter principle of Cetraria islandica, Cladonia rangiferina, etc., psoromic acid
(C₂₀H₁₄O₉), obtained from Alectoria implexa, Lecanora varia, Cladonia pyxidata and many other
lichens, and salazinic acid (C₁₉H₁₄O₁₀), recorded by Zopf as occurring in Stereocaulon salazinum
and in several Parmeliae, but now found by Lettau[829] to be very wide-spread. He used micro-
chemical methods and detected its presence in 72 species from twelve different families. The
distribution of the acid in the thallus varies considerably.
Group 5. This is called the atranorin group from one of the most important members. They are
colourless substances and, like the preceding group, are not affected by CaCl, but when split they
form bodies that colour a more or less deep red with that reagent. Atranorin (C₁₉H₁₈O₈) is one of
the most widely spread of all lichen-acids; it occurs in Lecanoraceae, Parmeliaceae, Physciaceae
and Lecideaceae. Barbatinic acid (C₁₉H₂₀O₇), another member, is found in Usnea ceratina,
Alectoria ochroleuca and in a variety of Rhizocarpon geographicum. A very large number of acids
more or less fully studied belong to this group.
Subseries II. Anthracene Derivatives
The constituents of this subseries are derived from the carbohydrate anthracene, and are
characterized by their brilliant colours, yellow, red, brown, red-brown or violet-brown. So far, only
ten different kinds have been isolated and studied. Parietin[830] (C₁₆H₁₂O₅), one of the best known,
has been extracted from Xanthoria parietina, Placodium murorum and several other bright-yellow
lichens; solorinic acid (C₁₅H₁₄O₅) occurs in orange-red crystals on the hyphae of the pith and
under surface of Solorina crocea; nephromin (C₁₆H₁₂O₆) is found in the yellow medulla of
Nephromium lusitanicum; rhodocladonic acid (C₁₂H₈O₆ or C₁₄H₁₀O₇) is the red substance in the
apothecia of the red-fruited Cladoniae.
There are, in addition, a short series of coloured substances which are of uncertain position.
They are imperfectly known and are of rare occurrence. An acid containing nitrogen has been
extracted from Roccella fuciformis, and named picroroccellin[831] (C₂₇H₂₉N₃O₅). It crystallizes in
comparatively large prisms, has an exceedingly bitter taste, and is very sparingly soluble. It is the
only lichen-acid in which nitrogen has been detected.
One acid at least, belonging to the Fat series, vulpinic acid, which gives the greenish-yellow
colour to Letharia vulpina, has been prepared synthetically by Volkard[832].
F. Chemical Reagents as Tests for Lichens
The employment of chemical reagents as colour tests in the determination of lichen species was
recommended by Nylander[833] in a paper published by him in 1866. Many acids had already been
extracted and examined, and as they were proved to be constant in the different species where they
occurred, he perceived their systematic importance. As an example of the new tests, he cited the
products with CaCl, and they yield on splitting everninic acid. They are: evernic acid (C₁₇H₁₆O₇),
found in Evernia prunastri var. vulgaris, ramalic acid (C₁₇H₁₆O₇) in Ramalina pollinaria, and
umbilicaric acid (C₂₅H₂₂O₁₁) in species of Gyrophora.
Group 4. The numerous acids of this group are not easily soluble and have a very bitter taste.
They are not coloured by CaCl; when extracted with concentrated sulphuric acid, the solution
obtained is reddish-yellow or deep red. Among the most frequent are fumarprotocetraric acid
(C₆₂H₅₀O₃₅), the bitter principle of Cetraria islandica, Cladonia rangiferina, etc., psoromic acid
(C₂₀H₁₄O₉), obtained from Alectoria implexa, Lecanora varia, Cladonia pyxidata and many other
lichens, and salazinic acid (C₁₉H₁₄O₁₀), recorded by Zopf as occurring in Stereocaulon salazinum
and in several Parmeliae, but now found by Lettau[829] to be very wide-spread. He used micro-
chemical methods and detected its presence in 72 species from twelve different families. The
distribution of the acid in the thallus varies considerably.
Group 5. This is called the atranorin group from one of the most important members. They are
colourless substances and, like the preceding group, are not affected by CaCl, but when split they
form bodies that colour a more or less deep red with that reagent. Atranorin (C₁₉H₁₈O₈) is one of
the most widely spread of all lichen-acids; it occurs in Lecanoraceae, Parmeliaceae, Physciaceae
and Lecideaceae. Barbatinic acid (C₁₉H₂₀O₇), another member, is found in Usnea ceratina,
Alectoria ochroleuca and in a variety of Rhizocarpon geographicum. A very large number of acids
more or less fully studied belong to this group.
Subseries II. Anthracene Derivatives
The constituents of this subseries are derived from the carbohydrate anthracene, and are
characterized by their brilliant colours, yellow, red, brown, red-brown or violet-brown. So far, only
ten different kinds have been isolated and studied. Parietin[830] (C₁₆H₁₂O₅), one of the best known,
has been extracted from Xanthoria parietina, Placodium murorum and several other bright-yellow
lichens; solorinic acid (C₁₅H₁₄O₅) occurs in orange-red crystals on the hyphae of the pith and
under surface of Solorina crocea; nephromin (C₁₆H₁₂O₆) is found in the yellow medulla of
Nephromium lusitanicum; rhodocladonic acid (C₁₂H₈O₆ or C₁₄H₁₀O₇) is the red substance in the
apothecia of the red-fruited Cladoniae.
There are, in addition, a short series of coloured substances which are of uncertain position.
They are imperfectly known and are of rare occurrence. An acid containing nitrogen has been
extracted from Roccella fuciformis, and named picroroccellin[831] (C₂₇H₂₉N₃O₅). It crystallizes in
comparatively large prisms, has an exceedingly bitter taste, and is very sparingly soluble. It is the
only lichen-acid in which nitrogen has been detected.
One acid at least, belonging to the Fat series, vulpinic acid, which gives the greenish-yellow
colour to Letharia vulpina, has been prepared synthetically by Volkard[832].
F. Chemical Reagents as Tests for Lichens
The employment of chemical reagents as colour tests in the determination of lichen species was
recommended by Nylander[833] in a paper published by him in 1866. Many acids had already been
extracted and examined, and as they were proved to be constant in the different species where they
occurred, he perceived their systematic importance. As an example of the new tests, he cited the
Page 307
use of hypochlorite of lime, a solution of which, applied directly to the thallus of species of
Roccella, produced a bright-red “erythrinic” reaction. Caustic potash was also found to be of
service in demonstrating the presence of parietin in lichens by a beautiful purple stain. Many
lichenologists eagerly adopted the new method, as a sure and ready means of distinguishing
doubtful species; but others have rejected the tests as unnecessary and not always to be relied on,
seeing that the acids are not always produced in sufficient abundance to give the desired reaction,
and that they tend to alter in time.
The reagents most commonly in use are caustic potash, generally indicated by K; hypochlorite
of calcium or bleaching powder by CaCl; and a solution of iodine by I. The sign + signifies a
colour reaction, while- indicates that no change has followed the application of the test solution.
Double signs ⁺₊ or any similar variation indicate the upper or lower parts of the thallus affected by
the reagent. In some instances the reaction only follows after the employment of two reagents
represented thus: K(CaCl)+. In such a case the potash breaks up the particular acid and compounds
are formed which become red, orange, etc., on the subsequent application of hypochlorite of lime.
As an instance of the value of chemical tests, Zopf cites the reaction of hypochlorite of lime on
the thallus of four different species of Gyrophora, the “tripe de roche”:—
Gyrophora torrefacta CaCl ⁻₊.
” polyrhiza CaCl ⁺₊.
” proboscidea CaCl ⁺₋.
” erosa CaCl ⁻₋.
It must however be borne in mind that these species are well differentiated and can be
recognized, without difficulty, by their morphological characters. Experienced systematists like
Weddell refuse to accept the tests unless they are supported by true morphological distinctions, as
the reactions are not sufficiently constant.
G. Chemical Reactions in Nature
Similar colour changes may often be observed in nature. The acids of the exposed thallus cortex
are not unfrequently split up by the gradual action of the ammonia in the atmosphere, one of the
compounds thus set free being at the same time coloured by the alkali. Thus salazinic acid, a
constituent of several of our native Parmeliae, is broken up into carbonic acid and salazininic acid,
the latter taking a red colour. Fumarprotocetraric acid is acted on somewhat similarly, and the red
colour may be seen in Cetraria at the base of the thallus where contact with soil containing
ammonia has affected the outer cortex of the plant. The same results are produced still more
effectively when the lichen comes into contact with animal excrement.
Gummy exudations from trees which are more or less ammoniacal may also act on the thallus
and form red-coloured products on contact with the acids present. Lecanora (Aspicilia) cinerea is
so easily affected by alkalies that a thin section left exposed may become red in time owing to the
ammonia in the atmosphere.
II. GENERAL NUTRITION
A. Absorption of Water
Roccella, produced a bright-red “erythrinic” reaction. Caustic potash was also found to be of
service in demonstrating the presence of parietin in lichens by a beautiful purple stain. Many
lichenologists eagerly adopted the new method, as a sure and ready means of distinguishing
doubtful species; but others have rejected the tests as unnecessary and not always to be relied on,
seeing that the acids are not always produced in sufficient abundance to give the desired reaction,
and that they tend to alter in time.
The reagents most commonly in use are caustic potash, generally indicated by K; hypochlorite
of calcium or bleaching powder by CaCl; and a solution of iodine by I. The sign + signifies a
colour reaction, while- indicates that no change has followed the application of the test solution.
Double signs ⁺₊ or any similar variation indicate the upper or lower parts of the thallus affected by
the reagent. In some instances the reaction only follows after the employment of two reagents
represented thus: K(CaCl)+. In such a case the potash breaks up the particular acid and compounds
are formed which become red, orange, etc., on the subsequent application of hypochlorite of lime.
As an instance of the value of chemical tests, Zopf cites the reaction of hypochlorite of lime on
the thallus of four different species of Gyrophora, the “tripe de roche”:—
Gyrophora torrefacta CaCl ⁻₊.
” polyrhiza CaCl ⁺₊.
” proboscidea CaCl ⁺₋.
” erosa CaCl ⁻₋.
It must however be borne in mind that these species are well differentiated and can be
recognized, without difficulty, by their morphological characters. Experienced systematists like
Weddell refuse to accept the tests unless they are supported by true morphological distinctions, as
the reactions are not sufficiently constant.
G. Chemical Reactions in Nature
Similar colour changes may often be observed in nature. The acids of the exposed thallus cortex
are not unfrequently split up by the gradual action of the ammonia in the atmosphere, one of the
compounds thus set free being at the same time coloured by the alkali. Thus salazinic acid, a
constituent of several of our native Parmeliae, is broken up into carbonic acid and salazininic acid,
the latter taking a red colour. Fumarprotocetraric acid is acted on somewhat similarly, and the red
colour may be seen in Cetraria at the base of the thallus where contact with soil containing
ammonia has affected the outer cortex of the plant. The same results are produced still more
effectively when the lichen comes into contact with animal excrement.
Gummy exudations from trees which are more or less ammoniacal may also act on the thallus
and form red-coloured products on contact with the acids present. Lecanora (Aspicilia) cinerea is
so easily affected by alkalies that a thin section left exposed may become red in time owing to the
ammonia in the atmosphere.
II. GENERAL NUTRITION
A. Absorption of Water
Page 308
Lichens are capable of enduring almost complete desiccation, but though they can exist with
little injury through long periods of drought, water is essential to active metabolism. They possess
no special organs for water conduction, but absorb moisture over their whole surface. Several
interdependent factors must therefore be taken into account in considering the question of
absorption: the type of thallus, whether gelatinous or non-gelatinous, crustaceous, foliose or
fruticose, as also the nature of the substratum and the prevailing condition of the atmosphere.
a. Gelatinous Lichens. The algal constituent of these lichens is some member of the
Myxophyceae and is provided with thick gelatinous walls which have great power of imbibition
and swell up enormously in damp surroundings, becoming reservoirs of water. Species of
Collema, for instance, when thoroughly wet, weigh thirty-five times more than when dry[834].
There are no interstices in the thallus and frequently no cortex in these lichens, but the gelatinous
substance itself forms on drying an outer skin that checks evaporation so that water is retained
within the thallus for a longer period than in non-gelatinous forms. They probably always retain
some amount of moisture, as they share with gelatinous algae the power of revival after long
desiccation.
Gelatinous lichens are entirely dependent on a surface supply of water: their hyphae—or
rhizinae when present—rarely penetrate the substratum.
b. Crustaceous non-gelatinous Lichens. The lichens with this type of thallus are in intimate
contact with the substratum whether it be soil, rock, tree or dead wood. The hyphae on the under
surface of the thallus function primarily as hold-fasts, but if water be retained in the substratum,
the lichen will undoubtedly benefit, and water, to some extent, will be absorbed by the walls of the
hyphae or will be drawn up by capillary attraction. In any case, it could only be surface water that
would be available, as lichens have no means of tapping any deeper sources of supply.
Lichens are, however, largely independent of the substratum for their supply of water.
Sievers[835], who gave attention to the subject, found that though some few crustaceous lichens
took up water from below, most of them absorbed the necessary moisture on the surface or at the
edges of the thallus or areolae, where the tissue is looser and more permeable. The swollen
gelatinous walls of the hyphae forming the upper layers of such lichens are admirably adapted for
the reception and storage of water, though, according to Zukal[836], less hygroscopic generally than
in the larger forms. Beckmann[837] proved this power of absorption, possessed by the upper cortex,
by placing a crustaceous lichen, Haematomma sp., in a damp chamber: he found after a while that
water had been taken up by the cortex and by the gonidial zone, while the lower medullary hyphae
had remained dry.
Herre[838] has recorded an astonishing abundance of lichens from the desert of Reno, Nevada,
and these are mostly crustaceous forms, belonging to a limited number of species. The yearly
rainfall of the region is only about eight or ten inches, and occurs during the winter months,
chiefly as snow. It is during that period that active vegetation goes on; but the plants still manage
to exist during the long arid summer, when their only possible water supply is that obtained from
the moisture of the atmosphere during the night, or from the surface deposit of dews.
c. Foliose Lichens. Though many of the leafy lichens are provided with a tomentum of single
hyphae, or with rhizinae on the under surface, the principal function of these structures is that of
attaching the thallus. Sievers[839] tested the areas of absorption by placing pieces of the thallus of
Parmeliae, of Evernia furfuracea, and of Cetraria glauca in a staining solution. After washing and
cutting sections, it was seen that the coloured fluid had penetrated by the upper surface and by the
edge of the thallus, as in crustaceous forms, but not through the lower cortex.
little injury through long periods of drought, water is essential to active metabolism. They possess
no special organs for water conduction, but absorb moisture over their whole surface. Several
interdependent factors must therefore be taken into account in considering the question of
absorption: the type of thallus, whether gelatinous or non-gelatinous, crustaceous, foliose or
fruticose, as also the nature of the substratum and the prevailing condition of the atmosphere.
a. Gelatinous Lichens. The algal constituent of these lichens is some member of the
Myxophyceae and is provided with thick gelatinous walls which have great power of imbibition
and swell up enormously in damp surroundings, becoming reservoirs of water. Species of
Collema, for instance, when thoroughly wet, weigh thirty-five times more than when dry[834].
There are no interstices in the thallus and frequently no cortex in these lichens, but the gelatinous
substance itself forms on drying an outer skin that checks evaporation so that water is retained
within the thallus for a longer period than in non-gelatinous forms. They probably always retain
some amount of moisture, as they share with gelatinous algae the power of revival after long
desiccation.
Gelatinous lichens are entirely dependent on a surface supply of water: their hyphae—or
rhizinae when present—rarely penetrate the substratum.
b. Crustaceous non-gelatinous Lichens. The lichens with this type of thallus are in intimate
contact with the substratum whether it be soil, rock, tree or dead wood. The hyphae on the under
surface of the thallus function primarily as hold-fasts, but if water be retained in the substratum,
the lichen will undoubtedly benefit, and water, to some extent, will be absorbed by the walls of the
hyphae or will be drawn up by capillary attraction. In any case, it could only be surface water that
would be available, as lichens have no means of tapping any deeper sources of supply.
Lichens are, however, largely independent of the substratum for their supply of water.
Sievers[835], who gave attention to the subject, found that though some few crustaceous lichens
took up water from below, most of them absorbed the necessary moisture on the surface or at the
edges of the thallus or areolae, where the tissue is looser and more permeable. The swollen
gelatinous walls of the hyphae forming the upper layers of such lichens are admirably adapted for
the reception and storage of water, though, according to Zukal[836], less hygroscopic generally than
in the larger forms. Beckmann[837] proved this power of absorption, possessed by the upper cortex,
by placing a crustaceous lichen, Haematomma sp., in a damp chamber: he found after a while that
water had been taken up by the cortex and by the gonidial zone, while the lower medullary hyphae
had remained dry.
Herre[838] has recorded an astonishing abundance of lichens from the desert of Reno, Nevada,
and these are mostly crustaceous forms, belonging to a limited number of species. The yearly
rainfall of the region is only about eight or ten inches, and occurs during the winter months,
chiefly as snow. It is during that period that active vegetation goes on; but the plants still manage
to exist during the long arid summer, when their only possible water supply is that obtained from
the moisture of the atmosphere during the night, or from the surface deposit of dews.
c. Foliose Lichens. Though many of the leafy lichens are provided with a tomentum of single
hyphae, or with rhizinae on the under surface, the principal function of these structures is that of
attaching the thallus. Sievers[839] tested the areas of absorption by placing pieces of the thallus of
Parmeliae, of Evernia furfuracea, and of Cetraria glauca in a staining solution. After washing and
cutting sections, it was seen that the coloured fluid had penetrated by the upper surface and by the
edge of the thallus, as in crustaceous forms, but not through the lower cortex.
Page 309
By the same methods of testing, he proved that water penetrates not only by capillarity between
the closely packed hyphae, but also within the cells. A considerable number of lichens were used
for experiment, and great variations were found to exist in the way in which water was taken up. It
has been proved that in some species of Gyrophora water is absorbed from below: in those in
which rhizinae are abundant, water is held by them and so gradually drawn up into the thallus; the
upper cortex in this genus is very thick and checks transpiration. Certain other northern lichens
such as Cetraria islandica, Cladonia rangiferina, etc., imbibe water very slowly, and they, as well
as Gyrophora, are able to endure prolonged wet periods.
That foliose lichens do not normally contain much water was proved by Jumelle[840] who
compared the weight of seven different species when freshly gathered, and after being dried; he
found that the proportion of fresh weight to dry weight showed least variation in Parmelia
acetabulum, as 1·14 to 1; in Xanthoria parietina it was as 1·21 to 1.
d. Fruticose Lichens. There is no water-conducting tissue in the elongate thallus of the shrubby
or filamentous lichens, as can easily be tested by placing the base in water: it will then be seen that
the submerged parts alone are affected. Many lichens are hygroscopic and become water-logged
when placed simply in damp surroundings. The thallus of Usnea, for instance, can absorb many
times its weight of water: a mass of Usnea filaments that weighed 3·8 grms. when dry increased to
13·3 grms. after having been soaked in water for twelve hours. Schrenk[841], who made the
experiment, records in a second instance an increase in weight from 3·97 grms. to 11·18 grms. The
Cladoniae retain large quantities of water in their upright hollow podetia. The Australian species,
Cladonia retepora, the podetium of which is a regular network of holes, competes with the
Sphagnum moss in its capacity to take up water.
To conclude: as a rule, heteromerous, non-gelatinous lichens do not contain large quantities of
water, the weight of fresh plants being generally about three times only that of the dry weight.
Their ordinary water content is indeed smaller than that of most other plants, though it varies at
once with a change in external conditions. It is noteworthy that a number of lichens have their
habitat on the sea-shore, constantly subject to spray from the waves, but scarcely any can exist
within the spray of a waterfall, possibly because the latter is never-ceasing.
B. Storage of Water
The gonidial algae Gloeocapsa, Scytonema, Nostoc, etc. among Myxophyceae, Palmella and
occasionally Trentepohlia among Chlorophyceae, have more or less gelatinous walls which act as
a natural reservoir of water for the lichens with which they are associated. In these lichens the
hyphae for the most part have thin walls, and the plectenchyma when formed—as below the
apothecium in Collema granuliferum, or as a cortical layer in Leptogium—is a thin-walled tissue.
In lichens where, on the contrary, the alga is non-gelatinous—as generally in Chlorophyceae—or
where the gelatinous sheath is not formed as in the altered Nostoc of the Peltigera thallus, the
fungal hyphae have swollen gelatinous walls both in the pith and the cortex, and not only imbibe
but store up water.
Bonnier[842] had his attention directed to this thickening of the cell-walls as he followed the
development of the lichen thallus. He made cultures from the ascospore of Physcia (Xanthoria)
parietina and obtained a fair amount of hyphal tissue, the cell-walls of which became thickened,
but more slowly and to a much less extent than when associated with the gonidia.
the closely packed hyphae, but also within the cells. A considerable number of lichens were used
for experiment, and great variations were found to exist in the way in which water was taken up. It
has been proved that in some species of Gyrophora water is absorbed from below: in those in
which rhizinae are abundant, water is held by them and so gradually drawn up into the thallus; the
upper cortex in this genus is very thick and checks transpiration. Certain other northern lichens
such as Cetraria islandica, Cladonia rangiferina, etc., imbibe water very slowly, and they, as well
as Gyrophora, are able to endure prolonged wet periods.
That foliose lichens do not normally contain much water was proved by Jumelle[840] who
compared the weight of seven different species when freshly gathered, and after being dried; he
found that the proportion of fresh weight to dry weight showed least variation in Parmelia
acetabulum, as 1·14 to 1; in Xanthoria parietina it was as 1·21 to 1.
d. Fruticose Lichens. There is no water-conducting tissue in the elongate thallus of the shrubby
or filamentous lichens, as can easily be tested by placing the base in water: it will then be seen that
the submerged parts alone are affected. Many lichens are hygroscopic and become water-logged
when placed simply in damp surroundings. The thallus of Usnea, for instance, can absorb many
times its weight of water: a mass of Usnea filaments that weighed 3·8 grms. when dry increased to
13·3 grms. after having been soaked in water for twelve hours. Schrenk[841], who made the
experiment, records in a second instance an increase in weight from 3·97 grms. to 11·18 grms. The
Cladoniae retain large quantities of water in their upright hollow podetia. The Australian species,
Cladonia retepora, the podetium of which is a regular network of holes, competes with the
Sphagnum moss in its capacity to take up water.
To conclude: as a rule, heteromerous, non-gelatinous lichens do not contain large quantities of
water, the weight of fresh plants being generally about three times only that of the dry weight.
Their ordinary water content is indeed smaller than that of most other plants, though it varies at
once with a change in external conditions. It is noteworthy that a number of lichens have their
habitat on the sea-shore, constantly subject to spray from the waves, but scarcely any can exist
within the spray of a waterfall, possibly because the latter is never-ceasing.
B. Storage of Water
The gonidial algae Gloeocapsa, Scytonema, Nostoc, etc. among Myxophyceae, Palmella and
occasionally Trentepohlia among Chlorophyceae, have more or less gelatinous walls which act as
a natural reservoir of water for the lichens with which they are associated. In these lichens the
hyphae for the most part have thin walls, and the plectenchyma when formed—as below the
apothecium in Collema granuliferum, or as a cortical layer in Leptogium—is a thin-walled tissue.
In lichens where, on the contrary, the alga is non-gelatinous—as generally in Chlorophyceae—or
where the gelatinous sheath is not formed as in the altered Nostoc of the Peltigera thallus, the
fungal hyphae have swollen gelatinous walls both in the pith and the cortex, and not only imbibe
but store up water.
Bonnier[842] had his attention directed to this thickening of the cell-walls as he followed the
development of the lichen thallus. He made cultures from the ascospore of Physcia (Xanthoria)
parietina and obtained a fair amount of hyphal tissue, the cell-walls of which became thickened,
but more slowly and to a much less extent than when associated with the gonidia.
Page 310
He noted also that when his cultures were kept in a continuously moist atmosphere there was
much less thickening, scarcely more than in fungi ordinarily; it was only when they were grown
under drier conditions with necessity for storage, that any considerable swelling of the walls took
place. Further he found that the thallus of forms cultivated in an abundance of moisture could not
resist desiccation as could those with the thicker membranes. These latter survived drying up and
resumed activity when moisture was supplied.
C. Supply of Inorganic Food
As in the higher plants, mineral substances can only be taken up when they are in a state of
solution. Lichens are therefore dependent on the substances that are contained in the water of
absorption: they must receive their inorganic nutriment by the same channels that water is
conveyed to them.
a. Foliose and Fruticose Lichens. These larger lichens are provided with rhizinae or with hold-
fasts, which are only absorptive to a very limited extent; the main source of water supply is from
the atmosphere and the salts required in the metabolism of the cell must be obtained there also—
from atmospheric dust dissolved in rain, or from wind-borne particles deposited on the surface of
the thallus which may be gradually dissolved and absorbed by the cortical and growing hyphae.
That substances received from the atmospheric environment may be all important is shown by the
exclusive habitat of some marine lichens; the Roccellae, Lichinae, some species of Ramalina and
others which grow only on rocky shores are almost as dependent on sea-water as are the
submerged algae. Other lichens, such as Hydrothyria venosa and Lecanora lacustris, grow in
streams, or on boulders that are subject to constant inundation, and they obtain their inorganic food
mainly, if not entirely, from an aqueous medium.
Though lichens cannot live in an atmosphere polluted by smoke, they thrive on trees and walls
by the road-side where they are liable to be almost smothered by soil-dust. West[843] has observed
that they flourish in valleys that are swept by moisture laden winds more especially if near to a
highway, where animal excreta are mingled with the dust. The favourite habitats of Xanthoria
parietina are the walls and roofs of farm-buildings where the dust must contain a large percentage
of nitrogenous material; or stones by the sea-shore that are the haunts of sea-birds. Sandstede[844]
found on the island of Rügen that while the perpendicular faces of the cliffs were quite bare, the
tops bore a plentiful crop of Lecanora saxicola, Xanthoria lychnea and Candellariella vitellina.
He attributed their selection of habitat to the presence of the excreta of sea-birds. As already stated
the connection of foliose and fruticose lichens with the substratum is mainly mechanical but
occasionally a kind of semiparasitism may arise. Friedrich[845] gives an instance in a species of
Usnea of unusually vigorous development. It grew on bark and the strands of hyphae, branching
from the root-base of the lichen, had reached down to the living tissue of the tree-trunk and had
penetrated between the cells by dissolving the middle lamella. It was possible to find holes pierced
in the cell-walls of the host, but it was difficult to decide if the hyphae had attacked living cells or
were merely preying on dead material. Lindau[846] held very strongly that lichen hyphae were non-
parasitic, and merely split apart the tissues already dead, and the instance recorded by Friedrich is
of rare occurrence[847].
That the substratum does have some indirect influence on these larger lichens has been proved
once and again. Uloth[848], a chemist as well as a botanist, made analyses of plants of Evernia
prunastri taken from birch bark and from sandstone. Qualitatively the composition of the lichen
substances was the same, but the quantities varied considerably. Zopf[849] has, more recently,
much less thickening, scarcely more than in fungi ordinarily; it was only when they were grown
under drier conditions with necessity for storage, that any considerable swelling of the walls took
place. Further he found that the thallus of forms cultivated in an abundance of moisture could not
resist desiccation as could those with the thicker membranes. These latter survived drying up and
resumed activity when moisture was supplied.
C. Supply of Inorganic Food
As in the higher plants, mineral substances can only be taken up when they are in a state of
solution. Lichens are therefore dependent on the substances that are contained in the water of
absorption: they must receive their inorganic nutriment by the same channels that water is
conveyed to them.
a. Foliose and Fruticose Lichens. These larger lichens are provided with rhizinae or with hold-
fasts, which are only absorptive to a very limited extent; the main source of water supply is from
the atmosphere and the salts required in the metabolism of the cell must be obtained there also—
from atmospheric dust dissolved in rain, or from wind-borne particles deposited on the surface of
the thallus which may be gradually dissolved and absorbed by the cortical and growing hyphae.
That substances received from the atmospheric environment may be all important is shown by the
exclusive habitat of some marine lichens; the Roccellae, Lichinae, some species of Ramalina and
others which grow only on rocky shores are almost as dependent on sea-water as are the
submerged algae. Other lichens, such as Hydrothyria venosa and Lecanora lacustris, grow in
streams, or on boulders that are subject to constant inundation, and they obtain their inorganic food
mainly, if not entirely, from an aqueous medium.
Though lichens cannot live in an atmosphere polluted by smoke, they thrive on trees and walls
by the road-side where they are liable to be almost smothered by soil-dust. West[843] has observed
that they flourish in valleys that are swept by moisture laden winds more especially if near to a
highway, where animal excreta are mingled with the dust. The favourite habitats of Xanthoria
parietina are the walls and roofs of farm-buildings where the dust must contain a large percentage
of nitrogenous material; or stones by the sea-shore that are the haunts of sea-birds. Sandstede[844]
found on the island of Rügen that while the perpendicular faces of the cliffs were quite bare, the
tops bore a plentiful crop of Lecanora saxicola, Xanthoria lychnea and Candellariella vitellina.
He attributed their selection of habitat to the presence of the excreta of sea-birds. As already stated
the connection of foliose and fruticose lichens with the substratum is mainly mechanical but
occasionally a kind of semiparasitism may arise. Friedrich[845] gives an instance in a species of
Usnea of unusually vigorous development. It grew on bark and the strands of hyphae, branching
from the root-base of the lichen, had reached down to the living tissue of the tree-trunk and had
penetrated between the cells by dissolving the middle lamella. It was possible to find holes pierced
in the cell-walls of the host, but it was difficult to decide if the hyphae had attacked living cells or
were merely preying on dead material. Lindau[846] held very strongly that lichen hyphae were non-
parasitic, and merely split apart the tissues already dead, and the instance recorded by Friedrich is
of rare occurrence[847].
That the substratum does have some indirect influence on these larger lichens has been proved
once and again. Uloth[848], a chemist as well as a botanist, made analyses of plants of Evernia
prunastri taken from birch bark and from sandstone. Qualitatively the composition of the lichen
substances was the same, but the quantities varied considerably. Zopf[849] has, more recently,
Page 311
compared the acid content of a form of Evernia furfuracea on rock with that of the same species
growing on the bark of a tree. In the case of the latter, the thallus produced 4 per cent. of physodic
acid and 2·2 per cent. of atranorin. In the rock specimen, which, he adds, was a more graceful
plant than the other, the quantities were 6 per cent. of physodic acid, and 2·75 per cent. of
atranorin. In both cases there was a slight formation of furfuracinnic acid. He found also that
specimens of Evernia prunastri on dead wood contained 8·4 per cent. of lichen-acids, while in
those from living trees there was only 4·4 per cent. or even less. Other conditions, however, might
have contributed to this result, as Zopf[850] found later that this lichen when very sorediate yielded
an increased supply of atranoric acid.
Ohlert[851], who made a study of lichens in relation to their habitat, found that though a certain
number grew more or less freely on either tree, rock or soil, none of them was entirely unaffected.
Usnea barbata, Evernia prunastri and Parmelia physodes were the most indifferent to habitat;
normally they are corticolous species, but Usnea on soil formed more slender filaments, and
Evernia on the same substratum showed a tendency to horizontal growth, and became attached at
various points instead of by the usual single base.
b. Crustaceous Lichens. The crustaceous forms on rocks are in a more favourable position for
obtaining inorganic salts, the lower medullary hyphae being in direct contact with mineral
substances and able to act directly on them. Many species are largely or even exclusively
calcicolous, and there must be something in the lime that is especially conducive to their growth.
The hyphae have been traced into the limestone to a depth of 15 mm.[852] and small depressions
are frequently scooped out of the rock by the action of the lichen, thus giving a lodgement to the
foveolate fruit.
On rocks mainly composed of silica, the lichen has a much harder substance to deal with, and
one less easily affected by acids, though even silica may be dissolved in time. Uloth[853] concluded
from his observations that the relation of plants to the substratum was chemical even more than
physical, so far as crustaceous species were concerned. He found that the surface of the area of
rock inhabited was distinctly marked: even such a hard substance as chalcedony was corroded by a
very luxuriant lichen flora, the border of growth being quite clearly outlined. The corrosive action
is due he considered to the carbon dioxide liberated by the plant, though oxalic acid, so frequent a
constituent of lichens, may also share in the corrosion. Egeling[854] made similar observations in
regard to the effect of lichen growth on granite rocks; and he further noticed that pieces of glass,
over which lichens had spread, had become clouded, the dulness of the surface being due to a
multitude of small cracks eaten out by the hyphae. Buchet[855] also gives an instance of glass
which had been corroded by the action of lichen hyphae. It formed part of an old stained window
in a chapel that was obscured by a lichen growth which adhered tenaciously. When the window
was taken down and cleaned, it was found that the surface of the glass was covered with small,
more or less hemispherical pits which were often confluent. The different colours in the picture
were unequally attacked, some of the figures or draperies being covered with the minute
excavations, while other parts were intact. It happened also, occasionally, that a colour while
slightly corroded in one pane would be uninjured in another, but the suggestion is made that there
might in that case have been a difference in the length of attack by the lichen. The selection of
colours by the lichens might also be influenced by some chemical or physical characters.
Bachmann[856] found that on granite there is equally a selection of material by the hyphae: as a
rule they avoid the acid silica constituents; while they penetrate and traverse the grains of mica
which are dissolved by them exactly as are lime granules.
growing on the bark of a tree. In the case of the latter, the thallus produced 4 per cent. of physodic
acid and 2·2 per cent. of atranorin. In the rock specimen, which, he adds, was a more graceful
plant than the other, the quantities were 6 per cent. of physodic acid, and 2·75 per cent. of
atranorin. In both cases there was a slight formation of furfuracinnic acid. He found also that
specimens of Evernia prunastri on dead wood contained 8·4 per cent. of lichen-acids, while in
those from living trees there was only 4·4 per cent. or even less. Other conditions, however, might
have contributed to this result, as Zopf[850] found later that this lichen when very sorediate yielded
an increased supply of atranoric acid.
Ohlert[851], who made a study of lichens in relation to their habitat, found that though a certain
number grew more or less freely on either tree, rock or soil, none of them was entirely unaffected.
Usnea barbata, Evernia prunastri and Parmelia physodes were the most indifferent to habitat;
normally they are corticolous species, but Usnea on soil formed more slender filaments, and
Evernia on the same substratum showed a tendency to horizontal growth, and became attached at
various points instead of by the usual single base.
b. Crustaceous Lichens. The crustaceous forms on rocks are in a more favourable position for
obtaining inorganic salts, the lower medullary hyphae being in direct contact with mineral
substances and able to act directly on them. Many species are largely or even exclusively
calcicolous, and there must be something in the lime that is especially conducive to their growth.
The hyphae have been traced into the limestone to a depth of 15 mm.[852] and small depressions
are frequently scooped out of the rock by the action of the lichen, thus giving a lodgement to the
foveolate fruit.
On rocks mainly composed of silica, the lichen has a much harder substance to deal with, and
one less easily affected by acids, though even silica may be dissolved in time. Uloth[853] concluded
from his observations that the relation of plants to the substratum was chemical even more than
physical, so far as crustaceous species were concerned. He found that the surface of the area of
rock inhabited was distinctly marked: even such a hard substance as chalcedony was corroded by a
very luxuriant lichen flora, the border of growth being quite clearly outlined. The corrosive action
is due he considered to the carbon dioxide liberated by the plant, though oxalic acid, so frequent a
constituent of lichens, may also share in the corrosion. Egeling[854] made similar observations in
regard to the effect of lichen growth on granite rocks; and he further noticed that pieces of glass,
over which lichens had spread, had become clouded, the dulness of the surface being due to a
multitude of small cracks eaten out by the hyphae. Buchet[855] also gives an instance of glass
which had been corroded by the action of lichen hyphae. It formed part of an old stained window
in a chapel that was obscured by a lichen growth which adhered tenaciously. When the window
was taken down and cleaned, it was found that the surface of the glass was covered with small,
more or less hemispherical pits which were often confluent. The different colours in the picture
were unequally attacked, some of the figures or draperies being covered with the minute
excavations, while other parts were intact. It happened also, occasionally, that a colour while
slightly corroded in one pane would be uninjured in another, but the suggestion is made that there
might in that case have been a difference in the length of attack by the lichen. The selection of
colours by the lichens might also be influenced by some chemical or physical characters.
Bachmann[856] found that on granite there is equally a selection of material by the hyphae: as a
rule they avoid the acid silica constituents; while they penetrate and traverse the grains of mica
which are dissolved by them exactly as are lime granules.
Page 312
On another rock consisting mainly of muscovite and quartz he[857] found that crystals of garnet
embedded in the rock were reduced to a powder by the action of the lichen. He concludes that the
destroying action of the hyphae is accelerated by the presence of carbon dioxide given off by the
lichen, and dissolved in the surrounding moisture. Lang[858] and Stahlecker[859] have both come to
the conclusion that even the quartz grains are corroded by the lichen hyphae. Stahlecker finds that
they change the quartz into amorphous silicic acid, and thus bring it into the cycle of organic life.
Chalk and magnesia are extracted from the silicates where no other plant could procure them.
Lichens are generally rare on pure quartz rocks, chiefly, however, for the mechanical reason that
the structure is of too close a grain to afford a foothold.
D. Supply of Organic Food
a. From the Substratum. The Ascomycetous fungi, from which so many of the lichens are
descended, are mainly saprophytes, obtaining their carbohydrates from dead plant material, and
lichen hyphae have in some instances undoubtedly retained their saprophytic capacity. It has been
proved that lichen hyphae, which naturally could not exist without the algal symbiont, may be
artificially cultivated on nutrient media without the presence of gonidia, though the chief and often
the only source of carbon supply is normally through the alga with which the hyphae are
associated in symbiotic union.
A large number of crustaceous lichens grow on the bark of trees, and their hyphae burrow
among the dead cells of the outer bark using up the material with which they come in contact.
Others live on dead wood, palings, etc. where the supply of disintegrated organic substance is even
greater; or they spread over withered mosses and soil rich in humus.
b. From other Lichens. Bitter[860] has recorded several instances observed by him of lichens
growing over other lichens and using up their substance as food material. Some lichens are
naturally more vigorous than others, and the weaker or more slow growing succumb when an
encounter takes place. Pertusaria globulifera is one of these marauding species; its habitat is
among mosses on the bark of trees, and, being a quick grower, it easily overspreads its more
sluggish neighbours. It can scarcely be considered a parasite, as the thallus of the victim is first
killed, probably by the action of an enzyme.
Lecanora subfusca and allied species which have a thin thallus are frequently overgrown by this
Pertusaria and a dark line generally precedes the invading lichen; the hyphae and the gonidia of
the Lecanorae are first killed and changed to a brown structureless mass which is then split up by
the advancing hyphae of the Pertusaria into small portions. A little way back from the edge of the
predatory thallus the dead particles are no longer visible, having been dissolved and completely
used up. Pertusaria amara also may overgrow Lecanorae, though, generally, its onward course is
checked and deflected towards a lateral direction; if however it is in a young and vigorous
condition, it attacks the thallus in its path, and ahead of it appears the rather broad blackish line
marking the fatal effect of the enzyme, the rest of the host thallus being unaffected. Neither
Pertusaria seems to profit much, and does not grow either faster or thicker; the thallus appears
indeed to be hindered rather than helped by the encounter. Biatora (Lecidea) quernea with a
looser, more furfuraceous thallus is also killed and dissolved by Pertusariae; but if the Biatora is
growing near to a withering or dead lichen it, also, profits by the food material at hand, grows over
it and uses it up. Bitter has also observed lichens overgrown by Haematomma sp.; the growth of
that lichen is indeed so rapid that few others can withstand its approach.
embedded in the rock were reduced to a powder by the action of the lichen. He concludes that the
destroying action of the hyphae is accelerated by the presence of carbon dioxide given off by the
lichen, and dissolved in the surrounding moisture. Lang[858] and Stahlecker[859] have both come to
the conclusion that even the quartz grains are corroded by the lichen hyphae. Stahlecker finds that
they change the quartz into amorphous silicic acid, and thus bring it into the cycle of organic life.
Chalk and magnesia are extracted from the silicates where no other plant could procure them.
Lichens are generally rare on pure quartz rocks, chiefly, however, for the mechanical reason that
the structure is of too close a grain to afford a foothold.
D. Supply of Organic Food
a. From the Substratum. The Ascomycetous fungi, from which so many of the lichens are
descended, are mainly saprophytes, obtaining their carbohydrates from dead plant material, and
lichen hyphae have in some instances undoubtedly retained their saprophytic capacity. It has been
proved that lichen hyphae, which naturally could not exist without the algal symbiont, may be
artificially cultivated on nutrient media without the presence of gonidia, though the chief and often
the only source of carbon supply is normally through the alga with which the hyphae are
associated in symbiotic union.
A large number of crustaceous lichens grow on the bark of trees, and their hyphae burrow
among the dead cells of the outer bark using up the material with which they come in contact.
Others live on dead wood, palings, etc. where the supply of disintegrated organic substance is even
greater; or they spread over withered mosses and soil rich in humus.
b. From other Lichens. Bitter[860] has recorded several instances observed by him of lichens
growing over other lichens and using up their substance as food material. Some lichens are
naturally more vigorous than others, and the weaker or more slow growing succumb when an
encounter takes place. Pertusaria globulifera is one of these marauding species; its habitat is
among mosses on the bark of trees, and, being a quick grower, it easily overspreads its more
sluggish neighbours. It can scarcely be considered a parasite, as the thallus of the victim is first
killed, probably by the action of an enzyme.
Lecanora subfusca and allied species which have a thin thallus are frequently overgrown by this
Pertusaria and a dark line generally precedes the invading lichen; the hyphae and the gonidia of
the Lecanorae are first killed and changed to a brown structureless mass which is then split up by
the advancing hyphae of the Pertusaria into small portions. A little way back from the edge of the
predatory thallus the dead particles are no longer visible, having been dissolved and completely
used up. Pertusaria amara also may overgrow Lecanorae, though, generally, its onward course is
checked and deflected towards a lateral direction; if however it is in a young and vigorous
condition, it attacks the thallus in its path, and ahead of it appears the rather broad blackish line
marking the fatal effect of the enzyme, the rest of the host thallus being unaffected. Neither
Pertusaria seems to profit much, and does not grow either faster or thicker; the thallus appears
indeed to be hindered rather than helped by the encounter. Biatora (Lecidea) quernea with a
looser, more furfuraceous thallus is also killed and dissolved by Pertusariae; but if the Biatora is
growing near to a withering or dead lichen it, also, profits by the food material at hand, grows over
it and uses it up. Bitter has also observed lichens overgrown by Haematomma sp.; the growth of
that lichen is indeed so rapid that few others can withstand its approach.
Page 313
Another common rock species, Lecanora sordida (L. glaucoma), has a vigorous thallus that
easily ousts its neighbours. Rhizocarpon geographicum, a slow-growing species, is especially
liable to be attacked; from the thallus of L. sordida the hyphae in strands push directly into the
other lichen in a horizontal direction and split up the tissues, the algae persist unharmed for some
time, but eventually they succumb and are used up; the apothecia, though more resistant than the
thallus, are also gradually undermined and hoisted up by the new growth, till finally no trace of the
original lichen is left. Lecanora sordida is however in turn invaded by Lecidea insularis (L.
intumescens) which is found forming small orbicular areas on the Lecanora thallus. It kills its host
in patches and the dead material mostly drifts away. On any strands that are left Candellariella
vitellina generally settles and evidently profits by the dead nutriment. It does not spread to the
living thallus. Lecanora polytropa also forms colonies on these vacant patches, with advantage to
its growth.
Even the larger lichens are attacked by these quick-growing crusts. Pertusaria globulifera
spreads over Parmelia perlata and P. physodes, gradually dissolving and consuming the different
thalline layers; the lower cortex of the victim holds out longest and can be seen as an undigested
black substance within the Pertusaria thallus for some time. As a rule, however, the lichens with
large lobes grow over the smaller thalli in a purely mechanical fashion.
c. From other Vegetation. Zukal[861] has given instances of association between mosses and
lichens in which the latter seemed to play the part of parasite. The terricolous species Baeomyces
rufus (Sphyridium) and Biatora decolorans, as well as forms of Lepraria and Variolaria, he found
growing over mosses and killing them. Stems and leaves of the moss Plagiothecium sylvaticum
were grown through and through by the hyphae of a Pertusaria, and he observed a leaf of
Polytrichum commune pierced by the rhizinae of a minute Cladonia squamule. The cells had been
invaded and the neighbouring tissue was brown and dead.
Perhaps the most voracious consumer of organic remains is Lecanora tartarea, more especially
the northern form frigida. It is the well-known cudbear lichen of West Scotland, and is normally a
rock species. It has an extremely vigorous thickly crustaceous and quick-growing thallus, and
spreads over everything that lies in its path—decaying mosses, dead leaves, other lichens, etc.
Kihlman[862] has furnished a graphic description of the way it covers up the vegetation on the high
altitudes of Russian Lapland. More than any other plant it is able to withstand the effect of the cold
winds that sweep across these inhospitable plains. Other plant groups at certain seasons or in
certain stages of growth are weakened or killed by the extreme cold of the wind, and, immediately,
a growth of the more hardy grey crust of Lecanora tartarea begins to spread over and take
possession of the area affected—very frequently a bank of mosses, of which the tips have been
destroyed, is thus covered up. In the same way the moorland Cladoniae, C. rangiferina (the
reindeer moss) and some allied species, are attacked. They have no continuous cortex, the outer
covering of the long branching podetia being a loose felt of hyphae; they are thus sensitive to cold
and liable to be destroyed by a high wind, and their stems, which are blackened as decay advances,
become very soon dotted with the whitish-grey crust of the more vigorous and resistant Lecanora.
III. ASSIMILATION AND RESPIRATION
A. Influence of Temperature
a. High Temperature. It has been proved that plants without chlorophyll are less affected by
great heat than those that contain chlorophyll. Lichens in which both types are present are more
easily ousts its neighbours. Rhizocarpon geographicum, a slow-growing species, is especially
liable to be attacked; from the thallus of L. sordida the hyphae in strands push directly into the
other lichen in a horizontal direction and split up the tissues, the algae persist unharmed for some
time, but eventually they succumb and are used up; the apothecia, though more resistant than the
thallus, are also gradually undermined and hoisted up by the new growth, till finally no trace of the
original lichen is left. Lecanora sordida is however in turn invaded by Lecidea insularis (L.
intumescens) which is found forming small orbicular areas on the Lecanora thallus. It kills its host
in patches and the dead material mostly drifts away. On any strands that are left Candellariella
vitellina generally settles and evidently profits by the dead nutriment. It does not spread to the
living thallus. Lecanora polytropa also forms colonies on these vacant patches, with advantage to
its growth.
Even the larger lichens are attacked by these quick-growing crusts. Pertusaria globulifera
spreads over Parmelia perlata and P. physodes, gradually dissolving and consuming the different
thalline layers; the lower cortex of the victim holds out longest and can be seen as an undigested
black substance within the Pertusaria thallus for some time. As a rule, however, the lichens with
large lobes grow over the smaller thalli in a purely mechanical fashion.
c. From other Vegetation. Zukal[861] has given instances of association between mosses and
lichens in which the latter seemed to play the part of parasite. The terricolous species Baeomyces
rufus (Sphyridium) and Biatora decolorans, as well as forms of Lepraria and Variolaria, he found
growing over mosses and killing them. Stems and leaves of the moss Plagiothecium sylvaticum
were grown through and through by the hyphae of a Pertusaria, and he observed a leaf of
Polytrichum commune pierced by the rhizinae of a minute Cladonia squamule. The cells had been
invaded and the neighbouring tissue was brown and dead.
Perhaps the most voracious consumer of organic remains is Lecanora tartarea, more especially
the northern form frigida. It is the well-known cudbear lichen of West Scotland, and is normally a
rock species. It has an extremely vigorous thickly crustaceous and quick-growing thallus, and
spreads over everything that lies in its path—decaying mosses, dead leaves, other lichens, etc.
Kihlman[862] has furnished a graphic description of the way it covers up the vegetation on the high
altitudes of Russian Lapland. More than any other plant it is able to withstand the effect of the cold
winds that sweep across these inhospitable plains. Other plant groups at certain seasons or in
certain stages of growth are weakened or killed by the extreme cold of the wind, and, immediately,
a growth of the more hardy grey crust of Lecanora tartarea begins to spread over and take
possession of the area affected—very frequently a bank of mosses, of which the tips have been
destroyed, is thus covered up. In the same way the moorland Cladoniae, C. rangiferina (the
reindeer moss) and some allied species, are attacked. They have no continuous cortex, the outer
covering of the long branching podetia being a loose felt of hyphae; they are thus sensitive to cold
and liable to be destroyed by a high wind, and their stems, which are blackened as decay advances,
become very soon dotted with the whitish-grey crust of the more vigorous and resistant Lecanora.
III. ASSIMILATION AND RESPIRATION
A. Influence of Temperature
a. High Temperature. It has been proved that plants without chlorophyll are less affected by
great heat than those that contain chlorophyll. Lichens in which both types are present are more
Page 314
capable of enduring high temperatures than the higher plants, but with undue heat the alga
succumbs first. In consequence, respiration, by the fungus alone, can go on after assimilation
(photosynthesis) and respiration in the alga have ceased.
Most Phanerogams cease assimilation and respiration after being subjected for ten minutes to a
temperature of 50° C. Jumelle[863] made a series of experiments with lichens, chiefly of the larger
fruticose or foliaceous types, with species of Ramalina, Physcia and Parmelia, also with Evernia
prunastri and Cladonia rangiferina. He found that as regards respiration, plants which had been
kept for three days at 45° C., fifteen hours at 50°, then five hours at 60°, showed an intensity of
respiration almost equal to untreated specimens, gaseous interchange being manifested by an
absorption of oxygen and a giving up of carbon dioxide.
The power of assimilation was more quickly destroyed: as a rule it failed after the plants had
been subjected successively to a temperature of one day at 45° C., then three hours at 50° and half-
an-hour at 60°. The assimilating green alga, being less able to resist extreme heat, as already
stated, succumbed more quickly than the fungus. Jumelle also gives the record of an experiment
with a crustaceous lichen, Lecidea (Lecanora) sulphurea, a rock species. It was kept in a chamber
heated to 50° for three hours and when subsequently placed in the sunlight respiration took place
but no assimilation.
Very high temperatures may be endured by lichen plants in quite natural conditions, when the
rock or stone on which they grow becomes heated by the sun. Zopf[864] tested the thalli of
crustaceous lichens in a hot June, under direct sunlight, and found that the thermometer registered
55° C.
b. Low Temperature. Lichens support extreme cold even better than extreme heat. In both cases
it is the power of drying up and entering at any season into a condition of lowered or latent vitality
that enables them to do so. In winter during a spell of severe cold they are generally in a state of
desiccation, though that is not always the case, and resistance to cold is not due to their dry
condition. The water of imbibition is stored in the cell-walls and it has been found that lichens
when thus charged with moisture are able to resist low temperatures, even down to -40° C. or -50°
as well as when they are dry. Respiration in that case was proved by Jumelle[865] to continue to
-10°, but assimilation was still possible at a temperature of -40°: Evernia prunastri exposed to that
extreme degree of cold, but in the presence of light, decomposed carbon dioxide and gave off
oxygen.
B. Influence of Moisture
a. On Vital Functions. Gaseous interchange has been found to vary according to the degree of
humidity present[865]. In lichens growing in sheltered positions, or on soil, there is less complete
desiccation, and assimilation and respiration may be only enfeebled. Lichens more exposed to the
air—those growing on trees, etc.—dry almost completely and gaseous interchange may be no
longer appreciable. In severe cold any water present would become frozen and the same effect of
desiccation would be produced. At normal temperatures, on the addition of even a small amount of
moisture the respiratory and assimilative functions at once become active, and to an increasing
degree as the plant is further supplied with water until a certain optimum is reached, after which
the vital processes begin somewhat to diminish.
Though able to exist with very little moisture, lichens do not endure desiccation indefinitely,
and both assimilation and respiration probably cease entirely during very dry seasons. A specimen
succumbs first. In consequence, respiration, by the fungus alone, can go on after assimilation
(photosynthesis) and respiration in the alga have ceased.
Most Phanerogams cease assimilation and respiration after being subjected for ten minutes to a
temperature of 50° C. Jumelle[863] made a series of experiments with lichens, chiefly of the larger
fruticose or foliaceous types, with species of Ramalina, Physcia and Parmelia, also with Evernia
prunastri and Cladonia rangiferina. He found that as regards respiration, plants which had been
kept for three days at 45° C., fifteen hours at 50°, then five hours at 60°, showed an intensity of
respiration almost equal to untreated specimens, gaseous interchange being manifested by an
absorption of oxygen and a giving up of carbon dioxide.
The power of assimilation was more quickly destroyed: as a rule it failed after the plants had
been subjected successively to a temperature of one day at 45° C., then three hours at 50° and half-
an-hour at 60°. The assimilating green alga, being less able to resist extreme heat, as already
stated, succumbed more quickly than the fungus. Jumelle also gives the record of an experiment
with a crustaceous lichen, Lecidea (Lecanora) sulphurea, a rock species. It was kept in a chamber
heated to 50° for three hours and when subsequently placed in the sunlight respiration took place
but no assimilation.
Very high temperatures may be endured by lichen plants in quite natural conditions, when the
rock or stone on which they grow becomes heated by the sun. Zopf[864] tested the thalli of
crustaceous lichens in a hot June, under direct sunlight, and found that the thermometer registered
55° C.
b. Low Temperature. Lichens support extreme cold even better than extreme heat. In both cases
it is the power of drying up and entering at any season into a condition of lowered or latent vitality
that enables them to do so. In winter during a spell of severe cold they are generally in a state of
desiccation, though that is not always the case, and resistance to cold is not due to their dry
condition. The water of imbibition is stored in the cell-walls and it has been found that lichens
when thus charged with moisture are able to resist low temperatures, even down to -40° C. or -50°
as well as when they are dry. Respiration in that case was proved by Jumelle[865] to continue to
-10°, but assimilation was still possible at a temperature of -40°: Evernia prunastri exposed to that
extreme degree of cold, but in the presence of light, decomposed carbon dioxide and gave off
oxygen.
B. Influence of Moisture
a. On Vital Functions. Gaseous interchange has been found to vary according to the degree of
humidity present[865]. In lichens growing in sheltered positions, or on soil, there is less complete
desiccation, and assimilation and respiration may be only enfeebled. Lichens more exposed to the
air—those growing on trees, etc.—dry almost completely and gaseous interchange may be no
longer appreciable. In severe cold any water present would become frozen and the same effect of
desiccation would be produced. At normal temperatures, on the addition of even a small amount of
moisture the respiratory and assimilative functions at once become active, and to an increasing
degree as the plant is further supplied with water until a certain optimum is reached, after which
the vital processes begin somewhat to diminish.
Though able to exist with very little moisture, lichens do not endure desiccation indefinitely,
and both assimilation and respiration probably cease entirely during very dry seasons. A specimen
Page 315
of Cladonia rangiferina was kept dry for three months, and then moistened: respiration followed
but it was very feeble and assimilation had almost entirely ceased. Somewhat similar results were
obtained with Ramalina farinacea and Usnea barbata.
In normal conditions of moisture, and with normal illumination, assimilation in lichens
predominates over respiration, more carbon dioxide being decomposed than is given forth; and
Jumelle has argued from that fact, that the alga is well able to secure from the atmosphere all the
carbon required for the nutrition of the whole plant. The intensity of assimilation, however, varies
enormously in different lichens and is generally more powerful in the larger forms than in the
crustaceous: the latter have often an extremely scanty thallus and they are also more in contact
with the substratum—rock, humus or wood—on which they may be partly saprophytic, thus
obtaining carbohydrates already formed, and demanding less from the alga.
An interesting comparison might be made with fungi in regard to which many records have
been taken as to their possible duration in a dry state, more especially on the viability of spores,
i.e. their persistent capacity of germination. A striking instance is reported by Weir[866] of the
regeneration of the sporophores of Polystictus sanguineus, a common fungus of warm countries.
The plant was collected in Brazil and sent to Munich. After about two years in the mycological
collection of the University, the branch on which it grew was exposed in the open among other
branches in a wood while snow still lay on the ground. In a short time the fungus revived and
before the end of spring not only had produced a new hymenium, but enlarged its hymenial
surface to about one-fourth of its original size and had also formed one entirely new, though small,
sporophore.
b. On General Development. Lichens are very strongly influenced by abundance or by lack of
moisture. The contour of the large majority of species is concentric, but they become excentric
owing to a more vigorous development towards the side of damper exposure, hence the frequent
one-sided increase of monophyllous species such as Umbilicaria pustulata. Wainio[867] observed
that species of Cladonia growing in dry places, and exposed to full sunlight, showed a tendency
not to develop scyphi, the dry conditions hindering the full formation of the secondary thallus. As
an instance may be cited Cl. foliacea, in which the primary thallus is much the most abundantly
developed, its favourite habitat being the exposed sandy soil of sea-dunes.
Too great moisture is however harmful: Nienburg[868] has recorded his observations on
Sphyridium (Baeomyces rufus): on clay soil the thallus was pulverulent, while on stones or other
dryer substratum it was granular—warted or even somewhat squamulose.
Parmelia physodes rarely forms fruits, but when growing in an atmosphere constantly charged
with moisture[869], apothecia are more readily developed, and the same observation has been made
in connection with other usually barren lichens. It has been suggested that, in these lichens, the
abrupt change from moist to dry conditions may have a harmful effect on the developing
ascogonium.
The perithecia of Pyrenula nitida are smaller on smooth bark[870] such as that of Corylus,
Carpinus, etc., probably because the even surface does not retain water.
IV. ILLUMINATION OF LICHENS
A. Effect of Light on the Thallus
but it was very feeble and assimilation had almost entirely ceased. Somewhat similar results were
obtained with Ramalina farinacea and Usnea barbata.
In normal conditions of moisture, and with normal illumination, assimilation in lichens
predominates over respiration, more carbon dioxide being decomposed than is given forth; and
Jumelle has argued from that fact, that the alga is well able to secure from the atmosphere all the
carbon required for the nutrition of the whole plant. The intensity of assimilation, however, varies
enormously in different lichens and is generally more powerful in the larger forms than in the
crustaceous: the latter have often an extremely scanty thallus and they are also more in contact
with the substratum—rock, humus or wood—on which they may be partly saprophytic, thus
obtaining carbohydrates already formed, and demanding less from the alga.
An interesting comparison might be made with fungi in regard to which many records have
been taken as to their possible duration in a dry state, more especially on the viability of spores,
i.e. their persistent capacity of germination. A striking instance is reported by Weir[866] of the
regeneration of the sporophores of Polystictus sanguineus, a common fungus of warm countries.
The plant was collected in Brazil and sent to Munich. After about two years in the mycological
collection of the University, the branch on which it grew was exposed in the open among other
branches in a wood while snow still lay on the ground. In a short time the fungus revived and
before the end of spring not only had produced a new hymenium, but enlarged its hymenial
surface to about one-fourth of its original size and had also formed one entirely new, though small,
sporophore.
b. On General Development. Lichens are very strongly influenced by abundance or by lack of
moisture. The contour of the large majority of species is concentric, but they become excentric
owing to a more vigorous development towards the side of damper exposure, hence the frequent
one-sided increase of monophyllous species such as Umbilicaria pustulata. Wainio[867] observed
that species of Cladonia growing in dry places, and exposed to full sunlight, showed a tendency
not to develop scyphi, the dry conditions hindering the full formation of the secondary thallus. As
an instance may be cited Cl. foliacea, in which the primary thallus is much the most abundantly
developed, its favourite habitat being the exposed sandy soil of sea-dunes.
Too great moisture is however harmful: Nienburg[868] has recorded his observations on
Sphyridium (Baeomyces rufus): on clay soil the thallus was pulverulent, while on stones or other
dryer substratum it was granular—warted or even somewhat squamulose.
Parmelia physodes rarely forms fruits, but when growing in an atmosphere constantly charged
with moisture[869], apothecia are more readily developed, and the same observation has been made
in connection with other usually barren lichens. It has been suggested that, in these lichens, the
abrupt change from moist to dry conditions may have a harmful effect on the developing
ascogonium.
The perithecia of Pyrenula nitida are smaller on smooth bark[870] such as that of Corylus,
Carpinus, etc., probably because the even surface does not retain water.
IV. ILLUMINATION OF LICHENS
A. Effect of Light on the Thallus
Page 316
As fungi possess no chlorophyll, their vegetative body has little or no use for light and often
develops in partial or total darkness. In lichens the alga requires more or less direct illumination;
the lichen fungus, therefore, in response to that requirement has come out into the open: it is an
adaptation to the symbiotic life, though some lichens, such as those immersed in the substratum,
grow with very little light. Like other plants they are sensitive to changes of illumination: some
species are shade plants, while others are as truly sun plants, and others again are able to adapt
themselves to varying degrees of light.
Wiesner[871] made a series of exact observations on what he has termed the “light-use” of
various plants. He took as his standard of unity for the higher plants the amount of light required to
darken photographic paper in one second. When dealing with lichens he adopted a more arbitrary
standard, calculating as the unit the average amount of light that lichens would receive in entirely
unshaded positions. He does not take account of the strength or duration of the light, and the
conclusions he draws, though interesting and instructive, are only comparative.
a. Sun Lichens. The illumination of the Tundra lichens is reckoned by Wiesner as representing
his unit of standard illumination. In the same category as these are included many of our most
familiar lichens, which grow on rocks subject to the direct incidence of the sun’s rays, such as, for
instance, Parmelia conspersa, P. prolixa, etc. Physcia tenella (hispida) is also extremely
dependent on light, and was never found by Wiesner under 1/8 of full illumination.
Dermatocarpon miniatum, a rock lichen with a peltate foliose thallus, is at its best from 1/3 to 1/8
of illumination, but it grows well in situations where the light varies in amount from 1 to 1/24.
Psora (Lecidea) lurida, with dark-coloured crowded squamules, grows on calcareous soil among
rocks well exposed to the sun and has an illumination from 1 to 1/30, but with a poorer
development at the lower figure. Many crustaceous rock lichens are also by preference sun-plants
as, for instance, Verrucaria calciseda which grows immersed in calcareous rocks but with an
illumination of 1 to 1/3; in more shady situations, where the light had declined to 1/29, it was
found to be less luxuriant and less healthy.
Sun lichens continue to grow in the shade, but the thallus is then reduced and the plant is sterile.
Zukal has made a list of those which grow best with a light-use of 1 to 1/10, though they are also
found not unfrequently in habitats where the light cannot be more than 1/50. Among these light-
loving plants are the Northern Tundra species of Cladonia, Stereocaulon, Cetraria, Parmelia,
Umbilicaria, and Gyrophora, as also Xanthoria parietina, Placodium elegans, P. murorum, etc.,
with some crustaceous species such as Lecanora atra, Haematomma ventosum, Diploschistes
scruposus, many species of Lecideaceae, some Collemaceae and some Pyrenolichens.
Wiesner’s conclusion is that the need of light increases with the lowering of the temperature,
and that full illumination is of still more importance in the life of the plants when they grow in
cold regions and are deprived of warmth: sun lichens are, therefore, to be looked for in northern or
Alpine regions rather than in the tropics.
b. Colour-Changes due to Light. Lichens growing in full sunlight frequently take on a darker
hue. Cetraria islandica for instance in an open situation is darker than when growing in woods; C.
aculeata on bare sand-dunes is a deeper shade of brown than when growing entangled among
heath plants. Parmelia saxatilis when growing on exposed rocks is frequently a deep brown
colour, while on shaded trees it is normally a light bluish-grey.
An example of colour-change due directly to light influences is given by Bitter[872]. He noted
that the thallus of Parmelia obscurata on pine trees, and therefore subject only to diffuse light,
grew to a large size and was of a light greyish-green colour marked by lighter-coloured lines, the
develops in partial or total darkness. In lichens the alga requires more or less direct illumination;
the lichen fungus, therefore, in response to that requirement has come out into the open: it is an
adaptation to the symbiotic life, though some lichens, such as those immersed in the substratum,
grow with very little light. Like other plants they are sensitive to changes of illumination: some
species are shade plants, while others are as truly sun plants, and others again are able to adapt
themselves to varying degrees of light.
Wiesner[871] made a series of exact observations on what he has termed the “light-use” of
various plants. He took as his standard of unity for the higher plants the amount of light required to
darken photographic paper in one second. When dealing with lichens he adopted a more arbitrary
standard, calculating as the unit the average amount of light that lichens would receive in entirely
unshaded positions. He does not take account of the strength or duration of the light, and the
conclusions he draws, though interesting and instructive, are only comparative.
a. Sun Lichens. The illumination of the Tundra lichens is reckoned by Wiesner as representing
his unit of standard illumination. In the same category as these are included many of our most
familiar lichens, which grow on rocks subject to the direct incidence of the sun’s rays, such as, for
instance, Parmelia conspersa, P. prolixa, etc. Physcia tenella (hispida) is also extremely
dependent on light, and was never found by Wiesner under 1/8 of full illumination.
Dermatocarpon miniatum, a rock lichen with a peltate foliose thallus, is at its best from 1/3 to 1/8
of illumination, but it grows well in situations where the light varies in amount from 1 to 1/24.
Psora (Lecidea) lurida, with dark-coloured crowded squamules, grows on calcareous soil among
rocks well exposed to the sun and has an illumination from 1 to 1/30, but with a poorer
development at the lower figure. Many crustaceous rock lichens are also by preference sun-plants
as, for instance, Verrucaria calciseda which grows immersed in calcareous rocks but with an
illumination of 1 to 1/3; in more shady situations, where the light had declined to 1/29, it was
found to be less luxuriant and less healthy.
Sun lichens continue to grow in the shade, but the thallus is then reduced and the plant is sterile.
Zukal has made a list of those which grow best with a light-use of 1 to 1/10, though they are also
found not unfrequently in habitats where the light cannot be more than 1/50. Among these light-
loving plants are the Northern Tundra species of Cladonia, Stereocaulon, Cetraria, Parmelia,
Umbilicaria, and Gyrophora, as also Xanthoria parietina, Placodium elegans, P. murorum, etc.,
with some crustaceous species such as Lecanora atra, Haematomma ventosum, Diploschistes
scruposus, many species of Lecideaceae, some Collemaceae and some Pyrenolichens.
Wiesner’s conclusion is that the need of light increases with the lowering of the temperature,
and that full illumination is of still more importance in the life of the plants when they grow in
cold regions and are deprived of warmth: sun lichens are, therefore, to be looked for in northern or
Alpine regions rather than in the tropics.
b. Colour-Changes due to Light. Lichens growing in full sunlight frequently take on a darker
hue. Cetraria islandica for instance in an open situation is darker than when growing in woods; C.
aculeata on bare sand-dunes is a deeper shade of brown than when growing entangled among
heath plants. Parmelia saxatilis when growing on exposed rocks is frequently a deep brown
colour, while on shaded trees it is normally a light bluish-grey.
An example of colour-change due directly to light influences is given by Bitter[872]. He noted
that the thallus of Parmelia obscurata on pine trees, and therefore subject only to diffuse light,
grew to a large size and was of a light greyish-green colour marked by lighter-coloured lines, the
Page 317
more exposed lobes being always the most deeply tinted. In a less shaded habitat or in full sunlight
the lichen was distinguished by a much darker colour, and the lobes were seamed and marked by
blackish lines and spots. Bruce Fink[873] noted a similar development of dark lines on the thallus
of certain rock lichens growing in the desert, more especially on Parmelia conspersa, Acarospora
xanthophana and Lecanora muralis. He attributes a protective function to the dark colour and
observes that it seemingly spreads from centres of continued exposure, and is thus more abundant
in older parts of the thallus. He contrasts this colouration with the browning of the tips of the
fronds of fruticose lichens by which the delicate growing hyphae are protected from intense light.
Galløe[874] finds that protection against too strong illumination is afforded both by white and
dark colourations, the latter because the pigments catch the light rays, the former because it throws
them back. The white colour is also often due to interspaces filled with air which prevent the
penetration of the heat rays.
A deepening of colour due to light effect often visible on exposed rock lichens such as Parmelia
saxatilis is more pronounced still in Alpine and tropical species: the cortex becomes thicker and
more opaque through the cuticularizing and browning of the hyphal membranes, and the massing
of crystals on the lighted areas. The gonidial layer becomes, in consequence, more reduced, and
may disappear altogether. Zukal[875] found instances of this in species of Cladonia, Parmelia,
Roccella, etc. The thickened cortex acts also as a check to transpiration and is characteristic of
desert species exposed to strong light and a dry atmosphere.
Bitter[876] remarked the same difference of development in plants of Parmelia physodes: he
found that the better lighted had a thicker cortex, about 20-30 µ in depth, as compared with 15-22
µ or even only 12 µ in the greener shade-plants, and also that there was a greater deposit of acids
in the more highly illuminated cortices, thus giving rise to the deeper shades of colour.
Many lichens owe their bright tints to the presence of coloured lichen-acids, the production of
which is strongly influenced by light and by clear air. Xanthoria parietina becomes a brilliant
yellow in the sunlight: in the shade it assumes a grey-green hue and yields only small quantities of
parietin. Placodium elegans, normally a brightly coloured yellow lichen, becomes, in the strong
light of the high Alps, a deep orange-red. Rhizocarpon geographicum is a vivid citrine-yellow on
high mountains, but is almost green at lesser elevations.
c. Shade Lichens. Many species grow where the light is abundant though diffuse. Those on tree-
trunks rarely receive direct illumination and may be generally included among shade-plants.
Wiesner found that corticolous forms of Parmelia saxatilis grew best with an illumination between
1/8 and 1/17 of full light, and Pertusaria amara from 1/12 to 1/21; both of them could thrive from
1/3 to 1/56, but were never observed on trees in direct light. Physcia ciliaris, which inhabits the
trunks of old trees, is also a plant that prefers diffuse light. In warm tropical regions, lichens are
mostly shade-plants: Wiesner records an instance of a species found on the aerial roots of a tree
with an illumination of only 1/250.
In a study of subterranean plants, Maheu[877] takes note of the lichens that he found growing in
limestone caves, in hollows and clefts of the rocks, etc. A fair number grew well just within the
opening of the caves; but species such as Cl. cervicornis, Placodium murorum and Xanthoria
parietina ceased abruptly where the solar rays failed. Only a few individuals of one or two species
were found to remain normal in semi-darkness: Opegrapha hapalea and Verrucaria muralis were
found at the bottom of a cave with the thallus only slightly reduced. The nature of the substratum
in these cases must however also be taken into account, as well as the light influences: limestone
the lichen was distinguished by a much darker colour, and the lobes were seamed and marked by
blackish lines and spots. Bruce Fink[873] noted a similar development of dark lines on the thallus
of certain rock lichens growing in the desert, more especially on Parmelia conspersa, Acarospora
xanthophana and Lecanora muralis. He attributes a protective function to the dark colour and
observes that it seemingly spreads from centres of continued exposure, and is thus more abundant
in older parts of the thallus. He contrasts this colouration with the browning of the tips of the
fronds of fruticose lichens by which the delicate growing hyphae are protected from intense light.
Galløe[874] finds that protection against too strong illumination is afforded both by white and
dark colourations, the latter because the pigments catch the light rays, the former because it throws
them back. The white colour is also often due to interspaces filled with air which prevent the
penetration of the heat rays.
A deepening of colour due to light effect often visible on exposed rock lichens such as Parmelia
saxatilis is more pronounced still in Alpine and tropical species: the cortex becomes thicker and
more opaque through the cuticularizing and browning of the hyphal membranes, and the massing
of crystals on the lighted areas. The gonidial layer becomes, in consequence, more reduced, and
may disappear altogether. Zukal[875] found instances of this in species of Cladonia, Parmelia,
Roccella, etc. The thickened cortex acts also as a check to transpiration and is characteristic of
desert species exposed to strong light and a dry atmosphere.
Bitter[876] remarked the same difference of development in plants of Parmelia physodes: he
found that the better lighted had a thicker cortex, about 20-30 µ in depth, as compared with 15-22
µ or even only 12 µ in the greener shade-plants, and also that there was a greater deposit of acids
in the more highly illuminated cortices, thus giving rise to the deeper shades of colour.
Many lichens owe their bright tints to the presence of coloured lichen-acids, the production of
which is strongly influenced by light and by clear air. Xanthoria parietina becomes a brilliant
yellow in the sunlight: in the shade it assumes a grey-green hue and yields only small quantities of
parietin. Placodium elegans, normally a brightly coloured yellow lichen, becomes, in the strong
light of the high Alps, a deep orange-red. Rhizocarpon geographicum is a vivid citrine-yellow on
high mountains, but is almost green at lesser elevations.
c. Shade Lichens. Many species grow where the light is abundant though diffuse. Those on tree-
trunks rarely receive direct illumination and may be generally included among shade-plants.
Wiesner found that corticolous forms of Parmelia saxatilis grew best with an illumination between
1/8 and 1/17 of full light, and Pertusaria amara from 1/12 to 1/21; both of them could thrive from
1/3 to 1/56, but were never observed on trees in direct light. Physcia ciliaris, which inhabits the
trunks of old trees, is also a plant that prefers diffuse light. In warm tropical regions, lichens are
mostly shade-plants: Wiesner records an instance of a species found on the aerial roots of a tree
with an illumination of only 1/250.
In a study of subterranean plants, Maheu[877] takes note of the lichens that he found growing in
limestone caves, in hollows and clefts of the rocks, etc. A fair number grew well just within the
opening of the caves; but species such as Cl. cervicornis, Placodium murorum and Xanthoria
parietina ceased abruptly where the solar rays failed. Only a few individuals of one or two species
were found to remain normal in semi-darkness: Opegrapha hapalea and Verrucaria muralis were
found at the bottom of a cave with the thallus only slightly reduced. The nature of the substratum
in these cases must however also be taken into account, as well as the light influences: limestone
Page 318
for instance is a more favourable habitat than gypsum; the latter, being more readily soluble,
provides a less permanent support.
Maheu has recorded observations on growth in its relation to light in the case of a number of
lichens growing in caves.
Physcia obscura grew in almost total darkness; Placodium murorum within the cave had lost
nearly all colour; Placodium variabile var. deep within the cave, sterile; Opegrapha endoleuca in
partial obscurity; Verrucaria rupestris f. in total obscurity, the thallus much reduced and sterile;
Verrucaria rupestris in partial obscurity, the asci empty; Homodium (Collema) granuliferum in the
inmost recess of the cave, sterile, and the hyphae more spongy than in the open.
Siliceous rocks in darkness were still more barren, but a few odd lichens were collected from
sandstone in various caves: Cladonia squamosa, Parmelia perlata var. ciliata, Diploschistes
scruposus, Lecidea grisella, Collema nigrescens and Leptogium lacerum.
d. Varying Shade Conditions. It has been frequently observed that on the trees of open park
lands lichens are more abundant on the side of the trunk that faces the prevailing winds.
Wiesner[878] remarks that spores and soredia would more naturally be conveyed to that side; but
there are other factors that would come into play: the tree and the branches frequently lean away
from the wind, giving more light and also an inclined surface that would retain water for a longer
period on the windward side[879]. Spores and soredia would also develop more readily in those
favourable conditions.
In forests there are other and different conditions: on the outskirts, whether northern or
southern, the plants requiring more light are to be found on the side of the trunk towards the
outside; in the depths of the forest, light may be reduced from 1/200 to 1/300, and any lichens
present tend to become mere leprose crusts. Krempelhuber[880] has recorded among his Bavarian
lichens those species that he found constantly growing in the shade: they are in general species of
Collemaceae and Caliciaceae, several species of Peltigera (P. venosa, P. horizontalis and P.
polydactyla); Solorina saccata; Gyalecta Flotovii, G. cupularis; Pannaria microphylla, P.
triptophylla, P. brunnea; Icmadophila aeruginosa, etc.
B. Effect on Reproductive Organs
In the higher plants, it is recognized that a certain light-intensity is necessary for the production
of flowers and fruit. In the lower plants, such as lichens, light is also necessary for reproduction; it
is a common observation that well-lighted individuals are the most abundantly fruited. In the
higher fungi also, the fruiting body is more or less formed in the light.
a. Position and Orientation of Fruits with regard to Light. There is an optimum of light for
the fruits as well as for the thallus in each species of lichen: in most cases it is the fullest light that
can be secured.
Zukal[881] finds an exception to that rule in species of Peltigera: when exposed to strong
sunlight, the lobes, fertile at the tips, curve over so that to some extent the back of the apothecium
is turned to the light; with diffuse light, the horizontal position is retained and the apothecia face
upwards. In the closely allied genera Nephroma, Nephromium and Nephromopsis, the apothecia
are produced on the back of the lobe at the extreme tip, but as they approach maturity the fertile
lobes turn right back and they become exposed to direct illumination. In a well-developed
specimen the full-grown fruits may thus become so prominent all over the thallus, that it is
provides a less permanent support.
Maheu has recorded observations on growth in its relation to light in the case of a number of
lichens growing in caves.
Physcia obscura grew in almost total darkness; Placodium murorum within the cave had lost
nearly all colour; Placodium variabile var. deep within the cave, sterile; Opegrapha endoleuca in
partial obscurity; Verrucaria rupestris f. in total obscurity, the thallus much reduced and sterile;
Verrucaria rupestris in partial obscurity, the asci empty; Homodium (Collema) granuliferum in the
inmost recess of the cave, sterile, and the hyphae more spongy than in the open.
Siliceous rocks in darkness were still more barren, but a few odd lichens were collected from
sandstone in various caves: Cladonia squamosa, Parmelia perlata var. ciliata, Diploschistes
scruposus, Lecidea grisella, Collema nigrescens and Leptogium lacerum.
d. Varying Shade Conditions. It has been frequently observed that on the trees of open park
lands lichens are more abundant on the side of the trunk that faces the prevailing winds.
Wiesner[878] remarks that spores and soredia would more naturally be conveyed to that side; but
there are other factors that would come into play: the tree and the branches frequently lean away
from the wind, giving more light and also an inclined surface that would retain water for a longer
period on the windward side[879]. Spores and soredia would also develop more readily in those
favourable conditions.
In forests there are other and different conditions: on the outskirts, whether northern or
southern, the plants requiring more light are to be found on the side of the trunk towards the
outside; in the depths of the forest, light may be reduced from 1/200 to 1/300, and any lichens
present tend to become mere leprose crusts. Krempelhuber[880] has recorded among his Bavarian
lichens those species that he found constantly growing in the shade: they are in general species of
Collemaceae and Caliciaceae, several species of Peltigera (P. venosa, P. horizontalis and P.
polydactyla); Solorina saccata; Gyalecta Flotovii, G. cupularis; Pannaria microphylla, P.
triptophylla, P. brunnea; Icmadophila aeruginosa, etc.
B. Effect on Reproductive Organs
In the higher plants, it is recognized that a certain light-intensity is necessary for the production
of flowers and fruit. In the lower plants, such as lichens, light is also necessary for reproduction; it
is a common observation that well-lighted individuals are the most abundantly fruited. In the
higher fungi also, the fruiting body is more or less formed in the light.
a. Position and Orientation of Fruits with regard to Light. There is an optimum of light for
the fruits as well as for the thallus in each species of lichen: in most cases it is the fullest light that
can be secured.
Zukal[881] finds an exception to that rule in species of Peltigera: when exposed to strong
sunlight, the lobes, fertile at the tips, curve over so that to some extent the back of the apothecium
is turned to the light; with diffuse light, the horizontal position is retained and the apothecia face
upwards. In the closely allied genera Nephroma, Nephromium and Nephromopsis, the apothecia
are produced on the back of the lobe at the extreme tip, but as they approach maturity the fertile
lobes turn right back and they become exposed to direct illumination. In a well-developed
specimen the full-grown fruits may thus become so prominent all over the thallus, that it is
Page 319
difficult to realize they are on reversed lobes. In one species of Cetraria (C. cucullata) the rarely
formed apothecia are adnate to the back of the lobe; but in that case the margins of the strap-
shaped fronds are incurved and connivent, and the back is more exposed than the front.
In Ramalina the frond frequently turns at a sharp angle at the point of insertion of the
apothecium which is thus well exposed and prominent; but Zukal[882] sees in this formation an
adaptation to enable the frond to avoid the shade cast by the apothecium which may exceed it in
width. In most lichens, however, and especially in shade or semi-shade species, the reproductive
organs are to be found in the best-lighted positions.
b. Influence of Light on Colour of Fruits. Lichen-acids are secreted freely in the apothecium
from the tips of the paraphyses which give the colour to the disc, and as acid-formation is
furthered by the sun’s rays, the well-lighted fruits are always deeper in hue. The most familiar
examples are the bright-yellow species that are rich in chrysophanic acid (parietin). Hedlund[883]
has recorded several instances of varying colour in species of Micarea (Biatorina, etc.) in which
very dark apothecia became paler in the shade. He also cites the case of two crustaceous species,
Lecidea helvola and L. sulphurella, which have white apothecia in the shade, but are darker in
colour when strongly lighted.
V. COLOUR OF LICHENS
The thalli of many lichens, more especially of those associated with blue-green gonidia, are
hygroscopic, and it frequently happens that any addition of moisture affects the colour by causing
the gelatinous cell-walls to swell, thus rendering the tissues more transparent and the green colour
of the gonidia more evident. As a general rule it is the dry state of the plant that is referred to in
any discussion of colour.
In the large majority of species the colouring is of a subdued tone—soft bluish-grey or ash-grey
predominating. There are, however, striking exceptions, and brilliant yellow and white thalli
frequently form a conspicuous feature of vegetation. Black lichens are rare, but occasionally the
very dark brown of foliaceous species such as Gyrophora or of crustaceous species such as
Verrucaria maura or Buellia atrata deepens to the more sombre hue.
A. Origin of Lichen-Colouring
The colours of lichens may be traced to several different causes.
a. Colour given by the Algal Constituent. As examples may be cited most of the gelatinous
lichens, Ephebaceae, Collemaceae, etc. which owe, as in Collema, their dark olivaceous-green
appearance, when somewhat moist, to the enclosed dark-green gonidia, and their black colour,
when dry, to the loss of transparency. When the thallus is of a thin texture as in Collema
nigrescens, the olivaceous hue may remain constant. Leptogium Burgessii, another thin plant of
the same family, is frequently of a purplish hue owing to the purple colour of the gonidial Nostoc
cells. The dull-grey crustaceous thallus of the Pannariaceae becomes more or less blue-green when
moistened, and the same change has been observed in the Hymenolichens, Cora, etc.
In Coenogonium, the alga is some species of Trentepohlia, a filamentous genus mostly yellow,
which often gives its colour to the slender lichen filaments, the covering hyphae being very scanty.
Other filamentous species, such as Usnea barbata, etc., are persistently greenish from the bright-
green Protococcaceous cells lying near the surface of the thalline strands. Many of the
formed apothecia are adnate to the back of the lobe; but in that case the margins of the strap-
shaped fronds are incurved and connivent, and the back is more exposed than the front.
In Ramalina the frond frequently turns at a sharp angle at the point of insertion of the
apothecium which is thus well exposed and prominent; but Zukal[882] sees in this formation an
adaptation to enable the frond to avoid the shade cast by the apothecium which may exceed it in
width. In most lichens, however, and especially in shade or semi-shade species, the reproductive
organs are to be found in the best-lighted positions.
b. Influence of Light on Colour of Fruits. Lichen-acids are secreted freely in the apothecium
from the tips of the paraphyses which give the colour to the disc, and as acid-formation is
furthered by the sun’s rays, the well-lighted fruits are always deeper in hue. The most familiar
examples are the bright-yellow species that are rich in chrysophanic acid (parietin). Hedlund[883]
has recorded several instances of varying colour in species of Micarea (Biatorina, etc.) in which
very dark apothecia became paler in the shade. He also cites the case of two crustaceous species,
Lecidea helvola and L. sulphurella, which have white apothecia in the shade, but are darker in
colour when strongly lighted.
V. COLOUR OF LICHENS
The thalli of many lichens, more especially of those associated with blue-green gonidia, are
hygroscopic, and it frequently happens that any addition of moisture affects the colour by causing
the gelatinous cell-walls to swell, thus rendering the tissues more transparent and the green colour
of the gonidia more evident. As a general rule it is the dry state of the plant that is referred to in
any discussion of colour.
In the large majority of species the colouring is of a subdued tone—soft bluish-grey or ash-grey
predominating. There are, however, striking exceptions, and brilliant yellow and white thalli
frequently form a conspicuous feature of vegetation. Black lichens are rare, but occasionally the
very dark brown of foliaceous species such as Gyrophora or of crustaceous species such as
Verrucaria maura or Buellia atrata deepens to the more sombre hue.
A. Origin of Lichen-Colouring
The colours of lichens may be traced to several different causes.
a. Colour given by the Algal Constituent. As examples may be cited most of the gelatinous
lichens, Ephebaceae, Collemaceae, etc. which owe, as in Collema, their dark olivaceous-green
appearance, when somewhat moist, to the enclosed dark-green gonidia, and their black colour,
when dry, to the loss of transparency. When the thallus is of a thin texture as in Collema
nigrescens, the olivaceous hue may remain constant. Leptogium Burgessii, another thin plant of
the same family, is frequently of a purplish hue owing to the purple colour of the gonidial Nostoc
cells. The dull-grey crustaceous thallus of the Pannariaceae becomes more or less blue-green when
moistened, and the same change has been observed in the Hymenolichens, Cora, etc.
In Coenogonium, the alga is some species of Trentepohlia, a filamentous genus mostly yellow,
which often gives its colour to the slender lichen filaments, the covering hyphae being very scanty.
Other filamentous species, such as Usnea barbata, etc., are persistently greenish from the bright-
green Protococcaceous cells lying near the surface of the thalline strands. Many of the
Page 320
furfuraceous lichens are greenish from the same cause, especially when moist, as are also the
larger lichens, Physcia ciliaris, Stereocaulons, Cladonias and others.
b. Colour due to Lichen-Acids. These substances, so characteristic of lichens, are excreted
from the hyphae, and lie in crystals on the outer walls; they are generally most plentiful on
exposed tissues such as the cortex of the upper surface or the discs of the apothecia. Many of these
crystals are colourless and are without visible effect, except in sometimes whitening the surface,
strikingly exemplified in Thamnolia vermicularis[884]; but others are very brightly coloured. These
latter belong to two chemical groups and are found in widely separated lichens[885]:
1. Derivatives of pulvinic acid which are usually of a bright-yellow colour. They are the
colouring substance of Letharia vulpina, a northern species, not found in our islands, of Cetraria
pinastri and C. juniperina[886] which inhabit mountainous or hilly regions. The crustaceous
species, Lecidea lucida and Rhizocarpon geographicum, owe their colour to rhizocarpic acid.
The brilliant yellow of the crusts of some species of Caliciaceae is due to the presence of the
substance calycin, while coniocybic acid gives the greenish sulphur-yellow hue to Coniocybe
furfuracea. Epanorin colours the hyphae and soredia of Lecanora epanora a citrine-yellow and
stictaurin is the deep-yellow substance found in the medulla and under surface of Sticta aurata and
S. crocata.
2. The second series of yellow acids are derivatives of anthracene. They include parietin,
formerly described as chrysophanic acid, which gives the conspicuous colour to Xanthoriae and to
various wall lichens; solorinic acid, the crystals of which cover the medullary hyphae and give a
reddish-grey tone to the upper cortex of Solorina crocea, and nephromin which similarly colours
the medulla of Nephromium lusitanicum a deep yellow, the colour of the general thallus being,
however, scarcely affected. In this group must also be included the acids that cause the yellow
colouring of the medulla in Parmelia subaurifera and the yellowish thallus of some Pertusariae.
In many cases, changes in the normal colouring[887] are caused by the breaking up of the acids
on contact with atmospheric or soil ammonia. Alkaline salts are thus formed which may be
oxidized by the oxygen in the air to yellow, red, brown, violet-brown or even to entirely black
humus-like products which are insoluble in water. These latter substances are frequently to be
found at the base of shrubby lichens or on the under surface of leafy forms that are closely
appressed to the substratum.
c. Colour due to Amorphous Substances. These are the various pigments which are deposited
in the cell-walls of the hyphae. The only instance, so far as is known, of colours within the cell
occurs in Baeomyces roseus, in which species the apothecia owe their rose-colour to oil-drops in
the cells of the paraphyses, and in Lecidea coarctata where the spores are rose-coloured when
young. In a few instances the colouring matter is excreted (Arthonia gregaria and Diploschistes
ocellatus); but Bachmann[888], who has made an extended study of this subject and has examined
120 widely diversified lichens, found that with few exceptions the pigment was in the membranes.
Bachmann was unable to determine whether the pigments were laid down by the protoplasm or
were due to changes in the cell-wall. The middle layer, he found, was generally more deeply
coloured than the inner one, though that was not universal. In other cases the outer sheath was the
darkest, especially in cortices one to two cells thick such as those of Parmelia olivacea, P.
fuliginosa and P. revoluta, and in the brown thick-walled spores of Physcia stellaris and of
Rhizocarpon geographicum. Still another variation occurs in Parmelia tristis in which the dark
cortical cells show an outer colourless membrane over the inner dark wall.
larger lichens, Physcia ciliaris, Stereocaulons, Cladonias and others.
b. Colour due to Lichen-Acids. These substances, so characteristic of lichens, are excreted
from the hyphae, and lie in crystals on the outer walls; they are generally most plentiful on
exposed tissues such as the cortex of the upper surface or the discs of the apothecia. Many of these
crystals are colourless and are without visible effect, except in sometimes whitening the surface,
strikingly exemplified in Thamnolia vermicularis[884]; but others are very brightly coloured. These
latter belong to two chemical groups and are found in widely separated lichens[885]:
1. Derivatives of pulvinic acid which are usually of a bright-yellow colour. They are the
colouring substance of Letharia vulpina, a northern species, not found in our islands, of Cetraria
pinastri and C. juniperina[886] which inhabit mountainous or hilly regions. The crustaceous
species, Lecidea lucida and Rhizocarpon geographicum, owe their colour to rhizocarpic acid.
The brilliant yellow of the crusts of some species of Caliciaceae is due to the presence of the
substance calycin, while coniocybic acid gives the greenish sulphur-yellow hue to Coniocybe
furfuracea. Epanorin colours the hyphae and soredia of Lecanora epanora a citrine-yellow and
stictaurin is the deep-yellow substance found in the medulla and under surface of Sticta aurata and
S. crocata.
2. The second series of yellow acids are derivatives of anthracene. They include parietin,
formerly described as chrysophanic acid, which gives the conspicuous colour to Xanthoriae and to
various wall lichens; solorinic acid, the crystals of which cover the medullary hyphae and give a
reddish-grey tone to the upper cortex of Solorina crocea, and nephromin which similarly colours
the medulla of Nephromium lusitanicum a deep yellow, the colour of the general thallus being,
however, scarcely affected. In this group must also be included the acids that cause the yellow
colouring of the medulla in Parmelia subaurifera and the yellowish thallus of some Pertusariae.
In many cases, changes in the normal colouring[887] are caused by the breaking up of the acids
on contact with atmospheric or soil ammonia. Alkaline salts are thus formed which may be
oxidized by the oxygen in the air to yellow, red, brown, violet-brown or even to entirely black
humus-like products which are insoluble in water. These latter substances are frequently to be
found at the base of shrubby lichens or on the under surface of leafy forms that are closely
appressed to the substratum.
c. Colour due to Amorphous Substances. These are the various pigments which are deposited
in the cell-walls of the hyphae. The only instance, so far as is known, of colours within the cell
occurs in Baeomyces roseus, in which species the apothecia owe their rose-colour to oil-drops in
the cells of the paraphyses, and in Lecidea coarctata where the spores are rose-coloured when
young. In a few instances the colouring matter is excreted (Arthonia gregaria and Diploschistes
ocellatus); but Bachmann[888], who has made an extended study of this subject and has examined
120 widely diversified lichens, found that with few exceptions the pigment was in the membranes.
Bachmann was unable to determine whether the pigments were laid down by the protoplasm or
were due to changes in the cell-wall. The middle layer, he found, was generally more deeply
coloured than the inner one, though that was not universal. In other cases the outer sheath was the
darkest, especially in cortices one to two cells thick such as those of Parmelia olivacea, P.
fuliginosa and P. revoluta, and in the brown thick-walled spores of Physcia stellaris and of
Rhizocarpon geographicum. Still another variation occurs in Parmelia tristis in which the dark
cortical cells show an outer colourless membrane over the inner dark wall.
Page 321
The coloured pigments are mainly to be found in the superficial tissues, but if the thallus is split
by areolation, as in crustaceous lichens, the internal hyphae may be coloured like those of the
outer cortex wherever they are exposed. The hyphae of the gonidial layer are persistently
colourless, but the lower surface and the rhizoids of many foliose lichens are frequently very
deeply stained, as are the hypothalli of crustaceous species.
The fruiting bodies in many different families of lichens have dark coloured discs owing to the
abundance of dark-brown pigment in the paraphyses. In these the walls, as determined by
Bachmann, are composed generally of an inner wall, a second outer wall, and the outermost sheath
which forms the middle lamella between adjacent cells. In some species the second wall is
pigmented, in others the middle lamella is the one deeply coloured. The hymenium of many
apothecia and the hyphae forming the amphithecium are often deeply impregnated with colour.
The wall hyphae of the pycnidia are also coloured in some forms; more frequently the cells round
the opening pore are more or less brown.
The presence of these coloured substances enables the cell-wall to resist chemical reactions
induced by the harmful influences of the atmosphere or of the substratum. The darker the cell-wall
and the more abundant the pigment, the less easily is the plant injured either by acids or alkalies.
The coloured tips of the paraphyses thus give much needed protection to the long lived sporiferous
asci, and the dark thalline tissues prevent premature rotting and decay.
d. Enumeration of Amorphous Pigments:
1. Green. Bachmann found several different green pigments: “Lecidea-green,” colouring red
with nitric acid, is the dark blue-green or olive-green (smaragdine) of the paraphyses of many
apothecia in the Lecideaceae, and may vary to a lighter blue; it appears almost black in thalline
cells[889]. “Aspicilia-green” occurs in the thalline margin and sometimes in the epithecium of the
fruits of species of Aspicilia; it becomes a brighter green on the application of nitric acid.
“Bacidia-green,” also a rare pigment, becomes violet with the same acid; it is found in the
epithecium of Bacidia muscorum and Bacidia acclinis (Lecideaceae). “Thalloidima-green” in the
apothecia of some species of Biatorina is changed to a dirty-red by nitric acid and to violet by
potash. Still another termed “rhizoid-green” gives the dark greenish colour to the rhizoids of
Physcia pulverulenta and P. aipolia and to the spores of some species of Physcia and Rhizocarpon.
It becomes more olive-green with potash.
2. Blue. A very rare colour in lichens, so far found in only a few species, Biatora (Lecidea)
atrofusca, Lecidea sanguinaria and Aspicilia flavida f. coerulescens. It forms a layer of
amorphous granules embedded in the outer wall of the paraphyses, becoming more dense towards
the epithecium. A few granules are also present in the hymenium.
3. Violet. “Arthonia-violet” as it is called by Bachmann is a constituent of the tissues of
Arthonia gregaria, occurring in minute masses always near the cortical cells; it is distinct from the
bright cinnabarine granules present in every part of the thallus.
4. Red. Several different kinds of red have been distinguished: “Urceolaria-red,” visible as an
interrupted layer on the upper side of the medulla in the thallus of Diploschistes ocellatus, a
continental species with a massive, crustaceous, whitish thallus that shows a faint rose tinge when
wetted. “Phialopsis-red” is confined to the epithecium of the brightly coloured apothecia of
Phialopsis rubra. “Lecanora-red,” by which Bachmann designates the purplish colour of the
hymenium, is an unfailing character of Lecanora atra; the colouring substance is lodged in the
middle lamella of the paraphysis cells; it occurs also in Rhizocarpon geographicum and in Rh.
viridiatrum; it becomes more deeply violet with potash. M. C. Knowles[890] noted the blue
by areolation, as in crustaceous lichens, the internal hyphae may be coloured like those of the
outer cortex wherever they are exposed. The hyphae of the gonidial layer are persistently
colourless, but the lower surface and the rhizoids of many foliose lichens are frequently very
deeply stained, as are the hypothalli of crustaceous species.
The fruiting bodies in many different families of lichens have dark coloured discs owing to the
abundance of dark-brown pigment in the paraphyses. In these the walls, as determined by
Bachmann, are composed generally of an inner wall, a second outer wall, and the outermost sheath
which forms the middle lamella between adjacent cells. In some species the second wall is
pigmented, in others the middle lamella is the one deeply coloured. The hymenium of many
apothecia and the hyphae forming the amphithecium are often deeply impregnated with colour.
The wall hyphae of the pycnidia are also coloured in some forms; more frequently the cells round
the opening pore are more or less brown.
The presence of these coloured substances enables the cell-wall to resist chemical reactions
induced by the harmful influences of the atmosphere or of the substratum. The darker the cell-wall
and the more abundant the pigment, the less easily is the plant injured either by acids or alkalies.
The coloured tips of the paraphyses thus give much needed protection to the long lived sporiferous
asci, and the dark thalline tissues prevent premature rotting and decay.
d. Enumeration of Amorphous Pigments:
1. Green. Bachmann found several different green pigments: “Lecidea-green,” colouring red
with nitric acid, is the dark blue-green or olive-green (smaragdine) of the paraphyses of many
apothecia in the Lecideaceae, and may vary to a lighter blue; it appears almost black in thalline
cells[889]. “Aspicilia-green” occurs in the thalline margin and sometimes in the epithecium of the
fruits of species of Aspicilia; it becomes a brighter green on the application of nitric acid.
“Bacidia-green,” also a rare pigment, becomes violet with the same acid; it is found in the
epithecium of Bacidia muscorum and Bacidia acclinis (Lecideaceae). “Thalloidima-green” in the
apothecia of some species of Biatorina is changed to a dirty-red by nitric acid and to violet by
potash. Still another termed “rhizoid-green” gives the dark greenish colour to the rhizoids of
Physcia pulverulenta and P. aipolia and to the spores of some species of Physcia and Rhizocarpon.
It becomes more olive-green with potash.
2. Blue. A very rare colour in lichens, so far found in only a few species, Biatora (Lecidea)
atrofusca, Lecidea sanguinaria and Aspicilia flavida f. coerulescens. It forms a layer of
amorphous granules embedded in the outer wall of the paraphyses, becoming more dense towards
the epithecium. A few granules are also present in the hymenium.
3. Violet. “Arthonia-violet” as it is called by Bachmann is a constituent of the tissues of
Arthonia gregaria, occurring in minute masses always near the cortical cells; it is distinct from the
bright cinnabarine granules present in every part of the thallus.
4. Red. Several different kinds of red have been distinguished: “Urceolaria-red,” visible as an
interrupted layer on the upper side of the medulla in the thallus of Diploschistes ocellatus, a
continental species with a massive, crustaceous, whitish thallus that shows a faint rose tinge when
wetted. “Phialopsis-red” is confined to the epithecium of the brightly coloured apothecia of
Phialopsis rubra. “Lecanora-red,” by which Bachmann designates the purplish colour of the
hymenium, is an unfailing character of Lecanora atra; the colouring substance is lodged in the
middle lamella of the paraphysis cells; it occurs also in Rhizocarpon geographicum and in Rh.
viridiatrum; it becomes more deeply violet with potash. M. C. Knowles[890] noted the blue
Page 322
colouring of Rh. geographicum growing in W. Ireland near the sea and she ascribed it to an
alkaline reaction. Two more rare pigments, “Sagedia-red” and “Verrucaria-red,” are found in
species of Verrucariaceae. These tinge the calcareous rocks in which the lichens are embedded a
beautiful rose-pink. They are scarcely represented in our country.
5. Brown. A frequent colouring substance, but also presenting several different kinds of pigment
which may be arranged in two groups:
(1) Substances with some characteristic chemical reaction. These are of somewhat rare
occurrence: “Bacidia-brown” in the middle lamella of the paraphyses of Bacidia fuscorubella
stains a clear yellow with acids or a violet colour with potash; “Sphaeromphale-brown,” which
occurs in the perithecia and in the cortex of Staurothele clopismoides, becomes deep olive-green
with potash, changing to yellow-brown on the application of sulphuric acid; “Segestria-brown” in
Porina lectissima changes to a beautiful violet colour with sulphuric acid, while “Glomellifera-
brown,” which is confined to the outer cortical cells of the upper surface of Parmelia glomellifera,
becomes blue with nitric and sulphuric acids, but gives no reaction with potash. Rosendahl[891]
confirmed Bachmann’s discovery of this colour and further located it in corresponding cells of
Parmelia prolixa and P. locarensis.
(2) Substances with little or no chemical reaction. There is only one such to be noted:
“Parmelia-brown,” usually a very dark pigment, which is lodged in the outer membranes of the
cells. It becomes a clearer colour with nitric acid, and if the reagent be sufficiently concentrated,
some of the pigment is dissolved out. Some tissues, such as the lower cortex of some Parmeliae,
may be so impregnated and hardened, that nothing short of boiling acid has any effect on the cells;
membranes less deeply coloured and changed, such as the cortex of the Gyrophorae, become
disintegrated with such drastic treatment. With potash the colour becomes darker, changing from a
clear brown to olivaceous-brown or-green, or in some cases, as in a more faintly coloured
epithecium, to a dirty-yellow, but the lighter colour produced there is largely due to the swelling
up of the underlying tissues to which the potash penetrates readily between the paraphyses.
“Parmelia-brown” is a colouring substance present in the dark epithecium and hypothecium of
the fruits of many widely diverse lichens, and in the cortical cells and rhizoids of many thalli. In
some plants the thallus is brown both above and below, in others, as in Parmelia revoluta, etc.
only the under surface is dark-coloured.
e. Colour due to Infiltration. There are several crustaceous lichens that are rusty-red, the
colour being due to the presence of iron. These lichens occur on siliceous rocks of gneiss, granite,
etc., and more especially on rocks rich in iron. Iron as a constituent of lichens was first
demonstrated by John[892] in Ramalina fraxinea and R. calicaris. Grimbel[893] proved that the
colour of rust lichens was due to an iron salt, and Molisch[894] by microscopic examination located
minute granules of ferrous oxide as incrustations on the hyphae of the upper surface of the thallus.
Molisch held that the rhizoids or penetrating hyphae dissolved the iron from the rocks by acid
secretions. Rust lichens however grow on rocks that are frequently under water in which the iron is
already present.
Among “rusty” lichens are the British forms, Lecanora lacustris, the thallus of which is
normally white, though generally more or less tinged with iron; it inhabits rocks liable to
inundation. L. Dicksonii owes its ferruginous colour to the same influences. Lecidea contigua var.
flavicunda and L. confluens f. oxydata are rusty conditions of whitish-grey lichens.
alkaline reaction. Two more rare pigments, “Sagedia-red” and “Verrucaria-red,” are found in
species of Verrucariaceae. These tinge the calcareous rocks in which the lichens are embedded a
beautiful rose-pink. They are scarcely represented in our country.
5. Brown. A frequent colouring substance, but also presenting several different kinds of pigment
which may be arranged in two groups:
(1) Substances with some characteristic chemical reaction. These are of somewhat rare
occurrence: “Bacidia-brown” in the middle lamella of the paraphyses of Bacidia fuscorubella
stains a clear yellow with acids or a violet colour with potash; “Sphaeromphale-brown,” which
occurs in the perithecia and in the cortex of Staurothele clopismoides, becomes deep olive-green
with potash, changing to yellow-brown on the application of sulphuric acid; “Segestria-brown” in
Porina lectissima changes to a beautiful violet colour with sulphuric acid, while “Glomellifera-
brown,” which is confined to the outer cortical cells of the upper surface of Parmelia glomellifera,
becomes blue with nitric and sulphuric acids, but gives no reaction with potash. Rosendahl[891]
confirmed Bachmann’s discovery of this colour and further located it in corresponding cells of
Parmelia prolixa and P. locarensis.
(2) Substances with little or no chemical reaction. There is only one such to be noted:
“Parmelia-brown,” usually a very dark pigment, which is lodged in the outer membranes of the
cells. It becomes a clearer colour with nitric acid, and if the reagent be sufficiently concentrated,
some of the pigment is dissolved out. Some tissues, such as the lower cortex of some Parmeliae,
may be so impregnated and hardened, that nothing short of boiling acid has any effect on the cells;
membranes less deeply coloured and changed, such as the cortex of the Gyrophorae, become
disintegrated with such drastic treatment. With potash the colour becomes darker, changing from a
clear brown to olivaceous-brown or-green, or in some cases, as in a more faintly coloured
epithecium, to a dirty-yellow, but the lighter colour produced there is largely due to the swelling
up of the underlying tissues to which the potash penetrates readily between the paraphyses.
“Parmelia-brown” is a colouring substance present in the dark epithecium and hypothecium of
the fruits of many widely diverse lichens, and in the cortical cells and rhizoids of many thalli. In
some plants the thallus is brown both above and below, in others, as in Parmelia revoluta, etc.
only the under surface is dark-coloured.
e. Colour due to Infiltration. There are several crustaceous lichens that are rusty-red, the
colour being due to the presence of iron. These lichens occur on siliceous rocks of gneiss, granite,
etc., and more especially on rocks rich in iron. Iron as a constituent of lichens was first
demonstrated by John[892] in Ramalina fraxinea and R. calicaris. Grimbel[893] proved that the
colour of rust lichens was due to an iron salt, and Molisch[894] by microscopic examination located
minute granules of ferrous oxide as incrustations on the hyphae of the upper surface of the thallus.
Molisch held that the rhizoids or penetrating hyphae dissolved the iron from the rocks by acid
secretions. Rust lichens however grow on rocks that are frequently under water in which the iron is
already present.
Among “rusty” lichens are the British forms, Lecanora lacustris, the thallus of which is
normally white, though generally more or less tinged with iron; it inhabits rocks liable to
inundation. L. Dicksonii owes its ferruginous colour to the same influences. Lecidea contigua var.
flavicunda and L. confluens f. oxydata are rusty conditions of whitish-grey lichens.
Page 323
Nilson[895] found rusty lichens occurring frequently in the Sarak-Gebirge, more especially on
glacier moraines where they were liable, even when uncovered by snow, to be flooded by water
from the higher reaches. It is the thallus that is affected by the iron, rarely if ever are apothecia
altered in colour.
Bachmann’s Pigment Reactions
Name of
Special
Pigment or Colour KOH NH₃ Ba(OH)₂ HNO₃ H₂SO₄
Reactions
Lichen
copper or KOH then
Lecidea-green green
brick-red HCl: blue
HNO₃:
Aspicilia-green green brighter
green
Bacidia-green green violet violet HCl: violet
HCl:
Thalloidima- indistinctly
green violet indistinctly
green purple-red
purple-red
olive-
bluish-
Rhizoid-green green to olive-green
green
brown
dissolves
with violet, then
Biatora H₂O
blue greenish- yellow, then dissolves
atrofusca insoluble
blue decolourized
colour
dirty
Phialopsis
brick-red purple- violet
rubra
red
deep
Lecanora-red purple-red
violet
greenish-
Sagedia blue blue then
bluish-red blue
declivum (green) grey-
black
KOH then
Verrucaria HNO₃ then
dark- dark-
Hoffmanni f. rose-red H₂SO₄:
green green
purpurascens violet
crystals
Bacidia yellowish-
violet violet violet
fuscorubella brown
glacier moraines where they were liable, even when uncovered by snow, to be flooded by water
from the higher reaches. It is the thallus that is affected by the iron, rarely if ever are apothecia
altered in colour.
Bachmann’s Pigment Reactions
Name of
Special
Pigment or Colour KOH NH₃ Ba(OH)₂ HNO₃ H₂SO₄
Reactions
Lichen
copper or KOH then
Lecidea-green green
brick-red HCl: blue
HNO₃:
Aspicilia-green green brighter
green
Bacidia-green green violet violet HCl: violet
HCl:
Thalloidima- indistinctly
green violet indistinctly
green purple-red
purple-red
olive-
bluish-
Rhizoid-green green to olive-green
green
brown
dissolves
with violet, then
Biatora H₂O
blue greenish- yellow, then dissolves
atrofusca insoluble
blue decolourized
colour
dirty
Phialopsis
brick-red purple- violet
rubra
red
deep
Lecanora-red purple-red
violet
greenish-
Sagedia blue blue then
bluish-red blue
declivum (green) grey-
black
KOH then
Verrucaria HNO₃ then
dark- dark-
Hoffmanni f. rose-red H₂SO₄:
green green
purpurascens violet
crystals
Bacidia yellowish-
violet violet violet
fuscorubella brown
Page 324
KOH, then
deep
Sphaeromphale leather- H₂SO₄, then
olive-
clopismoides brown HNO₃:
green
blackish
dilute
Segestria
yellow- bright H₂SO₄:
lectissima— rose-red
brown yellow bright
perithecia
yellow
Strong
Segestria brown
H₂SO₄: deep
lectissima— and
violet, then
entire tissue colourless
grey
CaCl₂O₂:
blue, then
Parmelia leather- blue, then
violet, at last
glomellifera brown grey; finally
grey
decolourized
yellow to dirty- to
Parmelia- bright red-
blackish- olive-
brown brown
brown brown
deep
Sphaeromphale leather- H₂SO₄, then
olive-
clopismoides brown HNO₃:
green
blackish
dilute
Segestria
yellow- bright H₂SO₄:
lectissima— rose-red
brown yellow bright
perithecia
yellow
Strong
Segestria brown
H₂SO₄: deep
lectissima— and
violet, then
entire tissue colourless
grey
CaCl₂O₂:
blue, then
Parmelia leather- blue, then
violet, at last
glomellifera brown grey; finally
grey
decolourized
yellow to dirty- to
Parmelia- bright red-
blackish- olive-
brown brown
brown brown
Page 325
CHAPTER VI
BIONOMICS
A. Growth and Duration
Lichens are perennial plants mostly of slow growth and of long continuance; there can therefore
only be approximate calculations either as to their rate of increase in dimensions or as to their
duration in time. A series of somewhat disconnected observations have however been made that
bear directly on the question, and they are of considerable interest.
Meyer[896] was among the first to be attracted by this aspect of lichen life, and after long study
he came to the conclusion that growth varied in rapidity according to the prevailing conditions of
the atmosphere and the nature of the substratum; but that nearly all species were very slow
growers. He enumerates several,—Lichen (Xanthoria) parietinus, L. (Parmelia) tiliaceus, L.
(Rhizocarpon) geographicus, L. (Haematomma) ventosus, and L. (Lecanora) saxicolus,—all
species with a well-defined outline, which, after having attained some considerable size, remained
practically unchanged for six and a half years, though, in some small specimens of foliose lichens,
he noted, during the same period, an increase of one-fourth to one-third of their size in diameter. In
one of the above crustaceous species, L. ventosus, the specimen had not perceptibly enlarged in
sixteen years, though during that time the centre of the thallus had been broken up by weathering
and had again been regenerated.
Meyer also records the results of culture experiments made in the open, possibly with soredia or
with thalline scraps: he obtained a growth of Xanthoria parietina (on wrought iron kept well
moistened), which fruited in the second year, and in five years had attained a width of 5-6 lines
(about 1 cm.); Lecanora saxicola growing on a moist rock facing south grew 4-7 lines in six and a
half years, and bore very minute apothecia.
Lindsay[897] quotes a statement that a specimen of Lobaria pulmonaria had been observed to
occupy the same area of a tree after the lapse of half a century. Berkeley[898] records that a plant of
Rhizocarpon geographicum remained in much the same condition of development during a period
of twenty-five years. The latter is a slow grower and, in ordinary circumstances, it does not fruit
till about fifteen years after the thallus has begun to form. Weddell[899], also commenting on the
long continuance of lichens, says there are crustaceous species occupying on the rock a space that
might be covered by a five-franc piece, that have taken a century to attain that size.
Phillips[900] on the other hand argues against the very great age of lichens, and suggests 20 years
as a sufficient time for small plants to establish themselves on hard rocks and attain full
development. He had observed a small vigorous plant of Xanthoria parietina that in the course of
five years had extended outwards to double its original size. The centre then began to break up and
the whole plant finally disappeared.
Exact measurements of growth have been made by several observers. Scott Elliot[901] found that
a Pertusaria had increased about half a millimetre from the 1st February to the end of September.
Vallot[902] kept under observation at first three then five different plants of Parmelia saxatilis
during a period of eight years: the yearly increase of the thallus was half a centimetre, so that
specimens of twenty centimetres in breadth must have been growing from forty to fifty years.
BIONOMICS
A. Growth and Duration
Lichens are perennial plants mostly of slow growth and of long continuance; there can therefore
only be approximate calculations either as to their rate of increase in dimensions or as to their
duration in time. A series of somewhat disconnected observations have however been made that
bear directly on the question, and they are of considerable interest.
Meyer[896] was among the first to be attracted by this aspect of lichen life, and after long study
he came to the conclusion that growth varied in rapidity according to the prevailing conditions of
the atmosphere and the nature of the substratum; but that nearly all species were very slow
growers. He enumerates several,—Lichen (Xanthoria) parietinus, L. (Parmelia) tiliaceus, L.
(Rhizocarpon) geographicus, L. (Haematomma) ventosus, and L. (Lecanora) saxicolus,—all
species with a well-defined outline, which, after having attained some considerable size, remained
practically unchanged for six and a half years, though, in some small specimens of foliose lichens,
he noted, during the same period, an increase of one-fourth to one-third of their size in diameter. In
one of the above crustaceous species, L. ventosus, the specimen had not perceptibly enlarged in
sixteen years, though during that time the centre of the thallus had been broken up by weathering
and had again been regenerated.
Meyer also records the results of culture experiments made in the open, possibly with soredia or
with thalline scraps: he obtained a growth of Xanthoria parietina (on wrought iron kept well
moistened), which fruited in the second year, and in five years had attained a width of 5-6 lines
(about 1 cm.); Lecanora saxicola growing on a moist rock facing south grew 4-7 lines in six and a
half years, and bore very minute apothecia.
Lindsay[897] quotes a statement that a specimen of Lobaria pulmonaria had been observed to
occupy the same area of a tree after the lapse of half a century. Berkeley[898] records that a plant of
Rhizocarpon geographicum remained in much the same condition of development during a period
of twenty-five years. The latter is a slow grower and, in ordinary circumstances, it does not fruit
till about fifteen years after the thallus has begun to form. Weddell[899], also commenting on the
long continuance of lichens, says there are crustaceous species occupying on the rock a space that
might be covered by a five-franc piece, that have taken a century to attain that size.
Phillips[900] on the other hand argues against the very great age of lichens, and suggests 20 years
as a sufficient time for small plants to establish themselves on hard rocks and attain full
development. He had observed a small vigorous plant of Xanthoria parietina that in the course of
five years had extended outwards to double its original size. The centre then began to break up and
the whole plant finally disappeared.
Exact measurements of growth have been made by several observers. Scott Elliot[901] found that
a Pertusaria had increased about half a millimetre from the 1st February to the end of September.
Vallot[902] kept under observation at first three then five different plants of Parmelia saxatilis
during a period of eight years: the yearly increase of the thallus was half a centimetre, so that
specimens of twenty centimetres in breadth must have been growing from forty to fifty years.
Page 326
Bitter’s[903] observations on Parmelia physodes agree in the main with those of Vallot: the
increase of the upper lobes during the year was 3-4 mm. In a more favourable climate Heere found
that Parmelia caperata (Fig. 49) on a trunk of Aesculus in California had grown longitudinally 1·5
cm. and transversely 1 cm. The measurements extended over a period of seven winter months, five
of them being wet and therefore the most favourable season of growth. In warm regions lichens
attain a much greater size than in temperate or northern countries, and growth must be more rapid.
A series of measurements was also made by Heere[904] on Ramalina reticulata (Fig. 64), a rapid
growing tree-lichen, and one of the largest American species. The shorter lobes were selected for
observation, and were tested during a period of seven months from September to May, five of the
months being in the wet season. There was great variation between the different lobes but the
average increase during that period was 41 per cent.
Krabbe[905] took notes of the colonization of Cladonia rangiferina (Fig. 127) on burnt soil: in
ten years the podetia had reached a height of 3 to 5 cm., giving an annual growth of about 3-5 mm.
It is not unusual to find specimens in northern latitudes 18 inches long (50 cm.), which, on that
computation, must have been 100 to 160 years old; but while increase goes on at the apex of the
podetia, there is constant perishing at the base of at least as much as half the added length and
these plants would therefore be 200 or 300 years old. Reinke[906] indeed has declared that apical
growth in these Cladina species may go on for centuries, given the necessary conditions of good
light and undisturbed habitat.
Other data as to rate of growth are furnished by Bonnier[907] in the account of his synthetic
cultures which developed apothecia only after two to three years. The culture experiments of
Darbishire[908] and Tobler[909] with Cladonia soredia are also instructive, the former with synthetic
spore- and alga-cultures having obtained a growth of soredia in about seven months; the latter,
starting with soredia, had a growth of well-formed squamules in nine months.
It has been frequently observed that abundance of moisture facilitates growth, and this is
nowhere better exemplified than in crustaceous soil-lichens. Meyer found that on lime-clay soil
which had been thrown up from a ditch in autumn, lichens such as Gyalecta geoica were fully
developed the following summer. He gives an account also of another soil species, Verrucaria
(Thrombium) epigaea, which attained maturity during the winter half of the year. Stahl[910] tells us
that Thelidium minutulum, a pyrenocarpous soil-lichen, with a primitive and scanty thallus, was
cultivated by him from spore to spore in the space of three months. Such lichens retain more of the
characteristics of fungi than do those with a better developed thallus. Rapid colonization by a soil-
lichen was also observed in Epping Forest by Paulson[911]. In autumn an extensive growth of
Lecidea uliginosa covered as if with a dark stain patches of soil that had been worn bare during the
previous spring. The lichen had reached full development and was well fruited.
These facts are quite in harmony with other observations on growth made on Epping Forest
lichens. The writers[912] of the report record the finding of “fruiting lichens overspreading
decaying leaves which can scarcely have lain on the ground more than two or three years; others
growing on old boots or on dung and fruiting freely; others overspreading growing mosses.” They
also cite a definite instance of a mass of concrete laid down in 1903 round a surface-water drain
which in 1910—seven years later—was covered with Lecanora galactina in abundant fruit; and of
another case of a Portland stone garden-ornament, new in 1904, and, in 1910, covered with
patches of a fruiting Verrucaria (probably V. nigrescens). Both these species, they add, have a
scanty thallus and generally fruit very freely.
increase of the upper lobes during the year was 3-4 mm. In a more favourable climate Heere found
that Parmelia caperata (Fig. 49) on a trunk of Aesculus in California had grown longitudinally 1·5
cm. and transversely 1 cm. The measurements extended over a period of seven winter months, five
of them being wet and therefore the most favourable season of growth. In warm regions lichens
attain a much greater size than in temperate or northern countries, and growth must be more rapid.
A series of measurements was also made by Heere[904] on Ramalina reticulata (Fig. 64), a rapid
growing tree-lichen, and one of the largest American species. The shorter lobes were selected for
observation, and were tested during a period of seven months from September to May, five of the
months being in the wet season. There was great variation between the different lobes but the
average increase during that period was 41 per cent.
Krabbe[905] took notes of the colonization of Cladonia rangiferina (Fig. 127) on burnt soil: in
ten years the podetia had reached a height of 3 to 5 cm., giving an annual growth of about 3-5 mm.
It is not unusual to find specimens in northern latitudes 18 inches long (50 cm.), which, on that
computation, must have been 100 to 160 years old; but while increase goes on at the apex of the
podetia, there is constant perishing at the base of at least as much as half the added length and
these plants would therefore be 200 or 300 years old. Reinke[906] indeed has declared that apical
growth in these Cladina species may go on for centuries, given the necessary conditions of good
light and undisturbed habitat.
Other data as to rate of growth are furnished by Bonnier[907] in the account of his synthetic
cultures which developed apothecia only after two to three years. The culture experiments of
Darbishire[908] and Tobler[909] with Cladonia soredia are also instructive, the former with synthetic
spore- and alga-cultures having obtained a growth of soredia in about seven months; the latter,
starting with soredia, had a growth of well-formed squamules in nine months.
It has been frequently observed that abundance of moisture facilitates growth, and this is
nowhere better exemplified than in crustaceous soil-lichens. Meyer found that on lime-clay soil
which had been thrown up from a ditch in autumn, lichens such as Gyalecta geoica were fully
developed the following summer. He gives an account also of another soil species, Verrucaria
(Thrombium) epigaea, which attained maturity during the winter half of the year. Stahl[910] tells us
that Thelidium minutulum, a pyrenocarpous soil-lichen, with a primitive and scanty thallus, was
cultivated by him from spore to spore in the space of three months. Such lichens retain more of the
characteristics of fungi than do those with a better developed thallus. Rapid colonization by a soil-
lichen was also observed in Epping Forest by Paulson[911]. In autumn an extensive growth of
Lecidea uliginosa covered as if with a dark stain patches of soil that had been worn bare during the
previous spring. The lichen had reached full development and was well fruited.
These facts are quite in harmony with other observations on growth made on Epping Forest
lichens. The writers[912] of the report record the finding of “fruiting lichens overspreading
decaying leaves which can scarcely have lain on the ground more than two or three years; others
growing on old boots or on dung and fruiting freely; others overspreading growing mosses.” They
also cite a definite instance of a mass of concrete laid down in 1903 round a surface-water drain
which in 1910—seven years later—was covered with Lecanora galactina in abundant fruit; and of
another case of a Portland stone garden-ornament, new in 1904, and, in 1910, covered with
patches of a fruiting Verrucaria (probably V. nigrescens). Both these species, they add, have a
scanty thallus and generally fruit very freely.
Page 327
A series of observations referring to growth and “ecesis” or the spreading of lichens have been
made by Bruce Fink[913] over a period of eight years. His aim was mainly to determine the time
required for a lichen to re-establish itself on areas from which it had been previously removed.
Thus a quadrat of limestone was scraped bare of moss and of Leptogium lacerum, except for bits
of the moss and particles of the lichen which adhered to the rock, especially in depressions of the
surface. After four years, the moss was colonizing many small areas on which grew patches of the
lichen 2 to 10 mm. across. Very little change occurred during the next four years.
Numerous results are also recorded as to the rate of growth, the average being 1 cm. per year or
somewhat under. The greatest rate seems to have been recorded for a plant of Peltigera canina
growing on “a mossy rock along a brook in a low moist wood, well-shaded.” A plant, measuring
10 by 14 cm., was deprived of several large apothecia. The lobes all pointed in the same direction,
and the plant increased 1·75 cm. in one year. Two other plants, deprived of their lobes, regenerated
and increased from 2 and 5 cm. respectively to 3·5 and 6 cm. No other measurements are quite so
high as these, though a plant of Parmelia caperata (sterile), measuring from 1 to 2 cm. across,
reached in eight years a dimension of 10 by 13 cm. Other plants of the same species gave much
slower rates of increase. A section of railing was marked bearing minute scattered squamules of
Cladonia pityrea. After two years the squamules had attained normal size and podetia were formed
2 to 4 mm. long.
Several areas of Verrucaria muralis were marked and after ten months were again measured; the
largest plants, measuring 2·12 by 2·4 cm. across, had somewhat altered in dimensions and gave
the measurements 2·2 by 3 cm. Some crustose species became established and produced thalli and
apothecia in two to eight years. Foliose lichens increased in diameter from 0·3 to 3·5 cm. per year.
So far as external appearance goes, apothecia are produced in one to eight years; it is concluded
that they require four to eight years to attain maturity in their natural habitats.
B. Season of Fruit Formation
The presence of apothecia (or perithecia) in lichens does not always imply the presence of
spores. In many instances they are barren, the spores having been scattered or not yet matured; the
disc in these cases is composed of paraphyses only, with possible traces of asci. In any month of
the year, however, some lichens may be found in fruit.
Baur[914] found, for instance, that Parmelia acetabulum developed carpogonia the whole year
round, though somewhat more abundantly in spring and autumn. Pertusaria communis similarly
has a maximum period of fruit-formation at these two seasons. This is probably true of tree-lichens
generally: in summer the shade of the foliage would inhibit the formation of fruits, as would the
extreme cold of winter; but were these conditions relaxed spore-bearing fruits might be expected
at any season though perhaps not continuously on the same specimen.
An exception has been noted by Baur in Pyrenula nitida, a crustaceous tree Pyrenolichen. He
found carpogonia only in February and April, and the perithecia matured in a few weeks,
presumably at a date before the trees were in full leaf; but even specimens of Pyrenula are not
unusual in full spore-bearing conditions in the autumn of the year.
To arrive at any true knowledge as to the date and duration of spore production, it would be
necessary to keep under observation a series of one species, examining them microscopically at
intervals of a few weeks or months and noting any conditions that might affect favourably or
unfavourably the reproductive organs. A comparison between corticolous and saxicolous species
made by Bruce Fink[913] over a period of eight years. His aim was mainly to determine the time
required for a lichen to re-establish itself on areas from which it had been previously removed.
Thus a quadrat of limestone was scraped bare of moss and of Leptogium lacerum, except for bits
of the moss and particles of the lichen which adhered to the rock, especially in depressions of the
surface. After four years, the moss was colonizing many small areas on which grew patches of the
lichen 2 to 10 mm. across. Very little change occurred during the next four years.
Numerous results are also recorded as to the rate of growth, the average being 1 cm. per year or
somewhat under. The greatest rate seems to have been recorded for a plant of Peltigera canina
growing on “a mossy rock along a brook in a low moist wood, well-shaded.” A plant, measuring
10 by 14 cm., was deprived of several large apothecia. The lobes all pointed in the same direction,
and the plant increased 1·75 cm. in one year. Two other plants, deprived of their lobes, regenerated
and increased from 2 and 5 cm. respectively to 3·5 and 6 cm. No other measurements are quite so
high as these, though a plant of Parmelia caperata (sterile), measuring from 1 to 2 cm. across,
reached in eight years a dimension of 10 by 13 cm. Other plants of the same species gave much
slower rates of increase. A section of railing was marked bearing minute scattered squamules of
Cladonia pityrea. After two years the squamules had attained normal size and podetia were formed
2 to 4 mm. long.
Several areas of Verrucaria muralis were marked and after ten months were again measured; the
largest plants, measuring 2·12 by 2·4 cm. across, had somewhat altered in dimensions and gave
the measurements 2·2 by 3 cm. Some crustose species became established and produced thalli and
apothecia in two to eight years. Foliose lichens increased in diameter from 0·3 to 3·5 cm. per year.
So far as external appearance goes, apothecia are produced in one to eight years; it is concluded
that they require four to eight years to attain maturity in their natural habitats.
B. Season of Fruit Formation
The presence of apothecia (or perithecia) in lichens does not always imply the presence of
spores. In many instances they are barren, the spores having been scattered or not yet matured; the
disc in these cases is composed of paraphyses only, with possible traces of asci. In any month of
the year, however, some lichens may be found in fruit.
Baur[914] found, for instance, that Parmelia acetabulum developed carpogonia the whole year
round, though somewhat more abundantly in spring and autumn. Pertusaria communis similarly
has a maximum period of fruit-formation at these two seasons. This is probably true of tree-lichens
generally: in summer the shade of the foliage would inhibit the formation of fruits, as would the
extreme cold of winter; but were these conditions relaxed spore-bearing fruits might be expected
at any season though perhaps not continuously on the same specimen.
An exception has been noted by Baur in Pyrenula nitida, a crustaceous tree Pyrenolichen. He
found carpogonia only in February and April, and the perithecia matured in a few weeks,
presumably at a date before the trees were in full leaf; but even specimens of Pyrenula are not
unusual in full spore-bearing conditions in the autumn of the year.
To arrive at any true knowledge as to the date and duration of spore production, it would be
necessary to keep under observation a series of one species, examining them microscopically at
intervals of a few weeks or months and noting any conditions that might affect favourably or
unfavourably the reproductive organs. A comparison between corticolous and saxicolous species
Page 328
would also be of great interest to determine the influence of the substratum as well as of light and
shade. But in any case it is profitable to collect and examine lichens at all seasons of the year, as
even when the bulk of the spores is shed, there may remain belated apothecia with a few asci still
intact.
C. Dispersal and Increase
The natural increase of lichen plants may primarily be sought for in the dispersal of the spores
produced in the fruiting-bodies. These are ejected, as in fungi, by the pressure of the paraphyses on
the mature ascus. The spores are then carried away by wind, water, insects, etc. In a few lichens
gonidia are enclosed in the hymenium and are ejected along with the spores, but, in most, the
necessary encounter with the alga is as fortuitous, and generally as certain, as the pollination of
anemophilous flowers. A case of dispersal in Sagedia microspora has been described by
Miyoshi[915] in which entire fruits, small round perithecia, were dislodged and carried away by the
wind. The addition of water caused them to swell enormously and brought about the ejection of
the spores. Areas covered by the thallus are also being continually enlarged by the spreading
growth of the hypothallus.
a. Dispersal of Crustaceous Lichens. These lichens are distributed fairly equally on trees or
wood (corticolous) and on rocks (saxicolous). Some species inhabit both substrata. As regards
corticolous lichens that live on smooth bark such as hazel or mountain-ash, the vegetative body or
thallus is generally embedded beneath the epidermis of the host. Soredia are absent and the thallus
is protected from dispersal. In these lichens there is rather an abundant and constant formation of
apothecia or perithecia.
Other species that affect rugged bark and are more superficial are less dependent on spore
production. The thallus is either loosely granular, or is broken up into areolae. The areolae are each
a centre of growth, and with an accession of moisture they swell up and exert pressure on each
other. Parts of the thallus thus become loosened and are dislodged and carried away. If anchored
on a suitable substratum they grow again to a complete lichen plant. Sorediate lichens are
dependent almost wholly on these bud-like portions for increase in number; soredia are easily
separated from the parent plant, and easily scattered. Darbishire[916] noted frequently that small
Poduridae in moving over the surface of Pertusaria amara became powdered with soredia and
very evidently took a considerable part in the dissemination of the species.
Crustaceous rock lichens are rarely sorediate, but they secure vegetative propagation[917] by the
dispersal of small portions of the thallus. The thalli most securely attached are cracked into small
areolae which, by unequal growth, become very soon lop-sided, or, by intercalary increase, form
little warts and excrescences on their surface. These irregularities of development give rise to more
or less tension which induces a loosening of the thallus from the substratum. Weather changes act
similarly and gradually the areolae are broken off. Loosening influence is also exercised by the
developing fruits, the expanding growth of which pushes aside the neighbouring tissues. Wind or
water then carries away the thalline particles which become new centres of growth if a suitable
substratum is reached.
b. Dispersal of Foliose Lichens. It is a matter of common observation that, in foliose lichens
where fruits are abundant, there are few or no soredia and vice versa. In either case propagation is
ensured. In addition to these obvious methods of increase many lichens form isidia, outgrowths
from the thallus which are easily detached. Bitter[918] considers for instance that the coralloid
branchlets, which occur in compact tufts on the thallus of Umbilicaria pustulata, are of immense
shade. But in any case it is profitable to collect and examine lichens at all seasons of the year, as
even when the bulk of the spores is shed, there may remain belated apothecia with a few asci still
intact.
C. Dispersal and Increase
The natural increase of lichen plants may primarily be sought for in the dispersal of the spores
produced in the fruiting-bodies. These are ejected, as in fungi, by the pressure of the paraphyses on
the mature ascus. The spores are then carried away by wind, water, insects, etc. In a few lichens
gonidia are enclosed in the hymenium and are ejected along with the spores, but, in most, the
necessary encounter with the alga is as fortuitous, and generally as certain, as the pollination of
anemophilous flowers. A case of dispersal in Sagedia microspora has been described by
Miyoshi[915] in which entire fruits, small round perithecia, were dislodged and carried away by the
wind. The addition of water caused them to swell enormously and brought about the ejection of
the spores. Areas covered by the thallus are also being continually enlarged by the spreading
growth of the hypothallus.
a. Dispersal of Crustaceous Lichens. These lichens are distributed fairly equally on trees or
wood (corticolous) and on rocks (saxicolous). Some species inhabit both substrata. As regards
corticolous lichens that live on smooth bark such as hazel or mountain-ash, the vegetative body or
thallus is generally embedded beneath the epidermis of the host. Soredia are absent and the thallus
is protected from dispersal. In these lichens there is rather an abundant and constant formation of
apothecia or perithecia.
Other species that affect rugged bark and are more superficial are less dependent on spore
production. The thallus is either loosely granular, or is broken up into areolae. The areolae are each
a centre of growth, and with an accession of moisture they swell up and exert pressure on each
other. Parts of the thallus thus become loosened and are dislodged and carried away. If anchored
on a suitable substratum they grow again to a complete lichen plant. Sorediate lichens are
dependent almost wholly on these bud-like portions for increase in number; soredia are easily
separated from the parent plant, and easily scattered. Darbishire[916] noted frequently that small
Poduridae in moving over the surface of Pertusaria amara became powdered with soredia and
very evidently took a considerable part in the dissemination of the species.
Crustaceous rock lichens are rarely sorediate, but they secure vegetative propagation[917] by the
dispersal of small portions of the thallus. The thalli most securely attached are cracked into small
areolae which, by unequal growth, become very soon lop-sided, or, by intercalary increase, form
little warts and excrescences on their surface. These irregularities of development give rise to more
or less tension which induces a loosening of the thallus from the substratum. Weather changes act
similarly and gradually the areolae are broken off. Loosening influence is also exercised by the
developing fruits, the expanding growth of which pushes aside the neighbouring tissues. Wind or
water then carries away the thalline particles which become new centres of growth if a suitable
substratum is reached.
b. Dispersal of Foliose Lichens. It is a matter of common observation that, in foliose lichens
where fruits are abundant, there are few or no soredia and vice versa. In either case propagation is
ensured. In addition to these obvious methods of increase many lichens form isidia, outgrowths
from the thallus which are easily detached. Bitter[918] considers for instance that the coralloid
branchlets, which occur in compact tufts on the thallus of Umbilicaria pustulata, are of immense
Page 329
service as organs of propagation. Apothecia and pycnidia are rarely present in that species, and the
plant thus falls back on vegetative production. Slender crisp thalline outgrowths, easily separable,
occur also on the edges of lobes, as in species of Peltigera, Platysma, etc.
Owing to the gelatinous character of lichen hyphae, the thallus quickly becomes soft with
moisture and is then easily torn and distributed by wind, animals, etc. The action of lichens on
rocks has been shown to be of a constantly disintegrating character, and the destruction of the
supporting rock finally entails the scattering of the plant. This cause of dispersal is common to
both crustaceous and foliose species. The older central parts of a lichen may thus have disappeared
while the areolae on lobes of the circumference are still intact and in full vigour.
As in crustaceous lichens the increase in the area of growth may take place by means of the
lichen mycelium which, originating from the rhizinae in contact with the substratum, spreads as a
hypothallus under the shelter of the lobes and far beyond them. When algae are encountered a new
lobe begins to form. The process can be seen perhaps most favourably in lichens on decaying
wood which harbours moisture and thus enables the wandering hyphae to retain life.
c. Dispersal of Fruticose Lichens. Many of these lichens are abundantly fruited; in others
soralia are as constantly developed. Species of Usnea, Alectoria, Ramalina and many Cladoniae
are mainly propagated by soredia. They are all peculiarly liable to be broken and portions of the
thallus scattered by the combined action of wind and rain.
Peirce[919] found that Ramalina reticulata (Fig. 65), of which the fronds are an open network,
was mainly distributed by the tearing of the lichen in high wind. This takes place during the winter
rains, when not only the lichen is wet and soft in texture, but when the deciduous trees are bare of
leaves, at a season, therefore, when the drifting thalline scraps can again catch on to branch or
stem. A series of observations on the dispersal of forms of long pendulous Usneas was made by
Schrenk[920]. In the Middle and North Atlantic States of America these filamentous species rarely
bear apothecia. The high winds break and disperse them when they are in a wet condition. They
generally grow on Spruces and Firs, because the drifting filaments are more easily caught and
entangled on short needles. The successive wetting and drying causes them to coil and uncoil,
resulting in a tangle impossible to unravel, which holds them securely anchored to the support.
D. Erratic Lichens
In certain lichens, there is a tendency for the thallus to develop excrescences of nodular form
which easily become free and drift about in the wind while still living and growing. They are
carried sometimes very long distances, and fall in thick deposits over localities far from their place
of origin. The most famous instance is the “manna lichen,” Lecanora esculenta, which has been
scientifically examined and described by Elenkin[921]. He distinguishes seven different forms of
the species: f. esculenta, f. affinis, f. alpina, and f. fruticulosa-foliacea which are Alpine lichens,
the remainder, f. desertoides, f. foliacea and f. esculenta-tarquina, grow on the steppes or in the
desert[922].
Elenkin[921] adds to the list of erratic lichens a variety of Parmelia molliuscula along with P.
ryssolea from S. Russia, from the Asiatic steppes and from Alpine regions. Mereschkovsky[923]
has also recorded from the Crimea Parmelia vagans, probably derived from P. conspersa f. vaga
(f. nov.). It drifts about in small rather flattened bits, and, like other erratics, it never fruits.
plant thus falls back on vegetative production. Slender crisp thalline outgrowths, easily separable,
occur also on the edges of lobes, as in species of Peltigera, Platysma, etc.
Owing to the gelatinous character of lichen hyphae, the thallus quickly becomes soft with
moisture and is then easily torn and distributed by wind, animals, etc. The action of lichens on
rocks has been shown to be of a constantly disintegrating character, and the destruction of the
supporting rock finally entails the scattering of the plant. This cause of dispersal is common to
both crustaceous and foliose species. The older central parts of a lichen may thus have disappeared
while the areolae on lobes of the circumference are still intact and in full vigour.
As in crustaceous lichens the increase in the area of growth may take place by means of the
lichen mycelium which, originating from the rhizinae in contact with the substratum, spreads as a
hypothallus under the shelter of the lobes and far beyond them. When algae are encountered a new
lobe begins to form. The process can be seen perhaps most favourably in lichens on decaying
wood which harbours moisture and thus enables the wandering hyphae to retain life.
c. Dispersal of Fruticose Lichens. Many of these lichens are abundantly fruited; in others
soralia are as constantly developed. Species of Usnea, Alectoria, Ramalina and many Cladoniae
are mainly propagated by soredia. They are all peculiarly liable to be broken and portions of the
thallus scattered by the combined action of wind and rain.
Peirce[919] found that Ramalina reticulata (Fig. 65), of which the fronds are an open network,
was mainly distributed by the tearing of the lichen in high wind. This takes place during the winter
rains, when not only the lichen is wet and soft in texture, but when the deciduous trees are bare of
leaves, at a season, therefore, when the drifting thalline scraps can again catch on to branch or
stem. A series of observations on the dispersal of forms of long pendulous Usneas was made by
Schrenk[920]. In the Middle and North Atlantic States of America these filamentous species rarely
bear apothecia. The high winds break and disperse them when they are in a wet condition. They
generally grow on Spruces and Firs, because the drifting filaments are more easily caught and
entangled on short needles. The successive wetting and drying causes them to coil and uncoil,
resulting in a tangle impossible to unravel, which holds them securely anchored to the support.
D. Erratic Lichens
In certain lichens, there is a tendency for the thallus to develop excrescences of nodular form
which easily become free and drift about in the wind while still living and growing. They are
carried sometimes very long distances, and fall in thick deposits over localities far from their place
of origin. The most famous instance is the “manna lichen,” Lecanora esculenta, which has been
scientifically examined and described by Elenkin[921]. He distinguishes seven different forms of
the species: f. esculenta, f. affinis, f. alpina, and f. fruticulosa-foliacea which are Alpine lichens,
the remainder, f. desertoides, f. foliacea and f. esculenta-tarquina, grow on the steppes or in the
desert[922].
Elenkin[921] adds to the list of erratic lichens a variety of Parmelia molliuscula along with P.
ryssolea from S. Russia, from the Asiatic steppes and from Alpine regions. Mereschkovsky[923]
has also recorded from the Crimea Parmelia vagans, probably derived from P. conspersa f. vaga
(f. nov.). It drifts about in small rather flattened bits, and, like other erratics, it never fruits.
Page 330
Meyer[924] long ago described the development of wandering lichens: scraps that were torn from
the parent thallus continued to grow if there were sufficient moisture, but at the same time
undergoing considerable change in appearance. The dark colour of the under surface disappears in
the frequently altered position, as the lobes grow out into narrow intermingling fronds forming a
more or less compact spherical mass; the rhizoids also become modified and, if near the edge,
grow out into thread-like structures which bind the mass together. Meyer says that “wanderers”
have been noted as belonging to Parmelia acetabulum, Platysma glaucum and Anaptychia ciliaris.
the parent thallus continued to grow if there were sufficient moisture, but at the same time
undergoing considerable change in appearance. The dark colour of the under surface disappears in
the frequently altered position, as the lobes grow out into narrow intermingling fronds forming a
more or less compact spherical mass; the rhizoids also become modified and, if near the edge,
grow out into thread-like structures which bind the mass together. Meyer says that “wanderers”
have been noted as belonging to Parmelia acetabulum, Platysma glaucum and Anaptychia ciliaris.
Page 331
Fig. 121. Parmelia revoluta var. concentrica Cromb. a, plant on flint with detached
fragment; b, upper surface of three specimens; c, three specimens as found on chalk downs;
d, specimens in section showing central cavity (S. H., Photo.).
The most notable instance in Britain of the “erratic” habit is that of Parmelia revoluta
var. concentrica (Fig. 121), first found on Melbury Hill near Shaftesbury, Dorset, and
described as “a spherical unattached lichen which rolls on the exposed downs.” It has
recently been observed on the downs near Seaford in Sussex, where, however, it seems
to be confined to a small area about eight acres in extent which is exposed to south-west
winds. The lichen is freely distributed over this locality. To R. Paulson and Somerville
Hastings[925] we owe an account of the occurrence and origin of the revoluta wanderers.
The specimens vary considerably in shape and size, and measure from 1 to 7 cm. in
longest diameter. Very few are truly spherical, some are more or less flattened and many
fragment; b, upper surface of three specimens; c, three specimens as found on chalk downs;
d, specimens in section showing central cavity (S. H., Photo.).
The most notable instance in Britain of the “erratic” habit is that of Parmelia revoluta
var. concentrica (Fig. 121), first found on Melbury Hill near Shaftesbury, Dorset, and
described as “a spherical unattached lichen which rolls on the exposed downs.” It has
recently been observed on the downs near Seaford in Sussex, where, however, it seems
to be confined to a small area about eight acres in extent which is exposed to south-west
winds. The lichen is freely distributed over this locality. To R. Paulson and Somerville
Hastings[925] we owe an account of the occurrence and origin of the revoluta wanderers.
The specimens vary considerably in shape and size, and measure from 1 to 7 cm. in
longest diameter. Very few are truly spherical, some are more or less flattened and many
Page 332
are quite irregular. The revolute edges of the overlapping lobes give a rough exterior to
the balls, which thereby become entangled amongst the grass, etc., and movement is
impeded or prevented, except in very high winds. Crombie[926] had suggested that the
concentric plant originated from a corticolous habitat, but no trees are near the Seaford
locality. Eventually specimens were found growing on flints in the immediate
neighbourhood. While still on the stone the lichen tends to become panniform, a felt of
intermingling imbricate lobes is formed, portions of which, in time, become crowded
out and dislodged. When scattered over the ground, these are liable to be trampled on
by sheep or other animals and so are broken up; each separate piece then forms the
nucleus of new concentric growth.
Crombie[926] observed at Braemar, drifting about on the detritus of Morrone, an
analogous structure in Parmelia omphalodes. He concluded that nodular excrescences
of the thallus had become detached from the rocks on which the lichen grew; while still
attached to the substratum Parmelia omphalodes and the allied species, P. saxatilis,
form dense cushion-like masses.
E. Parasitism
a. General Statement. The parasitism of Strigula complanata, an exotic lichen found
on the leaves of evergreen trees, has been already described[927]; Dufrenoy[928] records
an instance of hyphae from a Parmelia thallus piercing pine-needles through the
stomata and causing considerable injury. Lichen hyphae have attacked and destroyed
the protonemata of mosses. Cases have also been recorded of Usnea and Ramalina
penetrating to the living tissue of the tree on which they grew, and there may be other
similar parasitisms; but these exceptions serve to emphasize the independent symbiotic
growth of lichens.
There are however some lichens belonging to widely diverse genera that have
retained, or reverted to, the saprophytic or parasitic habit of their fungal ancestors,
though the cases that occur are generally of lichens preying on other lichens. The
conditions have been described as those of “antagonistic symbiosis” when one lichen is
hurtful or fatal in its action on the other, and as “parasymbiosis” when the association
does little or no injury to the host. The parasitism of fungi on lichens, though falling
under a different category, in many instances exhibits features akin to parasymbiosis.
The parasitism of fungus on fungus is not unusual; there are instances of its
occurrence in all the different classes. In the Phycomycetes there are genera wholly
parasitic on other fungi such as Woronina and other Chytridiaceae; Piptocephalus, one
of the Mucorini, is another instance. Cicinnobolus, one of the Sphaeropsideae, preys on
Perisporiae; a species of Cordyceps is found on Elaphomyces, and Orbilia coccinella
on Polyporus; while among Basidiomycetes, Nyctalis, an agaric, grows always on
Russula.
the balls, which thereby become entangled amongst the grass, etc., and movement is
impeded or prevented, except in very high winds. Crombie[926] had suggested that the
concentric plant originated from a corticolous habitat, but no trees are near the Seaford
locality. Eventually specimens were found growing on flints in the immediate
neighbourhood. While still on the stone the lichen tends to become panniform, a felt of
intermingling imbricate lobes is formed, portions of which, in time, become crowded
out and dislodged. When scattered over the ground, these are liable to be trampled on
by sheep or other animals and so are broken up; each separate piece then forms the
nucleus of new concentric growth.
Crombie[926] observed at Braemar, drifting about on the detritus of Morrone, an
analogous structure in Parmelia omphalodes. He concluded that nodular excrescences
of the thallus had become detached from the rocks on which the lichen grew; while still
attached to the substratum Parmelia omphalodes and the allied species, P. saxatilis,
form dense cushion-like masses.
E. Parasitism
a. General Statement. The parasitism of Strigula complanata, an exotic lichen found
on the leaves of evergreen trees, has been already described[927]; Dufrenoy[928] records
an instance of hyphae from a Parmelia thallus piercing pine-needles through the
stomata and causing considerable injury. Lichen hyphae have attacked and destroyed
the protonemata of mosses. Cases have also been recorded of Usnea and Ramalina
penetrating to the living tissue of the tree on which they grew, and there may be other
similar parasitisms; but these exceptions serve to emphasize the independent symbiotic
growth of lichens.
There are however some lichens belonging to widely diverse genera that have
retained, or reverted to, the saprophytic or parasitic habit of their fungal ancestors,
though the cases that occur are generally of lichens preying on other lichens. The
conditions have been described as those of “antagonistic symbiosis” when one lichen is
hurtful or fatal in its action on the other, and as “parasymbiosis” when the association
does little or no injury to the host. The parasitism of fungi on lichens, though falling
under a different category, in many instances exhibits features akin to parasymbiosis.
The parasitism of fungus on fungus is not unusual; there are instances of its
occurrence in all the different classes. In the Phycomycetes there are genera wholly
parasitic on other fungi such as Woronina and other Chytridiaceae; Piptocephalus, one
of the Mucorini, is another instance. Cicinnobolus, one of the Sphaeropsideae, preys on
Perisporiae; a species of Cordyceps is found on Elaphomyces, and Orbilia coccinella
on Polyporus; while among Basidiomycetes, Nyctalis, an agaric, grows always on
Russula.
Page 333
There are few instances of lichens finding a foothold on fungi, for the simple reason
that the latter are too short lived. On the perennial Polyporeae a few have been recorded
by Arnold[929], but these are not described as doing damage to the host. They are mostly
species of Lecidea or of allied genera. Kupfer[930] has also listed some 15 different
lichens that he found on Lenzites sp.
b. Antagonistic Symbiosis. In discussing the nutrition of lichens[931] note has been
taken of the extent to which some species by means of enzymes destroy the thallus of
other lichens in their vicinity and then prey on the dead tissues. A constantly cited[932]
example is that of Lecanora atriseda which in its early stages lives on the thallus of
Rhizocarpon geographicum inhabiting mountain rocks. A detailed examination of the
relationship between these two plants was made by Malme and later by Bitter[933]. Both
writers found that the Lecanora thallus as it advanced caused a blackening of the
Rhizocarpon areolae, the tissues of which were killed by the burrowing slender
filaments of the Lecanora, easily recognized by their longer cells. The invader
thereafter gradually formed its own medulla, gonidial layer and cortex right over the
surface of the destroyed thallus. Lecidea insularis (L. intumescens) similarly takes
possession of and destroys the thallus of Lecanora glaucoma and Malme[932] strongly
suspects that Buellia verruculosa and B. aethalea may be living on the thallus of
Rhizocarpon distinctum with which they are constantly associated.
Other cases of facultative parasitism have been studied by Hofmann[934], more
especially three different species, Lecanora dispersa, Lecanora sp. and Parmelia
hyperopta, which were found growing on the thick foliose thallus of Dermatocarpon
miniatum. These grew, at first independently, on a wall along with many examples of
Endocarpon on to which they spread as opportunity offered. The thallus of the latter
was in all cases distorted, the area occupied by the invaders being finally killed. The
attacking lichens had benefited materially by the more nutritive substratum: their
apothecia were more abundant and their thallus more luxuriant. The gonidia especially
had profited; they were larger, more brightly coloured, and they increased more freely.
Hoffmann offers the explanation that the strain on the algae of providing organic food
for the hyphal symbiont was relaxed for the time, hence their more vigorous
appearance.
Arthonia subvarians is always parasitic on the apothecia of Lecanora galactina, and
Almquist[935] discovered that the hymenium of the host alone is injured, the
hypothecium and excipulum being left intact.
The “parasitism” of Pertusaria globulifera on Parmelia perlata and P. physodes, as
described by Bitter[936], may also be included under antagonistic symbiosis. The hyphae
pierce the Parmelia thallus, break it up and gradually absorb it. Chemical as well as
mechanical influences are concerned in the work of destruction as both the fungus and
the alga of the victim are dissolved. Lecanora tartarea already dealt with as a
marauding lichen[937] over decaying vegetation may spread also to living lichens.
that the latter are too short lived. On the perennial Polyporeae a few have been recorded
by Arnold[929], but these are not described as doing damage to the host. They are mostly
species of Lecidea or of allied genera. Kupfer[930] has also listed some 15 different
lichens that he found on Lenzites sp.
b. Antagonistic Symbiosis. In discussing the nutrition of lichens[931] note has been
taken of the extent to which some species by means of enzymes destroy the thallus of
other lichens in their vicinity and then prey on the dead tissues. A constantly cited[932]
example is that of Lecanora atriseda which in its early stages lives on the thallus of
Rhizocarpon geographicum inhabiting mountain rocks. A detailed examination of the
relationship between these two plants was made by Malme and later by Bitter[933]. Both
writers found that the Lecanora thallus as it advanced caused a blackening of the
Rhizocarpon areolae, the tissues of which were killed by the burrowing slender
filaments of the Lecanora, easily recognized by their longer cells. The invader
thereafter gradually formed its own medulla, gonidial layer and cortex right over the
surface of the destroyed thallus. Lecidea insularis (L. intumescens) similarly takes
possession of and destroys the thallus of Lecanora glaucoma and Malme[932] strongly
suspects that Buellia verruculosa and B. aethalea may be living on the thallus of
Rhizocarpon distinctum with which they are constantly associated.
Other cases of facultative parasitism have been studied by Hofmann[934], more
especially three different species, Lecanora dispersa, Lecanora sp. and Parmelia
hyperopta, which were found growing on the thick foliose thallus of Dermatocarpon
miniatum. These grew, at first independently, on a wall along with many examples of
Endocarpon on to which they spread as opportunity offered. The thallus of the latter
was in all cases distorted, the area occupied by the invaders being finally killed. The
attacking lichens had benefited materially by the more nutritive substratum: their
apothecia were more abundant and their thallus more luxuriant. The gonidia especially
had profited; they were larger, more brightly coloured, and they increased more freely.
Hoffmann offers the explanation that the strain on the algae of providing organic food
for the hyphal symbiont was relaxed for the time, hence their more vigorous
appearance.
Arthonia subvarians is always parasitic on the apothecia of Lecanora galactina, and
Almquist[935] discovered that the hymenium of the host alone is injured, the
hypothecium and excipulum being left intact.
The “parasitism” of Pertusaria globulifera on Parmelia perlata and P. physodes, as
described by Bitter[936], may also be included under antagonistic symbiosis. The hyphae
pierce the Parmelia thallus, break it up and gradually absorb it. Chemical as well as
mechanical influences are concerned in the work of destruction as both the fungus and
the alga of the victim are dissolved. Lecanora tartarea already dealt with as a
marauding lichen[937] over decaying vegetation may spread also to living lichens.
Page 334
Fruticose soil species, such as Cetraria aculeata and others, die from the base and the
Lecanora gains entrance to their tissues at the decaying end which is open.
Arnold[938] speaks of these facultative parasites that have merely changed their
substratum as pseudo-parasites, and he gives a list of instances of such change. In many
cases it is rather the older thalli that are taken possession of, and, in nearly every case,
the invader is some crustaceous species. The plants attacked are generally ground
lichens or more particularly those that inhabit damp localities, such as Peltigera or
Cladonia or certain bark lichens. Drifting soredia or particles of a lichen would easily
take hold of the host thallus and develop in suitable conditions. To give a few of the
instances observed, there have been found, by Arnold, Crombie and others:
on Peltigera canina: Callopisma cerina, Rinodina turfacea var., Bilimbia obscurata
and Lecanora aurella;
on Peltigera aphthosa: Lecidea decolorans;
on Cladoniae: Bilimbia microcarpa, Bacidia Beckhausii and Urceolaria scruposa,
etc.
Urceolaria (Diploschistes) has a somewhat bulky crustaceous thallus which may be
almost evanescent in its semi-parasitic condition, the only gonidia retained being in the
margin of the apothecia. Nylander[939] found isolated apothecia growing vigorously on
Cladonia squamules.
Hue[940] describes Lecanora aspidophora f. errabunda, an Antarctic lichen, as not
only a wanderer but as a “shameless robber.” It is to be seen everywhere on and about
other lichens, settling small glomeruli of apothecia here and there on the thallus of
Umbilicariae or between the areolae of Buelliae, and always too vigorous to be ousted
from its position.
Bacidia flavovirescens has been regarded by some lichenologists[941] as a parasite on
Baeomyces, but recent work by Tobler[942] seems to have proved that the bright green
thallus is that of the Bacidia.
c. Parasymbiosis. There are certain lichens that are obligative parasites and pass their
whole existence on an alien thallus. They may possibly have degenerated from the
condition of facultative parasitism as the universal history of parasitism is one of
increased dependence on the host, and of growing atrophy of the parasite, but, in the
case of lichens, there is always the peculiar symbiotic condition to be considered: the
parasite produces its own vigorous hyphae and normal healthy fruits, it often claims
only a share of the carbohydrates manufactured by the gonidia. The host lichen is not
destroyed by this parasymbiosis though the tissues are very often excited to abnormal
growth by the presence of the invading organism.
Lauder Lindsay[943] was one of the first to study these “microlichens” as he called
them, and he published descriptions of those he had himself observed on various hosts.
Lecanora gains entrance to their tissues at the decaying end which is open.
Arnold[938] speaks of these facultative parasites that have merely changed their
substratum as pseudo-parasites, and he gives a list of instances of such change. In many
cases it is rather the older thalli that are taken possession of, and, in nearly every case,
the invader is some crustaceous species. The plants attacked are generally ground
lichens or more particularly those that inhabit damp localities, such as Peltigera or
Cladonia or certain bark lichens. Drifting soredia or particles of a lichen would easily
take hold of the host thallus and develop in suitable conditions. To give a few of the
instances observed, there have been found, by Arnold, Crombie and others:
on Peltigera canina: Callopisma cerina, Rinodina turfacea var., Bilimbia obscurata
and Lecanora aurella;
on Peltigera aphthosa: Lecidea decolorans;
on Cladoniae: Bilimbia microcarpa, Bacidia Beckhausii and Urceolaria scruposa,
etc.
Urceolaria (Diploschistes) has a somewhat bulky crustaceous thallus which may be
almost evanescent in its semi-parasitic condition, the only gonidia retained being in the
margin of the apothecia. Nylander[939] found isolated apothecia growing vigorously on
Cladonia squamules.
Hue[940] describes Lecanora aspidophora f. errabunda, an Antarctic lichen, as not
only a wanderer but as a “shameless robber.” It is to be seen everywhere on and about
other lichens, settling small glomeruli of apothecia here and there on the thallus of
Umbilicariae or between the areolae of Buelliae, and always too vigorous to be ousted
from its position.
Bacidia flavovirescens has been regarded by some lichenologists[941] as a parasite on
Baeomyces, but recent work by Tobler[942] seems to have proved that the bright green
thallus is that of the Bacidia.
c. Parasymbiosis. There are certain lichens that are obligative parasites and pass their
whole existence on an alien thallus. They may possibly have degenerated from the
condition of facultative parasitism as the universal history of parasitism is one of
increased dependence on the host, and of growing atrophy of the parasite, but, in the
case of lichens, there is always the peculiar symbiotic condition to be considered: the
parasite produces its own vigorous hyphae and normal healthy fruits, it often claims
only a share of the carbohydrates manufactured by the gonidia. The host lichen is not
destroyed by this parasymbiosis though the tissues are very often excited to abnormal
growth by the presence of the invading organism.
Lauder Lindsay[943] was one of the first to study these “microlichens” as he called
them, and he published descriptions of those he had himself observed on various hosts.
Page 335
He failed however to discriminate between lichens and parasitic fungi. It is only by
careful research in each case that the affinity to fungi or to lichens can be determined;
very frequently the whole of them, as possessing no visible thallus, have been classified
with fungi, but that view ignores the symbiosis that exists between the hyphae of the
parasite and the gonidia of the host.
Parasitic lichens are rather rare on gelatinous thalli; but even among these, a few
instances have been recorded. Winter[944] has described a species of Leptoraphis, the
perithecia of which are immersed in the thallus of Physma franconicum. The host is
wholly unaffected by the presence of the parasite except for a swelling where it is
situated. The foreign hyphae are easily distinguishable; they wander through the thallus
of the host with their free ends in the mucilage of the gonidial groups from which they
evidently extract nourishment. Species of the lichen genus Obryzum are also parasitic
on gelatinous lichens.
The parasitic genus Abrothallus[945] has been the subject of frequent study. There are
a number of species which occur as little black discs on various thalli of the large
foliose lichens. They were first of all described as parasitic fungi, later Tulasne[946]
affirmed their lichenoid nature as proved by the structure, consistence and long duration
of the apothecia. Lindsay[947] wrote a monograph of the genus dealing chiefly with
Abrothallus Smithii (Buellia Parmeliarum) and A. oxysporus, with their varieties and
forms that occur on several different hosts. In some instances the thallus is apparently
quite unaffected by the presence of Abrothallus, in others, as in Cetraria glauca, there is
considerable hypertrophy produced, the portion of the thallus on which the parasites are
situated showing abnormal growth in the form of swellings or pustules which may be
regarded as gall-formations. Crombie[948] points this out in a note on C. glauca var.
ampullacea, figured first by Dillenius, which is merely a swollen condition due to the
presence of Abrothallus.
The internal structure and behaviour of Abrothallus has more recently been followed
in detail by Kotte[949]. He recognized a number of different species growing on various
thalli of Parmelia and Cetraria, but Abrothallus Cetrariae was the only one that
produced gall-formation. The mycelium of the parasite in this instance penetrates to the
medulla of the host lichen as a loose weft of hyphae which are divided into more or less
elongate cells. These send out side branches, which grow towards the algal cells, and by
their short-celled filaments clasp them exactly in the same way as do the normal lichen
hyphae. Thus in the neighbourhood of the parasite an algal cell may be surrounded by
the hyphae not only of the host, but also by those of Abrothallus. The two different
hyphae can generally be distinguished by their reaction to iodine: in some cases
Abrothallus hyphae take the stain, in others the host hyphae. In addition to apothecia,
spermogonia or pycnidia are produced, but in one of the species examined by Kotte,
Abrothallus Peyritschii on Cetraria caperata, there was no spermogonial wall formed.
The hyphae also penetrate the host soredia or isidia, so that on the dispersal of these
vegetative bodies the perpetuation of both organisms is secured in the new growth.
careful research in each case that the affinity to fungi or to lichens can be determined;
very frequently the whole of them, as possessing no visible thallus, have been classified
with fungi, but that view ignores the symbiosis that exists between the hyphae of the
parasite and the gonidia of the host.
Parasitic lichens are rather rare on gelatinous thalli; but even among these, a few
instances have been recorded. Winter[944] has described a species of Leptoraphis, the
perithecia of which are immersed in the thallus of Physma franconicum. The host is
wholly unaffected by the presence of the parasite except for a swelling where it is
situated. The foreign hyphae are easily distinguishable; they wander through the thallus
of the host with their free ends in the mucilage of the gonidial groups from which they
evidently extract nourishment. Species of the lichen genus Obryzum are also parasitic
on gelatinous lichens.
The parasitic genus Abrothallus[945] has been the subject of frequent study. There are
a number of species which occur as little black discs on various thalli of the large
foliose lichens. They were first of all described as parasitic fungi, later Tulasne[946]
affirmed their lichenoid nature as proved by the structure, consistence and long duration
of the apothecia. Lindsay[947] wrote a monograph of the genus dealing chiefly with
Abrothallus Smithii (Buellia Parmeliarum) and A. oxysporus, with their varieties and
forms that occur on several different hosts. In some instances the thallus is apparently
quite unaffected by the presence of Abrothallus, in others, as in Cetraria glauca, there is
considerable hypertrophy produced, the portion of the thallus on which the parasites are
situated showing abnormal growth in the form of swellings or pustules which may be
regarded as gall-formations. Crombie[948] points this out in a note on C. glauca var.
ampullacea, figured first by Dillenius, which is merely a swollen condition due to the
presence of Abrothallus.
The internal structure and behaviour of Abrothallus has more recently been followed
in detail by Kotte[949]. He recognized a number of different species growing on various
thalli of Parmelia and Cetraria, but Abrothallus Cetrariae was the only one that
produced gall-formation. The mycelium of the parasite in this instance penetrates to the
medulla of the host lichen as a loose weft of hyphae which are divided into more or less
elongate cells. These send out side branches, which grow towards the algal cells, and by
their short-celled filaments clasp them exactly in the same way as do the normal lichen
hyphae. Thus in the neighbourhood of the parasite an algal cell may be surrounded by
the hyphae not only of the host, but also by those of Abrothallus. The two different
hyphae can generally be distinguished by their reaction to iodine: in some cases
Abrothallus hyphae take the stain, in others the host hyphae. In addition to apothecia,
spermogonia or pycnidia are produced, but in one of the species examined by Kotte,
Abrothallus Peyritschii on Cetraria caperata, there was no spermogonial wall formed.
The hyphae also penetrate the host soredia or isidia, so that on the dispersal of these
vegetative bodies the perpetuation of both organisms is secured in the new growth.
Page 336
Abrothallus draws its organic food from the gonidia in the same way as the host
species, and possibly the parasitic hyphae obtain also water and inorganic food along
with the host hyphae. They have been traced down to the rhizinae and may even reach
the hypothallus, but no injury to the host has been detected. It is a case of joint
symbiosis and not of parasitism. Microscopic research has therefore justified the
inclusion of these and other forms among lichens.
d. Parasymbiosis of Fungi. There occur on lichens, certain parasites classed as fungi
which at an early stage are more or less parasymbionts of the host; as growth advances
they may become parasitic and cause serious damage, killing the tissues on which they
have settled.
Zopf[950] found several instances of such parasymbiosis in his study of fungal
parasites, such as Rhymbocarpus punctiformis, a minute Discomycete which inhabits
the thallus of Rhizocarpon geographicum. By means of staining reagents he was able to
trace the course of the parasitic hyphae, and found that they travelled towards the
gonidia and clasped them lichen-wise without damaging them, since these remained
green and capable of division. At no stage was any harm caused to the host by the alien
organism. Another instance he observed was that of Conida rubescens on the thallus of
Rhizocarpon epipolium. By means of fine sections through the apothecia of Conida and
the thallus of the host, he proved the presence of numerous gonidia in the subhymenial
tissue, these being closely surrounded by the hyphae of the parasite, and entirely
undamaged: they retained their green colour, and in size and form were unchanged.
Zopf[951] at first described these parasites as fungi though later[951] he allows that they
may represent lower forms of lichens.
Tobler[952] has added two more of these parasymbiotic species on the border line
between lichens and fungi, similar to those described by Zopf. One of these, Phacopsis
vulpina, belonging to the fungus family Celidiaceae, is parasitic on Letharia vulpina.
The fronds of the host plant are considerably altered in form by its presence, being more
branched and curly. Where the parasite settles a swelling arises filled with its hyphae,
and the host gonidia almost disappear from the immediate neighbourhood, only a few
“nests” being found and these very mucilaginous. These nests as well as single gonidia
are surrounded by Phacopsis hyphae which have gradually displaced those of the
Letharia thallus. The gonidia are excited to division and increase in number on contact
with either lichen or fungus hyphae, but in the latter case the increase is more abundant
owing doubtless to a more powerful chemical irritant in the fungus. As development
advances, the Phacopsis hyphae multiply to the exclusion of both lichen hyphae and
gonidia from the area of invasion. Finally the host cortex is split, the fungus bursts
through, and the tissue beneath the parasite becomes brown and dead. Phacopsis begins
as a “parasymbiont,” then becomes parasitic, and is at last saprophytic on the dead cells.
The hyphae travel down into the medulla of the host and also into the soredial
outgrowths, and are dispersed along with the host. The effect of Verrucula on the host
thallus may also be cited[953].
species, and possibly the parasitic hyphae obtain also water and inorganic food along
with the host hyphae. They have been traced down to the rhizinae and may even reach
the hypothallus, but no injury to the host has been detected. It is a case of joint
symbiosis and not of parasitism. Microscopic research has therefore justified the
inclusion of these and other forms among lichens.
d. Parasymbiosis of Fungi. There occur on lichens, certain parasites classed as fungi
which at an early stage are more or less parasymbionts of the host; as growth advances
they may become parasitic and cause serious damage, killing the tissues on which they
have settled.
Zopf[950] found several instances of such parasymbiosis in his study of fungal
parasites, such as Rhymbocarpus punctiformis, a minute Discomycete which inhabits
the thallus of Rhizocarpon geographicum. By means of staining reagents he was able to
trace the course of the parasitic hyphae, and found that they travelled towards the
gonidia and clasped them lichen-wise without damaging them, since these remained
green and capable of division. At no stage was any harm caused to the host by the alien
organism. Another instance he observed was that of Conida rubescens on the thallus of
Rhizocarpon epipolium. By means of fine sections through the apothecia of Conida and
the thallus of the host, he proved the presence of numerous gonidia in the subhymenial
tissue, these being closely surrounded by the hyphae of the parasite, and entirely
undamaged: they retained their green colour, and in size and form were unchanged.
Zopf[951] at first described these parasites as fungi though later[951] he allows that they
may represent lower forms of lichens.
Tobler[952] has added two more of these parasymbiotic species on the border line
between lichens and fungi, similar to those described by Zopf. One of these, Phacopsis
vulpina, belonging to the fungus family Celidiaceae, is parasitic on Letharia vulpina.
The fronds of the host plant are considerably altered in form by its presence, being more
branched and curly. Where the parasite settles a swelling arises filled with its hyphae,
and the host gonidia almost disappear from the immediate neighbourhood, only a few
“nests” being found and these very mucilaginous. These nests as well as single gonidia
are surrounded by Phacopsis hyphae which have gradually displaced those of the
Letharia thallus. The gonidia are excited to division and increase in number on contact
with either lichen or fungus hyphae, but in the latter case the increase is more abundant
owing doubtless to a more powerful chemical irritant in the fungus. As development
advances, the Phacopsis hyphae multiply to the exclusion of both lichen hyphae and
gonidia from the area of invasion. Finally the host cortex is split, the fungus bursts
through, and the tissue beneath the parasite becomes brown and dead. Phacopsis begins
as a “parasymbiont,” then becomes parasitic, and is at last saprophytic on the dead cells.
The hyphae travel down into the medulla of the host and also into the soredial
outgrowths, and are dispersed along with the host. The effect of Verrucula on the host
thallus may also be cited[953].
Page 337
Tobler gives the results of his examination of still another fungus, Karschia
destructans. It becomes established on the thallus of Chaenotheca chrysocephala and its
hyphae gradually penetrate down to the underlying bark (larch). The lichen thallus
beneath the fungus is killed, but gonidia in the vicinity are sometimes clasped: Karschia
also is thus a parasymbiont, then a parasite, and finally a saprophyte.
Elenkin[954] describes certain fungi which to some extent are parasymbionts. One of
these, Conidella urceolata n. sp., grew on forms of Lecanora esculenta. The other, a
stroma-forming species, had invaded the thallus of Parmelia molliuscula, where it
caused gall-formation. As the growth of the gall was due to the co-operation of the
lichen gonidia, the fungus must at first have been a parasymbiont. Only dead gonidia
were present in the stroma; probably they had been digested by the parasite. Because of
the stroma Elenkin placed the fungus in a new genus, Trematosphaeriopsis.
e. Fungi Parasitic on Lichens. A solution or extract of lichen thallus is a very
advantageous medium in which to grow fungi. It is therefore not surprising that lichens
are a favourite habitat for parasitic fungi. Stahl[955] has noted that the lichens
themselves flourish best where there is frequent moistening by rain or dew with equally
frequent drying which effectively prevents the growth of fungi. Species of Peltigera are
however able to live in damp conditions: without being injured, they have been
observed to maintain their vigour when cultivated in a very moist hothouse while all the
other forms experimented with were attacked and finally destroyed by various fungi.
Lindsay[956] devoted a great deal of attention to the microscopic study of the minute
fruiting bodies so frequently present on lichen thalli and published descriptions of
microlichens, microfungi and spermogonia. He and others naturally considered these
parasitic organisms to be in many cases either the spermogonia or pycnidia of the lichen
itself. It is often not easy to determine their relationship or their exact systematic
position; many of them are still doubtful forms.
There exists however a very large number of fully recognized parasitic microfungi
belonging to various genera. Lindsay discovered many of them. Zopf[957] has given
exact descriptions of a series of forms, with special reference to their effect on the host
thallus. In an early paper he described a species, Pleospora collematum, that he found
on Physma compactum and other Collemaceae. The hyphae of the parasite differed from
those of the host in being of a yellow colour; they did not penetrate or spread far, being
restricted to rhizoid-like filaments at the base of their fruiting bodies (perithecia and
pycnidia). Their presence caused a slight protuberance but otherwise did no harm to the
host; the Nostoc cells in their immediate vicinity were even more brightly coloured than
in other parts of the thallus. In another paper[958] he gives an instance of gall-formation
in Collema pulposum induced by the presence of the fungus Didymosphaeria pulposi.
Small protuberances were formed on the margins of the apothecia, more rarely on the
lobes of the thallus, each one the seat of a perithecium of the fungus. No damage was
done to either constituent of the thallus.
destructans. It becomes established on the thallus of Chaenotheca chrysocephala and its
hyphae gradually penetrate down to the underlying bark (larch). The lichen thallus
beneath the fungus is killed, but gonidia in the vicinity are sometimes clasped: Karschia
also is thus a parasymbiont, then a parasite, and finally a saprophyte.
Elenkin[954] describes certain fungi which to some extent are parasymbionts. One of
these, Conidella urceolata n. sp., grew on forms of Lecanora esculenta. The other, a
stroma-forming species, had invaded the thallus of Parmelia molliuscula, where it
caused gall-formation. As the growth of the gall was due to the co-operation of the
lichen gonidia, the fungus must at first have been a parasymbiont. Only dead gonidia
were present in the stroma; probably they had been digested by the parasite. Because of
the stroma Elenkin placed the fungus in a new genus, Trematosphaeriopsis.
e. Fungi Parasitic on Lichens. A solution or extract of lichen thallus is a very
advantageous medium in which to grow fungi. It is therefore not surprising that lichens
are a favourite habitat for parasitic fungi. Stahl[955] has noted that the lichens
themselves flourish best where there is frequent moistening by rain or dew with equally
frequent drying which effectively prevents the growth of fungi. Species of Peltigera are
however able to live in damp conditions: without being injured, they have been
observed to maintain their vigour when cultivated in a very moist hothouse while all the
other forms experimented with were attacked and finally destroyed by various fungi.
Lindsay[956] devoted a great deal of attention to the microscopic study of the minute
fruiting bodies so frequently present on lichen thalli and published descriptions of
microlichens, microfungi and spermogonia. He and others naturally considered these
parasitic organisms to be in many cases either the spermogonia or pycnidia of the lichen
itself. It is often not easy to determine their relationship or their exact systematic
position; many of them are still doubtful forms.
There exists however a very large number of fully recognized parasitic microfungi
belonging to various genera. Lindsay discovered many of them. Zopf[957] has given
exact descriptions of a series of forms, with special reference to their effect on the host
thallus. In an early paper he described a species, Pleospora collematum, that he found
on Physma compactum and other Collemaceae. The hyphae of the parasite differed from
those of the host in being of a yellow colour; they did not penetrate or spread far, being
restricted to rhizoid-like filaments at the base of their fruiting bodies (perithecia and
pycnidia). Their presence caused a slight protuberance but otherwise did no harm to the
host; the Nostoc cells in their immediate vicinity were even more brightly coloured than
in other parts of the thallus. In another paper[958] he gives an instance of gall-formation
in Collema pulposum induced by the presence of the fungus Didymosphaeria pulposi.
Small protuberances were formed on the margins of the apothecia, more rarely on the
lobes of the thallus, each one the seat of a perithecium of the fungus. No damage was
done to either constituent of the thallus.
Page 338
Agyrium flavescens grows parasitically on the under surface of Peltigera polydactyla.
M. and Mme Moreau[959] found that the hyphae of the fungus spread between the
medullary filaments of the lichen; no haustoria were observed. The mature fruiting body
had no distinct excipulum, but was surrounded by a layer of dead lichen cells.
It is not easy to determine the difference between parasites that are of fungal nature
and those that are lichenoid; but as a general rule the fungi may be recognized by their
more transient character, very frequently by their effect on the host thallus, which is
more harmful than that produced by lichens, and generally by their affinity to fungi
rather than to lichens. Opinions differ and will continue to differ on this very difficult
question.
The number of such fungi determined and classified has gradually increased, and
now extends to a very long list. Even as far back as 1896 Zopf reckoned up 800
instances of parasitism of 400 species of fungi on about 350 different lichens and many
more have been added. Abbé Vouaux[960] is the latest writer on the subject, but his work
is mostly a compilation of species already known. He finds representatives of these
parasites in nine families of Pyrenomycetes and six of Discomycetes. He leaves out of
account the much debated Coniocarps, but he includes with fungi all those that have
been proved to be parasymbiotic, such as Abrothallus.
A number of fungus genera, such as Conida, etc., are parasitic only on lichens. Most
of them have one host only; others, such as Tichothecium pygmaeum, live on a number
of different thalli. Crustaceous species are often selected by the parasites, and no great
damage, if any, is caused to these hosts, except when the fungus is seated on the disc of
the apothecium, so that the spore-bearing capacity is lessened or destroyed.
In some of the larger lichens, however, harmful effects are more visible. In Lobaria
pulmonaria, the fruits of which are attacked by the Discomycete, Celidium
Stictarum[961], there is at first induced an increased and unusual formation of lichen
apothecia. These apothecia are normally seated for the most part on the margins of the
lobes or pustules, but when they are invaded by the fungus, they appear also in the
hollows between the pustules and even on the under surface of the thallus. In the large
majority of cases the fungus is partly or entirely embedded in the thallus; the gonidia in
the vicinity may remain green and healthy, or all the tissues in the immediate
neighbourhood of the parasite may be killed.
f. Mycetozoa Parasitic on Lichens. Mycetozoa live mostly on decayed wood, leaves,
humus, etc. One minute species, Listerella paradoxa, always inhabits the podetia of
Cladonia rangiferina. Another species, Hymenobolina parasitica, was first detected and
described by Zukal[962] as a true parasite on the thallus of Physciaceae; it has since been
recorded in the British Islands on Parmeliae[963]. This peculiar organism differs from
other mycetozoa in that the spores on germination produce amoebae. These unite to
form a rose-red plasmodium which slowly burrows into the lichen thallus and feeds on
the living hyphae. It is a minute species, but when abundant the plasmodia can just be
M. and Mme Moreau[959] found that the hyphae of the fungus spread between the
medullary filaments of the lichen; no haustoria were observed. The mature fruiting body
had no distinct excipulum, but was surrounded by a layer of dead lichen cells.
It is not easy to determine the difference between parasites that are of fungal nature
and those that are lichenoid; but as a general rule the fungi may be recognized by their
more transient character, very frequently by their effect on the host thallus, which is
more harmful than that produced by lichens, and generally by their affinity to fungi
rather than to lichens. Opinions differ and will continue to differ on this very difficult
question.
The number of such fungi determined and classified has gradually increased, and
now extends to a very long list. Even as far back as 1896 Zopf reckoned up 800
instances of parasitism of 400 species of fungi on about 350 different lichens and many
more have been added. Abbé Vouaux[960] is the latest writer on the subject, but his work
is mostly a compilation of species already known. He finds representatives of these
parasites in nine families of Pyrenomycetes and six of Discomycetes. He leaves out of
account the much debated Coniocarps, but he includes with fungi all those that have
been proved to be parasymbiotic, such as Abrothallus.
A number of fungus genera, such as Conida, etc., are parasitic only on lichens. Most
of them have one host only; others, such as Tichothecium pygmaeum, live on a number
of different thalli. Crustaceous species are often selected by the parasites, and no great
damage, if any, is caused to these hosts, except when the fungus is seated on the disc of
the apothecium, so that the spore-bearing capacity is lessened or destroyed.
In some of the larger lichens, however, harmful effects are more visible. In Lobaria
pulmonaria, the fruits of which are attacked by the Discomycete, Celidium
Stictarum[961], there is at first induced an increased and unusual formation of lichen
apothecia. These apothecia are normally seated for the most part on the margins of the
lobes or pustules, but when they are invaded by the fungus, they appear also in the
hollows between the pustules and even on the under surface of the thallus. In the large
majority of cases the fungus is partly or entirely embedded in the thallus; the gonidia in
the vicinity may remain green and healthy, or all the tissues in the immediate
neighbourhood of the parasite may be killed.
f. Mycetozoa Parasitic on Lichens. Mycetozoa live mostly on decayed wood, leaves,
humus, etc. One minute species, Listerella paradoxa, always inhabits the podetia of
Cladonia rangiferina. Another species, Hymenobolina parasitica, was first detected and
described by Zukal[962] as a true parasite on the thallus of Physciaceae; it has since been
recorded in the British Islands on Parmeliae[963]. This peculiar organism differs from
other mycetozoa in that the spores on germination produce amoebae. These unite to
form a rose-red plasmodium which slowly burrows into the lichen thallus and feeds on
the living hyphae. It is a minute species, but when abundant the plasmodia can just be
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detected with the naked eye as rosy specks scattered over the surface of the lichen. Later
the grey sporangia are produced on the same areas.
F. Diseases of Lichens
a. Caused by Parasitism. Zopf[964] has stated that of all plants, lichens are the most
subject to disease, reckoning as diseases all the instances of parasitism by fungi or by
other lichens. There are however only rare instances in which total destruction or indeed
any permanent harm to the host is the result of such parasitism. At worst the trouble is
localized and does not affect the organism as a whole. Some of these cases have been
already noted under antagonistic symbiosis or parasymbiosis. Several instances have
however been recorded where real injury has been caused by the penetration of some
undetermined fungus mycelium. Zukal[965] records two such observed by him in
Parmelia encausta and Physcia villosa: the thallus of the former was dwarfed and
deformed by the presence of the alien mycelium, the latter was excited to abnormal
proliferation.
b. Caused by crowding. Lichens suffer frequently from being overgrown by other
lichens; they may also be crowded out by other plants. My attention was called by Mr P.
Thompson to a burnt plot of ground in Epping Forest, which, after the fire, had been
colonized by Peltigera spuria. In the course of a few years, other vegetation had
followed, depriving the lichen of space and light and gradually driving it out. When last
examined only a few miserable specimens remained, and these were reduced in vitality
by an attack of the lichen parasite Illosporium carneum.
c. Caused by adverse conditions. Zukal considers as pathological, at least in origin,
the cracking of the thallus so frequent in crustaceous lichens as well as in the more
highly developed forms. As the cracks are beneficial in the aeration of the plant, they
can hardly be regarded as symptoms of a diseased condition. The more evident ringed
breaks in the cortex of Usneae, due probably to wind action, have more reason to be so
regarded; they are most pronounced in Usnea articulata, where the portions bounded by
the rings are contracted and swollen, and a hollow space is formed between the cortex
and the central axis. The swellings that are produced on lichen thalli, such as those of
Umbilicaria and some species of Gyrophora, due to intercalary growth are normal to
the plant, though occasionally the swollen weaker portions may become ruptured and
the cortex be thrown off. As pathological also must be regarded the loss of cortex
sometimes occasioned by excessive soredial formation at the margins of the lobes: the
upper cortex may be rolled back and eventually torn away; the gonidial layer is exposed
and transformed into soredia which are swept away by the wind and rain, till finally
only traces of the lower cortex are left.
Zukal[966] has instanced, as a case of diseased condition observed by him, the undue
thickening of the cortex in Pertusaria communis whereby the formation of the fruiting
bodies is inhibited and even vegetative development is rendered impossible. There
the grey sporangia are produced on the same areas.
F. Diseases of Lichens
a. Caused by Parasitism. Zopf[964] has stated that of all plants, lichens are the most
subject to disease, reckoning as diseases all the instances of parasitism by fungi or by
other lichens. There are however only rare instances in which total destruction or indeed
any permanent harm to the host is the result of such parasitism. At worst the trouble is
localized and does not affect the organism as a whole. Some of these cases have been
already noted under antagonistic symbiosis or parasymbiosis. Several instances have
however been recorded where real injury has been caused by the penetration of some
undetermined fungus mycelium. Zukal[965] records two such observed by him in
Parmelia encausta and Physcia villosa: the thallus of the former was dwarfed and
deformed by the presence of the alien mycelium, the latter was excited to abnormal
proliferation.
b. Caused by crowding. Lichens suffer frequently from being overgrown by other
lichens; they may also be crowded out by other plants. My attention was called by Mr P.
Thompson to a burnt plot of ground in Epping Forest, which, after the fire, had been
colonized by Peltigera spuria. In the course of a few years, other vegetation had
followed, depriving the lichen of space and light and gradually driving it out. When last
examined only a few miserable specimens remained, and these were reduced in vitality
by an attack of the lichen parasite Illosporium carneum.
c. Caused by adverse conditions. Zukal considers as pathological, at least in origin,
the cracking of the thallus so frequent in crustaceous lichens as well as in the more
highly developed forms. As the cracks are beneficial in the aeration of the plant, they
can hardly be regarded as symptoms of a diseased condition. The more evident ringed
breaks in the cortex of Usneae, due probably to wind action, have more reason to be so
regarded; they are most pronounced in Usnea articulata, where the portions bounded by
the rings are contracted and swollen, and a hollow space is formed between the cortex
and the central axis. The swellings that are produced on lichen thalli, such as those of
Umbilicaria and some species of Gyrophora, due to intercalary growth are normal to
the plant, though occasionally the swollen weaker portions may become ruptured and
the cortex be thrown off. As pathological also must be regarded the loss of cortex
sometimes occasioned by excessive soredial formation at the margins of the lobes: the
upper cortex may be rolled back and eventually torn away; the gonidial layer is exposed
and transformed into soredia which are swept away by the wind and rain, till finally
only traces of the lower cortex are left.
Zukal[966] has instanced, as a case of diseased condition observed by him, the undue
thickening of the cortex in Pertusaria communis whereby the formation of the fruiting
bodies is inhibited and even vegetative development is rendered impossible. There
Page 340
arrives finally a stage when splitting takes place and the whole thallus breaks down and
disappears. As a rule however there need be no limit to the age of the lichen plant.
There is no vital point or area in the thallus; injury of one part leaves the rest unhurt,
and any fragment in growing condition, if it combines both symbionts, can carry on the
life of the plant, the constant renewal of gonidia preventing either decay or death.
Barring accidents many lichens might exist as long as the world endures.
G. Harmful Effect of Lichens
One lichen only, Strigula complanata, a tropical species, has been proved to be truly
and constantly parasitic. It grows on the surface of thick leathery leaves such as those of
Camellia[967], etc. and the alga and fungus both penetrate the epidermis and burrow
beneath the cuticle and outer cells, causing them to become brown. It undoubtedly
injures the leaves.
Friedrich[968] has given an isolated instance of the hold-fast hyphae of Usnea piercing
through the cortex to the living tissue of the host, and not only destroying the middle
lamella by absorption, but entering the cells. The Usnea plant was characterized by
exceptionally vigorous growth. Practically all corticolous lichens are epiphytic and the
injury they cause is of an accidental nature. Crustaceous species on the outer bark
occupy the dead cortical layers and seem to be entirely harmless[969]. The larger foliose
and fruticose forms are not so innocuous: by their abundant enveloping growth they
hinder the entrance of air and moisture, and thus impede the life of the higher plant.
Gleditsch[970], one of the earliest writers on Forestry, first indicated the possibly
harmful effect of lichens especially on young trees and “in addition,” he says, “they
serve as cover for large numbers of small insects which are hurtful in many ways to the
trees.” Lindau[971] pointed out the damage done to pine-needles by Xanthoria parietina
which grew round them like a cuff and probably choked the stomata, the leaves so
clothed being mostly withered. Dufrenoy[972] states that he found the hyphae of a
Parmelia entering a pine-needle by the stomata, and that the starch disappeared from
the neighbouring parenchyma the cells of which tended to disintegrate.
It is no uncommon sight to see neglected fruit trees with their branches crowded with
various lichens, Evernia prunastri, Ramalina farinacea, etc. Such lichens often find the
lenticels a convenient opening for their hold-fasts and exercise a smothering effect on
the trees. Lilian Porter[973] distinctly states that Ramalinae by their penetrating bases
damage the tissues of the trees. The presence of lichens is however generally due to
unhealthy conditions already at work. Friedrich[974] reported of a forest which he
examined, in which the atmospheric moisture was very high, with the soil water scarce,
that those trees that were best supplied with soil water were free from lichens, while
those with little water at the base bore dead branches which gave foothold to a rich
growth of the epiphytes.
disappears. As a rule however there need be no limit to the age of the lichen plant.
There is no vital point or area in the thallus; injury of one part leaves the rest unhurt,
and any fragment in growing condition, if it combines both symbionts, can carry on the
life of the plant, the constant renewal of gonidia preventing either decay or death.
Barring accidents many lichens might exist as long as the world endures.
G. Harmful Effect of Lichens
One lichen only, Strigula complanata, a tropical species, has been proved to be truly
and constantly parasitic. It grows on the surface of thick leathery leaves such as those of
Camellia[967], etc. and the alga and fungus both penetrate the epidermis and burrow
beneath the cuticle and outer cells, causing them to become brown. It undoubtedly
injures the leaves.
Friedrich[968] has given an isolated instance of the hold-fast hyphae of Usnea piercing
through the cortex to the living tissue of the host, and not only destroying the middle
lamella by absorption, but entering the cells. The Usnea plant was characterized by
exceptionally vigorous growth. Practically all corticolous lichens are epiphytic and the
injury they cause is of an accidental nature. Crustaceous species on the outer bark
occupy the dead cortical layers and seem to be entirely harmless[969]. The larger foliose
and fruticose forms are not so innocuous: by their abundant enveloping growth they
hinder the entrance of air and moisture, and thus impede the life of the higher plant.
Gleditsch[970], one of the earliest writers on Forestry, first indicated the possibly
harmful effect of lichens especially on young trees and “in addition,” he says, “they
serve as cover for large numbers of small insects which are hurtful in many ways to the
trees.” Lindau[971] pointed out the damage done to pine-needles by Xanthoria parietina
which grew round them like a cuff and probably choked the stomata, the leaves so
clothed being mostly withered. Dufrenoy[972] states that he found the hyphae of a
Parmelia entering a pine-needle by the stomata, and that the starch disappeared from
the neighbouring parenchyma the cells of which tended to disintegrate.
It is no uncommon sight to see neglected fruit trees with their branches crowded with
various lichens, Evernia prunastri, Ramalina farinacea, etc. Such lichens often find the
lenticels a convenient opening for their hold-fasts and exercise a smothering effect on
the trees. Lilian Porter[973] distinctly states that Ramalinae by their penetrating bases
damage the tissues of the trees. The presence of lichens is however generally due to
unhealthy conditions already at work. Friedrich[974] reported of a forest which he
examined, in which the atmospheric moisture was very high, with the soil water scarce,
that those trees that were best supplied with soil water were free from lichens, while
those with little water at the base bore dead branches which gave foothold to a rich
growth of the epiphytes.
Page 341
Experiments to free fruit trees from their coating of lichens were made by Waite[975].
With a whitewash brush he painted over the infested branches with solutions of
Bordeaux mixture of varying strength, and found that this solution, commonly in use as
a fungicide, was entirely successful. The trees were washed down about the middle of
March, and some three weeks later the lichens were all dead, the fruticose and foliose
forms had changed in colour to a yellowish or brownish tint and were drooping and
shrivelled.
Waite was of opinion that the lichens did considerable damage to the trees, but it has
been held by others that in very cold climates they may provide protection against
severe frost. Instances of damage are however asserted by Bouly de Lesdain[976]. The
bark of willows he found was a favourite habitat of numerous lichens: certain species,
such as Xanthoria parietina, completely surrounded the branches, closing the stomata;
others, such as Physcia ascendens, by the mechanical strain of the rhizoids, first wet
and then dry, gradually loosened the outer bark and gave entry to fungi which
completed the work of destruction.
H. Gall-Formation
Several instances of gall-formation to a limited extent have been already noted as
caused by parasitic fungi or lichens. Greater abnormality of development is induced in a
few species by the presence of minute animals, mites, wood-lice, etc. Zopf[977] noted
these deformations of the thallus in specimens of Ramalina Kullensis collected on the
coasts of Sweden. The fronds were frequently swollen in a sausage-like manner, and
branching was hindered or altogether prevented; apothecia were rarely formed, though
pycnidia were abundant. Here and there, on the swollen portions of the thallus, small
holes could be detected and other larger openings of elliptical outline, about 1-1-1/2
mm. in diameter, the margins of which had a nibbled appearance. Three types of small
articulated animals were found within the openings: species of mites, spiders and wood-
lice. Mites were the most constant and were more or less abundant in all the
deformations; frequently a minute Diplopodon belonging to the genus Polyxenus was
also met with.
Zopf came to the conclusion that the gall-formation was mainly due to the mites: they
eat out the medulla and possibly through some chemical irritation excite the algal zone
and cortex to more active growth, so that an extensive tangential development takes
place. The small spiders may exercise the same power; evidently the larger holes were
formed by them.
Later Zopf added to gall-deformed plants Ramalina scopulorum var. incrassata and
R. cuspidata var. crassa. He found in the hollow swollen fronds abundant evidence of
mites, but whether identical with those that attacked R. Kullensis could not be
determined. These two Ramalinae are maritime species; they are morphologically
With a whitewash brush he painted over the infested branches with solutions of
Bordeaux mixture of varying strength, and found that this solution, commonly in use as
a fungicide, was entirely successful. The trees were washed down about the middle of
March, and some three weeks later the lichens were all dead, the fruticose and foliose
forms had changed in colour to a yellowish or brownish tint and were drooping and
shrivelled.
Waite was of opinion that the lichens did considerable damage to the trees, but it has
been held by others that in very cold climates they may provide protection against
severe frost. Instances of damage are however asserted by Bouly de Lesdain[976]. The
bark of willows he found was a favourite habitat of numerous lichens: certain species,
such as Xanthoria parietina, completely surrounded the branches, closing the stomata;
others, such as Physcia ascendens, by the mechanical strain of the rhizoids, first wet
and then dry, gradually loosened the outer bark and gave entry to fungi which
completed the work of destruction.
H. Gall-Formation
Several instances of gall-formation to a limited extent have been already noted as
caused by parasitic fungi or lichens. Greater abnormality of development is induced in a
few species by the presence of minute animals, mites, wood-lice, etc. Zopf[977] noted
these deformations of the thallus in specimens of Ramalina Kullensis collected on the
coasts of Sweden. The fronds were frequently swollen in a sausage-like manner, and
branching was hindered or altogether prevented; apothecia were rarely formed, though
pycnidia were abundant. Here and there, on the swollen portions of the thallus, small
holes could be detected and other larger openings of elliptical outline, about 1-1-1/2
mm. in diameter, the margins of which had a nibbled appearance. Three types of small
articulated animals were found within the openings: species of mites, spiders and wood-
lice. Mites were the most constant and were more or less abundant in all the
deformations; frequently a minute Diplopodon belonging to the genus Polyxenus was
also met with.
Zopf came to the conclusion that the gall-formation was mainly due to the mites: they
eat out the medulla and possibly through some chemical irritation excite the algal zone
and cortex to more active growth, so that an extensive tangential development takes
place. The small spiders may exercise the same power; evidently the larger holes were
formed by them.
Later Zopf added to gall-deformed plants Ramalina scopulorum var. incrassata and
R. cuspidata var. crassa. He found in the hollow swollen fronds abundant evidence of
mites, but whether identical with those that attacked R. Kullensis could not be
determined. These two Ramalinae are maritime species; they are morphologically
Page 342
identical, as are also the deformed varieties, and the presence of mites, excreta, etc., are
plainly visible in our British specimens.
Bouly de Lesdain[978] found evidence of mite action in Ramalina farinacea collected
from Pinus sylvestris on the dunes near Dunkirk. The cortex had been eaten off either
by mites or by a small mollusc (Pupa muscorum) and the fronds had collapsed to a
more or less convex compact mass. Somewhat similar deformations, though less
pronounced, were observed in other Ramalinae.
In Cladonia sylvatica and also in Cl. rangiformis Lesdain has indicated ff. abortiva
Harm. as evidently the result of insect attack. In both cases the tips of the podetia are
swollen, brown, bent and shrivelled.
One of the most curious and constant effects, also worked out by Lesdain, occurs in
Physcia hispida (Ph. stellaris var. tenella). In that lichen the gonidia at the tips of the
fronds are scooped out and eaten by mites, so that the upper cortex becomes separated
from the lower part of the thallus. As the hyphae of the cortex continue to develop, an
arched hood is formed of a whitish shell-like appearance and powdery inside.
Sometimes the mites penetrate at one point only, at other times the attack is at several
places which may ultimately coalesce into one large cavity. In a crustaceous species,
Caloplaca (Placodium) citrina he found constant evidence of the disturbing effect of
the small creatures, which by their action caused the areolae of the thallus to grow into
minute adherent squamules. A pathological variety, which he calls var. sorediosa, is
distinguished by the presence of cup-like hollows which are scooped out by Acarinae
and are filled by yellowish soredia. In another form, var. maritima, the margins of the
areolae, occasionally the whole surface, become powdery with a citrine yellow
efflorescence as a result of their nibbling.
Zukal[979] adds to the deformations due to organic agents, the hypertrophies and
abnormalities caused by climatic conditions. He finds such irregularities of structure
more especially developed in countries with a very limited rainfall, as in certain districts
of Chili, Australia and Africa, where changes in cortex and rhizoids and proliferations
of the thallus testify to the disturbance of normal development.
plainly visible in our British specimens.
Bouly de Lesdain[978] found evidence of mite action in Ramalina farinacea collected
from Pinus sylvestris on the dunes near Dunkirk. The cortex had been eaten off either
by mites or by a small mollusc (Pupa muscorum) and the fronds had collapsed to a
more or less convex compact mass. Somewhat similar deformations, though less
pronounced, were observed in other Ramalinae.
In Cladonia sylvatica and also in Cl. rangiformis Lesdain has indicated ff. abortiva
Harm. as evidently the result of insect attack. In both cases the tips of the podetia are
swollen, brown, bent and shrivelled.
One of the most curious and constant effects, also worked out by Lesdain, occurs in
Physcia hispida (Ph. stellaris var. tenella). In that lichen the gonidia at the tips of the
fronds are scooped out and eaten by mites, so that the upper cortex becomes separated
from the lower part of the thallus. As the hyphae of the cortex continue to develop, an
arched hood is formed of a whitish shell-like appearance and powdery inside.
Sometimes the mites penetrate at one point only, at other times the attack is at several
places which may ultimately coalesce into one large cavity. In a crustaceous species,
Caloplaca (Placodium) citrina he found constant evidence of the disturbing effect of
the small creatures, which by their action caused the areolae of the thallus to grow into
minute adherent squamules. A pathological variety, which he calls var. sorediosa, is
distinguished by the presence of cup-like hollows which are scooped out by Acarinae
and are filled by yellowish soredia. In another form, var. maritima, the margins of the
areolae, occasionally the whole surface, become powdery with a citrine yellow
efflorescence as a result of their nibbling.
Zukal[979] adds to the deformations due to organic agents, the hypertrophies and
abnormalities caused by climatic conditions. He finds such irregularities of structure
more especially developed in countries with a very limited rainfall, as in certain districts
of Chili, Australia and Africa, where changes in cortex and rhizoids and proliferations
of the thallus testify to the disturbance of normal development.
Page 343
CHAPTER VII
PHYLOGENY
I. GENERAL STATEMENT
A. Origin of Lichens
Though lichens are very old members of the vegetable kingdom, as symbiotic plants
they yet date necessarily from a time subsequent to the evolution of their component
symbionts. Phylogeny of lichens begins with symbiosis.
The algae, which belong to those families of Chlorophyceae and Myxophyceae that
live on dry land, had become aerial before their association with fungi to form lichens.
They must have been as fully developed then as now, since it is possible to refer them to
the genus or sometimes even to the species of free-living forms. The fungus hyphae
have combined with a considerable number of different algae, so that, even as regards
the algal symbiont, lichens are truly polyphyletic in origin.
The fungus is, however, the dominant partner, and the principal line of development
must be traced through it, as it provides the reproductive organs of the plant.
Representatives of two great groups of fungi are associated with lichens:
Basidiomycetes, found in only a few genera, and Ascomycetes which form with the
various algae the great bulk of lichen families. In respect of their fungal constituents
lichens are also polyphyletic, and more especially in the Ascolichens which can be
traced back to several starting points. But though lichens have no common origin, the
manner of life is common to them all and has influenced them all in certain directions:
they are fitted for a much longer existence than that of the fungi from which they
started; and both the thallus and the fruiting bodies—at least in the sub-class
Ascolichens—can persist through great climatic changes, and can pass unharmed
through prolonged periods of latent or suspended vitality.
Another striking note of similarity that runs through the members of this sub-class,
with perhaps the exception of the gelatinous lichens, is the formation of lichen-acids
which are excreted by the fungus. These substances are peculiar to lichens and go far to
mark their autonomy. The production of the acids and the many changes evolved in the
vegetative thallus suggest the great antiquity of lichens.
B. Algal Ancestors
It is unnecessary to look far for the algae as they have persisted through the ages in
the same form both without and within the lichen thallus. By many early lichenologists
PHYLOGENY
I. GENERAL STATEMENT
A. Origin of Lichens
Though lichens are very old members of the vegetable kingdom, as symbiotic plants
they yet date necessarily from a time subsequent to the evolution of their component
symbionts. Phylogeny of lichens begins with symbiosis.
The algae, which belong to those families of Chlorophyceae and Myxophyceae that
live on dry land, had become aerial before their association with fungi to form lichens.
They must have been as fully developed then as now, since it is possible to refer them to
the genus or sometimes even to the species of free-living forms. The fungus hyphae
have combined with a considerable number of different algae, so that, even as regards
the algal symbiont, lichens are truly polyphyletic in origin.
The fungus is, however, the dominant partner, and the principal line of development
must be traced through it, as it provides the reproductive organs of the plant.
Representatives of two great groups of fungi are associated with lichens:
Basidiomycetes, found in only a few genera, and Ascomycetes which form with the
various algae the great bulk of lichen families. In respect of their fungal constituents
lichens are also polyphyletic, and more especially in the Ascolichens which can be
traced back to several starting points. But though lichens have no common origin, the
manner of life is common to them all and has influenced them all in certain directions:
they are fitted for a much longer existence than that of the fungi from which they
started; and both the thallus and the fruiting bodies—at least in the sub-class
Ascolichens—can persist through great climatic changes, and can pass unharmed
through prolonged periods of latent or suspended vitality.
Another striking note of similarity that runs through the members of this sub-class,
with perhaps the exception of the gelatinous lichens, is the formation of lichen-acids
which are excreted by the fungus. These substances are peculiar to lichens and go far to
mark their autonomy. The production of the acids and the many changes evolved in the
vegetative thallus suggest the great antiquity of lichens.
B. Algal Ancestors
It is unnecessary to look far for the algae as they have persisted through the ages in
the same form both without and within the lichen thallus. By many early lichenologists
Page 344
the free-living algae, similar in type to lichen algae, were even supposed to be lichen
gonidia in a depauperate condition and were, for that reason, termed by Wallroth
“unfortunate brood-cells.” In the condition of symbiosis they may be considerably
modified, but they revert to their normal form, and resume their normal life-history of
spore production, etc., under suitable and free culture. The different algae taking part in
lichen-formation have been treated in an earlier chapter[980].
C. Fungal Ancestors
a. Hymenolichens. The problem of the fungal origin in this sub-class is
comparatively simple. It contains but three genera of tropical lichens which are all
associated with Myxophyceae, and the fungus in them, to judge from the form and habit
of the plants, is a member of the Thelephoraceae. It may be that Hymenolichens are of
comparatively recent origin and that the fungi belonging to the Basidiomycetes had, in
the course of time, become less labile and less capable of originating a new method of
existence. Whatever the reason, they lag immeasurably behind Ascomycetes in the
formation of lichens.
b. Ascolichens. Lichens are again polyphyletic within this sub-class. The main
groups from which they are derived are evident. Whether there has been a series of
origins within the different groups or a development from one starting point in each it
would be difficult to determine. In any case great changes have taken place after
symbiosis became established.
The main divisions within the Ascolichens are related to fungi thus:
Series 1. Pyrenocarpineae }
to Pyrenomycetes.
2. Coniocarpineae }
3. Graphidineae to Hysteriaceae.
4. Cyclocarpineae to Discomycetes.
II. THE REPRODUCTIVE ORGANS
A. Theories of Descent in Ascolichens
It has been suggested that ascomycetous fungi, from which Ascolichens are directly
derived, are allied to the Florideae, owing to the appearance of a trichogyne in the
carpogonium of both groups. That organ in the red seaweeds is a long delicate cell in
direct communication with the egg-cell of the carpogonium. It is a structure adapted to
totally submerged conditions, and fitted to attach the floating spermatia.
In fungi there is also a structure considered as a trichogyne[981], which, in the
Laboulbeniales, is a free, simple or branching organ. There is no other instance of any
gonidia in a depauperate condition and were, for that reason, termed by Wallroth
“unfortunate brood-cells.” In the condition of symbiosis they may be considerably
modified, but they revert to their normal form, and resume their normal life-history of
spore production, etc., under suitable and free culture. The different algae taking part in
lichen-formation have been treated in an earlier chapter[980].
C. Fungal Ancestors
a. Hymenolichens. The problem of the fungal origin in this sub-class is
comparatively simple. It contains but three genera of tropical lichens which are all
associated with Myxophyceae, and the fungus in them, to judge from the form and habit
of the plants, is a member of the Thelephoraceae. It may be that Hymenolichens are of
comparatively recent origin and that the fungi belonging to the Basidiomycetes had, in
the course of time, become less labile and less capable of originating a new method of
existence. Whatever the reason, they lag immeasurably behind Ascomycetes in the
formation of lichens.
b. Ascolichens. Lichens are again polyphyletic within this sub-class. The main
groups from which they are derived are evident. Whether there has been a series of
origins within the different groups or a development from one starting point in each it
would be difficult to determine. In any case great changes have taken place after
symbiosis became established.
The main divisions within the Ascolichens are related to fungi thus:
Series 1. Pyrenocarpineae }
to Pyrenomycetes.
2. Coniocarpineae }
3. Graphidineae to Hysteriaceae.
4. Cyclocarpineae to Discomycetes.
II. THE REPRODUCTIVE ORGANS
A. Theories of Descent in Ascolichens
It has been suggested that ascomycetous fungi, from which Ascolichens are directly
derived, are allied to the Florideae, owing to the appearance of a trichogyne in the
carpogonium of both groups. That organ in the red seaweeds is a long delicate cell in
direct communication with the egg-cell of the carpogonium. It is a structure adapted to
totally submerged conditions, and fitted to attach the floating spermatia.
In fungi there is also a structure considered as a trichogyne[981], which, in the
Laboulbeniales, is a free, simple or branching organ. There is no other instance of any
Page 345
similar emergent cell or cells connected with the ascogonium of the Ascomycetes,
though the term has been applied in these fungi to certain short hyphal branches from
the ascogonium which remain embedded in the tissue. In the Ascomycetes examined all
traces of emergent receptive organs, if they ever existed, have now disappeared; in some
few there are possible internal survivals which never reach the surface.
In Ascolichens, on the contrary, the “trichogyne,” a septate hyphal branch extending
upwards from the ascogonium, and generally reaching the open, has been demonstrated
in all the different groups except, as yet, in the Coniocarpineae which have not been
investigated. Its presence is a strong point in the argument of those who believe in the
Floridean ancestry of the Ascomycetes. It should be clearly borne in mind that
Ascolichens are evolved from the Ascomycetes: these latter stand between them and
any more remote ancestry.
In the Ascomycetes, there is a recognized progression of development in the form of
the sporophore from the closed perithecium of the Pyrenomycetes and possibly through
the Hysteriaceae, which are partially closed, to the open ascocarp of the Discomycetes.
If the fungal and lichenoid “trichogyne” is homologous with the carpogonial organ in
the Florideae, then it must have been retained in all the groups of Ascomycetes as an
emergent structure, and as such passed on from them to their lichen derivatives. Has
that organ then disappeared from fungi since symbiosis began? There is no trace of it
now, except as already stated in Laboulbeniales with which lichens are unconnected.
Were Ascolichens monophyletic in origin, one could more easily suppose that both
the fungal and lichen series might have started at some early stage from a common
fungal ancestor possessing a well-developed trichogyne which has persisted in lichens,
but has been reduced to insignificance in fungi, while fruit development proceeded on
parallel lines in both. There is no evidence that such progression has taken place among
lichens; the theory of a polyphyletic origin for the different series seems to be
unassailable. At the same time, there is no evidence to show in which series symbiosis
started first.
It is more reasonable to accept the polyphyletic origin, as outlined above, from forms
that had already lost the trichogyne, if they ever really possessed it, and to regard the
lichen trichogyne as a new organ developing in lichens in response to some requirement
of the deep-seated ascogonium. Its sexual function still awaits satisfactory proof, and it
is wiser to withhold judgment as to the service it renders to the developing fruit.
B. Relation of Lichens to Fungi
a. Pyrenocarpineae. In Phycolichens (containing blue-green gonidia) and especially
in the gelatinous forms, fructification is nearly always a more or less open apothecium.
The general absence of the perithecial type is doubtless due to the gelatinous
consistency of the vegetative structure; it is by the aid of moisture that the hymenial
elements become turgid enough to secure the ejection of the spores through the narrow
though the term has been applied in these fungi to certain short hyphal branches from
the ascogonium which remain embedded in the tissue. In the Ascomycetes examined all
traces of emergent receptive organs, if they ever existed, have now disappeared; in some
few there are possible internal survivals which never reach the surface.
In Ascolichens, on the contrary, the “trichogyne,” a septate hyphal branch extending
upwards from the ascogonium, and generally reaching the open, has been demonstrated
in all the different groups except, as yet, in the Coniocarpineae which have not been
investigated. Its presence is a strong point in the argument of those who believe in the
Floridean ancestry of the Ascomycetes. It should be clearly borne in mind that
Ascolichens are evolved from the Ascomycetes: these latter stand between them and
any more remote ancestry.
In the Ascomycetes, there is a recognized progression of development in the form of
the sporophore from the closed perithecium of the Pyrenomycetes and possibly through
the Hysteriaceae, which are partially closed, to the open ascocarp of the Discomycetes.
If the fungal and lichenoid “trichogyne” is homologous with the carpogonial organ in
the Florideae, then it must have been retained in all the groups of Ascomycetes as an
emergent structure, and as such passed on from them to their lichen derivatives. Has
that organ then disappeared from fungi since symbiosis began? There is no trace of it
now, except as already stated in Laboulbeniales with which lichens are unconnected.
Were Ascolichens monophyletic in origin, one could more easily suppose that both
the fungal and lichen series might have started at some early stage from a common
fungal ancestor possessing a well-developed trichogyne which has persisted in lichens,
but has been reduced to insignificance in fungi, while fruit development proceeded on
parallel lines in both. There is no evidence that such progression has taken place among
lichens; the theory of a polyphyletic origin for the different series seems to be
unassailable. At the same time, there is no evidence to show in which series symbiosis
started first.
It is more reasonable to accept the polyphyletic origin, as outlined above, from forms
that had already lost the trichogyne, if they ever really possessed it, and to regard the
lichen trichogyne as a new organ developing in lichens in response to some requirement
of the deep-seated ascogonium. Its sexual function still awaits satisfactory proof, and it
is wiser to withhold judgment as to the service it renders to the developing fruit.
B. Relation of Lichens to Fungi
a. Pyrenocarpineae. In Phycolichens (containing blue-green gonidia) and especially
in the gelatinous forms, fructification is nearly always a more or less open apothecium.
The general absence of the perithecial type is doubtless due to the gelatinous
consistency of the vegetative structure; it is by the aid of moisture that the hymenial
elements become turgid enough to secure the ejection of the spores through the narrow
Page 346
ostiole of the perithecium, and this process would be frustrated were the surrounding
and enveloping thallus also gelatinous. There is only one minutely foliose or fruticose
gelatinous family, the Pyrenidiaceae, in which Pyrenomycetes are established, and the
gonidia, even though blue-green, have lost the gelatinous sheath and do not swell up.
In Archilichens (with bright-green gonidia), perithecial fruits occur frequently; they
are nearly always simple and solitary; in only a few families with a few representatives,
is there any approach to the stroma formation so marked among fungi. The single
perithecium is generally semi-immersed in the thallus. It may be completely surrounded
by a hyphal “entire” wall, either soft and waxy or dark coloured and somewhat
carbonaceous. In numerous species the outer protective wall covers only the upper
portion that projects beyond the thallus, and such a perithecium is described as
“dimidiate,” a type of fruit occurring in several genera, though rare among fungi.
As to internal structure, there is a dissolution and disappearance of the paraphyses in
some genera, their protective function not being so necessary in closed fruits, a
character paralleled in fungi. There is a great variety of spore changes, from being
minute, simple and colourless, to varied septation, general increase in size, and brown
colouration. The different types may be traced to fungal ancestors with somewhat
similar spores, but more generally they have developed within the lichen series. From
the life of the individual it is possible to follow the course of evolution, and the spores
of all species begin as simple, colourless bodies; in some genera they remain so, in
others they undergo more or less change before reaching the final stage of colour or
septation that marks the mature condition.
As regards direct fungal ancestors, the Pyrenocarpineae, with solitary perithecia, are
nearest in fruit structure to the Mycosphaerellaceae, in which family are included
several fungus genera that are parasitic on lichens such as Ticothecium, Müllerella, etc.
In that family occurs also the genus Stigmatea, in which the perithecia in form and
structure are very similar to dimidiate Verrucariae.
Zahlbruckner[982] has suggested as the starting point for the Verrucariaceae the
fungus genus Verrucula. It was established by Steiner[983] to include two species, V.
cahirensis and V. aegyptica, their perithecia being exactly similar to those of
Verrucaria[984] in which genus they were originally placed. Both are parasitic on species
of Caloplaca (Placodium). The former, on C. gilvella, transforms the host thallus to the
appearance of a minutely lobed Placodium; the latter occupies an island-like area in the
centre of the thallus of Caloplaca interveniens, and gives it, with its accompanying
parasite, the character of an Endopyrenium (Dermatocarpon), while the rest of the
thallus is normal and fertile.
Zahlbruckner may have argued rightly, but it is also possible to regard these rare
desert species as reversions from an originally symbiotic to a purely parasitic condition.
Reinke came to the conclusion that if a parasitic species were derived directly from a
lichen type, then it must still rank as a lichen, a view that has a direct bearing on the
and enveloping thallus also gelatinous. There is only one minutely foliose or fruticose
gelatinous family, the Pyrenidiaceae, in which Pyrenomycetes are established, and the
gonidia, even though blue-green, have lost the gelatinous sheath and do not swell up.
In Archilichens (with bright-green gonidia), perithecial fruits occur frequently; they
are nearly always simple and solitary; in only a few families with a few representatives,
is there any approach to the stroma formation so marked among fungi. The single
perithecium is generally semi-immersed in the thallus. It may be completely surrounded
by a hyphal “entire” wall, either soft and waxy or dark coloured and somewhat
carbonaceous. In numerous species the outer protective wall covers only the upper
portion that projects beyond the thallus, and such a perithecium is described as
“dimidiate,” a type of fruit occurring in several genera, though rare among fungi.
As to internal structure, there is a dissolution and disappearance of the paraphyses in
some genera, their protective function not being so necessary in closed fruits, a
character paralleled in fungi. There is a great variety of spore changes, from being
minute, simple and colourless, to varied septation, general increase in size, and brown
colouration. The different types may be traced to fungal ancestors with somewhat
similar spores, but more generally they have developed within the lichen series. From
the life of the individual it is possible to follow the course of evolution, and the spores
of all species begin as simple, colourless bodies; in some genera they remain so, in
others they undergo more or less change before reaching the final stage of colour or
septation that marks the mature condition.
As regards direct fungal ancestors, the Pyrenocarpineae, with solitary perithecia, are
nearest in fruit structure to the Mycosphaerellaceae, in which family are included
several fungus genera that are parasitic on lichens such as Ticothecium, Müllerella, etc.
In that family occurs also the genus Stigmatea, in which the perithecia in form and
structure are very similar to dimidiate Verrucariae.
Zahlbruckner[982] has suggested as the starting point for the Verrucariaceae the
fungus genus Verrucula. It was established by Steiner[983] to include two species, V.
cahirensis and V. aegyptica, their perithecia being exactly similar to those of
Verrucaria[984] in which genus they were originally placed. Both are parasitic on species
of Caloplaca (Placodium). The former, on C. gilvella, transforms the host thallus to the
appearance of a minutely lobed Placodium; the latter occupies an island-like area in the
centre of the thallus of Caloplaca interveniens, and gives it, with its accompanying
parasite, the character of an Endopyrenium (Dermatocarpon), while the rest of the
thallus is normal and fertile.
Zahlbruckner may have argued rightly, but it is also possible to regard these rare
desert species as reversions from an originally symbiotic to a purely parasitic condition.
Reinke came to the conclusion that if a parasitic species were derived directly from a
lichen type, then it must still rank as a lichen, a view that has a direct bearing on the
Page 347
question. The parallel family of Pyrenulaceae which have Trentepohlia gonidia is
considered by Zahlbruckner to have originated from the fungus genus Didymella.
Compound or stromatoid fructifications occur once and again in lichen families; but,
according to Wainio[985], there is no true stroma formation, only a pseudostroma
resulting from adhesions and agglomerations of the thalline envelopes or from
cohesions of the margins of developing fruit bodies. These pseudostromata are present
in the genera Chiodecton and Glyphis (Graphidineae) and in Trypethelium,
Mycoporium, etc. (Pyrenocarpineae). This view of the nature of the compound fruits is
strengthened, as Wainio points out, by the presence in certain species of single
apothecia or perithecia on the same specimen as the stromatoid fruits.
b. Coniocarpineae. This subseries is entirely isolated. Its peculiarity lies in the
character of the mature fruit in which the spores, owing to the early breaking down of
the asci, lie as a loose mass in the hymenium, while dispersal is delayed for an
indefinite time. This type of fruit, termed a mazaedium by Acharius, is in the form of a
stalked or sessile roundish head—the capitulum—closed at first and only half-open at
maturity rarely, as in Cyphelium, an exposed disc. There is a suggestion, but only a
suggestion, of a similar fructification in the tropical fungus Camillea in which there is
sometimes a stalk with one or more perithecia at the tip, and in some species early
disintegration of the asci, leaving spore masses[986]. But neither in fungi nor in other
lichens is there any obvious connection with Coniocarpineae. In some of the genera the
fungus alone forms the stalk and the wall of the capitulum; in others the thallus shares
in the fruit-formation growing around it as an amphithecium.
The semi-closed fruits point to their affinity with Pyrenolichens, though they are
more advanced than these judging from the thalline wall that is present in some genera
and also from the half-open disc at maturity. The latter feature has influenced some
systematists to classify the whole subseries among Cyclocarpineae. The thallus, as in
Sphaerophorus, reaches a high degree of fruticose development; in other genera it is
crustaceous without any formation of cortex, while in several genera or species it is
non-existent, the fruits being parasites on the thalli of other lichens or saprophytes on
dead wood, humus, etc. These latter—both parasites and saprophytes—are included by
Rehm[987] and others among fungi, which has involved the breaking up of this very
distinctive series. Rehm has thus published as Discomycetes the lichen genera
Sphinctrina, Cyphelium, Coniocybe, Acolium, Calicium and Stenocybe, since some or
all of their species are regarded by him as fungi.
Reinke[988] in his lichen studies states that it might not be impossible for a
saprophytic fungus to be derived from a crustaceous lichen—a case of reversion—but
that no such instance was then known. More exact studies[989] of parasymbiosis and
antagonistic symbiosis have shown the wide range of possible life-conditions, and such
a reversion does not seem improbable. We must also bear in mind that in suitable
cultures, lichen hyphae can be grown without gonidia: they develop in that case as
saprophytes.
considered by Zahlbruckner to have originated from the fungus genus Didymella.
Compound or stromatoid fructifications occur once and again in lichen families; but,
according to Wainio[985], there is no true stroma formation, only a pseudostroma
resulting from adhesions and agglomerations of the thalline envelopes or from
cohesions of the margins of developing fruit bodies. These pseudostromata are present
in the genera Chiodecton and Glyphis (Graphidineae) and in Trypethelium,
Mycoporium, etc. (Pyrenocarpineae). This view of the nature of the compound fruits is
strengthened, as Wainio points out, by the presence in certain species of single
apothecia or perithecia on the same specimen as the stromatoid fruits.
b. Coniocarpineae. This subseries is entirely isolated. Its peculiarity lies in the
character of the mature fruit in which the spores, owing to the early breaking down of
the asci, lie as a loose mass in the hymenium, while dispersal is delayed for an
indefinite time. This type of fruit, termed a mazaedium by Acharius, is in the form of a
stalked or sessile roundish head—the capitulum—closed at first and only half-open at
maturity rarely, as in Cyphelium, an exposed disc. There is a suggestion, but only a
suggestion, of a similar fructification in the tropical fungus Camillea in which there is
sometimes a stalk with one or more perithecia at the tip, and in some species early
disintegration of the asci, leaving spore masses[986]. But neither in fungi nor in other
lichens is there any obvious connection with Coniocarpineae. In some of the genera the
fungus alone forms the stalk and the wall of the capitulum; in others the thallus shares
in the fruit-formation growing around it as an amphithecium.
The semi-closed fruits point to their affinity with Pyrenolichens, though they are
more advanced than these judging from the thalline wall that is present in some genera
and also from the half-open disc at maturity. The latter feature has influenced some
systematists to classify the whole subseries among Cyclocarpineae. The thallus, as in
Sphaerophorus, reaches a high degree of fruticose development; in other genera it is
crustaceous without any formation of cortex, while in several genera or species it is
non-existent, the fruits being parasites on the thalli of other lichens or saprophytes on
dead wood, humus, etc. These latter—both parasites and saprophytes—are included by
Rehm[987] and others among fungi, which has involved the breaking up of this very
distinctive series. Rehm has thus published as Discomycetes the lichen genera
Sphinctrina, Cyphelium, Coniocybe, Acolium, Calicium and Stenocybe, since some or
all of their species are regarded by him as fungi.
Reinke[988] in his lichen studies states that it might not be impossible for a
saprophytic fungus to be derived from a crustaceous lichen—a case of reversion—but
that no such instance was then known. More exact studies[989] of parasymbiosis and
antagonistic symbiosis have shown the wide range of possible life-conditions, and such
a reversion does not seem improbable. We must also bear in mind that in suitable
cultures, lichen hyphae can be grown without gonidia: they develop in that case as
saprophytes.
Page 348
On Reinke’s[988] view, however, that these saprophytic species, belonging to different
genera in the Coniocarpineae, are true fungi, they would represent the direct and closely
related ancestors of the corresponding lichen genera, giving a polyphyletic origin within
this group. As fungus genera he has united them in Protocaliciaceae, and the
representatives among fungi he distinguishes, as does Wainio[990], under such names as
Mycocalicium and Mycoconiocybe.
If we might consider the saprophytic forms as also retrogressive lichens, a
monophyletic origin from some remote fungal ancestor would prove a more satisfactory
solution of the inheritance problem. This view is even supported by a comparison
Reinke himself has drawn between the development of the fructification in
Mycocalicium parietinum, a saprophyte, and in his view a fungus, and Chaenotheca
chrysocephala, a closely allied lichen. Both grow on old timber. In the former (the
fungus), the mycelium pervades the outer weathered wood-cells, and the fruit stalk rises
from a clump of brownish hyphae; there is no trace of gonidia. Chaenotheca
chrysocephala differs in the presence of gonidia which are associated with the
mycelium in scattered granular warts; but the fruit stalk here also rises directly from the
mycelium between the granules. The presence of a lichen thallus chiefly differentiates
between the two plants, and this thallus is not a casual or recent association; it is
constant and of great antiquity as it is richly provided with lichen-acids.
Reinke has indicated the course of evolution within the series but that is on the lines
of thalline development and will be considered later.
c. Graphidineae. This series contains a considerable variety of lichen forms, but all
possess to a more or less marked degree the linear form of fructification termed a
“lirella” which has only a slit-like opening. There is a tendency to round discoid fruits
in the Roccellae and also in the Arthoniae; the apothecia of the latter, called by early
lichenologists “ardellae,” are without margins. In nearly all there is a formation of
carbonaceous black tissue either in the hypothecium or in the proper margins. In some
of them the paraphyses are branched and dark at the tips, the branches interlocking to
form a strong protective epithecium. There are, however, constant exceptions, in some
particular, to any generalization in genera and in species. Müller-Argau’s[991]
pronouncement might be held to have special reference to Graphidineae: “that in any
genus, species or groups of species are to be found which outwardly shew something
that is peculiar, though of slight importance.” The most constant type of gonidium is
Trentepohlia, but Palmella and Phycopeltis occasionally occur. The spores are various
in colour and form; they are rarely simple.
The genus Arthonia is derived from a member of the Patellariaceae, from which
family many of the Discomycetes have arisen. The course of development does not
follow from a closed to an open fruit; the apothecium is open from the first, and growth
proceeds from the centre outwards, the fertile cells gradually pushing aside the sterile
tissue of the exterior. The affinity of Xylographa (with Palmella gonidia) is to be found
in Stictis in the fungal family Stictidaceae, the apothecia of Stictis being at first closed,
genera in the Coniocarpineae, are true fungi, they would represent the direct and closely
related ancestors of the corresponding lichen genera, giving a polyphyletic origin within
this group. As fungus genera he has united them in Protocaliciaceae, and the
representatives among fungi he distinguishes, as does Wainio[990], under such names as
Mycocalicium and Mycoconiocybe.
If we might consider the saprophytic forms as also retrogressive lichens, a
monophyletic origin from some remote fungal ancestor would prove a more satisfactory
solution of the inheritance problem. This view is even supported by a comparison
Reinke himself has drawn between the development of the fructification in
Mycocalicium parietinum, a saprophyte, and in his view a fungus, and Chaenotheca
chrysocephala, a closely allied lichen. Both grow on old timber. In the former (the
fungus), the mycelium pervades the outer weathered wood-cells, and the fruit stalk rises
from a clump of brownish hyphae; there is no trace of gonidia. Chaenotheca
chrysocephala differs in the presence of gonidia which are associated with the
mycelium in scattered granular warts; but the fruit stalk here also rises directly from the
mycelium between the granules. The presence of a lichen thallus chiefly differentiates
between the two plants, and this thallus is not a casual or recent association; it is
constant and of great antiquity as it is richly provided with lichen-acids.
Reinke has indicated the course of evolution within the series but that is on the lines
of thalline development and will be considered later.
c. Graphidineae. This series contains a considerable variety of lichen forms, but all
possess to a more or less marked degree the linear form of fructification termed a
“lirella” which has only a slit-like opening. There is a tendency to round discoid fruits
in the Roccellae and also in the Arthoniae; the apothecia of the latter, called by early
lichenologists “ardellae,” are without margins. In nearly all there is a formation of
carbonaceous black tissue either in the hypothecium or in the proper margins. In some
of them the paraphyses are branched and dark at the tips, the branches interlocking to
form a strong protective epithecium. There are, however, constant exceptions, in some
particular, to any generalization in genera and in species. Müller-Argau’s[991]
pronouncement might be held to have special reference to Graphidineae: “that in any
genus, species or groups of species are to be found which outwardly shew something
that is peculiar, though of slight importance.” The most constant type of gonidium is
Trentepohlia, but Palmella and Phycopeltis occasionally occur. The spores are various
in colour and form; they are rarely simple.
The genus Arthonia is derived from a member of the Patellariaceae, from which
family many of the Discomycetes have arisen. The course of development does not
follow from a closed to an open fruit; the apothecium is open from the first, and growth
proceeds from the centre outwards, the fertile cells gradually pushing aside the sterile
tissue of the exterior. The affinity of Xylographa (with Palmella gonidia) is to be found
in Stictis in the fungal family Stictidaceae, the apothecia of Stictis being at first closed,
Page 349
then open, and with a thick margin; Xylographa has a more elongate lirella fruit, though
otherwise very similar, and has a very reduced thallus. Rehm[992] has classified
Xylographa as a fungus.
The genera with linear apothecia are closely connected with Hysteriaceae, and
evidently inherit their fruit form severally from that family. There is thus ample
evidence of polyphyletic descent in the series. Stromatoid fruits occur in
Chiodectonaceae, with deeply sunk, almost closed disc, but they have evidently evolved
within the series, possibly from a dividing up of the lirellae.
In Graphidineae there are also forms, more especially in Arthoniaceae, on the border
line between lichens and fungi: those with gonidia being classified as lichens, those
without gonidia having been placed in corresponding genera of fungi. These latter
athalline species live as parasites or saprophytes.
The larger number of genera have a poorly developed thallus; in many of them it is
embedded within the outer periderm-cells of trees, and is known as “hypophloeodal.”
But in some families, such as Roccellaceae, the thallus attains a very advanced form and
a very high production of acids.
The conception of Graphidineae as a whole is puzzling, but one or other
characteristic has brought the various members within the series. It is in this respect an
epitome of the lichen class of which the different groups, with all their various origins
and affinities, yet form a distinct and well-defined section of the vegetable kingdom.
d. Cyclocarpineae. This is by far the largest series of lichens. The genera are
associated with algae belonging both to the Myxophyceae and the Chlorophyceae, and
from the many different combinations are produced great variations in the form of the
vegetative body. The fruit is an emergent, round or roundish disc or open apothecium in
all the members of the series except Pertusariaceae, where it is partially immersed in
thalline “warts.” In its most primitive form, described as “biatorine” or “lecideine,” it
may be soft and waxy (Biatora) or hard and carbonaceous (Lecidea), in the latter the
paraphyses being mostly coloured at the tips; these are either simple or but sparingly
branched, so that the epithecium is a comparatively slight structure. The outer sterile
tissue forms a protective wall or “proper margin” which may be entirely pushed aside,
but generally persists as a distinct rim round the disc.
A great advance within the series arose when the gonidial elements of the thallus took
part in fruit-formation. In that case not only is the hymenium generally subtended by a
layer of algae, but thalline tissue containing algae grows up around the fruit, and forms
a second wall or thalline margin. This type of apothecium, termed “lecanorine,” is thus
intimately associated with the assimilating tissue and food supply, and it gains in
capacity of ascus renewal and of long duration. This development from non-marginate
to marginate ascomata is necessarily an accompaniment of symbiosis.
There is no doubt that the Cyclocarpineae derive from some simple form or forms of
Discomycete in the Patellariaceae. The relationship between that family and the lower
otherwise very similar, and has a very reduced thallus. Rehm[992] has classified
Xylographa as a fungus.
The genera with linear apothecia are closely connected with Hysteriaceae, and
evidently inherit their fruit form severally from that family. There is thus ample
evidence of polyphyletic descent in the series. Stromatoid fruits occur in
Chiodectonaceae, with deeply sunk, almost closed disc, but they have evidently evolved
within the series, possibly from a dividing up of the lirellae.
In Graphidineae there are also forms, more especially in Arthoniaceae, on the border
line between lichens and fungi: those with gonidia being classified as lichens, those
without gonidia having been placed in corresponding genera of fungi. These latter
athalline species live as parasites or saprophytes.
The larger number of genera have a poorly developed thallus; in many of them it is
embedded within the outer periderm-cells of trees, and is known as “hypophloeodal.”
But in some families, such as Roccellaceae, the thallus attains a very advanced form and
a very high production of acids.
The conception of Graphidineae as a whole is puzzling, but one or other
characteristic has brought the various members within the series. It is in this respect an
epitome of the lichen class of which the different groups, with all their various origins
and affinities, yet form a distinct and well-defined section of the vegetable kingdom.
d. Cyclocarpineae. This is by far the largest series of lichens. The genera are
associated with algae belonging both to the Myxophyceae and the Chlorophyceae, and
from the many different combinations are produced great variations in the form of the
vegetative body. The fruit is an emergent, round or roundish disc or open apothecium in
all the members of the series except Pertusariaceae, where it is partially immersed in
thalline “warts.” In its most primitive form, described as “biatorine” or “lecideine,” it
may be soft and waxy (Biatora) or hard and carbonaceous (Lecidea), in the latter the
paraphyses being mostly coloured at the tips; these are either simple or but sparingly
branched, so that the epithecium is a comparatively slight structure. The outer sterile
tissue forms a protective wall or “proper margin” which may be entirely pushed aside,
but generally persists as a distinct rim round the disc.
A great advance within the series arose when the gonidial elements of the thallus took
part in fruit-formation. In that case not only is the hymenium generally subtended by a
layer of algae, but thalline tissue containing algae grows up around the fruit, and forms
a second wall or thalline margin. This type of apothecium, termed “lecanorine,” is thus
intimately associated with the assimilating tissue and food supply, and it gains in
capacity of ascus renewal and of long duration. This development from non-marginate
to marginate ascomata is necessarily an accompaniment of symbiosis.
There is no doubt that the Cyclocarpineae derive from some simple form or forms of
Discomycete in the Patellariaceae. The relationship between that family and the lower
Page 350
Lecideae is very close. Rehm[993] finds the direct ancestors of Lecidea itself in the
fungus genus, Patinella, in which the apothecia are truly lecideine in character—open,
flat and slightly margined, the hypothecium nearly always dark-coloured and the
paraphyses branched, septate, clavate and coloured at the tips, forming a dark
epithecium. More definitely still he describes Patinella atroviridis, a new species he
discovered, as in all respects a Lecidea, but without gonidia.
In the crustaceous Lecideaceae, a number of genera have been delimited on spore
characters—colourless or brown, and simple or variously septate. In Patellariaceae as
described by Rehm are included a number of fungus genera which correspond to these
lichen genera. Only two of them—Patinella and Patellaria—are saprophytic; in all the
other genera of the family, the species with very few exceptions are parasitic on lichens:
they are parasymbionts sharing the algal food supply; in any case, they thrive on a
symbiotic thallus.
Rehm unhesitatingly derives the corresponding lichen genera from these fungi. He
takes no account of the difficulty that if these parasitic (or saprophytic) fungi are
primitive, they have yet appeared either later in time than the lichens on which they
exist, or else in the course of ages they have entirely changed their substratum.
He has traced, for instance, the lichen, Buellia, to a saprophytic fungus species,
Karschia lignyota, to a genus therefore in which most of the species are parasitic on
lichens and have generally been classified as parasitic lichens. There is no advance in
apothecial characters from the fungus, Karschia, to Buellia, merely the change to
symbiosis. It therefore seems more in accordance with facts to regard Buellia as a genus
evolved within the lichen series from Patinella through Lecidea, and to accept these
species of Karschia on the border line as parasitic, or even as saprophytic, reversions
from the lichen status. We may add that while these brown-spored lichens are fairly
abundant, the corresponding athalline or fungus forms are comparatively few in
number, which is exactly what might be expected from plants with a reversionary
history.
Occasionally in biatorine or lecideine species with a slight thalline development all
traces of the thallus disappear after the fructification has reached maturity. The
apothecia, if on wood or humus, appear to be saprophytic and would at first sight be
classified as fungi. They have undoubtedly retained the capacity to live at certain stages,
or in certain conditions, as saprophytes.
The thallus disappears also in some species of the crustaceous genera that possess
apothecia with a thalline margin, and the fruits may be left stranded and solitary on the
normal substratum, or on some neighbouring lichen thallus where they are more or less
parasitic; but as the thalline margin persists, there has been no question as to their nature
and affinity.
Rehm suggests that many species now included among lichens may be ultimately
proved to be fungi; but it is equally possible that the reverse may be the case, as for
fungus genus, Patinella, in which the apothecia are truly lecideine in character—open,
flat and slightly margined, the hypothecium nearly always dark-coloured and the
paraphyses branched, septate, clavate and coloured at the tips, forming a dark
epithecium. More definitely still he describes Patinella atroviridis, a new species he
discovered, as in all respects a Lecidea, but without gonidia.
In the crustaceous Lecideaceae, a number of genera have been delimited on spore
characters—colourless or brown, and simple or variously septate. In Patellariaceae as
described by Rehm are included a number of fungus genera which correspond to these
lichen genera. Only two of them—Patinella and Patellaria—are saprophytic; in all the
other genera of the family, the species with very few exceptions are parasitic on lichens:
they are parasymbionts sharing the algal food supply; in any case, they thrive on a
symbiotic thallus.
Rehm unhesitatingly derives the corresponding lichen genera from these fungi. He
takes no account of the difficulty that if these parasitic (or saprophytic) fungi are
primitive, they have yet appeared either later in time than the lichens on which they
exist, or else in the course of ages they have entirely changed their substratum.
He has traced, for instance, the lichen, Buellia, to a saprophytic fungus species,
Karschia lignyota, to a genus therefore in which most of the species are parasitic on
lichens and have generally been classified as parasitic lichens. There is no advance in
apothecial characters from the fungus, Karschia, to Buellia, merely the change to
symbiosis. It therefore seems more in accordance with facts to regard Buellia as a genus
evolved within the lichen series from Patinella through Lecidea, and to accept these
species of Karschia on the border line as parasitic, or even as saprophytic, reversions
from the lichen status. We may add that while these brown-spored lichens are fairly
abundant, the corresponding athalline or fungus forms are comparatively few in
number, which is exactly what might be expected from plants with a reversionary
history.
Occasionally in biatorine or lecideine species with a slight thalline development all
traces of the thallus disappear after the fructification has reached maturity. The
apothecia, if on wood or humus, appear to be saprophytic and would at first sight be
classified as fungi. They have undoubtedly retained the capacity to live at certain stages,
or in certain conditions, as saprophytes.
The thallus disappears also in some species of the crustaceous genera that possess
apothecia with a thalline margin, and the fruits may be left stranded and solitary on the
normal substratum, or on some neighbouring lichen thallus where they are more or less
parasitic; but as the thalline margin persists, there has been no question as to their nature
and affinity.
Rehm suggests that many species now included among lichens may be ultimately
proved to be fungi; but it is equally possible that the reverse may be the case, as for
Page 351
instance Bacidia flavovirescens, held by Rehm and others to be a parasitic fungus
species, but since proved by Tobler[994] to be a true lichen.
A note by Lightfoot[995], one of our old-time botanists who gave lichens a
considerable place in his Flora, foreshadows the theory of evolution by gradual
advance, and his views offer a suggestive commentary on the subject under discussion.
He was debating the systematic position of the maritime lichen genus Lichina,
considered then a kind of Fucus, and had observed its similarity with true lichens. “The
cavity,” he writes, “at the top of the fructification (in Lichina) is a proof how nearly this
species of Fucus is related to the scutellated lichens. Nature disdains to be limited to the
systematic rules of human invention. She never makes any sudden starts from one class
or genus to another, but is regularly progressive in all her works, uniting the various
links in the chain of beings by insensible connexions.”
III. THE THALLUS
A. General Outline of Development
a. Preliminary Considerations. The evolution of lichens, as such, has reference
mainly to the thallus. Certain developments of the fructification are evident, but the
changes in the reproductive organs have not kept pace with those of the vegetative
structures: the highest type of fruit, for instance, the apothecium with a thalline margin,
occurs in genera and species with a very primitive vegetative structure as well as in
those that have attained higher development.
Lichens are polyphyletic as regards their algal, as well as their fungal, ancestors, so
that it is impossible to indicate a straight line of progression, but there is a general
process of thalline development which appears once and again in the different phyla.
That process, from simpler to more complicated forms, follows on two lines: on the one
there is the endeavour to increase the assimilating surface, on the other the tendency to
free the plant from the substratum. In both, the aim has been the same, to secure more
favourable conditions for assimilation and aeration. Changes in structure have been
already described[996], and it is only needful to indicate here the main lines of evolution.
b. Course of Evolution in Hymenolichens. There is but little trace of development in
these lichens. The fungus has retained more or less the form of the ancestral Thelephora
which has a wide-spreading superficial basidiosporous hymenium. Three genera have
been recognized, the differences between them being due to the position within the
thallus, and the form of the Scytonema that constitutes the gonidium. The highest stage
of development and of outward form is reached in Cora, in which the gonidial zone is
central in the tissue and is bounded above and below by strata of hyphae.
c. Course of Evolution in Ascolichens. It is in the association with Ascomycetes that
evolution and adaptation have had full scope. In that sub-class there are four constantly
species, but since proved by Tobler[994] to be a true lichen.
A note by Lightfoot[995], one of our old-time botanists who gave lichens a
considerable place in his Flora, foreshadows the theory of evolution by gradual
advance, and his views offer a suggestive commentary on the subject under discussion.
He was debating the systematic position of the maritime lichen genus Lichina,
considered then a kind of Fucus, and had observed its similarity with true lichens. “The
cavity,” he writes, “at the top of the fructification (in Lichina) is a proof how nearly this
species of Fucus is related to the scutellated lichens. Nature disdains to be limited to the
systematic rules of human invention. She never makes any sudden starts from one class
or genus to another, but is regularly progressive in all her works, uniting the various
links in the chain of beings by insensible connexions.”
III. THE THALLUS
A. General Outline of Development
a. Preliminary Considerations. The evolution of lichens, as such, has reference
mainly to the thallus. Certain developments of the fructification are evident, but the
changes in the reproductive organs have not kept pace with those of the vegetative
structures: the highest type of fruit, for instance, the apothecium with a thalline margin,
occurs in genera and species with a very primitive vegetative structure as well as in
those that have attained higher development.
Lichens are polyphyletic as regards their algal, as well as their fungal, ancestors, so
that it is impossible to indicate a straight line of progression, but there is a general
process of thalline development which appears once and again in the different phyla.
That process, from simpler to more complicated forms, follows on two lines: on the one
there is the endeavour to increase the assimilating surface, on the other the tendency to
free the plant from the substratum. In both, the aim has been the same, to secure more
favourable conditions for assimilation and aeration. Changes in structure have been
already described[996], and it is only needful to indicate here the main lines of evolution.
b. Course of Evolution in Hymenolichens. There is but little trace of development in
these lichens. The fungus has retained more or less the form of the ancestral Thelephora
which has a wide-spreading superficial basidiosporous hymenium. Three genera have
been recognized, the differences between them being due to the position within the
thallus, and the form of the Scytonema that constitutes the gonidium. The highest stage
of development and of outward form is reached in Cora, in which the gonidial zone is
central in the tissue and is bounded above and below by strata of hyphae.
c. Course of Evolution in Ascolichens. It is in the association with Ascomycetes that
evolution and adaptation have had full scope. In that sub-class there are four constantly
Page 352
recurring and well-marked stages of thalline development. (1) The earliest, most
primitive stage, is the crustaceous: at first an accretion of separate granules which may
finally be united into a continuous crust with a protective covering of thick-walled
amorphous hyphae forming a “decomposed” cortex. The extension of a granule by
growth in one direction upwards and outwards gives detachment from the substratum,
and originates (2) the squamule which is, however, often of primitive structure and
attached to the support, like the granule, by the medullary hyphae. Further growth of the
squamule results in (3) the foliose thallus with all the adaptations of structure peculiar to
that form. In all of these, the principal area of growth is round the free edges of the
thallus. A greater change takes place in the advance to (4) the fruticose type in which
the more active growing tissue is restricted to the apex, and in which the frond or
filament adheres at one point only to the support, a new series of strengthening and
other structures being evolved at the same time.
The lichen fungi associate, as has been already stated, with two different types of
algae: those combined with the Myxophyceae have been designated Phycolichenes,
those with Chlorophyceae as Archilichenes. The latter predominate, not only in the
number of lichens, but also in the more varied advance of the thallus, although, in many
instances, genera and species of both series may be closely related.
B. Comparative Antiquity of Algal Symbionts
One of the first questions of inheritance concerns the comparative antiquity of the
two gonidial series: with which kind of alga did the fungus first form the symbiotic
relationship? No assistance in solving the problem is afforded by the type of
fructification. The fungus in Archilichens is frequently one of the more primitive
Pyrenomycetes, though more often a Discomycete, while in Phycolichens
Pyrenomycetes are very rare. There is, as already stated, no correlation of advance
between the fruit and the thallus, as the most highly evolved apothecia with well-formed
thalline margins are constantly combined with thalli of low type.
Forssell[997] gave considerable attention to the question of antiquity in his study of
gelatinous crustaceous lichens in the family Pyrenopsidaceae, termed by him
Gloeolichens, and he came to the conclusion that Archilichens represented the older
combination, Phycolichens being comparatively young.
His view is based on a study of the development of certain lichen fungi that seem
able to adapt themselves to either kind of algal symbiont. He found[997] in Euopsis
(Pyrenopsis) granatina, one of the Pyrenopsidaceae, that certain portions of the thallus
contained blue-green algae, while others contained Palmella, and that these latter,
though retrograde in development, might become fertile. The granules with blue-green
gonidia were stronger, more healthy and capable of displacing those with Palmella, but
not of bearing apothecia, though spermogonia were embedded in them—a first step,
according to Forssell, towards the formation of apothecia. These granules, not having
primitive stage, is the crustaceous: at first an accretion of separate granules which may
finally be united into a continuous crust with a protective covering of thick-walled
amorphous hyphae forming a “decomposed” cortex. The extension of a granule by
growth in one direction upwards and outwards gives detachment from the substratum,
and originates (2) the squamule which is, however, often of primitive structure and
attached to the support, like the granule, by the medullary hyphae. Further growth of the
squamule results in (3) the foliose thallus with all the adaptations of structure peculiar to
that form. In all of these, the principal area of growth is round the free edges of the
thallus. A greater change takes place in the advance to (4) the fruticose type in which
the more active growing tissue is restricted to the apex, and in which the frond or
filament adheres at one point only to the support, a new series of strengthening and
other structures being evolved at the same time.
The lichen fungi associate, as has been already stated, with two different types of
algae: those combined with the Myxophyceae have been designated Phycolichenes,
those with Chlorophyceae as Archilichenes. The latter predominate, not only in the
number of lichens, but also in the more varied advance of the thallus, although, in many
instances, genera and species of both series may be closely related.
B. Comparative Antiquity of Algal Symbionts
One of the first questions of inheritance concerns the comparative antiquity of the
two gonidial series: with which kind of alga did the fungus first form the symbiotic
relationship? No assistance in solving the problem is afforded by the type of
fructification. The fungus in Archilichens is frequently one of the more primitive
Pyrenomycetes, though more often a Discomycete, while in Phycolichens
Pyrenomycetes are very rare. There is, as already stated, no correlation of advance
between the fruit and the thallus, as the most highly evolved apothecia with well-formed
thalline margins are constantly combined with thalli of low type.
Forssell[997] gave considerable attention to the question of antiquity in his study of
gelatinous crustaceous lichens in the family Pyrenopsidaceae, termed by him
Gloeolichens, and he came to the conclusion that Archilichens represented the older
combination, Phycolichens being comparatively young.
His view is based on a study of the development of certain lichen fungi that seem
able to adapt themselves to either kind of algal symbiont. He found[997] in Euopsis
(Pyrenopsis) granatina, one of the Pyrenopsidaceae, that certain portions of the thallus
contained blue-green algae, while others contained Palmella, and that these latter,
though retrograde in development, might become fertile. The granules with blue-green
gonidia were stronger, more healthy and capable of displacing those with Palmella, but
not of bearing apothecia, though spermogonia were embedded in them—a first step,
according to Forssell, towards the formation of apothecia. These granules, not having
Page 353
reached a fruiting stage, were reckoned to be of a more recent type than those associated
with Palmella. In other instances, however, the line of evolution has been undoubtedly
from blue-green to more highly evolved bright-green thalli.
The striking case of similarity between Psoroma hypnorum (bright-green) and
Pannaria rubiginosa (blue-green) may also be adduced. Forssell considers that
Psoroma is the more ancient form, but as the fungus is adapted to associate with either
kind of alga, the type of squamules forming the thallus may be gradually transformed
by the substitution of blue-green for the earlier bright-green—the Pannaria superseding
the Psoroma. There is a close resemblance in the fructification—that is of the fungus—
in these two different lichens.
Hue[998] shares Forssell’s opinion as to the greater antiquity of the bright-green
gonidia and cites the case of Solorina crocea. In that lichen there is a layer of bright-
green gonidia in the usual dorsiventral position, below the upper cortex. Below this
zone there is a second formed entirely of blue-green cells. Hue proved by his study of
development in Solorina that the bright-green were the normal gonidia of the thallus,
and were the only ones present in the growing peripheral areas; the blue-green were a
later addition, and appeared first in small groups at some distance from the edge of the
lobes.
The whole subject of cephalodia-development[999] has a bearing on this question.
These bodies always contain blue-green algae, and are always associated with
Archilichens. Mostly they occur as excrescences, as in Stereocaulon and in Peltigera.
The fungus of the host-lichen though normally adapted to bright-green algae has the
added capacity of forming later a symbiosis with the blue-green. This tendency
generally pervades a whole genus or family, the members of which, as in Peltigeraceae,
are too closely related to allow as a rule of separate classification even when the algae
are totally distinct.
C. Evolution of Phycolichens
The association of lichen-forming fungi with blue-green algae may have taken place
later in time, or may have been less successful than with the bright-green: they are
fewer in number, and the blue-green type of thallus is less highly evolved, though
examples of very considerable development are to be found in such genera as Peltigera,
Sticta or Nephromium.
a. Gloeolichens. Among crustaceous forms the thallus is generally elementary, more
especially in the Gloeolichens (Pyrenopsidaceae). The algae of that family, Gloeocapsa,
Xanthocapsa or Chroococcus, are furnished with broad gelatinous sheaths which, in the
lichenoid state, are penetrated and traversed by the fungal filaments, a branch hypha
generally touching with its tip the algal cell-wall. Under the influence of symbiosis, the
algal masses become firmer and more compact, without much alteration in form; algae
entirely free from hyphae are often intermingled with the others. Even among
with Palmella. In other instances, however, the line of evolution has been undoubtedly
from blue-green to more highly evolved bright-green thalli.
The striking case of similarity between Psoroma hypnorum (bright-green) and
Pannaria rubiginosa (blue-green) may also be adduced. Forssell considers that
Psoroma is the more ancient form, but as the fungus is adapted to associate with either
kind of alga, the type of squamules forming the thallus may be gradually transformed
by the substitution of blue-green for the earlier bright-green—the Pannaria superseding
the Psoroma. There is a close resemblance in the fructification—that is of the fungus—
in these two different lichens.
Hue[998] shares Forssell’s opinion as to the greater antiquity of the bright-green
gonidia and cites the case of Solorina crocea. In that lichen there is a layer of bright-
green gonidia in the usual dorsiventral position, below the upper cortex. Below this
zone there is a second formed entirely of blue-green cells. Hue proved by his study of
development in Solorina that the bright-green were the normal gonidia of the thallus,
and were the only ones present in the growing peripheral areas; the blue-green were a
later addition, and appeared first in small groups at some distance from the edge of the
lobes.
The whole subject of cephalodia-development[999] has a bearing on this question.
These bodies always contain blue-green algae, and are always associated with
Archilichens. Mostly they occur as excrescences, as in Stereocaulon and in Peltigera.
The fungus of the host-lichen though normally adapted to bright-green algae has the
added capacity of forming later a symbiosis with the blue-green. This tendency
generally pervades a whole genus or family, the members of which, as in Peltigeraceae,
are too closely related to allow as a rule of separate classification even when the algae
are totally distinct.
C. Evolution of Phycolichens
The association of lichen-forming fungi with blue-green algae may have taken place
later in time, or may have been less successful than with the bright-green: they are
fewer in number, and the blue-green type of thallus is less highly evolved, though
examples of very considerable development are to be found in such genera as Peltigera,
Sticta or Nephromium.
a. Gloeolichens. Among crustaceous forms the thallus is generally elementary, more
especially in the Gloeolichens (Pyrenopsidaceae). The algae of that family, Gloeocapsa,
Xanthocapsa or Chroococcus, are furnished with broad gelatinous sheaths which, in the
lichenoid state, are penetrated and traversed by the fungal filaments, a branch hypha
generally touching with its tip the algal cell-wall. Under the influence of symbiosis, the
algal masses become firmer and more compact, without much alteration in form; algae
entirely free from hyphae are often intermingled with the others. Even among
Page 354
Gloeolichens there are signs of advancing development both in the internal structure
and in outward form. Lobes free from the substratum, though very minute, appear in the
genus Paulia, the single species of which comes from Polynesia. Much larger lobes are
characteristic of Thyrea, a Mediterranean and American genus. The fruticose type, with
upright fronds of minute size, also appears in our native genus Synalissa. It is still more
marked in the coralloid thalli of Peccania and Phleopeccania. In most of these genera
there is also a distinct tendency to differentiation of tissues, with the gonidia
congregating towards the better lighted surfaces. The only cortex formation occurs in
the crustaceous genus Forssellia in which, according to Zahlbruckner[1000], it is
plectenchymatous above, the thallus being attached below by hyphae penetrating the
substratum. In another genus, Anema[1001], which is minutely lobate-crustaceous, the
internal hyphae form a cellular network in which the algae are immeshed. As regards
algal symbionts, the members of this family are polyphyletic in origin.
b. Ephebaceae and Collemaceae. In Ephebaceae the algae are tufted and filamentous,
Scytonema, Stigonema or Rivularia, the trichomes of which are surrounded by a
common gelatinous sheath. The hyphae travel in the sheath alongside the cell-rows, and
the symbiotic plant retains the tufted form of the alga as in Lichina with Rivularia,
Leptogidium with Scytonema, and Ephebe with Stigonema. The last named lichen forms
a tangle of intricate branching filaments about an inch or more in length. The fruticose
habit in these plants is an algal characteristic; it has not been acquired as a result of
symbiosis, and does not signify any advance in evolution.
A plectenchymatous cortex marks some progress here also in Leptodendriscum,
Leptogidium and Polychidium, all of which are associated with Scytonema. These
genera may well be derived from an elementary form such as Thermutis. They differ
from each other in spore characters, etc., Polychidium being the most highly developed
with its cortex of two cell-rows and with two-celled spores.
Nostoc forms the gonidium of Collemaceae. In its free state it is extremely gelatinous
and transmits that character more or less to the lichen. In the crustaceous genus Physma,
which forms the base of the Collema group or phylum, there is but little difference in
form between the thalline warts of the lichen crust and the original small Nostoc
colonies such as are to be found on damp mosses, etc.
In Collema itself, the less advanced species are scarcely more than crusts, though the
more developed show considerable diversity of lobes, either short and pulpy, or
spreading out in a thin membrane. The Nostoc chains pervade the homoiomerous
thallus, but in some species they lie more towards the upper surface. There is no cortex,
though once and again plectenchyma appears in the apothecial margin, both in this
genus and in Leprocollema which is purely crustaceous.
Leptogium is a higher type than Collema, the thallus being distinguished by its
cellular cortex. The tips of the hyphae, lying close together at the surface, are cut off by
one or more septa, giving a one- or several-celled cortical layer. The species though
and in outward form. Lobes free from the substratum, though very minute, appear in the
genus Paulia, the single species of which comes from Polynesia. Much larger lobes are
characteristic of Thyrea, a Mediterranean and American genus. The fruticose type, with
upright fronds of minute size, also appears in our native genus Synalissa. It is still more
marked in the coralloid thalli of Peccania and Phleopeccania. In most of these genera
there is also a distinct tendency to differentiation of tissues, with the gonidia
congregating towards the better lighted surfaces. The only cortex formation occurs in
the crustaceous genus Forssellia in which, according to Zahlbruckner[1000], it is
plectenchymatous above, the thallus being attached below by hyphae penetrating the
substratum. In another genus, Anema[1001], which is minutely lobate-crustaceous, the
internal hyphae form a cellular network in which the algae are immeshed. As regards
algal symbionts, the members of this family are polyphyletic in origin.
b. Ephebaceae and Collemaceae. In Ephebaceae the algae are tufted and filamentous,
Scytonema, Stigonema or Rivularia, the trichomes of which are surrounded by a
common gelatinous sheath. The hyphae travel in the sheath alongside the cell-rows, and
the symbiotic plant retains the tufted form of the alga as in Lichina with Rivularia,
Leptogidium with Scytonema, and Ephebe with Stigonema. The last named lichen forms
a tangle of intricate branching filaments about an inch or more in length. The fruticose
habit in these plants is an algal characteristic; it has not been acquired as a result of
symbiosis, and does not signify any advance in evolution.
A plectenchymatous cortex marks some progress here also in Leptodendriscum,
Leptogidium and Polychidium, all of which are associated with Scytonema. These
genera may well be derived from an elementary form such as Thermutis. They differ
from each other in spore characters, etc., Polychidium being the most highly developed
with its cortex of two cell-rows and with two-celled spores.
Nostoc forms the gonidium of Collemaceae. In its free state it is extremely gelatinous
and transmits that character more or less to the lichen. In the crustaceous genus Physma,
which forms the base of the Collema group or phylum, there is but little difference in
form between the thalline warts of the lichen crust and the original small Nostoc
colonies such as are to be found on damp mosses, etc.
In Collema itself, the less advanced species are scarcely more than crusts, though the
more developed show considerable diversity of lobes, either short and pulpy, or
spreading out in a thin membrane. The Nostoc chains pervade the homoiomerous
thallus, but in some species they lie more towards the upper surface. There is no cortex,
though once and again plectenchyma appears in the apothecial margin, both in this
genus and in Leprocollema which is purely crustaceous.
Leptogium is a higher type than Collema, the thallus being distinguished by its
cellular cortex. The tips of the hyphae, lying close together at the surface, are cut off by
one or more septa, giving a one- or several-celled cortical layer. The species though
Page 355
generally homoiomerous are of thinner texture and are less gelatinous than those of
Collema.
c. Pyrenidiaceae. This small family of pyrenocarpous Phycolichens may be
considered here though its affinity, through the form of the fruiting body, is with
Archilichens. The gonidia are species of Nostoc, Scytonema and Stigonema. There are
only five genera; one of these, Eolichen, contains three species, the others are
monotypic.
The crustaceous genera have a non-corticate thallus, but an advance to lobate form
takes place in Placothelium, an African genus. The two genera that show most
development are both British: Coriscium (Normandina), which is lobate, heteromerous
and corticate—though always sterile—and Pyrenidium which is fruticose in habit; the
latter is associated with Nostoc and forms a minute sward of upright fronds, corticate all
round; the perithecium is provided with an entire wall and is immersed in the thallus.
If the thallus alone were under consideration these lichens would rank with
Pannariaceae.
d. Heppiaceae and Pannariaceae. The next stage in the development of Phycolichens
takes place through the algae, Scytonema and Nostoc, losing not only their gelatinous
sheaths, but also, to a large extent, their characteristic forms. Chains of cells can
frequently be observed, but accurate and certain identification of the algal genus is only
possible by making separate cultures of the gonidia.
Scytonema forms the gonidium of the squamulose Heppiaceae consisting of the
single genus Heppia. The ground tissue of the species is either wholly of plectenchyma
with algae in the interstices, or the centre is occupied by a narrow medulla of loose
filaments.
In the allied family Pannariaceae, a number of genera contain Scytonema or Nostoc,
while two, Psoroma and Psoromaria, have bright-green gonidia. The thallus varies from
crustaceous or minutely squamulose, to lobes of fair dimension in Parmeliella and in
Hydrothyria venosa, an aquatic lichen. Plectenchyma appears in the upper cortex of
both of these, and in the proper margin of the apothecia, while the under surface is
frequently provided with rhizoidal filaments.
These two families form a transition between the gelatinous, and mostly
homoiomerous thallus, and the more developed entirely heteromerous thallus of much
more advanced structure. The fructification in all of them, gelatinous and non-
gelatinous, is a more or less open apothecium, sometimes immarginate, and biatorine or
lecideine, but often, even in species nearly related to these, it is lecanorine with a
thalline amphithecium. Rarely are the sporiferous bodies sunk in the tissue, with a
pseudo-perithecium, as in Phylliscum. It would be difficult to trace advance in all this
group on the lines of fruit development. The two genera with bright-green gonidia,
Psoroma and Psoromaria, have been included in Pannariaceae owing to the very close
affinity of Psoroma hypnorum with Pannaria rubiginosa; they are alike in every respect
Collema.
c. Pyrenidiaceae. This small family of pyrenocarpous Phycolichens may be
considered here though its affinity, through the form of the fruiting body, is with
Archilichens. The gonidia are species of Nostoc, Scytonema and Stigonema. There are
only five genera; one of these, Eolichen, contains three species, the others are
monotypic.
The crustaceous genera have a non-corticate thallus, but an advance to lobate form
takes place in Placothelium, an African genus. The two genera that show most
development are both British: Coriscium (Normandina), which is lobate, heteromerous
and corticate—though always sterile—and Pyrenidium which is fruticose in habit; the
latter is associated with Nostoc and forms a minute sward of upright fronds, corticate all
round; the perithecium is provided with an entire wall and is immersed in the thallus.
If the thallus alone were under consideration these lichens would rank with
Pannariaceae.
d. Heppiaceae and Pannariaceae. The next stage in the development of Phycolichens
takes place through the algae, Scytonema and Nostoc, losing not only their gelatinous
sheaths, but also, to a large extent, their characteristic forms. Chains of cells can
frequently be observed, but accurate and certain identification of the algal genus is only
possible by making separate cultures of the gonidia.
Scytonema forms the gonidium of the squamulose Heppiaceae consisting of the
single genus Heppia. The ground tissue of the species is either wholly of plectenchyma
with algae in the interstices, or the centre is occupied by a narrow medulla of loose
filaments.
In the allied family Pannariaceae, a number of genera contain Scytonema or Nostoc,
while two, Psoroma and Psoromaria, have bright-green gonidia. The thallus varies from
crustaceous or minutely squamulose, to lobes of fair dimension in Parmeliella and in
Hydrothyria venosa, an aquatic lichen. Plectenchyma appears in the upper cortex of
both of these, and in the proper margin of the apothecia, while the under surface is
frequently provided with rhizoidal filaments.
These two families form a transition between the gelatinous, and mostly
homoiomerous thallus, and the more developed entirely heteromerous thallus of much
more advanced structure. The fructification in all of them, gelatinous and non-
gelatinous, is a more or less open apothecium, sometimes immarginate, and biatorine or
lecideine, but often, even in species nearly related to these, it is lecanorine with a
thalline amphithecium. Rarely are the sporiferous bodies sunk in the tissue, with a
pseudo-perithecium, as in Phylliscum. It would be difficult to trace advance in all this
group on the lines of fruit development. The two genera with bright-green gonidia,
Psoroma and Psoromaria, have been included in Pannariaceae owing to the very close
affinity of Psoroma hypnorum with Pannaria rubiginosa; they are alike in every respect
Page 356
except in their gonidia. Psoromaria is exactly like Psoroma, but with immarginate
biatorine apothecia, representing therefore a lower development in that respect.
These lichens not only mark the transition from gelatinous to non-gelatinous forms,
but in some of them there is an interchange of gonidia. The progression in the phylum
or phyla has evidently been from blue-green up to some highly evolved forms with
bright-green algae, though there may have been, at the beginning, a substitution of blue-
green in place of earlier bright-green algae, Phycolichens usurping as it were the
Archilichen condition.
e. Peltigeraceae and Stictaceae. The two families just examined marked a great
advance which culminated in the lobate aquatic lichen Hydrothyria. This lichen, as
Sturgis pointed out, shows affinity with other Pannariaceae in the structure of the single
large-celled cortical layer as well as with species of Nephroma (Peltigeraceae). A still
closer affinity may be traced with Peltigera in the presence in both plants of veins on
the under surface. The capacity of Peltigera species to grow in damp situations may
also be inherited from a form like the submerged Hydrothyria. In both families there are
transitions from blue-green to bright-green gonidia, or vice versa, in related species.
Thus in Peltigeraceae we find Peltigera containing Nostoc in the gonidial zone, with
Peltidea which may be regarded as a separate genus, or more naturally as a section of
Peltigera; it contains bright-green gonidia, but has cephalodia containing Nostoc
associated with its thallus.
The genus Nephroma is similarly divided into species with a bright-green gonidial
zone, chiefly Arctic or Antarctic in distribution, and species with Nostoc (subgenus
Nephromium) more numerous and more widely distributed.
Peltigera and Nephroma are also closely related in the character of the fructification.
It is a flat non-marginate disc borne on the edge of the thallus: in Peltigera on the upper
surface, in Nephroma on the under surface. The remaining genus Solorina contains
normally a layer of bright-green algae, but, along with these, there are always present
more or fewer Nostoc cells, either in a thin layer as in S. crocea or as cephalodia in
others, while, in three species the algae are altogether blue-green.
The members of the Peltigeraceae have a thick upper cortex of plectenchyma and in
some cases strengthening veins, and long rhizinae on the lower side. Some of the
species attain a large size, and, in some, soredia are formed, an evidence of advance,
this being a peculiarly lichenoid form of reproduction.
The Stictaceae form a parallel but more highly organized family, which also includes
closely related bright-green and blue-green series. They are all dorsiventral, but they are
mostly attached by a single hold-fast and the lobes in some species suggest the fruticose
type in their long narrow form. A wide cortex of plectenchyma protects both the upper
and the lower surface and a felt of hairs replaces the rhizinae of other foliose lichens. In
the genus Sticta (including the section Stictina) special aeration organs, cyphellae or
biatorine apothecia, representing therefore a lower development in that respect.
These lichens not only mark the transition from gelatinous to non-gelatinous forms,
but in some of them there is an interchange of gonidia. The progression in the phylum
or phyla has evidently been from blue-green up to some highly evolved forms with
bright-green algae, though there may have been, at the beginning, a substitution of blue-
green in place of earlier bright-green algae, Phycolichens usurping as it were the
Archilichen condition.
e. Peltigeraceae and Stictaceae. The two families just examined marked a great
advance which culminated in the lobate aquatic lichen Hydrothyria. This lichen, as
Sturgis pointed out, shows affinity with other Pannariaceae in the structure of the single
large-celled cortical layer as well as with species of Nephroma (Peltigeraceae). A still
closer affinity may be traced with Peltigera in the presence in both plants of veins on
the under surface. The capacity of Peltigera species to grow in damp situations may
also be inherited from a form like the submerged Hydrothyria. In both families there are
transitions from blue-green to bright-green gonidia, or vice versa, in related species.
Thus in Peltigeraceae we find Peltigera containing Nostoc in the gonidial zone, with
Peltidea which may be regarded as a separate genus, or more naturally as a section of
Peltigera; it contains bright-green gonidia, but has cephalodia containing Nostoc
associated with its thallus.
The genus Nephroma is similarly divided into species with a bright-green gonidial
zone, chiefly Arctic or Antarctic in distribution, and species with Nostoc (subgenus
Nephromium) more numerous and more widely distributed.
Peltigera and Nephroma are also closely related in the character of the fructification.
It is a flat non-marginate disc borne on the edge of the thallus: in Peltigera on the upper
surface, in Nephroma on the under surface. The remaining genus Solorina contains
normally a layer of bright-green algae, but, along with these, there are always present
more or fewer Nostoc cells, either in a thin layer as in S. crocea or as cephalodia in
others, while, in three species the algae are altogether blue-green.
The members of the Peltigeraceae have a thick upper cortex of plectenchyma and in
some cases strengthening veins, and long rhizinae on the lower side. Some of the
species attain a large size, and, in some, soredia are formed, an evidence of advance,
this being a peculiarly lichenoid form of reproduction.
The Stictaceae form a parallel but more highly organized family, which also includes
closely related bright-green and blue-green series. They are all dorsiventral, but they are
mostly attached by a single hold-fast and the lobes in some species suggest the fruticose
type in their long narrow form. A wide cortex of plectenchyma protects both the upper
and the lower surface and a felt of hairs replaces the rhizinae of other foliose lichens. In
the genus Sticta (including the section Stictina) special aeration organs, cyphellae or
Page 357
pseudocyphellae, are provided; in Lobaria these are replaced by naked areas which
serve the same purpose.
Nylander[1002] regarded the Stictaceae as the most highly developed of all lichens,
and they easily take a high place among dorsiventral forms, but it is generally conceded
that the fruticose type is the more highly organized. In any case they are the highest
reach of the phylum or phyla that started with Pyrenopsidaceae and Collemaceae; the
lowly gelatinous thalli changing to more elaborate structures with the abandonment of
the gelatinous algal sheath, as in the Pannariaceae, and with the replacement of blue-
green by bright-green gonidia. Reinke[1003], considers the Stictaceae as evolved from
the Pannariaceae more directly from the genus Massalongia. Their relationship is
certainly with Pannariaceae and Peltigeraceae rather than with Parmeliaceae; these
latter, as we shall see, belong to a wholly different series.
D. Evolution of Archilichens
The study of Archilichens as of Phycolichens is complicated by the many different
kinds of fungi and algae that have entered into combination; but the two principal types
of algae are the single-celled Protococcus group and the filamentous Trentepohlia: as
before only the broad lines of thalline development will be traced.
The elementary forms in the different series are of the simplest type—a somewhat
fortuitous association of alga and fungus, which in time bears the lichen fructification. It
has been stated that the greatest advance of all took place with the formation of a cortex
over the primitive granule, followed by a restricted area of growth outward or upward
which resulted finally in the foliose and fruticose thalli. Guidance in following the
course of evolution is afforded by the character of the fructification, which generally
shows some great similarity of type throughout the different phyla, and remains fairly
constant during the many changes of thalline evolution. Development starting from one
or many origins advances point by point in a series of parallel lines.
a. Thallus of Pyrenocarpineae. In this series there are two families of algae that
function as gonidia: Protococcaceae, consisting of single cells, and Trentepohliaceae,
filamentous. Phyllactidium (Cephaleuros) appears in a single genus, Strigula, a tropical
epiphytic lichen.
Associated with these types of algae are a large number of genera and species of an
elementary character, without any differentiation of tissue. In many instances the thallus
is partly or wholly embedded in the substratum.
Squamulose or foliose forms make their appearance in Dermatocarpaceae: in
Normandina the delicate shell-like squamules are non-corticate, but in other genera,
Endocarpon, Placidiopsis, etc., the squamules are corticate and of firmer texture, while
in Dermatocarpon, foliose fronds of considerable size are formed. The perithecial fruits
are embedded in the upper surface.
serve the same purpose.
Nylander[1002] regarded the Stictaceae as the most highly developed of all lichens,
and they easily take a high place among dorsiventral forms, but it is generally conceded
that the fruticose type is the more highly organized. In any case they are the highest
reach of the phylum or phyla that started with Pyrenopsidaceae and Collemaceae; the
lowly gelatinous thalli changing to more elaborate structures with the abandonment of
the gelatinous algal sheath, as in the Pannariaceae, and with the replacement of blue-
green by bright-green gonidia. Reinke[1003], considers the Stictaceae as evolved from
the Pannariaceae more directly from the genus Massalongia. Their relationship is
certainly with Pannariaceae and Peltigeraceae rather than with Parmeliaceae; these
latter, as we shall see, belong to a wholly different series.
D. Evolution of Archilichens
The study of Archilichens as of Phycolichens is complicated by the many different
kinds of fungi and algae that have entered into combination; but the two principal types
of algae are the single-celled Protococcus group and the filamentous Trentepohlia: as
before only the broad lines of thalline development will be traced.
The elementary forms in the different series are of the simplest type—a somewhat
fortuitous association of alga and fungus, which in time bears the lichen fructification. It
has been stated that the greatest advance of all took place with the formation of a cortex
over the primitive granule, followed by a restricted area of growth outward or upward
which resulted finally in the foliose and fruticose thalli. Guidance in following the
course of evolution is afforded by the character of the fructification, which generally
shows some great similarity of type throughout the different phyla, and remains fairly
constant during the many changes of thalline evolution. Development starting from one
or many origins advances point by point in a series of parallel lines.
a. Thallus of Pyrenocarpineae. In this series there are two families of algae that
function as gonidia: Protococcaceae, consisting of single cells, and Trentepohliaceae,
filamentous. Phyllactidium (Cephaleuros) appears in a single genus, Strigula, a tropical
epiphytic lichen.
Associated with these types of algae are a large number of genera and species of an
elementary character, without any differentiation of tissue. In many instances the thallus
is partly or wholly embedded in the substratum.
Squamulose or foliose forms make their appearance in Dermatocarpaceae: in
Normandina the delicate shell-like squamules are non-corticate, but in other genera,
Endocarpon, Placidiopsis, etc., the squamules are corticate and of firmer texture, while
in Dermatocarpon, foliose fronds of considerable size are formed. The perithecial fruits
are embedded in the upper surface.
Page 358
In only one extremely rare lichen, Pyrenothamnia Spraguei (N. America), is there
fruticose development: the thallus, round and stalk-like at the base, branches above into
broader more leaf-like expansions.
b. Thallus of Coniocarpineae. At the base of this series are genera and species that
are extremely elementary as regards thalline formation, with others that are saprophytic
and parasitic. The simplest type of thallus occurs in Caliciaceae, a spreading mycelium
with associated algae (Protococcaceae) collected in small scattered granules, resembling
somewhat a collection of loose soredia. The species grow mostly on old wood, trunks of
trees, etc. In Calicium (Chaenotheca) chrysocephalum as described by Neubner[1004] the
first thallus formation begins with these scattered minute granules; gradually they
increase in size and number till a thick granular coating of the substratum arises, but no
cortex is formed and there is no differentiation of tissue.
The genus Cyphelium (Cypheliaceae) is considered by Reinke to be more highly
developed, inasmuch as the thalline granules, though non-corticate, are more extended
horizontally, and, in vertical section, show a distinct differentiation into gonidial zone
and medulla. The sessile fruit also takes origin from the thallus, and is surrounded by a
thalline amphithecium, or rather it remains embedded in the thalline granule. A closely
allied tropical genus Pyrgillus has reached a somewhat similar stage of development,
but with a more coherent homogeneous thallus, while in Tylophoron, also tropical or
subtropical, the fruit is raised above the crustaceous thallus but is thickly surrounded by
a thalline margin. The alga of that genus is Trentepohlia, a rare constituent of
Coniocarpineae.
A much more advanced formation appears in the remaining family
Sphaerophoraceae. In Calycidium, a monotypic New Zealand genus, the thallus consists
of minute squamules, dorsiventral in structure but with a tendency to vertical growth,
the upper surface is corticate and the mazaedial apothecia—always open—are situated
on the margins. Tholurna dissimilis, (Scandinavian) still more highly developed, has
two kinds of rather small fronds corticate on both surfaces, the one horizontal in growth,
crenulate in outline, and sterile, the other vertical, about 2 mm. in height, hollow and
terminating in a papilla in which is seated the apothecium.
Two other monotypic subtropical genera form a connecting link with the more highly
evolved forms. In the first, Acroscyphus sphaerophoroides, the fronds are somewhat
similar to the fertile ones of Tholurna, but they possess a solid central strand and the
apical mazaedium is less enveloped by the thallus. The other, Pleurocybe
madagascarea, has narrow flattish branching fronds about 3 cm. in height, hollow in the
centre and corticate with marginal or surface fruits.
The third genus, Sphaerophorus, is cosmopolitan; three of the species are British and
are fairly common on moorlands, etc. They are fruticose in habit, being composed of
congregate upright branching stalks, either round or slightly compressed and varying in
height from about 1 to 8 cm. The structure is radiate with a well-developed outer cortex,
and a central strand which gives strength to the somewhat slender stalks. The fruits are
fruticose development: the thallus, round and stalk-like at the base, branches above into
broader more leaf-like expansions.
b. Thallus of Coniocarpineae. At the base of this series are genera and species that
are extremely elementary as regards thalline formation, with others that are saprophytic
and parasitic. The simplest type of thallus occurs in Caliciaceae, a spreading mycelium
with associated algae (Protococcaceae) collected in small scattered granules, resembling
somewhat a collection of loose soredia. The species grow mostly on old wood, trunks of
trees, etc. In Calicium (Chaenotheca) chrysocephalum as described by Neubner[1004] the
first thallus formation begins with these scattered minute granules; gradually they
increase in size and number till a thick granular coating of the substratum arises, but no
cortex is formed and there is no differentiation of tissue.
The genus Cyphelium (Cypheliaceae) is considered by Reinke to be more highly
developed, inasmuch as the thalline granules, though non-corticate, are more extended
horizontally, and, in vertical section, show a distinct differentiation into gonidial zone
and medulla. The sessile fruit also takes origin from the thallus, and is surrounded by a
thalline amphithecium, or rather it remains embedded in the thalline granule. A closely
allied tropical genus Pyrgillus has reached a somewhat similar stage of development,
but with a more coherent homogeneous thallus, while in Tylophoron, also tropical or
subtropical, the fruit is raised above the crustaceous thallus but is thickly surrounded by
a thalline margin. The alga of that genus is Trentepohlia, a rare constituent of
Coniocarpineae.
A much more advanced formation appears in the remaining family
Sphaerophoraceae. In Calycidium, a monotypic New Zealand genus, the thallus consists
of minute squamules, dorsiventral in structure but with a tendency to vertical growth,
the upper surface is corticate and the mazaedial apothecia—always open—are situated
on the margins. Tholurna dissimilis, (Scandinavian) still more highly developed, has
two kinds of rather small fronds corticate on both surfaces, the one horizontal in growth,
crenulate in outline, and sterile, the other vertical, about 2 mm. in height, hollow and
terminating in a papilla in which is seated the apothecium.
Two other monotypic subtropical genera form a connecting link with the more highly
evolved forms. In the first, Acroscyphus sphaerophoroides, the fronds are somewhat
similar to the fertile ones of Tholurna, but they possess a solid central strand and the
apical mazaedium is less enveloped by the thallus. The other, Pleurocybe
madagascarea, has narrow flattish branching fronds about 3 cm. in height, hollow in the
centre and corticate with marginal or surface fruits.
The third genus, Sphaerophorus, is cosmopolitan; three of the species are British and
are fairly common on moorlands, etc. They are fruticose in habit, being composed of
congregate upright branching stalks, either round or slightly compressed and varying in
height from about 1 to 8 cm. The structure is radiate with a well-developed outer cortex,
and a central strand which gives strength to the somewhat slender stalks. The fruits are
Page 359
lodged in the swollen tips and are at first enclosed; later, the covering thallus splits
irregularly and exposes the hymenium.
Coniocarpineae comprise only a comparatively small number of genera and species,
but the series is of unusual interest as being extremely well defined by the fruit-
formation and as representing all the various stages of thalline development from the
primitive crustaceous to the highly evolved fruticose type. With the primitive thallus is
associated a wholly fungal fruit, both stalk and capitulum, which in the higher forms is
surrounded and protected by the thallus. Lichen-acids are freely produced even in
crustaceous forms, and they, along with the high stage of development reached, testify
to the great antiquity of the series.
c. Thallus of Graphidineae. As formerly understood, this series included only
crustaceous forms with an extremely simple development of thallus, fungi and algae—
whether Palmellaceae, etc., or more frequently Trentepohliaceae—growing side by side
either superficially or embedded in tree or rock, the presence of the vegetative body
being often signalled only by a deeper colouration of the substratum. The researches of
Almquist, and more recently of Reinke and Darbishire, have enlarged our conception of
the series, and the families Dirinaceae and Roccellaceae are now classified in
Graphidineae.
Arthoniaceae, Graphidaceae and Chiodectonaceae are all wholly crustaceous. The
first thalline advance takes place in Dirinaceae with two allied genera, Dirina and
Dirinastrum. Though the thallus is still crustaceous, it is of considerable thickness, with
differentiation of tissues: on the lower side there is a loosely filamentous medulla from
which hyphae pierce the substratum and secure attachment. Trentepohlia gonidia lie in a
zone above the medulla, and the upper cortex is formed of regular palisade hyphae
forming a “fastigiate cortex.” It is the constant presence of Trentepohlia algae as well as
the tendency to ellipsoid or lirellate fruits that have influenced the inclusion of
Dirinaceae and Roccellaceae in the series.
The thallus of Dirinaceae is crustaceous, while the genera of Roccellaceae are mostly
of an advanced fruticose type, though in one, Roccellina, there is a crustaceous thallus
with an upright portion consisting of short swollen podetia-like structures with
apothecia at the tips; and in another, Roccellographa, the fronds broaden to leafy
expansions. They are nearly all rock-dwellers, often inhabiting wind-swept maritime
coasts, and a strong basal sheath has been evolved to strengthen their foothold. In some
genera the sheath contains gonidia; in others the tissue is wholly of hyphae—in nearly
every case it is protected by a cortex.
In the upright fronds the structure is radiate: generally a rather loose strand of hyphae
more or less parallel with the long axis of the plant forms a central medulla. The gonidia
lie outside the medulla and just within the outer cortex. The latter, in a few genera, is
fibrous, the parallel hyphae being very closely compacted; but in most members of the
family the fastigiate type prevails, as in the allied family Dirinaceae.
irregularly and exposes the hymenium.
Coniocarpineae comprise only a comparatively small number of genera and species,
but the series is of unusual interest as being extremely well defined by the fruit-
formation and as representing all the various stages of thalline development from the
primitive crustaceous to the highly evolved fruticose type. With the primitive thallus is
associated a wholly fungal fruit, both stalk and capitulum, which in the higher forms is
surrounded and protected by the thallus. Lichen-acids are freely produced even in
crustaceous forms, and they, along with the high stage of development reached, testify
to the great antiquity of the series.
c. Thallus of Graphidineae. As formerly understood, this series included only
crustaceous forms with an extremely simple development of thallus, fungi and algae—
whether Palmellaceae, etc., or more frequently Trentepohliaceae—growing side by side
either superficially or embedded in tree or rock, the presence of the vegetative body
being often signalled only by a deeper colouration of the substratum. The researches of
Almquist, and more recently of Reinke and Darbishire, have enlarged our conception of
the series, and the families Dirinaceae and Roccellaceae are now classified in
Graphidineae.
Arthoniaceae, Graphidaceae and Chiodectonaceae are all wholly crustaceous. The
first thalline advance takes place in Dirinaceae with two allied genera, Dirina and
Dirinastrum. Though the thallus is still crustaceous, it is of considerable thickness, with
differentiation of tissues: on the lower side there is a loosely filamentous medulla from
which hyphae pierce the substratum and secure attachment. Trentepohlia gonidia lie in a
zone above the medulla, and the upper cortex is formed of regular palisade hyphae
forming a “fastigiate cortex.” It is the constant presence of Trentepohlia algae as well as
the tendency to ellipsoid or lirellate fruits that have influenced the inclusion of
Dirinaceae and Roccellaceae in the series.
The thallus of Dirinaceae is crustaceous, while the genera of Roccellaceae are mostly
of an advanced fruticose type, though in one, Roccellina, there is a crustaceous thallus
with an upright portion consisting of short swollen podetia-like structures with
apothecia at the tips; and in another, Roccellographa, the fronds broaden to leafy
expansions. They are nearly all rock-dwellers, often inhabiting wind-swept maritime
coasts, and a strong basal sheath has been evolved to strengthen their foothold. In some
genera the sheath contains gonidia; in others the tissue is wholly of hyphae—in nearly
every case it is protected by a cortex.
In the upright fronds the structure is radiate: generally a rather loose strand of hyphae
more or less parallel with the long axis of the plant forms a central medulla. The gonidia
lie outside the medulla and just within the outer cortex. The latter, in a few genera, is
fibrous, the parallel hyphae being very closely compacted; but in most members of the
family the fastigiate type prevails, as in the allied family Dirinaceae.
Page 360
d. Thallus of Cyclocarpineae. This is by far the largest and most varied series of
Archilichens. It is derived, as regards the fungal constituent, from the Discomycetes, but
in these fungi, the vegetative or mycelial body gives no aid to the classification which
depends wholly on apothecial characters. In the symbiotic condition, on the contrary,
the thallus becomes of extreme importance in the determination of families, genera and
species. There has been within the series a great development both of apothecial and of
thalline characters in parallel lines or phyla.
AA. Lecideales. The type of fruit nearest to fungi in form and origin occurs in the
Lecideales. It is an open disc developed from the fungal symbiont alone, the alga taking
no part. There are several phyla to be considered.
aa. Coenogoniaceae. There are two types of gonidial algae in this family, and both
are filamentous forms, Trentepohlia in Coenogonium and Cladophora in Racodium.
The resulting lichens retain the slender thread-like form of the algae, their cells being
thinly invested by the hyphae and both symbionts growing apically. The thalline
filaments are generally very sparingly branched and grow radially side by side in a
loose flat expansion attached at one side by a sheath, or the strands spread irregularly
over the substratum. Plectenchyma appears in the apothecial margin in Coenogonium.
Fruiting bodies are unknown in Racodium.
Coenogoniaceae are a group apart and of slight development, only the one kind of
thallus appearing; the form is moulded on that of the gonidium, and is, as Reinke[1005]
remarks, perfectly adapted to receive the maximum of illumination and aeration.
bb. Lecideaceae and Gyrophoraceae. The origin of this thalline phylum is distinct
from that of the previous family, being associated with a different type of gonidium, the
single-celled alga of the Protococcaceae.
The more elementary species are of extremely simple structure as exemplified in such
species as Lecidea (Biatora) uliginosa or Lecidea granulosa. These lichens grow on
humus-soil and the thallus consists of a spreading mycelium or hypothallus with more
or less scattered thalline granules containing gonidia, but without any defined structure.
The first advance takes place in the aggregation and consolidation of such thalline
granules and the massing of the gonidia towards the light, thus substituting the
heteromerous for the homoiomerous arrangement of the tissues. The various characters
of thickness, areolation, colour, etc. of the thallus are constant and are expressed in
specific diagnoses. Frequently an amorphous cortex of swollen hyphae provides a
smooth upper surface and forms a protective covering for such long-lived species as
Rhizocarpon geographicum, etc.
The squamulose thallus is well represented in this phylum. The squamules vary in
size and texture but are mostly rather thick and stiff. In Lecidea ostreata they rise from
the substratum in serried rows forming a dense sward; in L. decipiens, also a British
species, the squamules are still larger, and more horizontal in direction; they are thick
Archilichens. It is derived, as regards the fungal constituent, from the Discomycetes, but
in these fungi, the vegetative or mycelial body gives no aid to the classification which
depends wholly on apothecial characters. In the symbiotic condition, on the contrary,
the thallus becomes of extreme importance in the determination of families, genera and
species. There has been within the series a great development both of apothecial and of
thalline characters in parallel lines or phyla.
AA. Lecideales. The type of fruit nearest to fungi in form and origin occurs in the
Lecideales. It is an open disc developed from the fungal symbiont alone, the alga taking
no part. There are several phyla to be considered.
aa. Coenogoniaceae. There are two types of gonidial algae in this family, and both
are filamentous forms, Trentepohlia in Coenogonium and Cladophora in Racodium.
The resulting lichens retain the slender thread-like form of the algae, their cells being
thinly invested by the hyphae and both symbionts growing apically. The thalline
filaments are generally very sparingly branched and grow radially side by side in a
loose flat expansion attached at one side by a sheath, or the strands spread irregularly
over the substratum. Plectenchyma appears in the apothecial margin in Coenogonium.
Fruiting bodies are unknown in Racodium.
Coenogoniaceae are a group apart and of slight development, only the one kind of
thallus appearing; the form is moulded on that of the gonidium, and is, as Reinke[1005]
remarks, perfectly adapted to receive the maximum of illumination and aeration.
bb. Lecideaceae and Gyrophoraceae. The origin of this thalline phylum is distinct
from that of the previous family, being associated with a different type of gonidium, the
single-celled alga of the Protococcaceae.
The more elementary species are of extremely simple structure as exemplified in such
species as Lecidea (Biatora) uliginosa or Lecidea granulosa. These lichens grow on
humus-soil and the thallus consists of a spreading mycelium or hypothallus with more
or less scattered thalline granules containing gonidia, but without any defined structure.
The first advance takes place in the aggregation and consolidation of such thalline
granules and the massing of the gonidia towards the light, thus substituting the
heteromerous for the homoiomerous arrangement of the tissues. The various characters
of thickness, areolation, colour, etc. of the thallus are constant and are expressed in
specific diagnoses. Frequently an amorphous cortex of swollen hyphae provides a
smooth upper surface and forms a protective covering for such long-lived species as
Rhizocarpon geographicum, etc.
The squamulose thallus is well represented in this phylum. The squamules vary in
size and texture but are mostly rather thick and stiff. In Lecidea ostreata they rise from
the substratum in serried rows forming a dense sward; in L. decipiens, also a British
species, the squamules are still larger, and more horizontal in direction; they are thick
Page 361
and firm and the upper cortex is a plectenchyma of cells with swollen walls. Solitary
hyphae from the medulla pass downwards into the support.
Changes in spore characters also arise in these different thalline series, as for instance
in genera such as Biatorina and Buellia, the one with colourless, the other with brown,
two-celled spores. These variations, along with changes in the thallus, are of specific or
generic importance following the significance accorded to the various characters.
In one lichen of the series, the monotypic Brazilian genus Sphaerophoropsis
stereocauloides, the thallus is described by Wainio[1006] as consisting of minute clavate
stalks of interwoven thick-walled hyphae, with gelatinous algae, like Gloeocapsa,
interspersed in groups, though with a tendency to congregate towards the outer surface.
The highest development along this line of advance is to be found in the
Gyrophoraceae, a family of lichens with a varied foliose character and dark lecideine
apothecia. The thallus may be monophyllous and of fairly large dimensions or
polyphyllous; it is mostly anchored by a central stout hold-fast and both surfaces are
thickly corticate with a layer of plectenchyma; the under surface is mostly bare, but may
be densely covered with rhizina-like strands of dark hyphae. They are all northern
species and rock-dwellers exposed to severe extremes of illumination and temperature,
but well protected by the thick cortex and the dark colouration common to them all.
cc. Cladoniaceae. This last phylum of Lecideales is the most interesting as it is the
most complicated. It possesses a primary, generally sterile, thallus which is dorsiventral
and crustaceous, squamulose or in some instances almost foliaceous, along with a
secondary thallus of upright radiate structure and of very varied form, known as the
podetium which bears at the summit the fertile organs.
A double thallus has been suggested in the spreading base, containing gonidia, of
some radiate lichens such as Roccella, but the upright portion of such lichens, though
analogous, is not homologous with that of Cladoniaceae.
The algal cells of the family belong to the Protococcaceae. Blue-green algae are
associated in the cephalodia of Pilophorus and Stereocaulon. The primary thallus is a
feature of all the members, though sometimes very slight and very short-lived, as in
Stereocaulon or in the section Cladina of the genus Cladonia. Where the primary
thallus is most largely developed, the secondary (the podetium) is less prominent.
This secondary thallus originates in two different ways: (1) the primary granule may
grow upward, the whole of the tissues taking part in the new development; or (2) the
origin may be endogenous and proceed from the hyphae only of the gonidial zone: these
push upwards in a compact fascicle, as in the apothecial development of Lecidea, but
instead of spreading outward on reaching the surface, they continue to grow in a vertical
direction and form the podetium. In origin this is an apothecial stalk, but generally it is
clothed with gonidial tissue. The gonidia may travel upwards from the base or they may
possibly be wind borne from the open. The podetium thus takes on an assimilative
function and is a secondary thallus.
hyphae from the medulla pass downwards into the support.
Changes in spore characters also arise in these different thalline series, as for instance
in genera such as Biatorina and Buellia, the one with colourless, the other with brown,
two-celled spores. These variations, along with changes in the thallus, are of specific or
generic importance following the significance accorded to the various characters.
In one lichen of the series, the monotypic Brazilian genus Sphaerophoropsis
stereocauloides, the thallus is described by Wainio[1006] as consisting of minute clavate
stalks of interwoven thick-walled hyphae, with gelatinous algae, like Gloeocapsa,
interspersed in groups, though with a tendency to congregate towards the outer surface.
The highest development along this line of advance is to be found in the
Gyrophoraceae, a family of lichens with a varied foliose character and dark lecideine
apothecia. The thallus may be monophyllous and of fairly large dimensions or
polyphyllous; it is mostly anchored by a central stout hold-fast and both surfaces are
thickly corticate with a layer of plectenchyma; the under surface is mostly bare, but may
be densely covered with rhizina-like strands of dark hyphae. They are all northern
species and rock-dwellers exposed to severe extremes of illumination and temperature,
but well protected by the thick cortex and the dark colouration common to them all.
cc. Cladoniaceae. This last phylum of Lecideales is the most interesting as it is the
most complicated. It possesses a primary, generally sterile, thallus which is dorsiventral
and crustaceous, squamulose or in some instances almost foliaceous, along with a
secondary thallus of upright radiate structure and of very varied form, known as the
podetium which bears at the summit the fertile organs.
A double thallus has been suggested in the spreading base, containing gonidia, of
some radiate lichens such as Roccella, but the upright portion of such lichens, though
analogous, is not homologous with that of Cladoniaceae.
The algal cells of the family belong to the Protococcaceae. Blue-green algae are
associated in the cephalodia of Pilophorus and Stereocaulon. The primary thallus is a
feature of all the members, though sometimes very slight and very short-lived, as in
Stereocaulon or in the section Cladina of the genus Cladonia. Where the primary
thallus is most largely developed, the secondary (the podetium) is less prominent.
This secondary thallus originates in two different ways: (1) the primary granule may
grow upward, the whole of the tissues taking part in the new development; or (2) the
origin may be endogenous and proceed from the hyphae only of the gonidial zone: these
push upwards in a compact fascicle, as in the apothecial development of Lecidea, but
instead of spreading outward on reaching the surface, they continue to grow in a vertical
direction and form the podetium. In origin this is an apothecial stalk, but generally it is
clothed with gonidial tissue. The gonidia may travel upwards from the base or they may
possibly be wind borne from the open. The podetium thus takes on an assimilative
function and is a secondary thallus.
Page 362
The same type of apothecium is common to all the genera; the spores are colourless
and mostly simple, but there are also changes in form and septation not commensurate
with thalline advance, as has been already noted. Thus in Gomphillus, with primitive
thallus and podetium, the spores are long and narrow with about 100 divisions.
1. Origin of Cladonia. There is no difficulty in deriving Cladoniaceae from Lecidea,
or, more exactly, from some crustaceous species of the section Biatora in which the
apothecia—as in Cladoniaceae—are waxy and more or less light-coloured and without
a thalline margin. In only a very few isolated instances has a thalline margin grown
round the Cladonia fruit.
There are ten genera included in the Cladoniaceae, of which five are British.
Considerable study has been devoted to the elucidation of developmental problems
within the family by various workers, more especially in the large and varied genus
Cladonia which is complicated by the presence of the two thalli. The family is
monophyletic in origin, though many subordinate phyla appear later.
2. Evolution of the Primary Thallus. At the base of the series we find here also an
elementary granular thallus which appears in some species of most of the genera. In
Gomphillus, a monospecific British genus, the granules have coalesced into a
continuous mucilaginous membrane. In Baeomyces, though mostly crustaceous, there is
an advance to the squamulose type in B. placophyllus, and in two Brazilian species
described by Wainio, one of which, owing to the form of the fronds, has been placed in
a separate genus Heteromyces. The primary thallus becomes almost foliose also in
Gymnoderma coccocarpum from the Himalayas, with dorsiventral stratose arrangement
of the tissues, but without rhizinae. The greatest diversity is however to be found in
Cladonia where granular, squamulose and almost foliose thalli occur. The various tissue
formations have already been described[1007].
3. Evolution of the Secondary Thallus. Most of the interest centres round the
development and function of the podetium. In several genera the primordium is
homologous with that of an apothecium; its elongation to an apothecial stalk is
associated with delayed fructification, and though it has taken on the function of the
vegetative thallus, the purpose of elongation has doubtless been to secure good light
conditions for the fruit, and to facilitate a wide distribution of spores: therefore, not only
in development but in function, its chief importance though now assimilative was
originally reproductive. The vegetative development of the podetium is correlated with
the reduction of the primary thallus which in many species bears little relation in size or
persistence to the structure produced from it, as, for instance, in Cladonia rangiferina
where the ground thallus is of the scantiest and very soon disappears, while the podetial
thallus continues to grow indefinitely and to considerable size.
4. Course of Podetial Development. In Baeomyces the podetial primordium is
wholly endogenous in some species, but in others the outer cortical layer of the primary
thallus as well as the gonidial hyphae take part in the formation of the new structure
which, in that case, is simply a vertical extension of the primary granule. This type of
and mostly simple, but there are also changes in form and septation not commensurate
with thalline advance, as has been already noted. Thus in Gomphillus, with primitive
thallus and podetium, the spores are long and narrow with about 100 divisions.
1. Origin of Cladonia. There is no difficulty in deriving Cladoniaceae from Lecidea,
or, more exactly, from some crustaceous species of the section Biatora in which the
apothecia—as in Cladoniaceae—are waxy and more or less light-coloured and without
a thalline margin. In only a very few isolated instances has a thalline margin grown
round the Cladonia fruit.
There are ten genera included in the Cladoniaceae, of which five are British.
Considerable study has been devoted to the elucidation of developmental problems
within the family by various workers, more especially in the large and varied genus
Cladonia which is complicated by the presence of the two thalli. The family is
monophyletic in origin, though many subordinate phyla appear later.
2. Evolution of the Primary Thallus. At the base of the series we find here also an
elementary granular thallus which appears in some species of most of the genera. In
Gomphillus, a monospecific British genus, the granules have coalesced into a
continuous mucilaginous membrane. In Baeomyces, though mostly crustaceous, there is
an advance to the squamulose type in B. placophyllus, and in two Brazilian species
described by Wainio, one of which, owing to the form of the fronds, has been placed in
a separate genus Heteromyces. The primary thallus becomes almost foliose also in
Gymnoderma coccocarpum from the Himalayas, with dorsiventral stratose arrangement
of the tissues, but without rhizinae. The greatest diversity is however to be found in
Cladonia where granular, squamulose and almost foliose thalli occur. The various tissue
formations have already been described[1007].
3. Evolution of the Secondary Thallus. Most of the interest centres round the
development and function of the podetium. In several genera the primordium is
homologous with that of an apothecium; its elongation to an apothecial stalk is
associated with delayed fructification, and though it has taken on the function of the
vegetative thallus, the purpose of elongation has doubtless been to secure good light
conditions for the fruit, and to facilitate a wide distribution of spores: therefore, not only
in development but in function, its chief importance though now assimilative was
originally reproductive. The vegetative development of the podetium is correlated with
the reduction of the primary thallus which in many species bears little relation in size or
persistence to the structure produced from it, as, for instance, in Cladonia rangiferina
where the ground thallus is of the scantiest and very soon disappears, while the podetial
thallus continues to grow indefinitely and to considerable size.
4. Course of Podetial Development. In Baeomyces the podetial primordium is
wholly endogenous in some species, but in others the outer cortical layer of the primary
thallus as well as the gonidial hyphae take part in the formation of the new structure
which, in that case, is simply a vertical extension of the primary granule. This type of
Page 363
podetium—called by Wainio[1008] a pseudopodetium—also recurs in Pilophorus and in
Stereocaulon. To emphasize the distinction of origin it has been proposed to classify
these two latter genera in a separate family, but in that case it would be necessary to
break up the genus Baeomyces. We may assume that the endogenous origin of the
“apothecial stalk” is the more primitive, as it occurs in the most primitive lecideine
lichens, whereas a vertical thallus is always an advanced stage of vegetative
development.
Podetia are essentially secondary structures, and they are associated both with
crustaceous and squamulose primary thalli. If monophyletic in origin their development
must have taken place while the primary thallus was still in the crustaceous stage, and
the inherited tendency to form podetia must then have persisted through the change to
the squamulose type. In species such as Cl. caespiticia the presence of rudimentary
podetia along with large squamules suggests a polyphyletic origin, but Wainio’s[1008]
opinion is that such instances may show retrogression from an advanced podetial form,
and that the evidence inclines to the monophyletic view of their origin.
The hollow centre of the podetium arises in the course of development and is
common to nearly all advanced stages of growth. There are however some exceptions:
in Glossodium aversum, a soil lichen from New Granada, and the only representative of
the genus, a simple or rarely forked stalk about 2 cm. in height rises from a granular or
minutely squamulose thallus. The apothecium occupies one side of the flattened and
somewhat wider apex. There is no external cortex and the central tissue is of loose
hyphae. In Thysanothecium Hookeri, also a monotypic genus from Australia, the
podetia are about the same height, but, though round at the base, they broaden upwards
into a leaf-like expansion. The central tissue below is of loose hyphae, but compact
strands occur above, where the apothecium spreads over the upper side. The under
surface is sterile and is traversed by nerve-like strands of hyphae.
5. Variation in Cladonia. It is in this genus that most variation is to be found.
Characters of importance and persistence have arisen by which secondary phyla may be
traced within the genus: these are mainly (1) the relative development of the horizontal
and vertical structures, (2) formation of the scyphus and branching of the podetium,
with (3) differences in colour both in the vegetative thallus and in the apothecia.
Wainio has indicated the course of evolution on the following lines: (1) the
crustaceous thallus is monophyletic in origin and here as elsewhere precedes the
squamulose. The latter he considers to be also monophyletic, though at more than one
point the more advanced and larger foliose forms have appeared: (2) the primitive
podetium was subulate and unbranched, and the apex was occupied by the apothecium.
Both scyphus and branching are later developments indicating progress. They are in
both cases associated with fruit-formation—scyphi generally arising from abortive
apothecia[1009], branching from aggregate apothecia. In forms such as Cl. fimbriata,
where both scyphiferous and subulate sterile podetia are frequent, the latter (subspecies
fibula) are retrogressive, and reproduce the ancestral pointed podetium. (3) In subgen.
Stereocaulon. To emphasize the distinction of origin it has been proposed to classify
these two latter genera in a separate family, but in that case it would be necessary to
break up the genus Baeomyces. We may assume that the endogenous origin of the
“apothecial stalk” is the more primitive, as it occurs in the most primitive lecideine
lichens, whereas a vertical thallus is always an advanced stage of vegetative
development.
Podetia are essentially secondary structures, and they are associated both with
crustaceous and squamulose primary thalli. If monophyletic in origin their development
must have taken place while the primary thallus was still in the crustaceous stage, and
the inherited tendency to form podetia must then have persisted through the change to
the squamulose type. In species such as Cl. caespiticia the presence of rudimentary
podetia along with large squamules suggests a polyphyletic origin, but Wainio’s[1008]
opinion is that such instances may show retrogression from an advanced podetial form,
and that the evidence inclines to the monophyletic view of their origin.
The hollow centre of the podetium arises in the course of development and is
common to nearly all advanced stages of growth. There are however some exceptions:
in Glossodium aversum, a soil lichen from New Granada, and the only representative of
the genus, a simple or rarely forked stalk about 2 cm. in height rises from a granular or
minutely squamulose thallus. The apothecium occupies one side of the flattened and
somewhat wider apex. There is no external cortex and the central tissue is of loose
hyphae. In Thysanothecium Hookeri, also a monotypic genus from Australia, the
podetia are about the same height, but, though round at the base, they broaden upwards
into a leaf-like expansion. The central tissue below is of loose hyphae, but compact
strands occur above, where the apothecium spreads over the upper side. The under
surface is sterile and is traversed by nerve-like strands of hyphae.
5. Variation in Cladonia. It is in this genus that most variation is to be found.
Characters of importance and persistence have arisen by which secondary phyla may be
traced within the genus: these are mainly (1) the relative development of the horizontal
and vertical structures, (2) formation of the scyphus and branching of the podetium,
with (3) differences in colour both in the vegetative thallus and in the apothecia.
Wainio has indicated the course of evolution on the following lines: (1) the
crustaceous thallus is monophyletic in origin and here as elsewhere precedes the
squamulose. The latter he considers to be also monophyletic, though at more than one
point the more advanced and larger foliose forms have appeared: (2) the primitive
podetium was subulate and unbranched, and the apex was occupied by the apothecium.
Both scyphus and branching are later developments indicating progress. They are in
both cases associated with fruit-formation—scyphi generally arising from abortive
apothecia[1009], branching from aggregate apothecia. In forms such as Cl. fimbriata,
where both scyphiferous and subulate sterile podetia are frequent, the latter (subspecies
fibula) are retrogressive, and reproduce the ancestral pointed podetium. (3) In subgen.
Page 364
Cenomyce, with a squamulose primary thallus, there is a sharp division into two main
phyla characterized by the colour of the apothecia, brown in Ochrophaeae—the colour
being due to a pigment—and red in Cocciferae where the colouring substance is a
lichen-acid, rhodocladonic acid. In the brown-fruited Ochrophaeae there are again
several secondary phyla. Two of these are distinguished primarily by the character of
the branching: (a) the Chasmariae in which two or several branches arise from the same
level, entailing perforation of the axils (Cl. furcata, Cl. rangiformis, Cl. squamosa, etc.),
the scyphi also are perforated. They are further characterized by peltate aggregate
apothecia, this grouping of the apothecia according to Wainio being the primary cause
of the complex branching, the several fruit stalks growing out as branches. The second
group (b), the Clausae, are not perforated and the apothecia are simple and broad-based
on the edge of the scyphus (Cl. pyxidata, Cl. fimbriata, etc.), or on the tips of the
podetia (Cl. cariosa, Cl. leptophylla, etc.). A third very small group also of Clausae
called (c) Foliosae has very large primary squamules and reduced podetia (Cl. foliacea,
etc.), while finally (d) the Ochroleucae, none of which is British, have poorly developed
squamules and variously formed yellowish podetia with pale-coloured apothecia.
The Cocciferae represent a phylum parallel in development with the Ochrophaeae.
The species have perhaps most affinity with the Clausae, the vegetative thallus—both
the squamules and the podetia—being very much alike in several species. Wainio
distinguishes two groups based on a difference of colour in the squamules, glaucous
green in one case, yellowish in the other.
6. Causes of Variation. External causes of variation in Cladonia are chiefly humidity
and light, excess or lack of either effecting changes which may have become fixed and
hereditary. Minor changes directly traceable to these influences are also frequent, viz.
size of podetia, proliferation and the production more or less of soredia or of squamules
on the podetia, though only in connection with species in which these variations are
already an acquired character. The squamules on the podetium more or less repeat the
form of the basal squamules.
7. Podetial Development and Spore-dissemination. In a recent paper by Hans
Sättler[1010] the problem of podetial development in Cladonia is viewed from a different
standpoint. He holds that as the podetia are apothecial stalks, their service to the plant
consists in the raising of the mature fruit in order to secure a wide distribution of the
spores, and that changes in the form of the podetium are therefore but new adaptations
for the more efficient discharge of this function.
Following out this idea he regards as the more primitive forms those in which both
the spermogonia, as male reproductive bodies, and the carpogonia occur on the primary
thallus, ascogonia and trichogynes being formed before the podetium emerges from the
thallus. Fertilization thus must take place at a very early period, though the ultimate
fruiting stage may be long delayed. Sättler considers that any doubt as to actual
fertilization is without bearing on the question, as sexuality he holds must have
originally existed and must have directed the course of evolution in the reproductive
phyla characterized by the colour of the apothecia, brown in Ochrophaeae—the colour
being due to a pigment—and red in Cocciferae where the colouring substance is a
lichen-acid, rhodocladonic acid. In the brown-fruited Ochrophaeae there are again
several secondary phyla. Two of these are distinguished primarily by the character of
the branching: (a) the Chasmariae in which two or several branches arise from the same
level, entailing perforation of the axils (Cl. furcata, Cl. rangiformis, Cl. squamosa, etc.),
the scyphi also are perforated. They are further characterized by peltate aggregate
apothecia, this grouping of the apothecia according to Wainio being the primary cause
of the complex branching, the several fruit stalks growing out as branches. The second
group (b), the Clausae, are not perforated and the apothecia are simple and broad-based
on the edge of the scyphus (Cl. pyxidata, Cl. fimbriata, etc.), or on the tips of the
podetia (Cl. cariosa, Cl. leptophylla, etc.). A third very small group also of Clausae
called (c) Foliosae has very large primary squamules and reduced podetia (Cl. foliacea,
etc.), while finally (d) the Ochroleucae, none of which is British, have poorly developed
squamules and variously formed yellowish podetia with pale-coloured apothecia.
The Cocciferae represent a phylum parallel in development with the Ochrophaeae.
The species have perhaps most affinity with the Clausae, the vegetative thallus—both
the squamules and the podetia—being very much alike in several species. Wainio
distinguishes two groups based on a difference of colour in the squamules, glaucous
green in one case, yellowish in the other.
6. Causes of Variation. External causes of variation in Cladonia are chiefly humidity
and light, excess or lack of either effecting changes which may have become fixed and
hereditary. Minor changes directly traceable to these influences are also frequent, viz.
size of podetia, proliferation and the production more or less of soredia or of squamules
on the podetia, though only in connection with species in which these variations are
already an acquired character. The squamules on the podetium more or less repeat the
form of the basal squamules.
7. Podetial Development and Spore-dissemination. In a recent paper by Hans
Sättler[1010] the problem of podetial development in Cladonia is viewed from a different
standpoint. He holds that as the podetia are apothecial stalks, their service to the plant
consists in the raising of the mature fruit in order to secure a wide distribution of the
spores, and that changes in the form of the podetium are therefore but new adaptations
for the more efficient discharge of this function.
Following out this idea he regards as the more primitive forms those in which both
the spermogonia, as male reproductive bodies, and the carpogonia occur on the primary
thallus, ascogonia and trichogynes being formed before the podetium emerges from the
thallus. Fertilization thus must take place at a very early period, though the ultimate
fruiting stage may be long delayed. Sättler considers that any doubt as to actual
fertilization is without bearing on the question, as sexuality he holds must have
originally existed and must have directed the course of evolution in the reproductive
Page 365
bodies. In this primitive group, called by him the “Floerkeana” group, the podetia are
always short and simple, they are terminated by the apothecium and no scyphi are
formed (Cl. Floerkeana, Cl. leptophylla, Cl. cariosa, Cl. caespiticia, Cl. papillaria,
etc.).
In his second or “pyxidata” group, he places those species in which the apothecia are
borne at the edge of a scyphus. That structure he follows Wainio in regarding as a
morphological reaction on the failure of the first formed apical apothecium: it is, he
adds, a new thallus in the form of a spreading cup and bears, as did the primary thallus,
both the female primordia and the spermogonia. In some species, such as Cl. foliacea,
there may be either scyphous or ascyphous podetia, and spermogonia normally
accompany the carpogonium appearing accordingly along with it either on the squamule
or on the scyphus.
As the pointed podetia are the more primitive, Sättler points out that they may
reappear as retrogressive structures, and have so appeared in the “pyxidata” group in
such species as Cl. fimbriata. He refers to Wainio’s statement that the abortion of the
apothecium being a retrogressive anomaly, while scyphus formation is an evolutionary
advance, the scyphiferous species present the singular case, “that a progressive
transmutation induced by a retrogressive anomaly has become constant.”
His third group includes those forms that grow in crowded tufts or swards such as Cl.
rangiferina, Cl. furcata, Cl. gracilis, etc. They originate, as did the pyxidata group, in
some Floerkeana-like form, but in the “rangiferina” group instead of cup-formation
there is extensive branching. In the closely packed phalanx of branches water is retained
as in similar growths of mosses, and moist conditions necessary for fertilization are thus
secured as efficiently as by the water-holding scyphus.
Sättler in his argument has passed over many important points. Above all he ignores
the fact that whatever may have been the original nature and function of the podetium, it
has now become a thalline structure and provides for the vegetative life of the plant, and
that it is in its thalline condition that the many variations have been formed; the scyphus
is not, as he contends, a new thallus, it is only an extension of thalline characters
already acquired.
8. Pilophorus, Stereocaulon and Argopsis. These closely related genera are
classified with Cladonia as they share with it the twofold thallus and the lecideine
apothecia. The origin of the podetium being different they may be held to constitute a
phylum apart, which has however taken origin also from some Biatora form.
The primary thallus is crustaceous or minutely squamulose and the podetia of
Pilophorus, which are short and unbranched (or very sparingly branched), are beset
with thalline granules. The podetia of Stereocaulon and Argopsis are copiously
branched and are more or less thickly covered with minute variously divided leaflets.
Cephalodia containing blue-green algae occur on the podetia of these latter genera; in
Pilophorus they are intermixed with the primary thallus.
always short and simple, they are terminated by the apothecium and no scyphi are
formed (Cl. Floerkeana, Cl. leptophylla, Cl. cariosa, Cl. caespiticia, Cl. papillaria,
etc.).
In his second or “pyxidata” group, he places those species in which the apothecia are
borne at the edge of a scyphus. That structure he follows Wainio in regarding as a
morphological reaction on the failure of the first formed apical apothecium: it is, he
adds, a new thallus in the form of a spreading cup and bears, as did the primary thallus,
both the female primordia and the spermogonia. In some species, such as Cl. foliacea,
there may be either scyphous or ascyphous podetia, and spermogonia normally
accompany the carpogonium appearing accordingly along with it either on the squamule
or on the scyphus.
As the pointed podetia are the more primitive, Sättler points out that they may
reappear as retrogressive structures, and have so appeared in the “pyxidata” group in
such species as Cl. fimbriata. He refers to Wainio’s statement that the abortion of the
apothecium being a retrogressive anomaly, while scyphus formation is an evolutionary
advance, the scyphiferous species present the singular case, “that a progressive
transmutation induced by a retrogressive anomaly has become constant.”
His third group includes those forms that grow in crowded tufts or swards such as Cl.
rangiferina, Cl. furcata, Cl. gracilis, etc. They originate, as did the pyxidata group, in
some Floerkeana-like form, but in the “rangiferina” group instead of cup-formation
there is extensive branching. In the closely packed phalanx of branches water is retained
as in similar growths of mosses, and moist conditions necessary for fertilization are thus
secured as efficiently as by the water-holding scyphus.
Sättler in his argument has passed over many important points. Above all he ignores
the fact that whatever may have been the original nature and function of the podetium, it
has now become a thalline structure and provides for the vegetative life of the plant, and
that it is in its thalline condition that the many variations have been formed; the scyphus
is not, as he contends, a new thallus, it is only an extension of thalline characters
already acquired.
8. Pilophorus, Stereocaulon and Argopsis. These closely related genera are
classified with Cladonia as they share with it the twofold thallus and the lecideine
apothecia. The origin of the podetium being different they may be held to constitute a
phylum apart, which has however taken origin also from some Biatora form.
The primary thallus is crustaceous or minutely squamulose and the podetia of
Pilophorus, which are short and unbranched (or very sparingly branched), are beset
with thalline granules. The podetia of Stereocaulon and Argopsis are copiously
branched and are more or less thickly covered with minute variously divided leaflets.
Cephalodia containing blue-green algae occur on the podetia of these latter genera; in
Pilophorus they are intermixed with the primary thallus.
Page 366
The tissue systems are less advanced in these genera than in Cladonia: there is no
cortex present either in Pilophorus or in Argopsis or in some species of Stereocaulon,
though in others a gelatinous amorphous layer covers the podetia and also the stalk
leaflets. The stalks are filled with loose hyphae in the centre.
BB. Lecanorales. This second group of Cyclocarpineae is distinguished by the
marginate apothecium, a thalline layer providing a protecting amphithecium. The
lecanorine apothecium is of a more or less soft and waxy consistency, and though the
disc is sometimes almost black, neither hypothecium nor parathecium is carbonaceous
as in Lecidea. The affinity of Lecanora is with sect. Biatora, and development must
have been from a biatorine form with a persistent thallus. The margin or amphithecium
varies in thickness: in some species it is but scanty and soon excluded by the over-
topping growth of the disc, so that a zone of gonidia underlying the hypothecium is
often the only evidence of gonidial intrusion left in fully formed fruits.
The marginate apothecium has appeared once and again as we have seen. It is
probable however that its first development was in this group of lichens, and even here
there may have been more than one origin as there is certainly more than one phylum.
aa. Course of Development. At the base of the series, the thallus is of the crustaceous
type somewhat similar to that of Lecidea, but there are none of the very simple
primitive forms. Lecanora must have originated when the crustaceous lecideine thallus
was already well established. Its affinity is with Lecidea and not with any fungus: where
the thallus is evanescent or scanty, its lack is due to retrogressive rather than to
primitive characters.
bb. Lecanoraceae. A number of genera have arisen in this large family, but they are
distinguished mainly if not entirely by spore characters, and by some systematists have
all been included in the one genus Lecanora, since the changes have taken place within
the developing apothecium.
There is one genus, Harpidium, which is based on thalline characters, represented by
one species, H. rutilans, common enough on the Continent, but not yet found in our
country. It has a thin crustaceous homoiomerous thallus, the component hyphae of
which are divided into short cells closely packed together and forming a kind of cellular
tissue in which the algae are interspersed. The dorsiventral stratose arrangement
prevails however in the other genera and a more or less amorphous “decomposed”
cortex is frequently present. The medulla rests on the substratum.
With the stouter thallus, there is slightly more variety of crustaceous form than in
Lecideaceae: there occurs occasionally an outgrowth of the thalline granules as in
Haematomma ventosum which marks the beginning of fruticulose structure. Of a more
advanced structure is the thallus of Lecanora esculenta, a desert lichen which becomes
detached and erratic, and which in some of its forms is almost coralline, owing to the
apical growth of the original granules or branches: a more or less radiate arrangement of
the tissues is thus acquired.
cortex present either in Pilophorus or in Argopsis or in some species of Stereocaulon,
though in others a gelatinous amorphous layer covers the podetia and also the stalk
leaflets. The stalks are filled with loose hyphae in the centre.
BB. Lecanorales. This second group of Cyclocarpineae is distinguished by the
marginate apothecium, a thalline layer providing a protecting amphithecium. The
lecanorine apothecium is of a more or less soft and waxy consistency, and though the
disc is sometimes almost black, neither hypothecium nor parathecium is carbonaceous
as in Lecidea. The affinity of Lecanora is with sect. Biatora, and development must
have been from a biatorine form with a persistent thallus. The margin or amphithecium
varies in thickness: in some species it is but scanty and soon excluded by the over-
topping growth of the disc, so that a zone of gonidia underlying the hypothecium is
often the only evidence of gonidial intrusion left in fully formed fruits.
The marginate apothecium has appeared once and again as we have seen. It is
probable however that its first development was in this group of lichens, and even here
there may have been more than one origin as there is certainly more than one phylum.
aa. Course of Development. At the base of the series, the thallus is of the crustaceous
type somewhat similar to that of Lecidea, but there are none of the very simple
primitive forms. Lecanora must have originated when the crustaceous lecideine thallus
was already well established. Its affinity is with Lecidea and not with any fungus: where
the thallus is evanescent or scanty, its lack is due to retrogressive rather than to
primitive characters.
bb. Lecanoraceae. A number of genera have arisen in this large family, but they are
distinguished mainly if not entirely by spore characters, and by some systematists have
all been included in the one genus Lecanora, since the changes have taken place within
the developing apothecium.
There is one genus, Harpidium, which is based on thalline characters, represented by
one species, H. rutilans, common enough on the Continent, but not yet found in our
country. It has a thin crustaceous homoiomerous thallus, the component hyphae of
which are divided into short cells closely packed together and forming a kind of cellular
tissue in which the algae are interspersed. The dorsiventral stratose arrangement
prevails however in the other genera and a more or less amorphous “decomposed”
cortex is frequently present. The medulla rests on the substratum.
With the stouter thallus, there is slightly more variety of crustaceous form than in
Lecideaceae: there occurs occasionally an outgrowth of the thalline granules as in
Haematomma ventosum which marks the beginning of fruticulose structure. Of a more
advanced structure is the thallus of Lecanora esculenta, a desert lichen which becomes
detached and erratic, and which in some of its forms is almost coralline, owing to the
apical growth of the original granules or branches: a more or less radiate arrangement of
the tissues is thus acquired.
Page 367
The squamulose type is well represented in Lecanora, and the species with that form
of thallus have frequently been placed in a separate genus, Squamaria. These squamules
are never very large; they possess an upper, somewhat amorphous, cortex; the medulla
rests on the substratum, except in such a species as Lecanora lentigera, where they are
free, a sort of fibrous cortex being formed of hyphae which grow in a direction parallel
with the surface. In none of them are rhizinae developed.
cc. Parmeliaceae. The chief advance, apart from size, of the squamulose to the
foliose type is the acquirement of a lower cortex along with definite organs of
attachment which in Parmeliaceae are invariably rhizoidal and are composed of
compact strands of hyphae extending from the cells of the lower cortex.
In the genus Parmelia rhizinae are almost a constant character, though in a few
species, such as Parmelia physodes, they are scanty or practically absent. It is not
possible, however, to consider that these species form a lower group, as in other
respects they are highly evolved, and rhizinae may be found at points on the lower
surface where there is irritation by friction. Soredia and isidia occur frequently and, in
several species, almost entirely replace reproduction by spores. In one or two northern
or Alpine species, P. stygia and P. pubescens, the lobes are linear or almost filamentous.
They are retained in Parmelia because the apothecia are superficial on the fronds which
are partly dorsiventral, and because rhizinae have occasionally been found. Some of the
Parmeliae attain to a considerable size; growth is centrifugal and long continued.
Two monotypic genera classified under Parmeliaceae, Physcidia and Heterodea, are
of considerable interest as they indicate the bases of parallel development in Parmelia
and Cetraria. The former, a small lichen, is corticate only on the upper surface, and
without rhizinae; and from the description, the cortex is of a fastigiate character. The
solitary species grows on bark in Cuba; it is related to Parmelia, as the apothecia are
superficial on the lobes. The second, Heterodea Mülleri, a soil-lichen from Australasia,
is more akin to Cetraria in that the apothecia are terminal. The upper surface is corticate
with marginal cilia, the lower surface naked or only protected by a weft of brownish
hyphae amongst which cyphellae are formed; pseudocyphellae appear in Cetraria.
The genus Cetraria contains very highly developed thalline forms, either horizontal
(subgenus Platysma), or upright (Eucetraria). Rhizinae are scanty or absent, but
marginal cilia in some upright species act as haptera. Cetraria aculeata is truly fruticose
with a radiate structure.
An extraordinary development of the under cortex characterizes the genera
Anzia[1011] and Pannoparmelia: rhizinae-like strands formed from the cortical cells
branch and anastomose with others till a wide mesh of a spongy nature is formed. They
are mostly tropical or subtropical or Australasian, and possibly the spongy mass may be
of service in retaining moisture. A species of Anzia has been recorded by
Darbishire[1012] from Tierra del Fuego.
of thallus have frequently been placed in a separate genus, Squamaria. These squamules
are never very large; they possess an upper, somewhat amorphous, cortex; the medulla
rests on the substratum, except in such a species as Lecanora lentigera, where they are
free, a sort of fibrous cortex being formed of hyphae which grow in a direction parallel
with the surface. In none of them are rhizinae developed.
cc. Parmeliaceae. The chief advance, apart from size, of the squamulose to the
foliose type is the acquirement of a lower cortex along with definite organs of
attachment which in Parmeliaceae are invariably rhizoidal and are composed of
compact strands of hyphae extending from the cells of the lower cortex.
In the genus Parmelia rhizinae are almost a constant character, though in a few
species, such as Parmelia physodes, they are scanty or practically absent. It is not
possible, however, to consider that these species form a lower group, as in other
respects they are highly evolved, and rhizinae may be found at points on the lower
surface where there is irritation by friction. Soredia and isidia occur frequently and, in
several species, almost entirely replace reproduction by spores. In one or two northern
or Alpine species, P. stygia and P. pubescens, the lobes are linear or almost filamentous.
They are retained in Parmelia because the apothecia are superficial on the fronds which
are partly dorsiventral, and because rhizinae have occasionally been found. Some of the
Parmeliae attain to a considerable size; growth is centrifugal and long continued.
Two monotypic genera classified under Parmeliaceae, Physcidia and Heterodea, are
of considerable interest as they indicate the bases of parallel development in Parmelia
and Cetraria. The former, a small lichen, is corticate only on the upper surface, and
without rhizinae; and from the description, the cortex is of a fastigiate character. The
solitary species grows on bark in Cuba; it is related to Parmelia, as the apothecia are
superficial on the lobes. The second, Heterodea Mülleri, a soil-lichen from Australasia,
is more akin to Cetraria in that the apothecia are terminal. The upper surface is corticate
with marginal cilia, the lower surface naked or only protected by a weft of brownish
hyphae amongst which cyphellae are formed; pseudocyphellae appear in Cetraria.
The genus Cetraria contains very highly developed thalline forms, either horizontal
(subgenus Platysma), or upright (Eucetraria). Rhizinae are scanty or absent, but
marginal cilia in some upright species act as haptera. Cetraria aculeata is truly fruticose
with a radiate structure.
An extraordinary development of the under cortex characterizes the genera
Anzia[1011] and Pannoparmelia: rhizinae-like strands formed from the cortical cells
branch and anastomose with others till a wide mesh of a spongy nature is formed. They
are mostly tropical or subtropical or Australasian, and possibly the spongy mass may be
of service in retaining moisture. A species of Anzia has been recorded by
Darbishire[1012] from Tierra del Fuego.
Page 368
dd. Usneaceae. As we have seen, the change to fruticose structure has arisen as an
ultimate development in a number of groups; it reaches however its highest and most
varied form in this family. Not only are there strap-shaped thalli, but a new form, the
filamentous and pendulous, appears; it attains to a great length, and is fitted to withstand
severe strain. The various adaptations of structure in these two types of thallus have
already been described[1013].
In Parmelia itself there are indications of this line of development in P. stygia, with
short stiff upright branching fronds, and in P. pubescens, with its tufts of filaments, but
these two species are more or less dorsiventral in structure and do not rise from the
substratum. In Cetraria also there is a tendency towards upright growth and in C.
aculeata even to radiate structure. But advance in these directions has stopped short, the
true line of evolution passing through species like Parmelia physodes with raised, and
in some varieties, tubular fronds, and the somewhat similar species P. Kamtschadalis
with straggling strap-like lobes, to Evernia. That genus is a true link between foliose
and fruticose forms and has been classified now with one series, now with the other.
In Evernia furfuracea, the lobes are free from the substratum except when friction
causes the development of a hold-fast and the branching out of new lobes from that
point. It is however dorsiventral in structure, the under surface is black and the gonidial
zone lies under the upper cortex. Evernia prunastri is white below and is more fruticose
in habit, the long fronds all rising from one base. They are thin and limp, no
strengthening tissue has been evolved, and they tend to lie over on one side; both
surfaces are corticate and gonidia sometimes travel round the edge, becoming
frequently lodged here and there along the under side.
The extreme of strap-shaped fruticose development is reached in the genus Ramalina.
In less advanced species such as R. evernioides there is a thin flat expansion anchored to
the substratum at one point and alike on both surfaces. In R. fraxinea the fronds may
reach considerable width (var. ampliata), but in that and in most species there is a
provision of sclerotic strands to support and strengthen the fronds. One of those best
fitted to resist bending strains is R. scopulorum (siliquosa) which grows by preference
on sea-cliffs and safely withstands the maximum of exposure to wind or weather.
The filamentous structure appears abruptly, unless we consider it as foreshadowed by
Parmelia pubescens. The base is secured by strong sheaths of enduring character;
tensile strains are provided for either by a chondroid axis, as in Usnea, or by cortical
development, as in Alectoria; the former method of securing strength seems to be the
most advantageous to the plant as a whole, since it leaves the outer structures more free
to develop, and there is therefore in Usnea a greater variety of branching and greater
growth in length, which are less possible with the thickened cortex of Alectoria.
ee. Physciaceae. There remains still an important phylum of Lecanorales well defined
by the polarilocular spores[1014]. It also arises from a Biatora species and forms a
parallel development. Even in this phylum there are two series: one with colourless
ultimate development in a number of groups; it reaches however its highest and most
varied form in this family. Not only are there strap-shaped thalli, but a new form, the
filamentous and pendulous, appears; it attains to a great length, and is fitted to withstand
severe strain. The various adaptations of structure in these two types of thallus have
already been described[1013].
In Parmelia itself there are indications of this line of development in P. stygia, with
short stiff upright branching fronds, and in P. pubescens, with its tufts of filaments, but
these two species are more or less dorsiventral in structure and do not rise from the
substratum. In Cetraria also there is a tendency towards upright growth and in C.
aculeata even to radiate structure. But advance in these directions has stopped short, the
true line of evolution passing through species like Parmelia physodes with raised, and
in some varieties, tubular fronds, and the somewhat similar species P. Kamtschadalis
with straggling strap-like lobes, to Evernia. That genus is a true link between foliose
and fruticose forms and has been classified now with one series, now with the other.
In Evernia furfuracea, the lobes are free from the substratum except when friction
causes the development of a hold-fast and the branching out of new lobes from that
point. It is however dorsiventral in structure, the under surface is black and the gonidial
zone lies under the upper cortex. Evernia prunastri is white below and is more fruticose
in habit, the long fronds all rising from one base. They are thin and limp, no
strengthening tissue has been evolved, and they tend to lie over on one side; both
surfaces are corticate and gonidia sometimes travel round the edge, becoming
frequently lodged here and there along the under side.
The extreme of strap-shaped fruticose development is reached in the genus Ramalina.
In less advanced species such as R. evernioides there is a thin flat expansion anchored to
the substratum at one point and alike on both surfaces. In R. fraxinea the fronds may
reach considerable width (var. ampliata), but in that and in most species there is a
provision of sclerotic strands to support and strengthen the fronds. One of those best
fitted to resist bending strains is R. scopulorum (siliquosa) which grows by preference
on sea-cliffs and safely withstands the maximum of exposure to wind or weather.
The filamentous structure appears abruptly, unless we consider it as foreshadowed by
Parmelia pubescens. The base is secured by strong sheaths of enduring character;
tensile strains are provided for either by a chondroid axis, as in Usnea, or by cortical
development, as in Alectoria; the former method of securing strength seems to be the
most advantageous to the plant as a whole, since it leaves the outer structures more free
to develop, and there is therefore in Usnea a greater variety of branching and greater
growth in length, which are less possible with the thickened cortex of Alectoria.
ee. Physciaceae. There remains still an important phylum of Lecanorales well defined
by the polarilocular spores[1014]. It also arises from a Biatora species and forms a
parallel development. Even in this phylum there are two series: one with colourless
Page 369
spores and mostly yellow or reddish either in thallus or apothecium, and the other with
brown spores and with cinereous-grey or brown thalli. The dark spores are in many of
the species typically polarilocular, though in some the median septum is not very wide
and no canal is visible. Practically all of the lighter coloured forms contain parietin
either in thallus or apothecia or in both; it is absent in the dark-spored series.
Among the lighter coloured forms it is difficult to decide which of these two striking
characteristics developed first, the acid or the peculiar spore. Probably the acid has the
priority: there is one common rock lichen in this country, Placodium rupestre (Lecanora
irrubata), which gives a strong red acid reaction with potash, but in which the spores
are still simple, and the fruit structure in the biatorine stage. Another species, Pl.
luteoalbum, with a purplish reaction in the fruit only, shows septate spores but with only
a rather narrow septum. The development continues through biatorine forms to
lecanorine with a fully formed thalline margin. Among these latter we encounter Pl.
nivale which is well provided with acid but in which the spores have become long and
fusiform with little trace of the polar cells or central canal. We must allow here also for
reversions, and wanderings from the straight road.
From crustaceous the advance is normal and simple to squamulose forms which in
this phylum maintain a stiff regularity of thalline outline termed “effigurate”; the
squamules, developing from the centre, extend outwards in a radiate-stellate manner.
There are also foliose thalli in the genus Xanthoria and fruticose in Teloschistes. The
cortex in the former horizontal genus is of plectenchyma, and no peculiar structures
have emerged. In Teloschistes the cortex is of compact parallel hyphae (fibrous) which
form the strengthening structure of the narrow compressed fronds (T. flavicans).
In the brown-spored series there is a considerable number of species that are
crustaceous united in the genus Rinodina, all of which have marginate apothecia. One
of them, Rinodina oreina, approaches in thalline structure the effigurate forms of
Placodium; while in R. isidioides, a rare British species, there is an isidioid squamulose
development.
Among foliose genera, the tropical genus Pyxine is peculiar in its almost lecideine
fruit, a few gonidia occurring only in the early stages; its affinity with Physcia holds,
however, through the one-septate brown spores with very thick walls and the reduced
lumen of the cells. The more simple type of fruit may be merely retrogressive.
Physcia, the remaining genus, is mainly foliose and with dorsiventral thallus. A few
species have straggling semi-upright fronds and these have sometimes been placed in a
separate genus Anaptychia. Only one “Anaptychia,” Ph. intricata, has a radiate structure
with fibrous cortex all round; in the others the upper cortex alone is fibrous—of long
parallel hyphae—but that character appears in nearly every one of the horizontal species
as well, sometimes in the upper, sometimes in the lower cortex.
In Physcia the horizontal thallus is of smaller dimensions than in Parmelia, and never
becomes so free from the substratum: it is attached by rhizinae and soredia appear
brown spores and with cinereous-grey or brown thalli. The dark spores are in many of
the species typically polarilocular, though in some the median septum is not very wide
and no canal is visible. Practically all of the lighter coloured forms contain parietin
either in thallus or apothecia or in both; it is absent in the dark-spored series.
Among the lighter coloured forms it is difficult to decide which of these two striking
characteristics developed first, the acid or the peculiar spore. Probably the acid has the
priority: there is one common rock lichen in this country, Placodium rupestre (Lecanora
irrubata), which gives a strong red acid reaction with potash, but in which the spores
are still simple, and the fruit structure in the biatorine stage. Another species, Pl.
luteoalbum, with a purplish reaction in the fruit only, shows septate spores but with only
a rather narrow septum. The development continues through biatorine forms to
lecanorine with a fully formed thalline margin. Among these latter we encounter Pl.
nivale which is well provided with acid but in which the spores have become long and
fusiform with little trace of the polar cells or central canal. We must allow here also for
reversions, and wanderings from the straight road.
From crustaceous the advance is normal and simple to squamulose forms which in
this phylum maintain a stiff regularity of thalline outline termed “effigurate”; the
squamules, developing from the centre, extend outwards in a radiate-stellate manner.
There are also foliose thalli in the genus Xanthoria and fruticose in Teloschistes. The
cortex in the former horizontal genus is of plectenchyma, and no peculiar structures
have emerged. In Teloschistes the cortex is of compact parallel hyphae (fibrous) which
form the strengthening structure of the narrow compressed fronds (T. flavicans).
In the brown-spored series there is a considerable number of species that are
crustaceous united in the genus Rinodina, all of which have marginate apothecia. One
of them, Rinodina oreina, approaches in thalline structure the effigurate forms of
Placodium; while in R. isidioides, a rare British species, there is an isidioid squamulose
development.
Among foliose genera, the tropical genus Pyxine is peculiar in its almost lecideine
fruit, a few gonidia occurring only in the early stages; its affinity with Physcia holds,
however, through the one-septate brown spores with very thick walls and the reduced
lumen of the cells. The more simple type of fruit may be merely retrogressive.
Physcia, the remaining genus, is mainly foliose and with dorsiventral thallus. A few
species have straggling semi-upright fronds and these have sometimes been placed in a
separate genus Anaptychia. Only one “Anaptychia,” Ph. intricata, has a radiate structure
with fibrous cortex all round; in the others the upper cortex alone is fibrous—of long
parallel hyphae—but that character appears in nearly every one of the horizontal species
as well, sometimes in the upper, sometimes in the lower cortex.
In Physcia the horizontal thallus is of smaller dimensions than in Parmelia, and never
becomes so free from the substratum: it is attached by rhizinae and soredia appear
Page 370
frequently. Very often the circular effigurate type of development prevails.
It is difficult to trace with any certainty the origin of this series of the phylum. Some
workers have associated it with the purely lecideine genus, Buellia, but the brown
septate spores of the latter are of simple structure, though occasionally approaching the
Rinodina type. There are also differences in the thallus, that of Buellia, especially when
it is saxicolous, inclining to Rhizocarpon in form. It is more consistent with the outer
and inner structure to derive Rinodina from some crustaceous Placodium form with a
marginate apothecium, therefore from a form of fairly advanced development. As the
parietin content disappeared—perhaps from the preponderance of other acids—the
colouration changed and the spores became dark-coloured.
Many genera and even families, such as Thelotremaceae, etc., have necessarily been
omitted from this survey of phylogeny in lichens, but the tracing of the main lines of
development has indicated the course of evolution, and has demonstrated not only the
close affinity between the members of this polyphyletic class of plants, as shown in the
constantly recurring thalline types, but it has proved the extraordinary vigour gained by
both the component organisms through the symbiotic association.
The principal phyla[1015], developing on somewhat parallel lines, are given in the
appended table:
Archilichens
Phyla Crustose Squamulose Foliose Fruticose
Pyrenolichens Verrucariaceae Dermatocarpaceae
Coniocarpineae Caliciaceae Sphaerophoraceae Sphaerophoraceae
Arthoniaceae
Graphidineae Graphidaceae Roccellaceae
Dirinaceae
Cyclocarpineae Gyrophoraceae
Lecideaceae
Coenogoniaceae (filamentous
Lecideales gonidia)
Cladoniaceae (primary and
secondary thalli)
Lecanorales Lecanoraceae Parmeliaceae Usneaceae
Polariloculares
Colourless spores Placodium Xanthoria Teloschistes
Brown spores Rinodina, Pyxine Physcia Physcia (Anaptychia)
It is difficult to trace with any certainty the origin of this series of the phylum. Some
workers have associated it with the purely lecideine genus, Buellia, but the brown
septate spores of the latter are of simple structure, though occasionally approaching the
Rinodina type. There are also differences in the thallus, that of Buellia, especially when
it is saxicolous, inclining to Rhizocarpon in form. It is more consistent with the outer
and inner structure to derive Rinodina from some crustaceous Placodium form with a
marginate apothecium, therefore from a form of fairly advanced development. As the
parietin content disappeared—perhaps from the preponderance of other acids—the
colouration changed and the spores became dark-coloured.
Many genera and even families, such as Thelotremaceae, etc., have necessarily been
omitted from this survey of phylogeny in lichens, but the tracing of the main lines of
development has indicated the course of evolution, and has demonstrated not only the
close affinity between the members of this polyphyletic class of plants, as shown in the
constantly recurring thalline types, but it has proved the extraordinary vigour gained by
both the component organisms through the symbiotic association.
The principal phyla[1015], developing on somewhat parallel lines, are given in the
appended table:
Archilichens
Phyla Crustose Squamulose Foliose Fruticose
Pyrenolichens Verrucariaceae Dermatocarpaceae
Coniocarpineae Caliciaceae Sphaerophoraceae Sphaerophoraceae
Arthoniaceae
Graphidineae Graphidaceae Roccellaceae
Dirinaceae
Cyclocarpineae Gyrophoraceae
Lecideaceae
Coenogoniaceae (filamentous
Lecideales gonidia)
Cladoniaceae (primary and
secondary thalli)
Lecanorales Lecanoraceae Parmeliaceae Usneaceae
Polariloculares
Colourless spores Placodium Xanthoria Teloschistes
Brown spores Rinodina, Pyxine Physcia Physcia (Anaptychia)
Page 371
SCHEME OF SUGGESTED PROGRESSION IN LICHEN STRUCTURE
Page 372
Page 373
CHAPTER VIII
SYSTEMATIC
I. CLASSIFICATION
A. Work of successive Systematists
Since the time when lichens were first recognized as a separate class—as
members of the genus Lichen by Tournefort[1016] or as “Musco-fungi” by
Morison[1017],—many schemes of classification have been outlined, and the
history of the science of lichenology, as we have seen, is a record of
attempts to understand their puzzling structure, and to express that
understanding by relating them to each other and to allied classes of plants.
The great diversity of opinion in regard to their affinities is directly due to
their composite nature.
a. Dillenius and Linnaeus. The first systematists were chiefly impressed
by their likeness to mosses, hepatics or algae. Dillenius[1018] in the Historia
Muscorum grouped them under the moss genera:—iv. Usnea, v.
Coralloides and vi. Lichenoides. Linnaeus[1019] classified them among algae
under the general name Lichen, dividing them into eight orders based on
thalline characters in all but one instance, the second order being
distinguished from the first by bearing scutellae. The British botanists of the
latter part of the eighteenth century—Hudson, Lightfoot and others—were
content to follow Linnaeus and in general adopted his arrangement.
b. Acharius. Early in the nineteenth century Acharius, the Swedish
Lichenologist, worked a revolution in the classification of lichens. He gave
first place to the form of the thallus, but he also noted the fundamental
differences in fruit-formation: his new system appeared in the Methodus
Lichenum[1020] with an introduction explaining the terms he had introduced,
many of them in use to this day.
SYSTEMATIC
I. CLASSIFICATION
A. Work of successive Systematists
Since the time when lichens were first recognized as a separate class—as
members of the genus Lichen by Tournefort[1016] or as “Musco-fungi” by
Morison[1017],—many schemes of classification have been outlined, and the
history of the science of lichenology, as we have seen, is a record of
attempts to understand their puzzling structure, and to express that
understanding by relating them to each other and to allied classes of plants.
The great diversity of opinion in regard to their affinities is directly due to
their composite nature.
a. Dillenius and Linnaeus. The first systematists were chiefly impressed
by their likeness to mosses, hepatics or algae. Dillenius[1018] in the Historia
Muscorum grouped them under the moss genera:—iv. Usnea, v.
Coralloides and vi. Lichenoides. Linnaeus[1019] classified them among algae
under the general name Lichen, dividing them into eight orders based on
thalline characters in all but one instance, the second order being
distinguished from the first by bearing scutellae. The British botanists of the
latter part of the eighteenth century—Hudson, Lightfoot and others—were
content to follow Linnaeus and in general adopted his arrangement.
b. Acharius. Early in the nineteenth century Acharius, the Swedish
Lichenologist, worked a revolution in the classification of lichens. He gave
first place to the form of the thallus, but he also noted the fundamental
differences in fruit-formation: his new system appeared in the Methodus
Lichenum[1020] with an introduction explaining the terms he had introduced,
many of them in use to this day.
Page 374
Diagnoses of twenty-three genera are given with their included species.
The work was further extended and emended in Lichenographia
Universalis[1021] and in the Synopsis Lichenum[1022]. In his final
arrangement the family “Lichenes” is divided into four classes, three of
which are characterized solely by apothecial characters; the fourth class has
no apothecia. They are as follows:
Class I. Idiothalami with three orders, Homogenei, Heterogenei and
Hyperogenei: the apothecia differ in texture and colouration from
the thallus: Lecidea, Opegrapha, Gyrophora, etc.
Class II. Coenothalami, with three orders, Phymaloidei, Discoidei and
Cephaloidei. The apothecia are partly formed from the thallus:
Lecanora, Parmelia, etc. The Pyrenolichens are also included by
him in this class, because “the thallus surrounds and is concrete
with the partly or wholly immersed apothecia.”
Class III. Homothalami with two orders, Scutellati and Peltati. The
apothecia are formed from the cortical and medullary tissue of the
thallus: Ramalina, Usnea, Collema, etc.
Class IV. Athalami, with but one sterile genus, Lepraria.
The orders are thus based on the form of the fruit; the genera in the
Synopsis number 41. Large genera such as Lecanora with 132 species are
divided into sections, many of which have in turn been established as
genera, by S. F. Gray in 1821, and later by other systematists.
The Synopsis was the text-book adopted by succeeding botanists for
some 40 years with slight alterations in the arrangement of classes, genera,
etc.
Wallroth[1023] and Meyer[1024] followed with their studies on the lichen
thallus, and Wallroth’s division into “Homoiomerous” and “Heteromerous”
was accepted as a useful guide in the maze of forms, representing as it did a
great natural distinction.
c. Schaerer. This valiant lichenologist worked continuously during the
first half of the nineteenth century, but with very partial use of the
microscope. His last publication in 1850, an Enumeration of Swiss Lichens,
The work was further extended and emended in Lichenographia
Universalis[1021] and in the Synopsis Lichenum[1022]. In his final
arrangement the family “Lichenes” is divided into four classes, three of
which are characterized solely by apothecial characters; the fourth class has
no apothecia. They are as follows:
Class I. Idiothalami with three orders, Homogenei, Heterogenei and
Hyperogenei: the apothecia differ in texture and colouration from
the thallus: Lecidea, Opegrapha, Gyrophora, etc.
Class II. Coenothalami, with three orders, Phymaloidei, Discoidei and
Cephaloidei. The apothecia are partly formed from the thallus:
Lecanora, Parmelia, etc. The Pyrenolichens are also included by
him in this class, because “the thallus surrounds and is concrete
with the partly or wholly immersed apothecia.”
Class III. Homothalami with two orders, Scutellati and Peltati. The
apothecia are formed from the cortical and medullary tissue of the
thallus: Ramalina, Usnea, Collema, etc.
Class IV. Athalami, with but one sterile genus, Lepraria.
The orders are thus based on the form of the fruit; the genera in the
Synopsis number 41. Large genera such as Lecanora with 132 species are
divided into sections, many of which have in turn been established as
genera, by S. F. Gray in 1821, and later by other systematists.
The Synopsis was the text-book adopted by succeeding botanists for
some 40 years with slight alterations in the arrangement of classes, genera,
etc.
Wallroth[1023] and Meyer[1024] followed with their studies on the lichen
thallus, and Wallroth’s division into “Homoiomerous” and “Heteromerous”
was accepted as a useful guide in the maze of forms, representing as it did a
great natural distinction.
c. Schaerer. This valiant lichenologist worked continuously during the
first half of the nineteenth century, but with very partial use of the
microscope. His last publication in 1850, an Enumeration of Swiss Lichens,
Page 375
was the final declaration of the older school that relied on field characters.
His classification is as follows:
Class I. Lichenes Discoidei, with ten orders from Usneacei to
Graphidei; fruits open.
Class II. Lichenes Capitati, with three orders: Calicioidei,
Sphaerophorei and Cladoniacei; fruits stalked.
Class III. Lichenes Verrucarioidei, with three orders: Verrucarii,
Pertusarii and Endocarpei: fruits closed.
An “Appendix” contains descriptions of Crustacei and Fruticulosi, all
sterile forms, except Coniocarpon and Arthonia, which seem out of place,
and finally a “Corollarium” of gelatinous lichens all classified under one
genus Collema.
d. Massalongo and Koerber. As a result of their microscopic studies,
these two workers proposed many changes based on fruit and spore
characters, and Koerber in the Systema Lichenum Germaniae (1855) gave
expression to these views in his classification. He also made use of
Wallroth’s distinctions of “homoiomerous” and “heteromerous,” thus
dividing lichens at the outset into those mostly with blue-green and those
with bright-green gonidia.
The following is the main outline of Koerber’s classification:
Series I. Lichenes Heteromerici.
Order I. Lich. Thamnoblasti (fruticose).
Order II. Lich. Phylloblasti (foliose).
Order III. Lich. Kryoblasti (crustaceous).
Series II. Lichenes Homoeomerici.
Order IV. Lich. Gelatinosi.
Order V. Lich. Byssacei.
With the exception of Order V all are subdivided into two sections,
“gymnocarpi” with open fruits and “angiocarpi” with closed fruits, a
His classification is as follows:
Class I. Lichenes Discoidei, with ten orders from Usneacei to
Graphidei; fruits open.
Class II. Lichenes Capitati, with three orders: Calicioidei,
Sphaerophorei and Cladoniacei; fruits stalked.
Class III. Lichenes Verrucarioidei, with three orders: Verrucarii,
Pertusarii and Endocarpei: fruits closed.
An “Appendix” contains descriptions of Crustacei and Fruticulosi, all
sterile forms, except Coniocarpon and Arthonia, which seem out of place,
and finally a “Corollarium” of gelatinous lichens all classified under one
genus Collema.
d. Massalongo and Koerber. As a result of their microscopic studies,
these two workers proposed many changes based on fruit and spore
characters, and Koerber in the Systema Lichenum Germaniae (1855) gave
expression to these views in his classification. He also made use of
Wallroth’s distinctions of “homoiomerous” and “heteromerous,” thus
dividing lichens at the outset into those mostly with blue-green and those
with bright-green gonidia.
The following is the main outline of Koerber’s classification:
Series I. Lichenes Heteromerici.
Order I. Lich. Thamnoblasti (fruticose).
Order II. Lich. Phylloblasti (foliose).
Order III. Lich. Kryoblasti (crustaceous).
Series II. Lichenes Homoeomerici.
Order IV. Lich. Gelatinosi.
Order V. Lich. Byssacei.
With the exception of Order V all are subdivided into two sections,
“gymnocarpi” with open fruits and “angiocarpi” with closed fruits, a
Page 376
distinction that had long been recognized both in lichens and in fungi.
e. Nylander. The above writers had been concerned with the
interrelationships of lichens; Nylander, who was now coming forward as a
lichenologist of note, gave a new turn to the study by dwelling on their
relation to other classes of plants. Without for a moment conceding that
they were either algal or fungal, he yet insisted on their remarkable affinity
to algae on the one hand, and to fungi on the other, and he sought to make
evident this double connection by his very ingenious scheme of
classification[1025]. He began with what we may call “algal lichens,” those
associated with blue-green gonidia in the family “Collemacei”; he
continued the series to the most highly evolved foliose forms and then
wound up with those that are most akin to fungi, that is, those with least
apparent thalline formation—according to him—the “Pyrenocarpei.”
In his scheme, which is the one followed by Leighton and Crombie, the
“family” represents the highest division; series, tribe, genus and species
come next in order. We have thus:
Fam. I. Collemacei.
Fam. II. Myriangiacei (now reckoned among fungi).
Fam. III. Lichenacei.
This last family, which includes the great bulk of lichens, is divided into
the following series: I. Epiconiodei; II. Cladoniodei; III. Ramalodei; IV.
Phyllodei; V. Placodei; VI. Pyrenodei. It is an ascending series up to the
Phyllodei, or foliaceous lichens, which he considers higher in development
than the fruticose or filamentous Ramalodei. The Placodei include four
tribes on a descending scale, the Lecanorei, Lecidinei, Xylographidei and
Graphidei. The classification is almost wholly based on thalline form,
except for the Pyrenodei in which are represented genera with closed fruits,
there being one tribe only, the Pyrenocarpei.
Nylander claims however to have had regard equally to the reproductive
system and was the first to give importance to the spermogonia. The
classification is coherent and easy to follow, though, like all classifications
based on imperfect knowledge, it is not a little artificial; also while
e. Nylander. The above writers had been concerned with the
interrelationships of lichens; Nylander, who was now coming forward as a
lichenologist of note, gave a new turn to the study by dwelling on their
relation to other classes of plants. Without for a moment conceding that
they were either algal or fungal, he yet insisted on their remarkable affinity
to algae on the one hand, and to fungi on the other, and he sought to make
evident this double connection by his very ingenious scheme of
classification[1025]. He began with what we may call “algal lichens,” those
associated with blue-green gonidia in the family “Collemacei”; he
continued the series to the most highly evolved foliose forms and then
wound up with those that are most akin to fungi, that is, those with least
apparent thalline formation—according to him—the “Pyrenocarpei.”
In his scheme, which is the one followed by Leighton and Crombie, the
“family” represents the highest division; series, tribe, genus and species
come next in order. We have thus:
Fam. I. Collemacei.
Fam. II. Myriangiacei (now reckoned among fungi).
Fam. III. Lichenacei.
This last family, which includes the great bulk of lichens, is divided into
the following series: I. Epiconiodei; II. Cladoniodei; III. Ramalodei; IV.
Phyllodei; V. Placodei; VI. Pyrenodei. It is an ascending series up to the
Phyllodei, or foliaceous lichens, which he considers higher in development
than the fruticose or filamentous Ramalodei. The Placodei include four
tribes on a descending scale, the Lecanorei, Lecidinei, Xylographidei and
Graphidei. The classification is almost wholly based on thalline form,
except for the Pyrenodei in which are represented genera with closed fruits,
there being one tribe only, the Pyrenocarpei.
Nylander claims however to have had regard equally to the reproductive
system and was the first to give importance to the spermogonia. The
classification is coherent and easy to follow, though, like all classifications
based on imperfect knowledge, it is not a little artificial; also while
Page 377
magnifying the significance of spermogonia and spermatia, he overlooked
the much more important characters of the ascospores.
f. Müller(-Argau). In preparing his lists of Genevan lichens (1862),
Müller realized that Nylander’s series was unnatural, and he found as he
studied more deeply that lichens must be ranged in parallel or convergent
but detached groups. He recognized three main groups:
1. Eulichens, divided into Capitularieae, Discocarpeae and
Verrucaroideae.
2. Epiconiaceae.
3. Collemaceae.
He suggested that, in relation to other plants, Eulichens approach
Pezizae, Hysteriaceae and Sphaeriaceae; Epiconiaceae have affinity with
Lycoperdaceae, while Collemaceae are allied to the algal family
Nostocaceae. These three groups of Eulichens, he held, advanced on
somewhat parallel lines, but reached a very varied development, the
Discocarpeae attaining the highest stage of thalline form. Müller accepted
as characters of generic importance the form and structure of the fruiting
body, the presence or absence of paraphyses, and the septation, colour, etc.
of the spores.
A few years later (1867) the composite nature of the lichen thallus was
announced by Schwendener, and, after some time, was acknowledged by
most botanists to be in accordance with the facts of nature. Any system of
classification, therefore, that claims to be a natural one, must, while
following as far as possible the line of plant development, take into account
the double origin of lichens both from algae and fungi, the essential unity
and coherence of the class being however proved by the recurring similarity
between the thalline types of the different phyla. As Müller had surmised:
“they are a series of parallel detached though convergent groups.”
g. Reinke. The arrangement of Ascolichens on these lines was first
seriously studied by Reinke[1026], and his conclusions, which are
embodied[1027] in the Lichens of Schleswig-Holstein, have been largely
accepted by succeeding workers. He recognizes three great subclasses: 1.
Coniocarpi; 2. Discocarpi; 3. Pyrenocarpi.
the much more important characters of the ascospores.
f. Müller(-Argau). In preparing his lists of Genevan lichens (1862),
Müller realized that Nylander’s series was unnatural, and he found as he
studied more deeply that lichens must be ranged in parallel or convergent
but detached groups. He recognized three main groups:
1. Eulichens, divided into Capitularieae, Discocarpeae and
Verrucaroideae.
2. Epiconiaceae.
3. Collemaceae.
He suggested that, in relation to other plants, Eulichens approach
Pezizae, Hysteriaceae and Sphaeriaceae; Epiconiaceae have affinity with
Lycoperdaceae, while Collemaceae are allied to the algal family
Nostocaceae. These three groups of Eulichens, he held, advanced on
somewhat parallel lines, but reached a very varied development, the
Discocarpeae attaining the highest stage of thalline form. Müller accepted
as characters of generic importance the form and structure of the fruiting
body, the presence or absence of paraphyses, and the septation, colour, etc.
of the spores.
A few years later (1867) the composite nature of the lichen thallus was
announced by Schwendener, and, after some time, was acknowledged by
most botanists to be in accordance with the facts of nature. Any system of
classification, therefore, that claims to be a natural one, must, while
following as far as possible the line of plant development, take into account
the double origin of lichens both from algae and fungi, the essential unity
and coherence of the class being however proved by the recurring similarity
between the thalline types of the different phyla. As Müller had surmised:
“they are a series of parallel detached though convergent groups.”
g. Reinke. The arrangement of Ascolichens on these lines was first
seriously studied by Reinke[1026], and his conclusions, which are
embodied[1027] in the Lichens of Schleswig-Holstein, have been largely
accepted by succeeding workers. He recognizes three great subclasses: 1.
Coniocarpi; 2. Discocarpi; 3. Pyrenocarpi.
Page 378
The Coniocarpi are a group apart, but as their fruit is at first entirely
closed—at least in some of the genera—the more natural position for them
is between Discocarpi and Pyrenocarpi. It is in the arrangement of the
Discocarpi that variation occurs. Reinke’s arrangement of orders and
families in that sub-class is as follows:
Subclass 2. Discocarpi.
Order I. GRAMMOPHORI: Fam. Graphidacei and Xylographacei.
Order II. LECIDEALES: Fam. Gyalectacei, Lecideacei,
Umbilicariaceiand Cladoniacei.
Order III. PARMELIALES: Fam. Urceolariacei, Pertusariacei,
Parmeliacei,Physciacei, Teloschistacei and Acarosporacei.
Order IV. CYANOPHILI: Fam. Lichinacei, Ephebacei,
Pannariacei,Stictacei, Peltigeracei, Collemacei and
Omphalariacei.
The orders represent generally the principal phyla or groups, the families
subordinate parallel phyla within the orders. The first three orders are stages
of advance as regards fruit development; the Cyanophili are a group apart.
Wainio[1028] rendered great service to Phylogeny in his elaborate work on
Cladoniaceae, the most complicated of all the lichen phyla. He also drew up
a scheme of arrangement in his work on Brazil Lichens[1029]. There is in it
some divergence from Reinke’s arrangement, as he tends to give more
importance to the thallus than to fruit characters as a guide. He places, for
instance, Gyrophorei beside Parmelei and at a long distance from his
Lecidei. The Cyanophili group of families he has interpolated between
Buelliae (Physciaceae) and Lecideae. Many workers approve of Wainio’s
classification but it presents some difficult problems.
h. Zahlbruckner. The systematist of greatest weight in recent times is A.
Zahlbruckner, who is responsible for the systematic account of lichens in
Engler and Prantl’s Natürlichen Pflanzenfamilien. It is difficult to express
the very great service he has rendered to Lichenology, in that and other
world-wide studies of lichens. The sketch of lichen phylogeny as given in
the present volume owes a great deal to the sound and clear guidance of his
closed—at least in some of the genera—the more natural position for them
is between Discocarpi and Pyrenocarpi. It is in the arrangement of the
Discocarpi that variation occurs. Reinke’s arrangement of orders and
families in that sub-class is as follows:
Subclass 2. Discocarpi.
Order I. GRAMMOPHORI: Fam. Graphidacei and Xylographacei.
Order II. LECIDEALES: Fam. Gyalectacei, Lecideacei,
Umbilicariaceiand Cladoniacei.
Order III. PARMELIALES: Fam. Urceolariacei, Pertusariacei,
Parmeliacei,Physciacei, Teloschistacei and Acarosporacei.
Order IV. CYANOPHILI: Fam. Lichinacei, Ephebacei,
Pannariacei,Stictacei, Peltigeracei, Collemacei and
Omphalariacei.
The orders represent generally the principal phyla or groups, the families
subordinate parallel phyla within the orders. The first three orders are stages
of advance as regards fruit development; the Cyanophili are a group apart.
Wainio[1028] rendered great service to Phylogeny in his elaborate work on
Cladoniaceae, the most complicated of all the lichen phyla. He also drew up
a scheme of arrangement in his work on Brazil Lichens[1029]. There is in it
some divergence from Reinke’s arrangement, as he tends to give more
importance to the thallus than to fruit characters as a guide. He places, for
instance, Gyrophorei beside Parmelei and at a long distance from his
Lecidei. The Cyanophili group of families he has interpolated between
Buelliae (Physciaceae) and Lecideae. Many workers approve of Wainio’s
classification but it presents some difficult problems.
h. Zahlbruckner. The systematist of greatest weight in recent times is A.
Zahlbruckner, who is responsible for the systematic account of lichens in
Engler and Prantl’s Natürlichen Pflanzenfamilien. It is difficult to express
the very great service he has rendered to Lichenology, in that and other
world-wide studies of lichens. The sketch of lichen phylogeny as given in
the present volume owes a great deal to the sound and clear guidance of his
Page 379
work, though his conclusions may not always have been accepted. The
classification in the Pflanzenfamilien is the one now generally followed.
The class Lichenes is divided by Zahlbruckner[1030] into two subclasses,
I. Ascolichens and II. Hymenolichens. He gives a third class,
Gasterolichens[1031], but as it was founded on error[1032], it need not concern
us here. The Ascolichens are by far the more important. These are
subdivided into:
Series 1. PYRENOCARPEAE, with perithecial fruits.
Series 2. GYMNOCARPEAE, with apothecial fruits.
These are again broken up into families, and in the arrangement and
sequence of the families Zahlbruckner indicates his view of development
and relationship. They occur in the following order:
Series 1. PYRENOCARPEAE
Algal cells Protococcaceae or Palmella.
I. MORIOLACEAE. }
Thallus crustaceous, perithecia
II. EPIGLOEACEAE. }
solitary.
III. VERRUCARIACEAE. }
IV. DERMATOCARPACEAE. Thallus squamulose or foliose.
V. PYRENOTHAMNIACEAE. Thallus fruticose.
Algal cells Prasiola.
VI. MASTOIDIACEAE.
Algal cells Trentepohlia.
VII. PYRENULACEAE. } Thallus crustaceous, perithecia
VIII. PARATHELIACEAE. } occurring singly.
IX. TRYPETHELIACEAE. } Thallus crustaceous, perithecia united
X. ASTROTHELIACEAE. } (stromatoid).
XI. MYCOPORACEAE. Thallus crustaceous, perithecia in
compact groups with a common
outer wall.
XII. PHYLLOPYRENIACEAE. Thallus minutely foliose.
Algal cells Phyllactidium or Mycoidea.
XIII. STRIGULACEAE. Tropical leaf-lichens.
classification in the Pflanzenfamilien is the one now generally followed.
The class Lichenes is divided by Zahlbruckner[1030] into two subclasses,
I. Ascolichens and II. Hymenolichens. He gives a third class,
Gasterolichens[1031], but as it was founded on error[1032], it need not concern
us here. The Ascolichens are by far the more important. These are
subdivided into:
Series 1. PYRENOCARPEAE, with perithecial fruits.
Series 2. GYMNOCARPEAE, with apothecial fruits.
These are again broken up into families, and in the arrangement and
sequence of the families Zahlbruckner indicates his view of development
and relationship. They occur in the following order:
Series 1. PYRENOCARPEAE
Algal cells Protococcaceae or Palmella.
I. MORIOLACEAE. }
Thallus crustaceous, perithecia
II. EPIGLOEACEAE. }
solitary.
III. VERRUCARIACEAE. }
IV. DERMATOCARPACEAE. Thallus squamulose or foliose.
V. PYRENOTHAMNIACEAE. Thallus fruticose.
Algal cells Prasiola.
VI. MASTOIDIACEAE.
Algal cells Trentepohlia.
VII. PYRENULACEAE. } Thallus crustaceous, perithecia
VIII. PARATHELIACEAE. } occurring singly.
IX. TRYPETHELIACEAE. } Thallus crustaceous, perithecia united
X. ASTROTHELIACEAE. } (stromatoid).
XI. MYCOPORACEAE. Thallus crustaceous, perithecia in
compact groups with a common
outer wall.
XII. PHYLLOPYRENIACEAE. Thallus minutely foliose.
Algal cells Phyllactidium or Mycoidea.
XIII. STRIGULACEAE. Tropical leaf-lichens.
Page 380
Algal cells Nostoc or Scytonema.
XIV. PYRENIDIACEAE. Thallus minutely squamulose or
fruticose.
Series 2. GYMNOCARPEAE
Subseries 1. Coniocarpineae, with subperithecial fruits.
Subseries 2. Graphidineae, with elongate, narrow fruits.
Subseries 3. Cyclocarpineae, with round open fruits.
Subseries 1. CONIOCARPINEAE
This is a well-defined group, peculiar in the disappearance of the asci at
an early stage so that the spores lie like a powder in the globose partly
closed fruits. Algal cells, bright-green; Protococcaceae. There are only three
families:
XV. CALICIACEAE. Thallus crustaceous, apothecia stalked.
XVI. CYPHELIACEAE. Thallus crustaceous, apothecia sessile.
XVII. SPHAEROPHORACEAE. Thallus foliose or fruticose, apothecia
sessile.
Subseries 2. GRAPHIDINEAE
This subseries comes next in the form of fruit development; generally the
apothecia are elongate, with a narrow slit-like opening, so that a transverse
section shows almost a perithecial outline. Algal cells are mostly
Trentepohlia.
XVIII. ARTHONIACEAE. Thallus crustaceous, apothecia oval or
linear, flat.
XIX. GRAPHIDACEAE. Thallus crustaceous, apothecia linear,
raised.
XX. CHIODECTONACEAE. Thallus crustaceous, apothecia generally
immersed in a stroma.
XIV. PYRENIDIACEAE. Thallus minutely squamulose or
fruticose.
Series 2. GYMNOCARPEAE
Subseries 1. Coniocarpineae, with subperithecial fruits.
Subseries 2. Graphidineae, with elongate, narrow fruits.
Subseries 3. Cyclocarpineae, with round open fruits.
Subseries 1. CONIOCARPINEAE
This is a well-defined group, peculiar in the disappearance of the asci at
an early stage so that the spores lie like a powder in the globose partly
closed fruits. Algal cells, bright-green; Protococcaceae. There are only three
families:
XV. CALICIACEAE. Thallus crustaceous, apothecia stalked.
XVI. CYPHELIACEAE. Thallus crustaceous, apothecia sessile.
XVII. SPHAEROPHORACEAE. Thallus foliose or fruticose, apothecia
sessile.
Subseries 2. GRAPHIDINEAE
This subseries comes next in the form of fruit development; generally the
apothecia are elongate, with a narrow slit-like opening, so that a transverse
section shows almost a perithecial outline. Algal cells are mostly
Trentepohlia.
XVIII. ARTHONIACEAE. Thallus crustaceous, apothecia oval or
linear, flat.
XIX. GRAPHIDACEAE. Thallus crustaceous, apothecia linear,
raised.
XX. CHIODECTONACEAE. Thallus crustaceous, apothecia generally
immersed in a stroma.
Page 381
XXI. DIRINACEAE. Thallus crustaceous, corticate above,
apothecia round.
XXII. ROCCELLACEAE. Thallus fruticose, apothecia round or
elongate.
Subseries 3. CYCLOCARPINEAE
A large and very varied group! In most of the families the algal cells are
bright-green (Chlorophyceae), in some they are blue-green
(Cyanophyceae), these latter corresponding to Reinke’s order Cyanophili.
The apothecia, as the name implies, are round and open; the “Cyanophili”
have been placed by Zahlbruckner after those families in which the
apothecium has no thalline margin. They form a phylum distinct from those
that precede and those that follow.
The first family of the Cyclocarpineae, the Lecanactidaceae, is often
placed under Graphidineae; in any case it forms a link between the two
subseries.
1. Lecideine group (apothecia without a thalline margin).
XXIII. LECANACTIDACEAE. Thallus crustaceous. Algal cells
Trentepohlia. Apothecium with
carbonaceous hypothecium or
parathecium.
XXIV. PILOCARPACEAE. Thallus crustaceous. Algal cells
Protococcaceae. Apothecia
with a dense rather dark
hypothecium.
XXV. CHRYSOTHRICACEAE. Thallus felted, loose in texture.
Algal cells Palmella,
Protococcaceae or
Trentepohlia. Apothecia with
or without a thalline margin.
The affinity of the “Family”
seems to be with
Pilocarpaceae.
apothecia round.
XXII. ROCCELLACEAE. Thallus fruticose, apothecia round or
elongate.
Subseries 3. CYCLOCARPINEAE
A large and very varied group! In most of the families the algal cells are
bright-green (Chlorophyceae), in some they are blue-green
(Cyanophyceae), these latter corresponding to Reinke’s order Cyanophili.
The apothecia, as the name implies, are round and open; the “Cyanophili”
have been placed by Zahlbruckner after those families in which the
apothecium has no thalline margin. They form a phylum distinct from those
that precede and those that follow.
The first family of the Cyclocarpineae, the Lecanactidaceae, is often
placed under Graphidineae; in any case it forms a link between the two
subseries.
1. Lecideine group (apothecia without a thalline margin).
XXIII. LECANACTIDACEAE. Thallus crustaceous. Algal cells
Trentepohlia. Apothecium with
carbonaceous hypothecium or
parathecium.
XXIV. PILOCARPACEAE. Thallus crustaceous. Algal cells
Protococcaceae. Apothecia
with a dense rather dark
hypothecium.
XXV. CHRYSOTHRICACEAE. Thallus felted, loose in texture.
Algal cells Palmella,
Protococcaceae or
Trentepohlia. Apothecia with
or without a thalline margin.
The affinity of the “Family”
seems to be with
Pilocarpaceae.
Page 382
XXVI. THELOTREMACEAE. } Thallus crustaceous. Algal cells in
the first Trentepohlia; in the
second Protococcaceae. In both
XXVII. DIPLOSCHISTACEAE. } there are prominent double
margins round the apothecium.
XXVIII. ECTOLECHIACEAE. Thallus very primitive in type. Algal
cells Protococcaceae.
Apothecia with or without a
thalline margin. Nearly related
to Chrysothricaceae.
XXIX. GYALECTACEAE. Thallus crustaceous. Algal cells
Trentepohlia, Phyllactidium or
rarely Scytonema. Apothecia
biatorine, i.e. of soft
consistency and without
gonidia.
XXX. COENOGONIACEAE. Thallus confusedly filamentous
(byssoid). Algal cells
Trentepohlia or Cladophora.
Apothecia biatorine.
XXXI. LECIDEACEAE. Thallus crustaceous or squamulose.
Algal cells Protococcaceae.
Apothecia biatorine (soft), or
lecideine (carbonaceous).
XXXII. PHYLLOPSORACEAE. Thallus squamulose or foliose.
Algal cells Protococcaceae.
Apothecia biatorine or
lecideine.
XXXIII. CLADONIACEAE. Thallus twofold. Algal cells
Protococcaceae. Apothecia
biatorine or lecideine.
XXXIV. GYROPHORACEAE. Thallus foliose. Algal cells
Protococcaceae. Apothecia
lecideine.
XXXV. ACAROSPORACEAE. Thallus primitive crustaceous,
squamulose or foliose. Algal
the first Trentepohlia; in the
second Protococcaceae. In both
XXVII. DIPLOSCHISTACEAE. } there are prominent double
margins round the apothecium.
XXVIII. ECTOLECHIACEAE. Thallus very primitive in type. Algal
cells Protococcaceae.
Apothecia with or without a
thalline margin. Nearly related
to Chrysothricaceae.
XXIX. GYALECTACEAE. Thallus crustaceous. Algal cells
Trentepohlia, Phyllactidium or
rarely Scytonema. Apothecia
biatorine, i.e. of soft
consistency and without
gonidia.
XXX. COENOGONIACEAE. Thallus confusedly filamentous
(byssoid). Algal cells
Trentepohlia or Cladophora.
Apothecia biatorine.
XXXI. LECIDEACEAE. Thallus crustaceous or squamulose.
Algal cells Protococcaceae.
Apothecia biatorine (soft), or
lecideine (carbonaceous).
XXXII. PHYLLOPSORACEAE. Thallus squamulose or foliose.
Algal cells Protococcaceae.
Apothecia biatorine or
lecideine.
XXXIII. CLADONIACEAE. Thallus twofold. Algal cells
Protococcaceae. Apothecia
biatorine or lecideine.
XXXIV. GYROPHORACEAE. Thallus foliose. Algal cells
Protococcaceae. Apothecia
lecideine.
XXXV. ACAROSPORACEAE. Thallus primitive crustaceous,
squamulose or foliose. Algal
Page 383
cells Protococcaceae.
Apothecia with or without a
thalline margin; very various,
but always with many-spored
asci.
2. Cyanophili group.
In this group the classification depends almost entirely on the nature of
the algal constituents. The apothecia are in most genera provided with a
thalline margin.
a. More or less gelatinous when moist.
XXXVI. EPHEBACEAE. Algal cells Scytonema or Stigonema.
Thallus minutely fruticose or
filamentous.
XXXVII. PYRENOPSIDACEAE. Algal cells Gloeocapsa (Gloeocapsa,
Xanthocapsa or Chroococcus).
Thallus crustaceous, minutely
foliose or fruticose.
XXXVIII. LICHINACEAE. Algal cells Rivularia. Thallus
crustaceous, squamulose or
minutely fruticose.
XXXIX. COLLEMACEAE. Algal cells Nostoc. Thallus
crustaceous, minutely fruticose,
or squamulose to foliose.
XL. HEPPIACEAE. Algal cells Scytonema. Thallus
generally squamulose and formed
of plectenchyma.
b. Not gelatinous when moist.
XLI. PANNARIACEAE. Algal cells Nostoc, Scytonema or rarely
bright-green, Protococcaceae. Thallus
crustaceous, squamulose or foliose.
XLII. STICTACEAE. Algal cells Nostoc or Protococcaceae. Thallus
foliose, and very highly developed,
Apothecia with or without a
thalline margin; very various,
but always with many-spored
asci.
2. Cyanophili group.
In this group the classification depends almost entirely on the nature of
the algal constituents. The apothecia are in most genera provided with a
thalline margin.
a. More or less gelatinous when moist.
XXXVI. EPHEBACEAE. Algal cells Scytonema or Stigonema.
Thallus minutely fruticose or
filamentous.
XXXVII. PYRENOPSIDACEAE. Algal cells Gloeocapsa (Gloeocapsa,
Xanthocapsa or Chroococcus).
Thallus crustaceous, minutely
foliose or fruticose.
XXXVIII. LICHINACEAE. Algal cells Rivularia. Thallus
crustaceous, squamulose or
minutely fruticose.
XXXIX. COLLEMACEAE. Algal cells Nostoc. Thallus
crustaceous, minutely fruticose,
or squamulose to foliose.
XL. HEPPIACEAE. Algal cells Scytonema. Thallus
generally squamulose and formed
of plectenchyma.
b. Not gelatinous when moist.
XLI. PANNARIACEAE. Algal cells Nostoc, Scytonema or rarely
bright-green, Protococcaceae. Thallus
crustaceous, squamulose or foliose.
XLII. STICTACEAE. Algal cells Nostoc or Protococcaceae. Thallus
foliose, and very highly developed,
Page 384
corticate on both surfaces.
XLIII. PELTIGERACEAE. Algal cells Nostoc or Protococcaceae. Thallus
foliose, corticate above.
3. Lecanorine group (apothecia with a thalline margin).
The remaining families have all bright-green gonidia and nearly always
apothecia with a thalline margin. The group includes several distinct phyla:
XLIV. PERTUSARIACEAE. Thallus crustaceous. Apothecia, one or
several immersed in thalline
tubercles; spores mostly very large.
XLV. LECANORACEAE. Thallus crustaceous or squamulose.
Apothecia mostly superficial.
XLVI. PARMELIACEAE. Thallus foliose, rarely almost fruticose or
filamentous. Apothecia scattered
over the surface or marginal, sessile.
XLVII. USNEACEAE. Thallus fruticose or filamentous.
Apothecia sessile or shortly stalked.
XLVIII. CALOPLACACEAE. Thallus crustaceous, squamulose or
minutely fruticose. Apothecia with
polarilocular colourless spores.
XLIX. TELOSCHISTACEAE. Thallus foliose or fruticose. Apothecia
with polarilocular colourless spores.
L. BUELLIACEAE. Thallus crustaceous or squamulose.
Apothecia (lecideine or lecanorine)
with two-celled, thick-walled brown
spores (polarilocular in part).
LI. PHYSCIACEAE. Thallus foliose, rarely partly fruticose.
Apothecia with two-celled thick-
walled brown spores (polarilocular
in part).
Subclass 2. Hymenolichens.
There are only three closely related genera of Hymenolichens, Cora,
Corella and Dictyonema with Chroococcus or Scytonema algae.
XLIII. PELTIGERACEAE. Algal cells Nostoc or Protococcaceae. Thallus
foliose, corticate above.
3. Lecanorine group (apothecia with a thalline margin).
The remaining families have all bright-green gonidia and nearly always
apothecia with a thalline margin. The group includes several distinct phyla:
XLIV. PERTUSARIACEAE. Thallus crustaceous. Apothecia, one or
several immersed in thalline
tubercles; spores mostly very large.
XLV. LECANORACEAE. Thallus crustaceous or squamulose.
Apothecia mostly superficial.
XLVI. PARMELIACEAE. Thallus foliose, rarely almost fruticose or
filamentous. Apothecia scattered
over the surface or marginal, sessile.
XLVII. USNEACEAE. Thallus fruticose or filamentous.
Apothecia sessile or shortly stalked.
XLVIII. CALOPLACACEAE. Thallus crustaceous, squamulose or
minutely fruticose. Apothecia with
polarilocular colourless spores.
XLIX. TELOSCHISTACEAE. Thallus foliose or fruticose. Apothecia
with polarilocular colourless spores.
L. BUELLIACEAE. Thallus crustaceous or squamulose.
Apothecia (lecideine or lecanorine)
with two-celled, thick-walled brown
spores (polarilocular in part).
LI. PHYSCIACEAE. Thallus foliose, rarely partly fruticose.
Apothecia with two-celled thick-
walled brown spores (polarilocular
in part).
Subclass 2. Hymenolichens.
There are only three closely related genera of Hymenolichens, Cora,
Corella and Dictyonema with Chroococcus or Scytonema algae.
Page 385
There is reason to dissent from the arrangement in one or two instances
which will be pointed out in the following examination of families and
genera.
B. Families and Genera of Ascolichens
The necessity for a well-reasoned and well-arranged system of
classification is self-evident: without a working knowledge of the plants
that are the subject of study no progress can be made. The recognition of
plants as isolated individuals is not sufficient, it must be possible to place
them in relation to others; hence the importance of a natural system. In
identifying species artificial aids, such as habitat and substratum, are also
often of great value, and a good working system should take account of all
characteristics.
Lichen development is the result of two organisms mutually affecting
each other, but as the fungus provides the reproductive system, it is the
dominant partner: the main lines of classification are necessarily determined
by fruit characters. The algae occupy a subsidiary position, but they also are
of importance in shaping the form and structure of the thallus. The different
phyla are often determined by the presence of some particular alga; it is in
the delimitation of families that the algal influence is of most effect.
Zahlbruckner’s system gives due weight to the inheritance from both
fungus and alga with, however, the fungus as the chief factor in
development, and as his work is certain to be generally followed by modern
lichenologists, it is the one of most immediate interest. His scheme has been
accepted in the following more detailed account of families and genera, and
for the benefit of home workers those that have not so far been recorded
from the British Isles have been marked with an asterisk.
It cannot be affirmed that nomenclature is as yet firmly established in
lichenology. Both on historical grounds and on those of convenience, the
subject is one of extreme importance, and interest in it is one of the main
avenues by which we secure continuity with the past, and by which we are
able to realize not only the difficulty, but the romance of pioneer work.
Besides, there can be no exchange of opinion between students nor assured
knowledge of plants, until the names given to them are beyond dispute.
which will be pointed out in the following examination of families and
genera.
B. Families and Genera of Ascolichens
The necessity for a well-reasoned and well-arranged system of
classification is self-evident: without a working knowledge of the plants
that are the subject of study no progress can be made. The recognition of
plants as isolated individuals is not sufficient, it must be possible to place
them in relation to others; hence the importance of a natural system. In
identifying species artificial aids, such as habitat and substratum, are also
often of great value, and a good working system should take account of all
characteristics.
Lichen development is the result of two organisms mutually affecting
each other, but as the fungus provides the reproductive system, it is the
dominant partner: the main lines of classification are necessarily determined
by fruit characters. The algae occupy a subsidiary position, but they also are
of importance in shaping the form and structure of the thallus. The different
phyla are often determined by the presence of some particular alga; it is in
the delimitation of families that the algal influence is of most effect.
Zahlbruckner’s system gives due weight to the inheritance from both
fungus and alga with, however, the fungus as the chief factor in
development, and as his work is certain to be generally followed by modern
lichenologists, it is the one of most immediate interest. His scheme has been
accepted in the following more detailed account of families and genera, and
for the benefit of home workers those that have not so far been recorded
from the British Isles have been marked with an asterisk.
It cannot be affirmed that nomenclature is as yet firmly established in
lichenology. Both on historical grounds and on those of convenience, the
subject is one of extreme importance, and interest in it is one of the main
avenues by which we secure continuity with the past, and by which we are
able to realize not only the difficulty, but the romance of pioneer work.
Besides, there can be no exchange of opinion between students nor assured
knowledge of plants, until the names given to them are beyond dispute.
Page 386
According to the ruling of the Brussels Botanical Congress in 1910,
Linnaeus’s[1033] list of lichens in the Species Plantarum has been selected as
the basis of nomenclature, but since his day many new families, genera and
species have been described and often insufficiently delimited. It is not easy
to decide between priority, which appeals to the historical sense, and recent
use which is the plea of convenience. Here also it seems there can be no
rigid decision; the one aim should be to arrive at a conclusion satisfactory to
all, and accepted by all.
In the following necessarily brief account of families and genera, the
“spermogonia” or “pycnidia” have in most cases been left out of account, as
in many instances they vary within the family and occasionally even within
the genus. Their taxonomic value is not without importance, but, in the
general systematic arrangement, they are only subsidiary characters. An
account of them has already been given, and for more detailed statements
the student is referred to purely systematic works.
There are two main types of spore production in the “pycnidia” which
have been shortly described by Steiner[1034] as “exobasidial” and
“endobasidial.” In the former the sporophores are simple or branched
filaments, at the apices of which a short process grows out and buds off a
pycnidiospore; in the latter the spores are budded directly from cells lining
the walls or filling the cavity of the pycnidium. The exobasidial type is
more simply rendered in the following pages by “acrogenous,” the
endobasidial by “pleurogenous” spore production. In many cases the
“spermogonia” or “pycnidia” are still imperfectly known. In designating the
gonidial algae, the more comprehensive Protococcaceae has been
substituted for Protococcus, as in many cases the alga is probably not
Protococcus as now understood, but some other genus of the family[1035].
Subclass I. ASCOLICHENS
Series I. PYRENOCARPINEAE
It is on mycological grounds that Pyrenocarpineae are placed at the base
of lichen classification. There is no evidence that the series was first in
time.
I. Moriolaceae
Linnaeus’s[1033] list of lichens in the Species Plantarum has been selected as
the basis of nomenclature, but since his day many new families, genera and
species have been described and often insufficiently delimited. It is not easy
to decide between priority, which appeals to the historical sense, and recent
use which is the plea of convenience. Here also it seems there can be no
rigid decision; the one aim should be to arrive at a conclusion satisfactory to
all, and accepted by all.
In the following necessarily brief account of families and genera, the
“spermogonia” or “pycnidia” have in most cases been left out of account, as
in many instances they vary within the family and occasionally even within
the genus. Their taxonomic value is not without importance, but, in the
general systematic arrangement, they are only subsidiary characters. An
account of them has already been given, and for more detailed statements
the student is referred to purely systematic works.
There are two main types of spore production in the “pycnidia” which
have been shortly described by Steiner[1034] as “exobasidial” and
“endobasidial.” In the former the sporophores are simple or branched
filaments, at the apices of which a short process grows out and buds off a
pycnidiospore; in the latter the spores are budded directly from cells lining
the walls or filling the cavity of the pycnidium. The exobasidial type is
more simply rendered in the following pages by “acrogenous,” the
endobasidial by “pleurogenous” spore production. In many cases the
“spermogonia” or “pycnidia” are still imperfectly known. In designating the
gonidial algae, the more comprehensive Protococcaceae has been
substituted for Protococcus, as in many cases the alga is probably not
Protococcus as now understood, but some other genus of the family[1035].
Subclass I. ASCOLICHENS
Series I. PYRENOCARPINEAE
It is on mycological grounds that Pyrenocarpineae are placed at the base
of lichen classification. There is no evidence that the series was first in
time.
I. Moriolaceae
Page 387
This family was described by Norman[1036] in 1872 from specimens
collected by himself in Norway or in the Tyrol, on soil or more frequently
on trees. There seems to have been no further record, and Zahlbruckner,
while accepting the family, suggests that an examination or revision may be
necessary.
The thallus is crustaceous. The algal cells, Protococcaceae, occur either
in groups (sometimes stalked) surrounded by a plectenchymatous wall and
called by Norman “goniocysts,” or they form nests in the thallus termed
“nuclei” which are surrounded by a double wall of plectenchyma,
colourless in the interior and brown outside. Norman invented the term
“Allelositismus,” which may be rendered “mutualism,” to indicate this
peculiar form of thallus. The species of Spheconisca are fairly numerous on
poplars, willows and conifers:
Algae in “goniocysts” 1. *Moriola Norm.[1037]
Algae in double-walled “nuclei” 2. *Spheconisca Norm.
II. Epigloeaceae
The family consists of but one genus and one species, Epigloea
bactrospora, and, according to Zahlbruckner, further examination is
necessary to make certain as to the lichenoid nature of the plant.
Zukal[1038] found the perithecia scattered over the leaves of mosses, and
he alleges that hyphae connected with the perithecium were closely
associated with the alga, Palmella botryoides, and were causing it no harm.
Along with the perithecia he also found minute pycnidia. The “thallus” is of
a gelatinous nature and homoiomerous in structure; the perithecia are soft
and clear-coloured with many-spored asci and colourless one-septate
spores.
The small globose pycnidia contain simple sporophores and acrogenous
straight or slightly bent rod-like spores.
Asci many-spored; spores one-septate 1. *Epigloea Zukal.
III. Verrucariaceae
collected by himself in Norway or in the Tyrol, on soil or more frequently
on trees. There seems to have been no further record, and Zahlbruckner,
while accepting the family, suggests that an examination or revision may be
necessary.
The thallus is crustaceous. The algal cells, Protococcaceae, occur either
in groups (sometimes stalked) surrounded by a plectenchymatous wall and
called by Norman “goniocysts,” or they form nests in the thallus termed
“nuclei” which are surrounded by a double wall of plectenchyma,
colourless in the interior and brown outside. Norman invented the term
“Allelositismus,” which may be rendered “mutualism,” to indicate this
peculiar form of thallus. The species of Spheconisca are fairly numerous on
poplars, willows and conifers:
Algae in “goniocysts” 1. *Moriola Norm.[1037]
Algae in double-walled “nuclei” 2. *Spheconisca Norm.
II. Epigloeaceae
The family consists of but one genus and one species, Epigloea
bactrospora, and, according to Zahlbruckner, further examination is
necessary to make certain as to the lichenoid nature of the plant.
Zukal[1038] found the perithecia scattered over the leaves of mosses, and
he alleges that hyphae connected with the perithecium were closely
associated with the alga, Palmella botryoides, and were causing it no harm.
Along with the perithecia he also found minute pycnidia. The “thallus” is of
a gelatinous nature and homoiomerous in structure; the perithecia are soft
and clear-coloured with many-spored asci and colourless one-septate
spores.
The small globose pycnidia contain simple sporophores and acrogenous
straight or slightly bent rod-like spores.
Asci many-spored; spores one-septate 1. *Epigloea Zukal.
III. Verrucariaceae
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In all the genera of this family the thallus is crustaceous, and, with very
few exceptions, the species are saxicolous or terricolous. The thallus is
variable within the crustaceous limits, and may be superficial and very
conspicuous, almost imperceptible, or wholly immersed in the substratum.
The algal cells are Protococcaceae, and in two of the genera the green cells
penetrate the hymenium and grow in rows alongside of the asci. The
perithecia are small roundish structures scattered over the thallus, the base
immersed, but the upper portion generally projecting. An outer dark-
coloured wall surrounds the whole perithecium (entire) or only the upper
exposed portion (dimidiate); it opens above by a pore or ostiole more or less
prominent.
In some of the genera the paraphyses become dissolved at an early stage,
and somewhat similar filaments near the ostiole, termed periphyses, aid in
the expulsion of the spores. The spores vary in septation, colour and size,
and these variations have served to delimit the genera which have been
formed from the original very large genus Verrucaria. The ascus may be 1-,
2-, 4- or 8-spored. In only one genus is it many-spored (Trimmatothele).
The genera are as follows:
Perithecia with simple ostioles.
Paraphyses disappearing early, or wanting.
Spores simple, ellipsoid 1. Verrucaria Web.
Spores simple, elongate vermiform 2. Sarcopyrenia Nyl.
Spores simple, numerous in the ascus 3. *Trimmatothele
Norm.
Spores 1-3-septate 4. Thelidium Massal.
Spores muriform (with transverse and
longitudinal divisions).
Without hymenial gonidia 5. Polyblastia Massal.
With hymenial gonidia 6. Staurothele Norm.
Paraphyses present.
Spores simple.
Without hymenial gonidia 7. Thrombium Wallr.
With hymenial gonidia 8. *Thelenidia Nyl.
Spores 3-septate, broadly ellipsoid 9. *Geisleria Nitschke.
few exceptions, the species are saxicolous or terricolous. The thallus is
variable within the crustaceous limits, and may be superficial and very
conspicuous, almost imperceptible, or wholly immersed in the substratum.
The algal cells are Protococcaceae, and in two of the genera the green cells
penetrate the hymenium and grow in rows alongside of the asci. The
perithecia are small roundish structures scattered over the thallus, the base
immersed, but the upper portion generally projecting. An outer dark-
coloured wall surrounds the whole perithecium (entire) or only the upper
exposed portion (dimidiate); it opens above by a pore or ostiole more or less
prominent.
In some of the genera the paraphyses become dissolved at an early stage,
and somewhat similar filaments near the ostiole, termed periphyses, aid in
the expulsion of the spores. The spores vary in septation, colour and size,
and these variations have served to delimit the genera which have been
formed from the original very large genus Verrucaria. The ascus may be 1-,
2-, 4- or 8-spored. In only one genus is it many-spored (Trimmatothele).
The genera are as follows:
Perithecia with simple ostioles.
Paraphyses disappearing early, or wanting.
Spores simple, ellipsoid 1. Verrucaria Web.
Spores simple, elongate vermiform 2. Sarcopyrenia Nyl.
Spores simple, numerous in the ascus 3. *Trimmatothele
Norm.
Spores 1-3-septate 4. Thelidium Massal.
Spores muriform (with transverse and
longitudinal divisions).
Without hymenial gonidia 5. Polyblastia Massal.
With hymenial gonidia 6. Staurothele Norm.
Paraphyses present.
Spores simple.
Without hymenial gonidia 7. Thrombium Wallr.
With hymenial gonidia 8. *Thelenidia Nyl.
Spores 3-septate, broadly ellipsoid 9. *Geisleria Nitschke.
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Spores acicular, many-septate 10. Gongylia Koerb.
Spores muriform 11. Microglaena Lönnr.
Perithecia with a wide ring round the ostiole.
Spores muriform; paraphyses unbranched 12. *Aspidothelium
Wain.
Spores elongate, many-septate; paraphyses 13. *Aspidopyrenium
branched Wain.
IV. Dermatocarpaceae
In this family there is a much more advanced thalline development—
generally squamulose or with some degree of foliose structure, though in
the genus Endocarpon, some of the species are little more than crustaceous.
The gonidia are bright-green Protococcaceae (according to Chodat,
Coccobotrys in Dermatocarpon). In Endocarpon they appear in the
hymenium.
The least developed in structure is Normandina: the thallus of the single
species consists of delicate shell-like squamules which are non-corticate
above and below. In the other genera there is a cortex of plectenchyma.
The perithecia are almost wholly immersed, and open above by a straight
ostiole. The fructification of Dacampia is considered by some
lichenologists to be only a parasite on the white thickish squamulose thallus
with which it is associated.
Hymenial gonidia present.
Spores muriform 1. Endocarpon Hedw.
Hymenial gonidia absent.
Thallus non-corticate 2. Normandina Wain.
Thallus corticate.
Spores simple, colourless 3. Dermatocarpon Eschw.
Spores simple, brown 4. *Anapyrenium Müll.-Arg.
Spores elongate-septate, colourless 5. *Placidiopsis Beltr.
Spores elongate-septate, brown 6. *Heterocarpon Müll.-Arg.
Spores muriform, colourless 7. *Psoroglaena Müll.-Arg.
Spores muriform, brown 8. Dacampia Massal.
Spores muriform 11. Microglaena Lönnr.
Perithecia with a wide ring round the ostiole.
Spores muriform; paraphyses unbranched 12. *Aspidothelium
Wain.
Spores elongate, many-septate; paraphyses 13. *Aspidopyrenium
branched Wain.
IV. Dermatocarpaceae
In this family there is a much more advanced thalline development—
generally squamulose or with some degree of foliose structure, though in
the genus Endocarpon, some of the species are little more than crustaceous.
The gonidia are bright-green Protococcaceae (according to Chodat,
Coccobotrys in Dermatocarpon). In Endocarpon they appear in the
hymenium.
The least developed in structure is Normandina: the thallus of the single
species consists of delicate shell-like squamules which are non-corticate
above and below. In the other genera there is a cortex of plectenchyma.
The perithecia are almost wholly immersed, and open above by a straight
ostiole. The fructification of Dacampia is considered by some
lichenologists to be only a parasite on the white thickish squamulose thallus
with which it is associated.
Hymenial gonidia present.
Spores muriform 1. Endocarpon Hedw.
Hymenial gonidia absent.
Thallus non-corticate 2. Normandina Wain.
Thallus corticate.
Spores simple, colourless 3. Dermatocarpon Eschw.
Spores simple, brown 4. *Anapyrenium Müll.-Arg.
Spores elongate-septate, colourless 5. *Placidiopsis Beltr.
Spores elongate-septate, brown 6. *Heterocarpon Müll.-Arg.
Spores muriform, colourless 7. *Psoroglaena Müll.-Arg.
Spores muriform, brown 8. Dacampia Massal.
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V. Pyrenothamniaceae
Thallus more or less fruticose and corticate on both surfaces. Algal cells
Protococcaceae.
Only two genera are included in this family: Nylanderiella with one
species from New Zealand, with a small laciniate thallus up to 15 mm. in
height, partly upright, partly decumbent, and attached to the substratum by
basal rhizinae; the other small genus, Pyrenothamnia, belongs to N.
America; the thallus has a short rounded stalk which expands above to an
irregular frond. The perithecia are immersed in the fronds.
Spores colourless, 1-septate 1. *Nylanderiella Hue[1039].
Spores brown, muriform 2. *Pyrenothamnia Tuckerm.
VI. Mastoideaceae
A family containing one genus and one species, with a wide distribution,
having been found in Siberia, on the Antarctic continent (Graham’s Land),
as also in Tierra del Fuego, South Georgia, South Shetland Islands and
Kerguelen. The thallus is foliose, of small thin lobes, and without rhizinae.
Algal cells Prasiola[1040]. The perithecia are globose and partly project
from the thallus; the asci are 8-spored; the paraphyses are mucilaginous and
partly dissolving.
Spores elongate-fusiform, simple, 1. *Mastoidea Hook. and
colourless Harv.
VII. Pyrenulaceae
This family of crustaceous lichens differs from Verrucariaceae chiefly in
the gonidium which is a species of Trentepohlia. Genera and species are
largely corticolous and the thallus is inconspicuous, often developing within
the substratum. The perithecia, like those of Verrucariae, are immersed or
partly emergent and have an entire or dimidiate outer wall. They are
scattered over the thallus except in Anthracothecium where they are often
coalescent. This genus is tropical or subtropical except for one species
which inhabits S.W. Ireland.
Thallus more or less fruticose and corticate on both surfaces. Algal cells
Protococcaceae.
Only two genera are included in this family: Nylanderiella with one
species from New Zealand, with a small laciniate thallus up to 15 mm. in
height, partly upright, partly decumbent, and attached to the substratum by
basal rhizinae; the other small genus, Pyrenothamnia, belongs to N.
America; the thallus has a short rounded stalk which expands above to an
irregular frond. The perithecia are immersed in the fronds.
Spores colourless, 1-septate 1. *Nylanderiella Hue[1039].
Spores brown, muriform 2. *Pyrenothamnia Tuckerm.
VI. Mastoideaceae
A family containing one genus and one species, with a wide distribution,
having been found in Siberia, on the Antarctic continent (Graham’s Land),
as also in Tierra del Fuego, South Georgia, South Shetland Islands and
Kerguelen. The thallus is foliose, of small thin lobes, and without rhizinae.
Algal cells Prasiola[1040]. The perithecia are globose and partly project
from the thallus; the asci are 8-spored; the paraphyses are mucilaginous and
partly dissolving.
Spores elongate-fusiform, simple, 1. *Mastoidea Hook. and
colourless Harv.
VII. Pyrenulaceae
This family of crustaceous lichens differs from Verrucariaceae chiefly in
the gonidium which is a species of Trentepohlia. Genera and species are
largely corticolous and the thallus is inconspicuous, often developing within
the substratum. The perithecia, like those of Verrucariae, are immersed or
partly emergent and have an entire or dimidiate outer wall. They are
scattered over the thallus except in Anthracothecium where they are often
coalescent. This genus is tropical or subtropical except for one species
which inhabits S.W. Ireland.
Page 391
Paraphyses are variable, and in some species tend to disappear, but do not
dissolve in mucilage. The spores are generally colourless, only in one
monotypic genus, Coccotrema, are they simple. The cells into which the
spore is divided differ in form according to the genus.
Paraphyses branched and entangled or
wanting.
Perithecia opening above by stellate lobes 1. *Asteroporum Müll.-
Arg.
Perithecia opening by a pore.
Spores variously septate.
Spore cells cylindrical or cuboid.
Spores colourless, elongate or ovate 1-5- 2. Arthopyrenia Massal.
septate
Spores colourless, filiform 1-multi- 3. Leptorhaphis Koerb.
septate
Spores colourless, muriform 4. Polyblastropsis A.
Zahlbr.
Spores brown, ovoid or elongate 2-5- 5. Microthelia Koerb.
septate
Spore cells globose or lentiform, 3- 6. *Pseudopyrenula
multi-septate Müll.-Arg.
Paraphyses unbranched free.
Spore cells cylindrical or cuboid.
Perithecia beset with hairs 7. *Stereochlamys Müll.-
Arg.
Perithecia naked.
Asci disappearing; spores elongate 8. *Belonia Koerb.
multi-septate, colourless
Asci persistent.
Spores simple, ellipsoid, colourless 9. *Coccotrema Müll.-
Arg.
Spores elongate, 1-multi-septate, 10. Porina Müll.-Arg.
colourless
Spores elongate, 1-multi-septate, 11. Blastodesmia Massal.
brown
dissolve in mucilage. The spores are generally colourless, only in one
monotypic genus, Coccotrema, are they simple. The cells into which the
spore is divided differ in form according to the genus.
Paraphyses branched and entangled or
wanting.
Perithecia opening above by stellate lobes 1. *Asteroporum Müll.-
Arg.
Perithecia opening by a pore.
Spores variously septate.
Spore cells cylindrical or cuboid.
Spores colourless, elongate or ovate 1-5- 2. Arthopyrenia Massal.
septate
Spores colourless, filiform 1-multi- 3. Leptorhaphis Koerb.
septate
Spores colourless, muriform 4. Polyblastropsis A.
Zahlbr.
Spores brown, ovoid or elongate 2-5- 5. Microthelia Koerb.
septate
Spore cells globose or lentiform, 3- 6. *Pseudopyrenula
multi-septate Müll.-Arg.
Paraphyses unbranched free.
Spore cells cylindrical or cuboid.
Perithecia beset with hairs 7. *Stereochlamys Müll.-
Arg.
Perithecia naked.
Asci disappearing; spores elongate 8. *Belonia Koerb.
multi-septate, colourless
Asci persistent.
Spores simple, ellipsoid, colourless 9. *Coccotrema Müll.-
Arg.
Spores elongate, 1-multi-septate, 10. Porina Müll.-Arg.
colourless
Spores elongate, 1-multi-septate, 11. Blastodesmia Massal.
brown
Page 392
Spores muriform, colourless 12. *Clathroporina Müll.-
Arg.
Spores elongate, 2-3-septate, 13. Thelopsis Nyl.
colourless
Spore cells globose or lentiform.
Spores elongate, 1-5-septate, brown 14. Pyrenula Massal.
Spores muriform, brown 15. Anthracothecium
Massal.
VIII. Paratheliaceae
This family is peculiar in that the perithecia open by a somewhat
elongate ostiole that slants at an oblique angle. The algal cells are
Trentepohlia. Genera and species are endemic in tropical or subtropical
regions of the Western hemisphere, though a species of Pleurotrema has
been found in subantarctic America. They are corticolous and the thallus is
either superficial or embedded. The genera are arranged according to spore
characters:
Spores elongate, 2- or more-septate.
Spore cells cylindrical, colourless 1. *Pleurotrema Müll.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Plagiotrema Müll.-Arg.
Spores brown 3. *Parathelium Müll.-Arg.
Spores muriform.
Spores colourless 4. *Campylothelium Müll.-Arg.
Spores brown 5. *Pleurothelium Müll.-Arg.
IX. Trypetheliaceae
This and the following two families are distinguished by the
pseudostroma or compound fruit, a character rare among lichens, though
the true stroma is frequent in Pyrenomycetes in such genera as Dothidea,
Valsa, etc. The genera are crustaceous and corticolous and occur with few
exceptions in tropical or subtropical regions, mostly in the Western
Hemisphere. Several grow on officinal bark (Cinchona, etc.). Algal cells are
Arg.
Spores elongate, 2-3-septate, 13. Thelopsis Nyl.
colourless
Spore cells globose or lentiform.
Spores elongate, 1-5-septate, brown 14. Pyrenula Massal.
Spores muriform, brown 15. Anthracothecium
Massal.
VIII. Paratheliaceae
This family is peculiar in that the perithecia open by a somewhat
elongate ostiole that slants at an oblique angle. The algal cells are
Trentepohlia. Genera and species are endemic in tropical or subtropical
regions of the Western hemisphere, though a species of Pleurotrema has
been found in subantarctic America. They are corticolous and the thallus is
either superficial or embedded. The genera are arranged according to spore
characters:
Spores elongate, 2- or more-septate.
Spore cells cylindrical, colourless 1. *Pleurotrema Müll.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Plagiotrema Müll.-Arg.
Spores brown 3. *Parathelium Müll.-Arg.
Spores muriform.
Spores colourless 4. *Campylothelium Müll.-Arg.
Spores brown 5. *Pleurothelium Müll.-Arg.
IX. Trypetheliaceae
This and the following two families are distinguished by the
pseudostroma or compound fruit, a character rare among lichens, though
the true stroma is frequent in Pyrenomycetes in such genera as Dothidea,
Valsa, etc. The genera are crustaceous and corticolous and occur with few
exceptions in tropical or subtropical regions, mostly in the Western
Hemisphere. Several grow on officinal bark (Cinchona, etc.). Algal cells are
Page 393
Trentepohlia. As in many tropical lichens, the spores are large. The genera
are based chiefly on spore characters, on septation, and on the form of the
spore cells:
Spore cells cylindrical or cuboid.
Spores colourless, elongate, multi-septate 1. *Tomasiella Müll.-Arg.
Spores colourless, muriform 2. *Laurera Rehb.
Spores brown, muriform 3. *Bottaria Massal.
Spore cells globose-lentiform.
Spores colourless, elongate, multi-septate 4. *Trypethelium Spreng.
Spores brown, elongate, multi-septate 5. Melanotheca Müll.-Arg.
X. Astrotheliaceae
The perithecia are either upright or inclined, and occur usually in radiate
groups. They are free or united in a stroma, and the elongate ostioles open
separately or coalesce in a common canal. The genera are all crustaceous,
with Trentepohlia gonidia. They are tropical or subtropical, mostly in the
Western Hemisphere; but species of Parmentaria and Astrothelium have
been recorded also from Australia.
The spores are all many-celled and the form of their cells is a generic
character:
Spores elongate, multi-septate.
Spore cells cylindrical 1. *Lithothelium Müll.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Astrothelium Trev.
Spores brown 3. *Pyrenastrum Eschw.
Spores muriform.
Spores colourless 4. *Heufleria Trev.
Spores brown 5. *Parmentaria Fée.
XI. Mycoporaceae
A small family with only two genera which are found in both
Hemispheres; species of both occur in Great Britain. They are all
are based chiefly on spore characters, on septation, and on the form of the
spore cells:
Spore cells cylindrical or cuboid.
Spores colourless, elongate, multi-septate 1. *Tomasiella Müll.-Arg.
Spores colourless, muriform 2. *Laurera Rehb.
Spores brown, muriform 3. *Bottaria Massal.
Spore cells globose-lentiform.
Spores colourless, elongate, multi-septate 4. *Trypethelium Spreng.
Spores brown, elongate, multi-septate 5. Melanotheca Müll.-Arg.
X. Astrotheliaceae
The perithecia are either upright or inclined, and occur usually in radiate
groups. They are free or united in a stroma, and the elongate ostioles open
separately or coalesce in a common canal. The genera are all crustaceous,
with Trentepohlia gonidia. They are tropical or subtropical, mostly in the
Western Hemisphere; but species of Parmentaria and Astrothelium have
been recorded also from Australia.
The spores are all many-celled and the form of their cells is a generic
character:
Spores elongate, multi-septate.
Spore cells cylindrical 1. *Lithothelium Müll.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Astrothelium Trev.
Spores brown 3. *Pyrenastrum Eschw.
Spores muriform.
Spores colourless 4. *Heufleria Trev.
Spores brown 5. *Parmentaria Fée.
XI. Mycoporaceae
A small family with only two genera which are found in both
Hemispheres; species of both occur in Great Britain. They are all
Page 394
corticolous. The perithecia are united into a partially chambered fruiting
body surrounded by a common wall, but opening by separate ostioles. The
thallus is thinly crustaceous, with Palmella gonidia in Mycoporum, and
Trentepohlia in Mycoporellum. The spores are colourless or brown in both
genera:
Spores muriform 1. Mycoporum Flot.
Spores elongate, multi-septate 2. Mycoporellum A. Zahlbr.
XII. Phyllopyreniaceae
Thallus foliose with both surfaces corticate and attached by rhizinae.
Algal cells Trentepohlia. There is but one genus, Lepolichen, which has a
laciniate somewhat upward growing thallus. Two species, both from South
America, have been described, L. granulatus Müll.-Arg. and L. coccophora
Hue. The latter has been recently examined by Hue[1041] who finds, on the
thalli, cephalodia which are peculiar in containing bright-green gelatinous
algae either Urococcus or Gloeocystis, one of the few instances known of
chlorophyllaceous algae forming part of a cephalodium. Gloeocystis may be
the only alga present in the cephalodium; Urococcus is always accompanied
by Scytonema.
The perithecia are immersed in thalline tubercles:
Spores colourless, simple, ovoid or ovoid- 1. *Lepolichen
elongate Trevis.
XIII. Strigulaceae
A family of epiphyllous lichens inhabiting and disfiguring coriaceous
evergreen leaves, or occasionally fern leaves in tropical or subtropical
regions. The algae associated are Mycoidea and Phycopeltis
(Phyllactidium). The only truly parasitic lichen, Strigula, belongs to this
family: the alga precedes the lichen on the leaves and is gradually invaded
by the hyphae of the lichen and altered in character. The small black
perithecia are scattered over the surface. In Strigula the lichen retains the
spreading rounded form of the alga. The other genera are more irregular.
body surrounded by a common wall, but opening by separate ostioles. The
thallus is thinly crustaceous, with Palmella gonidia in Mycoporum, and
Trentepohlia in Mycoporellum. The spores are colourless or brown in both
genera:
Spores muriform 1. Mycoporum Flot.
Spores elongate, multi-septate 2. Mycoporellum A. Zahlbr.
XII. Phyllopyreniaceae
Thallus foliose with both surfaces corticate and attached by rhizinae.
Algal cells Trentepohlia. There is but one genus, Lepolichen, which has a
laciniate somewhat upward growing thallus. Two species, both from South
America, have been described, L. granulatus Müll.-Arg. and L. coccophora
Hue. The latter has been recently examined by Hue[1041] who finds, on the
thalli, cephalodia which are peculiar in containing bright-green gelatinous
algae either Urococcus or Gloeocystis, one of the few instances known of
chlorophyllaceous algae forming part of a cephalodium. Gloeocystis may be
the only alga present in the cephalodium; Urococcus is always accompanied
by Scytonema.
The perithecia are immersed in thalline tubercles:
Spores colourless, simple, ovoid or ovoid- 1. *Lepolichen
elongate Trevis.
XIII. Strigulaceae
A family of epiphyllous lichens inhabiting and disfiguring coriaceous
evergreen leaves, or occasionally fern leaves in tropical or subtropical
regions. The algae associated are Mycoidea and Phycopeltis
(Phyllactidium). The only truly parasitic lichen, Strigula, belongs to this
family: the alga precedes the lichen on the leaves and is gradually invaded
by the hyphae of the lichen and altered in character. The small black
perithecia are scattered over the surface. In Strigula the lichen retains the
spreading rounded form of the alga. The other genera are more irregular.
Page 395
Thallus orbicular in outline 1. *Strigula Fries.
Thallus irregular.
Perithecia without hairs.
Spores colourless.
Spores elongate, multi-septate 2. *Phylloporina Müll.-Arg.
Spores muriform 3. *Phyllobathelium Müll.-Arg.
Spores brown.
Spores simple 4. *Haplopyrenula Müll.-Arg.
Spores elongate, 1-3-septate 5. *Microtheliopsis Müll.-Arg.
Perithecia beset with stiff hairs 6. *Trichothelium Müll.-Arg.
XIV. Pyrenidiaceae
The only family of Pyrenocarpineae associated with blue-green algae.
The genera of Pyrenidiaceae are all monotypic, only one is common and of
wide distribution, Coriscium (Normandina Nyl.). Pyrenidium is the only
member that has a fruticose thallus, and that is of minute dimensions.
Eolichen Heppii, found and described by Zukal, is a doubtful lichen.
“Lophothelium” Stirton is a case of parasitism of a fungus, Ticothecium, on
the squamules of Stereocaulon condensatum.
Algal cells Scytonema or Stigonema.
Thallus crustaceous[1042]; spores simple, 1. *Rhabdopsora Müll.-
colourless Arg.
Thallus crustaceous; spores 1-septate, 2. *Eolichen Zuk.
colourless
Thallus crustaceous; spores muriform, brown 3. *Pyrenothrix
Riddle[1043].
Thallus squamulose; spores numerous, simple 4. *Placothelium Müll.-
Arg.
Algal cells Nostoc.
Thallus crustaceous; spores filiform, simple, 5. *Hassea A. Zahlbr.
colourless
Thallus fruticose; spores elongate, 3-septate, 6. Pyrenidium Nyl.
brown
Thallus irregular.
Perithecia without hairs.
Spores colourless.
Spores elongate, multi-septate 2. *Phylloporina Müll.-Arg.
Spores muriform 3. *Phyllobathelium Müll.-Arg.
Spores brown.
Spores simple 4. *Haplopyrenula Müll.-Arg.
Spores elongate, 1-3-septate 5. *Microtheliopsis Müll.-Arg.
Perithecia beset with stiff hairs 6. *Trichothelium Müll.-Arg.
XIV. Pyrenidiaceae
The only family of Pyrenocarpineae associated with blue-green algae.
The genera of Pyrenidiaceae are all monotypic, only one is common and of
wide distribution, Coriscium (Normandina Nyl.). Pyrenidium is the only
member that has a fruticose thallus, and that is of minute dimensions.
Eolichen Heppii, found and described by Zukal, is a doubtful lichen.
“Lophothelium” Stirton is a case of parasitism of a fungus, Ticothecium, on
the squamules of Stereocaulon condensatum.
Algal cells Scytonema or Stigonema.
Thallus crustaceous[1042]; spores simple, 1. *Rhabdopsora Müll.-
colourless Arg.
Thallus crustaceous; spores 1-septate, 2. *Eolichen Zuk.
colourless
Thallus crustaceous; spores muriform, brown 3. *Pyrenothrix
Riddle[1043].
Thallus squamulose; spores numerous, simple 4. *Placothelium Müll.-
Arg.
Algal cells Nostoc.
Thallus crustaceous; spores filiform, simple, 5. *Hassea A. Zahlbr.
colourless
Thallus fruticose; spores elongate, 3-septate, 6. Pyrenidium Nyl.
brown
Page 396
Algal cells Microcystis (Polycoccus).
Thallus squamulose; fructification unknown 7. Coriscium Wainio.
Series II. GYMNOCARPEAE
Subseries 1. Coniocarpineae
This small subseries is marked by the peculiar “mazaedium” type of fruit
with its disappearing asci. It forms a connecting link between the families
with perithecia and those with apothecia. The thallus is crustaceous or
fruticose, often poorly developed and sometimes absent. The algal cells are
Protococcaceae or rarely Trentepohlia.
XV. Caliceaceae
The thallus is thinly crustaceous, sometimes brightly coloured,
sometimes absent, taking no part in the formation of the fruits; these have
upright stalks with a small capitulum, and often look like minute nails. One
genus, Sphinctrina, is parasitic on the thallus of other lichens, mostly
Pertusariae.
Fruits with slender stalks.
Spores simple.
Spores colourless 1. Coniocybe Ach.
Spores brown 2. Chaenotheca Th. Fr.
Spores septate, brown.
Spores 1-septate 3. Calicium De Not.
Spores 3-7-septate 4. Stenocybe Nyl.
Fruits with short thick stalks.
Spores globose, brown (parasitic) 5. Sphinctrina Fries.
Spores 1-septate, brown 6. *Pyrgidium Nyl.
XVI. Cypheliaceae
Thallus crustaceous. Algal cells Protococcaceae or Trentepohlia.
Apothecia sessile, more widely open than in the previous family; in some
genera the thallus forms an outer apothecial margin. The genera Farriola
Thallus squamulose; fructification unknown 7. Coriscium Wainio.
Series II. GYMNOCARPEAE
Subseries 1. Coniocarpineae
This small subseries is marked by the peculiar “mazaedium” type of fruit
with its disappearing asci. It forms a connecting link between the families
with perithecia and those with apothecia. The thallus is crustaceous or
fruticose, often poorly developed and sometimes absent. The algal cells are
Protococcaceae or rarely Trentepohlia.
XV. Caliceaceae
The thallus is thinly crustaceous, sometimes brightly coloured,
sometimes absent, taking no part in the formation of the fruits; these have
upright stalks with a small capitulum, and often look like minute nails. One
genus, Sphinctrina, is parasitic on the thallus of other lichens, mostly
Pertusariae.
Fruits with slender stalks.
Spores simple.
Spores colourless 1. Coniocybe Ach.
Spores brown 2. Chaenotheca Th. Fr.
Spores septate, brown.
Spores 1-septate 3. Calicium De Not.
Spores 3-7-septate 4. Stenocybe Nyl.
Fruits with short thick stalks.
Spores globose, brown (parasitic) 5. Sphinctrina Fries.
Spores 1-septate, brown 6. *Pyrgidium Nyl.
XVI. Cypheliaceae
Thallus crustaceous. Algal cells Protococcaceae or Trentepohlia.
Apothecia sessile, more widely open than in the previous family; in some
genera the thallus forms an outer apothecial margin. The genera Farriola
Page 397
from Norway and Tylophorella from New Granada are monotypic. The
British genus Cyphelium has been known as Trachylia.
Thallus with Protococcaceae.
Spores colourless, simple 1. *Farriola Norm.
Spores brown, 1-3-septate (rarely simple or 2. Cyphelium Th. Fr.
muriform)
Thallus with Trentepohlia.
Spores simple, many in the ascus 3. *Tylophorella
Wainio.
Spores 8 in the ascus.
Apothecia with a thalline margin 4. *Tylophoron Nyl.
Apothecia without a thalline margin 5. *Pyrgillus Nyl.
XVII. Sphaerophoraceae
The most highly evolved family of the subseries, as regards the thallus.
Algal cells Protococcaceae. In Tholurna, a small lichen endemic in
Scandinavia, there is a double thallus: one of horizontal much-divided
squamules, the other swollen, upright, terminating in the capitulum. The
fruit is lateral in Calycidium, a squamulose form from New Zealand, and in
Pleurocybe from Madagascar, with stiff strap-shaped fronds. All the genera
are monotypic except Sphaerophorus, of which genus ten species are
recorded, some of them with a world-wide distribution. The spores are
brown and simple or 1-septate.
Thallus squamulose and upright 1. *Tholurna Norm.
Thallus wholly squamulose 2. *Calycidium Stirton.
Thallus fruticose.
Fronds hollow in the centre 3. *Pleurocybe Müll.-Arg.
Fronds not hollow.
Fruit without a thalline margin 4. *Acroscyphus Lév.
Fruit inclosed in the tip of the fronds 5. Sphaerophorus Pers.
Subseries 2. Graphidineae
British genus Cyphelium has been known as Trachylia.
Thallus with Protococcaceae.
Spores colourless, simple 1. *Farriola Norm.
Spores brown, 1-3-septate (rarely simple or 2. Cyphelium Th. Fr.
muriform)
Thallus with Trentepohlia.
Spores simple, many in the ascus 3. *Tylophorella
Wainio.
Spores 8 in the ascus.
Apothecia with a thalline margin 4. *Tylophoron Nyl.
Apothecia without a thalline margin 5. *Pyrgillus Nyl.
XVII. Sphaerophoraceae
The most highly evolved family of the subseries, as regards the thallus.
Algal cells Protococcaceae. In Tholurna, a small lichen endemic in
Scandinavia, there is a double thallus: one of horizontal much-divided
squamules, the other swollen, upright, terminating in the capitulum. The
fruit is lateral in Calycidium, a squamulose form from New Zealand, and in
Pleurocybe from Madagascar, with stiff strap-shaped fronds. All the genera
are monotypic except Sphaerophorus, of which genus ten species are
recorded, some of them with a world-wide distribution. The spores are
brown and simple or 1-septate.
Thallus squamulose and upright 1. *Tholurna Norm.
Thallus wholly squamulose 2. *Calycidium Stirton.
Thallus fruticose.
Fronds hollow in the centre 3. *Pleurocybe Müll.-Arg.
Fronds not hollow.
Fruit without a thalline margin 4. *Acroscyphus Lév.
Fruit inclosed in the tip of the fronds 5. Sphaerophorus Pers.
Subseries 2. Graphidineae
Page 398
In this subseries are included five families that differ rather widely from
each other both in thallus and apothecia; the latter are more or less
carbonaceous and mostly with a proper margin only. Families and genera
are widely distributed, though most abundant in warm regions. Algal cells
mostly Trentepohlia.
A comprehensive study of the apothecia of this series by Bioret[1044]
gives some interesting results in regard to the paraphyses: in Arthonia they
are irregular in direction and much-branched; in Opegrapha, the paraphyses
are vertical and parallel with more regular branching; Stigmatidium
(Enterographa) resembles Opegrapha in this respect as does also
Platygrapha, a genus of Lecanactidaceae, while in Graphis the paraphyses
are vertical, unbranched and free; Melaspilea paraphyses are somewhat
similar to those of Graphis.
XVIII. Arthoniaceae
The thallus of Arthoniaceae is corticolous with few exceptions and is
very inconspicuous, being largely embedded in the substratum. The
apothecia (ardellae) are round, irregular or stellate, without any margin, the
hymenium being protected by the dense branching of the paraphyses at the
tips.
Arthonia is abundant everywhere. The species of the other genera belong
mostly to tropical or subtropical countries. Arthoniopsis is similar to
Arthonia in the character of the fruits, but the gonidium is a Phycopeltis,
and it is only found on leaves. Synarthonia with peculiar stromatoid
fructification is monotypic; it occurs in Costa Rica.
Thallus with Trentepohlia gonidia.
Apothecia scattered.
Spores elongate 1- or pluri-septate 1. Arthonia Ach.
Spores muriform 2. Arthothelium Massal.
Apothecia stromatoid.
Spores elongate, multi-septate 3. *Synarthonia Müll.-Arg.
Thallus with Palmella gonidia.
Spores 1- or more-septate 4. Allarthonia Nyl.
Spores muriform 5. *Allarthothelium Wain.
each other both in thallus and apothecia; the latter are more or less
carbonaceous and mostly with a proper margin only. Families and genera
are widely distributed, though most abundant in warm regions. Algal cells
mostly Trentepohlia.
A comprehensive study of the apothecia of this series by Bioret[1044]
gives some interesting results in regard to the paraphyses: in Arthonia they
are irregular in direction and much-branched; in Opegrapha, the paraphyses
are vertical and parallel with more regular branching; Stigmatidium
(Enterographa) resembles Opegrapha in this respect as does also
Platygrapha, a genus of Lecanactidaceae, while in Graphis the paraphyses
are vertical, unbranched and free; Melaspilea paraphyses are somewhat
similar to those of Graphis.
XVIII. Arthoniaceae
The thallus of Arthoniaceae is corticolous with few exceptions and is
very inconspicuous, being largely embedded in the substratum. The
apothecia (ardellae) are round, irregular or stellate, without any margin, the
hymenium being protected by the dense branching of the paraphyses at the
tips.
Arthonia is abundant everywhere. The species of the other genera belong
mostly to tropical or subtropical countries. Arthoniopsis is similar to
Arthonia in the character of the fruits, but the gonidium is a Phycopeltis,
and it is only found on leaves. Synarthonia with peculiar stromatoid
fructification is monotypic; it occurs in Costa Rica.
Thallus with Trentepohlia gonidia.
Apothecia scattered.
Spores elongate 1- or pluri-septate 1. Arthonia Ach.
Spores muriform 2. Arthothelium Massal.
Apothecia stromatoid.
Spores elongate, multi-septate 3. *Synarthonia Müll.-Arg.
Thallus with Palmella gonidia.
Spores 1- or more-septate 4. Allarthonia Nyl.
Spores muriform 5. *Allarthothelium Wain.
Page 399
Thallus with Phycopeltis gonidia.
Spores elongate 1- or more-septate 6. *Arthoniopsis Müll.-Arg.
XIX. Graphidaceae
Thallus crustaceous, inconspicuous, partly immersed, mainly growing on
bark but occasionally on dead wood or stone. Algal cells chiefly
Trentepohlia, very rarely Palmella or Phycopeltis (epiphyllous). Apothecia
(lirellae) carbonaceous more or less linear, opening by a narrow slit with a
well-developed proper margin except in Gymnographa, a monotypic
Australian genus. In two genera, the fruit is of a compound nature, several
parallel discs occurring in one lirella: these are Ptychographa (on bark in
Scotland) and Diplogramma (Australia), both are monotypic. They must not
be confused with Graphis elegans and allied species in which the sterile
carbonaceous margin is furrowed. Two tropical genera associated with
Phycopeltis are epiphyllous.
Graphidaceae are among the oldest recorded lichens, attention having
been drawn to them since early times by the resemblance of the lirellae on
the bark of trees to hieroglyphic writing.
Thallus with Palmella gonidia.
Apothecia single.
Hypothecium dark-brown.
Spores simple 1. Lithographa Nyl.
Hypothecium colourless or brownish.
Spores colourless.
Spores simple 2. Xylographa Fries.
Spores elongate 3-8-septate 3. *Aulaxina Fée.
Spores brown.
Spores 1-septate 4. Encephalographa
Massal.
Spores pluri-septate, then muriform 5. *Xyloschistes Wain.
Apothecia compound.
Spores simple, colourless 6. Ptychographa Nyl.
Spores elongate 1- or more-septate 6. *Arthoniopsis Müll.-Arg.
XIX. Graphidaceae
Thallus crustaceous, inconspicuous, partly immersed, mainly growing on
bark but occasionally on dead wood or stone. Algal cells chiefly
Trentepohlia, very rarely Palmella or Phycopeltis (epiphyllous). Apothecia
(lirellae) carbonaceous more or less linear, opening by a narrow slit with a
well-developed proper margin except in Gymnographa, a monotypic
Australian genus. In two genera, the fruit is of a compound nature, several
parallel discs occurring in one lirella: these are Ptychographa (on bark in
Scotland) and Diplogramma (Australia), both are monotypic. They must not
be confused with Graphis elegans and allied species in which the sterile
carbonaceous margin is furrowed. Two tropical genera associated with
Phycopeltis are epiphyllous.
Graphidaceae are among the oldest recorded lichens, attention having
been drawn to them since early times by the resemblance of the lirellae on
the bark of trees to hieroglyphic writing.
Thallus with Palmella gonidia.
Apothecia single.
Hypothecium dark-brown.
Spores simple 1. Lithographa Nyl.
Hypothecium colourless or brownish.
Spores colourless.
Spores simple 2. Xylographa Fries.
Spores elongate 3-8-septate 3. *Aulaxina Fée.
Spores brown.
Spores 1-septate 4. Encephalographa
Massal.
Spores pluri-septate, then muriform 5. *Xyloschistes Wain.
Apothecia compound.
Spores simple, colourless 6. Ptychographa Nyl.
Page 400
Spores pluri-septate, colourless 7. *Diplogramma Müll.-
Arg.
Thallus with Trentepohlia gonidia.
Spores elongate 1-multi-septate, the cells
longer than wide.
Spores brown.
Spores 1-(rarely more)-septate 8. Melaspilea Nyl.
Spores 3-septate (apothecia rudimentary) 9. *Gymnographa Müll.-
Arg.
Spores colourless.
Spores acicular, coiled (many in the 10. *Spirographa A.
ascus) Zahlbr.
Spores fusiform, straight 11. Opegrapha Humb.
Spores muriform.
Spores elongate, central cells finally 12. *Dictyographa Müll.-
muriform Arg.
Spores elongate, septate, cells wider than
long.
Paraphyses unbranched, filiform.
Spores multi-septate, colourless 13. Graphis Adans.
Spores multi-septate, brown 14. Phaeographis Müll.-
Arg.
Spores muriform, colourless 15. Graphina Müll.-Arg.
Spores muriform, brown 16. Phaeographina Müll.-
Arg.
Paraphyses clavate, warted at tips 17. *Acanthothecium
Wain.
Paraphyses branched, interwoven above 18. *Helminthocarpon Fée.
Thallus with Phycopeltis gonidia (epiphyllous).
Spores elongate, 3-9-septate, colourless 19. *Opegraphella Müll.-
Arg.
Spores elongate, 1-septate, brown 20. *Micrographa Müll.-
Arg.
XX. Chiodectonaceae
Arg.
Thallus with Trentepohlia gonidia.
Spores elongate 1-multi-septate, the cells
longer than wide.
Spores brown.
Spores 1-(rarely more)-septate 8. Melaspilea Nyl.
Spores 3-septate (apothecia rudimentary) 9. *Gymnographa Müll.-
Arg.
Spores colourless.
Spores acicular, coiled (many in the 10. *Spirographa A.
ascus) Zahlbr.
Spores fusiform, straight 11. Opegrapha Humb.
Spores muriform.
Spores elongate, central cells finally 12. *Dictyographa Müll.-
muriform Arg.
Spores elongate, septate, cells wider than
long.
Paraphyses unbranched, filiform.
Spores multi-septate, colourless 13. Graphis Adans.
Spores multi-septate, brown 14. Phaeographis Müll.-
Arg.
Spores muriform, colourless 15. Graphina Müll.-Arg.
Spores muriform, brown 16. Phaeographina Müll.-
Arg.
Paraphyses clavate, warted at tips 17. *Acanthothecium
Wain.
Paraphyses branched, interwoven above 18. *Helminthocarpon Fée.
Thallus with Phycopeltis gonidia (epiphyllous).
Spores elongate, 3-9-septate, colourless 19. *Opegraphella Müll.-
Arg.
Spores elongate, 1-septate, brown 20. *Micrographa Müll.-
Arg.
XX. Chiodectonaceae
Page 401
Specially distinguished in this subseries by the grouping of the somewhat
rudimentary apothecia in pseudostromata in which they are almost wholly
immersed. In form they are roundish or linear; the spores are septate or
muriform. The thallus is thinly crustaceous and continuous: in Glyphis,
Sarcographa and Sarcographina there is an amorphous upper cortex, the
other genera are non-corticate. Algal cells are Trentepohlia with the
exception of two epiphyllous genera associated with Phycopeltis.
Genera and species are mostly tropical. Sclerophyton with five species is
represented in Europe by a single British specimen, S. circumscriptum.
The form of the paraphyses is a distinguishing character of the genera.
Thallus with Trentepohlia gonidia.
Paraphyses free, unbranched.
Spore cells short or almost globose.
Spores elongate, multi-septate, 1. Glyphis Fée.
colourless
Spores elongate, multi-septate, brown 2. *Sarcographa Fée.
Spores muriform, brown 3. *Sarcographina Müll.-
Arg.
Spore cells longer and cuboid.
Spores muriform, colourless 4. *Enterodictyon Müll.-
Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate, 5. Chiodecton Ach.
colourless
Spores elongate, multi-septate, brown 6. Sclerophyton Eschw.
Spores muriform, colourless 7. *Minksia Müll.-Arg.
Spores muriform, brown 8. *Enterostigma Müll.-Arg.
Thallus with Phycopeltis gonidia (epiphyllous).
Paraphyses free.
Spores unequally 2-celled, colourless 9. *Pycnographa Müll.-Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate, 10. *Mazosia Massal.
colourless
rudimentary apothecia in pseudostromata in which they are almost wholly
immersed. In form they are roundish or linear; the spores are septate or
muriform. The thallus is thinly crustaceous and continuous: in Glyphis,
Sarcographa and Sarcographina there is an amorphous upper cortex, the
other genera are non-corticate. Algal cells are Trentepohlia with the
exception of two epiphyllous genera associated with Phycopeltis.
Genera and species are mostly tropical. Sclerophyton with five species is
represented in Europe by a single British specimen, S. circumscriptum.
The form of the paraphyses is a distinguishing character of the genera.
Thallus with Trentepohlia gonidia.
Paraphyses free, unbranched.
Spore cells short or almost globose.
Spores elongate, multi-septate, 1. Glyphis Fée.
colourless
Spores elongate, multi-septate, brown 2. *Sarcographa Fée.
Spores muriform, brown 3. *Sarcographina Müll.-
Arg.
Spore cells longer and cuboid.
Spores muriform, colourless 4. *Enterodictyon Müll.-
Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate, 5. Chiodecton Ach.
colourless
Spores elongate, multi-septate, brown 6. Sclerophyton Eschw.
Spores muriform, colourless 7. *Minksia Müll.-Arg.
Spores muriform, brown 8. *Enterostigma Müll.-Arg.
Thallus with Phycopeltis gonidia (epiphyllous).
Paraphyses free.
Spores unequally 2-celled, colourless 9. *Pycnographa Müll.-Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate, 10. *Mazosia Massal.
colourless
Page 402
XXI. Dirinaceae
A small family, which is associated with and often included under
Graphidaceae. The thallus is crustaceous and corticate on the upper surface,
the cortex being formed of palisade hyphae. Algal cells Trentepohlia.
Apothecia are rounded or with a tendency to elongation, and, in addition to
a thin proper margin, possess a stout thalline margin; the hypothecium is
thick and carbonaceous. There are two genera: Dirina with twelve species
has a wide distribution; Dirinastrum is monotypic and occurs on maritime
rocks in Australia. In both the spores are elongate-septate, differing only in
colour:
Spores colourless 1. Dirina Fr.
Spores brown 2. *Dirinastrum Müll.-Arg.
XXII. Roccellaceae
The Roccellaceae differ from the preceding Dirinaceae chiefly in the
fruticose thallus which is more or less characteristic of all the genera,
though in Roccellographa it expands into foliose dimensions and in
Roccellina is reduced to short podetia-like processes from a crustose base.
The fronds—mostly long and strap-shaped—are protected in most of the
genera by a cortex of compact palisade hyphae; in a few the outer hyphae
are parallel with the long axis. The medulla is of parallel hyphae, either
loose or compact. The algal cells are Trentepohlia.
The apothecia are lateral except in Roccellina where they occur at the
tips of the short upright fronds, and only in Roccellaria is there no thalline
margin. They are superficial in all of the genera except Roccellographa, in
which they are immersed and almost closed, recalling the perithecia-like
fruits of Chiodecton (sect. Enterographa). The spores are elongate, narrow,
pluri-septate, and colourless or brownish, except in Darbishirella in which
they are ovoid, 2-septate and brown.
The affinity of Dirinaceae and Roccellaceae with Graphidaceae was first
indicated by Reinke[1045] and elaborated later by Darbishire[1046] in his
monograph of Roccellaceae. The apothecia in some species of Dirina are
ellipsoid rather than round; in several genera of Roccellaceae they are
A small family, which is associated with and often included under
Graphidaceae. The thallus is crustaceous and corticate on the upper surface,
the cortex being formed of palisade hyphae. Algal cells Trentepohlia.
Apothecia are rounded or with a tendency to elongation, and, in addition to
a thin proper margin, possess a stout thalline margin; the hypothecium is
thick and carbonaceous. There are two genera: Dirina with twelve species
has a wide distribution; Dirinastrum is monotypic and occurs on maritime
rocks in Australia. In both the spores are elongate-septate, differing only in
colour:
Spores colourless 1. Dirina Fr.
Spores brown 2. *Dirinastrum Müll.-Arg.
XXII. Roccellaceae
The Roccellaceae differ from the preceding Dirinaceae chiefly in the
fruticose thallus which is more or less characteristic of all the genera,
though in Roccellographa it expands into foliose dimensions and in
Roccellina is reduced to short podetia-like processes from a crustose base.
The fronds—mostly long and strap-shaped—are protected in most of the
genera by a cortex of compact palisade hyphae; in a few the outer hyphae
are parallel with the long axis. The medulla is of parallel hyphae, either
loose or compact. The algal cells are Trentepohlia.
The apothecia are lateral except in Roccellina where they occur at the
tips of the short upright fronds, and only in Roccellaria is there no thalline
margin. They are superficial in all of the genera except Roccellographa, in
which they are immersed and almost closed, recalling the perithecia-like
fruits of Chiodecton (sect. Enterographa). The spores are elongate, narrow,
pluri-septate, and colourless or brownish, except in Darbishirella in which
they are ovoid, 2-septate and brown.
The affinity of Dirinaceae and Roccellaceae with Graphidaceae was first
indicated by Reinke[1045] and elaborated later by Darbishire[1046] in his
monograph of Roccellaceae. The apothecia in some species of Dirina are
ellipsoid rather than round; in several genera of Roccellaceae they are
Page 403
distinctly lirellate, and in Roccella itself some species have ellipsoid fruits.
The fruticose thallus is predominant in Roccellaceae, but its evolution from
the crustaceous type may be traced through Roccellina which is partly
crustaceous and only imperfectly fruticose.
In most of the genera only one species is recorded. Roccella, represented
by twelve species, is well known for its dyeing properties, and has a wide
distribution. Like other Graphidineae they are mainly plants of warm
regions, many of them exclusively maritime rock-dwellers.
The following synopsis of the genera is the one given by Darbishire in
his monograph.
Cortex fastigate, of palisade hyphae.
Spores colourless.
Hypothecium black-carbonaceous.
Apothecia round.
Thallus fruticose 1. Roccella DC.
Thallus crustaceous-fruticose 2. *Roccellina Darbish.
Apothecia lirellate 3. *Reinkella Darbish.
Hypothecium colourless.
Gonidia present under the 4. *Pentagenella Darbish.
hypothecium
Gonidia absent from hypothecium 5. *Combea De Not.
Spores brown or brownish.
Medulla of parallel somewhat loose 6. *Schizopelte Th. Fr.
hyphae
Medulla solid, black 7. *Simonyella Steiner.
Cortex fibrous, of parallel hyphae.
Apothecia round.
Hypothecium black-carbonaceous.
Apothecia with thalline margin 8. *Dendrographa
Darbish.
Apothecia with proper margin 9. *Roccellaria Darbish.
Hypothecium colourless 10. *Darbishirella A.
Zahlbr.
Apothecia lirellate 11. *Ingaderia Darbish.
The fruticose thallus is predominant in Roccellaceae, but its evolution from
the crustaceous type may be traced through Roccellina which is partly
crustaceous and only imperfectly fruticose.
In most of the genera only one species is recorded. Roccella, represented
by twelve species, is well known for its dyeing properties, and has a wide
distribution. Like other Graphidineae they are mainly plants of warm
regions, many of them exclusively maritime rock-dwellers.
The following synopsis of the genera is the one given by Darbishire in
his monograph.
Cortex fastigate, of palisade hyphae.
Spores colourless.
Hypothecium black-carbonaceous.
Apothecia round.
Thallus fruticose 1. Roccella DC.
Thallus crustaceous-fruticose 2. *Roccellina Darbish.
Apothecia lirellate 3. *Reinkella Darbish.
Hypothecium colourless.
Gonidia present under the 4. *Pentagenella Darbish.
hypothecium
Gonidia absent from hypothecium 5. *Combea De Not.
Spores brown or brownish.
Medulla of parallel somewhat loose 6. *Schizopelte Th. Fr.
hyphae
Medulla solid, black 7. *Simonyella Steiner.
Cortex fibrous, of parallel hyphae.
Apothecia round.
Hypothecium black-carbonaceous.
Apothecia with thalline margin 8. *Dendrographa
Darbish.
Apothecia with proper margin 9. *Roccellaria Darbish.
Hypothecium colourless 10. *Darbishirella A.
Zahlbr.
Apothecia lirellate 11. *Ingaderia Darbish.
Page 404
Subseries 3. Cyclocarpineae
This last subseries includes the remaining twenty-nine families of
Ascolichens. They are very varied both in the fungal and the algal
symbionts. The fruit is more or less a discoid open apothecium. The gonidia
belong to different genera of Myxophyceae and Chlorophyceae, but the
most frequent are Protococcaceae. Families are based largely on thalline
structure.
XXIII. Lecanactidaceae
By many systematists this family is included under Graphidineae on
account of the fruit structure which in some of the forms is carbonaceous
and almost lirellate, and also because the algal symbiont is Trentepohlia.
The thallus is primitive, being thinly crustaceous and non-corticate; the
apothecium has a black carbonaceous hypothecium in two of the genera,
Lecanactis and Schismatomma (Platygrapha); in the third genus,
Melampydium, it is colourless. The latter is monotypic, and the spores
become muriform. In the other genera they are elongate and multi-septate.
Apothecia with prominent proper margin 1. Lecanactis Eschw.
Apothecia with thin proper margin 2. *Melampydium Müll.-Arg.
Apothecia with thalline margin 3. Schismatomma Flot.
XXIV. Pilocarpaceae
A small family with but one genus, Pilocarpon. It is distinguished as one
of the few epiphyllous genera of lichens associated with Protococcaceous
gonidia and with a distribution extending far beyond the tropics. The best
known species, P. leucoblepharum, encircles the base of pine-needles with a
white felted crust, or inhabits coriaceous evergreen leaves. Another species
lives on fern leaves. The fruit is a discoid apothecium with a dark
carbonaceous hypothecium and proper margin, and with a second thalline
margin. The paraphyses are branched and interwoven above.
Spores elongate, 3-septate, colourless 1. Pilocarpon Wain.
XXV. Chrysotrichaceae
This last subseries includes the remaining twenty-nine families of
Ascolichens. They are very varied both in the fungal and the algal
symbionts. The fruit is more or less a discoid open apothecium. The gonidia
belong to different genera of Myxophyceae and Chlorophyceae, but the
most frequent are Protococcaceae. Families are based largely on thalline
structure.
XXIII. Lecanactidaceae
By many systematists this family is included under Graphidineae on
account of the fruit structure which in some of the forms is carbonaceous
and almost lirellate, and also because the algal symbiont is Trentepohlia.
The thallus is primitive, being thinly crustaceous and non-corticate; the
apothecium has a black carbonaceous hypothecium in two of the genera,
Lecanactis and Schismatomma (Platygrapha); in the third genus,
Melampydium, it is colourless. The latter is monotypic, and the spores
become muriform. In the other genera they are elongate and multi-septate.
Apothecia with prominent proper margin 1. Lecanactis Eschw.
Apothecia with thin proper margin 2. *Melampydium Müll.-Arg.
Apothecia with thalline margin 3. Schismatomma Flot.
XXIV. Pilocarpaceae
A small family with but one genus, Pilocarpon. It is distinguished as one
of the few epiphyllous genera of lichens associated with Protococcaceous
gonidia and with a distribution extending far beyond the tropics. The best
known species, P. leucoblepharum, encircles the base of pine-needles with a
white felted crust, or inhabits coriaceous evergreen leaves. Another species
lives on fern leaves. The fruit is a discoid apothecium with a dark
carbonaceous hypothecium and proper margin, and with a second thalline
margin. The paraphyses are branched and interwoven above.
Spores elongate, 3-septate, colourless 1. Pilocarpon Wain.
XXV. Chrysotrichaceae
Page 405
This family now, according to Hue[1047], includes two genera, Crocynia
and Chrysothrix. In both there is a thallus of interlaced hyphae with
Protococcaceous algae scattered through it or in groups. The structure is
thus homoiomerous, and Hue has suggested for it a new series,
“Intertextae.” The only British species, Crocynia lanuginosa, first placed by
Nylander[1048] in Amphiloma and later transferred by him to
Leproloma[1049], has a soft crustaceous lobate thallus, furfuraceous on the
surface; no fructification has been found. A West Indian species, C.
gossypina, has discoid apothecia with a thalline margin. There is only one
species of Chrysothrix, Ch. nolitangere, which forms small clumps or tufts
on the spines of Cactus in Chili. The structure is somewhat similar to that of
Crocynia.
Spores colourless, simple 1. Crocynia Nyl.
Spores colourless, 2-3-septate 2. *Chrysothrix Mont.
XXVI. Thelotremaceae
A tropical or subtropical family of which the leading characteristic is the
deeply sunk disc of the apothecium: it has a proper hyphal margin, and,
round that, an overarching thalline margin. The apothecia occur singly, or
they are united in a kind of pseudostroma: in Tremotylium several grow
together, while in Polystroma each new apothecium develops as an
outgrowth from the thalline margin of the one already formed, so that an
upright, branching succession of fruits is built up. It is a very unusual type
of lichen fructification, with one species, P. Ferdinandezii, found in Spain
and in Guiana.
The thallus in all the genera is crustaceous with an amorphous
(decomposed) cortex; or it is non-corticate. The algal cells are Trentepohlia
except in Phyllophthalmaria, an epiphyllous genus associated with the alga
Phycopeltis. In Polystroma the alga is unknown.
Only one genus is represented in the British Isles.
Apothecia growing singly.
Thallus with Trentepohlia gonidia.
and Chrysothrix. In both there is a thallus of interlaced hyphae with
Protococcaceous algae scattered through it or in groups. The structure is
thus homoiomerous, and Hue has suggested for it a new series,
“Intertextae.” The only British species, Crocynia lanuginosa, first placed by
Nylander[1048] in Amphiloma and later transferred by him to
Leproloma[1049], has a soft crustaceous lobate thallus, furfuraceous on the
surface; no fructification has been found. A West Indian species, C.
gossypina, has discoid apothecia with a thalline margin. There is only one
species of Chrysothrix, Ch. nolitangere, which forms small clumps or tufts
on the spines of Cactus in Chili. The structure is somewhat similar to that of
Crocynia.
Spores colourless, simple 1. Crocynia Nyl.
Spores colourless, 2-3-septate 2. *Chrysothrix Mont.
XXVI. Thelotremaceae
A tropical or subtropical family of which the leading characteristic is the
deeply sunk disc of the apothecium: it has a proper hyphal margin, and,
round that, an overarching thalline margin. The apothecia occur singly, or
they are united in a kind of pseudostroma: in Tremotylium several grow
together, while in Polystroma each new apothecium develops as an
outgrowth from the thalline margin of the one already formed, so that an
upright, branching succession of fruits is built up. It is a very unusual type
of lichen fructification, with one species, P. Ferdinandezii, found in Spain
and in Guiana.
The thallus in all the genera is crustaceous with an amorphous
(decomposed) cortex; or it is non-corticate. The algal cells are Trentepohlia
except in Phyllophthalmaria, an epiphyllous genus associated with the alga
Phycopeltis. In Polystroma the alga is unknown.
Only one genus is represented in the British Isles.
Apothecia growing singly.
Thallus with Trentepohlia gonidia.
Page 406
Paraphyses numerous, unbranched,
free.
Spores colourless.
Spores elongate, 2- or multi- 1. *Ocellularia Spreng.
septate
Spores muriform 2. Thelotrema Ach.
Spores brown.
Spores elongate, septate 3. *Phaeotrema Müll.-Arg.
Spores muriform 4. *Leptotrema Mont.
Paraphyses scanty, branched.
Spores muriform, brown 5. *Gyrostomum Fr.
Thallus with Phycopeltis gonidia 6. *Phyllophthalmaria A.
Zahlbr.
Apothecia in pseudostromata.
Apothecia united in tubercles 7. *Tremotylium Nyl.
Apothecia united by the margins 8. *Polystroma Clem.
XXVII. Diploschistaceae
Scarcely differing from the preceding family except in the gonidia which
are Protococcaceous algae. The thallus is crustaceous and non-corticate.
The apothecia have a double margin but the outer thalline margin is less
overarching than in Thelotremaceae. The spores in the two genera are
somewhat peculiar: in Conotrema they are exceedingly long and divided by
parallel septa into thirty to forty small cells; in Diploschistes (Urceolaria)
they are large, muriform and brown. Conotrema contains two corticolous
species; Diploschistes about thirty species mostly saxicolous. Both genera
are represented in the British Isles.
Spores elongate, multi-septate, colourless 1. Conotrema Tuck.
Spores muriform, brown 2. Diploschistes Norm.
XXVIII. Ectolechiaceae
A family of tropical epiphyllous lichens that are associated with
Protococcaceous gonidia. The thallus is primitive in character, mostly a
free.
Spores colourless.
Spores elongate, 2- or multi- 1. *Ocellularia Spreng.
septate
Spores muriform 2. Thelotrema Ach.
Spores brown.
Spores elongate, septate 3. *Phaeotrema Müll.-Arg.
Spores muriform 4. *Leptotrema Mont.
Paraphyses scanty, branched.
Spores muriform, brown 5. *Gyrostomum Fr.
Thallus with Phycopeltis gonidia 6. *Phyllophthalmaria A.
Zahlbr.
Apothecia in pseudostromata.
Apothecia united in tubercles 7. *Tremotylium Nyl.
Apothecia united by the margins 8. *Polystroma Clem.
XXVII. Diploschistaceae
Scarcely differing from the preceding family except in the gonidia which
are Protococcaceous algae. The thallus is crustaceous and non-corticate.
The apothecia have a double margin but the outer thalline margin is less
overarching than in Thelotremaceae. The spores in the two genera are
somewhat peculiar: in Conotrema they are exceedingly long and divided by
parallel septa into thirty to forty small cells; in Diploschistes (Urceolaria)
they are large, muriform and brown. Conotrema contains two corticolous
species; Diploschistes about thirty species mostly saxicolous. Both genera
are represented in the British Isles.
Spores elongate, multi-septate, colourless 1. Conotrema Tuck.
Spores muriform, brown 2. Diploschistes Norm.
XXVIII. Ectolechiaceae
A family of tropical epiphyllous lichens that are associated with
Protococcaceous gonidia. The thallus is primitive in character, mostly a
Page 407
weft of hyphae with intermingled algal cells, described as homoiomerous.
The apothecia are without a thalline margin, and with a scarcely
developed proper margin: their affinity is with the Lecideaceae, though in
two genera, Lecaniella and Arthotheliopsis, there are gonidia below the
hypothecium, a character of Lecanoraceae. The genera are nearly all
monotypic; in Sporopodium has been included Lecidea phyllocharis Wainio
(Sect. Gonothecium), which is distinguished by hymenial gonidia.
Apothecia at first covered by a “veil.”
Spores elongate, colourless, septate 1. *Asterothyrium Müll.-
Arg.
Apothecia uncovered from the first.
Gonidia not present below the
hypothecium.
Paraphyses unbranched, free.
Spores muriform 2. *Lopadiopsis Wain.
Paraphyses branched.
Spores 1-septate 3. *Actinoplaca Müll.-Arg.
Spores elongate, multi-septate 4. *Tapellaria Müll.-Arg.
Spores muriform 5. *Sporopodium Mont.
Gonidia present below the hypothecium.
Spores elongate, 2-septate 6. *Lecaniella Wain.
Spores muriform 7. *Arthotheliopsis Wain.
XXIX. Gyalectaceae
The algal cells in this family are filamentous; either Myxophyceae
(Scytonema) or Chlorophyceae (Trentepohlia or Phyllactidium). The thallus
is crustaceous, and in some cases homoiomerous, as in Petractis, where the
alga, Scytonema, penetrates the substratum as deeply as the hyphae.
Monophiale, a tropical genus, possesses two kinds of gonidia: the species
that grow on bark or mosses are associated with Trentepohlia; others that
have invaded the surface of leathery evergreen leaves resemble most
epiphyllous lichens in being associated with the leaf alga Phyllactidium
(Phycopeltis). Some species of Trentepohlia exhale when moist an odour of
violets. This scent is retained in at least one genus, Jonaspis.
The apothecia are without a thalline margin, and with a scarcely
developed proper margin: their affinity is with the Lecideaceae, though in
two genera, Lecaniella and Arthotheliopsis, there are gonidia below the
hypothecium, a character of Lecanoraceae. The genera are nearly all
monotypic; in Sporopodium has been included Lecidea phyllocharis Wainio
(Sect. Gonothecium), which is distinguished by hymenial gonidia.
Apothecia at first covered by a “veil.”
Spores elongate, colourless, septate 1. *Asterothyrium Müll.-
Arg.
Apothecia uncovered from the first.
Gonidia not present below the
hypothecium.
Paraphyses unbranched, free.
Spores muriform 2. *Lopadiopsis Wain.
Paraphyses branched.
Spores 1-septate 3. *Actinoplaca Müll.-Arg.
Spores elongate, multi-septate 4. *Tapellaria Müll.-Arg.
Spores muriform 5. *Sporopodium Mont.
Gonidia present below the hypothecium.
Spores elongate, 2-septate 6. *Lecaniella Wain.
Spores muriform 7. *Arthotheliopsis Wain.
XXIX. Gyalectaceae
The algal cells in this family are filamentous; either Myxophyceae
(Scytonema) or Chlorophyceae (Trentepohlia or Phyllactidium). The thallus
is crustaceous, and in some cases homoiomerous, as in Petractis, where the
alga, Scytonema, penetrates the substratum as deeply as the hyphae.
Monophiale, a tropical genus, possesses two kinds of gonidia: the species
that grow on bark or mosses are associated with Trentepohlia; others that
have invaded the surface of leathery evergreen leaves resemble most
epiphyllous lichens in being associated with the leaf alga Phyllactidium
(Phycopeltis). Some species of Trentepohlia exhale when moist an odour of
violets. This scent is retained in at least one genus, Jonaspis.
Page 408
The apothecia are superficial, and are soft, waxy and bright-coloured,
with prominent margins which are however entirely hyphal: the affinity is
therefore with Lecideaceae. In one genus, Sagiolechia, the fruit is
carbonaceous and dark coloured. The spores of all the genera are colourless.
Apothecia waxy, bright-coloured.
Thallus with Scytonema gonidia.
Spores elongate, 3-septate 1. Petractis Fr.
Thallus with Trentepholia gonidia.
Asci 6-8-spored.
Spores simple 2. Jonaspis Th. Fr.
Spores 1-septate 3. *Microphiale A.
Zahlbr.
Spores septate or muriform 4. Gyalecta Ach.
Asci 12-many-spored.
Spores 1-septate 5. *Ramonia Stizenb.
Spores fusiform or acicular, many- 6. Pachyphiale Lönnr.
septate
Apothecia carbonaceous.
Spores elongate, 2-3-septate 7. *Sagiolechia Massal.
XXX. Coenogoniaceae
There are only two genera in this small family, Coenogonium with
Trentepohlia gonidia, and Racodium with Cladophora. Both genera follow
the algal form and are filamentous. In Coenogonium the filaments are
sometimes matted into a loose felted expansion. The genus is mainly
tropical or subtropical and mostly rather light-coloured. There is only one
British species, C. ebeneum[1050], a sterile form, in which the hyphae are
very dark-brown; it often covers large areas of stone or rock with its sooty-
like creeping filaments.
Racodium includes 2 (?) species. One of these, R. rupestre, is sterile and
resembles C. ebeneum in form and colour.
The apothecia of Coenogonium are waxy and light-coloured; they are
borne laterally on the filaments; the spores are simple or 1-septate.
with prominent margins which are however entirely hyphal: the affinity is
therefore with Lecideaceae. In one genus, Sagiolechia, the fruit is
carbonaceous and dark coloured. The spores of all the genera are colourless.
Apothecia waxy, bright-coloured.
Thallus with Scytonema gonidia.
Spores elongate, 3-septate 1. Petractis Fr.
Thallus with Trentepholia gonidia.
Asci 6-8-spored.
Spores simple 2. Jonaspis Th. Fr.
Spores 1-septate 3. *Microphiale A.
Zahlbr.
Spores septate or muriform 4. Gyalecta Ach.
Asci 12-many-spored.
Spores 1-septate 5. *Ramonia Stizenb.
Spores fusiform or acicular, many- 6. Pachyphiale Lönnr.
septate
Apothecia carbonaceous.
Spores elongate, 2-3-septate 7. *Sagiolechia Massal.
XXX. Coenogoniaceae
There are only two genera in this small family, Coenogonium with
Trentepohlia gonidia, and Racodium with Cladophora. Both genera follow
the algal form and are filamentous. In Coenogonium the filaments are
sometimes matted into a loose felted expansion. The genus is mainly
tropical or subtropical and mostly rather light-coloured. There is only one
British species, C. ebeneum[1050], a sterile form, in which the hyphae are
very dark-brown; it often covers large areas of stone or rock with its sooty-
like creeping filaments.
Racodium includes 2 (?) species. One of these, R. rupestre, is sterile and
resembles C. ebeneum in form and colour.
The apothecia of Coenogonium are waxy and light-coloured; they are
borne laterally on the filaments; the spores are simple or 1-septate.
Page 409
Thallus with Trentepohlia gonidia 1. Coenogonium Ehrenb.
Thallus with Cladophora gonidia 2. Racodium Fr.
XXXI. Lecideaceae
One of the largest lichen families as regards both genera and species, and
of world-wide distribution. The algal cells are Protococcaceae. The thallus
is mostly crustaceous but it becomes squamulose in Psora, a section of
Lecidea; and in Sphaerophoropsis, a Brazilian genus, there are small
upright fronds or stalks with lateral apothecia. The prevailing colour of the
thallus is some shade of grey, but it ranges from white or yellow to dark-
brown or almost black. Cephalodia appear in some of the species.
The apothecia have a proper margin only, no gonidia taking part in the
fruit-formation. They may be soft and waxy (biatorine) or hard and
carbonaceous (lecideine). The genera are mainly based on spore characters
which are very varied.
The arrangement of genera given below follows that of Zahlbruckner; in
several instances, both as to the limitations of genera and to the
nomenclature, it differs from that of British text-books, though the general
principle of classification is the same.
Thallus crustaceous non-corticate.
Spores simple.
Spores small, thin-walled.
Spores colourless 1. Lecidea Ach.
Spores brown 2. *Orphniospora Koerb.
Spores large, thick-walled 3. Mycoblastus Norm.
Spores 1-septate.
Spores small, thin-walled 4. Catillaria Th. Fr.
Spores large, thick-walled 5. Megalospora Mey. and
Flot.
Spores elongate, 3-multi-septate.
Spores elongate, narrow, thin-walled 6. Bacidia A. Zahlbr.
Spores elongate, large and thick- 7. Bombyliospora De Not.
walled
Thallus with Cladophora gonidia 2. Racodium Fr.
XXXI. Lecideaceae
One of the largest lichen families as regards both genera and species, and
of world-wide distribution. The algal cells are Protococcaceae. The thallus
is mostly crustaceous but it becomes squamulose in Psora, a section of
Lecidea; and in Sphaerophoropsis, a Brazilian genus, there are small
upright fronds or stalks with lateral apothecia. The prevailing colour of the
thallus is some shade of grey, but it ranges from white or yellow to dark-
brown or almost black. Cephalodia appear in some of the species.
The apothecia have a proper margin only, no gonidia taking part in the
fruit-formation. They may be soft and waxy (biatorine) or hard and
carbonaceous (lecideine). The genera are mainly based on spore characters
which are very varied.
The arrangement of genera given below follows that of Zahlbruckner; in
several instances, both as to the limitations of genera and to the
nomenclature, it differs from that of British text-books, though the general
principle of classification is the same.
Thallus crustaceous non-corticate.
Spores simple.
Spores small, thin-walled.
Spores colourless 1. Lecidea Ach.
Spores brown 2. *Orphniospora Koerb.
Spores large, thick-walled 3. Mycoblastus Norm.
Spores 1-septate.
Spores small, thin-walled 4. Catillaria Th. Fr.
Spores large, thick-walled 5. Megalospora Mey. and
Flot.
Spores elongate, 3-multi-septate.
Spores elongate, narrow, thin-walled 6. Bacidia A. Zahlbr.
Spores elongate, large and thick- 7. Bombyliospora De Not.
walled
Page 410
Spores muriform.
Spores colourless; on trees 8. Lopadium Koerb.
Spores colourless to brown; on rocks 9. Rhizocarpon Th. Kr.
Thallus warted or squamulose, corticate.
Spores elongate, 1-7-septate, thin- 10. Toninia Th. Fr.
walled
Thallus of upright podetia-like small
fronds.
Spores ellipsoid, becoming 1-septate 11. *Sphaerophoropsis Wain.
XXXII. Phyllopsoraceae
A small family of exotic lichens with a somewhat more developed thallus
than that of the Lecideaceae, being in both of the genera squamulose or
almost foliose.
The apothecia are without a thalline margin; they are biatorine or
lecideine; the hypothecium is formed of plectenchyma and is purple-red in
one species, Phyllopsora furfuracca. The two genera differ only in spore
characters. There are fifteen species, mostly corticolous, belonging to
Phyllopsora; only one, from New Zealand, is recorded for Psorella.
Spores simple 1. *Phyllopsora Müll.-Arg.
Spores elongate, septate 2. *Psorella Müll.-Arg.
XXXIII. Cladoniaceae
Associated with Lecideaceae in the type of apothecium, but differing
widely in thallus formation. The latter is of a twofold type: the primary
thallus is crustaceous, squamulose, or very rarely foliose; the secondary
thallus or podetium, upright, simple or branched, is terminated by the
apothecia, or broadens upwards to cup-like scyphi. Algal cells,
Protococcaceae, according to Chodat, Cystococcus.
Much attention has been given to the origin and development of the
podetia in this family. They are superficial on granule or squamule except in
the monotypic Himalayan genus Gymnoderma where they are marginal on
Spores colourless; on trees 8. Lopadium Koerb.
Spores colourless to brown; on rocks 9. Rhizocarpon Th. Kr.
Thallus warted or squamulose, corticate.
Spores elongate, 1-7-septate, thin- 10. Toninia Th. Fr.
walled
Thallus of upright podetia-like small
fronds.
Spores ellipsoid, becoming 1-septate 11. *Sphaerophoropsis Wain.
XXXII. Phyllopsoraceae
A small family of exotic lichens with a somewhat more developed thallus
than that of the Lecideaceae, being in both of the genera squamulose or
almost foliose.
The apothecia are without a thalline margin; they are biatorine or
lecideine; the hypothecium is formed of plectenchyma and is purple-red in
one species, Phyllopsora furfuracca. The two genera differ only in spore
characters. There are fifteen species, mostly corticolous, belonging to
Phyllopsora; only one, from New Zealand, is recorded for Psorella.
Spores simple 1. *Phyllopsora Müll.-Arg.
Spores elongate, septate 2. *Psorella Müll.-Arg.
XXXIII. Cladoniaceae
Associated with Lecideaceae in the type of apothecium, but differing
widely in thallus formation. The latter is of a twofold type: the primary
thallus is crustaceous, squamulose, or very rarely foliose; the secondary
thallus or podetium, upright, simple or branched, is terminated by the
apothecia, or broadens upwards to cup-like scyphi. Algal cells,
Protococcaceae, according to Chodat, Cystococcus.
Much attention has been given to the origin and development of the
podetia in this family. They are superficial on granule or squamule except in
the monotypic Himalayan genus Gymnoderma where they are marginal on
Page 411
the large leaf-like lobes. Though in origin the podetia are doubtless fruit
stalks, they have become in most cases vegetative in function.
The fruits are coloured yellowish, brown or red (or dark and
carbonaceous in Pilophorus), and are borne on the tips of the branches or
on the margins of the scyphi. In Glossodium and Thysanothecium—the
former from New Granada, the latter from Australia—the apothecia occupy
one side of the widened surface at the tips.
Cephalodia are developed on the primary thallus of Pilophorus, and on
the podetia of Stereocaulon and Argopsis.
Podetia simple, short, not widening
upwards.
Podetial stalks naked.
Primary thallus thin, continuous 1. Gomphillus Nyl.
Primary thallus granular or 2. Baeomyces Pers.
squamulose
Primary thallus foliose.
Podetia superficial 3. *Heteromyces Müll.-Arg.
Podetia marginal 4. *Gymnoderma[1051] Nyl.
Podetial stalks granular, squamulose 5. Pilophorus Th. Fr.
Podetia short, widening upwards.
Podetia simple above, rarely 6. *Glossodium Nyl.
divided
Podetia lobed, leaf-like 7. *Thysanothecium Berk. &
Mont.
Podetia elongate, variously branched, or 8. Cladonia Hill.
scyphous and hollow
Podetia elongate, not scyphous, the stalks
solid.
Spores elongate, septate 9. Stereocaulon Schreb.
Spores muriform 10. *Argopsis Th. Fr.
XXXIV. Gyrophoraceae
stalks, they have become in most cases vegetative in function.
The fruits are coloured yellowish, brown or red (or dark and
carbonaceous in Pilophorus), and are borne on the tips of the branches or
on the margins of the scyphi. In Glossodium and Thysanothecium—the
former from New Granada, the latter from Australia—the apothecia occupy
one side of the widened surface at the tips.
Cephalodia are developed on the primary thallus of Pilophorus, and on
the podetia of Stereocaulon and Argopsis.
Podetia simple, short, not widening
upwards.
Podetial stalks naked.
Primary thallus thin, continuous 1. Gomphillus Nyl.
Primary thallus granular or 2. Baeomyces Pers.
squamulose
Primary thallus foliose.
Podetia superficial 3. *Heteromyces Müll.-Arg.
Podetia marginal 4. *Gymnoderma[1051] Nyl.
Podetial stalks granular, squamulose 5. Pilophorus Th. Fr.
Podetia short, widening upwards.
Podetia simple above, rarely 6. *Glossodium Nyl.
divided
Podetia lobed, leaf-like 7. *Thysanothecium Berk. &
Mont.
Podetia elongate, variously branched, or 8. Cladonia Hill.
scyphous and hollow
Podetia elongate, not scyphous, the stalks
solid.
Spores elongate, septate 9. Stereocaulon Schreb.
Spores muriform 10. *Argopsis Th. Fr.
XXXIV. Gyrophoraceae
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A small family of foliose lichens allied to Lecideaceae by the character of
the fruit—a superficial apothecium in the formation of which the gonidia
take no share. There are only three genera, distinguished by differences in
spore and other characters. Dermatiscum has light-coloured thallus and
fruits; of the two species, one occurs in Central Europe, the other in North
America. Umbilicaria and Gyrophora are British; they are dark-coloured
rock-lichens and are extremely abundant in Northern regions where they are
known as “tripe de roche.” Algal cells Protococcaceae.
Umbilicaria, Dermatiscum, and some species of Gyrophora are attached
to the substratum by a central point. Other species of Gyrophora are
rhizinose. In all there is a cortex of plectenchyma above and below. In
Gyrophora the thallus may be monophyllous as in Umbilicaria, or
polyphyllous and with or without rhizinae. New lobes frequently arise from
protuberances or warts on the older parts of the thallus. At the periphery, in
most species, growth is equal along the margins, in G. erosa[1052] the edge
is formed of numerous anastomosing lobes with lateral branching, the
whole forming a broadly meshed open network. Further back the tissues
become continuous owing to the active growth of the lower tissue or
hypothallus, which grows out from all sides and meets across the opening.
The overlying layers, with gonidia, follow more slowly, but they also in
time become continuous, so that the “erose” character persists only near the
periphery. This forward growth of the lower thallus occurs in other species,
though to a much less marked degree.
There is abundant detritus formation in this family; the outer layers of the
cortex are continually being sloughed, the dead tissues lying on the upper
surface as a dark gelatinous layer, continuous or in small patches. On the
under surface the cast-off cortex gathers into a loose confused mass of dead
tissues.
Asci 8-spored.
Spores mostly simple (disc gyrose) 1. Gyrophora Ach.
Spores 1-septate 2. *Dermatiscum Nyl.
Asci 1-2-spored.
Spores muriform 3. Umbilicaria Hoffm.
XXXV. Acarosporaceae
the fruit—a superficial apothecium in the formation of which the gonidia
take no share. There are only three genera, distinguished by differences in
spore and other characters. Dermatiscum has light-coloured thallus and
fruits; of the two species, one occurs in Central Europe, the other in North
America. Umbilicaria and Gyrophora are British; they are dark-coloured
rock-lichens and are extremely abundant in Northern regions where they are
known as “tripe de roche.” Algal cells Protococcaceae.
Umbilicaria, Dermatiscum, and some species of Gyrophora are attached
to the substratum by a central point. Other species of Gyrophora are
rhizinose. In all there is a cortex of plectenchyma above and below. In
Gyrophora the thallus may be monophyllous as in Umbilicaria, or
polyphyllous and with or without rhizinae. New lobes frequently arise from
protuberances or warts on the older parts of the thallus. At the periphery, in
most species, growth is equal along the margins, in G. erosa[1052] the edge
is formed of numerous anastomosing lobes with lateral branching, the
whole forming a broadly meshed open network. Further back the tissues
become continuous owing to the active growth of the lower tissue or
hypothallus, which grows out from all sides and meets across the opening.
The overlying layers, with gonidia, follow more slowly, but they also in
time become continuous, so that the “erose” character persists only near the
periphery. This forward growth of the lower thallus occurs in other species,
though to a much less marked degree.
There is abundant detritus formation in this family; the outer layers of the
cortex are continually being sloughed, the dead tissues lying on the upper
surface as a dark gelatinous layer, continuous or in small patches. On the
under surface the cast-off cortex gathers into a loose confused mass of dead
tissues.
Asci 8-spored.
Spores mostly simple (disc gyrose) 1. Gyrophora Ach.
Spores 1-septate 2. *Dermatiscum Nyl.
Asci 1-2-spored.
Spores muriform 3. Umbilicaria Hoffm.
XXXV. Acarosporaceae
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Thallus foliose, squamulose or crustaceous, sometimes scarcely
developed. Algal cells Protococcaceae.
Into this family Zahlbruckner has gathered the genera in which the asci
are many-spored, as he considers that a character of great importance in
determining relationship, but he has in doing so overlooked other very great
differences. The fruit-bodies are round and completely enclosed in a thalline
wall in Thelocarpon, which has however no perithecial wall. They have a
proper margin only (lecideine) in Biatorella, and a thalline margin
(lecanorine) in the remaining genera. In Acarospora the apothecia are sunk
in the thallus. Stirton’s genus Cryptothecia[1053] is allied to Thelocarpon in
the fruit-formation, but the basal thallus is well developed and the spores
are few in number and variously divided.
Thallus none.
Apothecia (or perithecia) in thalline warts 1. Thelocarpon Nyl.
Thallus crustaceous.
Apothecia lecideine; spores simple 2. Biatorella Th. Fr.
Apothecia lecanorine; spores septate 3. *Maronea Massal.
Thallus of small squamules 4. Acarospora Massal.
Thallus almost foliose, attached centrally 5. *Glypholecia Nyl.
XXXVI. Ephebaceae
A family of very simple structure either filamentous, foliose or
crustaceous. The algal cells which give a dark colour to the thallus are
Stigonema or Scytonema, members of the blue-green Myxophyceae, and
consist of minute simple or branched filaments—single cell-rows in
Scytonema, compound in Stigonema.
In some of the genera the lichen hyphae travel within the gelatinous
sheath of the filaments, both algae and hyphae increasing by apical growth
so that filaments many times the length of the alga are formed as in Ephebe.
In others the filaments scarcely increase beyond the normal size of the alga
as in Thermutis (Gonionema); or the gelatinous algal cells may be
distributed in a stratum of hyphae.
developed. Algal cells Protococcaceae.
Into this family Zahlbruckner has gathered the genera in which the asci
are many-spored, as he considers that a character of great importance in
determining relationship, but he has in doing so overlooked other very great
differences. The fruit-bodies are round and completely enclosed in a thalline
wall in Thelocarpon, which has however no perithecial wall. They have a
proper margin only (lecideine) in Biatorella, and a thalline margin
(lecanorine) in the remaining genera. In Acarospora the apothecia are sunk
in the thallus. Stirton’s genus Cryptothecia[1053] is allied to Thelocarpon in
the fruit-formation, but the basal thallus is well developed and the spores
are few in number and variously divided.
Thallus none.
Apothecia (or perithecia) in thalline warts 1. Thelocarpon Nyl.
Thallus crustaceous.
Apothecia lecideine; spores simple 2. Biatorella Th. Fr.
Apothecia lecanorine; spores septate 3. *Maronea Massal.
Thallus of small squamules 4. Acarospora Massal.
Thallus almost foliose, attached centrally 5. *Glypholecia Nyl.
XXXVI. Ephebaceae
A family of very simple structure either filamentous, foliose or
crustaceous. The algal cells which give a dark colour to the thallus are
Stigonema or Scytonema, members of the blue-green Myxophyceae, and
consist of minute simple or branched filaments—single cell-rows in
Scytonema, compound in Stigonema.
In some of the genera the lichen hyphae travel within the gelatinous
sheath of the filaments, both algae and hyphae increasing by apical growth
so that filaments many times the length of the alga are formed as in Ephebe.
In others the filaments scarcely increase beyond the normal size of the alga
as in Thermutis (Gonionema); or the gelatinous algal cells may be
distributed in a stratum of hyphae.
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The apothecia are minute and almost closed; they may be embedded in
swellings of the thallus, or are more or less superficial. The spores are
rather small, colourless and simple or 1-septate.
The lichens of this family are rock-dwellers and are mostly to be found in
hilly or Alpine regions. A tropical species, Leptogidium dendriscum, occurs
in sterile condition in south-west Ireland. There are few species in any of
the genera.
Algal cells Scytonema.
Thallus minutely fruticose, non-corticate 1. Thermutis Fr.
Thallus minute, of felted filaments,
cortex one cell thick 2. *Leptodendriscum Wain.
Thallus of elongate filaments, cortex of
several cells 3. Leptogidium Nyl.
Thallus foliose or fruticose,
cellular throughout 4. Polychidium Ach.
Thallus crustaceous, non-corticate 5. Porocyphus Koerb.
Algal cells Stigonema.
Thallus minutely fruticose, non-corticate 6. Spilonema Born.
Thallus of long branching filaments.
Spores septate; paraphyses wanting 7. Ephebe Fr.
Spores simple; paraphyses present 8. Ephebeia Nyl.
Thallus crustaceous; upper surface
non-corticate, lower surface corticate 9. *Pterygiopsis Wain.
XXXVII. Pyrenopsidaceae
In this family are included gelatinous lichens of which the gonidium is a
blue-green alga with a thick gelatinous coat, either Gloeocapsa (including
Xanthocapsa) or Chroococcus. In Gloeocapsa and Chroococcus the
gelatinous envelope is often red, in Xanthocapsa it is yellow, and these
colours persist more or less in the lichens, especially in the outer layers.
The thallus is in many cases a formless gelatinous crust of hyphal
filaments mingling with colonies of algal cells as in Pyrenopsis; but small
fruticose tufts are characteristic of Synalissa, and larger foliose and
swellings of the thallus, or are more or less superficial. The spores are
rather small, colourless and simple or 1-septate.
The lichens of this family are rock-dwellers and are mostly to be found in
hilly or Alpine regions. A tropical species, Leptogidium dendriscum, occurs
in sterile condition in south-west Ireland. There are few species in any of
the genera.
Algal cells Scytonema.
Thallus minutely fruticose, non-corticate 1. Thermutis Fr.
Thallus minute, of felted filaments,
cortex one cell thick 2. *Leptodendriscum Wain.
Thallus of elongate filaments, cortex of
several cells 3. Leptogidium Nyl.
Thallus foliose or fruticose,
cellular throughout 4. Polychidium Ach.
Thallus crustaceous, non-corticate 5. Porocyphus Koerb.
Algal cells Stigonema.
Thallus minutely fruticose, non-corticate 6. Spilonema Born.
Thallus of long branching filaments.
Spores septate; paraphyses wanting 7. Ephebe Fr.
Spores simple; paraphyses present 8. Ephebeia Nyl.
Thallus crustaceous; upper surface
non-corticate, lower surface corticate 9. *Pterygiopsis Wain.
XXXVII. Pyrenopsidaceae
In this family are included gelatinous lichens of which the gonidium is a
blue-green alga with a thick gelatinous coat, either Gloeocapsa (including
Xanthocapsa) or Chroococcus. In Gloeocapsa and Chroococcus the
gelatinous envelope is often red, in Xanthocapsa it is yellow, and these
colours persist more or less in the lichens, especially in the outer layers.
The thallus is in many cases a formless gelatinous crust of hyphal
filaments mingling with colonies of algal cells as in Pyrenopsis; but small
fruticose tufts are characteristic of Synalissa, and larger foliose and
Page 415
fruticose thalli appear in some exotic genera. A plectenchymatous cortex is
formed on the thallus of Forssellia, a crustaceous genus from Central
Europe, with two species only; the whole thallus is built up of a kind of
plectenchyma in some others, but in most of the genera there is no tissue
formed.
The apothecia, as in Ephebaceae, are generally half-closed.
Thallus with Gloeocapsa gonidia.
Thallus crustaceous.
Spores simple 1. Pyrenopsis Nyl.
Spores 1-septate 2. *Cryptothele Forss.
Thallus shortly fruticose 3. Synalissa Fr.
Thallus lobate, centrally attached 4. *Phylliscidium Forss.
Thallus with Chroococcus gonidia.
Thallus crustaceous 5. Pyrenopsidium Forss.
Thallus lobate, centrally attached 6. *Phylliscum Nyl.
Thallus with Xanthocapsa gonidia.
Thallus crustaceous.
Thallus non-corticate.
Spores simple.
Apothecia open, asci 8-spored 7. Psorotichia Forss.
Apothecia covered, asci many- 8. *Gonohymenia Stein.
spored
Spores 1-septate.
Apothecia closed 9. *Collemopsidium Nyl.
Thallus with plectenchymatous cortex 10. *Forssellia A. Zahlbr.
Thallus lobate, centrally attached.
Spores simple.
Thallus plectenchymatous throughout 11. *Anema Nyl.
Thalline tissue of loose hyphae 12. *Thyrea Massal.
Cortex of upright parallel hyphae 13. *Jenmania Wächt.
Spores 1-septate.
Thalline tissue of loose hyphae 14. *Paulia Fée.
Thallus fruticose.
formed on the thallus of Forssellia, a crustaceous genus from Central
Europe, with two species only; the whole thallus is built up of a kind of
plectenchyma in some others, but in most of the genera there is no tissue
formed.
The apothecia, as in Ephebaceae, are generally half-closed.
Thallus with Gloeocapsa gonidia.
Thallus crustaceous.
Spores simple 1. Pyrenopsis Nyl.
Spores 1-septate 2. *Cryptothele Forss.
Thallus shortly fruticose 3. Synalissa Fr.
Thallus lobate, centrally attached 4. *Phylliscidium Forss.
Thallus with Chroococcus gonidia.
Thallus crustaceous 5. Pyrenopsidium Forss.
Thallus lobate, centrally attached 6. *Phylliscum Nyl.
Thallus with Xanthocapsa gonidia.
Thallus crustaceous.
Thallus non-corticate.
Spores simple.
Apothecia open, asci 8-spored 7. Psorotichia Forss.
Apothecia covered, asci many- 8. *Gonohymenia Stein.
spored
Spores 1-septate.
Apothecia closed 9. *Collemopsidium Nyl.
Thallus with plectenchymatous cortex 10. *Forssellia A. Zahlbr.
Thallus lobate, centrally attached.
Spores simple.
Thallus plectenchymatous throughout 11. *Anema Nyl.
Thalline tissue of loose hyphae 12. *Thyrea Massal.
Cortex of upright parallel hyphae 13. *Jenmania Wächt.
Spores 1-septate.
Thalline tissue of loose hyphae 14. *Paulia Fée.
Thallus fruticose.
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Thallus without a cortex 15. *Peccania Forss.
Thallus with cortex of parallel hyphae 16. *Phloeopeccania
Stein.
XXXVIII. Lichinaceae
The only family of lichens associated with Rivularia gonidia, the
trichomes of which retain their filamentous form to some extent in the more
highly developed genera; they lie parallel to the long axis of the squamule
or of the frond except in Lichinella in which genus they are vertical to the
surface. The thallus may be crustaceous, or minutely foliose, or fruticose; in
all cases it is dark-brown in colour, and the gelatinous character is evident
in the moist condition. The best known British genus is Lichina which
grows on rocks by the sea.
The apothecia are more or less immersed in the tissue; in Pterygium and
Steinera they are open and superficial (the latter monotypic genus confined
to Kerguelen). They are also open in Lichinella and Homopsella, both very
rare genera. The spores are colourless and simple except in Pterygium and
Steinera where they are elongate, and 1-3-septate.
Thallus crustaceous squamulose.
Apothecia immersed in thalline warts 1. *Calothricopsis
Wain.
Apothecia superficial, with thalline margin 2. *Steinera A. Zahlbr.
Apothecia superficial, without a thalline 3. Pterygium Nyl.
margin
Thallus of small fruticose fronds.
Gonidia occupying the central strand 4. *Lichinodium Nyl.
Gonidia not in the centre.
Apothecia immersed 5. Lichina Ag.
Apothecia superficial.
Paraphyses present 6. *Lichinella Nyl.
Paraphyses absent 7. *Homopsella Nyl.
XXXIX. Collemaceae
Thallus with cortex of parallel hyphae 16. *Phloeopeccania
Stein.
XXXVIII. Lichinaceae
The only family of lichens associated with Rivularia gonidia, the
trichomes of which retain their filamentous form to some extent in the more
highly developed genera; they lie parallel to the long axis of the squamule
or of the frond except in Lichinella in which genus they are vertical to the
surface. The thallus may be crustaceous, or minutely foliose, or fruticose; in
all cases it is dark-brown in colour, and the gelatinous character is evident
in the moist condition. The best known British genus is Lichina which
grows on rocks by the sea.
The apothecia are more or less immersed in the tissue; in Pterygium and
Steinera they are open and superficial (the latter monotypic genus confined
to Kerguelen). They are also open in Lichinella and Homopsella, both very
rare genera. The spores are colourless and simple except in Pterygium and
Steinera where they are elongate, and 1-3-septate.
Thallus crustaceous squamulose.
Apothecia immersed in thalline warts 1. *Calothricopsis
Wain.
Apothecia superficial, with thalline margin 2. *Steinera A. Zahlbr.
Apothecia superficial, without a thalline 3. Pterygium Nyl.
margin
Thallus of small fruticose fronds.
Gonidia occupying the central strand 4. *Lichinodium Nyl.
Gonidia not in the centre.
Apothecia immersed 5. Lichina Ag.
Apothecia superficial.
Paraphyses present 6. *Lichinella Nyl.
Paraphyses absent 7. *Homopsella Nyl.
XXXIX. Collemaceae
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The most important family of the gelatinous lichens and the most
numerous. Collema is historically interesting as having first suggested the
composite thallus. Algal cells, Nostoc, which retain the chain-like form
except in Leprocollema, a doubtful member of the family. The thallus varies
from indeterminate crusts to lobes of considerable size; occasionally the
lobes are narrow and erect, forming minute fruticose structures. In the more
primitive genera the thallus is non-corticate, but in the more evolved, the
apical cells of the hyphae coalesce to form a continuous cellular cortex, one
or more cells thick, well marked in some species, in others rudimentary; the
formation of plectenchyma also occurs occasionally in the apothecial
tissues of some non-corticate species.
The apothecia are superficial except in Pyrenocollema, a monotypic
genus of unknown locality. They are generally lecanorine, with gonidia
entering into the formation of the apothecium: in some genera they are
lecideine or biatorine, being formed of hyphae alone. The spores are
colourless and vary in form, size and septation.
Apothecia immersed; spores fusiform, 1- 1. *Pyrenocollema
septate Reinke.
Apothecia superficial.
Thallus without a cortex.
Spores simple, globose or ellipsoid.
Thallus crustaceous 2. *Leprocollema Wain.
Thallus largely squamulose-fruticose.
Apothecia lecideine (dark-coloured) 3. *Leciophysma Th. Fr.
Apothecia lecanorine 4. Physma Massal.
Spores variously septate or muriform.
Apothecia biatorine (light-coloured) 5. *Homothecium Mont.
Apothecia lecanorine 6. Collema Wigg.
Thallus with cortex of plectenchyma.
Spores simple.
Spores globose 7. Lemmopsis A. Zahlbr.
Spores ellipsoid, with thick 8. *Dichodium Nyl.
subverrucose wall
Spores vermiform, spirally curved 9. *Koerberia Massal.
numerous. Collema is historically interesting as having first suggested the
composite thallus. Algal cells, Nostoc, which retain the chain-like form
except in Leprocollema, a doubtful member of the family. The thallus varies
from indeterminate crusts to lobes of considerable size; occasionally the
lobes are narrow and erect, forming minute fruticose structures. In the more
primitive genera the thallus is non-corticate, but in the more evolved, the
apical cells of the hyphae coalesce to form a continuous cellular cortex, one
or more cells thick, well marked in some species, in others rudimentary; the
formation of plectenchyma also occurs occasionally in the apothecial
tissues of some non-corticate species.
The apothecia are superficial except in Pyrenocollema, a monotypic
genus of unknown locality. They are generally lecanorine, with gonidia
entering into the formation of the apothecium: in some genera they are
lecideine or biatorine, being formed of hyphae alone. The spores are
colourless and vary in form, size and septation.
Apothecia immersed; spores fusiform, 1- 1. *Pyrenocollema
septate Reinke.
Apothecia superficial.
Thallus without a cortex.
Spores simple, globose or ellipsoid.
Thallus crustaceous 2. *Leprocollema Wain.
Thallus largely squamulose-fruticose.
Apothecia lecideine (dark-coloured) 3. *Leciophysma Th. Fr.
Apothecia lecanorine 4. Physma Massal.
Spores variously septate or muriform.
Apothecia biatorine (light-coloured) 5. *Homothecium Mont.
Apothecia lecanorine 6. Collema Wigg.
Thallus with cortex of plectenchyma.
Spores simple.
Spores globose 7. Lemmopsis A. Zahlbr.
Spores ellipsoid, with thick 8. *Dichodium Nyl.
subverrucose wall
Spores vermiform, spirally curved 9. *Koerberia Massal.
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Spores variously septate or muriform.
Apothecia biatorine (light-coloured) 10. *Arctomia Th. Fr.
Apothecia lecanorine 11. Leptogium S. F. Gray.
XL. Heppiaceae
A family belonging to the “blue-green” series as it is associated with a
gelatinous alga, Scytonema, but is of almost entirely cellular structure and is
non-gelatinous. The thallus is squamulose or minutely foliose, or is formed
of narrow almost fruticose lobes; the apothecia are semi-immersed; the asci
are 4-many-spored.
Heppia is a wide-spread genus both in northern and tropical regions with
about forty species that live on soil or rock. So far, no representative has
been recorded in our Islands.
Spores simple, colourless, globose or ellipsoid 1. *Heppia Naeg.
Spores muriform, colourless, ellipsoid 2. *Amphidium[1054] Nyl.
XLI. Pannariaceae
The members of this family are also non-gelatinous, though for the most
part associated with blue-green gelatinous algae, Nostoc or Scytonema. The
gonidia are bright-green in the genera Psoroma and Psoromaria, the former
often included under Lecanora, but too closely resembling Pannaria to be
dissociated from that genus.
The thallus varies from being crustaceous to squamulose or foliose, and
has a cortex of plectenchyma on the upper and sometimes also on the lower
surface. The apothecia are superficial or lateral and with or without a
thalline margin (lecanorine or biatorine), the spores are colourless.
Zahlbruckner has included Hydrothyria in this family. It is a monotypic
aquatic genus found in North America and very closely allied to Peltigera.
The British species of the genus, familiarly known as Coccocarpia, have
been placed under Parmeliella, the former name being restricted to the
tropical or subtropical species first assigned to Coccocarpia and
Apothecia biatorine (light-coloured) 10. *Arctomia Th. Fr.
Apothecia lecanorine 11. Leptogium S. F. Gray.
XL. Heppiaceae
A family belonging to the “blue-green” series as it is associated with a
gelatinous alga, Scytonema, but is of almost entirely cellular structure and is
non-gelatinous. The thallus is squamulose or minutely foliose, or is formed
of narrow almost fruticose lobes; the apothecia are semi-immersed; the asci
are 4-many-spored.
Heppia is a wide-spread genus both in northern and tropical regions with
about forty species that live on soil or rock. So far, no representative has
been recorded in our Islands.
Spores simple, colourless, globose or ellipsoid 1. *Heppia Naeg.
Spores muriform, colourless, ellipsoid 2. *Amphidium[1054] Nyl.
XLI. Pannariaceae
The members of this family are also non-gelatinous, though for the most
part associated with blue-green gelatinous algae, Nostoc or Scytonema. The
gonidia are bright-green in the genera Psoroma and Psoromaria, the former
often included under Lecanora, but too closely resembling Pannaria to be
dissociated from that genus.
The thallus varies from being crustaceous to squamulose or foliose, and
has a cortex of plectenchyma on the upper and sometimes also on the lower
surface. The apothecia are superficial or lateral and with or without a
thalline margin (lecanorine or biatorine), the spores are colourless.
Zahlbruckner has included Hydrothyria in this family. It is a monotypic
aquatic genus found in North America and very closely allied to Peltigera.
The British species of the genus, familiarly known as Coccocarpia, have
been placed under Parmeliella, the former name being restricted to the
tropical or subtropical species first assigned to Coccocarpia and
Page 419
distinguished by the cortex, the hyphae forming it lying parallel with the
surface though forming a regular plectenchyma.
An Antarctic lichen Thelidea corrugata with Palmella gonidia is
doubtfully included: the thallus is foliose, the apothecia biatorine with
colourless 1-septate spores.
Thallus with bright-green gonidia.
With Palmella 1. *Thelidea Hue.
With Protococcaceae.
Apothecia non-marginate (biatorine) 2. *Psoromaria Nyl.
Apothecia marginate 3. Psoroma Nyl.
Thallus with Scytonema gonidia.
Apothecia marginate, spores 1-septate 4. Massalongia Koerb.
Apothecia non-marginate; spores simple.
Upper surface smooth 5. *Coccocarpia Pers.
Upper surface felted 6. *Erioderma Fée.
Thallus with Nostoc gonidia.
Apothecia marginate; spores simple 7. Pannaria Del.
Apothecia non-marginate; spores various.
Thallus crustaceous or minutely 8. Placynthium Ach.
squamulose
Thallus squamulose, cortex indistinct 9. *Lepidocollema
Wain.
Thallus squamulose or foliose, cortex 10. Parmeliella Müll.-
cellular Arg.
Thallus foliose, thin veined below 11. *Hydrothyria Russ.
XLII. Stictaceae
Thallus foliose, mostly horizontal, with a plectenchymatous cortex on
both surfaces, a tomentum of hair-like hyphae taking the place of rhizinae
on the lower surface. Algal cells Protococcaceae or Nostoc. Cephalodia and
cyphellae or pseudocyphellae often present. Apothecia superficial or lateral;
spores colourless or brown, variously septate.
surface though forming a regular plectenchyma.
An Antarctic lichen Thelidea corrugata with Palmella gonidia is
doubtfully included: the thallus is foliose, the apothecia biatorine with
colourless 1-septate spores.
Thallus with bright-green gonidia.
With Palmella 1. *Thelidea Hue.
With Protococcaceae.
Apothecia non-marginate (biatorine) 2. *Psoromaria Nyl.
Apothecia marginate 3. Psoroma Nyl.
Thallus with Scytonema gonidia.
Apothecia marginate, spores 1-septate 4. Massalongia Koerb.
Apothecia non-marginate; spores simple.
Upper surface smooth 5. *Coccocarpia Pers.
Upper surface felted 6. *Erioderma Fée.
Thallus with Nostoc gonidia.
Apothecia marginate; spores simple 7. Pannaria Del.
Apothecia non-marginate; spores various.
Thallus crustaceous or minutely 8. Placynthium Ach.
squamulose
Thallus squamulose, cortex indistinct 9. *Lepidocollema
Wain.
Thallus squamulose or foliose, cortex 10. Parmeliella Müll.-
cellular Arg.
Thallus foliose, thin veined below 11. *Hydrothyria Russ.
XLII. Stictaceae
Thallus foliose, mostly horizontal, with a plectenchymatous cortex on
both surfaces, a tomentum of hair-like hyphae taking the place of rhizinae
on the lower surface. Algal cells Protococcaceae or Nostoc. Cephalodia and
cyphellae or pseudocyphellae often present. Apothecia superficial or lateral;
spores colourless or brown, variously septate.
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The highly organized cortex and the presence of aeration organs—
cyphellae or pseudocyphellae—which are almost solely confined to the
genus Sticta give this family a high position as regards vegetative
development. The two genera are of wide distribution, but Sticta is more
abundant in the Southern Hemisphere. Lobaria pulmonaria is one of our
largest lichens.
Under surface dotted with cyphellae or 1. Sticta Schreb.
pseudocyphellae
Under surface without these organs 2. Lobaria
Schreb.
XLIII. Peltigeraceae
A family of heteromerous foliose lichens containing in some instances
blue-green (Nostoc), in others bright-green (Protococcaceae) gonidia, and
thus representing a transition between these two series. They have large or
small lobes and grow on the ground or on trees.
Cephalodia, either ectotrophic (Peltidea) or endotrophic (Solorina), occur
in the family and further exemplify the capacity of the fungus hyphae to
combine with different types of algae.
The upper surface is a wide cortex of plectenchyma, which in some
forms (Nephromium) is continued below. In the non-corticate under surface
of Peltigera, the lower hyphae grow out in hairs or rhizinae, very frequently
brown in colour. Intercalary growth of the upper tissues stretches the thallus
and tears apart the lower under surface so that the hair-bearing areas
become a network of veins, with the white exposed medulla between. In
Peltigera canina there is further growth and branching of the hyphae in the
veins, adding to the bulk of the interlacing ridges.
From all other foliose lichens Peltigeraceae are distinguished by the flat
wholly appressed or peltate apothecia without a thalline margin which arise
mostly on the upper surface, but in Nephromium on the extreme margin of
the under surface, the tip of the fertile lobe in that case is turned back as the
apothecium matures, so that the fruit eventually faces the light. In
Nephroma has been included Eunephroma with bright-green gonidia and
Nephromium with blue-green.
cyphellae or pseudocyphellae—which are almost solely confined to the
genus Sticta give this family a high position as regards vegetative
development. The two genera are of wide distribution, but Sticta is more
abundant in the Southern Hemisphere. Lobaria pulmonaria is one of our
largest lichens.
Under surface dotted with cyphellae or 1. Sticta Schreb.
pseudocyphellae
Under surface without these organs 2. Lobaria
Schreb.
XLIII. Peltigeraceae
A family of heteromerous foliose lichens containing in some instances
blue-green (Nostoc), in others bright-green (Protococcaceae) gonidia, and
thus representing a transition between these two series. They have large or
small lobes and grow on the ground or on trees.
Cephalodia, either ectotrophic (Peltidea) or endotrophic (Solorina), occur
in the family and further exemplify the capacity of the fungus hyphae to
combine with different types of algae.
The upper surface is a wide cortex of plectenchyma, which in some
forms (Nephromium) is continued below. In the non-corticate under surface
of Peltigera, the lower hyphae grow out in hairs or rhizinae, very frequently
brown in colour. Intercalary growth of the upper tissues stretches the thallus
and tears apart the lower under surface so that the hair-bearing areas
become a network of veins, with the white exposed medulla between. In
Peltigera canina there is further growth and branching of the hyphae in the
veins, adding to the bulk of the interlacing ridges.
From all other foliose lichens Peltigeraceae are distinguished by the flat
wholly appressed or peltate apothecia without a thalline margin which arise
mostly on the upper surface, but in Nephromium on the extreme margin of
the under surface, the tip of the fertile lobe in that case is turned back as the
apothecium matures, so that the fruit eventually faces the light. In
Nephroma has been included Eunephroma with bright-green gonidia and
Nephromium with blue-green.
Page 421
Bitter[1055] has recorded the finding of apothecia on the under surface of
Peltigera malacea and not at the margin, as in Nephromium. The plant was
otherwise normal and healthy. Solorinella, from Central Europe and
Asteristion from Ceylon are monotypic genera with poorly developed thalli.
Thallus poorly developed.
Asci 6-8-spored; spores 3-5-septate 1. *Asteristion Leight.
Asci many-spored; spores 1-septate 2. *Solorinella Anzi.
Thallus generally well developed.
Apothecia superficial, sunk in the thallus 3. Solorina Ach.
Apothecia terminal on upper surface of lobes 4. Peltigera Willd.
Apothecia terminal on lower surface of lobes 5. Nephroma Ach.
XLIV. Pertusariaceae
Thallus crustaceous, often rather thick and with an amorphous cortex on
the upper surface. Algal cells Protococcaceae. Apothecia solitary or several
immersed in thalline warts, generally with a narrow opening which barely
exposes the disc, and which in one genus, Perforaria, is so small as almost
to constitute a perithecium; spores are often very large and with thick walls;
some if not all are multinucleate and germinate at many points.
In the form of the fruit, this family stands between Pyrenocarpeae and
Gymnocarpeae, though more akin to the latter. Perforaria, with two
species, belongs to New Zealand and Japan. Pertusaria has a world-wide
distribution, and Varicellaria, a monotypic genus, with a very large two-
celled spore, is an Alpine plant, recorded from Europe and from Antarctic
America.
Spores simple.
Apothecia with pore-like opening 1. *Perforaria Müll.-Arg.
Apothecia with a wider opening 2. Pertusaria DC.
Spores 1-septate 3. Varicellaria Nyl.
XLV. Lecanoraceae
Peltigera malacea and not at the margin, as in Nephromium. The plant was
otherwise normal and healthy. Solorinella, from Central Europe and
Asteristion from Ceylon are monotypic genera with poorly developed thalli.
Thallus poorly developed.
Asci 6-8-spored; spores 3-5-septate 1. *Asteristion Leight.
Asci many-spored; spores 1-septate 2. *Solorinella Anzi.
Thallus generally well developed.
Apothecia superficial, sunk in the thallus 3. Solorina Ach.
Apothecia terminal on upper surface of lobes 4. Peltigera Willd.
Apothecia terminal on lower surface of lobes 5. Nephroma Ach.
XLIV. Pertusariaceae
Thallus crustaceous, often rather thick and with an amorphous cortex on
the upper surface. Algal cells Protococcaceae. Apothecia solitary or several
immersed in thalline warts, generally with a narrow opening which barely
exposes the disc, and which in one genus, Perforaria, is so small as almost
to constitute a perithecium; spores are often very large and with thick walls;
some if not all are multinucleate and germinate at many points.
In the form of the fruit, this family stands between Pyrenocarpeae and
Gymnocarpeae, though more akin to the latter. Perforaria, with two
species, belongs to New Zealand and Japan. Pertusaria has a world-wide
distribution, and Varicellaria, a monotypic genus, with a very large two-
celled spore, is an Alpine plant, recorded from Europe and from Antarctic
America.
Spores simple.
Apothecia with pore-like opening 1. *Perforaria Müll.-Arg.
Apothecia with a wider opening 2. Pertusaria DC.
Spores 1-septate 3. Varicellaria Nyl.
XLV. Lecanoraceae
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Thallus mostly crustaceous, occasionally squamulose or very rarely
minutely fruticulose. The squamulose thallus is corticate above, the under
surface appressed and attached to the substratum by penetrating hyphae,
often effigurate at the circumference. Algal cells Protococcaceae. Apothecia
well distinguished by the thalline margin; spores colourless, simple or
variously septate or muriform.
Lecanora, Ochrolechia, Lecania, Haematomma and Phlyctis are
cosmopolitan genera, some of them with a very large number of species; the
other genera are more restricted in distribution and generally with few
species.
The genus Candelariella is of uncertain position; the spores are 8 or
many in the ascus and are simple or 1-septate, and not unfrequently become
polarilocular as in Caloplacaceae, but there is no parietin present.
Algae distributed through the thallus. Spores 1. *Harpidium Koerb.
simple
Algae restricted to a definite zone.
Spores simple.
Thallus grey, white or yellowish.
Spores rather small 2. Lecanora Ach.
Spores large 3. Ochrolechia Massal.
Thallus bright yellow.
Spores simple or 1-septate 4. Candelariella Müll.-
Arg.
Spores 1-septate (rarely pluri-septate).
Paraphyses free.
Thallus squamulose, effigurate 5. Placolecania Zahlbr.
Thallus crustaceous.
Apothecial disc brownish 6. Lecania Zahlbr.
Apothecial disc flesh-coloured 7. Icmadophila Trevis.
Paraphyses branched, intricate 8. *Calenia Müll.-Arg.
Spores elongate, pluri-septate.
Apothecia superficial 9. Haematomma Massal.
Apothecia immersed.
Paraphyses free 10. *Phlyctella Müll.-Arg.
minutely fruticulose. The squamulose thallus is corticate above, the under
surface appressed and attached to the substratum by penetrating hyphae,
often effigurate at the circumference. Algal cells Protococcaceae. Apothecia
well distinguished by the thalline margin; spores colourless, simple or
variously septate or muriform.
Lecanora, Ochrolechia, Lecania, Haematomma and Phlyctis are
cosmopolitan genera, some of them with a very large number of species; the
other genera are more restricted in distribution and generally with few
species.
The genus Candelariella is of uncertain position; the spores are 8 or
many in the ascus and are simple or 1-septate, and not unfrequently become
polarilocular as in Caloplacaceae, but there is no parietin present.
Algae distributed through the thallus. Spores 1. *Harpidium Koerb.
simple
Algae restricted to a definite zone.
Spores simple.
Thallus grey, white or yellowish.
Spores rather small 2. Lecanora Ach.
Spores large 3. Ochrolechia Massal.
Thallus bright yellow.
Spores simple or 1-septate 4. Candelariella Müll.-
Arg.
Spores 1-septate (rarely pluri-septate).
Paraphyses free.
Thallus squamulose, effigurate 5. Placolecania Zahlbr.
Thallus crustaceous.
Apothecial disc brownish 6. Lecania Zahlbr.
Apothecial disc flesh-coloured 7. Icmadophila Trevis.
Paraphyses branched, intricate 8. *Calenia Müll.-Arg.
Spores elongate, pluri-septate.
Apothecia superficial 9. Haematomma Massal.
Apothecia immersed.
Paraphyses free 10. *Phlyctella Müll.-Arg.
Page 423
Paraphyses branched, intricate 11. *Phlyctidia Müll.-Arg.
Spores muriform.
Apothecia superficial 12. *Myxodictyon
Massal.
Apothecia immersed 13. Phlyctis Wallr.
XLVI. Parmeliaceae
A very familiar family of foliose lichens. Genera and species are
dorsiventral and stratose in structure, though some Cetrariae are fruticose
in habit. Algal cells are Protococcaceae; in Physcidia they are Palmellae. In
every case the upper surface of the thallus is corticate and generally of
plectenchyma, the lower being somewhat similar, but in Heterodea and
Physcidia, monotypic Australasian genera, the upper cortex is of branching
hyphae parallel with the surface, the lower surface being non-corticate.
The Parmeliae are mostly provided with abundant rhizinae; in Cetrariae
and Nephromopsis these are very sparingly present, while in Anzia
(including Pannoparmelia) the medulla passes into a wide net-like structure
of anastomosing hyphae.
In Heterodea, cyphellae occur on the under surface as in Stictaceae; and
in Cetraria islandica bare patches have been described as pseudocyphellae.
The latter lichen is one of the few that are of value as human food. Special
aeration structures are present on the upper cortex of Parmelia aspidota.
Thallus non-corticate below.
Apothecia terminal 1. *Heterodea Nyl.
Apothecia superficial 2. *Physcidia Tuck.
Thallus spongy below 3. *Anzia Stizenb.
Thallus corticate below.
Asci poly-spored 4. Candelaria Massal.
Asci 8-spored.
Spermatia acrogenous 5. Parmeliopsis Nyl.
Spermatia pleurogenous.
Apothecia superficial 6. Parmelia Ach.
Apothecia lateral.
Spores muriform.
Apothecia superficial 12. *Myxodictyon
Massal.
Apothecia immersed 13. Phlyctis Wallr.
XLVI. Parmeliaceae
A very familiar family of foliose lichens. Genera and species are
dorsiventral and stratose in structure, though some Cetrariae are fruticose
in habit. Algal cells are Protococcaceae; in Physcidia they are Palmellae. In
every case the upper surface of the thallus is corticate and generally of
plectenchyma, the lower being somewhat similar, but in Heterodea and
Physcidia, monotypic Australasian genera, the upper cortex is of branching
hyphae parallel with the surface, the lower surface being non-corticate.
The Parmeliae are mostly provided with abundant rhizinae; in Cetrariae
and Nephromopsis these are very sparingly present, while in Anzia
(including Pannoparmelia) the medulla passes into a wide net-like structure
of anastomosing hyphae.
In Heterodea, cyphellae occur on the under surface as in Stictaceae; and
in Cetraria islandica bare patches have been described as pseudocyphellae.
The latter lichen is one of the few that are of value as human food. Special
aeration structures are present on the upper cortex of Parmelia aspidota.
Thallus non-corticate below.
Apothecia terminal 1. *Heterodea Nyl.
Apothecia superficial 2. *Physcidia Tuck.
Thallus spongy below 3. *Anzia Stizenb.
Thallus corticate below.
Asci poly-spored 4. Candelaria Massal.
Asci 8-spored.
Spermatia acrogenous 5. Parmeliopsis Nyl.
Spermatia pleurogenous.
Apothecia superficial 6. Parmelia Ach.
Apothecia lateral.
Page 424
Apothecia on upper surface 7. Cetraria Ach.
Apothecia on lower surface 8. *Nephromopsis Müll.-Arg.
XLVII. Usneaceae
This also is a familiar family of lichens, Usnea barbata the “bearded
moss” being one of the first lichens noted and chronicled. Algal cells
Protococcaceae. Structure radiate, the upright or pendulous habit
characteristic of the family securing all-round illumination. Special
adaptations of the cortex or of the internal tissues have been evolved to
strengthen the thallus against the strains incidental to their habit of growth
as they are attached in nearly all cases by one point only, by a special
sheath, or by penetrating hold-fasts.
Apothecia are superficial or marginal and sometimes shortly stalked;
spores are simple or variously septate.
Ramalina and Usnea, the most numerous, are cosmopolitan genera;
Alectoria inhabits northern or hilly regions.
The genus Evernia, also cosmopolitan, represents a transition between
foliose and fruticose types; the fronds of the two species, though strap-
shaped and generally upright, are dorsiventral and stratose, the gonidia for
the most part lying beneath one surface; the other (lower) surface is either
white or very dark-coloured. Everniopsis, formed of thin branching strap-
shaped fronds, is also dorsiventral.
A number of genera, Thamnolia, Siphula, etc. are of podetia-like
structure, generally growing in swards. Several of them have been classified
with Cladoniae, but they lack the double thallus. One of these, Endocena, a
sterile monotypic Patagonian lichen, with stiff hollow coralloid fronds, was
classified by Hue[1056] along with Siphula; recently he has transferred it to
his family Polycaulionaceae[1057] based on Polycauliona regale (Placodium
frustulosum Darbish.), and allied to Placodium Sect. Thamnoma[1058]. In
recent studies Hue has laid most stress on thalline characters. He places the
new family between “Ramalinaceae” and “Alectoriaceae.” Dactylina
arctica is a common Arctic soil-lichen.
Thallus strap-shaped.
Apothecia on lower surface 8. *Nephromopsis Müll.-Arg.
XLVII. Usneaceae
This also is a familiar family of lichens, Usnea barbata the “bearded
moss” being one of the first lichens noted and chronicled. Algal cells
Protococcaceae. Structure radiate, the upright or pendulous habit
characteristic of the family securing all-round illumination. Special
adaptations of the cortex or of the internal tissues have been evolved to
strengthen the thallus against the strains incidental to their habit of growth
as they are attached in nearly all cases by one point only, by a special
sheath, or by penetrating hold-fasts.
Apothecia are superficial or marginal and sometimes shortly stalked;
spores are simple or variously septate.
Ramalina and Usnea, the most numerous, are cosmopolitan genera;
Alectoria inhabits northern or hilly regions.
The genus Evernia, also cosmopolitan, represents a transition between
foliose and fruticose types; the fronds of the two species, though strap-
shaped and generally upright, are dorsiventral and stratose, the gonidia for
the most part lying beneath one surface; the other (lower) surface is either
white or very dark-coloured. Everniopsis, formed of thin branching strap-
shaped fronds, is also dorsiventral.
A number of genera, Thamnolia, Siphula, etc. are of podetia-like
structure, generally growing in swards. Several of them have been classified
with Cladoniae, but they lack the double thallus. One of these, Endocena, a
sterile monotypic Patagonian lichen, with stiff hollow coralloid fronds, was
classified by Hue[1056] along with Siphula; recently he has transferred it to
his family Polycaulionaceae[1057] based on Polycauliona regale (Placodium
frustulosum Darbish.), and allied to Placodium Sect. Thamnoma[1058]. In
recent studies Hue has laid most stress on thalline characters. He places the
new family between “Ramalinaceae” and “Alectoriaceae.” Dactylina
arctica is a common Arctic soil-lichen.
Thallus strap-shaped.
Page 425
Structure dorsiventral.
Greyish-green above 1. Evernia Ach.
Whitish-yellow above 2. *Everniopsis Nyl.
Structure radiate alike on both surfaces.
Fronds grey; medulla of loose hyphae 3. Ramalina Ach.
Fronds yellow; medulla traversed by 4. *Letharia A. Zahlbr.
strands
Thallus filamentous.
Medulla a strong “chondroid” strand 5. Usnea Dill.
Medulla of loose hyphae.
Spores simple 6. Alectoria Ach.
Spores muriform, brown 7. *Oropogon Fr.
Thallus of upright podetia-like fronds.
Fronds rather long (about two inches), 8. Thamnolia Ach.
tapering, white (Cerania S. F.
Gray).
Fronds shorter, blunt.
Medulla solid 9. *Siphula Fr.
Medulla partly or entirely hollow.
Fronds swollen and tall (about two 10. *Dactylina Nyl.
inches)
Fronds coralloid, entangled 11. *Endocena Cromb.
Fronds short, upright 12. *Dufourea Nyl.
XLVIII. Caloplacaceae
In this family Zahlbruckner has included the squamulose or crustaceous
lichens with colourless polarilocular spores, relegating those with more
highly developed thallus or with brown spores to other families. He has also
substituted the name Caloplaca for the older Placodium, the latter being, as
he considers, less well defined.
Algal cells are Protococcaceae. The thallus is mostly light-coloured,
generally some shade of yellow, and, with few exceptions, contains parietin,
which gives a purple colour on the application of potash. The squamulose
forms are closely appressed to the substratum, and have often a definite
Greyish-green above 1. Evernia Ach.
Whitish-yellow above 2. *Everniopsis Nyl.
Structure radiate alike on both surfaces.
Fronds grey; medulla of loose hyphae 3. Ramalina Ach.
Fronds yellow; medulla traversed by 4. *Letharia A. Zahlbr.
strands
Thallus filamentous.
Medulla a strong “chondroid” strand 5. Usnea Dill.
Medulla of loose hyphae.
Spores simple 6. Alectoria Ach.
Spores muriform, brown 7. *Oropogon Fr.
Thallus of upright podetia-like fronds.
Fronds rather long (about two inches), 8. Thamnolia Ach.
tapering, white (Cerania S. F.
Gray).
Fronds shorter, blunt.
Medulla solid 9. *Siphula Fr.
Medulla partly or entirely hollow.
Fronds swollen and tall (about two 10. *Dactylina Nyl.
inches)
Fronds coralloid, entangled 11. *Endocena Cromb.
Fronds short, upright 12. *Dufourea Nyl.
XLVIII. Caloplacaceae
In this family Zahlbruckner has included the squamulose or crustaceous
lichens with colourless polarilocular spores, relegating those with more
highly developed thallus or with brown spores to other families. He has also
substituted the name Caloplaca for the older Placodium, the latter being, as
he considers, less well defined.
Algal cells are Protococcaceae. The thallus is mostly light-coloured,
generally some shade of yellow, and, with few exceptions, contains parietin,
which gives a purple colour on the application of potash. The squamulose
forms are closely appressed to the substratum, and have often a definite
Page 426
rounded outline (effigurate). The spores have a thick median septum with a
loculus at each end and a connecting canal[1059].
In Blastenia the outer thalline margin is obscure or absent—though
gonidia are frequently present below the hymenium. Caloplacaceae occur
all over the globe; they are among the most brilliantly coloured of all
lichens. Polycauliona Hue[1060] possibly belongs here: though based on
thalline rather than on spore characters, one species at least has
polarilocular spores.
Apothecia with a distinct thalline margin 1. Caloplaca Th. Fr.
Apothecia without a thalline margin 2. Blastenia Th. Fr.
XLIX. Teloschistaceae
Polarilocular colourless spores are the distinguishing feature of this
family as of the Caloplacaceae. Algal cells Protococcaceae. The thallus of
Teloschistaceae is more highly developed, being either foliose or fruticose,
though never attaining to very large dimensions. The cortex of Xanthoria
(foliose) is plectenchymatous, that of Teloschistes (fruticose) is fibrous. The
species of both genera are yellow or greenish-yellow due to the presence of
the lichen-acid parietin.
Both genera have a wide distribution over the globe, more especially in
maritime regions.
Thallus foliose 1. Xanthoria Th. Fr.
Thallus fruticose 2. Teloschistes Norm.
L. Buelliaceae
A family of crustaceous lichens distinguished by the brown two-celled
spores. Algal cells Protococcaceae. Zahlbruckner has included here Buellia
and Rinodina; the former with a distinctly lecideine fruit and with thinly
septate spores; the latter lecanorine and with spores of the polarilocular
type, with a very wide central septum pierced in most of the species by a
canal which may or may not traverse the middle lamella of the wall.
loculus at each end and a connecting canal[1059].
In Blastenia the outer thalline margin is obscure or absent—though
gonidia are frequently present below the hymenium. Caloplacaceae occur
all over the globe; they are among the most brilliantly coloured of all
lichens. Polycauliona Hue[1060] possibly belongs here: though based on
thalline rather than on spore characters, one species at least has
polarilocular spores.
Apothecia with a distinct thalline margin 1. Caloplaca Th. Fr.
Apothecia without a thalline margin 2. Blastenia Th. Fr.
XLIX. Teloschistaceae
Polarilocular colourless spores are the distinguishing feature of this
family as of the Caloplacaceae. Algal cells Protococcaceae. The thallus of
Teloschistaceae is more highly developed, being either foliose or fruticose,
though never attaining to very large dimensions. The cortex of Xanthoria
(foliose) is plectenchymatous, that of Teloschistes (fruticose) is fibrous. The
species of both genera are yellow or greenish-yellow due to the presence of
the lichen-acid parietin.
Both genera have a wide distribution over the globe, more especially in
maritime regions.
Thallus foliose 1. Xanthoria Th. Fr.
Thallus fruticose 2. Teloschistes Norm.
L. Buelliaceae
A family of crustaceous lichens distinguished by the brown two-celled
spores. Algal cells Protococcaceae. Zahlbruckner has included here Buellia
and Rinodina; the former with a distinctly lecideine fruit and with thinly
septate spores; the latter lecanorine and with spores of the polarilocular
type, with a very wide central septum pierced in most of the species by a
canal which may or may not traverse the middle lamella of the wall.
Page 427
Rinodina is closely allied to Physciaceae, while Buellia has more affinity
with Lecideaceae and is near to Rhizocarpon.
Both genera are of world-wide distribution.
Apothecia lecideine, without a thalline margin 1. Buellia De Not.
Apothecia lecanorine, with a thalline margin 2. Rinodina Massal.
LI. Physciaceae
Thallus foliose or partly fruticose, and generally attached by rhizinae.
Algal cells Protococcaceae. The spores resemble those of Rinodina, dark-
coloured with a thick septum and reduced cell-lumina. As in that species
there may be a second septum in each cell, giving a 3-septate spore; but that
is rare.
Pyxine, a tropical or subtropical genus, is lecanorine only in the very
early stages; it soon loses the thalline margin. Anaptychia is differentiated
from Physcia by the subfruticose habit, though the species are nearly all
dorsiventral in structure, only a few of them being truly radiate and
corticate on both surfaces. The upper cortex of Anaptychia is fibrous, but
that character appears also in most species of Physcia either on the upper or
the lower side. Physcia and Anaptychia are widely distributed.
Thalline margin absent in apothecia 1. *Pyxine Nyl.
Thalline margin present in apothecia.
Thallus foliose 2. Physcia Schreb.
Thallus fruticose 3. Anaptychia Koerb.
C. *Hymenolichens
Fungus a Basidiomycete, akin to Thelephora. Algal cells Scytonema or
Chroococcus. Thallus crustaceous, squamulose or foliose. Spores
colourless, produced on basidia, on the under surface of the free thallus.
The Hymenolichens[1061] are few in number and are endemic in tropical
or warm countries. They inhabit soil or trees.
with Lecideaceae and is near to Rhizocarpon.
Both genera are of world-wide distribution.
Apothecia lecideine, without a thalline margin 1. Buellia De Not.
Apothecia lecanorine, with a thalline margin 2. Rinodina Massal.
LI. Physciaceae
Thallus foliose or partly fruticose, and generally attached by rhizinae.
Algal cells Protococcaceae. The spores resemble those of Rinodina, dark-
coloured with a thick septum and reduced cell-lumina. As in that species
there may be a second septum in each cell, giving a 3-septate spore; but that
is rare.
Pyxine, a tropical or subtropical genus, is lecanorine only in the very
early stages; it soon loses the thalline margin. Anaptychia is differentiated
from Physcia by the subfruticose habit, though the species are nearly all
dorsiventral in structure, only a few of them being truly radiate and
corticate on both surfaces. The upper cortex of Anaptychia is fibrous, but
that character appears also in most species of Physcia either on the upper or
the lower side. Physcia and Anaptychia are widely distributed.
Thalline margin absent in apothecia 1. *Pyxine Nyl.
Thalline margin present in apothecia.
Thallus foliose 2. Physcia Schreb.
Thallus fruticose 3. Anaptychia Koerb.
C. *Hymenolichens
Fungus a Basidiomycete, akin to Thelephora. Algal cells Scytonema or
Chroococcus. Thallus crustaceous, squamulose or foliose. Spores
colourless, produced on basidia, on the under surface of the free thallus.
The Hymenolichens[1061] are few in number and are endemic in tropical
or warm countries. They inhabit soil or trees.
Page 428
Thallus of extended lobes.
Gonidia near the upper surface 1. *Dictyonema Zahlbr.
Gonidia in centre of tissue 2. *Cora Fr.
Thallus squamulose, irregular 3. *Corella Wain.
II. NUMBER AND DISTRIBUTION OF LICHENS
1. ESTIMATES OF NUMBER
Calculations have been made and published, once and again, as to the
number of lichen species occurring over the globe or in definite areas. In
1898 Fünfstück stated that about 20,000 different species had been
described, but as many of them had been proved to be synonyms, and since
many must rank as forms or varieties, the number of well-authenticated
species did not then, according to his estimate, exceed 4000. Many
additional genera and species have, however, been discovered since then. In
Engler and Prantl’s Pflanzenfamilien, over 50 families and nearly 300
genera find a place, but even in these larger groupings opinions differ as to
the limits both of genera and families, and lichenologists would not all
accept the arrangement given in that volume.
Fünfstück has reckoned that of his estimated 4000, about 1500 are
European and of these at least 1200 occur in Germany. Probably this is too
low an estimate for that large country. Leighton in 1879 listed, in his British
Lichen Flora, 1710 in all, and, as the compilation includes varieties, it
cannot be considered as very far astray. On comparing it with Olivier’s[1062]
recent statistics of lichens, we find that of the larger fruticose and foliose
species, 310 are recognized by him for the whole of Europe, 206 of these
occurring in the British Isles. Leighton’s estimate of similar species is about
145, without including varieties now reckoned as good species. In a more
circumscribed area, Th. Fries[1063] described for Spitzbergen about 210
different lichens, a number that closely approximates to the 206 recent
records by Darbishire[1064] for the same area.
A general idea of the comparative numbers of the different types of
lichens may be gathered from Hue’s compilation of exotic lichens[1065],
examined or described by Nylander, and now in the Paris herbarium. There
Gonidia near the upper surface 1. *Dictyonema Zahlbr.
Gonidia in centre of tissue 2. *Cora Fr.
Thallus squamulose, irregular 3. *Corella Wain.
II. NUMBER AND DISTRIBUTION OF LICHENS
1. ESTIMATES OF NUMBER
Calculations have been made and published, once and again, as to the
number of lichen species occurring over the globe or in definite areas. In
1898 Fünfstück stated that about 20,000 different species had been
described, but as many of them had been proved to be synonyms, and since
many must rank as forms or varieties, the number of well-authenticated
species did not then, according to his estimate, exceed 4000. Many
additional genera and species have, however, been discovered since then. In
Engler and Prantl’s Pflanzenfamilien, over 50 families and nearly 300
genera find a place, but even in these larger groupings opinions differ as to
the limits both of genera and families, and lichenologists would not all
accept the arrangement given in that volume.
Fünfstück has reckoned that of his estimated 4000, about 1500 are
European and of these at least 1200 occur in Germany. Probably this is too
low an estimate for that large country. Leighton in 1879 listed, in his British
Lichen Flora, 1710 in all, and, as the compilation includes varieties, it
cannot be considered as very far astray. On comparing it with Olivier’s[1062]
recent statistics of lichens, we find that of the larger fruticose and foliose
species, 310 are recognized by him for the whole of Europe, 206 of these
occurring in the British Isles. Leighton’s estimate of similar species is about
145, without including varieties now reckoned as good species. In a more
circumscribed area, Th. Fries[1063] described for Spitzbergen about 210
different lichens, a number that closely approximates to the 206 recent
records by Darbishire[1064] for the same area.
A general idea of the comparative numbers of the different types of
lichens may be gathered from Hue’s compilation of exotic lichens[1065],
examined or described by Nylander, and now in the Paris herbarium. There
Page 429
are 135 genera with 3686 species. Of these, about 829 belong to the larger
foliose and fruticose lichens (including Cladoniae); the remaining 2857
belong to the smaller kinds, most of them crustaceous.
2. GEOGRAPHICAL DISTRIBUTION
A. General Survey
The larger foliose and fruticose lichens are now fairly well known and
described for Europe, and the knowledge of lichens in other continents is
gradually increasing. It is the smaller crustaceous forms that baffle the
investigator. The distribution of all lichens over the surface of the earth is
controlled by two principal factors, climate and substratum; for although
lichens as a rule require only support, they are most of them restricted to
one or another particular substratum, either organic or inorganic. As
organisms which develop slowly, they require an unchanging substratum,
and as sun-plants they avoid deeply shaded woodlands: their occurrence
thus depends to a large extent on the configuration and general vegetation
of the country.
Though so numerous and so widely distributed, lichens have not evolved
that great variety of families and genera characteristic of the allied fungi
and algae. They conform to a few leading types of structure, and thus the
Orders and Families are comparatively few, and more or less universal.
They are most of them undoubtedly very old plants and were probably
wide-spread before continents and climates had attained their present
stability. Arnold[1066] indeed considers that a large part of the present-day
lichens were almost certainly already evolved at the end of the Tertiary
period, and that they originated in a warm or probably subtropical climate.
As proof of this he cites such genera as Graphis, Thelotrema and
Arthonia[1067] which are numerous in the tropics though rare in the colder
European countries; and he sees further proof in the fact that many fruticose
and gelatinous lichens do not occur further north than the forest belt, though
they are adapted to cold conditions. Several genera that are abundant in the
tropics are represented outside these regions by only one or few species, as
for instance Conotrema urceolatum and Bombyliospora incana.
foliose and fruticose lichens (including Cladoniae); the remaining 2857
belong to the smaller kinds, most of them crustaceous.
2. GEOGRAPHICAL DISTRIBUTION
A. General Survey
The larger foliose and fruticose lichens are now fairly well known and
described for Europe, and the knowledge of lichens in other continents is
gradually increasing. It is the smaller crustaceous forms that baffle the
investigator. The distribution of all lichens over the surface of the earth is
controlled by two principal factors, climate and substratum; for although
lichens as a rule require only support, they are most of them restricted to
one or another particular substratum, either organic or inorganic. As
organisms which develop slowly, they require an unchanging substratum,
and as sun-plants they avoid deeply shaded woodlands: their occurrence
thus depends to a large extent on the configuration and general vegetation
of the country.
Though so numerous and so widely distributed, lichens have not evolved
that great variety of families and genera characteristic of the allied fungi
and algae. They conform to a few leading types of structure, and thus the
Orders and Families are comparatively few, and more or less universal.
They are most of them undoubtedly very old plants and were probably
wide-spread before continents and climates had attained their present
stability. Arnold[1066] indeed considers that a large part of the present-day
lichens were almost certainly already evolved at the end of the Tertiary
period, and that they originated in a warm or probably subtropical climate.
As proof of this he cites such genera as Graphis, Thelotrema and
Arthonia[1067] which are numerous in the tropics though rare in the colder
European countries; and he sees further proof in the fact that many fruticose
and gelatinous lichens do not occur further north than the forest belt, though
they are adapted to cold conditions. Several genera that are abundant in the
tropics are represented outside these regions by only one or few species, as
for instance Conotrema urceolatum and Bombyliospora incana.
Page 430
During the Ice age of the Quaternary period, not many new species can
have arisen, and such forms as were not killed off must have been driven
towards the south. As the ice retreated the valleys were again stocked with
southern forms, and northern species were left behind on mountain tops all
over the globe.
In examining therefore the distribution of lichens, it will be found that the
distinction between different countries is relative, certain families being
more or less abundant in some regions than others, but, in general, nearly
all being represented. Certain species are universal, where similar
conditions prevail. This is especially true of those species adapted to
extreme cold, as that condition, normal in polar regions, recurs even on the
equator if the mountains reach the limit of perpetual snow; the vertical
distribution thus follows on the lines of the horizontal.
In all the temperate countries we find practically the same families, with
some few exceptions; there is naturally more diversity of genera and
species. Genera that are limited in locality consist, as a rule, of one or few
species. In this category, however, are not included the tropical families or
genera which may be very rich in species: these are adapted to extreme
conditions of heat and often of moisture, and cannot exist outside tropical or
subtropical regions, extreme heat being more restricted as to geographical
position than extreme cold.
In the study of distribution the question which arises as to the place of
origin of such widely distributed plants is one that is difficult to solve.
Wainio[1068] has attempted the task in regard to Cladonia, one of the most
unstable genera, the variations of form, which are dependent on external
circumstances, being numerous and often bewildering. In his fine
monograph of the genus, 132 species are described and 25 of these are
cosmopolitan.
The distribution of Phanerogams is connected, as Wainio points out, with
causes anterior to the present geological era, but this cannot be the case in a
genus so labile and probably so recent as Cladonia, though some of the
species have existed long enough to spread and establish themselves from
pole to pole. Endemic species, or those that are confined to a comparatively
limited area, are easily traced to their place of origin, that being generally
the locality where they are found in most abundance, and as a general rule
have arisen, and such forms as were not killed off must have been driven
towards the south. As the ice retreated the valleys were again stocked with
southern forms, and northern species were left behind on mountain tops all
over the globe.
In examining therefore the distribution of lichens, it will be found that the
distinction between different countries is relative, certain families being
more or less abundant in some regions than others, but, in general, nearly
all being represented. Certain species are universal, where similar
conditions prevail. This is especially true of those species adapted to
extreme cold, as that condition, normal in polar regions, recurs even on the
equator if the mountains reach the limit of perpetual snow; the vertical
distribution thus follows on the lines of the horizontal.
In all the temperate countries we find practically the same families, with
some few exceptions; there is naturally more diversity of genera and
species. Genera that are limited in locality consist, as a rule, of one or few
species. In this category, however, are not included the tropical families or
genera which may be very rich in species: these are adapted to extreme
conditions of heat and often of moisture, and cannot exist outside tropical or
subtropical regions, extreme heat being more restricted as to geographical
position than extreme cold.
In the study of distribution the question which arises as to the place of
origin of such widely distributed plants is one that is difficult to solve.
Wainio[1068] has attempted the task in regard to Cladonia, one of the most
unstable genera, the variations of form, which are dependent on external
circumstances, being numerous and often bewildering. In his fine
monograph of the genus, 132 species are described and 25 of these are
cosmopolitan.
The distribution of Phanerogams is connected, as Wainio points out, with
causes anterior to the present geological era, but this cannot be the case in a
genus so labile and probably so recent as Cladonia, though some of the
species have existed long enough to spread and establish themselves from
pole to pole. Endemic species, or those that are confined to a comparatively
limited area, are easily traced to their place of origin, that being generally
the locality where they are found in most abundance, and as a general rule
Page 431
in the centre of that area, though there may be exceptions: a plant for
instance that originated on a mountain would migrate only in one direction
—towards the regions of greater cold.
The difficulty of determining the primitive stations of cosmopolitan, or of
widely spread, species is much greater, but generally they also may be
referred to their area of greatest abundance. Thus a species may occur
frequently in one continent and but rarely in another, even where the
conditions of climate, etc., are largely comparable. It may therefore be
inferred that the plant has not yet reached the full extent of possible
distribution in the less frequented area. As examples of this, Wainio cites,
among other instances, Cladonia papillaria, which has a very wide
distribution in Europe, but, as yet, has been found only in the eastern parts
of North America; and Cl. pycnoclada, a plant which braves the climate of
Cape Horn and the Falkland Islands, but has not travelled northward
beyond temperate North America: the southern origin of that species is thus
plainly indicated. Wainio also finds that evidence of the primitive locality of
a very widely spread species may be obtained by observing the locality of
species derived from it, which are as yet of limited distribution; presumably
these arose in the ancestral place of origin, though this indication is not
always to be relied on. If, however, the ancestral plant has given rise to
several of these rarer related species, those of them that are most closely
allied to the primitive plant would be found near to it in the original locality.
A detailed account of species distribution according to these indications
is given by Wainio and is full of interest. No such attempt has been made to
deal with any other group, and the distribution of genera and species can
only be suggested. An exhaustive comparison of the lichens of different
regions is beyond the purpose of our study and is indeed impossible as,
except in some limited areas, or for certain species, the occurrence and
distribution are not fully known. It is in any case only tentatively that
genera or species can be described as local or rare, until diligent search has
been made for them over a wider field. The study of lichens from a floristic
point of view lags behind that of most other groups of plants. The larger
lichen forms have received more attention, as they are more evident and
more easily collected; but the more minute species are not easily detected,
and, as they are largely inseparable from their substratum of rocks, or trees,
etc., on which they grow, they are often difficult to collect. They are also in
instance that originated on a mountain would migrate only in one direction
—towards the regions of greater cold.
The difficulty of determining the primitive stations of cosmopolitan, or of
widely spread, species is much greater, but generally they also may be
referred to their area of greatest abundance. Thus a species may occur
frequently in one continent and but rarely in another, even where the
conditions of climate, etc., are largely comparable. It may therefore be
inferred that the plant has not yet reached the full extent of possible
distribution in the less frequented area. As examples of this, Wainio cites,
among other instances, Cladonia papillaria, which has a very wide
distribution in Europe, but, as yet, has been found only in the eastern parts
of North America; and Cl. pycnoclada, a plant which braves the climate of
Cape Horn and the Falkland Islands, but has not travelled northward
beyond temperate North America: the southern origin of that species is thus
plainly indicated. Wainio also finds that evidence of the primitive locality of
a very widely spread species may be obtained by observing the locality of
species derived from it, which are as yet of limited distribution; presumably
these arose in the ancestral place of origin, though this indication is not
always to be relied on. If, however, the ancestral plant has given rise to
several of these rarer related species, those of them that are most closely
allied to the primitive plant would be found near to it in the original locality.
A detailed account of species distribution according to these indications
is given by Wainio and is full of interest. No such attempt has been made to
deal with any other group, and the distribution of genera and species can
only be suggested. An exhaustive comparison of the lichens of different
regions is beyond the purpose of our study and is indeed impossible as,
except in some limited areas, or for certain species, the occurrence and
distribution are not fully known. It is in any case only tentatively that
genera or species can be described as local or rare, until diligent search has
been made for them over a wider field. The study of lichens from a floristic
point of view lags behind that of most other groups of plants. The larger
lichen forms have received more attention, as they are more evident and
more easily collected; but the more minute species are not easily detected,
and, as they are largely inseparable from their substratum of rocks, or trees,
etc., on which they grow, they are often difficult to collect. They are also in
Page 432
many instances so indefinite, or so alike in outward form, that they are
liable to be overlooked, only a microscopic examination revealing the
differences in fruit and vegetative structure.
Though much remains to be done, still enough is known to make the
geographical distribution of lichens a subject of extreme interest. It will be
found most instructive to follow the usual lines of treatment, which give the
three great divisions: the Polar, the Temperate and the Tropical regions of
the globe.
B. Lichens of Polar Regions
Strictly speaking, this section should include only lichens growing within
the Polar Circles; but in practice the lichens of the whole of Greenland and
those of Iceland are included in the Arctic series, as are those of Alaska: the
latitudinal line of demarcation is not closely adhered to. With the northern
lichens may also be considered those of the Antarctic continent, as well as
those of the islands just outside the Antarctic Circle, the South Shetlands,
South Orkneys, Tierra del Fuego, South Georgia and the Falkland Islands.
During the Glacial period, the polar forms must have spread with the
advancing cold; as the snow and ice retreated, these forms have been left, as
already stated, on the higher colder grounds, and representatives of polar
species are thus to be found very far from their original haunts. There are
few exclusively boreal genera: the same types occur at the Poles as in the
higher subtemperate zones. One of the most definitely polar species, for
instance, Usnea (Neuropogon) melaxantha grows in the whole Arctic zone,
and, in the Antarctic, is more luxuriant than any other lichen, but it has also
been recorded from the Andes in Chili, Bolivia and Peru, and from New
Zealand (South Island).
Cold winds are a great feature of both poles, and the lichens that by
structure or habit can withstand these are the most numerous; those that
have a stout cortical layer are able to resist the low temperatures, or those
that grow in tufts and thus secure mutual protection. In Arctic and Subarctic
regions, 495 lichens have been recorded, most of them crustaceous. Among
the larger forms the most frequently met are certain species of Peltigera,
Parmelia, Gyrophora, Cetraria, Cladonia, Stereocaulon and Alectoria.
Among smaller species Lecanora tartarea spreads everywhere, especially
liable to be overlooked, only a microscopic examination revealing the
differences in fruit and vegetative structure.
Though much remains to be done, still enough is known to make the
geographical distribution of lichens a subject of extreme interest. It will be
found most instructive to follow the usual lines of treatment, which give the
three great divisions: the Polar, the Temperate and the Tropical regions of
the globe.
B. Lichens of Polar Regions
Strictly speaking, this section should include only lichens growing within
the Polar Circles; but in practice the lichens of the whole of Greenland and
those of Iceland are included in the Arctic series, as are those of Alaska: the
latitudinal line of demarcation is not closely adhered to. With the northern
lichens may also be considered those of the Antarctic continent, as well as
those of the islands just outside the Antarctic Circle, the South Shetlands,
South Orkneys, Tierra del Fuego, South Georgia and the Falkland Islands.
During the Glacial period, the polar forms must have spread with the
advancing cold; as the snow and ice retreated, these forms have been left, as
already stated, on the higher colder grounds, and representatives of polar
species are thus to be found very far from their original haunts. There are
few exclusively boreal genera: the same types occur at the Poles as in the
higher subtemperate zones. One of the most definitely polar species, for
instance, Usnea (Neuropogon) melaxantha grows in the whole Arctic zone,
and, in the Antarctic, is more luxuriant than any other lichen, but it has also
been recorded from the Andes in Chili, Bolivia and Peru, and from New
Zealand (South Island).
Cold winds are a great feature of both poles, and the lichens that by
structure or habit can withstand these are the most numerous; those that
have a stout cortical layer are able to resist the low temperatures, or those
that grow in tufts and thus secure mutual protection. In Arctic and Subarctic
regions, 495 lichens have been recorded, most of them crustaceous. Among
the larger forms the most frequently met are certain species of Peltigera,
Parmelia, Gyrophora, Cetraria, Cladonia, Stereocaulon and Alectoria.
Among smaller species Lecanora tartarea spreads everywhere, especially
Page 433
over other vegetation, Lecanora varia reaches the farthest limits to which
wood, on which it grows, has drifted, and several species of Placodium
occur constantly, though not in such great abundance. Over the rocks spread
also many crustaceous Lecideaceae too numerous to mention, one of the
most striking being the cosmopolitan Rhizocarpon geographicum.
Wainio[1069] has described the lichens collected by Almquist at Pitlekai in
N.E. Siberia just on the borders of the Arctic Circle, and he gives a vivid
account of the general topography. The snow lies on the ground till June
and falls again in September, but many lichens succeed in growing and
fruiting. It is a region of tundra and sand, strewn more or less with stones.
Most of the sand is bare of all vegetation; but where mosses, etc., have
gained a footing, there are also a fair number of lichens: Lecanora tartarea,
Psoroma hypnorum, with Lecideae, Parmeliae, Cladoniae, Stereocaulon
alpinum, Solorina crocea, Sphaerophorus globosus, Alectoria nigricans and
Gyrophora proboscidea. Some granite rocks in that neighbourhood rise to a
height of 200 ft., and though bare of vegetation on the north side, yet, in
sheltered nooks, several species are to be found. Stunted bushes of willow
grow here and there, and on these occur always the same species:
Placodium ferrugineum, Rinodina archaea, Buellia myriocarpa and
Arthopyrenia punctiformis. Some species such as Sphaerophorus globosus,
Dactylina arctica (a purely Arctic genus and species) and Thamnolia
vermicularis are so abundant that they bulk as largely as other better
represented genera such as Cladoniae, Lecanorae or Lecideae. On the soil,
Lecanorae cover the largest areas.
Wainio determined a large number of lichens with many new species, but
the region is colder than that of Lappland, and trees with tree-lichens are
absent, with the exception of those given above. In Arctic Siberia,
Elenkin[1070] discovered a new lichen Placodium subfruticulosum which
scarcely differs from Darbishire’s[1071] Antarctic species Pl. fruticulosum
(or P. regale); both are distinguished by the fruticose growth of the thallus,
for which reason Hue[1072] placed them in a new genus, Polycauliona.
The Antarctic Zone and the neighbouring lands are less hospitable to
plant life than the northern regions, and there is practically no accumulation
of detritus. Collections have been made by explorers, and several lists have
been published which include a marvellous number of species common to
wood, on which it grows, has drifted, and several species of Placodium
occur constantly, though not in such great abundance. Over the rocks spread
also many crustaceous Lecideaceae too numerous to mention, one of the
most striking being the cosmopolitan Rhizocarpon geographicum.
Wainio[1069] has described the lichens collected by Almquist at Pitlekai in
N.E. Siberia just on the borders of the Arctic Circle, and he gives a vivid
account of the general topography. The snow lies on the ground till June
and falls again in September, but many lichens succeed in growing and
fruiting. It is a region of tundra and sand, strewn more or less with stones.
Most of the sand is bare of all vegetation; but where mosses, etc., have
gained a footing, there are also a fair number of lichens: Lecanora tartarea,
Psoroma hypnorum, with Lecideae, Parmeliae, Cladoniae, Stereocaulon
alpinum, Solorina crocea, Sphaerophorus globosus, Alectoria nigricans and
Gyrophora proboscidea. Some granite rocks in that neighbourhood rise to a
height of 200 ft., and though bare of vegetation on the north side, yet, in
sheltered nooks, several species are to be found. Stunted bushes of willow
grow here and there, and on these occur always the same species:
Placodium ferrugineum, Rinodina archaea, Buellia myriocarpa and
Arthopyrenia punctiformis. Some species such as Sphaerophorus globosus,
Dactylina arctica (a purely Arctic genus and species) and Thamnolia
vermicularis are so abundant that they bulk as largely as other better
represented genera such as Cladoniae, Lecanorae or Lecideae. On the soil,
Lecanorae cover the largest areas.
Wainio determined a large number of lichens with many new species, but
the region is colder than that of Lappland, and trees with tree-lichens are
absent, with the exception of those given above. In Arctic Siberia,
Elenkin[1070] discovered a new lichen Placodium subfruticulosum which
scarcely differs from Darbishire’s[1071] Antarctic species Pl. fruticulosum
(or P. regale); both are distinguished by the fruticose growth of the thallus,
for which reason Hue[1072] placed them in a new genus, Polycauliona.
The Antarctic Zone and the neighbouring lands are less hospitable to
plant life than the northern regions, and there is practically no accumulation
of detritus. Collections have been made by explorers, and several lists have
been published which include a marvellous number of species common to
Page 434
both Poles, if the subantarctic lands are included in the survey. An analytic
study of the various lists has been published by Darbishire[1073]. He
recognizes 106 true Antarctic lichens half of which are Arctic as well. The
greater number are crustaceous and are plants common also to other lands
though a certain number are endemic. The most abundant genera in species
as well as individuals are Lecidea and Lecanora. Several bright yellow
species of Placodium—Pl. elegans, Pl. murorum, etc., are there as at the
North Pole. Among the larger forms, Parmeliae, Cetrariae, and Cladoniae
are fairly numerous; Usneae and Ramalinae rather uncommon, while
members of the Stictaceae are much more abundant than in the North. The
common species of Peltigera also occur in Antarctica, though P. aphthosa
and P. venosa are wanting; both of these latter are boreal species. Darbishire
adds that lichens have so great a capacity to withstand cold, that they are
only checked by the snow covering, and were bare rocks to be found at the
South Pole, he is sure lichens would take possession of them. The most
southerly point at which any plant has been found is 78° South latitude and
162° East longitude, in which locality the lichen Lecanora subfusca was
collected by members of Scott’s Antarctic expedition (1901-1904) at a
height of 5000 ft.
A somewhat different view of the Antarctic lichen flora is indicated by
Hue[1072] in his account of the plants brought back by the second French
Antarctic Expedition. The collection was an extremely favourable and
important one: great blocks of stone with their communities of lichens were
secured, and these blocks were entirely covered, the crustaceous species,
especially, spreading over every inch of space.
Hue determined 126 species, but as 15 of these came from the Magellan
regions only 111 were truly Antarctic. Of these 90 are new species, 29 of
them belonging to the genus Buellia. Hue considers, therefore, that in
Antarctica there is a flora that, with the exception of cosmopolitan species,
is different from every other, and is special to these southern regions.
Darbishire himself described 34 new Antarctic species, but only 10 of these
are from true Antarctica; the others were collected in South Georgia, the
Falkland Islands or Tierra del Fuego. Even though many species are
endemic in the south, the fact remains that a remarkable number of lichens
which occur intermediately on mountain summits are common to both Polar
areas.
study of the various lists has been published by Darbishire[1073]. He
recognizes 106 true Antarctic lichens half of which are Arctic as well. The
greater number are crustaceous and are plants common also to other lands
though a certain number are endemic. The most abundant genera in species
as well as individuals are Lecidea and Lecanora. Several bright yellow
species of Placodium—Pl. elegans, Pl. murorum, etc., are there as at the
North Pole. Among the larger forms, Parmeliae, Cetrariae, and Cladoniae
are fairly numerous; Usneae and Ramalinae rather uncommon, while
members of the Stictaceae are much more abundant than in the North. The
common species of Peltigera also occur in Antarctica, though P. aphthosa
and P. venosa are wanting; both of these latter are boreal species. Darbishire
adds that lichens have so great a capacity to withstand cold, that they are
only checked by the snow covering, and were bare rocks to be found at the
South Pole, he is sure lichens would take possession of them. The most
southerly point at which any plant has been found is 78° South latitude and
162° East longitude, in which locality the lichen Lecanora subfusca was
collected by members of Scott’s Antarctic expedition (1901-1904) at a
height of 5000 ft.
A somewhat different view of the Antarctic lichen flora is indicated by
Hue[1072] in his account of the plants brought back by the second French
Antarctic Expedition. The collection was an extremely favourable and
important one: great blocks of stone with their communities of lichens were
secured, and these blocks were entirely covered, the crustaceous species,
especially, spreading over every inch of space.
Hue determined 126 species, but as 15 of these came from the Magellan
regions only 111 were truly Antarctic. Of these 90 are new species, 29 of
them belonging to the genus Buellia. Hue considers, therefore, that in
Antarctica there is a flora that, with the exception of cosmopolitan species,
is different from every other, and is special to these southern regions.
Darbishire himself described 34 new Antarctic species, but only 10 of these
are from true Antarctica; the others were collected in South Georgia, the
Falkland Islands or Tierra del Fuego. Even though many species are
endemic in the south, the fact remains that a remarkable number of lichens
which occur intermediately on mountain summits are common to both Polar
areas.
Page 435
C. Lichens of the Temperate Zones
Regions outside the Polar Circles which enjoy, on the whole, cool moist
climates, are specially favourable to lichen growth, and the recorded
numbers are very large. The European countries are naturally those in
which the lichen flora is best known. Whereas polar and high Alpine
species are stunted in growth and often sterile, those in milder localities
grow and fruit well, and the more highly developed species are more
frequent. Parmeliae, Nephromae, Usneae and Ramalinae become
prominent, especially in the more northern districts. Many Arctic plants are
represented on the higher altitudes. A comparison has been made between
the lichens of Greenland and those of Germany: of 286 species recorded for
the former country, 213 have been found in Germany, the largest number of
species common to both countries being crustaceous. Lindsay[1074]
considered that Greenland lichens were even more akin to those of
Scandinavia.
There is an astonishing similarity of lichens in the Temperate Zone all
round the world. Commenting on a list of Chicago lichens by Calkins[1075],
Hue[1076] pointed out that with the exception of a few endemic species they
resemble those of Normandy. The same result appears in Bruce Fink’s[1077]
careful compilation of Minnesota lichens, which may be accepted as typical
of the Eastern and Middle States of North Temperate America. The genera
from that region number nearly 70, and only two of these, Omphalaria and
Heppia, are absent from our British Flora. The species naturally present
much greater diversity. Very few Graphideae are reported. In other States of
North America there occurs the singular aquatic lichen, Hydrothyria
venosa, nearly akin to Peltigera.
If we contrast American lichens with these collected in South Siberia
near Lake Baikal[1078], we recognize there also the influence of temperate
conditions. Several species of Usnea are listed, U. barbata, U. florida, U.
hirta and U. longissima, all of them also American forms, U. longissima
having been found in Wisconsin. Xanthoria parietina, an almost
cosmopolitan lichen, is absent from this district, and is not recorded from
Minnesota. The opinion[1079] in America is that it is a maritime species:
Tuckerman gives its habitat as “the neighbourhood of a great water,” and
reports it from near Lake Superior. In our country it grows at a good
Regions outside the Polar Circles which enjoy, on the whole, cool moist
climates, are specially favourable to lichen growth, and the recorded
numbers are very large. The European countries are naturally those in
which the lichen flora is best known. Whereas polar and high Alpine
species are stunted in growth and often sterile, those in milder localities
grow and fruit well, and the more highly developed species are more
frequent. Parmeliae, Nephromae, Usneae and Ramalinae become
prominent, especially in the more northern districts. Many Arctic plants are
represented on the higher altitudes. A comparison has been made between
the lichens of Greenland and those of Germany: of 286 species recorded for
the former country, 213 have been found in Germany, the largest number of
species common to both countries being crustaceous. Lindsay[1074]
considered that Greenland lichens were even more akin to those of
Scandinavia.
There is an astonishing similarity of lichens in the Temperate Zone all
round the world. Commenting on a list of Chicago lichens by Calkins[1075],
Hue[1076] pointed out that with the exception of a few endemic species they
resemble those of Normandy. The same result appears in Bruce Fink’s[1077]
careful compilation of Minnesota lichens, which may be accepted as typical
of the Eastern and Middle States of North Temperate America. The genera
from that region number nearly 70, and only two of these, Omphalaria and
Heppia, are absent from our British Flora. The species naturally present
much greater diversity. Very few Graphideae are reported. In other States of
North America there occurs the singular aquatic lichen, Hydrothyria
venosa, nearly akin to Peltigera.
If we contrast American lichens with these collected in South Siberia
near Lake Baikal[1078], we recognize there also the influence of temperate
conditions. Several species of Usnea are listed, U. barbata, U. florida, U.
hirta and U. longissima, all of them also American forms, U. longissima
having been found in Wisconsin. Xanthoria parietina, an almost
cosmopolitan lichen, is absent from this district, and is not recorded from
Minnesota. The opinion[1079] in America is that it is a maritime species:
Tuckerman gives its habitat as “the neighbourhood of a great water,” and
reports it from near Lake Superior. In our country it grows at a good
Page 436
distance from the sea, in Yorkshire dales, etc., but all our counties would
rank as maritime in the American sense. Lecanora tartarea which is rare in
Minnesota is also absent from the Lake Baikal region. It occurs frequently
both in Arctic and in Antarctic regions, and is probably also somewhat
maritime in habitat. Many of the Parmeliae, Nephromiae and Peltigerae,
common to all northern temperate climes, are Siberian as are also
Cladoniae and many crustaceous species. There is only one Sticta, St.
Wrightii, a Japanese lichen, recorded by Wainio from this Siberian locality.
A marked difference as regards species is noted between the Flora of
Minnesota and that of California. Herre[1080] has directed attention to the
great similarity between the lichens of the latter state and those of Europe:
many European species occur along the coast and nowhere else in America
so far as is yet known; as examples he cites, among others, Calicium
hyperellum, Lecidea quernea, L. aromatica, Gyrophora polyrhiza,
Pertusaria amara, Roccella fuciformis, R. fucoides and R. tinctoria. The
Scandinavian lichen, Letharia vulpina, grows abundantly there and fruits
freely; it is very rare in other parts of America. Herre found, however, no
specimens of Cladonia rangiferina, Cl. alpestris or Cl. sylvatica, nor any
species of Graphis; he is unable to explain these anomalies in distribution,
but he considers that the cool equable climate is largely responsible: it is so
much more like that of the milder countries of Europe than of the states east
of the Sierra Nevada. His contention is supported by a consideration of
Japanese lichens. With a somewhat similar climate there is a great
preponderance of European forms. Out of 382 species determined by
Nylander[1081], 209 were European. There were 17 Graphideae, 31
Parmeliae, and 23 Cladoniae, all of the last named being European. These
results of Nylander’s accord well with a short list of 30 species from Japan
compiled by Müller[1082] at an earlier date. They were chiefly crustaceous
tree-lichens; but the Cladoniae recorded are the familiar British species Cl.
fimbriata, Cl. pyxidata and Cl. verticillata.
With the Japanese Flora may be compared a list[1083] of Maingay’s
lichens from China, 35 in all. Collema limosum, the only representative of
Collemaceae in the list, is European, as are the two species of Ramalina, R.
gracilenta and R. pollinaria; four species of Physcia are European, the
remaining Ph. picta being a common tropical or subtropical plant. Lecanora
saxicola, L. cinerea, Placodium callopismum and Pl. citrinum are
rank as maritime in the American sense. Lecanora tartarea which is rare in
Minnesota is also absent from the Lake Baikal region. It occurs frequently
both in Arctic and in Antarctic regions, and is probably also somewhat
maritime in habitat. Many of the Parmeliae, Nephromiae and Peltigerae,
common to all northern temperate climes, are Siberian as are also
Cladoniae and many crustaceous species. There is only one Sticta, St.
Wrightii, a Japanese lichen, recorded by Wainio from this Siberian locality.
A marked difference as regards species is noted between the Flora of
Minnesota and that of California. Herre[1080] has directed attention to the
great similarity between the lichens of the latter state and those of Europe:
many European species occur along the coast and nowhere else in America
so far as is yet known; as examples he cites, among others, Calicium
hyperellum, Lecidea quernea, L. aromatica, Gyrophora polyrhiza,
Pertusaria amara, Roccella fuciformis, R. fucoides and R. tinctoria. The
Scandinavian lichen, Letharia vulpina, grows abundantly there and fruits
freely; it is very rare in other parts of America. Herre found, however, no
specimens of Cladonia rangiferina, Cl. alpestris or Cl. sylvatica, nor any
species of Graphis; he is unable to explain these anomalies in distribution,
but he considers that the cool equable climate is largely responsible: it is so
much more like that of the milder countries of Europe than of the states east
of the Sierra Nevada. His contention is supported by a consideration of
Japanese lichens. With a somewhat similar climate there is a great
preponderance of European forms. Out of 382 species determined by
Nylander[1081], 209 were European. There were 17 Graphideae, 31
Parmeliae, and 23 Cladoniae, all of the last named being European. These
results of Nylander’s accord well with a short list of 30 species from Japan
compiled by Müller[1082] at an earlier date. They were chiefly crustaceous
tree-lichens; but the Cladoniae recorded are the familiar British species Cl.
fimbriata, Cl. pyxidata and Cl. verticillata.
With the Japanese Flora may be compared a list[1083] of Maingay’s
lichens from China, 35 in all. Collema limosum, the only representative of
Collemaceae in the list, is European, as are the two species of Ramalina, R.
gracilenta and R. pollinaria; four species of Physcia are European, the
remaining Ph. picta being a common tropical or subtropical plant. Lecanora
saxicola, L. cinerea, Placodium callopismum and Pl. citrinum are
Page 437
cosmopolitan, other Lecanorae and most of the Lecideae are new. Graphis
scripta, Opegrapha subsiderella and Arthonia cinnabarina—the few
Graphideae collected—are more or less familiar home plants. Among the
Pyrenocarpei, Verrucaria (Pyrenula) nitida occurs; it is a widely distributed
tree-lichen.
It is unnecessary to describe in detail the British lichens. Some districts
have been thoroughly worked, others have barely been touched. The flora
as a whole is of a western European type showing the influence of the Gulf
Stream, though there is also a representative boreal growth on the
moorlands and higher hills, especially in Scotland. Such species as
Parmelia pubescens, P. stygia and P. alpicola recall the Arctic Circle while
Alectoriae, Cetrariae and Gyrophorae represent affinity with the colder
temperate zone.
In the southern counties such species as Sticta aurata, S. damaecornis,
Phaeographis Lyellii and Lecanora (Lecania) holophaea belong to the flora
of the Atlantic seaboard, while in S.W. Ireland the tropical genera
Leptogidium and Anthracothecium are each represented by a single species.
The tropical or subtropical genus Coenogonium occurs in Great Britain and
in Germany, with one sterile species, C. ebeneum. Enterographa crassa is
another of our common western lichens which however has travelled
eastwards as far as Wiesbaden. Roccella is essentially a maritime genus of
warm climates: two species, R. fuciformis and R. fucoides, grow on our
south and west coasts. The famous R. tinctoria is a Mediterranean plant,
though it is recorded also from a number of localities outside that region
and has been collected in Australia.
In the temperate zones of the southern hemisphere are situated the great
narrowing projections of South Africa and South America with Australia
and New Zealand. As we have seen, the Antarctic flora prevails more or less
in the extreme southern part of America, and the similarity between the
lichens of that country and those of New Zealand is very striking, especially
in the fruticulose forms. There is a very abundant flora in the New Zealand
islands with their cool moist climate and high mountains. Churchill
Babington[1084] described the collections made by Hooker. Stirton[1085]
added many species, among others Calycidium cuneatum, evidently
endemic. Later, Nylander[1086] published the species already known, and
scripta, Opegrapha subsiderella and Arthonia cinnabarina—the few
Graphideae collected—are more or less familiar home plants. Among the
Pyrenocarpei, Verrucaria (Pyrenula) nitida occurs; it is a widely distributed
tree-lichen.
It is unnecessary to describe in detail the British lichens. Some districts
have been thoroughly worked, others have barely been touched. The flora
as a whole is of a western European type showing the influence of the Gulf
Stream, though there is also a representative boreal growth on the
moorlands and higher hills, especially in Scotland. Such species as
Parmelia pubescens, P. stygia and P. alpicola recall the Arctic Circle while
Alectoriae, Cetrariae and Gyrophorae represent affinity with the colder
temperate zone.
In the southern counties such species as Sticta aurata, S. damaecornis,
Phaeographis Lyellii and Lecanora (Lecania) holophaea belong to the flora
of the Atlantic seaboard, while in S.W. Ireland the tropical genera
Leptogidium and Anthracothecium are each represented by a single species.
The tropical or subtropical genus Coenogonium occurs in Great Britain and
in Germany, with one sterile species, C. ebeneum. Enterographa crassa is
another of our common western lichens which however has travelled
eastwards as far as Wiesbaden. Roccella is essentially a maritime genus of
warm climates: two species, R. fuciformis and R. fucoides, grow on our
south and west coasts. The famous R. tinctoria is a Mediterranean plant,
though it is recorded also from a number of localities outside that region
and has been collected in Australia.
In the temperate zones of the southern hemisphere are situated the great
narrowing projections of South Africa and South America with Australia
and New Zealand. As we have seen, the Antarctic flora prevails more or less
in the extreme southern part of America, and the similarity between the
lichens of that country and those of New Zealand is very striking, especially
in the fruticulose forms. There is a very abundant flora in the New Zealand
islands with their cool moist climate and high mountains. Churchill
Babington[1084] described the collections made by Hooker. Stirton[1085]
added many species, among others Calycidium cuneatum, evidently
endemic. Later, Nylander[1086] published the species already known, and
Page 438
Hellbom[1087] followed with an account of New Zealand lichens based on
Berggsen’s collections; many more must be still undiscovered. Especially
noticeable as compared with the north, are the numbers of Stictaceae which
reach their highest development of species and individuals in Australasia.
They are as numerous and as prominent as are Gyrophoraceae in the north.
A genus of Parmeliaceae, Hetorodea, which, like the Stictae, bears
cyphellae on the lower surface, is peculiar to Australia.
A warm current from the tropical Pacific Ocean passes southwards along
the East Coast of Australia, and Wilson[1088] has traced its influence on the
lichens of Australia and Tasmania to which countries a few tropical species
of Graphis, Chiodecton and Trypethelium have migrated. Various unusual
types are to be found there also: the beautiful Cladonia retepora (Fig. 71),
which spreads over the ground in cushion-like growths, with the genera
Thysanothecium and Neophyllis, genera of Cladoniaceae endemic in these
regions.
The continent of Africa on the north and east is in so close connection
with Europe and Asia that little peculiarity in the flora could be expected. In
comparing small representative collections of lichens, 37 species from
Egypt and 20 from Palestine, Müller[1089] found that there was a great
affinity between these two countries. Of the Palestine species, eight were
cosmopolitan; among the crustaceous genera, Lecanorae were the most
numerous. There was no record of new genera.
The vast African continent—more especially the central region—has
been but little explored in a lichenological sense; but in 1895
Stizenberger[1090] listed all of the species known, amounting to 1593, and
new plants and new records have been added since that day. The familiar
genera are well represented, Nephromium, Xanthoria, Physcia, Parmelia,
Ramalina and Roccella, some of them by large and handsome species. In
the Sahara Steiner[1091] found that genera with blue-green algae such as the
Gloeolichens were particularly abundant; Heppia and Endocarpon were
also frequent. Algeria has a Mediterranean Flora rather than tropical or
subtropical. Flagey[1092] records no species of Graphis for the province of
Constantine, and only 22 species of other Graphideae. Most of the 519
lichens listed by him there are crustaceous species. South America stretches
from the Tropics in the north to Antarctica in the south. Tropical conditions
Berggsen’s collections; many more must be still undiscovered. Especially
noticeable as compared with the north, are the numbers of Stictaceae which
reach their highest development of species and individuals in Australasia.
They are as numerous and as prominent as are Gyrophoraceae in the north.
A genus of Parmeliaceae, Hetorodea, which, like the Stictae, bears
cyphellae on the lower surface, is peculiar to Australia.
A warm current from the tropical Pacific Ocean passes southwards along
the East Coast of Australia, and Wilson[1088] has traced its influence on the
lichens of Australia and Tasmania to which countries a few tropical species
of Graphis, Chiodecton and Trypethelium have migrated. Various unusual
types are to be found there also: the beautiful Cladonia retepora (Fig. 71),
which spreads over the ground in cushion-like growths, with the genera
Thysanothecium and Neophyllis, genera of Cladoniaceae endemic in these
regions.
The continent of Africa on the north and east is in so close connection
with Europe and Asia that little peculiarity in the flora could be expected. In
comparing small representative collections of lichens, 37 species from
Egypt and 20 from Palestine, Müller[1089] found that there was a great
affinity between these two countries. Of the Palestine species, eight were
cosmopolitan; among the crustaceous genera, Lecanorae were the most
numerous. There was no record of new genera.
The vast African continent—more especially the central region—has
been but little explored in a lichenological sense; but in 1895
Stizenberger[1090] listed all of the species known, amounting to 1593, and
new plants and new records have been added since that day. The familiar
genera are well represented, Nephromium, Xanthoria, Physcia, Parmelia,
Ramalina and Roccella, some of them by large and handsome species. In
the Sahara Steiner[1091] found that genera with blue-green algae such as the
Gloeolichens were particularly abundant; Heppia and Endocarpon were
also frequent. Algeria has a Mediterranean Flora rather than tropical or
subtropical. Flagey[1092] records no species of Graphis for the province of
Constantine, and only 22 species of other Graphideae. Most of the 519
lichens listed by him there are crustaceous species. South America stretches
from the Tropics in the north to Antarctica in the south. Tropical conditions
Page 439
prevail over the central countries and tropical tree-lichens, Graphidaceae,
Thelotremaceae, etc. are frequent; further West, on the Pacific slopes,
Usneae and Ramalinae hang in great festoons from the branches, while the
foliose Parmeliae and Stictae grow to a large size on the trunks of the trees.
Wainio’s[1093] Lichens du Brésil is one of the classic systematic books
and embodies the writer’s views on lichen classification. There are no new
families recorded though a number of genera and many species are new,
and, so far as is yet known, these are endemic. Many of our common forms
are absent; thus Peltigera is represented by three species only, P.
leptoderma, P. spuriella and P. Americana, the two latter being new species.
Sticta (including Stictina) includes only five species, and Coenogonium
three. There are 39 species of Parmelia with 33 of Lecanora and 68 of
Lecidea, many of them new species.
D. Lichens of Tropical Regions
In the tropics lichens come under the influence of many climates: on the
high mountains there is a region of perpetual snow, lower down a gradual
change to temperate and finally to tropical conditions of extreme heat, and,
in some instances, extreme moisture. There is thus a bewildering variety of
forms. By “tropical” however the warmer climate is always implied.
Several families and genera seem to flourish best in these warm moist
conditions and our familiar species grow there to a large size. Among
crustaceous families Thelotremaceae and Graphidaceae are especially
abundant, and probably originated there. In the old comprehensive genus
Graphis, 300 species were recorded from the tropics. It should be borne in
mind that Trentepohlia, the alga that forms the gonidia of these lichens, is
very abundant in the tropics. Coenogonium, a genus containing about
twelve species and also associated with Trentepohlia, is scarcely found in
Europe, except one sterile species, C. ebeneum. Other species of the genus
have been recorded as far north as Algeria in the Eastern Hemisphere and
Louisiana in the Western, while one species, C. implexum, occurs in the
southern temperate zone in Australia and New Zealand.
Of exclusively tropical lichens, the Hymenolichens are the most
noteworthy. They include three genera, Cora, Corella and Dictyonema, the
Thelotremaceae, etc. are frequent; further West, on the Pacific slopes,
Usneae and Ramalinae hang in great festoons from the branches, while the
foliose Parmeliae and Stictae grow to a large size on the trunks of the trees.
Wainio’s[1093] Lichens du Brésil is one of the classic systematic books
and embodies the writer’s views on lichen classification. There are no new
families recorded though a number of genera and many species are new,
and, so far as is yet known, these are endemic. Many of our common forms
are absent; thus Peltigera is represented by three species only, P.
leptoderma, P. spuriella and P. Americana, the two latter being new species.
Sticta (including Stictina) includes only five species, and Coenogonium
three. There are 39 species of Parmelia with 33 of Lecanora and 68 of
Lecidea, many of them new species.
D. Lichens of Tropical Regions
In the tropics lichens come under the influence of many climates: on the
high mountains there is a region of perpetual snow, lower down a gradual
change to temperate and finally to tropical conditions of extreme heat, and,
in some instances, extreme moisture. There is thus a bewildering variety of
forms. By “tropical” however the warmer climate is always implied.
Several families and genera seem to flourish best in these warm moist
conditions and our familiar species grow there to a large size. Among
crustaceous families Thelotremaceae and Graphidaceae are especially
abundant, and probably originated there. In the old comprehensive genus
Graphis, 300 species were recorded from the tropics. It should be borne in
mind that Trentepohlia, the alga that forms the gonidia of these lichens, is
very abundant in the tropics. Coenogonium, a genus containing about
twelve species and also associated with Trentepohlia, is scarcely found in
Europe, except one sterile species, C. ebeneum. Other species of the genus
have been recorded as far north as Algeria in the Eastern Hemisphere and
Louisiana in the Western, while one species, C. implexum, occurs in the
southern temperate zone in Australia and New Zealand.
Of exclusively tropical lichens, the Hymenolichens are the most
noteworthy. They include three genera, Cora, Corella and Dictyonema, the
Page 440
few species of which grow on trees or on the ground both in eastern and
western tropical countries.
Other tropical or subtropical forms are Oropogon loxensis, similar to
Alectoria in form and habit, but with one brown muriform spore in the
ascus; it is only found in tropical or subtropical lands. Physcidia Wrightii
(Parmeliaceae) is exclusively a Cuban lichen. Several small genera of
Pyrenopsidaceae such as Jenmania (British Guiana), Paulia (Polynesia) and
Phloeopeccania (South Arabia) seem to be confined to very hot localities.
On the other hand Collemaceae are rare: Wainio records from Brazil only
four species of Collema, with nine of Leptogium.
Among Pyrenolichens, Paratheliaceae, Mycoporaceae and
Astrotheliaceae are almost exclusively of tropical distribution, and finally
the leaf lichens with very few exceptions. These follow the leaf algae,
Mycoidea, Phycopeltis, etc., which are so abundant on the coriaceous long-
lived green leaves of a number of tropical Phanerogams. All the
Strigulaceae are epiphytic lichens. Phyllophthalmaria (Thelotremaceae) is
also a leaf genus; one of the species, Ph. coccinea, has beautiful carmine-
red apothecia. The genera of the tropical family Ectolechiaceae also inhabit
leaves, but they are associated with Protococcaceae; one of the genera
Sporopodium[1094] is remarkable as having hymenial gonidia. Though
tropical in the main, epiphyllous lichens may spread to the regions beyond:
Sporopodium Caucasium and a sterile Strigula were found by Elenkin and
Woronichin[1095] on leaves of Buxus sempervirens in the Caucasus, well
outside the tropics.
Pilocarpon, an epiphytic genus, is associated with Protococcaceae; one
of the species, P. leucoblepharum, spreads from the bark to the leaves of
pine-trees; it is widely distributed and has also been reported in the
Caucasus[1096]. Chrysothrix, in which the gonidia belong to the algal genus
Palmella, grows on Cactus spines in Chili, and may also rank as a
subtropical epiphyllous lichen.
A series of lichens from the warm temperate region of Transcaucasia
investigated by Steiner[1097] were found to be very similar to those of
Central Europe. Lecanoraceae were, however, more abundant than
Lecideaceae and Verrucariaceae were comparatively rare.
western tropical countries.
Other tropical or subtropical forms are Oropogon loxensis, similar to
Alectoria in form and habit, but with one brown muriform spore in the
ascus; it is only found in tropical or subtropical lands. Physcidia Wrightii
(Parmeliaceae) is exclusively a Cuban lichen. Several small genera of
Pyrenopsidaceae such as Jenmania (British Guiana), Paulia (Polynesia) and
Phloeopeccania (South Arabia) seem to be confined to very hot localities.
On the other hand Collemaceae are rare: Wainio records from Brazil only
four species of Collema, with nine of Leptogium.
Among Pyrenolichens, Paratheliaceae, Mycoporaceae and
Astrotheliaceae are almost exclusively of tropical distribution, and finally
the leaf lichens with very few exceptions. These follow the leaf algae,
Mycoidea, Phycopeltis, etc., which are so abundant on the coriaceous long-
lived green leaves of a number of tropical Phanerogams. All the
Strigulaceae are epiphytic lichens. Phyllophthalmaria (Thelotremaceae) is
also a leaf genus; one of the species, Ph. coccinea, has beautiful carmine-
red apothecia. The genera of the tropical family Ectolechiaceae also inhabit
leaves, but they are associated with Protococcaceae; one of the genera
Sporopodium[1094] is remarkable as having hymenial gonidia. Though
tropical in the main, epiphyllous lichens may spread to the regions beyond:
Sporopodium Caucasium and a sterile Strigula were found by Elenkin and
Woronichin[1095] on leaves of Buxus sempervirens in the Caucasus, well
outside the tropics.
Pilocarpon, an epiphytic genus, is associated with Protococcaceae; one
of the species, P. leucoblepharum, spreads from the bark to the leaves of
pine-trees; it is widely distributed and has also been reported in the
Caucasus[1096]. Chrysothrix, in which the gonidia belong to the algal genus
Palmella, grows on Cactus spines in Chili, and may also rank as a
subtropical epiphyllous lichen.
A series of lichens from the warm temperate region of Transcaucasia
investigated by Steiner[1097] were found to be very similar to those of
Central Europe. Lecanoraceae were, however, more abundant than
Lecideaceae and Verrucariaceae were comparatively rare.
Page 441
Much of Asia lies within tropical or subtropical influences. Several
regions have received some amount of attention from collectors. From
Persia there has been published a list of 59 species determined by
Müller[1098]; several of them are Egyptian or Arabian plants, 15 are new
species, but the greater number are European.
A small collection of 53 species from India, near to Calcutta, published
by Nylander[1099], included a new genus of Caliciaceae, Pyrgidium (P.
bengalense), allied to Sphinctrina. He also recorded Ramalina angulosa in
African species, along with R. calicaris, R. farinacea and Parmelia perlata,
f. isidiophora, which are British. Other foliose forms, Physcia picta, Pyxine
Cocoës and P. Meissnerii are tropical or subtropical; along with these were
collected crustaceous tropical species belonging to Lecanorae, Lecideae,
Graphideae, etc.
Leighton[1100] published a collection of Ceylon lichens and found that
Graphideae predominated. Nylander[1101] came to the same conclusion with
regard to lichens referred to him: out of 159 species investigated from
Ceylon, there were 36 species of Graphideae. In another list[1102] of Labuan,
Singapore and Malacca lichens, 164 in all, he found that 56 belonged to the
Graphidei, 36 to Pyrenocarpei, 14 to Thelotremei and 11 to Parmelei; only
15 species were European.
On the whole it is safe to conclude from the above and other publications
that the exceptional conditions of the tropics have produced many
distinctive lichens, but that a greater abundance both of species and
individuals is now to be found in temperate and cold climates.
III. FOSSIL LICHENS
In pronouncing on the great antiquity of lichens, proof has been adduced
from physiological rather than from phytogeological evidence. It would
have been of surpassing interest to trace back these plants through the ages,
even if it were never possible to assign to any definite period the first
symbiosis of the fungus and alga; but among fossil plants there are only
scanty records of lichens and even these few are of doubtful determination.
The reason for this is fairly obvious: not only are the primitive thalline
forms too indistinct for recognizable preservation, but all lichens are
regions have received some amount of attention from collectors. From
Persia there has been published a list of 59 species determined by
Müller[1098]; several of them are Egyptian or Arabian plants, 15 are new
species, but the greater number are European.
A small collection of 53 species from India, near to Calcutta, published
by Nylander[1099], included a new genus of Caliciaceae, Pyrgidium (P.
bengalense), allied to Sphinctrina. He also recorded Ramalina angulosa in
African species, along with R. calicaris, R. farinacea and Parmelia perlata,
f. isidiophora, which are British. Other foliose forms, Physcia picta, Pyxine
Cocoës and P. Meissnerii are tropical or subtropical; along with these were
collected crustaceous tropical species belonging to Lecanorae, Lecideae,
Graphideae, etc.
Leighton[1100] published a collection of Ceylon lichens and found that
Graphideae predominated. Nylander[1101] came to the same conclusion with
regard to lichens referred to him: out of 159 species investigated from
Ceylon, there were 36 species of Graphideae. In another list[1102] of Labuan,
Singapore and Malacca lichens, 164 in all, he found that 56 belonged to the
Graphidei, 36 to Pyrenocarpei, 14 to Thelotremei and 11 to Parmelei; only
15 species were European.
On the whole it is safe to conclude from the above and other publications
that the exceptional conditions of the tropics have produced many
distinctive lichens, but that a greater abundance both of species and
individuals is now to be found in temperate and cold climates.
III. FOSSIL LICHENS
In pronouncing on the great antiquity of lichens, proof has been adduced
from physiological rather than from phytogeological evidence. It would
have been of surpassing interest to trace back these plants through the ages,
even if it were never possible to assign to any definite period the first
symbiosis of the fungus and alga; but among fossil plants there are only
scanty records of lichens and even these few are of doubtful determination.
The reason for this is fairly obvious: not only are the primitive thalline
forms too indistinct for recognizable preservation, but all lichens are
Page 442
characterized by the gelatinous nature of the hyphal or of the algal
membranes which readily imbibe water. They thus become soft and flaccid
and unfit to leave any impress on sedimentary rocks. It has also been
pointed out by Schimper[1103] that while deciduous leaves with fungi on
them are abundant in fossil beds, lichens are entirely wanting. These latter
are so firmly attached to the rocks or trees on which they grow that they are
rarely dislodged, and form no part of wind- or autumn-fall. Trunks and
branches of trees lose their bark by decay long before they become
fossilized and thus all trace of their lichen covering disappears.
The few records that have been made are here tabulated in chronological
order:
1. Palaeozoic. Schimper decides that there are no records of lichens in
the earlier epochs. Any allusions[1104] to their occurrence are held to be
extremely vague and speculative.
2. Mesozoic. Braun[1105] has recorded a Ramalinites lacerus from the
Keuper sandstone at Eckersdorf, though later[1106] he seemed to be doubtful
as to his determination. One other lichen, an Opegrapha, has been
described[1107] from the chalk at Aix.
3. Cainozoic. In the brown-coal formations of Saxony Engelhardt[1108]
finds two lichens: Ramalina tertiaria, a much branched plant, the fronds
being flat and not channelled “and of further interest that it is attached to a
carbonized stem.” The second form, Lichen dichotomus, has a
dichotomously branching strap-shaped frond. “There is sufficient evidence
that these fronds were cylindrical and that the width is due to pressure. In
one place a channel is visible, filled with an ochraceous yellow substance.”
Other records on brown coal or lignite are: Verrucarites geanthricis[1109]
Goepp., somewhat similar to Pyrenula nitida, found at Muskau in Silesia;
Opegrapha Thomasiana[1110] Goepp., near to Opegrapha varia, and
Graphis scripta succinea Goepp.[1111] on a piece of lignite in amber beds,
all of them doubtful.
Schimper has questioned, as he well might, Ludwig’s[1112] records from
lignite from the Rhein-Wetterau Tertiary formations; these are: Cladonia
rosea, Lichen albineus, L. diffissus and L. orbiculatus; he thinks they are
membranes which readily imbibe water. They thus become soft and flaccid
and unfit to leave any impress on sedimentary rocks. It has also been
pointed out by Schimper[1103] that while deciduous leaves with fungi on
them are abundant in fossil beds, lichens are entirely wanting. These latter
are so firmly attached to the rocks or trees on which they grow that they are
rarely dislodged, and form no part of wind- or autumn-fall. Trunks and
branches of trees lose their bark by decay long before they become
fossilized and thus all trace of their lichen covering disappears.
The few records that have been made are here tabulated in chronological
order:
1. Palaeozoic. Schimper decides that there are no records of lichens in
the earlier epochs. Any allusions[1104] to their occurrence are held to be
extremely vague and speculative.
2. Mesozoic. Braun[1105] has recorded a Ramalinites lacerus from the
Keuper sandstone at Eckersdorf, though later[1106] he seemed to be doubtful
as to his determination. One other lichen, an Opegrapha, has been
described[1107] from the chalk at Aix.
3. Cainozoic. In the brown-coal formations of Saxony Engelhardt[1108]
finds two lichens: Ramalina tertiaria, a much branched plant, the fronds
being flat and not channelled “and of further interest that it is attached to a
carbonized stem.” The second form, Lichen dichotomus, has a
dichotomously branching strap-shaped frond. “There is sufficient evidence
that these fronds were cylindrical and that the width is due to pressure. In
one place a channel is visible, filled with an ochraceous yellow substance.”
Other records on brown coal or lignite are: Verrucarites geanthricis[1109]
Goepp., somewhat similar to Pyrenula nitida, found at Muskau in Silesia;
Opegrapha Thomasiana[1110] Goepp., near to Opegrapha varia, and
Graphis scripta succinea Goepp.[1111] on a piece of lignite in amber beds,
all of them doubtful.
Schimper has questioned, as he well might, Ludwig’s[1112] records from
lignite from the Rhein-Wetterau Tertiary formations; these are: Cladonia
rosea, Lichen albineus, L. diffissus and L. orbiculatus; he thinks they are
Page 443
probably fungus mycelia. Another lichen, a Parmelia with apothecia, which
recalls somewhat P. saxatilis or P. conspersa, collected by Geyler also in
the brown coal of Wetterau is accepted by Schimper[1113] as more
trustworthy.
More authentic also are the lichens from the amber beds of Königsberg
and elsewhere collected by Goeppert and others. These deposits are
Cainozoic and have been described by Goeppert and Menge[1114] as middle
Miocene. Schimper gives the list as: Parmelia lacunosa Meng. and Goepp.,
fragments of thallus near to P. saxatilis; Sphaerophorus coralloides;
Cladonia divaricata Meng. and Goepp.; Cl. furcata; Ramalina calicaris
vars. fraxinea and canaliculata; Cornicularia aculeata, C. subpubescens
Goepp., C. ochroleuca, C. succinea Goepp., and Usnea barbata var. hirta.
Schimper rather deprecates specific determinations when dealing with such
imperfect fragments.
In a later work Goeppert and Menge[1114] state that they have found
twelve different amber lichens and that among these are Physcia ciliaris,
Parmelia physodes and Graphis (probably G. scripta succinea) along with
Peziza resinae which is more generally classified among lichens as Lecidea
(Biatorella) resinae.
Another series of lichens found in recent deposits in North Europe has
been described by Sernander[1115] as “subfossil.” While engaged on the
investigations undertaken by the Swedish Turf-Moor Commission, he noted
the alternation of slightly raised Sphagnum beds with lower-lying stretches
of Calluna and lichen moor—in some instances dense communities of
Cladonia rangiferina. In time the turf-forming Sphagnum overtopped and
invaded the drier moorland, covering it with a new formation of turf.
Beneath these layers of “regenerated turf” were found local accumulations
of blackened remains of the Cladonia still recognizable by the form and
branching. Some specimens of Cetraria islandica were also determined.
Of especial lichenological interest in these northern regions was the
Calcareous Tufa or Calc-sinter in which Sernander also found subfossil
lichens—distinct impressions of Peltigera spp. and the foveolae of
endolithic calcicolous species.
recalls somewhat P. saxatilis or P. conspersa, collected by Geyler also in
the brown coal of Wetterau is accepted by Schimper[1113] as more
trustworthy.
More authentic also are the lichens from the amber beds of Königsberg
and elsewhere collected by Goeppert and others. These deposits are
Cainozoic and have been described by Goeppert and Menge[1114] as middle
Miocene. Schimper gives the list as: Parmelia lacunosa Meng. and Goepp.,
fragments of thallus near to P. saxatilis; Sphaerophorus coralloides;
Cladonia divaricata Meng. and Goepp.; Cl. furcata; Ramalina calicaris
vars. fraxinea and canaliculata; Cornicularia aculeata, C. subpubescens
Goepp., C. ochroleuca, C. succinea Goepp., and Usnea barbata var. hirta.
Schimper rather deprecates specific determinations when dealing with such
imperfect fragments.
In a later work Goeppert and Menge[1114] state that they have found
twelve different amber lichens and that among these are Physcia ciliaris,
Parmelia physodes and Graphis (probably G. scripta succinea) along with
Peziza resinae which is more generally classified among lichens as Lecidea
(Biatorella) resinae.
Another series of lichens found in recent deposits in North Europe has
been described by Sernander[1115] as “subfossil.” While engaged on the
investigations undertaken by the Swedish Turf-Moor Commission, he noted
the alternation of slightly raised Sphagnum beds with lower-lying stretches
of Calluna and lichen moor—in some instances dense communities of
Cladonia rangiferina. In time the turf-forming Sphagnum overtopped and
invaded the drier moorland, covering it with a new formation of turf.
Beneath these layers of “regenerated turf” were found local accumulations
of blackened remains of the Cladonia still recognizable by the form and
branching. Some specimens of Cetraria islandica were also determined.
Of especial lichenological interest in these northern regions was the
Calcareous Tufa or Calc-sinter in which Sernander also found subfossil
lichens—distinct impressions of Peltigera spp. and the foveolae of
endolithic calcicolous species.
Page 444
In another category he has placed Ramalina fraxinea, Graphis sp. and
Opegrapha sp., traces of which were embedded with drift in the Tufa. In the
two Graphideae the walls of apothecia and pycnidia were preserved.
Sernander considers their presence of interest as testifying to warmer
conditions than now prevail in these latitudes.
Opegrapha sp., traces of which were embedded with drift in the Tufa. In the
two Graphideae the walls of apothecia and pycnidia were preserved.
Sernander considers their presence of interest as testifying to warmer
conditions than now prevail in these latitudes.
Page 445
CHAPTER IX
ECOLOGY
A. General Introduction
Ecology is the science that deals with the habitats of plants and their
response to the environment of climate or of substratum. Ecology in the
lichen kingdom is habitat “writ large,” and though it will not be possible in
so wide a field to enter into much detail, even a short examination of
lichens in this aspect should yield interesting results, especially as lichens
have never, at any time, been described without reference to their habitat. In
very early days, medicinal Usneas were supposed to possess peculiar
virtues according to the trees on which they grew and which are therefore
carefully recorded, and all down the pages of lichen literature, no diagnosis
has been drawn up without definite reference to the nature of the
substratum. Not only rocks and trees are recorded, but the kind of rock and
the kind of tree are often specified. The important part played by rock
lichens in preparing soil for other plants has also received much
attention[1116].
Several comprehensive works on Ecology have been published in recent
times and though they deal mainly with the higher vegetation, the general
plan of study of land plants is well adapted to lichens. A series of definitions
and explanations of the terms used will be of service:
Thus in a work by Moss[1117] we read “The flora is composed of the
individual species: the vegetation comprises the groupings of these species
into ensembles termed vegetation units or plant communities.” And again:
1. “A plant formation is the whole of the vegetation which occurs on a
definite and essentially uniform habitat.”—All kinds of plants are included
in the formation, so that strictly speaking a lichen formation is one in which
lichens are the dominant plants. Cf. p. 394. The term however is very
loosely used in the literature. A uniform habitat, as regards lichens, would
be that of the different kinds of soil, of rock, of tree, etc.
ECOLOGY
A. General Introduction
Ecology is the science that deals with the habitats of plants and their
response to the environment of climate or of substratum. Ecology in the
lichen kingdom is habitat “writ large,” and though it will not be possible in
so wide a field to enter into much detail, even a short examination of
lichens in this aspect should yield interesting results, especially as lichens
have never, at any time, been described without reference to their habitat. In
very early days, medicinal Usneas were supposed to possess peculiar
virtues according to the trees on which they grew and which are therefore
carefully recorded, and all down the pages of lichen literature, no diagnosis
has been drawn up without definite reference to the nature of the
substratum. Not only rocks and trees are recorded, but the kind of rock and
the kind of tree are often specified. The important part played by rock
lichens in preparing soil for other plants has also received much
attention[1116].
Several comprehensive works on Ecology have been published in recent
times and though they deal mainly with the higher vegetation, the general
plan of study of land plants is well adapted to lichens. A series of definitions
and explanations of the terms used will be of service:
Thus in a work by Moss[1117] we read “The flora is composed of the
individual species: the vegetation comprises the groupings of these species
into ensembles termed vegetation units or plant communities.” And again:
1. “A plant formation is the whole of the vegetation which occurs on a
definite and essentially uniform habitat.”—All kinds of plants are included
in the formation, so that strictly speaking a lichen formation is one in which
lichens are the dominant plants. Cf. p. 394. The term however is very
loosely used in the literature. A uniform habitat, as regards lichens, would
be that of the different kinds of soil, of rock, of tree, etc.
Page 446
2. “A plant association is of lower rank than a formation, and is
characterized by minor differences within the generally uniform habitat.”—
It represents a more limited community within the formation.
3. “A plant society is of lower rank than an association, and is marked by
still less fundamental differences of the habitat.”—The last-named term
represents chiefly aggregations of single species. Moss adds that: “plant
community is a convenient and general term used for a vegetation unit of
any rank.”
Climatic conditions and geographical position are included in any
consideration of habitat, as lichens like other plants are susceptible to
external influences.
Ecological plant-geography has been well defined by Macmillan[1118] as
“the science which treats of the reciprocal relation between physiographic
conditions and life requirements of organisms in so far as such relations
manifest themselves in choice of habitats and method of establishment upon
them ... resulting in the origin and development of plant formations.”
B. External Influences
The climatic factors most favourable to lichen development are direct
light (already discussed)[1119], a moderate or cold temperature, constant
moisture and a clear pure atmosphere. Wind also affects their growth.
a. Temperature. Lichens, as we have seen, can endure the heat of direct
sunlight owing to the protection afforded by thickened cortices, colour
pigments, etc. Where such heat is so intense as to be injurious the gonidia
succumb first[1120].
Lichens endure low temperatures better than other plants, their
xerophytic structure rendering them proof against extreme conditions: the
hyphae have thick walls with reduced cell lumen and extremely meagre
contents. Freezing for prolonged periods does them little injury; they revive
again when conditions become more favourable. Efficient protection is also
afforded by the thickened cortex of such lichens as exist in Polar areas, or at
high altitudes. Thus various species of Cetrariae with a stout “decomposed”
amorphous cortex can withstand very low temperatures and grow freely on
characterized by minor differences within the generally uniform habitat.”—
It represents a more limited community within the formation.
3. “A plant society is of lower rank than an association, and is marked by
still less fundamental differences of the habitat.”—The last-named term
represents chiefly aggregations of single species. Moss adds that: “plant
community is a convenient and general term used for a vegetation unit of
any rank.”
Climatic conditions and geographical position are included in any
consideration of habitat, as lichens like other plants are susceptible to
external influences.
Ecological plant-geography has been well defined by Macmillan[1118] as
“the science which treats of the reciprocal relation between physiographic
conditions and life requirements of organisms in so far as such relations
manifest themselves in choice of habitats and method of establishment upon
them ... resulting in the origin and development of plant formations.”
B. External Influences
The climatic factors most favourable to lichen development are direct
light (already discussed)[1119], a moderate or cold temperature, constant
moisture and a clear pure atmosphere. Wind also affects their growth.
a. Temperature. Lichens, as we have seen, can endure the heat of direct
sunlight owing to the protection afforded by thickened cortices, colour
pigments, etc. Where such heat is so intense as to be injurious the gonidia
succumb first[1120].
Lichens endure low temperatures better than other plants, their
xerophytic structure rendering them proof against extreme conditions: the
hyphae have thick walls with reduced cell lumen and extremely meagre
contents. Freezing for prolonged periods does them little injury; they revive
again when conditions become more favourable. Efficient protection is also
afforded by the thickened cortex of such lichens as exist in Polar areas, or at
high altitudes. Thus various species of Cetrariae with a stout “decomposed”
amorphous cortex can withstand very low temperatures and grow freely on
Page 447
the tundra, while Cladonia rangiferina, also a northern lichen, but without a
continuous cortex, cannot exist in such cold conditions, unless in localities
where it is protected by a covering of snow during the most inclement
seasons.
b. Humidity. A high degree of humidity is distinctly of advantage to the
growth of the lichen thallus, though when the moist conditions are
excessive the plants become turgid and soredial states are developed.
The great abundance of lichens in the western districts of the British
Isles, where the rainfall is heaviest, is proof enough of the advantage of
moisture, and on trees it is the side exposed to wind and rain that is most
plentifully covered. A series of observations on lichens and rainfall were
made by West[1121] and have been published since his death. He has
remarked in more than one of his papers that a most favourable situation for
lichen growth is one that is subject to a drive of wind with much rain. In
localities with an average of 216 days of rain in the year, he found abundant
and luxuriant growths of the larger foliose species. In West Ireland there
were specimens of Ricasolia laetevirens measuring 165 by 60 cm. In West
Scotland with an “average of total days of rain, 225,” he found plants of
Ricasolia amplissima 150 × 90 cm. in size, of R. laetevirens 120 × 90 cm.,
while Pertusaria globulifera formed a continuous crust on the trees as much
as 120 × 90 cm. Lecanora tartarea seemed to thrive exceptionally well
when subject to driving mists and rains from mountain or moorland, and
was in these circumstances frequently the dominant epiphyte. Bruce
Fink[1122] also observed in his ecological excursions that the number of
species and individuals was greater near lakes or rivers.
Though a fair number of lichens are adapted to life wholly or partly
under water, land forms are mostly xerophytic in structure, and die off if
submerged for any length of time. The Peltigerae are perhaps the most
hydrophilous of purely land species. Many Alpine or Polar forms are
covered with snow for long periods. In the extreme north it affords more or
less protection; and Kihlman[1123] and others have remarked on the scarcity
of lichens in localities denuded of the snow mantle and exposed to severe
winter cold. On the other hand lichens on the high Alpine summits that are
covered with snow the greater part of the year suffer, according to
Nilson[1124], from the excessive moisture and the deprivation of light.
continuous cortex, cannot exist in such cold conditions, unless in localities
where it is protected by a covering of snow during the most inclement
seasons.
b. Humidity. A high degree of humidity is distinctly of advantage to the
growth of the lichen thallus, though when the moist conditions are
excessive the plants become turgid and soredial states are developed.
The great abundance of lichens in the western districts of the British
Isles, where the rainfall is heaviest, is proof enough of the advantage of
moisture, and on trees it is the side exposed to wind and rain that is most
plentifully covered. A series of observations on lichens and rainfall were
made by West[1121] and have been published since his death. He has
remarked in more than one of his papers that a most favourable situation for
lichen growth is one that is subject to a drive of wind with much rain. In
localities with an average of 216 days of rain in the year, he found abundant
and luxuriant growths of the larger foliose species. In West Ireland there
were specimens of Ricasolia laetevirens measuring 165 by 60 cm. In West
Scotland with an “average of total days of rain, 225,” he found plants of
Ricasolia amplissima 150 × 90 cm. in size, of R. laetevirens 120 × 90 cm.,
while Pertusaria globulifera formed a continuous crust on the trees as much
as 120 × 90 cm. Lecanora tartarea seemed to thrive exceptionally well
when subject to driving mists and rains from mountain or moorland, and
was in these circumstances frequently the dominant epiphyte. Bruce
Fink[1122] also observed in his ecological excursions that the number of
species and individuals was greater near lakes or rivers.
Though a fair number of lichens are adapted to life wholly or partly
under water, land forms are mostly xerophytic in structure, and die off if
submerged for any length of time. The Peltigerae are perhaps the most
hydrophilous of purely land species. Many Alpine or Polar forms are
covered with snow for long periods. In the extreme north it affords more or
less protection; and Kihlman[1123] and others have remarked on the scarcity
of lichens in localities denuded of the snow mantle and exposed to severe
winter cold. On the other hand lichens on the high Alpine summits that are
covered with snow the greater part of the year suffer, according to
Nilson[1124], from the excessive moisture and the deprivation of light.
Page 448
Foliose and fruticose forms were, he found, dwarfed in size; the crustaceous
species had a very thin thallus and in all of them the colour was impure.
Gyrophorae seemed to be most affected: folds and outgrowths of the thallus
were formed and the internal tissues were partly disintegrated. Lichens on
the blocks of the glacier moraines which are subject to inundations of ice-
cold water after the snow has melted, were unhealthy looking, poorly
developed and often sterile, though able to persist in a barren state.
Lindsay[1125] noted as a result of such conditions on Cladoniae not only
sterility but also deformity both of vegetative and reproductive organs;
discolouration and mottling of the thallus and an increased development of
squamules of the primary thallus and on the podetia.
c. Wind. Horizontal crustaceous or foliose lichens are not liable to direct
injury by wind as their close adherence to the substratum sufficiently
shelters them. It is only when the wind carries with it any considerable
quantity of sand that the tree or rock surfaces are swept bare and prevented
from ever harbouring any vegetation, and also, as has been already noted,
the terrible winds round the poles are fatal to lichens exposed to the blasts
unless they are provided with a special protective cortex. After crustaceous
forms, species of Cetraria, Stereocaulon and Cladonia are best fitted for
weathering wind storms: the tufted[1126] cushion-like growth adopted by
these lichens gives them mutual protection, not only against wind, but
against superincumbent masses of snow. Kihlman[1123] has given us a vivid
account of wind action in the Tundra region. He noted numerous hollows
completely scooped out down to the sand: in these sheltered nooks he
observed the gradual colonization of the depressions, first by a growth of
hepatics and mosses and by such ground lichens as Peltigera canina, P.
aphthosa and Nephromium arcticum; they cover the soil and in time the
hollow becomes filled with a mass of vegetation consisting of Cladonias,
mosses, etc. On reaching a certain more exposed level these begin to wither
and die off at the tips, killed by the high cold winds. Then arrives Lecanora
tartarea, one of the commonest Arctic lichens, and one which is readily a
saprophyte on decayed vegetation. It covers completely the mound of
weakened plants which are thus smothered and finally killed. The collapse
of the substratum entails in turn the breaking of the Lecanora crust, and the
next high wind sweeps away the whole crumbling mass. How long
recolonization takes, it was impossible to find out.
species had a very thin thallus and in all of them the colour was impure.
Gyrophorae seemed to be most affected: folds and outgrowths of the thallus
were formed and the internal tissues were partly disintegrated. Lichens on
the blocks of the glacier moraines which are subject to inundations of ice-
cold water after the snow has melted, were unhealthy looking, poorly
developed and often sterile, though able to persist in a barren state.
Lindsay[1125] noted as a result of such conditions on Cladoniae not only
sterility but also deformity both of vegetative and reproductive organs;
discolouration and mottling of the thallus and an increased development of
squamules of the primary thallus and on the podetia.
c. Wind. Horizontal crustaceous or foliose lichens are not liable to direct
injury by wind as their close adherence to the substratum sufficiently
shelters them. It is only when the wind carries with it any considerable
quantity of sand that the tree or rock surfaces are swept bare and prevented
from ever harbouring any vegetation, and also, as has been already noted,
the terrible winds round the poles are fatal to lichens exposed to the blasts
unless they are provided with a special protective cortex. After crustaceous
forms, species of Cetraria, Stereocaulon and Cladonia are best fitted for
weathering wind storms: the tufted[1126] cushion-like growth adopted by
these lichens gives them mutual protection, not only against wind, but
against superincumbent masses of snow. Kihlman[1123] has given us a vivid
account of wind action in the Tundra region. He noted numerous hollows
completely scooped out down to the sand: in these sheltered nooks he
observed the gradual colonization of the depressions, first by a growth of
hepatics and mosses and by such ground lichens as Peltigera canina, P.
aphthosa and Nephromium arcticum; they cover the soil and in time the
hollow becomes filled with a mass of vegetation consisting of Cladonias,
mosses, etc. On reaching a certain more exposed level these begin to wither
and die off at the tips, killed by the high cold winds. Then arrives Lecanora
tartarea, one of the commonest Arctic lichens, and one which is readily a
saprophyte on decayed vegetation. It covers completely the mound of
weakened plants which are thus smothered and finally killed. The collapse
of the substratum entails in turn the breaking of the Lecanora crust, and the
next high wind sweeps away the whole crumbling mass. How long
recolonization takes, it was impossible to find out.
Page 449
Upright fruticose lichens are necessarily more liable to damage by wind,
but maritime Ramalinae and Roccellae do not seem to suffer in temperate
climates, though in regions of extreme cold fruticose forms are dwarfed and
stunted. The highest development of filamentous lichens is to be found in
more or less sheltered woods, but the effect of wind on these lichens is not
wholly unfavourable. Observations have been made by Peirce[1127] on two
American pendulous lichens which are dependent on wind for
dissemination. On the Californian coasts a very large and very frequent
species, Ramalina reticulata (Fig. 64), is seldom found undamaged by
wind. In Northern California the deciduous oaks Quercus alba and Q.
Douglasii are festooned with the lichen, while the evergreen “live oak,” Q.
chrysolepis, with persistent foliage, only bears scraps that have been blown
on to it. Nearer the coast and southward the lichen grows on all kinds of
trees and shrubs. The fronds of this Ramalina form a delicate reticulation
and when moist are easily torn. In the winter season, when the leaves are off
the trees, wind- and rain-storms are frequent; the lichen is then exposed to
the full force of the elements and fragments and shreds are blown to other
trees, becoming coiled and entangled round the naked branches and barky
excrescences, on which they continue to grow and fruit perfectly well. A
succeeding storm may loosen them and carry them still further. Peirce noted
that only plants developed from the spore formed hold-fasts and they were
always small, the largest formed measuring seven inches in length. Both the
hold-fast and the primary stalk were too slight to resist the tearing action of
the wind.
Schrenk[1128] made a series of observations and experiments with the
lichens Usnea plicata and U. dasypoga, long hanging forms common on
short-leaved conifers such as spruce and juniper. The branches of these trees
are often covered with tangled masses of the lichens not due to local
growth, but to wind-borne strands and to coiling and intertwining of the
filaments owing to successive wetting and drying. Tests were made as to the
force of wind required to tear the lichens and it was found that velocities of
77 miles per hour were not sufficient to cause any pieces of the lichen to fly
off when it was dry; but after soaking in water, the first pieces were torn off
at 50 miles an hour. These figures are, however, considered by Schrenk to
be too high as it was found impossible in artificially created wind to keep
but maritime Ramalinae and Roccellae do not seem to suffer in temperate
climates, though in regions of extreme cold fruticose forms are dwarfed and
stunted. The highest development of filamentous lichens is to be found in
more or less sheltered woods, but the effect of wind on these lichens is not
wholly unfavourable. Observations have been made by Peirce[1127] on two
American pendulous lichens which are dependent on wind for
dissemination. On the Californian coasts a very large and very frequent
species, Ramalina reticulata (Fig. 64), is seldom found undamaged by
wind. In Northern California the deciduous oaks Quercus alba and Q.
Douglasii are festooned with the lichen, while the evergreen “live oak,” Q.
chrysolepis, with persistent foliage, only bears scraps that have been blown
on to it. Nearer the coast and southward the lichen grows on all kinds of
trees and shrubs. The fronds of this Ramalina form a delicate reticulation
and when moist are easily torn. In the winter season, when the leaves are off
the trees, wind- and rain-storms are frequent; the lichen is then exposed to
the full force of the elements and fragments and shreds are blown to other
trees, becoming coiled and entangled round the naked branches and barky
excrescences, on which they continue to grow and fruit perfectly well. A
succeeding storm may loosen them and carry them still further. Peirce noted
that only plants developed from the spore formed hold-fasts and they were
always small, the largest formed measuring seven inches in length. Both the
hold-fast and the primary stalk were too slight to resist the tearing action of
the wind.
Schrenk[1128] made a series of observations and experiments with the
lichens Usnea plicata and U. dasypoga, long hanging forms common on
short-leaved conifers such as spruce and juniper. The branches of these trees
are often covered with tangled masses of the lichens not due to local
growth, but to wind-borne strands and to coiling and intertwining of the
filaments owing to successive wetting and drying. Tests were made as to the
force of wind required to tear the lichens and it was found that velocities of
77 miles per hour were not sufficient to cause any pieces of the lichen to fly
off when it was dry; but after soaking in water, the first pieces were torn off
at 50 miles an hour. These figures are, however, considered by Schrenk to
be too high as it was found impossible in artificially created wind to keep
Page 450
up the condition of saturation. It is the combination of wind and rain that is
so effective in ensuring the dispersal of both these lichens.
d. Human Agency. Though lichens are generally associated with
undisturbed areas and undisturbed conditions, yet accidents or convulsions
of nature, as well as changes effected by man, may at times prove
favourable to their development. The opening up of forests by thinning or
clearing will be followed in time by a growth of tree and ground forms;
newly planted trees may furnish a new lichen flora, and the building of
houses and walls with their intermixture of calcareous mortar will attract a
particular series of siliceous or of lime-loving lichens. A few lichens are
partial to the trees of cultivated areas, such as park-lands, avenues or road-
sides. Among these are several species of Physcia: Ph. pulverulenta, Ph.
ciliaris and Ph. stellaris, some species of Placodium, and those lichens such
as Lecanora varia that frequently grow on old palings.
On the other hand lichens are driven away from areas of dense
population, or from regions affected by the contaminated air of industrial
centres. In our older British Floras there are records of lichens collected in
London during the eighteenth century—in Hyde Park and on Hampstead
Heath—but these have long disappeared. A variety of Lecanora galactina
seems to be the only lichen left within the London district: it has been found
at Camden Town, Notting Hill and South Kensington.
So recently as 1866, Nylander[1129] made a list of the lichens growing in
the Luxembourg gardens in Paris; the chestnuts in the alley of the
Observatory were the most thickly covered, and the list includes about 35
different species or varieties, some of them poorly developed and occurring
but rarely, others always sterile, but quite a number in healthy fruiting
condition. All of them were crustaceous or squamulose forms except
Parmelia acetabulum, which was very rare and sterile; Physcia obscura var.
and Ph. pulverulenta var., also sterile; Physcia stellaris with occasional
abortive apothecia and Xanthoria parietina, abundant and fertile. In 1898,
Hue[1130] tells us, there were no lichens to be found on the trees and only
traces of lichen growth on the stone balustrades.
The question of atmospheric pollution in manufacturing districts and its
effect on vegetation, more especially on lichen vegetation, has received
special attention from Wheldon and Wilson[1131] in their account of the
so effective in ensuring the dispersal of both these lichens.
d. Human Agency. Though lichens are generally associated with
undisturbed areas and undisturbed conditions, yet accidents or convulsions
of nature, as well as changes effected by man, may at times prove
favourable to their development. The opening up of forests by thinning or
clearing will be followed in time by a growth of tree and ground forms;
newly planted trees may furnish a new lichen flora, and the building of
houses and walls with their intermixture of calcareous mortar will attract a
particular series of siliceous or of lime-loving lichens. A few lichens are
partial to the trees of cultivated areas, such as park-lands, avenues or road-
sides. Among these are several species of Physcia: Ph. pulverulenta, Ph.
ciliaris and Ph. stellaris, some species of Placodium, and those lichens such
as Lecanora varia that frequently grow on old palings.
On the other hand lichens are driven away from areas of dense
population, or from regions affected by the contaminated air of industrial
centres. In our older British Floras there are records of lichens collected in
London during the eighteenth century—in Hyde Park and on Hampstead
Heath—but these have long disappeared. A variety of Lecanora galactina
seems to be the only lichen left within the London district: it has been found
at Camden Town, Notting Hill and South Kensington.
So recently as 1866, Nylander[1129] made a list of the lichens growing in
the Luxembourg gardens in Paris; the chestnuts in the alley of the
Observatory were the most thickly covered, and the list includes about 35
different species or varieties, some of them poorly developed and occurring
but rarely, others always sterile, but quite a number in healthy fruiting
condition. All of them were crustaceous or squamulose forms except
Parmelia acetabulum, which was very rare and sterile; Physcia obscura var.
and Ph. pulverulenta var., also sterile; Physcia stellaris with occasional
abortive apothecia and Xanthoria parietina, abundant and fertile. In 1898,
Hue[1130] tells us, there were no lichens to be found on the trees and only
traces of lichen growth on the stone balustrades.
The question of atmospheric pollution in manufacturing districts and its
effect on vegetation, more especially on lichen vegetation, has received
special attention from Wheldon and Wilson[1131] in their account of the
Page 451
lichens of South Lancashire, a district peculiarly suitable for such an
inquiry, as nowhere, according to the observations, are the evil effects of
impure air so evident or so wide-spread. The unfavourable conditions have
prevailed for a long time and the lichens have consequently become very
rare, those that still survive leading but a meagre existence. The chief
impurity is coal smoke which is produced not only from factories but from
private dwellings, and its harmful effect goes far beyond the limits of the
towns or suburbs, lichens being seen to deteriorate as soon as there is the
slightest deposition of coal combustion products—especially sulphur
compounds—either on the plants or on the surfaces on which they grow.
The larger foliose and fruticose forms have evidently been the most
severely affected. “While genera of bark-loving lichens such as Calicium,
Usnea, Ramalina, Graphis, Opegrapha, Arthonia etc. are either wholly
absent or are poorly represented in the district,” corticolous species now
represent about 15 per cent. of those that are left; those that seem best to
resist the pernicious influences of the smoky atmosphere are, principally,
Lecanora varia, Parmelia saxatilis, P. physodes and to a less degree P.
sulcata, P. fuliginosa var. laetevirens and Pertusaria amara.
Saxicolous lichens have also suffered severely in South Lancashire; not
only the number of species, but the number of individuals is enormously
reduced and the specimens that have persisted are usually poorly developed.
The smoke-producing towns are situated in the valley-bottoms, and the
smoke rises and drifts on to the surrounding hills and moorlands. The
authors noted that crustaceous rock-lichens were in better condition on
horizontal surfaces such as the copings of walls, or half-buried stones, etc.
than on the perpendicular or sloping faces of rocks or walls. This was
probably due to what they observed as to the effect of water trickling down
the inclined substrata and becoming charged with acid from the rock
surfaces. They also observed further that a calcareous substratum seemed to
counteract the effect of the smoke, the sulphuric acid combining with the
lime to form calcium sulphate, and the surface-washings thus being
neutralized, the lichens there are more favourably situated. They found in
good fruiting condition, on mortar, cement or concrete, the species
Lecanora urbana, L. campestris, L. crenulata, Verrucaria muralis, V.
rupestris, Thelidium microcarpum and Staurothele hymenogonia. Some of
these occurred on the mortar of sandstone walls close to the town, “whilst
on the surface of the sandstone itself no lichens were present.”
inquiry, as nowhere, according to the observations, are the evil effects of
impure air so evident or so wide-spread. The unfavourable conditions have
prevailed for a long time and the lichens have consequently become very
rare, those that still survive leading but a meagre existence. The chief
impurity is coal smoke which is produced not only from factories but from
private dwellings, and its harmful effect goes far beyond the limits of the
towns or suburbs, lichens being seen to deteriorate as soon as there is the
slightest deposition of coal combustion products—especially sulphur
compounds—either on the plants or on the surfaces on which they grow.
The larger foliose and fruticose forms have evidently been the most
severely affected. “While genera of bark-loving lichens such as Calicium,
Usnea, Ramalina, Graphis, Opegrapha, Arthonia etc. are either wholly
absent or are poorly represented in the district,” corticolous species now
represent about 15 per cent. of those that are left; those that seem best to
resist the pernicious influences of the smoky atmosphere are, principally,
Lecanora varia, Parmelia saxatilis, P. physodes and to a less degree P.
sulcata, P. fuliginosa var. laetevirens and Pertusaria amara.
Saxicolous lichens have also suffered severely in South Lancashire; not
only the number of species, but the number of individuals is enormously
reduced and the specimens that have persisted are usually poorly developed.
The smoke-producing towns are situated in the valley-bottoms, and the
smoke rises and drifts on to the surrounding hills and moorlands. The
authors noted that crustaceous rock-lichens were in better condition on
horizontal surfaces such as the copings of walls, or half-buried stones, etc.
than on the perpendicular or sloping faces of rocks or walls. This was
probably due to what they observed as to the effect of water trickling down
the inclined substrata and becoming charged with acid from the rock
surfaces. They also observed further that a calcareous substratum seemed to
counteract the effect of the smoke, the sulphuric acid combining with the
lime to form calcium sulphate, and the surface-washings thus being
neutralized, the lichens there are more favourably situated. They found in
good fruiting condition, on mortar, cement or concrete, the species
Lecanora urbana, L. campestris, L. crenulata, Verrucaria muralis, V.
rupestris, Thelidium microcarpum and Staurothele hymenogonia. Some of
these occurred on the mortar of sandstone walls close to the town, “whilst
on the surface of the sandstone itself no lichens were present.”
Page 452
Soil-lichens were also strongly affected, the Cladoniae of the moorlands
being in a very depauperate condition, and there was no trace of
Stereocaulon or of Sphaerophorus species, which, according to older
records, previously occurred on the high uplands.
The influence of human agency is well exemplified in one of the London
districts. In 1883 Crombie published a list of the lichens recorded from
Epping Forest during the nineteenth century. They numbered 171 species,
varieties or forms, but, at the date of publication, many had died out owing
to the destruction of the older trees; the undue crowding of the trees that
were left and the ever increasing population on the outskirts of the Forest.
Crombie himself made a systematic search for those that remained, and
could only find some 85 different kinds, many of them in a fragmentary or
sterile condition.
R. Paulson and P. Thompson[1132] commenced a lichen exploration of the
Forest 27 years after Crombie’s report was published, and they have found
that though the houses and the population have continued to increase round
the area, the lichens have not suffered. “Species considered by Crombie as
rare or sterile are now fairly abundant, and produce numerous apothecia.
Such are Baeomyces rufus, B. roseus, Cladonia pyxidata, Cl. macilenta var.
coronata, Cl. Floerkeana f. trachypoda, Lecanora varia, Lecidea
decolorans and Lecidea tricolor.” They conclude that “some at least of the
Forest lichens are in a far more healthy and fertile condition than they were
27 years ago.” They attribute the improvement mainly to the thinning of
trees and the opening up of glades through the Forest, letting in light and air
not only to the tree trunks but to the soil. In 1912[1133] the authors in a
second paper reported that 109 different kinds had been determined, and
these, though still falling far short of the older lichen flora, considerably
exceed the list of 85 recorded in 1883.
C. Lichen Communities
Lichen communities fall into a few definite groups, though, as we shall
see, not a few species may be found to occur in several groups—species
that have been designated by some workers as “wanderers.” The leading
communities are:
being in a very depauperate condition, and there was no trace of
Stereocaulon or of Sphaerophorus species, which, according to older
records, previously occurred on the high uplands.
The influence of human agency is well exemplified in one of the London
districts. In 1883 Crombie published a list of the lichens recorded from
Epping Forest during the nineteenth century. They numbered 171 species,
varieties or forms, but, at the date of publication, many had died out owing
to the destruction of the older trees; the undue crowding of the trees that
were left and the ever increasing population on the outskirts of the Forest.
Crombie himself made a systematic search for those that remained, and
could only find some 85 different kinds, many of them in a fragmentary or
sterile condition.
R. Paulson and P. Thompson[1132] commenced a lichen exploration of the
Forest 27 years after Crombie’s report was published, and they have found
that though the houses and the population have continued to increase round
the area, the lichens have not suffered. “Species considered by Crombie as
rare or sterile are now fairly abundant, and produce numerous apothecia.
Such are Baeomyces rufus, B. roseus, Cladonia pyxidata, Cl. macilenta var.
coronata, Cl. Floerkeana f. trachypoda, Lecanora varia, Lecidea
decolorans and Lecidea tricolor.” They conclude that “some at least of the
Forest lichens are in a far more healthy and fertile condition than they were
27 years ago.” They attribute the improvement mainly to the thinning of
trees and the opening up of glades through the Forest, letting in light and air
not only to the tree trunks but to the soil. In 1912[1133] the authors in a
second paper reported that 109 different kinds had been determined, and
these, though still falling far short of the older lichen flora, considerably
exceed the list of 85 recorded in 1883.
C. Lichen Communities
Lichen communities fall into a few definite groups, though, as we shall
see, not a few species may be found to occur in several groups—species
that have been designated by some workers as “wanderers.” The leading
communities are:
Page 453
1. Arboreal, including those that grow on leaves, bark or wood.
2. Terricolous, ground-lichens.
3. Saxicolous, rock-lichens.
4. Omnicolous, lichens that can exist on the most varied substrata, such
as bones, leather, iron, etc.
5. Localized Communities in which owing to special conditions the
lichens may become permanent and dominant.
In all the groups lichens are more or less abundant. In arboreal and
terricolous formations they may be associated with other plants; in
saxicolous and omnicolous formations they are the dominant vegetation. It
will be desirable to select only a few of the typical communities that have
been observed and recorded by workers in various lands.
1. ARBOREAL
Arboreal communities may be held to comprise those lichens that grow
on wood, bark or leaves. They are usually the dominant and often the sole
vegetation, but in some localities there may be a considerable development
of mosses, etc., or a mantle of protococcaceous algae may cover the bark.
Certain lichens that are normally corticolous may also be found on dead
wood or may be erratic on neighbouring rocks: Usnea florida for instance is
a true corticolous species, but it grows occasionally on rocks or boulders
generally in crowded association with other foliose or fruticose lichens.
Most of the larger lichens are arboreal, though there are many exceptions:
Parmelia perlata develops to a large size on boulders as well as on trees;
some species of Ramalinae are constantly saxicolous while there are only
rare instances of Roccellae that grow on trees. The purely tropical or
subtropical genera are corticolous rather than saxicolous, but species that
have appeared in colder regions may have acquired the saxicolous habit:
thus Coenogonium in the tropics grows on trees, but the European species,
C. ebeneum, grows on stone.
a. Epiphyllous. These grow on Ferns or on the coriaceous leaves of
evergreens in the tropics. Many of them are associated with Phycopeltis,
Phyllactidium or Mycoidea, and follow in the wake of these algae.
2. Terricolous, ground-lichens.
3. Saxicolous, rock-lichens.
4. Omnicolous, lichens that can exist on the most varied substrata, such
as bones, leather, iron, etc.
5. Localized Communities in which owing to special conditions the
lichens may become permanent and dominant.
In all the groups lichens are more or less abundant. In arboreal and
terricolous formations they may be associated with other plants; in
saxicolous and omnicolous formations they are the dominant vegetation. It
will be desirable to select only a few of the typical communities that have
been observed and recorded by workers in various lands.
1. ARBOREAL
Arboreal communities may be held to comprise those lichens that grow
on wood, bark or leaves. They are usually the dominant and often the sole
vegetation, but in some localities there may be a considerable development
of mosses, etc., or a mantle of protococcaceous algae may cover the bark.
Certain lichens that are normally corticolous may also be found on dead
wood or may be erratic on neighbouring rocks: Usnea florida for instance is
a true corticolous species, but it grows occasionally on rocks or boulders
generally in crowded association with other foliose or fruticose lichens.
Most of the larger lichens are arboreal, though there are many exceptions:
Parmelia perlata develops to a large size on boulders as well as on trees;
some species of Ramalinae are constantly saxicolous while there are only
rare instances of Roccellae that grow on trees. The purely tropical or
subtropical genera are corticolous rather than saxicolous, but species that
have appeared in colder regions may have acquired the saxicolous habit:
thus Coenogonium in the tropics grows on trees, but the European species,
C. ebeneum, grows on stone.
a. Epiphyllous. These grow on Ferns or on the coriaceous leaves of
evergreens in the tropics. Many of them are associated with Phycopeltis,
Phyllactidium or Mycoidea, and follow in the wake of these algae.
Page 454
Observations are lacking as to the associations or societies of these lichens
whether they grow singly or in companies. The best known are the
Strigulaceae: there are six genera in that family, and some of the species
have a wide distribution. The most frequent genus is Strigula associated
with Phycopeltis which forms round grey spots on leaves, and is almost
entirely confined to tropical regions. Chodat[1134] records a sterile species,
S. Buxi, on box leaves from the neighbourhood of Geneva.
Other genera, such as those of Ectolechiaceae, which inhabit fern scales
and evergreen leaves, are associated with Protococcaceae. Pilocarpon
leucoblepharum with similar gonidia grows round the base of pine-needles.
It is found in the Caucasus. In our own woods, along the outer edges, the
lower spreading branches of the fir-trees are often decked with numerous
plants of Parmelia physodes, a true “plant society,” but that lichen is a
confirmed “wanderer.” Biatorina Bouteillei, on box leaves, is a British and
Continental lichen.
b. Corticolous. In this series are to be found many varying groups, the
type of lichen depending more on the physical nature of the bark than on
the kind of trees. Those with a smooth bark such as hazel, beech, lime, etc.,
and younger trees in general, bear only crustaceous species, many of them
with a very thin thallus, often partly immersed below the surface. As the
trees become older and the bark takes on a more ragged character, other
types of lichens gain a foothold, such as the thicker crustaceous forms like
Pertusaria, or the larger foliose and fruticose species. The moisture that is
collected and retained by the rough bark is probably the important factor in
the establishment of the thicker crusts, and, as regards the larger lichens,
both rhizinae and hold-fasts are able to gain a secure grip of the broken-up
unequal surface, such as would be quite impossible on trees with smooth
bark.
Among the first to pay attention to the ecological grouping of corticolous
lichens was A.L. Fée[1135], a Professor of Natural Science and an Army
doctor, who wrote on many literary and botanical subjects. In his account of
the Cryptogams that grow on “officinal bark,” he states that the most
lichenized of all the Cinchonae was the one known as “Loxa,” the bark of
which was covered with species of Parmelia, Sticta and Usnea along with
crustaceous forms of Lecanora, Lecidea, Graphis and Verrucaria. Another
species, Cinchona cordifolia, was completely covered, but with crustaceous
whether they grow singly or in companies. The best known are the
Strigulaceae: there are six genera in that family, and some of the species
have a wide distribution. The most frequent genus is Strigula associated
with Phycopeltis which forms round grey spots on leaves, and is almost
entirely confined to tropical regions. Chodat[1134] records a sterile species,
S. Buxi, on box leaves from the neighbourhood of Geneva.
Other genera, such as those of Ectolechiaceae, which inhabit fern scales
and evergreen leaves, are associated with Protococcaceae. Pilocarpon
leucoblepharum with similar gonidia grows round the base of pine-needles.
It is found in the Caucasus. In our own woods, along the outer edges, the
lower spreading branches of the fir-trees are often decked with numerous
plants of Parmelia physodes, a true “plant society,” but that lichen is a
confirmed “wanderer.” Biatorina Bouteillei, on box leaves, is a British and
Continental lichen.
b. Corticolous. In this series are to be found many varying groups, the
type of lichen depending more on the physical nature of the bark than on
the kind of trees. Those with a smooth bark such as hazel, beech, lime, etc.,
and younger trees in general, bear only crustaceous species, many of them
with a very thin thallus, often partly immersed below the surface. As the
trees become older and the bark takes on a more ragged character, other
types of lichens gain a foothold, such as the thicker crustaceous forms like
Pertusaria, or the larger foliose and fruticose species. The moisture that is
collected and retained by the rough bark is probably the important factor in
the establishment of the thicker crusts, and, as regards the larger lichens,
both rhizinae and hold-fasts are able to gain a secure grip of the broken-up
unequal surface, such as would be quite impossible on trees with smooth
bark.
Among the first to pay attention to the ecological grouping of corticolous
lichens was A.L. Fée[1135], a Professor of Natural Science and an Army
doctor, who wrote on many literary and botanical subjects. In his account of
the Cryptogams that grow on “officinal bark,” he states that the most
lichenized of all the Cinchonae was the one known as “Loxa,” the bark of
which was covered with species of Parmelia, Sticta and Usnea along with
crustaceous forms of Lecanora, Lecidea, Graphis and Verrucaria. Another
species, Cinchona cordifolia, was completely covered, but with crustaceous
Page 455
forms only: species of Graphidaceae, Lecanora and Lecidea were abundant,
but Trypethelium, Chiodecton, Pyrenula and Verrucaria were also
represented. On each species of tree some particular lichen was generally
dominant:
A species of Thelotrema on Cinchona oblongifolia.
A species of Chiodecton on C. cordifolia.
A species of Sarcographa on C. condaminea.
Fries[1136], in his geography of lichens, distinguished as arboreal and
“hypophloeodal” species of Verrucariaceae, while the Graphideae, which
also grew on bark, were erumpent. Usnea barbata, Evernia prunastri, etc.,
though growing normally on trees might, he says, be associated with rock
species.
More extensive studies of habitat were made by Krempelhuber[1137] in
his Bavarian Lichens. In summing up the various “formations” of lichens,
he gives lists of those that grow, in that district, exclusively on either
coniferous or deciduous trees, with added lists of those that grow on either
type of tree indifferently. Among those found always on conifers or on
coniferous wood are: Letharia vulpina, Cetraria Laureri, Parmelia
aleurites and a number of crustaceous species. Those that are restricted to
the trunks and branches of leafy trees are crustaceous with the exception of
some foliose Collemaceae such as Leptogium Hildenbrandii, Collema
nigrescens, etc.
Arnold[1138] carried to its furthest limit the method of arranging lichens
ecologically, in his account of those plants from the neighbourhood of
Munich. He gives “formation” lists, not only for particular substrata and in
special situations, but he recapitulates the species that he found on the
several different trees. It is not possible to reproduce such a detailed survey,
which indeed only emphasizes the fact that the physical characters of the
bark are the most important factors in lichen ecology: that on smooth bark,
whether of young trees, or on bark that never becomes really rugged, there
is a preponderance of species with a semi-immersed thallus, and very
generally of those that are associated with Trentepohlia gonidia, such as
but Trypethelium, Chiodecton, Pyrenula and Verrucaria were also
represented. On each species of tree some particular lichen was generally
dominant:
A species of Thelotrema on Cinchona oblongifolia.
A species of Chiodecton on C. cordifolia.
A species of Sarcographa on C. condaminea.
Fries[1136], in his geography of lichens, distinguished as arboreal and
“hypophloeodal” species of Verrucariaceae, while the Graphideae, which
also grew on bark, were erumpent. Usnea barbata, Evernia prunastri, etc.,
though growing normally on trees might, he says, be associated with rock
species.
More extensive studies of habitat were made by Krempelhuber[1137] in
his Bavarian Lichens. In summing up the various “formations” of lichens,
he gives lists of those that grow, in that district, exclusively on either
coniferous or deciduous trees, with added lists of those that grow on either
type of tree indifferently. Among those found always on conifers or on
coniferous wood are: Letharia vulpina, Cetraria Laureri, Parmelia
aleurites and a number of crustaceous species. Those that are restricted to
the trunks and branches of leafy trees are crustaceous with the exception of
some foliose Collemaceae such as Leptogium Hildenbrandii, Collema
nigrescens, etc.
Arnold[1138] carried to its furthest limit the method of arranging lichens
ecologically, in his account of those plants from the neighbourhood of
Munich. He gives “formation” lists, not only for particular substrata and in
special situations, but he recapitulates the species that he found on the
several different trees. It is not possible to reproduce such a detailed survey,
which indeed only emphasizes the fact that the physical characters of the
bark are the most important factors in lichen ecology: that on smooth bark,
whether of young trees, or on bark that never becomes really rugged, there
is a preponderance of species with a semi-immersed thallus, and very
generally of those that are associated with Trentepohlia gonidia, such as
Page 456
Graphidaceae or Pyrenulaceae, though certain species of Lecidea, Lecanora
and others also prefer the smooth substratum.
Bruce Fink[1139] has published a series of important papers on lichen
communities in America, some of them similar to what we should find in
the British Isles.
On trees with smooth bark he records in the Minnesota district:
Xanthoria polycarpa.
Candelaria concolor.
Parmelia olivacea, P. adglutinata.
Placodium cerinum.
Lecanora subfusca.
Bacidia fusca-rubella.
Lecidea enteroleuca.
Graphis scripta.
Arthonia lecideella, A. dispersa.
Arthopyrenia punctiformis, A. fallax.
Pyrenula nitida, P. thelena, P. cinerella, P. leucoplaca.
and others also prefer the smooth substratum.
Bruce Fink[1139] has published a series of important papers on lichen
communities in America, some of them similar to what we should find in
the British Isles.
On trees with smooth bark he records in the Minnesota district:
Xanthoria polycarpa.
Candelaria concolor.
Parmelia olivacea, P. adglutinata.
Placodium cerinum.
Lecanora subfusca.
Bacidia fusca-rubella.
Lecidea enteroleuca.
Graphis scripta.
Arthonia lecideella, A. dispersa.
Arthopyrenia punctiformis, A. fallax.
Pyrenula nitida, P. thelena, P. cinerella, P. leucoplaca.
Page 457
On rough bark he records:
Ramalina calicaris, R. fraxinea, R. fastigiata.
Teloschistes chrysophthalmus.
Xanthoria polycarpa, X. lychnea.
Candelaria concolor.
Parmelia perforata, P. crinita, P. Borreri, P. tiliacea, P. saxatilis, P.
caperata.
Physcia granulifera, Ph. pulverulenta, Ph. stellaris, Ph. tribacia, Ph.
obscura.
Collema pycnocarpum, C. flaccidum.
Leptogium mycochroum.
Placodium aurantiacum, Pl. cerinum.
Lecanora subfusca.
Pertusaria leioplaca, P. velata.
Bacidia rubella, B. fuscorubella.
Lecidea enteroleuca.
Rhizocarpon alboatrum, Buellia parasema.
Opegrapha varia.
Graphis scripta.
Arthonia lecideella, A. radiata.
Arthopyrenia quinqueseptata, A. macrospora.
Pyrenula nitida, P. leucoplaca.
Finally, as generally representative of the commonest lichens in our
woods of deciduous trees, including both smooth- and rough-barked, the
community of oak-hazel woods as observed by Watson[1140] in Somerset
may be quoted:
Ramalina calicaris, R. fraxinea, R. fastigiata.
Teloschistes chrysophthalmus.
Xanthoria polycarpa, X. lychnea.
Candelaria concolor.
Parmelia perforata, P. crinita, P. Borreri, P. tiliacea, P. saxatilis, P.
caperata.
Physcia granulifera, Ph. pulverulenta, Ph. stellaris, Ph. tribacia, Ph.
obscura.
Collema pycnocarpum, C. flaccidum.
Leptogium mycochroum.
Placodium aurantiacum, Pl. cerinum.
Lecanora subfusca.
Pertusaria leioplaca, P. velata.
Bacidia rubella, B. fuscorubella.
Lecidea enteroleuca.
Rhizocarpon alboatrum, Buellia parasema.
Opegrapha varia.
Graphis scripta.
Arthonia lecideella, A. radiata.
Arthopyrenia quinqueseptata, A. macrospora.
Pyrenula nitida, P. leucoplaca.
Finally, as generally representative of the commonest lichens in our
woods of deciduous trees, including both smooth- and rough-barked, the
community of oak-hazel woods as observed by Watson[1140] in Somerset
may be quoted:
Page 458
Collema flaccidum.
Calicium hyperellum.
Ramalina calicaris, R. fraxinea with var. ampliata, R. fastigiata, R.
farinacea and R. pollinaria.
Parmelia saxatilis and f. furfuracea, P. caperata, P. physodes.
Physcia pulverulenta, Ph. tenella (hispida).
Lecanora subfusca, L. rugosa.
Pertusaria amara, P. globulifera, P. communis, P. Wulfenii.
Lecidea (Buellia) canescens.
Graphis scripta.
And on the soil of these woods:
Cladonia pyxidata, Cl. pungens, Cl. macilenta, Cl. pityrea, Cl.
squamosa and Cl. sylvatica.
Paulson[1141], from his observations of lichens in Hertfordshire, has
concluded that the presence or absence of lichens on trees is influenced to a
considerable degree by the nature of the soil. They were more abundant in
woods on light well-drained soils than on similar communities of trees on
heavier soils, though the shade in the former was slightly more dense and
therefore less favourable to their development; the cause of this connection
is not known.
c. Lignicolous. Lichens frequenting the branches of trees do not long
continue when these have fallen to the ground. This may be due to the lack
of light and air, but Bouly de Lesdain[1142] has suggested that the chemical
reactions produced by the decomposition of the bast fibres are fatal to them,
Lecidea parasema alone continuing to grow and even existing for some
time on the detached shreds of bark.
On worked wood, such as old doors or old palings, light and air are well
provided and there is often an abundant growth of lichens, many of which
seem to prefer that substratum: the fibres of the wood loosened by
weathering retain moisture and yield some nutriment to the lichen hyphae
Calicium hyperellum.
Ramalina calicaris, R. fraxinea with var. ampliata, R. fastigiata, R.
farinacea and R. pollinaria.
Parmelia saxatilis and f. furfuracea, P. caperata, P. physodes.
Physcia pulverulenta, Ph. tenella (hispida).
Lecanora subfusca, L. rugosa.
Pertusaria amara, P. globulifera, P. communis, P. Wulfenii.
Lecidea (Buellia) canescens.
Graphis scripta.
And on the soil of these woods:
Cladonia pyxidata, Cl. pungens, Cl. macilenta, Cl. pityrea, Cl.
squamosa and Cl. sylvatica.
Paulson[1141], from his observations of lichens in Hertfordshire, has
concluded that the presence or absence of lichens on trees is influenced to a
considerable degree by the nature of the soil. They were more abundant in
woods on light well-drained soils than on similar communities of trees on
heavier soils, though the shade in the former was slightly more dense and
therefore less favourable to their development; the cause of this connection
is not known.
c. Lignicolous. Lichens frequenting the branches of trees do not long
continue when these have fallen to the ground. This may be due to the lack
of light and air, but Bouly de Lesdain[1142] has suggested that the chemical
reactions produced by the decomposition of the bast fibres are fatal to them,
Lecidea parasema alone continuing to grow and even existing for some
time on the detached shreds of bark.
On worked wood, such as old doors or old palings, light and air are well
provided and there is often an abundant growth of lichens, many of which
seem to prefer that substratum: the fibres of the wood loosened by
weathering retain moisture and yield some nutriment to the lichen hyphae
Page 459
which burrow among them. Though a number of lichens grow willingly on
dead wood, there are probably none that are wholly restricted to such a
habitat. A few, such as the species of Coniocybe, are generally to be found
on dead roots of trees or creeping loosely over dead twigs. They are shade
lichens and fond of moisture.
The species on palings—or “dead wood communities”—most familiar to
us in our country are:
Usnea hirta.
Cetraria diffusa.
Evernia furfuracea.
Parmelia scortia, P. physodes.
Xanthoria parietina.
Placodium cerinum.
Rinodina exigua.
Lecanora Hageni, L. varia and its allies.
Lecidea ostreata, L. parasema.
Buellia myriocarpa.
Cladoniaceae and Caliciaceae (several species).
These may be found in very varying association. It has indeed been
remarked that the dominant plant may be simply the one that has first
gained a footing, though the larger and more vigorous lichens tend to crowd
out the others. Bruce Fink[1143] has recorded associations in Minnesota:
On wood:
Teloschistes chrysophthalmus.
Placodium cerinum.
Lecanora Hageni, L. varia.
Rinodina sophodes, R. exigua.
dead wood, there are probably none that are wholly restricted to such a
habitat. A few, such as the species of Coniocybe, are generally to be found
on dead roots of trees or creeping loosely over dead twigs. They are shade
lichens and fond of moisture.
The species on palings—or “dead wood communities”—most familiar to
us in our country are:
Usnea hirta.
Cetraria diffusa.
Evernia furfuracea.
Parmelia scortia, P. physodes.
Xanthoria parietina.
Placodium cerinum.
Rinodina exigua.
Lecanora Hageni, L. varia and its allies.
Lecidea ostreata, L. parasema.
Buellia myriocarpa.
Cladoniaceae and Caliciaceae (several species).
These may be found in very varying association. It has indeed been
remarked that the dominant plant may be simply the one that has first
gained a footing, though the larger and more vigorous lichens tend to crowd
out the others. Bruce Fink[1143] has recorded associations in Minnesota:
On wood:
Teloschistes chrysophthalmus.
Placodium cerinum.
Lecanora Hageni, L. varia.
Rinodina sophodes, R. exigua.
Page 460
Buellia parasema (disciformis), B. turgescens.
Calicium parietinum.
Thelocarpon prasinellum.
On rotten stumps and prostrate logs: Peltigera canina, Cladonia
fimbriata var. tubaeformis, Cl. gracilis, Cl. verticillata, Cl. symphicarpia,
Cl. macilenta, Cl. cristatella.
Except for one or two species such as Buellia turgescens, Cladonia
symphicarpia, etc., the associations could be easy paralleled in our own
country, though with us Peltigera canina, Cladonia gracilis and Cl.
verticillata are ground forms.
2. TERRICOLOUS
In this community other vegetation is dominant, lichens are subsidiary. In
certain conditions, as on heaths, they gain a permanent footing, in others
they are temporary denizens and are easily crowded out. As they are
generally in close contact with the ground they are peculiarly dependent on
the nature of the soil and the water content. There are several distinct
substrata to be considered each with its characteristic flora. Cultivated soil
and grass lands need scarcely be included, as in the former the processes of
cultivation are too harassing for lichen growth, and only on the more
permament somewhat damp mossy meadows do we get such a species as
Peltigera canina in abundance. Some of the earth-lichens are among the
quickest growers: the apothecia of Baeomyces roseus appear and disappear
within a year. Thrombium epigaeum develops in half a year; Thelidium
minutulum in cultures grew from spore to spore, according to Stahl[1144], in
three months.
There are three principal types of soil composition: (1) that in which
there is more or less of lime; (2) soils in which silica in some form or other
predominates, and (3) soils which contain an appreciable amount of humus.
Communities restricted to certain soils such as sand-dunes, etc., are
treated separately.
a. On calcareous soil. Any admixture of lime in the soil, either as chalk,
limy clay or shell sand is at once reflected in the character of the lichen
Calicium parietinum.
Thelocarpon prasinellum.
On rotten stumps and prostrate logs: Peltigera canina, Cladonia
fimbriata var. tubaeformis, Cl. gracilis, Cl. verticillata, Cl. symphicarpia,
Cl. macilenta, Cl. cristatella.
Except for one or two species such as Buellia turgescens, Cladonia
symphicarpia, etc., the associations could be easy paralleled in our own
country, though with us Peltigera canina, Cladonia gracilis and Cl.
verticillata are ground forms.
2. TERRICOLOUS
In this community other vegetation is dominant, lichens are subsidiary. In
certain conditions, as on heaths, they gain a permanent footing, in others
they are temporary denizens and are easily crowded out. As they are
generally in close contact with the ground they are peculiarly dependent on
the nature of the soil and the water content. There are several distinct
substrata to be considered each with its characteristic flora. Cultivated soil
and grass lands need scarcely be included, as in the former the processes of
cultivation are too harassing for lichen growth, and only on the more
permament somewhat damp mossy meadows do we get such a species as
Peltigera canina in abundance. Some of the earth-lichens are among the
quickest growers: the apothecia of Baeomyces roseus appear and disappear
within a year. Thrombium epigaeum develops in half a year; Thelidium
minutulum in cultures grew from spore to spore, according to Stahl[1144], in
three months.
There are three principal types of soil composition: (1) that in which
there is more or less of lime; (2) soils in which silica in some form or other
predominates, and (3) soils which contain an appreciable amount of humus.
Communities restricted to certain soils such as sand-dunes, etc., are
treated separately.
a. On calcareous soil. Any admixture of lime in the soil, either as chalk,
limy clay or shell sand is at once reflected in the character of the lichen
Page 461
flora. On calcareous soil we may look for any of the squamulose Lecanorae
or Lecideae that are terricolous species, such as Lecanora crassa, L.
lentigera, Placodium fulgens, Lecidea lurida and L. decipiens. There are
also the many lichens that grow on mortar or on the accumulated debris
mixed with lime in the crevices of walls, such as Biatorina
coeruleonigricans, species of Placodium, several species of Collema and of
Verrucariaceae.
Bruce Fink[1145] found in N.W. Minnesota an association on exposed
calcareous earth as follows:
Heppia Despreauxii.
Urceolaria scruposa.
Biatora (Lecidea) decipiens.
Biatora (Bacidia) muscorum.
Dermatocarpon hepaticum.
This particular association occupied the slope of a hill that was washed
by lime-impregnated water. It was normally a dry habitat and the lichens
were distinguished by small closely adnate thalli.
There are more lichens confined to limy than to sandy soil. Arnold[1146]
gives a list of those he observed near Munich on the former habitat:
Cladonia sylvatica f. alpestris.
Cladonia squamosa f. subsquamosa.
Cladonia rangiformis f. foliosa.
Cladonia cariosa and f. symphicarpa.
Peltigera canina f. soreumatica.
Solorina spongiosa.
Heppia virescens.
Lecanora crassa.
Urceolaria scruposa f. argillacea.
or Lecideae that are terricolous species, such as Lecanora crassa, L.
lentigera, Placodium fulgens, Lecidea lurida and L. decipiens. There are
also the many lichens that grow on mortar or on the accumulated debris
mixed with lime in the crevices of walls, such as Biatorina
coeruleonigricans, species of Placodium, several species of Collema and of
Verrucariaceae.
Bruce Fink[1145] found in N.W. Minnesota an association on exposed
calcareous earth as follows:
Heppia Despreauxii.
Urceolaria scruposa.
Biatora (Lecidea) decipiens.
Biatora (Bacidia) muscorum.
Dermatocarpon hepaticum.
This particular association occupied the slope of a hill that was washed
by lime-impregnated water. It was normally a dry habitat and the lichens
were distinguished by small closely adnate thalli.
There are more lichens confined to limy than to sandy soil. Arnold[1146]
gives a list of those he observed near Munich on the former habitat:
Cladonia sylvatica f. alpestris.
Cladonia squamosa f. subsquamosa.
Cladonia rangiformis f. foliosa.
Cladonia cariosa and f. symphicarpa.
Peltigera canina f. soreumatica.
Solorina spongiosa.
Heppia virescens.
Lecanora crassa.
Urceolaria scruposa f. argillacea.
Page 462
Verrucaria (Thrombium) epigaea.
Lecidea decipiens.
Dermatocarpon cinereum.
Collema granulatum.
Collema tenax.
Leptogium byssinum.
It is interesting to note how many of these lichens specialized as to
habitat are forms of species that grow in other situations.
b. On siliceous soil. Lichens are not generally denizens of cultivated soil;
a few settle on clay or on sandbanks. Cladonia fimbriata and Cl. pyxidata
grow frequently in such situations; others more or less confined to sandy or
gravelly soil are, in the British Isles:
Baeomyces roseus.
Baeomyces rufus.
Baeomyces placophyllus.
Endocarpon spp.
Gongylia viridis.
Dermatocarpon lachneum
Dermatocarpon hepaticum.
Dermatocarpon cinereum.
These very generally grow in extended societies of one species only.
In his enumeration of soil-lichens Arnold[1146] gives 40 species that grow
on siliceous soil, as against 57 on calcareous. Many of them occurred on
both. Those around Munich on siliceous soil only were:
Cladonia coccifera.
Cladonia agariciformis.
Secoliga (Gyalecta) bryophaga.
Lecidea decipiens.
Dermatocarpon cinereum.
Collema granulatum.
Collema tenax.
Leptogium byssinum.
It is interesting to note how many of these lichens specialized as to
habitat are forms of species that grow in other situations.
b. On siliceous soil. Lichens are not generally denizens of cultivated soil;
a few settle on clay or on sandbanks. Cladonia fimbriata and Cl. pyxidata
grow frequently in such situations; others more or less confined to sandy or
gravelly soil are, in the British Isles:
Baeomyces roseus.
Baeomyces rufus.
Baeomyces placophyllus.
Endocarpon spp.
Gongylia viridis.
Dermatocarpon lachneum
Dermatocarpon hepaticum.
Dermatocarpon cinereum.
These very generally grow in extended societies of one species only.
In his enumeration of soil-lichens Arnold[1146] gives 40 species that grow
on siliceous soil, as against 57 on calcareous. Many of them occurred on
both. Those around Munich on siliceous soil only were:
Cladonia coccifera.
Cladonia agariciformis.
Secoliga (Gyalecta) bryophaga.
Page 463
Baeomyces rufus.
Lecidea gelatinosa.
Psorotichia lutophila.
Mayfield[1147] in his account of the Boulder Clay lichen flora of Suffolk
found only four species that attained to full development on banks and
hedgerows. These were: Collema pulposum, Cladonia pyxidata, Cl. furcata
var. corymbosa and Peltigera polydactyla.
On bare heaths of gravelly soil in Epping Forest Paulson and
Thompson[1148] describe an association of such lichens as:
Baeomyces roseus.
Baeomyces rufus.
Pycnothelia papillaria.
Cladonia coccifera.
Lecidea granulosa.
Cladonia macilenta.
Cladonia furcata.
Cetraria aculeata.
Peltigera spuria.
And on flints in the soil: Lecidea crustulata and Rhizocarpon
confervoides. They found that Peltigera spuria colonized very quickly the
burnt patches of earth which are of frequent occurrence in Epping Forest,
while on wet sandy heaths amongst heather they found associated Cladonia
sylvatica f. tenuis and Cl. fimbriata subsp. fibula.
c. On bricks, etc. Closely allied with siliceous soil-lichens are those that
form communities on bricks. As these when built into walls are more or less
smeared with mortar, a mixture of lime-loving species also arrives. Roof
tiles are more free from calcareous matter. Lesdain[1149] noted that on the
dunes, though stray bricks were covered by algae, lichens rarely or never
seemed to gain a footing.
Lecidea gelatinosa.
Psorotichia lutophila.
Mayfield[1147] in his account of the Boulder Clay lichen flora of Suffolk
found only four species that attained to full development on banks and
hedgerows. These were: Collema pulposum, Cladonia pyxidata, Cl. furcata
var. corymbosa and Peltigera polydactyla.
On bare heaths of gravelly soil in Epping Forest Paulson and
Thompson[1148] describe an association of such lichens as:
Baeomyces roseus.
Baeomyces rufus.
Pycnothelia papillaria.
Cladonia coccifera.
Lecidea granulosa.
Cladonia macilenta.
Cladonia furcata.
Cetraria aculeata.
Peltigera spuria.
And on flints in the soil: Lecidea crustulata and Rhizocarpon
confervoides. They found that Peltigera spuria colonized very quickly the
burnt patches of earth which are of frequent occurrence in Epping Forest,
while on wet sandy heaths amongst heather they found associated Cladonia
sylvatica f. tenuis and Cl. fimbriata subsp. fibula.
c. On bricks, etc. Closely allied with siliceous soil-lichens are those that
form communities on bricks. As these when built into walls are more or less
smeared with mortar, a mixture of lime-loving species also arrives. Roof
tiles are more free from calcareous matter. Lesdain[1149] noted that on the
dunes, though stray bricks were covered by algae, lichens rarely or never
seemed to gain a footing.
Page 464
There are many references in literature to lichens that live on tiles. A
fairly representative list is given by Lettau[1150] of “tegulicolous” species.
Verrucaria nigrescens.
Lecidea coarctata.
Candelariella vitellina.
Lecanora dispersa.
Lecanora galactina.
Lecanora Hageni.
Lecanora saxicola.
Parmelia conspersa.
Placodium teicholytum.
Placodium pyraceum.
Placodium decipiens.
Placodium elegans.
Placodium murorum.
Xanthoria parietina.
Rhizocarpon alboatrum var.
Buellia myriocarpa.
Lecidea demissa.
Physcia ascendens.
Physcia caesia.
Physcia obscura.
Physcia sciastrella.
Several of these are more or less calcicolous and others are wanderers,
indifferent to the substratum. Though certain species form communities on
bricks, tiles, etc., none of them is restricted to such artificial substrata.
fairly representative list is given by Lettau[1150] of “tegulicolous” species.
Verrucaria nigrescens.
Lecidea coarctata.
Candelariella vitellina.
Lecanora dispersa.
Lecanora galactina.
Lecanora Hageni.
Lecanora saxicola.
Parmelia conspersa.
Placodium teicholytum.
Placodium pyraceum.
Placodium decipiens.
Placodium elegans.
Placodium murorum.
Xanthoria parietina.
Rhizocarpon alboatrum var.
Buellia myriocarpa.
Lecidea demissa.
Physcia ascendens.
Physcia caesia.
Physcia obscura.
Physcia sciastrella.
Several of these are more or less calcicolous and others are wanderers,
indifferent to the substratum. Though certain species form communities on
bricks, tiles, etc., none of them is restricted to such artificial substrata.
Page 465
d. On humus. Lichens are never found on loose humus, but rocks or
stumps of trees covered with a thin layer of earth and humus are a favourite
habitat, especially of Cladoniae. One such “formation” is given by Bruce
Fink[1151] from N. Minnesota; with the exception of Cladonia cristatella,
the species are British as well as American:
Cladonia furcata.
Cladonia cristatella.
Cladonia gracilis.
Cladonia verticillata.
Cladonia rangiferina.
Cladonia uncialis.
Cladonia alpestris.
Cladonia turgida.
Cladonia coccifera.
Cladonia pyxidata.
Cladonia fimbriata.
Peltigera malacea.
Peltigera canina.
Peltigera aphthosa.
e. On peaty soil. Peat is generally found in most abundance in northern
and upland regions, and is characteristic of mountain and moorland, though
there are great moss-lands, barely above sea-level, even in our own country.
Such soil is of an acid nature and attracts a special type of plant life. The
lichens form no inconsiderable part of the flora, the most frequent species
being members of the Cladoniaceae.
The principal crustaceous species on bare peaty soil in the British Isles
are Lecidea uliginosa and L. granulosa. The former is not easily
distinguishable from the soil as both thallus and apothecia are brownish
black. The latter, which is often associated with it, has a lighter coloured
stumps of trees covered with a thin layer of earth and humus are a favourite
habitat, especially of Cladoniae. One such “formation” is given by Bruce
Fink[1151] from N. Minnesota; with the exception of Cladonia cristatella,
the species are British as well as American:
Cladonia furcata.
Cladonia cristatella.
Cladonia gracilis.
Cladonia verticillata.
Cladonia rangiferina.
Cladonia uncialis.
Cladonia alpestris.
Cladonia turgida.
Cladonia coccifera.
Cladonia pyxidata.
Cladonia fimbriata.
Peltigera malacea.
Peltigera canina.
Peltigera aphthosa.
e. On peaty soil. Peat is generally found in most abundance in northern
and upland regions, and is characteristic of mountain and moorland, though
there are great moss-lands, barely above sea-level, even in our own country.
Such soil is of an acid nature and attracts a special type of plant life. The
lichens form no inconsiderable part of the flora, the most frequent species
being members of the Cladoniaceae.
The principal crustaceous species on bare peaty soil in the British Isles
are Lecidea uliginosa and L. granulosa. The former is not easily
distinguishable from the soil as both thallus and apothecia are brownish
black. The latter, which is often associated with it, has a lighter coloured
Page 466
thallus and apothecia that change from brick-red to dark brown or black;
Wheldon and Wilson[1152] remarked that after the burning of the heath it
was the first vegetation to appear and covered large spaces with its grey
thallus. Another peat species is Icmadophila ericetorum, but it prefers
damper localities than the two Lecideae.
To quote again from Arnold[1153]: 24 species were found on turf around
Munich, 13 of which were Cladoniae, but only four species could be
considered as exclusively peat-lichens. These were:
Cladonia Floerkeana.
Biatora terricola.
Thelocarpon turficolum.
Geisleria sychnogonioides.
The last is a very rare lichen in Central Europe and is generally found on
sandy soil. Arnold considered that near Munich, for various reasons, there
was a very poor representation of turf-lichens.
f. On mosses. Very many lichens grow along with or over mosses, either
on the ground, on rocks or on the bark of trees, doubtless owing to the
moisture accumulated and retained by these plants. Besides Cladoniae the
commonest “moss” species in the British Isles are Bilimbia sabulosa,
Bacidia muscorum, Rinodina Conradi, Lecidea sanguineoatra, Pannaria
brunnea, Psoroma hypnorum and Lecanora tartarea, with species of
Collema and Leptogium and Diploschistes bryophilus.
Wheldon and Wilson[1154] have listed the lichens that they found in
Perthshire on subalpine heath lands, on the ground, or on banks amongst
mosses:
Leptogrum spp.
Peltigera spp.
Cetraria spp.
Parmelia physodes.
Psoroma hypnorum.
Wheldon and Wilson[1152] remarked that after the burning of the heath it
was the first vegetation to appear and covered large spaces with its grey
thallus. Another peat species is Icmadophila ericetorum, but it prefers
damper localities than the two Lecideae.
To quote again from Arnold[1153]: 24 species were found on turf around
Munich, 13 of which were Cladoniae, but only four species could be
considered as exclusively peat-lichens. These were:
Cladonia Floerkeana.
Biatora terricola.
Thelocarpon turficolum.
Geisleria sychnogonioides.
The last is a very rare lichen in Central Europe and is generally found on
sandy soil. Arnold considered that near Munich, for various reasons, there
was a very poor representation of turf-lichens.
f. On mosses. Very many lichens grow along with or over mosses, either
on the ground, on rocks or on the bark of trees, doubtless owing to the
moisture accumulated and retained by these plants. Besides Cladoniae the
commonest “moss” species in the British Isles are Bilimbia sabulosa,
Bacidia muscorum, Rinodina Conradi, Lecidea sanguineoatra, Pannaria
brunnea, Psoroma hypnorum and Lecanora tartarea, with species of
Collema and Leptogium and Diploschistes bryophilus.
Wheldon and Wilson[1154] have listed the lichens that they found in
Perthshire on subalpine heath lands, on the ground, or on banks amongst
mosses:
Leptogrum spp.
Peltigera spp.
Cetraria spp.
Parmelia physodes.
Psoroma hypnorum.
Page 467
Lecanora epibryon.
Lecanora tartarea.
Lecidea coarctata.
Lecidea granulosa.
Lecidea uliginosa.
Lecidea neglecta.
Bilimbia sabulosa.
Bilimbia liguiaria.
Bilimbia melaena.
Baeomyces spp.
Cladonia spp.
As already described Lecanora tartarea[1155] spreads freely over the
mosses of the tundra. Aigret[1156] in a study of Cladoniae notes that Cl.
pyxidata, var. neglecta chooses little cushions of acrocarpous mosses, which
are particularly well adapted to retain water. Cl. digitata, Cl. flabelliformis
and some others grow on the mosses which cover old logs or the bases of
trees.
g. On fungi. Some of the fungi, such as Polyporei, are long lived, and of
hard texture. On species of Lenzites in Lorraine, Kieffer[1157] has recorded
15 different forms, but they are such as naturally grow on wood and can
scarcely rank as a separate association.
3. SAXICOLOUS
Lichens are the dominant plants of this and the following formations,
they alone being able to live on bare rock; only when there has been formed
a nidus of soil can other plants become established.
a. Characters of Mineral Substrata. It has been often observed that
lichens are influenced not only by the chemical composition of the rocks on
which they grow but also by the physical structure. Rocks that weather
quickly are almost entirely bare of lichens: the breaking up of the surface
Lecanora tartarea.
Lecidea coarctata.
Lecidea granulosa.
Lecidea uliginosa.
Lecidea neglecta.
Bilimbia sabulosa.
Bilimbia liguiaria.
Bilimbia melaena.
Baeomyces spp.
Cladonia spp.
As already described Lecanora tartarea[1155] spreads freely over the
mosses of the tundra. Aigret[1156] in a study of Cladoniae notes that Cl.
pyxidata, var. neglecta chooses little cushions of acrocarpous mosses, which
are particularly well adapted to retain water. Cl. digitata, Cl. flabelliformis
and some others grow on the mosses which cover old logs or the bases of
trees.
g. On fungi. Some of the fungi, such as Polyporei, are long lived, and of
hard texture. On species of Lenzites in Lorraine, Kieffer[1157] has recorded
15 different forms, but they are such as naturally grow on wood and can
scarcely rank as a separate association.
3. SAXICOLOUS
Lichens are the dominant plants of this and the following formations,
they alone being able to live on bare rock; only when there has been formed
a nidus of soil can other plants become established.
a. Characters of Mineral Substrata. It has been often observed that
lichens are influenced not only by the chemical composition of the rocks on
which they grow but also by the physical structure. Rocks that weather
quickly are almost entirely bare of lichens: the breaking up of the surface
Page 468
giving no time for the formation either of thallus or fruit. Close-grained
rocks such as quartzite have also a poor lichen flora, the rooting hyphae
being unable to penetrate and catch hold. Other factors, such as incidence of
light, and proximity of water, are of importance in determining the nature of
the flora, even where the rocks are of similar formation.
b. Colonization on Rocks. When a rock surface is laid bare it becomes
covered in time with lichens, and quite fresh surfaces are taken possession
of preferably to weathered surfaces[1158]. The number of species is largest at
first and the kind of lichen depends on the flora existing in the near
neighbourhood. Link[1159], for instance, has stated that Lichen candelarius
was the first lichen to appear on the rocks he observed, and, if trees were
growing near, then Lichen parietinus and Lichen tenellus followed soon
after. After a time the lichens change, the more slow-growing being
crowded out by the more vigorous. Crustaceous species, according to
Malinowski[1160], are most subject to this struggle for existence, and certain
types from the nature of their thallus are more easily displaced than others.
Those with a deeply cracked areolated thallus become disintegrated in the
older central areas by repeated swelling and contracting of the areolae as
they change from wet to dry conditions. Particles of the thallus are thus
easily dislodged, and bare places are left, which in time are colonized again
by the same lichen or by some invading species. There may result a
bewildering mosaic of different thalli and fruits mingling together. Some
forms such as Rhizocarpum geographicum which have a very close firm
thallus do not break away. In the course of time lichen communities come
and go, and the plants of one locality may be different from those of another
for no apparent reason.
The question of colonization[1161] was studied by Bruce Fink[1162] on a
“riprap” wall of quartz, 30 years old, built to protect and brace a railway in
Iowa. Near by was a grass swamp which supplied moisture especially to the
lower end of the wall. A few boulders were present in the vicinity, but the
nearest lichen “society” was on trees about 150 metres away and these bore
corticolous Parmelias, Physcias, Ramalinas, Placodiums, Lecanoras and
Rinodines which were only very sparingly represented on the riprap.
Moisture-loving species never gained a footing; the extreme xerophytic
conditions were evidenced by the character of the lichens, Biatora
myriocarpoides (Lecidea sylvicola) occupying the driest parts of the wall.
rocks such as quartzite have also a poor lichen flora, the rooting hyphae
being unable to penetrate and catch hold. Other factors, such as incidence of
light, and proximity of water, are of importance in determining the nature of
the flora, even where the rocks are of similar formation.
b. Colonization on Rocks. When a rock surface is laid bare it becomes
covered in time with lichens, and quite fresh surfaces are taken possession
of preferably to weathered surfaces[1158]. The number of species is largest at
first and the kind of lichen depends on the flora existing in the near
neighbourhood. Link[1159], for instance, has stated that Lichen candelarius
was the first lichen to appear on the rocks he observed, and, if trees were
growing near, then Lichen parietinus and Lichen tenellus followed soon
after. After a time the lichens change, the more slow-growing being
crowded out by the more vigorous. Crustaceous species, according to
Malinowski[1160], are most subject to this struggle for existence, and certain
types from the nature of their thallus are more easily displaced than others.
Those with a deeply cracked areolated thallus become disintegrated in the
older central areas by repeated swelling and contracting of the areolae as
they change from wet to dry conditions. Particles of the thallus are thus
easily dislodged, and bare places are left, which in time are colonized again
by the same lichen or by some invading species. There may result a
bewildering mosaic of different thalli and fruits mingling together. Some
forms such as Rhizocarpum geographicum which have a very close firm
thallus do not break away. In the course of time lichen communities come
and go, and the plants of one locality may be different from those of another
for no apparent reason.
The question of colonization[1161] was studied by Bruce Fink[1162] on a
“riprap” wall of quartz, 30 years old, built to protect and brace a railway in
Iowa. Near by was a grass swamp which supplied moisture especially to the
lower end of the wall. A few boulders were present in the vicinity, but the
nearest lichen “society” was on trees about 150 metres away and these bore
corticolous Parmelias, Physcias, Ramalinas, Placodiums, Lecanoras and
Rinodines which were only very sparingly represented on the riprap.
Moisture-loving species never gained a footing; the extreme xerophytic
conditions were evidenced by the character of the lichens, Biatora
myriocarpoides (Lecidea sylvicola) occupying the driest parts of the wall.
Page 469
Lower down where more moisture prevailed Bacidia inundata and
Stereocaulon paschale were the dominant species. Some 30 species or
forms were listed of which 11 were Cladonias that grew mainly on debris
from the disintegration of the wall. With the exception of two or three
species the number of individuals was very small.
Some of these lichens had doubtless come from the boulders, others from
the trees; the Cladonias were all known to occur within a few miles, but
most of the species had been wind-borne from some distance. The
Stereocaulon present did not exist elsewhere in Iowa; it had evidently been
brought by the railroad cars, possibly on telegraph poles.
A similar wall on the south side of the railway, subject to even more
xerophytic conditions but with less disintegration of the surface, had a
larger number of individuals though fewer species. Only one Cladonia and
one Parmelia had gained a footing, the rest were crustaceous, Buellia
myriocarpa being one of the most frequent.
There are two types of rock of extreme importance in lichen ecology:
those mainly composed of lime (calcareous), and those in which silica or
silicates preponderate (siliceous). They give foothold to two corresponding
groups of lichen communities, calcicolous and silicicolous.
c. Calcicolous. The pioneer in this section of lichen ecology is H. F.
Link, who was a Professor of Natural Science and Botany at Rostock, then
at Breslau, and finally in Berlin. He[1163] published in 1789, while still at
Rostock, an account of limestone plants in his neighbourhood, most of them
being lichens. In a later work he continues his Botanical Geography or
“Geology” and gives more precise details as to the plants, some of which
are essentially calcicolous though many of them he records also on siliceous
rocks.
Most calcicolous lichens are almost completely dependent on the lime
substratum which evidently supplies some constituent that has become
necessary to their healthy growth. Calcareous rocks are usually of softer
texture than those mainly composed of silica, and not only the rhizoidal
hyphae but the whole thallus—both hyphae and gonidia—may be deeply
embedded. Only the fruits are visible and they are, in some species, lodged
in tiny depressions (foveolae) scooped out of the surface by the lichen-acids
acting on the easily dissolved lime.
Stereocaulon paschale were the dominant species. Some 30 species or
forms were listed of which 11 were Cladonias that grew mainly on debris
from the disintegration of the wall. With the exception of two or three
species the number of individuals was very small.
Some of these lichens had doubtless come from the boulders, others from
the trees; the Cladonias were all known to occur within a few miles, but
most of the species had been wind-borne from some distance. The
Stereocaulon present did not exist elsewhere in Iowa; it had evidently been
brought by the railroad cars, possibly on telegraph poles.
A similar wall on the south side of the railway, subject to even more
xerophytic conditions but with less disintegration of the surface, had a
larger number of individuals though fewer species. Only one Cladonia and
one Parmelia had gained a footing, the rest were crustaceous, Buellia
myriocarpa being one of the most frequent.
There are two types of rock of extreme importance in lichen ecology:
those mainly composed of lime (calcareous), and those in which silica or
silicates preponderate (siliceous). They give foothold to two corresponding
groups of lichen communities, calcicolous and silicicolous.
c. Calcicolous. The pioneer in this section of lichen ecology is H. F.
Link, who was a Professor of Natural Science and Botany at Rostock, then
at Breslau, and finally in Berlin. He[1163] published in 1789, while still at
Rostock, an account of limestone plants in his neighbourhood, most of them
being lichens. In a later work he continues his Botanical Geography or
“Geology” and gives more precise details as to the plants, some of which
are essentially calcicolous though many of them he records also on siliceous
rocks.
Most calcicolous lichens are almost completely dependent on the lime
substratum which evidently supplies some constituent that has become
necessary to their healthy growth. Calcareous rocks are usually of softer
texture than those mainly composed of silica, and not only the rhizoidal
hyphae but the whole thallus—both hyphae and gonidia—may be deeply
embedded. Only the fruits are visible and they are, in some species, lodged
in tiny depressions (foveolae) scooped out of the surface by the lichen-acids
acting on the easily dissolved lime.
Page 470
Those obligate lime species may be found in associations on almost any
calcareous rock. Watson[1164] has given us a list of species that inhabit
carboniferous limestone in Britain. Wheldon and Wilson[1165] have
described in West Lancashire the “grey calcareous rocks blotched with
black patches of Pannarias (Placynthium nigrum) and Verrucarias, or dark
gelatinous rosettes of Collemas. White and grey Lecanorae and Verrucariae
spread extensively, some of them deeply pitting the surface. These more
sombre or colourless species are enlivened by an intermixture of orange-
yellow Physciae (Xanthoriae) and Placodii by the ochrey films of Lecanora
ochracea and lemon-yellow of Lecanora xantholyta. Amongst the greenish
scaly crusts of Lecanora crassa may be seen the bluish cushions of Lecidea
coeruleonigricans, the whole forming an exquisite blend of tints.”
The flora recorded by Flagey[1166] on the cretaceous rocks of Algeria in
the Province of Constantine does not greatly differ, some of the species
being identical with those of our own country. Placodiums and Rinodinas
were abundant, as also Lecanora calcarea, Acarospora percaenoides and
Urceolaria actinostoma var. calcarea. Also a few Lecideae along with
Verrucaria lecideoides, V. fuscella, V. calciseda and Endocarpon
monstrosum. The rocks of that region are sometimes so covered with
lichens that the stone is no longer visible.
Bruce Fink[1167] gives a typical community on limestone bluffs in
Minnesota:
Pannaria (Placynthium) nigra.
Crocynia lanuginosa.
Omphalaria pulvinata.
Collema plicatile.
Collema pustulatum.
Leptogium lacerum.
Placodium citrinum.
Bacidia inundata.
Rhizocarpon alboatrum var.
calcareous rock. Watson[1164] has given us a list of species that inhabit
carboniferous limestone in Britain. Wheldon and Wilson[1165] have
described in West Lancashire the “grey calcareous rocks blotched with
black patches of Pannarias (Placynthium nigrum) and Verrucarias, or dark
gelatinous rosettes of Collemas. White and grey Lecanorae and Verrucariae
spread extensively, some of them deeply pitting the surface. These more
sombre or colourless species are enlivened by an intermixture of orange-
yellow Physciae (Xanthoriae) and Placodii by the ochrey films of Lecanora
ochracea and lemon-yellow of Lecanora xantholyta. Amongst the greenish
scaly crusts of Lecanora crassa may be seen the bluish cushions of Lecidea
coeruleonigricans, the whole forming an exquisite blend of tints.”
The flora recorded by Flagey[1166] on the cretaceous rocks of Algeria in
the Province of Constantine does not greatly differ, some of the species
being identical with those of our own country. Placodiums and Rinodinas
were abundant, as also Lecanora calcarea, Acarospora percaenoides and
Urceolaria actinostoma var. calcarea. Also a few Lecideae along with
Verrucaria lecideoides, V. fuscella, V. calciseda and Endocarpon
monstrosum. The rocks of that region are sometimes so covered with
lichens that the stone is no longer visible.
Bruce Fink[1167] gives a typical community on limestone bluffs in
Minnesota:
Pannaria (Placynthium) nigra.
Crocynia lanuginosa.
Omphalaria pulvinata.
Collema plicatile.
Collema pustulatum.
Leptogium lacerum.
Placodium citrinum.
Bacidia inundata.
Rhizocarpon alboatrum var.
Page 471
Dermatocarpon miniatum.
Staurothele umbrinum.
Forssell[1168] pointed out an interesting selective quality in the
Gloeolichens which are associated with the gelatinous algae, Chroococcus,
Gloeocapsa and Xanthocapsa. The genera containing the two former grow
on siliceous rocks with the exception of Synalissa. The genera Omphalaria,
Peccania, Anema, Psorotichia and Enchylium, in which Xanthocapsa is the
gonidium, grow on calcareous rocks. Collemopsidium is the only
Xanthocapsa associate that is silicicolous.
d. Silicicolous. There is greater variety in the mineral composition and in
the nature of the surface in siliceous than in calcareous rocks; they are also
more durable and give support to a large number of slow-growing forms.
Silicon enters into the composition of many different types, from the
oldest volcanic to the most recent of sedimentary rocks. Some of these are
of hard unyielding surface on which only a few lichens are able to attach
themselves. Such a rock is instanced by Servit[1169] as occurring in
Bohemia, and is known as Lydite or Lydian stone, a black flinty jasper. The
association of lichens on this smooth rock was almost entirely Acarospora
chlorophana and Rinodina oreina, which as we shall see occur again as a
“desert” association in Nevada; these two lichens grow equally well in sun
or shade, and either sheltered or exposed as regards wind and rain.
Acarospora chlorophana, according to Malinowski[1170], arrives among the
first on rocks newly laid bare, and forms large societies, though in time it
gives place to Lecanora glaucoma (L. sordida), a common silicicolous
lichen.
A difference has been pointed out by Bachmann[1171] between the lichens
of acid and of basic rocks. The acid series, such as quartz- and granite-
porphyry, contain 70 per cent. and more of oxide of silica; the basic—
diabase and basalt—not nearly 50 per cent. He observed that Rhizocarpon
geographicum was the most frequent lichen of the acid porphyry, while on
basalt there were only small scattered patches. Pertusaria corallina was
abundant only on granitic rocks. On the other hand Pertusaria lactea f.
cinerascens, Diploschistes scruposus, D. bryophilus and Buellia leptocline
preferred the basic substratum of diabase and basalt. In this case it is the
Staurothele umbrinum.
Forssell[1168] pointed out an interesting selective quality in the
Gloeolichens which are associated with the gelatinous algae, Chroococcus,
Gloeocapsa and Xanthocapsa. The genera containing the two former grow
on siliceous rocks with the exception of Synalissa. The genera Omphalaria,
Peccania, Anema, Psorotichia and Enchylium, in which Xanthocapsa is the
gonidium, grow on calcareous rocks. Collemopsidium is the only
Xanthocapsa associate that is silicicolous.
d. Silicicolous. There is greater variety in the mineral composition and in
the nature of the surface in siliceous than in calcareous rocks; they are also
more durable and give support to a large number of slow-growing forms.
Silicon enters into the composition of many different types, from the
oldest volcanic to the most recent of sedimentary rocks. Some of these are
of hard unyielding surface on which only a few lichens are able to attach
themselves. Such a rock is instanced by Servit[1169] as occurring in
Bohemia, and is known as Lydite or Lydian stone, a black flinty jasper. The
association of lichens on this smooth rock was almost entirely Acarospora
chlorophana and Rinodina oreina, which as we shall see occur again as a
“desert” association in Nevada; these two lichens grow equally well in sun
or shade, and either sheltered or exposed as regards wind and rain.
Acarospora chlorophana, according to Malinowski[1170], arrives among the
first on rocks newly laid bare, and forms large societies, though in time it
gives place to Lecanora glaucoma (L. sordida), a common silicicolous
lichen.
A difference has been pointed out by Bachmann[1171] between the lichens
of acid and of basic rocks. The acid series, such as quartz- and granite-
porphyry, contain 70 per cent. and more of oxide of silica; the basic—
diabase and basalt—not nearly 50 per cent. He observed that Rhizocarpon
geographicum was the most frequent lichen of the acid porphyry, while on
basalt there were only small scattered patches. Pertusaria corallina was
abundant only on granitic rocks. On the other hand Pertusaria lactea f.
cinerascens, Diploschistes scruposus, D. bryophilus and Buellia leptocline
preferred the basic substratum of diabase and basalt. In this case it is the
Page 472
chemical rather than the physical character of the rocks that affects the
lichen flora, as porphyry and basalt are both close-grained, and are
outwardly alike except in colouration.
Other rocks, such as granite, in which the different crystals, quartz, mica
and felspar are of varying hardness, are favourite habitats as affording not
only durability but a certain openness to the rhizoidal hyphae, though in
Shetland, West[1172] found the granitic rocks bare owing to their too rapid
weathering. In these rocks the softer basic constituents such as the mica are
colonized first; the quartz remains a long time naked, though in time it also
is covered. Wheldon and Wilson[1173] point out that the sandstone near to
intrusive igneous rocks has become close-grained and indurated and bears
Lecanora squamulosa, L. picea, Lecidea rivulosa and Rhizocarpon
petraeum, which were not seen on the unaltered sandstone. It was also
observed by Stahlecker[1174], that, in layered rocks, the lichen chose the
surface at right angles to the layering as the hyphae thus gain an easier
entrance.
It will only be possible to give a few typical associations from the many
that have been published. Crustaceous forms are the most abundant.
On granite and on quartzite not disintegrated Malinowski[1175] listed:
Acarospora chlorophana.
Lecanora glaucoma.
Rhizocarpon viridiatrum.
Lecidea tumida.
Biatorella sporostatia.
Biatorella testudinea.
On granite and quartzite disintegrated:
Aspicilia cinerea.
Aspicilia gibbosa.
Aspicilia tenebrosa.
lichen flora, as porphyry and basalt are both close-grained, and are
outwardly alike except in colouration.
Other rocks, such as granite, in which the different crystals, quartz, mica
and felspar are of varying hardness, are favourite habitats as affording not
only durability but a certain openness to the rhizoidal hyphae, though in
Shetland, West[1172] found the granitic rocks bare owing to their too rapid
weathering. In these rocks the softer basic constituents such as the mica are
colonized first; the quartz remains a long time naked, though in time it also
is covered. Wheldon and Wilson[1173] point out that the sandstone near to
intrusive igneous rocks has become close-grained and indurated and bears
Lecanora squamulosa, L. picea, Lecidea rivulosa and Rhizocarpon
petraeum, which were not seen on the unaltered sandstone. It was also
observed by Stahlecker[1174], that, in layered rocks, the lichen chose the
surface at right angles to the layering as the hyphae thus gain an easier
entrance.
It will only be possible to give a few typical associations from the many
that have been published. Crustaceous forms are the most abundant.
On granite and on quartzite not disintegrated Malinowski[1175] listed:
Acarospora chlorophana.
Lecanora glaucoma.
Rhizocarpon viridiatrum.
Lecidea tumida.
Biatorella sporostatia.
Biatorella testudinea.
On granite and quartzite disintegrated:
Aspicilia cinerea.
Aspicilia gibbosa.
Aspicilia tenebrosa.
Page 473
Buellia coracina.
Catillaria (Biatorina) Hochstetteri.
Rhizocarpon petraeum.
Rhizocarpon geographicum vars.
Biatorella cinerea.
Lecanora badia.
Lecanora cenisia.
Lecidea confluens.
Lecidea fuscoatra.
Lecidea platycarpa.
Lecidea lapicida.
Haematomma ventosum.
On these disintegrated rocks there is a constant struggle for existence
between the various species; the victorious association finally consists of
Lecanora badia, L. cenisia and Lecidea confluens with occasional growths
of the following species:
Aspicilia cinerea.
Haematomma ventosum.
Rhizocarpon geographicum vars.
Biatorella cinerea.
Lecidea platycarpa.
A number of rock associations have been tabulated by Wheldon and
Wilson[1176] for Perthshire. Among others they give some of the most
typical lichens on granitic and eruptive rocks:
Sphaerophorus coralloides.
Sphaerophorus fragilis.
Catillaria (Biatorina) Hochstetteri.
Rhizocarpon petraeum.
Rhizocarpon geographicum vars.
Biatorella cinerea.
Lecanora badia.
Lecanora cenisia.
Lecidea confluens.
Lecidea fuscoatra.
Lecidea platycarpa.
Lecidea lapicida.
Haematomma ventosum.
On these disintegrated rocks there is a constant struggle for existence
between the various species; the victorious association finally consists of
Lecanora badia, L. cenisia and Lecidea confluens with occasional growths
of the following species:
Aspicilia cinerea.
Haematomma ventosum.
Rhizocarpon geographicum vars.
Biatorella cinerea.
Lecidea platycarpa.
A number of rock associations have been tabulated by Wheldon and
Wilson[1176] for Perthshire. Among others they give some of the most
typical lichens on granitic and eruptive rocks:
Sphaerophorus coralloides.
Sphaerophorus fragilis.
Page 474
Platysma Fahlunense.
Platysma commixtum.
Platysma glaucum.
Platysma lacunosum.
Parmelia saxatilis.
Parmelia omphalodes.
Parmelia Mougeotii.
Parmelia stygia.
Parmelia tristis.
Parmelia lanata.
Gyrophora proboscidea.
Gyrophora cylindrica.
Gyrophora torrefacta.
Gyrophora polyphylla.
Gyrophora flocculosa.
Lecanora gelida.
Lecanora atra.
Lecanora badia.
Lecanora tartarea.
Lecanora parella.
Lecanora ventosa.
Lecanora Dicksonii.
Lecanora cinerea.
Lecanora peliocypha.
Pertusaria dealbata.
Stereocaulon Delisei.
Platysma commixtum.
Platysma glaucum.
Platysma lacunosum.
Parmelia saxatilis.
Parmelia omphalodes.
Parmelia Mougeotii.
Parmelia stygia.
Parmelia tristis.
Parmelia lanata.
Gyrophora proboscidea.
Gyrophora cylindrica.
Gyrophora torrefacta.
Gyrophora polyphylla.
Gyrophora flocculosa.
Lecanora gelida.
Lecanora atra.
Lecanora badia.
Lecanora tartarea.
Lecanora parella.
Lecanora ventosa.
Lecanora Dicksonii.
Lecanora cinerea.
Lecanora peliocypha.
Pertusaria dealbata.
Stereocaulon Delisei.
Page 475
Stereocaulon evolutum.
Stereocaulon coralloides.
Stereocaulon denudatum.
Psorotichia lugubris.
Lecidea inserena.
Lecidea panaeola.
Lecidea contigua.
Lecidea confluens.
Lecidea lapicida.
Lecidea plana.
Lecidea mesotropa.
Lecidea auriculata.
Lecidea diducens.
Lecidea aglaea.
Lecidea rivulosa.
Lecidea Kochiana.
Lecidea pycnocarpa.
Buellia atrata.
Rhizocarpon Oederi.
On siliceous rocks in West Lancashire the same authors[1177] depict the
lichen flora as follows: “There are many grey Parmeliae and Cladoniae
with coral-like Sphaerophorei on the rocks, and on the walls smoky-looking
patches of Parmelia fuliginosa and ragged fringes of Platysma glaucum and
Evernia furfuracea. On the higher scars, flat topped tabular blocks exhibit
black scaly Gyrophoreae, dingy green Lecidea (Rhizocarpon) viridiatra and
mouse-coloured L. rivulosa. Suborbicular (whitish) patches of Pertusaria
lactea and P. dealbata enliven the general sadness of tone, and everywhere
Stereocaulon coralloides.
Stereocaulon denudatum.
Psorotichia lugubris.
Lecidea inserena.
Lecidea panaeola.
Lecidea contigua.
Lecidea confluens.
Lecidea lapicida.
Lecidea plana.
Lecidea mesotropa.
Lecidea auriculata.
Lecidea diducens.
Lecidea aglaea.
Lecidea rivulosa.
Lecidea Kochiana.
Lecidea pycnocarpa.
Buellia atrata.
Rhizocarpon Oederi.
On siliceous rocks in West Lancashire the same authors[1177] depict the
lichen flora as follows: “There are many grey Parmeliae and Cladoniae
with coral-like Sphaerophorei on the rocks, and on the walls smoky-looking
patches of Parmelia fuliginosa and ragged fringes of Platysma glaucum and
Evernia furfuracea. On the higher scars, flat topped tabular blocks exhibit
black scaly Gyrophoreae, dingy green Lecidea (Rhizocarpon) viridiatra and
mouse-coloured L. rivulosa. Suborbicular (whitish) patches of Pertusaria
lactea and P. dealbata enliven the general sadness of tone, and everywhere
Page 476
loose rocks and stones are covered with the greyish-black spotted thallus of
Lecidea contigua.”
On the Silurian series of rocks in the same district they describe a
somewhat brighter coloured flora: “First Stereocaulons invite attention, and
greenish or yellowish shades are introduced by an abundance of Lecanora
sulphurea, L. polytropa, Rhizocarpon geographicum and Parmelia
conspersa, often beautifully commingled with grey species such as Lecidea
contigua and L. stellulata, and reddish angular patches of Lecanora
Dicksonii. Also an abundance of orbicular patches of Haematomma
ventosum with its reddish-brown apothecia.” A brightly coloured
association on the cretaceous sand-rocks of Saxon Switzerland has been
described as “Sulphur lichens.” These have recently[1178] been determined
as chiefly Lepraria chlorina, in less abundance Lecidea lucida and
Calicium arenarium, with occasional growths of Coniocybe furfuracea and
Calicium corynellum.
4. OMNICOLOUS LICHENS
Some account must be taken in any ecological survey of those lichens
that are indifferent to substrata. Certain species have become so adapted to
some special habitat that they never or rarely wander; others, on the
contrary, are true vagabonds in the lichen kingdom and settle on any
substance that affords a foothold: on leather, bones, iron, pottery, etc. There
can be no sustenance drawn from these supports, or at most extremely little,
and it is interesting to note in this connection that while some rock-lichens
are changed to a rusty-red colour by the infiltration of iron—often from a
water medium containing iron-salts—those that live directly on iron are
unaffected.
The “wanderers” are more or less the same in every locality and they
pass easily from one support to another. Bouly de Lesdain[1179] made a
tabulation of such as he found growing on varied substances on the dunes
round Dunkirk and they well represent these omnicolous communities. It is
in such a no man’s land that one would expect to find an accumulation of
derelict materials, not only favourably exposed to light and moisture, but
undisturbed for long periods and bordering on normal lichen associations of
soil, tree and stones. Arnold[1180] also noted many of these peculiar habitats.
Lecidea contigua.”
On the Silurian series of rocks in the same district they describe a
somewhat brighter coloured flora: “First Stereocaulons invite attention, and
greenish or yellowish shades are introduced by an abundance of Lecanora
sulphurea, L. polytropa, Rhizocarpon geographicum and Parmelia
conspersa, often beautifully commingled with grey species such as Lecidea
contigua and L. stellulata, and reddish angular patches of Lecanora
Dicksonii. Also an abundance of orbicular patches of Haematomma
ventosum with its reddish-brown apothecia.” A brightly coloured
association on the cretaceous sand-rocks of Saxon Switzerland has been
described as “Sulphur lichens.” These have recently[1178] been determined
as chiefly Lepraria chlorina, in less abundance Lecidea lucida and
Calicium arenarium, with occasional growths of Coniocybe furfuracea and
Calicium corynellum.
4. OMNICOLOUS LICHENS
Some account must be taken in any ecological survey of those lichens
that are indifferent to substrata. Certain species have become so adapted to
some special habitat that they never or rarely wander; others, on the
contrary, are true vagabonds in the lichen kingdom and settle on any
substance that affords a foothold: on leather, bones, iron, pottery, etc. There
can be no sustenance drawn from these supports, or at most extremely little,
and it is interesting to note in this connection that while some rock-lichens
are changed to a rusty-red colour by the infiltration of iron—often from a
water medium containing iron-salts—those that live directly on iron are
unaffected.
The “wanderers” are more or less the same in every locality and they
pass easily from one support to another. Bouly de Lesdain[1179] made a
tabulation of such as he found growing on varied substances on the dunes
round Dunkirk and they well represent these omnicolous communities. It is
in such a no man’s land that one would expect to find an accumulation of
derelict materials, not only favourably exposed to light and moisture, but
undisturbed for long periods and bordering on normal lichen associations of
soil, tree and stones. Arnold[1180] also noted many of these peculiar habitats.
Page 477
The following were noted by Lesdain and other workers:
On iron—Xanthoria parietina, Physcia obscura and var. virella, Ph.
ascendens, Placodium (flavescens) sympageum, Pl. pyraceum, Pl. citrinum,
Candelariella vitellinum, Rinodina exigua, Lecanora campestris, L.
umbrina, L. galactina, Lecania erysibe, Bacidia inundata. Xanthoria
parietina is one of the commonest wandering species; it was found by
Richard[1181] on an old cannon lying near water, that was exfoliated by rust.
On tar—Lecanora umbrina.
On charcoal—Rinodina exigua, Lecanora umbrina.
On bones—Xanthoria parietina, Physcia ascendens, Ph. tenella,
Placodium citrinum, Pl. lacteum, Rinodina exigua, Lecanora galactina, L.
dispersa, L. umbrina, Lecania erysibe, L. cyrtella, Acarospora pruinosa, A.
Heppii, Bacidia inundata, B. muscorum, Verrucaria anceps, V. papillosa.
In Arctic regions in Ellesmere Land and King Oscar Land,
Darbishire[1182] found on bones: Lecanora varia, L. Hageni, Rinodina
turfacea and Buellia parasema (disciformis). He could not trace any effect
of the lichens on the substratum.
On charcoal—Rinodina exigua, Lecanora umbrina.
On dross or clinkers—Parmelia dubia, Physcia obscura, Ph. ascendens
f. tenella, Ph. pulverulenta, Xanthoria parietina, Placodium pyraceum, Pl.
citrinum, Rinodina exigua, Lecanora dispersa, L. umbrina, Lecania erysibe.
On glass[1183]—Physcia ascendens f. tenella, Buellia canescens. Richard
has recorded the same lichens on the broken glass of walls and in addition:
Xanthoria parietina, Lecanora crenulata, L. dispersa, Lecania erysibe,
Rinodina exigua, and Buellia canescens.
On earthenware, china, etc.—Physcia ascendens f. tenella, Lecanora
umbrina, L. dispersa, Lecania (? Biatorina) cyrtella, Verrucaria papillosa,
Bacidia inundata.
On leather—Nearly fifty species or varieties were found by Lesdain on
old leather on the dunes. Cladonias, Parmelias and Physcias were well
represented with one Evernia and a large series of crustaceous forms. He
adds a note that leather is an excellent substratum: lichens covered most of
On iron—Xanthoria parietina, Physcia obscura and var. virella, Ph.
ascendens, Placodium (flavescens) sympageum, Pl. pyraceum, Pl. citrinum,
Candelariella vitellinum, Rinodina exigua, Lecanora campestris, L.
umbrina, L. galactina, Lecania erysibe, Bacidia inundata. Xanthoria
parietina is one of the commonest wandering species; it was found by
Richard[1181] on an old cannon lying near water, that was exfoliated by rust.
On tar—Lecanora umbrina.
On charcoal—Rinodina exigua, Lecanora umbrina.
On bones—Xanthoria parietina, Physcia ascendens, Ph. tenella,
Placodium citrinum, Pl. lacteum, Rinodina exigua, Lecanora galactina, L.
dispersa, L. umbrina, Lecania erysibe, L. cyrtella, Acarospora pruinosa, A.
Heppii, Bacidia inundata, B. muscorum, Verrucaria anceps, V. papillosa.
In Arctic regions in Ellesmere Land and King Oscar Land,
Darbishire[1182] found on bones: Lecanora varia, L. Hageni, Rinodina
turfacea and Buellia parasema (disciformis). He could not trace any effect
of the lichens on the substratum.
On charcoal—Rinodina exigua, Lecanora umbrina.
On dross or clinkers—Parmelia dubia, Physcia obscura, Ph. ascendens
f. tenella, Ph. pulverulenta, Xanthoria parietina, Placodium pyraceum, Pl.
citrinum, Rinodina exigua, Lecanora dispersa, L. umbrina, Lecania erysibe.
On glass[1183]—Physcia ascendens f. tenella, Buellia canescens. Richard
has recorded the same lichens on the broken glass of walls and in addition:
Xanthoria parietina, Lecanora crenulata, L. dispersa, Lecania erysibe,
Rinodina exigua, and Buellia canescens.
On earthenware, china, etc.—Physcia ascendens f. tenella, Lecanora
umbrina, L. dispersa, Lecania (? Biatorina) cyrtella, Verrucaria papillosa,
Bacidia inundata.
On leather—Nearly fifty species or varieties were found by Lesdain on
old leather on the dunes. Cladonias, Parmelias and Physcias were well
represented with one Evernia and a large series of crustaceous forms. He
adds a note that leather is an excellent substratum: lichens covered most of
Page 478
the pieces astray on the dunes. Similar records have been made in Epping
Forest by Paulson and Thompson[1184] who found Cladonia fimbriata var.
tubaeformis and Lecidea granulosa growing on an old boot. These authors
connect the sodden condition of the leather with its attraction for lichens.
On pasteboard—Even on such a transient substance as this Lesdain
found a number of forms, most of them, however, but poorly developed:
Cladonia furcata (thallus), Parmelia subaurifera (beginning), Xanthoria
parietina (beginning), Physcia obscura, Placodium citrinum (thallus), Pl.
pyraceum, Lecanora umbrina, Bacidia inundata and Polyblastia Vouauxi
var. charticola.
On linoleum—Xanthoria parietina, Physcia ascendens f. tenella,
Rinodina exigua, Lecanora umbrina.
On indiarubber—Physcia ascendens f. tenella.
On tarred cloth—Xanthoria parietina, Placodium citrinum, Pl.
pyraceum, Rinodina exigua, Lecanora umbrina, Lecania erysibe, Bacidia
inundata.
On felt—Bacidia inundata, B. muscorum.
On cloth (cotton, etc.)—Bacidia inundata.
On silk—Physcia ascendens, Ph. obscura, Placodium citrinum (thallus),
Lecanora umbrina, Bacidia inundata.
On cord—Physcia ascendens f. tenella, Placodium citrinum (thallus).
On excreta—One would scarcely expect to find lichens on animal
droppings, but as some of these harden and lie exposed for a considerable
time, some quick-growing species attain to more or less development on
what is, in any case, an extremely favourable habitat for fungi and for many
minute organisms. Paulson and Thompson found tiny fruiting individuals of
Cladonia macilenta and Cl. fimbriata var. tubaeformis growing on the dry
dung of rabbits in Epping Forest. On the same type of pellets Lesdain
records Physcia ascendens f. leptalea, Cladonia pyxidata, Bacidia inundata
and B. muscorum; and on sheep pellets: Physcia ascendens f. leptalea and
Placodium citrinum; while on droppings of musk-ox in Ellesmere Land
Darbishire found Biatorina globulosa, Placodium pyraceum, Gyalolechia
Forest by Paulson and Thompson[1184] who found Cladonia fimbriata var.
tubaeformis and Lecidea granulosa growing on an old boot. These authors
connect the sodden condition of the leather with its attraction for lichens.
On pasteboard—Even on such a transient substance as this Lesdain
found a number of forms, most of them, however, but poorly developed:
Cladonia furcata (thallus), Parmelia subaurifera (beginning), Xanthoria
parietina (beginning), Physcia obscura, Placodium citrinum (thallus), Pl.
pyraceum, Lecanora umbrina, Bacidia inundata and Polyblastia Vouauxi
var. charticola.
On linoleum—Xanthoria parietina, Physcia ascendens f. tenella,
Rinodina exigua, Lecanora umbrina.
On indiarubber—Physcia ascendens f. tenella.
On tarred cloth—Xanthoria parietina, Placodium citrinum, Pl.
pyraceum, Rinodina exigua, Lecanora umbrina, Lecania erysibe, Bacidia
inundata.
On felt—Bacidia inundata, B. muscorum.
On cloth (cotton, etc.)—Bacidia inundata.
On silk—Physcia ascendens, Ph. obscura, Placodium citrinum (thallus),
Lecanora umbrina, Bacidia inundata.
On cord—Physcia ascendens f. tenella, Placodium citrinum (thallus).
On excreta—One would scarcely expect to find lichens on animal
droppings, but as some of these harden and lie exposed for a considerable
time, some quick-growing species attain to more or less development on
what is, in any case, an extremely favourable habitat for fungi and for many
minute organisms. Paulson and Thompson found tiny fruiting individuals of
Cladonia macilenta and Cl. fimbriata var. tubaeformis growing on the dry
dung of rabbits in Epping Forest. On the same type of pellets Lesdain
records Physcia ascendens f. leptalea, Cladonia pyxidata, Bacidia inundata
and B. muscorum; and on sheep pellets: Physcia ascendens f. leptalea and
Placodium citrinum; while on droppings of musk-ox in Ellesmere Land
Darbishire found Biatorina globulosa, Placodium pyraceum, Gyalolechia
Page 479
subsimilis, Lecanora epibryon, L. verrucosa, Rinodina turfacea and even,
firmly attached, Thamnolia vermicularis.
It would be difficult to estimate the age of these lichens, but it seems
evident that the “wanderers” are all more or less quick growers, and the lists
also prove conclusively their complete indifference to the substratum, as the
same species occur again and again on the very varied substances.
5. LOCALIZED COMMUNITIES
Lichens may be grouped ecologically under other conditions than those
of substratum. They respond very readily to special environments, and
associations arise either of species also met with elsewhere, or of species
restricted to one type of surroundings. Such associations or communities
might be multiplied indefinitely, but only a few of the outstanding ones will
be touched on.
a. Maritime Lichens. This community is the most specialized of any,
many of the lichens having become exclusively adapted to salt-water
surroundings. They are mainly saxicolous, but the presence of sea-water is
the factor of greatest influence on their growth and distribution, and they
occur indifferently on any kind of shore rock either siliceous or calcareous.
Wheldon and Wilson[1185] noted this indifference to substratum on the
Arran shores, where a few calcicolous species such as Verrucaria
nigrescens, V. maculiformis, Placodium tegularis and Pl. lobulatum, grow
by the sea on siliceous rocks. They suggest that the spray-washed habitat
affords the conditions, which, in other places, are furnished by limestone.
The greater or less proximity of the salt water induces in lichens, as in
other maritime plants, a distribution into belts or zones which recede
gradually or abruptly according to the slope of the shore and the reach of
the tide. Weddell[1186] on the Isle d’Yeu delimited three such zones: (1)
marine, those nearest the sea and immersed for a longer or shorter period at
each tide; (2) semi-marine, not immersed but subject to the direct action of
the waves, and (3) maritime or littoral, the area beyond the reach of the
waves but within the influence of sea-spray. In the course of his work he
indicates the lichens of each zone.
firmly attached, Thamnolia vermicularis.
It would be difficult to estimate the age of these lichens, but it seems
evident that the “wanderers” are all more or less quick growers, and the lists
also prove conclusively their complete indifference to the substratum, as the
same species occur again and again on the very varied substances.
5. LOCALIZED COMMUNITIES
Lichens may be grouped ecologically under other conditions than those
of substratum. They respond very readily to special environments, and
associations arise either of species also met with elsewhere, or of species
restricted to one type of surroundings. Such associations or communities
might be multiplied indefinitely, but only a few of the outstanding ones will
be touched on.
a. Maritime Lichens. This community is the most specialized of any,
many of the lichens having become exclusively adapted to salt-water
surroundings. They are mainly saxicolous, but the presence of sea-water is
the factor of greatest influence on their growth and distribution, and they
occur indifferently on any kind of shore rock either siliceous or calcareous.
Wheldon and Wilson[1185] noted this indifference to substratum on the
Arran shores, where a few calcicolous species such as Verrucaria
nigrescens, V. maculiformis, Placodium tegularis and Pl. lobulatum, grow
by the sea on siliceous rocks. They suggest that the spray-washed habitat
affords the conditions, which, in other places, are furnished by limestone.
The greater or less proximity of the salt water induces in lichens, as in
other maritime plants, a distribution into belts or zones which recede
gradually or abruptly according to the slope of the shore and the reach of
the tide. Weddell[1186] on the Isle d’Yeu delimited three such zones: (1)
marine, those nearest the sea and immersed for a longer or shorter period at
each tide; (2) semi-marine, not immersed but subject to the direct action of
the waves, and (3) maritime or littoral, the area beyond the reach of the
waves but within the influence of sea-spray. In the course of his work he
indicates the lichens of each zone.
Page 480
Fig. 122. Ramalina siliquosa A. L. Sm. Upper zone of barren
plants (after M. C. Knowles, R. Welch. Photo.).
In Ireland, a thorough examination has been made of a rocky coast at
Howth near Dublin by M. C. Knowles[1187]. She recognizes five distinct
belts beginning with those furthest from the shore though within the
influence of the salt water:
1. The Ramalina belt.
2. The Orange belt.
3. Lichina Vegetation.
4. Verrucaria maura belt.
5. The belt of Marine Verrucarias.
(1) The Ramalina belt. In this belt there are two zones of lichen
vegetation: those in the upper zone consist mainly of barren plants of
Ramalina siliquosa[1188], rather dark or glaucous in colour with much
branched fronds which are incurved at the tips (Fig. 122). They are beyond
the direct action of the waves. The lower zone consists also mainly of the
same Ramalina, the plants bearing straight, stiff, simple, or slightly
branched fertile fronds of a pale-green or straw colour (Fig. 123). The pale
colour may be partly due to frequent splashings by sea-spray.
plants (after M. C. Knowles, R. Welch. Photo.).
In Ireland, a thorough examination has been made of a rocky coast at
Howth near Dublin by M. C. Knowles[1187]. She recognizes five distinct
belts beginning with those furthest from the shore though within the
influence of the salt water:
1. The Ramalina belt.
2. The Orange belt.
3. Lichina Vegetation.
4. Verrucaria maura belt.
5. The belt of Marine Verrucarias.
(1) The Ramalina belt. In this belt there are two zones of lichen
vegetation: those in the upper zone consist mainly of barren plants of
Ramalina siliquosa[1188], rather dark or glaucous in colour with much
branched fronds which are incurved at the tips (Fig. 122). They are beyond
the direct action of the waves. The lower zone consists also mainly of the
same Ramalina, the plants bearing straight, stiff, simple, or slightly
branched fertile fronds of a pale-green or straw colour (Fig. 123). The pale
colour may be partly due to frequent splashings by sea-spray.
Page 481
Ramalina siliquosum in both zones takes several distinct forms,
according to exposure to light, wind or spray, the effects of which are most
marked in the upper zone. The plants growing above the ordinary spray
zone generally form sward-like growths (Fig. 124); at the higher levels the
sward growth is replaced by isolated tufts with a smaller more amorphous
thallus which passes into a very small stunted condition. The latter form
alone has gained and retained a footing on the steep faces of the hard and
close-grained quartzite rocks. “On the western faces, indeed, it is the only
visible vegetation.” The dwarfed tufts with lacerated fronds measuring from
1/4 to 1/2 an inch in height are dotted all over the quartzites. On the sea
faces the plants are larger, but everywhere they are closely appressed to the
rock surface. At lower levels the fronds lengthen to more normal
dimensions. “On these steep rock-faces there is a complete absence of any
of the crustaceous species. The problem, therefore, as to how the Ramalina
has obtained a foothold on these very hard precipitous rocks, which are too
inhospitable even for crustaceous species is an interesting and puzzling
one.”
In the Ramalina zone along with the dominant species there occur
occasional tufts of R. Curnowii and R. subfarinacea, the latter more
especially in shady and rather moist situations. There are also numerous
foliaceous and crustaceous lichens mingling with the Ramalina vegetation
(Fig. 125), several Parmelias, Physcia aquila, Xanthoria parietina, Buellia
canescens, B. ryssolea, Lecanora atra, L. sordida, Rhizocarpon
geographicum and others. In the main these are arranged in the following
order descending towards the sea:
1. Parmeliae.
2. Physcia aquila.
3. Xanthoria parietina.
4. Crustaceous species.
according to exposure to light, wind or spray, the effects of which are most
marked in the upper zone. The plants growing above the ordinary spray
zone generally form sward-like growths (Fig. 124); at the higher levels the
sward growth is replaced by isolated tufts with a smaller more amorphous
thallus which passes into a very small stunted condition. The latter form
alone has gained and retained a footing on the steep faces of the hard and
close-grained quartzite rocks. “On the western faces, indeed, it is the only
visible vegetation.” The dwarfed tufts with lacerated fronds measuring from
1/4 to 1/2 an inch in height are dotted all over the quartzites. On the sea
faces the plants are larger, but everywhere they are closely appressed to the
rock surface. At lower levels the fronds lengthen to more normal
dimensions. “On these steep rock-faces there is a complete absence of any
of the crustaceous species. The problem, therefore, as to how the Ramalina
has obtained a foothold on these very hard precipitous rocks, which are too
inhospitable even for crustaceous species is an interesting and puzzling
one.”
In the Ramalina zone along with the dominant species there occur
occasional tufts of R. Curnowii and R. subfarinacea, the latter more
especially in shady and rather moist situations. There are also numerous
foliaceous and crustaceous lichens mingling with the Ramalina vegetation
(Fig. 125), several Parmelias, Physcia aquila, Xanthoria parietina, Buellia
canescens, B. ryssolea, Lecanora atra, L. sordida, Rhizocarpon
geographicum and others. In the main these are arranged in the following
order descending towards the sea:
1. Parmeliae.
2. Physcia aquila.
3. Xanthoria parietina.
4. Crustaceous species.
Page 482
Fig. 123. Ramalina siliquosa A. L. Sm. Lower zone of fertile
plants (after M. C. Knowles, R. Welch, Photo.).
Fig. 124. Sward of young Ramalinae (after M. C. Knowles, R.
Welch, Photo.).
Parmelia prolixa is the most abundant of the Parmelias: it covers large
spaces of the rocks and frequently competes for room with the Ramalinas,
or in other areas with Physcia aquila and Lecanora parella.
A number of crustaceous species which form the sub-vegetation of the
Ramalina belt, and also on the same level, clothe the steeper rock faces
plants (after M. C. Knowles, R. Welch, Photo.).
Fig. 124. Sward of young Ramalinae (after M. C. Knowles, R.
Welch, Photo.).
Parmelia prolixa is the most abundant of the Parmelias: it covers large
spaces of the rocks and frequently competes for room with the Ramalinas,
or in other areas with Physcia aquila and Lecanora parella.
A number of crustaceous species which form the sub-vegetation of the
Ramalina belt, and also on the same level, clothe the steeper rock faces
Page 483
where shelter and moisture are insufficient to support the foliose forms. “In
general the sub-vegetation of the eastern and northern coasts is largely
composed of species that are common in Alpine and upland regions. This is
due to the steepness of the rocks and also to the colder and drier conditions
prevailing on these coasts.” An association of Rhizocarpon geographicum,
Lecanora (sordida) glaucoma and Pertusaria concreta f. Westringii forms
an almost continuous covering in some places, descending nearly to sea-
level.
Fig. 125. Crustaceous communities in the Ramalina belt.
Lecanora atra Ach. (grey patches) and Buellia ryssolea A. L. Sm.
(dark patches). (After M. C. Knowles, R. Welch, Photo.)
On sunnier and moister rocks with a south and south-west aspect the
association is of more lowland forms such as Buellia colludens, B.
stellulata, Lecanora smaragdula and L. simplex f. strepsodina.
(2) The Orange belt. “Below the Ramalinas, and between them and the
sea, several deep yellow or orange-coloured lichens form a belt of varying
width all round the coast. In summer, the colour of these lichens is so
brilliant that the belt is easily recognized from a considerable distance.” The
general the sub-vegetation of the eastern and northern coasts is largely
composed of species that are common in Alpine and upland regions. This is
due to the steepness of the rocks and also to the colder and drier conditions
prevailing on these coasts.” An association of Rhizocarpon geographicum,
Lecanora (sordida) glaucoma and Pertusaria concreta f. Westringii forms
an almost continuous covering in some places, descending nearly to sea-
level.
Fig. 125. Crustaceous communities in the Ramalina belt.
Lecanora atra Ach. (grey patches) and Buellia ryssolea A. L. Sm.
(dark patches). (After M. C. Knowles, R. Welch, Photo.)
On sunnier and moister rocks with a south and south-west aspect the
association is of more lowland forms such as Buellia colludens, B.
stellulata, Lecanora smaragdula and L. simplex f. strepsodina.
(2) The Orange belt. “Below the Ramalinas, and between them and the
sea, several deep yellow or orange-coloured lichens form a belt of varying
width all round the coast. In summer, the colour of these lichens is so
brilliant that the belt is easily recognized from a considerable distance.” The
Page 484
most abundant species occur mainly in the following order descending
towards the sea:
1. Xanthoria parietina.
2. Placodium murorum.
3. Placodium tegularis.
4. Placodium decipiens.
5. Placodium lobulatum.
“On the stones and low shore rocks that lie just above the ordinary high-
tide level Placodium lobulatum grows abundantly, covering the rocks with a
continuous sheet of brilliant colour.” With these brightly coloured lichens
are associated several with greyish thalli such as:
Lecanora prosechoides.
Lecanora umbrina.
Lecanora Hageni.
Rhizocarpon alboatrum.
Biatorina lenticularis.
Rinodina exigua var. demissa.
Opegrapha calcarea f. heteromorpha.
(3) The Lichina vegetation, and (4) The Verrucaria maura belt. These
two communities are intermingled, and it will therefore be better to
consider them together. There are only two species of Lichina on this or any
other shore, L. pygmaea and L. confinis; the latter grows above the tide-
level, and sometimes high up on the cliffs, where it is subject to only
occasional showers of spray: it forms on the Howth coast a band of
vegetation four to five inches wide above the Verrucaria belt. Lichina
pygmaea occurs nearer the water, and therefore mixed with and below
Verrucaria maura. Those three zones were first pointed out by
Nylander[1189] at Pornic, where however they were all submerged at high
tide.
towards the sea:
1. Xanthoria parietina.
2. Placodium murorum.
3. Placodium tegularis.
4. Placodium decipiens.
5. Placodium lobulatum.
“On the stones and low shore rocks that lie just above the ordinary high-
tide level Placodium lobulatum grows abundantly, covering the rocks with a
continuous sheet of brilliant colour.” With these brightly coloured lichens
are associated several with greyish thalli such as:
Lecanora prosechoides.
Lecanora umbrina.
Lecanora Hageni.
Rhizocarpon alboatrum.
Biatorina lenticularis.
Rinodina exigua var. demissa.
Opegrapha calcarea f. heteromorpha.
(3) The Lichina vegetation, and (4) The Verrucaria maura belt. These
two communities are intermingled, and it will therefore be better to
consider them together. There are only two species of Lichina on this or any
other shore, L. pygmaea and L. confinis; the latter grows above the tide-
level, and sometimes high up on the cliffs, where it is subject to only
occasional showers of spray: it forms on the Howth coast a band of
vegetation four to five inches wide above the Verrucaria belt. Lichina
pygmaea occurs nearer the water, and therefore mixed with and below
Verrucaria maura. Those three zones were first pointed out by
Nylander[1189] at Pornic, where however they were all submerged at high
tide.
Page 485
Verrucaria maura is one of the most abundant lichens of our rocky
coasts, and is reported from Spitzbergen in the North to Graham Land in the
Antarctic. It grows well within the range of sea-spray, covering great
stretches of boulders and rocks with its dull-black crustaceous thallus. At
Howth it is submerged only by the highest spring tides. Though it is the
dominant lichen on that beach, other species such as V. memnonia, V.
prominula, and V. aquatilis form part of the association, and more rarely V.
scotina along with Arthopyrenia halodytes, A. leptotera and A. halizoa.
(5) The belt of marine Verrucarias. This association includes the
species that are submerged by the tide for a longer or shorter period each
day. The dominant species are Verrucaria microspora, V. striatula and V.
mucosa. Arthopyrenia halodytes is also abundant; A. halizoa and A. marina
are more rarely represented. Among the plants of Fucus spiralis, Verrucaria
mucosa, the most wide-spreading of these marine forms, is “very
conspicuous as a dark-green, almost black, band of greasy appearance
stretching along the shore.” When growing in the shade, the thallus is of a
brighter green colour.
An examination[1190] of the west coast of Ireland yielded much the same
results, but with a still higher “white belt” formed mainly of Lecanora
parella and L. atra which covered the rocks lying above high-water mark,
“giving them the appearance of having been whitewashed.” A more general
association for the same position as regards the tide is given by Wheldon
and Wilson[1191] on the coasts of Arran as:
Physcia aquila.
Xanthoria parietina.
Lecanora parella.
Lecanora atra.
Lecanora campestris.
Placodium ferrugineum var. festivum.
Placodium tegularis.
Ramalina cuspidata.
Physcia stellaris.
coasts, and is reported from Spitzbergen in the North to Graham Land in the
Antarctic. It grows well within the range of sea-spray, covering great
stretches of boulders and rocks with its dull-black crustaceous thallus. At
Howth it is submerged only by the highest spring tides. Though it is the
dominant lichen on that beach, other species such as V. memnonia, V.
prominula, and V. aquatilis form part of the association, and more rarely V.
scotina along with Arthopyrenia halodytes, A. leptotera and A. halizoa.
(5) The belt of marine Verrucarias. This association includes the
species that are submerged by the tide for a longer or shorter period each
day. The dominant species are Verrucaria microspora, V. striatula and V.
mucosa. Arthopyrenia halodytes is also abundant; A. halizoa and A. marina
are more rarely represented. Among the plants of Fucus spiralis, Verrucaria
mucosa, the most wide-spreading of these marine forms, is “very
conspicuous as a dark-green, almost black, band of greasy appearance
stretching along the shore.” When growing in the shade, the thallus is of a
brighter green colour.
An examination[1190] of the west coast of Ireland yielded much the same
results, but with a still higher “white belt” formed mainly of Lecanora
parella and L. atra which covered the rocks lying above high-water mark,
“giving them the appearance of having been whitewashed.” A more general
association for the same position as regards the tide is given by Wheldon
and Wilson[1191] on the coasts of Arran as:
Physcia aquila.
Xanthoria parietina.
Lecanora parella.
Lecanora atra.
Lecanora campestris.
Placodium ferrugineum var. festivum.
Placodium tegularis.
Ramalina cuspidata.
Physcia stellaris.
Page 486
Physcia tenella.
Verrucaria maura.
A somewhat similar series of “formations” was determined by
Sandstede[1192] on the coast of Rügen. On erratic granite boulders washed
by the tide he found:
Verrucaria maura.
Lichina confinis.
Lecanora prosechoides.
Placodium lobulatum.
While in a higher position on similar boulders:
Lecanora exigua.
Lecanora dispersa.
Lecanora galactina.
Lecanora sulphurea.
Lecanora saxicola.
Lecanora caesiocinerea.
Lecanora gibbosa.
Lecanora atra.
Lecanora parella.
Lecidea colludens.
Lecidea lavata.
Lecidea nigroclavata f. lenticularis.
Xanthoria parietina and f. aureola.
Physcia subobscura.
Physcia caesia.
Verrucaria maura.
A somewhat similar series of “formations” was determined by
Sandstede[1192] on the coast of Rügen. On erratic granite boulders washed
by the tide he found:
Verrucaria maura.
Lichina confinis.
Lecanora prosechoides.
Placodium lobulatum.
While in a higher position on similar boulders:
Lecanora exigua.
Lecanora dispersa.
Lecanora galactina.
Lecanora sulphurea.
Lecanora saxicola.
Lecanora caesiocinerea.
Lecanora gibbosa.
Lecanora atra.
Lecanora parella.
Lecidea colludens.
Lecidea lavata.
Lecidea nigroclavata f. lenticularis.
Xanthoria parietina and f. aureola.
Physcia subobscura.
Physcia caesia.
Page 487
And more rarely a few species of Lecidea.
b. Lichens of Sand-dunes. These lichens might be included with those of
the terricolous communities, but they really represent a maritime
community of xerophytic type, subject to the influence of salt spray but not
within reach of the tide. They are sun-lichens and react to the strong light in
the deeper colour of the thallus. In such a sun-baked area at Findhorn a
luxuriant association of lichens was observed growing among short grass
and plant debris. It consisted chiefly of:
Parmelia physodes.
Evernia prunastri.
Cetraria aculeata.
Cladonia cervicornis.
Cladonia endiviaefolia.
Peltigera spp.
On very arid situations the species of Cladonia are those that have a well-
developed rather thick primary thallus, probably because such a thallus is
able to retain moisture for a prolonged period[1193]. On shifting sand, as in
the desert, there are no lichens; it is only on surfaces more or less fixed by
marram grass that lichens begin to develop, though in the cool damp
weather of autumn and winter, as observed by Wheldon and Wilson[1194],
certain species associated with Myxophyceae, such as Collemaceae, may
make their appearance, among others Leptogium scotinum, Collemodium
turgidum and Collema ceranoides. Watson[1195] makes the same observation
in his study of sand-dunes.
When the loose sand on the dunes of South Lancashire becomes
cemented by algae and mosses several rare Lecideae are to be found on the
decaying vegetation, and with further accumulation of humus Cladoniae
appear and spread rapidly along with several species of Peltigera and the
ubiquitous Parmelia physodes. The latter starts on dead twigs of Salix
repens and spreads on to the surrounding soil where it forms patches some
inches in diameter. The association also includes Lecidea uliginosa and
Bilimbia sphaeroides.
b. Lichens of Sand-dunes. These lichens might be included with those of
the terricolous communities, but they really represent a maritime
community of xerophytic type, subject to the influence of salt spray but not
within reach of the tide. They are sun-lichens and react to the strong light in
the deeper colour of the thallus. In such a sun-baked area at Findhorn a
luxuriant association of lichens was observed growing among short grass
and plant debris. It consisted chiefly of:
Parmelia physodes.
Evernia prunastri.
Cetraria aculeata.
Cladonia cervicornis.
Cladonia endiviaefolia.
Peltigera spp.
On very arid situations the species of Cladonia are those that have a well-
developed rather thick primary thallus, probably because such a thallus is
able to retain moisture for a prolonged period[1193]. On shifting sand, as in
the desert, there are no lichens; it is only on surfaces more or less fixed by
marram grass that lichens begin to develop, though in the cool damp
weather of autumn and winter, as observed by Wheldon and Wilson[1194],
certain species associated with Myxophyceae, such as Collemaceae, may
make their appearance, among others Leptogium scotinum, Collemodium
turgidum and Collema ceranoides. Watson[1195] makes the same observation
in his study of sand-dunes.
When the loose sand on the dunes of South Lancashire becomes
cemented by algae and mosses several rare Lecideae are to be found on the
decaying vegetation, and with further accumulation of humus Cladoniae
appear and spread rapidly along with several species of Peltigera and the
ubiquitous Parmelia physodes. The latter starts on dead twigs of Salix
repens and spreads on to the surrounding soil where it forms patches some
inches in diameter. The association also includes Lecidea uliginosa and
Bilimbia sphaeroides.
Page 488
On the more inland portions of the dunes numerous rather poorly
developed Cladoniae and Cetraria aculeata were associated, while on the
sides of “slacks” or “dune-pans” Collema pulposum, Cladonia sylvatica and
several crustaceous lichens covered the soil. The wetter parts of the dunes
were not found to be favourable to lichen growth.
Sandstede[1196] found on the sandy shores of Rügen, from the shore
upwards: first a stretch of bare sand, then a few dune grasses with scattered
scraps of Cladoniae, Peltigerae and Cetraria aculeata. Next in order
sandbanks with Parmelia physodes, Cladonia sylvatica, Cl. alcicornis and
Stereocaulon paschale. All these are species that occur on similar shores in
the British Islands. Sandstede adds an extensive list of maritime species
observed by him in Rügen.
A very careful tabulation of lichens at Blakeney Point in Norfolk was
made by McLean[1197] and the table on p. 386 is reproduced from his paper.
Sand, he writes, is present in all the associations and the presence or
absence of stones marks the great difference between the two formations
determined by dune and shingle.
(1) Bare sand, which is the first association listed, is an area practically
without phanerogams; the few lichen plants, Cladonia furcata and Cetraria
aculeata f. acanthella, are attached by slight embedding in the soil.
(2) Grey dune. The sand-loving lichens of the association grow in
company with Hypnum cupressiforme and attain their greatest development.
Other species which also occur there are Parmelia physodes and Evernia
prunastri var. stictocera.
(3) Derelict dune. This part of the dune formation occurs here and there
on the seaward margin where the grey dune has been worn down by the
wind. It is more shingly, hence the presence of stone lichens; dune
phanerogams are interspersed and with them a few fruticose lichens, such
as Cladonia furcata.
(4) High shingle. The term indicates shingle aggregated into banks lying
well above all except the highest tides. A large percentage of sand may be
mixed with the stones and if no humus is present and the stones of small
size, lichens may be absent altogether. Those occurring in the “loose
shingle” are saxicolous. In the “bound shingle” where there is no grass the
developed Cladoniae and Cetraria aculeata were associated, while on the
sides of “slacks” or “dune-pans” Collema pulposum, Cladonia sylvatica and
several crustaceous lichens covered the soil. The wetter parts of the dunes
were not found to be favourable to lichen growth.
Sandstede[1196] found on the sandy shores of Rügen, from the shore
upwards: first a stretch of bare sand, then a few dune grasses with scattered
scraps of Cladoniae, Peltigerae and Cetraria aculeata. Next in order
sandbanks with Parmelia physodes, Cladonia sylvatica, Cl. alcicornis and
Stereocaulon paschale. All these are species that occur on similar shores in
the British Islands. Sandstede adds an extensive list of maritime species
observed by him in Rügen.
A very careful tabulation of lichens at Blakeney Point in Norfolk was
made by McLean[1197] and the table on p. 386 is reproduced from his paper.
Sand, he writes, is present in all the associations and the presence or
absence of stones marks the great difference between the two formations
determined by dune and shingle.
(1) Bare sand, which is the first association listed, is an area practically
without phanerogams; the few lichen plants, Cladonia furcata and Cetraria
aculeata f. acanthella, are attached by slight embedding in the soil.
(2) Grey dune. The sand-loving lichens of the association grow in
company with Hypnum cupressiforme and attain their greatest development.
Other species which also occur there are Parmelia physodes and Evernia
prunastri var. stictocera.
(3) Derelict dune. This part of the dune formation occurs here and there
on the seaward margin where the grey dune has been worn down by the
wind. It is more shingly, hence the presence of stone lichens; dune
phanerogams are interspersed and with them a few fruticose lichens, such
as Cladonia furcata.
(4) High shingle. The term indicates shingle aggregated into banks lying
well above all except the highest tides. A large percentage of sand may be
mixed with the stones and if no humus is present and the stones of small
size, lichens may be absent altogether. Those occurring in the “loose
shingle” are saxicolous. In the “bound shingle” where there is no grass the
Page 489
stones, fixed in a mixture of sand and humus, are well covered with lichens.
With the presence of grass, a thin layer of humus covers the stones and a
dense lichen vegetation is developed both of shingle and of dune species.
(5) Low shingle. This last association lies in the hollows among plants of
Suacda fruticosa. Stability is high and tidal immersions regular and
frequent. The dominant factor of the association is the quantity of humus
and mud deposited around and over the stones. The lichens cover almost
every available spot on the firmly embedded pebbles. The characteristic
species of such areas are Lecanora badia and L. (Placodium) citrina which
effect the primary colonization. To these succeed Lecanora atra and
Xanthoria parietina. In time the mud overwhelms and partly destroys the
lichens, so that the phase of luxuriant growth is only temporary.
Lecanora badia is conspicuously abundant at the sand end of this
formation. Lecanora (Placodium) citrina disappears as the mud is left
behind. Collema spp. also occur frequently on the mixture of mud and sand
round the stones. The species on “low shingle” are those most tolerant of
submersion: Verrucaria maura is confined to this area, where it is covered
by the tide several hours each day.
Formation Association Principal Species
Dune Cetraria aculeata f.
acanthella
1. Bare Sand
Cladonia furcata
Cladonia
rangiferina,
Peltigera rufescens
2. Grey Dune
Cladonia furcata,
Cl. alcicornis
3. Derelict Dune Cladonia furcata,
Parmelia fuliginosa
With the presence of grass, a thin layer of humus covers the stones and a
dense lichen vegetation is developed both of shingle and of dune species.
(5) Low shingle. This last association lies in the hollows among plants of
Suacda fruticosa. Stability is high and tidal immersions regular and
frequent. The dominant factor of the association is the quantity of humus
and mud deposited around and over the stones. The lichens cover almost
every available spot on the firmly embedded pebbles. The characteristic
species of such areas are Lecanora badia and L. (Placodium) citrina which
effect the primary colonization. To these succeed Lecanora atra and
Xanthoria parietina. In time the mud overwhelms and partly destroys the
lichens, so that the phase of luxuriant growth is only temporary.
Lecanora badia is conspicuously abundant at the sand end of this
formation. Lecanora (Placodium) citrina disappears as the mud is left
behind. Collema spp. also occur frequently on the mixture of mud and sand
round the stones. The species on “low shingle” are those most tolerant of
submersion: Verrucaria maura is confined to this area, where it is covered
by the tide several hours each day.
Formation Association Principal Species
Dune Cetraria aculeata f.
acanthella
1. Bare Sand
Cladonia furcata
Cladonia
rangiferina,
Peltigera rufescens
2. Grey Dune
Cladonia furcata,
Cl. alcicornis
3. Derelict Dune Cladonia furcata,
Parmelia fuliginosa
Page 490
Rhizocarpon
confervoides
Shingle 4. High Shingle Lecanora atra, L.
galactina
With sand Rhizocarpon
confervoides
Lecanora citrina
Loose
Physcia tenella,
Lecanora citrina,
Xanthoria parietina
Without sand
Squamaria saxicola
Parmelia saxatilis,
P. fuliginosa
Bound Cladonia
rangiferina, Cl.
With grasses furcata, Cl. pungens
Cetraria aculeata
Without grasses Xanthoria parietina,
Biatorina chalybeia,
Lecanora atra
Aspicilia gibbosa,
Buellia colludens,
Verrucaria
microspora
confervoides
Shingle 4. High Shingle Lecanora atra, L.
galactina
With sand Rhizocarpon
confervoides
Lecanora citrina
Loose
Physcia tenella,
Lecanora citrina,
Xanthoria parietina
Without sand
Squamaria saxicola
Parmelia saxatilis,
P. fuliginosa
Bound Cladonia
rangiferina, Cl.
With grasses furcata, Cl. pungens
Cetraria aculeata
Without grasses Xanthoria parietina,
Biatorina chalybeia,
Lecanora atra
Aspicilia gibbosa,
Buellia colludens,
Verrucaria
microspora
Page 491
Physcia tenella,
Lecanora atroflava
Rhizocarpon
confervoides,
Lecanora citrina
var. incrustans
5. Low Shingle
L. badia, L. atra,
Xanthoria parietina
Verrucaria maura
McLean adds that Xanthoria parietina in its virescent form on Suaeda
fruticosa also endures constant immersion; Lecanora badia does not occur
above the tidal line and Lecanora galactina does not descend below tidal
limits; the latter is an arenicolous species and colonizes some of the loosest
and sandiest areas of shingle. Rhizocarpon confervoides is ubiquitous.
c. Mountain Lichens. On the mountain summits of our own and other
lands are to be found lichens very similar to those of the far North the
climatic conditions being the chief factors of importance in determining the
formations. These regions are occupied by what Wheldon and Wilson[1198]
describe as “a zone of Arctic-Alpine vegetation,” and they have recorded a
series of lichen associations belonging to that zone on the schistose summits
of the Perthshire mountains. The following is one of the most typical:
Euopsis granatina.
Sphaerophorus coralloides.
Sphaerophorus fragilis.
Gyrophora polyphylla.
Cetraria tristis.
Lecanora atroflava
Rhizocarpon
confervoides,
Lecanora citrina
var. incrustans
5. Low Shingle
L. badia, L. atra,
Xanthoria parietina
Verrucaria maura
McLean adds that Xanthoria parietina in its virescent form on Suaeda
fruticosa also endures constant immersion; Lecanora badia does not occur
above the tidal line and Lecanora galactina does not descend below tidal
limits; the latter is an arenicolous species and colonizes some of the loosest
and sandiest areas of shingle. Rhizocarpon confervoides is ubiquitous.
c. Mountain Lichens. On the mountain summits of our own and other
lands are to be found lichens very similar to those of the far North the
climatic conditions being the chief factors of importance in determining the
formations. These regions are occupied by what Wheldon and Wilson[1198]
describe as “a zone of Arctic-Alpine vegetation,” and they have recorded a
series of lichen associations belonging to that zone on the schistose summits
of the Perthshire mountains. The following is one of the most typical:
Euopsis granatina.
Sphaerophorus coralloides.
Sphaerophorus fragilis.
Gyrophora polyphylla.
Cetraria tristis.
Page 492
Cetraria nivalis.
Lecanora tartarea var. frigida.
Lecanora upsaliensis.
Aspicilia oculata.
Pertusaria dactylina.
Pertusaria glomerata.
Stereocaulon denudatum.
Parmelia saxatilis.
Parmelia omphalodes.
Parmelia lanata.
Parmelia stygia.
Stereocaulon tomentosum.
Stereocaulon alpinum.
Cladonia coccinca.
Cladonia gracilis.
Cladonia uncialis.
Cladonia destricta.
Cladonia racemosa.
Lecidea arctica.
Parmelia alpicola.
Cetraria aculeata.
Cetraria crispa.
Cetraria islandica.
Lecidea limosa.
Lecidea alpestris.
Lecidea demissa.
Lecanora tartarea var. frigida.
Lecanora upsaliensis.
Aspicilia oculata.
Pertusaria dactylina.
Pertusaria glomerata.
Stereocaulon denudatum.
Parmelia saxatilis.
Parmelia omphalodes.
Parmelia lanata.
Parmelia stygia.
Stereocaulon tomentosum.
Stereocaulon alpinum.
Cladonia coccinca.
Cladonia gracilis.
Cladonia uncialis.
Cladonia destricta.
Cladonia racemosa.
Lecidea arctica.
Parmelia alpicola.
Cetraria aculeata.
Cetraria crispa.
Cetraria islandica.
Lecidea limosa.
Lecidea alpestris.
Lecidea demissa.
Page 493
Lecidea uliginosa.
Lecidea cuprea.
Lecidea Berengeriana.
Lecidea cupreiformis.
Lecidea atrofusca.
Again on the summit of Ben-y-Gloe the same authors[1199] have recorded
Gyrophora erosa, G. torrefacta and G. cylindrica, Parmelia alpicola,
Lecanora tartarea var. frigida, Lecidea limosa and L. arctica, the last two
lichens thriving in the most bleak and exposed situations. Cladonia
cervicornis grew in reduced squamulose cushions; Stereocaulon and
Sphaerophorus in very compact forms, the outer stalks prostrate, the next
inclined, the central ones erect so that points only are exposed and no lateral
stress is caused by wind storms. Erect fruticose lichens are absent in this
region, being represented only by Parmelia lanata, a semi-decumbent plant,
and by Thamnolia vermicularis which is prostrate on the ground except
where the points of the stalks turn up to catch the dew. Many of the
Lecideae were observed to have large fruits and very little thallus: “the
hyphae ramify in the minute interstices of the stone and the gonidia cluster
under the lea of the apothecia: this is especially the case on loose stones
where conditions are extremely dry.”
On the Continent an interesting study of the lichens of high altitudes was
made by Maheu[1200] in the Savoyard Oberland. On the Great Casse at a
height of 3861 m. he collected four mosses and sixteen lichens. These were:
Stereocaulon condensatum.
Gyrophora cylindrica.
Gyrophora spodochroa.
Solorina crocea.
Solorina saccata.
Parmelia encausta.
Candelaria concolor.
Lecidea cuprea.
Lecidea Berengeriana.
Lecidea cupreiformis.
Lecidea atrofusca.
Again on the summit of Ben-y-Gloe the same authors[1199] have recorded
Gyrophora erosa, G. torrefacta and G. cylindrica, Parmelia alpicola,
Lecanora tartarea var. frigida, Lecidea limosa and L. arctica, the last two
lichens thriving in the most bleak and exposed situations. Cladonia
cervicornis grew in reduced squamulose cushions; Stereocaulon and
Sphaerophorus in very compact forms, the outer stalks prostrate, the next
inclined, the central ones erect so that points only are exposed and no lateral
stress is caused by wind storms. Erect fruticose lichens are absent in this
region, being represented only by Parmelia lanata, a semi-decumbent plant,
and by Thamnolia vermicularis which is prostrate on the ground except
where the points of the stalks turn up to catch the dew. Many of the
Lecideae were observed to have large fruits and very little thallus: “the
hyphae ramify in the minute interstices of the stone and the gonidia cluster
under the lea of the apothecia: this is especially the case on loose stones
where conditions are extremely dry.”
On the Continent an interesting study of the lichens of high altitudes was
made by Maheu[1200] in the Savoyard Oberland. On the Great Casse at a
height of 3861 m. he collected four mosses and sixteen lichens. These were:
Stereocaulon condensatum.
Gyrophora cylindrica.
Gyrophora spodochroa.
Solorina crocea.
Solorina saccata.
Parmelia encausta.
Candelaria concolor.
Page 494
Caloplaca pyracea var. nivalis.
Haematomma ventosum.
Acarospora smaragdula.
Psora decipiens.
Buellia discolor.
Buellia stellulata.
Lecidea contigua var. steriza.
Lecidea confluens.
Dermatocarpon hepaticum.
He found that as he climbed higher and higher foliaceous species became
rarer and crustaceous more abundant. The colour of the lichens on the high
summits was slightly weakened and the thallus often reduced, but all were
fertile and the apothecia normal and sporiferous. Lichens at less high
altitudes where they emerge from the snow covering for longer periods and
enjoy light and sunshine are, as already observed, often very brightly
coloured and of luxuriant growth.
d. Tundra Lichens. In phyto-geography the term “tundra” is given to
great stretches of country practically treeless and unsheltered within the
Polar climate; the tundra extends from the zone of dwarfed trees on to the
permanent ice or snow fields. The vegetation includes a few dwarfed trees,
shrubs, etc., but is mainly composed of mosses and lichens; the latter being
the most abundant. These are true climatic lichen formations.
Leighton[1201], in describing lichens from Arctic America brought home
by the traveller, Sir John Richardson, quotes from the latter that: “the
terrestrial lichens were gathered on Great Bear, and Great Slave Lakes
before starting on our summer voyages after the snow had melted.... The
barren grounds are densely covered for many hundreds of miles with
Corniculariae and Cetrariae, and where the ground is moist with
Cladoniae, while the boulders thickly scattered over the surface are clothed
with Gyrophorae.... The smaller stones on the gravelly ridges of the Barren
Grounds are covered with lichens.”
Haematomma ventosum.
Acarospora smaragdula.
Psora decipiens.
Buellia discolor.
Buellia stellulata.
Lecidea contigua var. steriza.
Lecidea confluens.
Dermatocarpon hepaticum.
He found that as he climbed higher and higher foliaceous species became
rarer and crustaceous more abundant. The colour of the lichens on the high
summits was slightly weakened and the thallus often reduced, but all were
fertile and the apothecia normal and sporiferous. Lichens at less high
altitudes where they emerge from the snow covering for longer periods and
enjoy light and sunshine are, as already observed, often very brightly
coloured and of luxuriant growth.
d. Tundra Lichens. In phyto-geography the term “tundra” is given to
great stretches of country practically treeless and unsheltered within the
Polar climate; the tundra extends from the zone of dwarfed trees on to the
permanent ice or snow fields. The vegetation includes a few dwarfed trees,
shrubs, etc., but is mainly composed of mosses and lichens; the latter being
the most abundant. These are true climatic lichen formations.
Leighton[1201], in describing lichens from Arctic America brought home
by the traveller, Sir John Richardson, quotes from the latter that: “the
terrestrial lichens were gathered on Great Bear, and Great Slave Lakes
before starting on our summer voyages after the snow had melted.... The
barren grounds are densely covered for many hundreds of miles with
Corniculariae and Cetrariae, and where the ground is moist with
Cladoniae, while the boulders thickly scattered over the surface are clothed
with Gyrophorae.... The smaller stones on the gravelly ridges of the Barren
Grounds are covered with lichens.”
Page 495
The accounts of tundra lichens that have been given by various travellers
deal chiefly with the more prominent terricolous forms. They have been
classified as “Cladina tundra,” including Cladonia rangiferina and
Sphaerophorus coralloides, “Cetraria tundra,” and “Alectoria heath,” the
latter the hardiest of all. Great swards of these lichens often alternate with
naked stony soil.
Kihlman[1202] has noted, as characteristic of tundra formations, the
compact cushion-like growth of the mosses which are thus enabled to store
up water and to conduct it by capillarity throughout the mass to the highest
stalks. Certain tundra lichens take on the same growth character as
adaptations to the strenuous life conditions. Cetraria glauca f. spadicea
with f. congesta and C. crispa are examples of this compact growth: they
form a soft thick carpet of a yellowish-grey colour. Cladoniae also grow in
crowded tufts, but are generally to be found in the more sheltered positions,
in valleys between the tundra hills and in the clefts of the rocks, or between
great boulders and stones where there is also more moisture.
The same kinds of lichens occur all over these northern regions. Birger
Nilson[1203] gives as the principal earth-lichens in Swedish Lappland,
Alectoria ochroleuca, A. nigricans, Cetraria nivalis, C. cucullata, Cladonia
uncialis, Thamnolia (Cerania) vermicularis and Sphaerophorus coralloides.
Darbishire[1204] speaks of the extensive beds of various species of
Cetraria in Ellesmere Land and King Oscar Land. Alectoria nigricans and
A. ochrolenca were often found in pure communities, but even more
frequently in close company with mosses. Though these fruticose lichens
are not represented by many species in Arctic regions, they cover a very
extensive area and form a very important feature in the vegetation.
Crustaceous lichens are not wanting: Lecanora tartarea f. frigida, L.
epibryon and others are to be found in great sheets covering the mosses or
the soil, or spreading over the stones and boulders. Cold has no deterrent
effect, and their advance is only checked by the presence of perpetual snow.
e. Desert Lichens. The reduced rainfall of desert countries is
unfavourable to general lichen growth and only the more xerophytic species
—those with a stout cortex—can flourish in the adverse conditions of
excessive light and dryness. Lichens, however, there are, in great numbers
as far as individuals are concerned, though the variety is not great. The
deal chiefly with the more prominent terricolous forms. They have been
classified as “Cladina tundra,” including Cladonia rangiferina and
Sphaerophorus coralloides, “Cetraria tundra,” and “Alectoria heath,” the
latter the hardiest of all. Great swards of these lichens often alternate with
naked stony soil.
Kihlman[1202] has noted, as characteristic of tundra formations, the
compact cushion-like growth of the mosses which are thus enabled to store
up water and to conduct it by capillarity throughout the mass to the highest
stalks. Certain tundra lichens take on the same growth character as
adaptations to the strenuous life conditions. Cetraria glauca f. spadicea
with f. congesta and C. crispa are examples of this compact growth: they
form a soft thick carpet of a yellowish-grey colour. Cladoniae also grow in
crowded tufts, but are generally to be found in the more sheltered positions,
in valleys between the tundra hills and in the clefts of the rocks, or between
great boulders and stones where there is also more moisture.
The same kinds of lichens occur all over these northern regions. Birger
Nilson[1203] gives as the principal earth-lichens in Swedish Lappland,
Alectoria ochroleuca, A. nigricans, Cetraria nivalis, C. cucullata, Cladonia
uncialis, Thamnolia (Cerania) vermicularis and Sphaerophorus coralloides.
Darbishire[1204] speaks of the extensive beds of various species of
Cetraria in Ellesmere Land and King Oscar Land. Alectoria nigricans and
A. ochrolenca were often found in pure communities, but even more
frequently in close company with mosses. Though these fruticose lichens
are not represented by many species in Arctic regions, they cover a very
extensive area and form a very important feature in the vegetation.
Crustaceous lichens are not wanting: Lecanora tartarea f. frigida, L.
epibryon and others are to be found in great sheets covering the mosses or
the soil, or spreading over the stones and boulders. Cold has no deterrent
effect, and their advance is only checked by the presence of perpetual snow.
e. Desert Lichens. The reduced rainfall of desert countries is
unfavourable to general lichen growth and only the more xerophytic species
—those with a stout cortex—can flourish in the adverse conditions of
excessive light and dryness. Lichens, however, there are, in great numbers
as far as individuals are concerned, though the variety is not great. The
Page 496
abundance of the crustaceous Lecanora esculenta in the deserts of Asia has
already been noted. Flagey[1205] found it one of the dominant species at
Biskra in the Sahara where it grows on the rocks. Patouillard[1206] in
describing the flora of Tunis speaks of the great patches (societies) of
Lecanora crassa f. deserti which at a distance look like milk spilled on the
ground, or if growing on unequal surfaces take the aspect of plaster that has
been passed over by some wheeled vehicle. At Biskra species of Heppia
grow on the sand. Steiner[1207] also records the frequency of Heppia and of
Endocarpon in the Sahara as well as of Gloeolichens which, as they are
associated with gelatinous blue-green algae, can endure extreme and long-
continued desiccation. These lichens, however, only form communities in
clefts among the rocks where these abut on the desert. In the great plains the
sand is too mobile and too often shifted by the sirocco to enable them to
settle.
Bruce Fink[1208] discusses desert lichens and their adaptive characters:
crustaceous species with a stout cortex are best able to withstand the long
dry periods; conspicuously lobed thalli are lacking, as are lichens with
fruticose structure though he thinks the latter are prevented from developing
by the exposure to high winds and driving sand storms. Herre’s[1209] study
of the desert lichen flora at Reno, Nevada, is full of interest. The district is
situated at an altitude of 4500 feet east of the Sierra Nevada Mountains. The
annual rainfall averages 8·21 inches, and a large part falls as snow during
the winter months or as early spring rain. The summer is hot and dry and
the diurnal changes of temperature are very great. Strong drying winds from
the west or north are frequent.
At 5000 feet and upwards lichens are, in general, exceedingly abundant
on all rock substrata and represent 57 species or subspecies, only three of
these being arboreal: Buellia triphragmia occurs rarely, Xanthoria
polycarpa is frequent on sage brush, while Candelariella cerinella though a
rock-lichen grows occasionally on the same substratum. Caloplaca
(Placodium) elegans is one of the most successful and abundant species and
along with Lecanora (nine forms), Acarospora (seven forms) and Lecidia
(five forms) comprises three-fourths of the rock surface occupied by
lichens. The addition of Rinodina with two species and Gyrophora with
four brings the computation of individuals in these desert rock formations
up to nine-tenths of the whole. As the desert rocks pass to the Alpine,
already been noted. Flagey[1205] found it one of the dominant species at
Biskra in the Sahara where it grows on the rocks. Patouillard[1206] in
describing the flora of Tunis speaks of the great patches (societies) of
Lecanora crassa f. deserti which at a distance look like milk spilled on the
ground, or if growing on unequal surfaces take the aspect of plaster that has
been passed over by some wheeled vehicle. At Biskra species of Heppia
grow on the sand. Steiner[1207] also records the frequency of Heppia and of
Endocarpon in the Sahara as well as of Gloeolichens which, as they are
associated with gelatinous blue-green algae, can endure extreme and long-
continued desiccation. These lichens, however, only form communities in
clefts among the rocks where these abut on the desert. In the great plains the
sand is too mobile and too often shifted by the sirocco to enable them to
settle.
Bruce Fink[1208] discusses desert lichens and their adaptive characters:
crustaceous species with a stout cortex are best able to withstand the long
dry periods; conspicuously lobed thalli are lacking, as are lichens with
fruticose structure though he thinks the latter are prevented from developing
by the exposure to high winds and driving sand storms. Herre’s[1209] study
of the desert lichen flora at Reno, Nevada, is full of interest. The district is
situated at an altitude of 4500 feet east of the Sierra Nevada Mountains. The
annual rainfall averages 8·21 inches, and a large part falls as snow during
the winter months or as early spring rain. The summer is hot and dry and
the diurnal changes of temperature are very great. Strong drying winds from
the west or north are frequent.
At 5000 feet and upwards lichens are, in general, exceedingly abundant
on all rock substrata and represent 57 species or subspecies, only three of
these being arboreal: Buellia triphragmia occurs rarely, Xanthoria
polycarpa is frequent on sage brush, while Candelariella cerinella though a
rock-lichen grows occasionally on the same substratum. Caloplaca
(Placodium) elegans is one of the most successful and abundant species and
along with Lecanora (nine forms), Acarospora (seven forms) and Lecidia
(five forms) comprises three-fourths of the rock surface occupied by
lichens. The addition of Rinodina with two species and Gyrophora with
four brings the computation of individuals in these desert rock formations
up to nine-tenths of the whole. As the desert rocks pass to the Alpine,
Page 497
Gyrophora becomes easily the dominant genus followed by Acarospora,
Caloplaca and Lecidea.
“The colouring characteristic of the rock ledges of the desert and cañon
walls is often entirely due to lichens, and in a general way they form the
only brilliant plant formations in a landscape notable for its subdued pale
monotonous tones. Most conspicuous are Acarospora chlorophana and
Caloplaca elegans, which form striking landmarks when covering great
crags and rock walls. The next most conspicuous lichens are Rinodina
oreina and Lecanora rubina and its allies, which often entirely cover
immense boulders and northerly sloping rock walls.” Herre concludes that
though desert conditions are unfavourable to most species of lichens, yet
some are perfectly at home there and the rocks are just as thickly covered as
in regions of greater humidity and less sunshine.
f. Aquatic Lichens. There is only one of the larger lichens that has
acquired a purely aquatic habit, Hydrothyria venosa, a North American
plant. It grows on rocks[1210] in the beds of streams, covering them often
with a thick felt; it is attached at the base and the rather narrow fronds float
freely in the current. The gonidium is Nostoc sp., and the thallus is of a
bluish-grey colour; the fruits are small discoid reddish apothecia with an
evanescent margin. It is closely allied to Peltigerae, some of which are
moisture-loving though not truly aquatic.
The nearest approach to aquatic habit among the foliose forms in our
country is Dermatocarpon aquaticum, with thick coriaceous rather
contorted lobes; it inhabits rocks and stones in streams and lakes.
Somewhat less continuously aquatic is D. miniatum var. complicatum which
grows on damp rocks exposed to spray or occasionally to inundation.
Lindsay[1211] has described it “on boulders by the side of the Tay, frequently
covered by the river when flooded, and of a deep olive colour when under
water”: both these lichens have a wide distribution in Europe, Africa,
America and New Zealand.
In a discussion of lake shore plants Conway Macmillan[1212] describes on
the flat shores a Dermatocarpon zone on the wet area nearest the lake,
behind that a Biatora zone and further landward a Cladonia zone. On
rounded rocky shores the same zones followed each other but were less
broad: they were so close together that the Cladoniae, which with
Caloplaca and Lecidea.
“The colouring characteristic of the rock ledges of the desert and cañon
walls is often entirely due to lichens, and in a general way they form the
only brilliant plant formations in a landscape notable for its subdued pale
monotonous tones. Most conspicuous are Acarospora chlorophana and
Caloplaca elegans, which form striking landmarks when covering great
crags and rock walls. The next most conspicuous lichens are Rinodina
oreina and Lecanora rubina and its allies, which often entirely cover
immense boulders and northerly sloping rock walls.” Herre concludes that
though desert conditions are unfavourable to most species of lichens, yet
some are perfectly at home there and the rocks are just as thickly covered as
in regions of greater humidity and less sunshine.
f. Aquatic Lichens. There is only one of the larger lichens that has
acquired a purely aquatic habit, Hydrothyria venosa, a North American
plant. It grows on rocks[1210] in the beds of streams, covering them often
with a thick felt; it is attached at the base and the rather narrow fronds float
freely in the current. The gonidium is Nostoc sp., and the thallus is of a
bluish-grey colour; the fruits are small discoid reddish apothecia with an
evanescent margin. It is closely allied to Peltigerae, some of which are
moisture-loving though not truly aquatic.
The nearest approach to aquatic habit among the foliose forms in our
country is Dermatocarpon aquaticum, with thick coriaceous rather
contorted lobes; it inhabits rocks and stones in streams and lakes.
Somewhat less continuously aquatic is D. miniatum var. complicatum which
grows on damp rocks exposed to spray or occasionally to inundation.
Lindsay[1211] has described it “on boulders by the side of the Tay, frequently
covered by the river when flooded, and of a deep olive colour when under
water”: both these lichens have a wide distribution in Europe, Africa,
America and New Zealand.
In a discussion of lake shore plants Conway Macmillan[1212] describes on
the flat shores a Dermatocarpon zone on the wet area nearest the lake,
behind that a Biatora zone and further landward a Cladonia zone. On
rounded rocky shores the same zones followed each other but were less
broad: they were so close together that the Cladoniae, which with
Page 498
Stereocaulon paschale grow in profusion on all such shores, occurred
within a couple of feet of the high-water mark.
M. C. Knowles[1213] reports concerning the lichen flora of some
mountain lakes in Waterford, that a band of Dermatocarpon miniatum var.
complicatum six feet wide grew all the way round the lakes between the
winter and summer level of the water. Below that zone D. aquaticum
formed another belt mingled with the moss Fontinalis and several species
of crustaceous lichens Staurotheleae, Polyblastiae, etc.
Bruce Fink[1214] gives as a typical “amphibious angiocarpous lichen
formation” of wet rocks in Minnesota: Dermatocarpon aquaticum, D.
miniatum var. complicatum, Staurothele clopima and Verrucaria viridula.
These “formations,” he says, “may be seen complete in places along the
shores of Vermillion Lake and less well represented at other portions of the
lake shore.” Macmillan found that on the rocky shores of Lake Superior the
Dermatocarpon zone also occurred nearest the water.
Species with closed fruits such as Pyrenolichens, or with apothecia
deeply sunk in the thallus and thus also well protected, seem to be best
adapted to the aquatic life. Such in our own country are Lecanora lacustris,
Bacidia inundata and others, with a number of Verrucariae: V. aethiobola,
V. hydrela, V. margacea, etc.
Lettau[1215] gives as “formations” on rocks or boulders in the beds of
streams in Thuringia:
Verrucaria aethiobola.
Verrucaria hydrela.
Dermatocarpon aquaticum.
Bacidia inundata.
Lecanora aquatica.
In their ecological study of Perthshire lichens Wheldon and Wilson[1216]
give two “formations.” The first is on rocks submerged for long periods,
though in dry weather the lichens may be exposed, and can withstand
desiccation for a considerable time:
within a couple of feet of the high-water mark.
M. C. Knowles[1213] reports concerning the lichen flora of some
mountain lakes in Waterford, that a band of Dermatocarpon miniatum var.
complicatum six feet wide grew all the way round the lakes between the
winter and summer level of the water. Below that zone D. aquaticum
formed another belt mingled with the moss Fontinalis and several species
of crustaceous lichens Staurotheleae, Polyblastiae, etc.
Bruce Fink[1214] gives as a typical “amphibious angiocarpous lichen
formation” of wet rocks in Minnesota: Dermatocarpon aquaticum, D.
miniatum var. complicatum, Staurothele clopima and Verrucaria viridula.
These “formations,” he says, “may be seen complete in places along the
shores of Vermillion Lake and less well represented at other portions of the
lake shore.” Macmillan found that on the rocky shores of Lake Superior the
Dermatocarpon zone also occurred nearest the water.
Species with closed fruits such as Pyrenolichens, or with apothecia
deeply sunk in the thallus and thus also well protected, seem to be best
adapted to the aquatic life. Such in our own country are Lecanora lacustris,
Bacidia inundata and others, with a number of Verrucariae: V. aethiobola,
V. hydrela, V. margacea, etc.
Lettau[1215] gives as “formations” on rocks or boulders in the beds of
streams in Thuringia:
Verrucaria aethiobola.
Verrucaria hydrela.
Dermatocarpon aquaticum.
Bacidia inundata.
Lecanora aquatica.
In their ecological study of Perthshire lichens Wheldon and Wilson[1216]
give two “formations.” The first is on rocks submerged for long periods,
though in dry weather the lichens may be exposed, and can withstand
desiccation for a considerable time:
Page 499
Pterygium Kenmorensis.
Collema fluviatile.
Lecanora lacustris.
Lecanora epulotica.
Bacidia inundata.
Rhizocarpum obscuration.
Rhizocarpum petraeum.
Lecidea contigua.
Lecidea albocoerulescens.
Dermatocarpon miniatum var. complicatum.
Dermatocarpon aquaticum.
Verrucaria laevata.
Verrucaria aethiobola.
Verrucaria margacea.
The second group of species usually inhabits damp, shaded rocks of
ravines or large boulders by streams or near waterfalls. It includes species
of Collema, Sticta, Peltigera, Solorina, Pannaria, etc., with Opegrapha
zonata, Porina lectissima and Verrucaria nigrescens.
The last-mentioned lichen grows by preference on limestone, but in
excessive moisture[1217], as by the sea-side, the substratum seems to be of
minor importance.
D. Lichens As Pioneers
a. Soil-formers. The part played by lichens in the “Economy of Nature”
is of very real importance: to them is allotted the pioneer work of breaking
down the hard rock surfaces and preparing a soil on which more highly
developed plants can grow. This was pointed out by Linnaeus[1218] who thus
describes the succession of plants: “Crustaceous lichens,” he writes, “are
the first foundation of vegetation. Though hitherto we have considered
Collema fluviatile.
Lecanora lacustris.
Lecanora epulotica.
Bacidia inundata.
Rhizocarpum obscuration.
Rhizocarpum petraeum.
Lecidea contigua.
Lecidea albocoerulescens.
Dermatocarpon miniatum var. complicatum.
Dermatocarpon aquaticum.
Verrucaria laevata.
Verrucaria aethiobola.
Verrucaria margacea.
The second group of species usually inhabits damp, shaded rocks of
ravines or large boulders by streams or near waterfalls. It includes species
of Collema, Sticta, Peltigera, Solorina, Pannaria, etc., with Opegrapha
zonata, Porina lectissima and Verrucaria nigrescens.
The last-mentioned lichen grows by preference on limestone, but in
excessive moisture[1217], as by the sea-side, the substratum seems to be of
minor importance.
D. Lichens As Pioneers
a. Soil-formers. The part played by lichens in the “Economy of Nature”
is of very real importance: to them is allotted the pioneer work of breaking
down the hard rock surfaces and preparing a soil on which more highly
developed plants can grow. This was pointed out by Linnaeus[1218] who thus
describes the succession of plants: “Crustaceous lichens,” he writes, “are
the first foundation of vegetation. Though hitherto we have considered
Page 500
theirs a trifling place among plants, nevertheless they are of great
importance at that first stage in the economy of nature. When the rocks
emerge from the seas, they are so polished by the force of the waves, that
scarcely any kind of plant could settle on them, seen more especially near
the sea. But very soon, in truth, the smallest crustaceous lichens begin to
cover those arid rocks, and are sustained by minute quantities of soil and by
imperceptible particles brought to them by rain and by the atmosphere.
These lichens in time become converted by decay into a thin layer of
humus, so that at length imbricate lichens are able to thrust their rhizoids
into it. As these in turn change to humus by natural decay, various mosses
such as Hypnum, Bryum and Polytrichum follow, and find suitable place
and nourishment. In time there is produced by the dying down of the
mosses such a quantity of soil that herbs and shrubs are able to establish
themselves and maintain their existence.”
Similar observations have been made since Linnaeus’s day, among others
by Guembel[1219] in his account of Lecanora ventosa. Either by the
excretion of carbon dioxide which acidifies the surrounding moisture, or by
the mechanical action of hyphae and rhizinae, the component particles of
rocks such as granite are gradually dissolved and broken up. Rocks exposed
to weather alone are unchanged, while those covered with lichens have their
surface disintegrated and destroyed.
The decaying parts of the lichen thallus add to the soil material as
observed by Linnaeus, and in time mosses follow, and, later, phanerogams.
Goeppert[1220] has pointed out the succession observed on roofs of houses
as: “first some lichen such as Lecanora saxicola, then the moss Grimmia
pulvinata, which forms compact cushions on which later grow Poa
compressa, small crucifers, etc.”
Goeppert[1220] has noted as special rock-destroyers some foliaceous
species, Parmelia saxatilis, P. stygia and P. encausta, the underlying rock
being roughened and broken up by their rhizoids. Species of Gyrophora and
Sphaerophorus have the same disintegrating effect, so that the surface of
the rock may in time lose its coherence to a depth of 2 to 4 inches.
Crustaceous species such as Lecanora polytropa, Candelariella vitellina,
etc., exercise an equally powerful solvent action, while underneath closely
appressed growers like Lecanora atra and Acarospora smaragdula the
importance at that first stage in the economy of nature. When the rocks
emerge from the seas, they are so polished by the force of the waves, that
scarcely any kind of plant could settle on them, seen more especially near
the sea. But very soon, in truth, the smallest crustaceous lichens begin to
cover those arid rocks, and are sustained by minute quantities of soil and by
imperceptible particles brought to them by rain and by the atmosphere.
These lichens in time become converted by decay into a thin layer of
humus, so that at length imbricate lichens are able to thrust their rhizoids
into it. As these in turn change to humus by natural decay, various mosses
such as Hypnum, Bryum and Polytrichum follow, and find suitable place
and nourishment. In time there is produced by the dying down of the
mosses such a quantity of soil that herbs and shrubs are able to establish
themselves and maintain their existence.”
Similar observations have been made since Linnaeus’s day, among others
by Guembel[1219] in his account of Lecanora ventosa. Either by the
excretion of carbon dioxide which acidifies the surrounding moisture, or by
the mechanical action of hyphae and rhizinae, the component particles of
rocks such as granite are gradually dissolved and broken up. Rocks exposed
to weather alone are unchanged, while those covered with lichens have their
surface disintegrated and destroyed.
The decaying parts of the lichen thallus add to the soil material as
observed by Linnaeus, and in time mosses follow, and, later, phanerogams.
Goeppert[1220] has pointed out the succession observed on roofs of houses
as: “first some lichen such as Lecanora saxicola, then the moss Grimmia
pulvinata, which forms compact cushions on which later grow Poa
compressa, small crucifers, etc.”
Goeppert[1220] has noted as special rock-destroyers some foliaceous
species, Parmelia saxatilis, P. stygia and P. encausta, the underlying rock
being roughened and broken up by their rhizoids. Species of Gyrophora and
Sphaerophorus have the same disintegrating effect, so that the surface of
the rock may in time lose its coherence to a depth of 2 to 4 inches.
Crustaceous species such as Lecanora polytropa, Candelariella vitellina,
etc., exercise an equally powerful solvent action, while underneath closely
appressed growers like Lecanora atra and Acarospora smaragdula the
Page 501
stone is converted to a friable substance that can be sliced away with a
knife.
Salter[1221] concluded that oxalic acid was the principal agent in
disintegration. He found that it acted more or less rapidly on minerals and
almost any class of saline compounds; it even attacked glass finely
powdered, though silica remained unchanged.
Bachmann[1222] found that granite was reduced by lichens to a clay-like
granular yellow mass in a comparatively short time, the lichen seizing on
the particles of mica first; but the spread of the lichen over the rock, he
observes, is largely directed by the amount of humidity and by the chance
of gaining a foothold. In the case of calcareous rocks he[1223] tested the
relative dampness of those containing lichens and those that were lichen-
free. In the former case water was absorbed more freely and retained much
longer than in the barren rock, thus encouraging further vegetation.
Lucy E. Braun[1224] has described the successive colonization of
limestone conglomerate in Cincinnati. The rock is somewhat resistant to
erosion and stands out in irregular outcrops on the hillsides of the region.
The first plants to gain a footing are certain crustaceous lichens, Lecidea
sp., Pertusaria communis, Staurothele umbrina, Verrucaria muralis and
Placodium citrinum which occur as patches on the smoother and more
exposed rock faces. With these were associated small quantities of a moss,
Grimmia apocarpa. In the second stage of growth Dermatocarpon
miniatum, and, to a lesser degree, a gelatinous Omphalaria sp. were the
most prominent plants, but mosses were more in evidence, and the next
stage consisted almost exclusively of mosses and hepatics with Peltigera
canina. A thick layer of humus was gradually built up by these plants on
which Phanerogamous plants were able to flourish.
In tropical countries the first vegetation to settle on bare rocks would
seem to be blue-green gelatinous algae. Three years after the eruption of
Krakatoa, dark-green layers of these plants were found by Treub[1225] on the
surface of the pumice and ash, and on the loose stones in the ravines of the
mountain. It was only at a later stage that lichens appeared.
b. Outposts of vegetation. Lichens are the only plants that can survive
extreme conditions of cold or of heat. They grow in Polar regions where no
knife.
Salter[1221] concluded that oxalic acid was the principal agent in
disintegration. He found that it acted more or less rapidly on minerals and
almost any class of saline compounds; it even attacked glass finely
powdered, though silica remained unchanged.
Bachmann[1222] found that granite was reduced by lichens to a clay-like
granular yellow mass in a comparatively short time, the lichen seizing on
the particles of mica first; but the spread of the lichen over the rock, he
observes, is largely directed by the amount of humidity and by the chance
of gaining a foothold. In the case of calcareous rocks he[1223] tested the
relative dampness of those containing lichens and those that were lichen-
free. In the former case water was absorbed more freely and retained much
longer than in the barren rock, thus encouraging further vegetation.
Lucy E. Braun[1224] has described the successive colonization of
limestone conglomerate in Cincinnati. The rock is somewhat resistant to
erosion and stands out in irregular outcrops on the hillsides of the region.
The first plants to gain a footing are certain crustaceous lichens, Lecidea
sp., Pertusaria communis, Staurothele umbrina, Verrucaria muralis and
Placodium citrinum which occur as patches on the smoother and more
exposed rock faces. With these were associated small quantities of a moss,
Grimmia apocarpa. In the second stage of growth Dermatocarpon
miniatum, and, to a lesser degree, a gelatinous Omphalaria sp. were the
most prominent plants, but mosses were more in evidence, and the next
stage consisted almost exclusively of mosses and hepatics with Peltigera
canina. A thick layer of humus was gradually built up by these plants on
which Phanerogamous plants were able to flourish.
In tropical countries the first vegetation to settle on bare rocks would
seem to be blue-green gelatinous algae. Three years after the eruption of
Krakatoa, dark-green layers of these plants were found by Treub[1225] on the
surface of the pumice and ash, and on the loose stones in the ravines of the
mountain. It was only at a later stage that lichens appeared.
b. Outposts of vegetation. Lichens are the only plants that can survive
extreme conditions of cold or of heat. They grow in Polar regions where no
Page 502
other vegetation could obtain sustenance; they are to be found at great
heights on mountains all over the globe; and, on arid desert rocks they
persist through long dry seasons, depending almost entirely on night dews
for the supply of moisture. Here we have true lichen formations in the sense
of modern ecology.
heights on mountains all over the globe; and, on arid desert rocks they
persist through long dry seasons, depending almost entirely on night dews
for the supply of moisture. Here we have true lichen formations in the sense
of modern ecology.
Page 503
CHAPTER X
ECONOMIC AND TECHNICAL
A. Lichens as Food.
a. Food for Insects, etc. Some of the earlier botanists made careful
observations on the important place occupied by lichens in nature as
affording food to many small animals. In 1791 Jacques Brez[1226] wrote his
Flore des Insectophyles, and in the list of food-plants he includes seven
species of lichens. The “insects” that frequented these lichens were species
of the genera Acarus (mites) and Phalena (moths). A few years later
Persoon[1227] noted that lichens formed the main food supply of many
insects, slugs, etc. Zukal[1228], quoting from Otto Wilde (Die Pflanzen und
Raupen Deutschlands, Berlin, 1860), gives a list of caterpillars that are
known to feed on and destroy lichens.
A very considerable number of small creatures feed eagerly on lichens,
and traces of their depredations are constantly to be seen in the empty fruit
discs, and in the cortices eaten away in patches so as to expose the white
medulla. It has been argued by Zukal[1229] that the great formation of acid
substances in lichens is for shielding them against the attacks of animals;
Zopf[1230] on the contrary insists that these substances afford the plants no
real protection. He made a series of experiments with snails, feeding them
with slices of potato smeared with pure lichen acids. Many snails ate the
slices with great readiness even when covered with bitter acids such as
cetraric, or with those which are poisonous for other animals such as
rhizocarpic and pinastrinic. The only acid they refused was vulpinic, which
is said to be poisonous for vertebrates. The crystals of the acids passed
unchanged through the alimentary canal of the snails, and were found in
masses in the excreta. They were undissolved, but, enclosed in slime, their
sharp edges did no damage to the digestive tract.
Stahl[1231] however upholds Zukal’s theory of the protective function of
lichen acids against the attacks of small animals. Some few snails,
ECONOMIC AND TECHNICAL
A. Lichens as Food.
a. Food for Insects, etc. Some of the earlier botanists made careful
observations on the important place occupied by lichens in nature as
affording food to many small animals. In 1791 Jacques Brez[1226] wrote his
Flore des Insectophyles, and in the list of food-plants he includes seven
species of lichens. The “insects” that frequented these lichens were species
of the genera Acarus (mites) and Phalena (moths). A few years later
Persoon[1227] noted that lichens formed the main food supply of many
insects, slugs, etc. Zukal[1228], quoting from Otto Wilde (Die Pflanzen und
Raupen Deutschlands, Berlin, 1860), gives a list of caterpillars that are
known to feed on and destroy lichens.
A very considerable number of small creatures feed eagerly on lichens,
and traces of their depredations are constantly to be seen in the empty fruit
discs, and in the cortices eaten away in patches so as to expose the white
medulla. It has been argued by Zukal[1229] that the great formation of acid
substances in lichens is for shielding them against the attacks of animals;
Zopf[1230] on the contrary insists that these substances afford the plants no
real protection. He made a series of experiments with snails, feeding them
with slices of potato smeared with pure lichen acids. Many snails ate the
slices with great readiness even when covered with bitter acids such as
cetraric, or with those which are poisonous for other animals such as
rhizocarpic and pinastrinic. The only acid they refused was vulpinic, which
is said to be poisonous for vertebrates. The crystals of the acids passed
unchanged through the alimentary canal of the snails, and were found in
masses in the excreta. They were undissolved, but, enclosed in slime, their
sharp edges did no damage to the digestive tract.
Stahl[1231] however upholds Zukal’s theory of the protective function of
lichen acids against the attacks of small animals. Some few snails,
Page 504
caterpillars, etc., that are omnivorous feeders consume most lichens with
impunity, and the bitter taste seems to attract rather than repel them; but
many others he contends are certainly prevented from eating lichens by the
presence of the acids. He proved this by soaking portions of the thalli of
certain bitter species for about twenty-four hours in a one per cent. soda
solution, which was sufficiently strong to extract the acids. He found that
these treated specimens were in most cases preferred to fresh portions that
had been simply moistened with water.
Even the omnivorous snail, Helix hortensis, was several times observed
to touch the fresh thallus and then creep away, while it ate continuously the
soda-washed portion as soon as it came into contact with it. Calcium
Oxalate, on the other hand, formed no protection; omnivorous feeders ate
indifferently calcicolous lichens such as Aspicilia calcarea and Lecanora
saxicola, whether treated with soda or not, but would only accept lichens
with acid contents, such as Parmelia caperata, Evernia prunastri, etc., after
they had been duly soaked.
Experiments were also made with wood-lice (Oniscus murarius), and
with earwigs (Forficula auricularia), and the result was the same: they
would only eat bitter lichens after the acids had been extracted by the soda
method. Stahl therefore concludes that acids must be regarded as eminently
adapted to protect lichens which otherwise, owing to their slowness of
growth, would scarcely escape extinction.
The gelatinous Collemaceae, as also Nostoc, the alga with which these
are associated, are unharmed by snails, etc., on account of their slippery
consistency when moist, which prevents the creatures from getting a
foothold on the thallus. These lichens however do not contain acids, and if,
when dry, they are reduced to powder and then moistened, they are eagerly
eaten both by snails and by wood-lice. Peltigera canina, on account of a
disagreeable odour it acquires on being chewed, is avoided to a certain
extent, but even so it is frequently found with much of the thallus eaten
away.
Hue[1232] in his study of Antarctic lichens, comments on the abundance
and perfect development of the lichens, especially the crustaceous species,
which cover every inch of rock surface. He ascribes this to the absence of
impunity, and the bitter taste seems to attract rather than repel them; but
many others he contends are certainly prevented from eating lichens by the
presence of the acids. He proved this by soaking portions of the thalli of
certain bitter species for about twenty-four hours in a one per cent. soda
solution, which was sufficiently strong to extract the acids. He found that
these treated specimens were in most cases preferred to fresh portions that
had been simply moistened with water.
Even the omnivorous snail, Helix hortensis, was several times observed
to touch the fresh thallus and then creep away, while it ate continuously the
soda-washed portion as soon as it came into contact with it. Calcium
Oxalate, on the other hand, formed no protection; omnivorous feeders ate
indifferently calcicolous lichens such as Aspicilia calcarea and Lecanora
saxicola, whether treated with soda or not, but would only accept lichens
with acid contents, such as Parmelia caperata, Evernia prunastri, etc., after
they had been duly soaked.
Experiments were also made with wood-lice (Oniscus murarius), and
with earwigs (Forficula auricularia), and the result was the same: they
would only eat bitter lichens after the acids had been extracted by the soda
method. Stahl therefore concludes that acids must be regarded as eminently
adapted to protect lichens which otherwise, owing to their slowness of
growth, would scarcely escape extinction.
The gelatinous Collemaceae, as also Nostoc, the alga with which these
are associated, are unharmed by snails, etc., on account of their slippery
consistency when moist, which prevents the creatures from getting a
foothold on the thallus. These lichens however do not contain acids, and if,
when dry, they are reduced to powder and then moistened, they are eagerly
eaten both by snails and by wood-lice. Peltigera canina, on account of a
disagreeable odour it acquires on being chewed, is avoided to a certain
extent, but even so it is frequently found with much of the thallus eaten
away.
Hue[1232] in his study of Antarctic lichens, comments on the abundance
and perfect development of the lichens, especially the crustaceous species,
which cover every inch of rock surface. He ascribes this to the absence of
Page 505
snails and insects which in other regions so seriously interfere with the
normal and continuous growth of these plants.
Snails do not eat lichens when they are dry and hard, but on damp or
dewy nights, and on rainy days, all kinds, both large and small, come out of
their shells and devour the lichen thalli softened by moisture. Large slugs
(Limax) have been seen devouring with great satisfaction Pertusaria
faginea, a bitter crustaceous lichen. The same Limax species eats many
different lichens, some of them containing very bitter substances. Zopf[1233]
observed that Helix cingulata ate ten different lichens, containing as many
different kinds of acid.
Other creatures such as mites, wood-lice, and the caterpillars of many
butterflies live on lichens, though, with the exception of the caterpillars,
they eat them only when moist. Very frequently the apothecial discs and the
soredia are taken first as being evidently the choicest portions. All lichens
are, however, not equally palatable. Bitter[1234] observed that the insect
Psocus (Orthoptera) had a distinct preference for certain species, and
restricted its attention to them probably because of their chemical
constitution. He noted that in a large spreading thallus of Graphis elegans
on holly, irregular bare spots appeared, due to the ravages of insects—
probably Psocus. In other places, the thallus alone had been consumed,
leaving the rather hard black fruits (lirellae) untouched. In time the thallus
of Thelotrema lepadinum, also a crustaceous lichen, invaded the naked
areas, and surrounded the Graphis lirellae. The new comer was not to the
taste of the insects and was left untouched.
Petch[1235] says that lichens form the staple food of Termes monoceros,
the black termite of Ceylon. These ants really prefer algae, but as the supply
is limited they fall back on lichens, though they only consume those of a
particular type, or at a particular stage of development. Those with a tough
smooth cortex are avoided, preference being given to thalli with a loose
powdery surface. At the feeding ground the ants congregate on the suitable
lichens. With their mandibles they scrape off small fragments of the thallus
which they form into balls, varying in size from 1·5 mm. to 2·5 mm. in
diameter. The workers then convey these to the nests in their mandibles. It
would seem that they carry about these balls of food, and allow the ants
normal and continuous growth of these plants.
Snails do not eat lichens when they are dry and hard, but on damp or
dewy nights, and on rainy days, all kinds, both large and small, come out of
their shells and devour the lichen thalli softened by moisture. Large slugs
(Limax) have been seen devouring with great satisfaction Pertusaria
faginea, a bitter crustaceous lichen. The same Limax species eats many
different lichens, some of them containing very bitter substances. Zopf[1233]
observed that Helix cingulata ate ten different lichens, containing as many
different kinds of acid.
Other creatures such as mites, wood-lice, and the caterpillars of many
butterflies live on lichens, though, with the exception of the caterpillars,
they eat them only when moist. Very frequently the apothecial discs and the
soredia are taken first as being evidently the choicest portions. All lichens
are, however, not equally palatable. Bitter[1234] observed that the insect
Psocus (Orthoptera) had a distinct preference for certain species, and
restricted its attention to them probably because of their chemical
constitution. He noted that in a large spreading thallus of Graphis elegans
on holly, irregular bare spots appeared, due to the ravages of insects—
probably Psocus. In other places, the thallus alone had been consumed,
leaving the rather hard black fruits (lirellae) untouched. In time the thallus
of Thelotrema lepadinum, also a crustaceous lichen, invaded the naked
areas, and surrounded the Graphis lirellae. The new comer was not to the
taste of the insects and was left untouched.
Petch[1235] says that lichens form the staple food of Termes monoceros,
the black termite of Ceylon. These ants really prefer algae, but as the supply
is limited they fall back on lichens, though they only consume those of a
particular type, or at a particular stage of development. Those with a tough
smooth cortex are avoided, preference being given to thalli with a loose
powdery surface. At the feeding ground the ants congregate on the suitable
lichens. With their mandibles they scrape off small fragments of the thallus
which they form into balls, varying in size from 1·5 mm. to 2·5 mm. in
diameter. The workers then convey these to the nests in their mandibles. It
would seem that they carry about these balls of food, and allow the ants
Page 506
busy in the nest to nibble off portions. Lichen balls are not used by termites
as fungi are, for “gardens.”
Other observations have been made by Paulson and Thompson[1236] in
their study of Epping Forest lichens: “Mites of the family Oribatidae must
be reckoned among the chief foes of these plants upon which they feed,
seeming to have a special predilection for the ripe fruits. We have had
excellent specimens of Physcia parietina spoiled by hidden mites of this
family, which have eaten out the contents of the mature apothecia after the
lichens have been gathered. One can sometimes see small flocks of the
mites browsing upon the thallus of tree-dwelling lichens, like cattle in a
meadow.” The Oribatidae, sometimes called beetle-mites, a family of
Acarinae, are minute creatures familiar to microscopists. They live chiefly
on or about mosses, but Michael[1237] is of opinion that a large number
frequent these plants for the fungi and lichens which grow in and about the
mosses. In Michael’s Monograph of British Oribatidae, four species are
mentioned as true lichen-lovers, Leiosoma palmicinetum found on Peltigera
canina and allied species; Cepteus ocellatus and Oribata parmeliae which
live on Physciae, the latter exclusively on Physcia (Xanthoria) parietina;
and Scutovertes maculatus which confines itself to lichens by the sea-shore.
Another species, Notaspis lucorum, frequents maritime lichens, but it is also
found on other substrata; while Tegeocranus labyrinthicus, though usually a
lichen-eating species, lives either on mosses or on lichens on walls.
Zopf[1238] reckoned twenty-nine species of lichens, mostly the larger foliose
and fruticose kinds, that were eaten by mites. Lesdain[1239] in his
observations on mite action notes that frequently the thallus round the base
of the perithecia of Verrucaria sp. was eaten clean away, leaving the
perithecia solitary and extremely difficult to determine.
as fungi are, for “gardens.”
Other observations have been made by Paulson and Thompson[1236] in
their study of Epping Forest lichens: “Mites of the family Oribatidae must
be reckoned among the chief foes of these plants upon which they feed,
seeming to have a special predilection for the ripe fruits. We have had
excellent specimens of Physcia parietina spoiled by hidden mites of this
family, which have eaten out the contents of the mature apothecia after the
lichens have been gathered. One can sometimes see small flocks of the
mites browsing upon the thallus of tree-dwelling lichens, like cattle in a
meadow.” The Oribatidae, sometimes called beetle-mites, a family of
Acarinae, are minute creatures familiar to microscopists. They live chiefly
on or about mosses, but Michael[1237] is of opinion that a large number
frequent these plants for the fungi and lichens which grow in and about the
mosses. In Michael’s Monograph of British Oribatidae, four species are
mentioned as true lichen-lovers, Leiosoma palmicinetum found on Peltigera
canina and allied species; Cepteus ocellatus and Oribata parmeliae which
live on Physciae, the latter exclusively on Physcia (Xanthoria) parietina;
and Scutovertes maculatus which confines itself to lichens by the sea-shore.
Another species, Notaspis lucorum, frequents maritime lichens, but it is also
found on other substrata; while Tegeocranus labyrinthicus, though usually a
lichen-eating species, lives either on mosses or on lichens on walls.
Zopf[1238] reckoned twenty-nine species of lichens, mostly the larger foliose
and fruticose kinds, that were eaten by mites. Lesdain[1239] in his
observations on mite action notes that frequently the thallus round the base
of the perithecia of Verrucaria sp. was eaten clean away, leaving the
perithecia solitary and extremely difficult to determine.
Page 507
Fig. 126. 1, Tetranychus lapidus, enlarged; 2, Verrucaria calciseda with eggs in
situ, slightly enlarged; 3 and 4, eggs attached to lichen fruits, much magnified
(after Wheldon).
J. A. Wheldon[1240] found the eggs of a species of mite, Tetranychus
lapidus, attached to the fruits of Verrucaria calciseda, Lecidea immersa and
L. Metzleri, calcicolous lichens of which the thallus not only burrows deep
down into the limestone, but the fruits form in shallow excavated pits (Fig.
126). The eggs of this stone mite are found fairly frequently on exposed
limestone rocks, bare of vegetation, except for a few crustaceous lichens.
“There is usually a single egg, rarely two, in each pit apparently attached to
the old lichen apothecium. The eggs are very attractive objects under a lens;
they measure ·5 mm. in diameter, and are disc-like with a central circular
depression from which numerous ridges radiate to the circumference, like
the spokes of a wheel. When fresh, they have a white pearly lustre,
becoming chalk-white when dry and old.” Wheldon’s observations were
made in the Carnforth and Silverdale district of West Lancashire.
situ, slightly enlarged; 3 and 4, eggs attached to lichen fruits, much magnified
(after Wheldon).
J. A. Wheldon[1240] found the eggs of a species of mite, Tetranychus
lapidus, attached to the fruits of Verrucaria calciseda, Lecidea immersa and
L. Metzleri, calcicolous lichens of which the thallus not only burrows deep
down into the limestone, but the fruits form in shallow excavated pits (Fig.
126). The eggs of this stone mite are found fairly frequently on exposed
limestone rocks, bare of vegetation, except for a few crustaceous lichens.
“There is usually a single egg, rarely two, in each pit apparently attached to
the old lichen apothecium. The eggs are very attractive objects under a lens;
they measure ·5 mm. in diameter, and are disc-like with a central circular
depression from which numerous ridges radiate to the circumference, like
the spokes of a wheel. When fresh, they have a white pearly lustre,
becoming chalk-white when dry and old.” Wheldon’s observations were
made in the Carnforth and Silverdale district of West Lancashire.
Page 508
A minute organism, Hymenobolina parasitica[1241], first described by
Zukal and doubtfully grouped among the mycetozoa, feeds, in the
plasmodium stage, on living lichens. The parasitic habit is unlike that of
true mycetozoa. It has recently been recorded from Aberdeenshire.
b. Insect mimicry of Lichens. Paulson and Thompson[1242] give instances
of moth caterpillars, which not only feed on lichens, but which take on the
coloration of the lichens they affect, either in the larval or in the perfect
moth stage. “One of the most remarkable examples of this protective
resemblance to lichens is that of the larva of the geometrid moth, Cleora
lichenaria, which feeds upon foliose lichens growing upon tree-trunks and
palings, and being of a green-grey hue, and possessed of two little humps
on many of their body-segments, they so exactly resemble the lichens in
colour and appearance as to be extremely difficult of detection.” Several
instances are recorded of moths that resemble the lichens on which they
settle: perfect examples of such similarity are exhibited at the Natural
History Museum, South Kensington, where Teras literana, Moma orion,
and other moths are shown at rest on lichen-covered bark from which they
can hardly be distinguished.
Another curious instance of suggested mimicry is recorded by G.E.
Stone[1243]. He spotted a number of bodies on the bark of some sickly elms
in Massachusetts. They were about 1/8 of an inch in diameter “with a dark
centre and a drab foliaceous margin.” They were principally lodged in the
crevices of the bark and Stone collected them under the impression that
they were the apothecia of a lichen most nearly resembling those of Physcia
hypoleuca. Some of the bodies were even attached to the thallus of a
species of Physcia; others were on the naked bark and had every
appearance of lichen fruits. Only closer examination proved their insect
nature, and they were identified as belonging to a species Gossypina Ulmi,
an elm-leaf beetle common in Europe where it causes a disease of the tree.
It had been imported into the United States and had attacked American
elms.
It is stated by Tutt[1244] that the larvae of many of the Psychides
(Lepidoptera) live on the lichens of trees and walls, such as Candelaria
concolor, Xanthoria parietina, Physcia pulverulenta and Buellia canescens,
and that their larvae pupate on their feeding grounds. Each species makes a
Zukal and doubtfully grouped among the mycetozoa, feeds, in the
plasmodium stage, on living lichens. The parasitic habit is unlike that of
true mycetozoa. It has recently been recorded from Aberdeenshire.
b. Insect mimicry of Lichens. Paulson and Thompson[1242] give instances
of moth caterpillars, which not only feed on lichens, but which take on the
coloration of the lichens they affect, either in the larval or in the perfect
moth stage. “One of the most remarkable examples of this protective
resemblance to lichens is that of the larva of the geometrid moth, Cleora
lichenaria, which feeds upon foliose lichens growing upon tree-trunks and
palings, and being of a green-grey hue, and possessed of two little humps
on many of their body-segments, they so exactly resemble the lichens in
colour and appearance as to be extremely difficult of detection.” Several
instances are recorded of moths that resemble the lichens on which they
settle: perfect examples of such similarity are exhibited at the Natural
History Museum, South Kensington, where Teras literana, Moma orion,
and other moths are shown at rest on lichen-covered bark from which they
can hardly be distinguished.
Another curious instance of suggested mimicry is recorded by G.E.
Stone[1243]. He spotted a number of bodies on the bark of some sickly elms
in Massachusetts. They were about 1/8 of an inch in diameter “with a dark
centre and a drab foliaceous margin.” They were principally lodged in the
crevices of the bark and Stone collected them under the impression that
they were the apothecia of a lichen most nearly resembling those of Physcia
hypoleuca. Some of the bodies were even attached to the thallus of a
species of Physcia; others were on the naked bark and had every
appearance of lichen fruits. Only closer examination proved their insect
nature, and they were identified as belonging to a species Gossypina Ulmi,
an elm-leaf beetle common in Europe where it causes a disease of the tree.
It had been imported into the United States and had attacked American
elms.
It is stated by Tutt[1244] that the larvae of many of the Psychides
(Lepidoptera) live on the lichens of trees and walls, such as Candelaria
concolor, Xanthoria parietina, Physcia pulverulenta and Buellia canescens,
and that their larvae pupate on their feeding grounds. Each species makes a
Page 509
“case” peculiar to itself, but those of the lower families are usually covered
externally with grains of sand, scraps of lichens, etc. The “case” of Narcyria
monilifera, for instance, is somewhat raised on a flat base and is obscured
with particles of sand and yellow lichen, giving the whole a yellow
appearance. That of Luffia lapidella is roughly conical and is held up at an
angle of 30° to 45° when the larva moves. The “cases” of Bacotia sepium
are always upright; they measure about 5·5 mm. in height and 2·75 mm. in
width and present a hoary appearance from the minute particles of lichen
with which they are covered, so that the structure is not unlike the podetium
of a Cladonia.
c. Food for the Higher Animals. It has been affirmed, especially by
Henneguy, that many lichens, if deprived of the bitter principle they
contain, by soaking in water, or with the addition of sodium or potassium
carbonate, might be used with advantage as fodder for animals. He cites as
examples of such, Lobaria pulmonaria, Evernia prunastri, Ramalina
fraxinea, R. farinacea, and R. fastigiata, all of which grow abundantly on
trees, and owe their nutritive quality to the presence of lichenin, a
carbohydrate allied to starch.
Fig. 127. Cladonia rangiferina Web. (S. H., Photo.).
Cladonia rangiferina (Fig. 127), the well-known “reindeer moss,” is,
however, the lichen of most economic importance, as food for reindeer,
cattle, etc. It is a social plant and forms dense tufts and swards of slender,
externally with grains of sand, scraps of lichens, etc. The “case” of Narcyria
monilifera, for instance, is somewhat raised on a flat base and is obscured
with particles of sand and yellow lichen, giving the whole a yellow
appearance. That of Luffia lapidella is roughly conical and is held up at an
angle of 30° to 45° when the larva moves. The “cases” of Bacotia sepium
are always upright; they measure about 5·5 mm. in height and 2·75 mm. in
width and present a hoary appearance from the minute particles of lichen
with which they are covered, so that the structure is not unlike the podetium
of a Cladonia.
c. Food for the Higher Animals. It has been affirmed, especially by
Henneguy, that many lichens, if deprived of the bitter principle they
contain, by soaking in water, or with the addition of sodium or potassium
carbonate, might be used with advantage as fodder for animals. He cites as
examples of such, Lobaria pulmonaria, Evernia prunastri, Ramalina
fraxinea, R. farinacea, and R. fastigiata, all of which grow abundantly on
trees, and owe their nutritive quality to the presence of lichenin, a
carbohydrate allied to starch.
Fig. 127. Cladonia rangiferina Web. (S. H., Photo.).
Cladonia rangiferina (Fig. 127), the well-known “reindeer moss,” is,
however, the lichen of most economic importance, as food for reindeer,
cattle, etc. It is a social plant and forms dense tufts and swards of slender,
Page 510
much branched, hollow stalks of a greenish-grey colour which may reach a
height of twelve inches or even more; the stalks decay slowly at the base as
they increase at the apex, so that very great length is never attained. In
normal conditions they neither wither nor die, and growth continues
indefinitely. It is comparatively rare in the northern or hilly regions of the
British Isles, and is frequently confused with the somewhat smaller species
Cl. sylvatica which is very common on our moorlands, a species which
Zopf[1245] tells us reindeer absolutely refuse to eat.
The true reindeer moss is abundant in northern countries, more especially
in forest regions[1246] and in valleys between the tundra hills which are
more or less sheltered from the high winds; it is independent of the
substratum and flourishes equally on barren sand and on wet turf; but grows
especially well on soil devastated by fire. For long periods it may be
covered with snow without injury and the reindeer are accustomed to dig
down with horns and hoofs in order to reach their favourite food. Though
always considered as peculiarly “reindeer” moss, deer, roebuck and other
wild animals, such as Lemming rats[1247], feed on it largely during the
winter. In some northern districts it is collected and stored as fodder for
domestic cattle; hot water is poured over it and it is then mixed with straw
and sprinkled with a little salt. Johnson[1248] has reported that the richness
of the milk yielded by the small cows of Northern Scandinavia is attributed
by some to their feeding in great measure on the “reindeer moss.”
height of twelve inches or even more; the stalks decay slowly at the base as
they increase at the apex, so that very great length is never attained. In
normal conditions they neither wither nor die, and growth continues
indefinitely. It is comparatively rare in the northern or hilly regions of the
British Isles, and is frequently confused with the somewhat smaller species
Cl. sylvatica which is very common on our moorlands, a species which
Zopf[1245] tells us reindeer absolutely refuse to eat.
The true reindeer moss is abundant in northern countries, more especially
in forest regions[1246] and in valleys between the tundra hills which are
more or less sheltered from the high winds; it is independent of the
substratum and flourishes equally on barren sand and on wet turf; but grows
especially well on soil devastated by fire. For long periods it may be
covered with snow without injury and the reindeer are accustomed to dig
down with horns and hoofs in order to reach their favourite food. Though
always considered as peculiarly “reindeer” moss, deer, roebuck and other
wild animals, such as Lemming rats[1247], feed on it largely during the
winter. In some northern districts it is collected and stored as fodder for
domestic cattle; hot water is poured over it and it is then mixed with straw
and sprinkled with a little salt. Johnson[1248] has reported that the richness
of the milk yielded by the small cows of Northern Scandinavia is attributed
by some to their feeding in great measure on the “reindeer moss.”
Page 511
Fig. 128. Cetraria islandica Ach. (S. H., Photo.).
When Cladonia rangiferina is scarce, a few other lichens[1249] are made
use of, Alectoria jubata, a brownish-black filamentous tree-lichen being one
of the most frequent substitutes. Stereocaulon paschale, which grows in
large dense tufts on the ground in mountainous regions, is also eaten by
reindeer and other animals; and Iceland moss, Cetraria islandica, is stored
up in large quantities by the Icelanders and used as fodder. Willemet[1250]
reports it as good for horses, oxen, cows and pigs.
It is interesting to recall a discovery of prehistoric remains at the Abbey
of Schussenried on the Lake of Constance and described by F. Keller[1251]:
under successive beds of peat and crumbly tufa, there was found a layer, 3
feet thick, containing flints, horns of reindeer and bones of various animals,
and, along with these, masses of reindeer moss; a sufficient proof of its
antiquity as a fodder-plant.
d. Food for Man. Lichens contain no true starch nor cellulose, but the
lichenin present in the cell-walls of the hyphae has long been utilized as a
food substance. It is peculiarly abundant in Cetraria islandica (Fig. 128),
which grows in northern countries, covering great stretches of ground with
its upright strap-shaped branching fronds of varying shades of brown. In
more southern lands it is to be found on high hills or on upland moors, but
in much smaller quantities. Commercial “Iceland moss” is supplied from
Sweden, Norway or Iceland. In the last-named country the inhabitants
harvest the lichen preferably from bare stony soil where there is no
admixture of other vegetation. They revisit the locality at intervals of three
years, the time required for the lichen to grow to a profitable size; and they
select the wet season for the ingathering of the plants as they are more
easily detached when they are wet. If the weather should be dry, they collect
it during the night. When gathered it is cleansed from foreign matter and
washed in water to remove as much as possible of the bitter principle. It is
then dried and reduced to powder. When required, the powder is put to
macerate in water for 24 hours, or it is soaked in a weak solution of soda or
of carbonate of potassium, by which means the bitter cetraric acid is nearly
all eliminated. When boiled[1252] it yields a jelly which forms the basis of
various light and easily digested soups or of other delicacies prepared by
boiling in milk, which have been proved to be valuable for dyspeptics or
sufferers from chest diseases. The northern nations also make the powder
When Cladonia rangiferina is scarce, a few other lichens[1249] are made
use of, Alectoria jubata, a brownish-black filamentous tree-lichen being one
of the most frequent substitutes. Stereocaulon paschale, which grows in
large dense tufts on the ground in mountainous regions, is also eaten by
reindeer and other animals; and Iceland moss, Cetraria islandica, is stored
up in large quantities by the Icelanders and used as fodder. Willemet[1250]
reports it as good for horses, oxen, cows and pigs.
It is interesting to recall a discovery of prehistoric remains at the Abbey
of Schussenried on the Lake of Constance and described by F. Keller[1251]:
under successive beds of peat and crumbly tufa, there was found a layer, 3
feet thick, containing flints, horns of reindeer and bones of various animals,
and, along with these, masses of reindeer moss; a sufficient proof of its
antiquity as a fodder-plant.
d. Food for Man. Lichens contain no true starch nor cellulose, but the
lichenin present in the cell-walls of the hyphae has long been utilized as a
food substance. It is peculiarly abundant in Cetraria islandica (Fig. 128),
which grows in northern countries, covering great stretches of ground with
its upright strap-shaped branching fronds of varying shades of brown. In
more southern lands it is to be found on high hills or on upland moors, but
in much smaller quantities. Commercial “Iceland moss” is supplied from
Sweden, Norway or Iceland. In the last-named country the inhabitants
harvest the lichen preferably from bare stony soil where there is no
admixture of other vegetation. They revisit the locality at intervals of three
years, the time required for the lichen to grow to a profitable size; and they
select the wet season for the ingathering of the plants as they are more
easily detached when they are wet. If the weather should be dry, they collect
it during the night. When gathered it is cleansed from foreign matter and
washed in water to remove as much as possible of the bitter principle. It is
then dried and reduced to powder. When required, the powder is put to
macerate in water for 24 hours, or it is soaked in a weak solution of soda or
of carbonate of potassium, by which means the bitter cetraric acid is nearly
all eliminated. When boiled[1252] it yields a jelly which forms the basis of
various light and easily digested soups or of other delicacies prepared by
boiling in milk, which have been proved to be valuable for dyspeptics or
sufferers from chest diseases. The northern nations also make the powder
Page 512
into bread, porridge or gruel. Johnson[1253] states in his account of “Useful
Plants” that considerable quantities of Iceland moss were formerly
employed in the manufacture of sea biscuit, and that ship’s bread mixed
with it was said to be less liable to the attacks of weevil than when made
from wheat flour only.
An examination of the real food value of the mucilaginous extract from
“Iceland moss” has been made by several workers. Church[1254] states that
for one part of flesh formers, there are eight parts of heat-givers reckoned as
starch. Brown[1255] isolated the two carbohydrates, lichenin and isolichenin.
The former, a jelly which yields on hydrolysis a large quantity of a reducing
sugar, dextrose, ferments with yeast and gives no phloroglucin reaction; it is
unaffected by digestion and probably does not form glycogen. Iso-lichenin
is much less abundant and resembles soluble starch, but on digestion yields
only dextrins—no sugar. It may be concluded, judging from the chemical
nature of the mucilage, from the resistance of its constituents to digestion
and from the small amount present in the jelly, that its nutritive value is
practically nil[1256].
It has been stated that “reindeer moss” in times of food scarcity is
powdered and mixed with “Iceland moss” and rye to make bread in North
Finland. Johnson confirms this and cites the evidence of a Dr Clarke that:
“to our surprise we found we might eat of it with as much ease as of the
heart of a fine lettuce. It tasted like wheat-bran, but after swallowing it,
there remained in the throat and upon the palate a gentle heat, or sense of
burning, as if a small quantity of pepper had been mixed with the lichen.”
The Egyptians[1257] have used Evernia prunastri, more rarely E.
furfuracea, in baking. In the eighteenth century fermentative agents such as
yeast were unknown to them, and these lichens, which were imported from
more northern lands, were soaked in water for two hours and the solution
then mixed with the flour to give a much appreciated flavour to the
unleavened bread.
In India[1258] a species of Parmelia (near to P. perlata) known in the
Telegu language as “rathapu” or rock-flower has been used as a food,
generally prepared as a curry, by the natives in the Bellary district (Madras
Presidency), and is esteemed as a delicacy. It is also used medicinally. The
Plants” that considerable quantities of Iceland moss were formerly
employed in the manufacture of sea biscuit, and that ship’s bread mixed
with it was said to be less liable to the attacks of weevil than when made
from wheat flour only.
An examination of the real food value of the mucilaginous extract from
“Iceland moss” has been made by several workers. Church[1254] states that
for one part of flesh formers, there are eight parts of heat-givers reckoned as
starch. Brown[1255] isolated the two carbohydrates, lichenin and isolichenin.
The former, a jelly which yields on hydrolysis a large quantity of a reducing
sugar, dextrose, ferments with yeast and gives no phloroglucin reaction; it is
unaffected by digestion and probably does not form glycogen. Iso-lichenin
is much less abundant and resembles soluble starch, but on digestion yields
only dextrins—no sugar. It may be concluded, judging from the chemical
nature of the mucilage, from the resistance of its constituents to digestion
and from the small amount present in the jelly, that its nutritive value is
practically nil[1256].
It has been stated that “reindeer moss” in times of food scarcity is
powdered and mixed with “Iceland moss” and rye to make bread in North
Finland. Johnson confirms this and cites the evidence of a Dr Clarke that:
“to our surprise we found we might eat of it with as much ease as of the
heart of a fine lettuce. It tasted like wheat-bran, but after swallowing it,
there remained in the throat and upon the palate a gentle heat, or sense of
burning, as if a small quantity of pepper had been mixed with the lichen.”
The Egyptians[1257] have used Evernia prunastri, more rarely E.
furfuracea, in baking. In the eighteenth century fermentative agents such as
yeast were unknown to them, and these lichens, which were imported from
more northern lands, were soaked in water for two hours and the solution
then mixed with the flour to give a much appreciated flavour to the
unleavened bread.
In India[1258] a species of Parmelia (near to P. perlata) known in the
Telegu language as “rathapu” or rock-flower has been used as a food,
generally prepared as a curry, by the natives in the Bellary district (Madras
Presidency), and is esteemed as a delicacy. It is also used medicinally. The
Page 513
collecting of rathapu is carried on during the hot weather in April and May,
and forms a profitable business.
A note has been published by Calkins[1259], on the authority of a
correspondent in Japan, that large quantities of Endocarpon
(Dermatocarpon) miniatum (Fig. 56) are collected in the mountains of that
country for culinary purposes, and largely exported to China as an article of
luxury. The local name is “iwataka,” meaning stone-mushroom. Properly
prepared it resembles tripe. It is possibly the same lichen under a different
name, Gyrophora esculenta, which is described by Manabu Miyoshi[1260] as
of great food value in Japan where it is known as “iwatake.” It is a greyish-
brown leathery “monophyllous” plant of somewhat circular outline and
fairly large size, measuring 3 to 13 cm. across. Fertile specimens are rare,
and are smaller than the sterile. It grows generally on the steep declivities of
damp granitic rocks and is common in various districts of Japan, being
especially abundant on such mountains as Kiso, Nikko, Kimano, etc. The
face of the precipices is often thickly covered with the lichen growth. The
inhabitants collect the plants in large quantities. They dry them and send
them to the towns, where they are sold in all vegetable stores; some are
even exported to other countries. These lichens are not bitter to the taste,
nor are they irritating as are other species of the genus. They are on the
contrary quite harmless and are much relished by the Japanese on account
of their agreeable flavour, in spite of their being somewhat indigestible.
Though only determined scientifically in recent times, this edible lichen has
long been known, and the risks attending its collection have frequently been
described in Old Chinese and Japanese writings.
and forms a profitable business.
A note has been published by Calkins[1259], on the authority of a
correspondent in Japan, that large quantities of Endocarpon
(Dermatocarpon) miniatum (Fig. 56) are collected in the mountains of that
country for culinary purposes, and largely exported to China as an article of
luxury. The local name is “iwataka,” meaning stone-mushroom. Properly
prepared it resembles tripe. It is possibly the same lichen under a different
name, Gyrophora esculenta, which is described by Manabu Miyoshi[1260] as
of great food value in Japan where it is known as “iwatake.” It is a greyish-
brown leathery “monophyllous” plant of somewhat circular outline and
fairly large size, measuring 3 to 13 cm. across. Fertile specimens are rare,
and are smaller than the sterile. It grows generally on the steep declivities of
damp granitic rocks and is common in various districts of Japan, being
especially abundant on such mountains as Kiso, Nikko, Kimano, etc. The
face of the precipices is often thickly covered with the lichen growth. The
inhabitants collect the plants in large quantities. They dry them and send
them to the towns, where they are sold in all vegetable stores; some are
even exported to other countries. These lichens are not bitter to the taste,
nor are they irritating as are other species of the genus. They are on the
contrary quite harmless and are much relished by the Japanese on account
of their agreeable flavour, in spite of their being somewhat indigestible.
Though only determined scientifically in recent times, this edible lichen has
long been known, and the risks attending its collection have frequently been
described in Old Chinese and Japanese writings.
Page 514
Fig. 129. Gyrophora polyrhiza Koerb. (S. H., Photo., reduced).
Other species of Gyrophora including G. polyrhiza (Fig. 129) and
Umbilicaria, black leathery lichens which grow on rocks in northern
regions, have also been used as food. They are the “Tripe de Roche” or
Rock Tripe of Arctic regions, a name given to the plants by Canadian fur-
hunters. They have been eaten by travellers and others in desperate straits
for food; but though to a certain extent nutritious, they are bitter and
nauseous, and cause severe internal irritation if the bitter acids are not first
extracted by boiling or soaking.
Of more historical interest is the desert lichen Lecanora esculenta,
supposed to be the manna[1261] of the Israelites, and still called “bread from
heaven.” Eversmann[1262] wrote an account of its occurrence and qualities,
and fuller information was given by Berkeley[1263]: when mixed with meal
to a third of its weight it is made into bread and eaten by the desert tribes. It
grows abundantly in North Africa and in many parts of Western Asia, on the
rocks or on soil. It is easily broken off and driven into heaps by the wind;
and has been reported as covering the soil to a depth of 15 cm. to 20 cm.
with irregular contorted lumps varying in size from a pea to a small nut
(Fig. 130). Externally these are clear brown or whitish; the interior is white,
and consists of branching interlaced hyphae, with masses of calcium oxalate
crystals, averaging about 60 per cent. or more of the whole substance.
Other species of Gyrophora including G. polyrhiza (Fig. 129) and
Umbilicaria, black leathery lichens which grow on rocks in northern
regions, have also been used as food. They are the “Tripe de Roche” or
Rock Tripe of Arctic regions, a name given to the plants by Canadian fur-
hunters. They have been eaten by travellers and others in desperate straits
for food; but though to a certain extent nutritious, they are bitter and
nauseous, and cause severe internal irritation if the bitter acids are not first
extracted by boiling or soaking.
Of more historical interest is the desert lichen Lecanora esculenta,
supposed to be the manna[1261] of the Israelites, and still called “bread from
heaven.” Eversmann[1262] wrote an account of its occurrence and qualities,
and fuller information was given by Berkeley[1263]: when mixed with meal
to a third of its weight it is made into bread and eaten by the desert tribes. It
grows abundantly in North Africa and in many parts of Western Asia, on the
rocks or on soil. It is easily broken off and driven into heaps by the wind;
and has been reported as covering the soil to a depth of 15 cm. to 20 cm.
with irregular contorted lumps varying in size from a pea to a small nut
(Fig. 130). Externally these are clear brown or whitish; the interior is white,
and consists of branching interlaced hyphae, with masses of calcium oxalate
crystals, averaging about 60 per cent. or more of the whole substance.
Page 515
A still more exhaustive account is given by
Visiani[1264], who quotes the experience of a
certain General Jussuf, who had tested its value
in the Sahara as food for his soldiers. When
bread was made from the lichen alone it was
friable and without consistency; when mixed
with a tenth portion of meal it was similar to the
Fig. 130. Lecanora esculenta
Eversm. Loose nodules of the soldiers’ ordinary bread, and had something of
sterile thallus. the same taste. The General also gave it as
fodder to the horses, some of them being
nourished with the lichen and a mixture of
barley for three weeks without showing any ill effects. It is also said that
camels, gazelles and other quadrupeds eat it with advantage, though it is in
any case a very defective food.
A remarkable deposit of the lichen occurred in recent times in
Mesopotamia during a violent storm of hail. After the hail had melted, the
ground was seen to be covered, and specimens were sent to Errera[1265] for
examination. He identified it as Lecanora esculenta. In his opinion two
kinds of manna are alluded to in the Bible: in one case (Exodus xvi.) it is
the sweet gum exuded from the tamarisk that is described; the other kind
(Numbers xi.), he thinks, plainly refers to the lichen. He considers that its
nutritive value must be very low, and it can only be valued as food in times
of famine.
B. Lichens as Medicine
a. Ancient Remedies. An interesting note has been published by Müller-
Argau[1266] which seems to trace back the medicinal use of lichens to a very
remote age. He tells us that Dr Schweinfurth, the distinguished traveller,
who made a journey through the valley of the Nile in 1864, sent to him
from Cairo a piece of lichen thallus found in a vase along with berries of
Juniperus excelsa and of Sapindus, with some other undetermined seeds.
The vase dated from the 18th Dynasty (1700 to 1600 b.c.), and the plants
contained in it must thus have lain undisturbed over 3000 years. The broken
pieces of the lichen thallus were fairly well preserved; they were extremely
soft and yellowish-white and almost entirely decorticate, but on the under
Visiani[1264], who quotes the experience of a
certain General Jussuf, who had tested its value
in the Sahara as food for his soldiers. When
bread was made from the lichen alone it was
friable and without consistency; when mixed
with a tenth portion of meal it was similar to the
Fig. 130. Lecanora esculenta
Eversm. Loose nodules of the soldiers’ ordinary bread, and had something of
sterile thallus. the same taste. The General also gave it as
fodder to the horses, some of them being
nourished with the lichen and a mixture of
barley for three weeks without showing any ill effects. It is also said that
camels, gazelles and other quadrupeds eat it with advantage, though it is in
any case a very defective food.
A remarkable deposit of the lichen occurred in recent times in
Mesopotamia during a violent storm of hail. After the hail had melted, the
ground was seen to be covered, and specimens were sent to Errera[1265] for
examination. He identified it as Lecanora esculenta. In his opinion two
kinds of manna are alluded to in the Bible: in one case (Exodus xvi.) it is
the sweet gum exuded from the tamarisk that is described; the other kind
(Numbers xi.), he thinks, plainly refers to the lichen. He considers that its
nutritive value must be very low, and it can only be valued as food in times
of famine.
B. Lichens as Medicine
a. Ancient Remedies. An interesting note has been published by Müller-
Argau[1266] which seems to trace back the medicinal use of lichens to a very
remote age. He tells us that Dr Schweinfurth, the distinguished traveller,
who made a journey through the valley of the Nile in 1864, sent to him
from Cairo a piece of lichen thallus found in a vase along with berries of
Juniperus excelsa and of Sapindus, with some other undetermined seeds.
The vase dated from the 18th Dynasty (1700 to 1600 b.c.), and the plants
contained in it must thus have lain undisturbed over 3000 years. The broken
pieces of the lichen thallus were fairly well preserved; they were extremely
soft and yellowish-white and almost entirely decorticate, but on the under
Page 516
surfaces there remained a few black patches, which, on microscopical
examination, enabled Müller to identify them as scraps of Evernia
furfuracea. This lichen does not grow in Egypt, but it is still sold there
along with Cetraria islandica and some other lichens as foreign drugs. Dr
Schweinfurth considered his discovery important as proving the use of
foreign remedies by the ancient Egyptians.
b. Doctrine of “Signatures.” In the fifteenth century a.d. there was in the
study and treatment of disease a constant attempt to follow the guidance of
nature. It was believed that Providence had scattered here and there on
plants “signatures,” or resemblances more or less vague to parts of the
human body, or to the diseases to which man is subject, thus indicating the
appropriate specific.
Fig. 131. Parmelia saxatilis Ach. (S. H., Photo.).
Lichens among other plants in which any “signature” could be detected
or imagined were therefore constantly prescribed: the long filaments of
Usnea barbata were used to strengthen the hair; Lobaria pulmonaria, the
true lung-wort, with its pitted reticulate surface (Fig. 72), was marked as a
suitable remedy for lung troubles; Xanthoria parietina being a yellow
examination, enabled Müller to identify them as scraps of Evernia
furfuracea. This lichen does not grow in Egypt, but it is still sold there
along with Cetraria islandica and some other lichens as foreign drugs. Dr
Schweinfurth considered his discovery important as proving the use of
foreign remedies by the ancient Egyptians.
b. Doctrine of “Signatures.” In the fifteenth century a.d. there was in the
study and treatment of disease a constant attempt to follow the guidance of
nature. It was believed that Providence had scattered here and there on
plants “signatures,” or resemblances more or less vague to parts of the
human body, or to the diseases to which man is subject, thus indicating the
appropriate specific.
Fig. 131. Parmelia saxatilis Ach. (S. H., Photo.).
Lichens among other plants in which any “signature” could be detected
or imagined were therefore constantly prescribed: the long filaments of
Usnea barbata were used to strengthen the hair; Lobaria pulmonaria, the
true lung-wort, with its pitted reticulate surface (Fig. 72), was marked as a
suitable remedy for lung troubles; Xanthoria parietina being a yellow
Page 517
lichen was supposed to cure jaundice, and Peltigera aphthosa, the thallus of
which is dotted with small wart-like tubercles[1267], was recommended for
children who suffered from the “thrush” eruption.
The doctrine reached the height of absurdity in the extravagant value set
on a lichen found growing on human skulls, “Muscus cranii humani” or
“Muscus ex cranio humano.” There are a number of lichens that grow
indifferently on a variety of substances, and not infrequently on bones lying
in the open. This skull lichen[1268], Parmelia saxatilis (Fig. 131) or some
other, was supposed to be worth its weight in gold as a cure for epilepsy.
Parkinson[1269] tells us in all confidence “it groweth upon the bare scalps of
men and women that have lyen long ... in former times much accounted of
because it is rare and hardly gotten, but in our own times much more set by,
to make the ‘Unguentum Sympatheticum’ which cureth wounds without the
local application of salves ... but as Crollius hath it, it should be taken from
the sculls of those that have been hanged or executed for offences.”
Ray[1270] says that the same gruesome plant “is celebrated by several
authors as useful in haemorrhages and is said to be an ingredient of the
famous ‘Unguentum Armarium[1271],’ reported to have been invented by
Paracelsus.” Another lost ointment!
c. Cure for Hydrophobia. Still another lichen to which extraordinary
virtue was ascribed, was the very common ground species Peltigera canina
(Fig. 54), a preparation of which was used in the cure of rabies.
Dillenius[1272] has published in full the prescription as “A certain Cure for
the Bite of a Mad Dog” which was given to him by a very celebrated
physician of that day, Dr Richard Mead, who had found it effective:
“Let the patient be blooded at the arm, nine or ten ounces. Take of the
herb called in Latin Lichen cinereus terrestris, in English Ash-coloured
ground liverwort, clean’d, dry’d and powder’d half an ounce. Of black
pepper powder’d two drachms.
“Mix these well together and divide the Powder into four Doses, one of
which must be taken every Morning, fasting, for four Mornings
successively in half a Pint of Cow’s Milk warm. After these four Doses are
taken, the Patient must go into the cold bath, or a cold Spring or River,
every Morning fasting, for a Month. He must be dipt all over but not stay in
which is dotted with small wart-like tubercles[1267], was recommended for
children who suffered from the “thrush” eruption.
The doctrine reached the height of absurdity in the extravagant value set
on a lichen found growing on human skulls, “Muscus cranii humani” or
“Muscus ex cranio humano.” There are a number of lichens that grow
indifferently on a variety of substances, and not infrequently on bones lying
in the open. This skull lichen[1268], Parmelia saxatilis (Fig. 131) or some
other, was supposed to be worth its weight in gold as a cure for epilepsy.
Parkinson[1269] tells us in all confidence “it groweth upon the bare scalps of
men and women that have lyen long ... in former times much accounted of
because it is rare and hardly gotten, but in our own times much more set by,
to make the ‘Unguentum Sympatheticum’ which cureth wounds without the
local application of salves ... but as Crollius hath it, it should be taken from
the sculls of those that have been hanged or executed for offences.”
Ray[1270] says that the same gruesome plant “is celebrated by several
authors as useful in haemorrhages and is said to be an ingredient of the
famous ‘Unguentum Armarium[1271],’ reported to have been invented by
Paracelsus.” Another lost ointment!
c. Cure for Hydrophobia. Still another lichen to which extraordinary
virtue was ascribed, was the very common ground species Peltigera canina
(Fig. 54), a preparation of which was used in the cure of rabies.
Dillenius[1272] has published in full the prescription as “A certain Cure for
the Bite of a Mad Dog” which was given to him by a very celebrated
physician of that day, Dr Richard Mead, who had found it effective:
“Let the patient be blooded at the arm, nine or ten ounces. Take of the
herb called in Latin Lichen cinereus terrestris, in English Ash-coloured
ground liverwort, clean’d, dry’d and powder’d half an ounce. Of black
pepper powder’d two drachms.
“Mix these well together and divide the Powder into four Doses, one of
which must be taken every Morning, fasting, for four Mornings
successively in half a Pint of Cow’s Milk warm. After these four Doses are
taken, the Patient must go into the cold bath, or a cold Spring or River,
every Morning fasting, for a Month. He must be dipt all over but not stay in
Page 518
(with his head above water) longer than half a minute, if the Water be very
cold. After this he must go in three Times a Week for a Fortnight longer.”
Lightfoot[1273], some forty years later, refers to this medicine as “the once
celebrated ‘Pulvis antilyssus,’ much recommended by the great Dr Mead.”
He adds that “it is much to be lamented that the success of this medicine has
not always answered the expectation. There are instances where the
application has not prevented the Hydrophobia, and it is very uncertain
whether it has been at all instrumental in keeping off that disorder.” Belief
in the efficacy of the powder died out before the end of the century but the
echo of the famous remedy remains in the name Peltigera canina, the dog
lichen.
d. Popular Remedies. Lichens with very few exceptions are non-
poisonous plants. They owed their repute as curative herbs to the presence
in the thallus of lichenin and of some bitter or astringent substances, which,
in various ailments, proved of real service to the patient, though they have
now been discarded in favour of more effective drugs. Some of them, on
account of their bitter taste, were frequently used as tonics to replace
quinine in attacks of fever. Several species of Pertusaria, such as the bitter
P. amara (Fig. 132), and of Cladonia as well as Cetraria islandica (Fig.
128), were recommended in cases of intermittent fever; species of Usnea
and others, as for instance Evernia furfuracea, were used as astringents in
haemorrhages; others were given for coughs, Cladonia pyxidata (Fig. 69)
being supposed to be specially valuable in whooping cough.
cold. After this he must go in three Times a Week for a Fortnight longer.”
Lightfoot[1273], some forty years later, refers to this medicine as “the once
celebrated ‘Pulvis antilyssus,’ much recommended by the great Dr Mead.”
He adds that “it is much to be lamented that the success of this medicine has
not always answered the expectation. There are instances where the
application has not prevented the Hydrophobia, and it is very uncertain
whether it has been at all instrumental in keeping off that disorder.” Belief
in the efficacy of the powder died out before the end of the century but the
echo of the famous remedy remains in the name Peltigera canina, the dog
lichen.
d. Popular Remedies. Lichens with very few exceptions are non-
poisonous plants. They owed their repute as curative herbs to the presence
in the thallus of lichenin and of some bitter or astringent substances, which,
in various ailments, proved of real service to the patient, though they have
now been discarded in favour of more effective drugs. Some of them, on
account of their bitter taste, were frequently used as tonics to replace
quinine in attacks of fever. Several species of Pertusaria, such as the bitter
P. amara (Fig. 132), and of Cladonia as well as Cetraria islandica (Fig.
128), were recommended in cases of intermittent fever; species of Usnea
and others, as for instance Evernia furfuracea, were used as astringents in
haemorrhages; others were given for coughs, Cladonia pyxidata (Fig. 69)
being supposed to be specially valuable in whooping cough.
Page 519
Fig. 132. Pertusaria amara Nyl. on bark (S. H.,
Photo.).
One of the most frequently prescribed lichens was the tree lung-wort
(Lobaria pulmonaria) (Fig. 72). It was first included among medical plants
by Dorstenius[1274], a Professor at Marburg; he gives a good figure and
supplies directions for its preparation as a cure for chest complaints. The
doctrine of “signatures” influenced practitioners in its favour, but it contains
lichenin which acts as an emollient. In England, it was taken up by the
famous Dr Culpepper[1275], who, however, believed in astrology even more
than in signatures. He says: “it is of great use with many physicians to help
the diseases of the lungs and for coughs, wheesings and shortness of breath
which it cureth both in man and beast.” He adds that “Jupiter seems to own
the herb.” A century later we find Dr John Hill[1276], who was a physician as
well as a naturalist, stating that the great tree lung-wort has been at all times
famous in diseases of the breast and lungs, but by that time “it was not
much used owing to change in fashions.”
The only lichen that has stood the test of time and experience as a real
remedy is Cetraria islandica, and even the “Iceland moss” is now rarely
Photo.).
One of the most frequently prescribed lichens was the tree lung-wort
(Lobaria pulmonaria) (Fig. 72). It was first included among medical plants
by Dorstenius[1274], a Professor at Marburg; he gives a good figure and
supplies directions for its preparation as a cure for chest complaints. The
doctrine of “signatures” influenced practitioners in its favour, but it contains
lichenin which acts as an emollient. In England, it was taken up by the
famous Dr Culpepper[1275], who, however, believed in astrology even more
than in signatures. He says: “it is of great use with many physicians to help
the diseases of the lungs and for coughs, wheesings and shortness of breath
which it cureth both in man and beast.” He adds that “Jupiter seems to own
the herb.” A century later we find Dr John Hill[1276], who was a physician as
well as a naturalist, stating that the great tree lung-wort has been at all times
famous in diseases of the breast and lungs, but by that time “it was not
much used owing to change in fashions.”
The only lichen that has stood the test of time and experience as a real
remedy is Cetraria islandica, and even the “Iceland moss” is now rarely
Page 520
prescribed. The first mention in literature of this famous plant occurs in
Cordus[1277] as the Muscus with crisp leaves. Some years later it figures
among the medicinal plants in Sibbald’s[1278] Chronicle of the Scottish
Flora, and Ray[1279] wrote of it about the same time as being known for its
curative and alimentary properties. It was Linnaeus[1280], and later
Scopoli[1281], who gave it the important place it held so long in medicine. It
has been used with advantage in many chronic affections as an emollient
and tonic. Cramer[1282] in a lengthy dissertation gathered together the facts
pertaining to its use as a food, a medicine and for dyeing, and he gives
recipes he had himself prescribed with marked success in many different
maladies. It has been said that if “Iceland moss” accomplished all the good
it was alleged to do, it was indeed a “Divine gift to man.”
The physiological action of cetrarin (acid principle of the lichen) on
living creatures has been studied by Kobert[1283] and his pupils. It has not
any poisonous effect when injected into the blood, nor does it work any
harm when taken into the stomach even of small animals, so that it may be
safely given to the most delicate patients. Nearly always after small doses
peristaltic movements in the intestines are induced which indicate that as a
drug it might be of service in the case of enfeebled organs. In larger doses it
may cause collapse in animals, but if administered as free cetraric acid it
passes through the stomach unchanged to become slowly and completely
dissolved in the intestine. The mucous membrane of the intestine of animals
that had been treated with an overdose, was found to be richer in blood so
that it seems as if cetrarin might be of service in chlorosis and in assisting
digestion.
Cetrarin has also been proved to be a nerve excitant which might be used
with advantage in mental maladies.
C. Lichens as Poisons
Though the acid substances of lichens are most of them extremely
irritating when taken internally, very few lichens are poisonous.
Keegan[1284] writing on this subject considers this quality of comparative
innocuousness as a distinctive difference between fungi and lichens and he
decides that it proves the latter to be higher organisms from a physiological
Cordus[1277] as the Muscus with crisp leaves. Some years later it figures
among the medicinal plants in Sibbald’s[1278] Chronicle of the Scottish
Flora, and Ray[1279] wrote of it about the same time as being known for its
curative and alimentary properties. It was Linnaeus[1280], and later
Scopoli[1281], who gave it the important place it held so long in medicine. It
has been used with advantage in many chronic affections as an emollient
and tonic. Cramer[1282] in a lengthy dissertation gathered together the facts
pertaining to its use as a food, a medicine and for dyeing, and he gives
recipes he had himself prescribed with marked success in many different
maladies. It has been said that if “Iceland moss” accomplished all the good
it was alleged to do, it was indeed a “Divine gift to man.”
The physiological action of cetrarin (acid principle of the lichen) on
living creatures has been studied by Kobert[1283] and his pupils. It has not
any poisonous effect when injected into the blood, nor does it work any
harm when taken into the stomach even of small animals, so that it may be
safely given to the most delicate patients. Nearly always after small doses
peristaltic movements in the intestines are induced which indicate that as a
drug it might be of service in the case of enfeebled organs. In larger doses it
may cause collapse in animals, but if administered as free cetraric acid it
passes through the stomach unchanged to become slowly and completely
dissolved in the intestine. The mucous membrane of the intestine of animals
that had been treated with an overdose, was found to be richer in blood so
that it seems as if cetrarin might be of service in chlorosis and in assisting
digestion.
Cetrarin has also been proved to be a nerve excitant which might be used
with advantage in mental maladies.
C. Lichens as Poisons
Though the acid substances of lichens are most of them extremely
irritating when taken internally, very few lichens are poisonous.
Keegan[1284] writing on this subject considers this quality of comparative
innocuousness as a distinctive difference between fungi and lichens and he
decides that it proves the latter to be higher organisms from a physiological
Page 521
point of view: “the colouring matters being true products of deassimilation,
whereas those of fungi are decomposition or degradation waste products of
the albuminoids akin to alkaloids.”
The two outstanding exceptions to this general statement are the two
Alpine species Letharia vulpina and Cetraria pinastri. The former contains
vulpinic acid in the cortical cells, the crystals of which are lemon-yellow in
the mass. Cetraria pinastri produces pinastrinic acid in the hyphae of the
medulla and the crystals are a beautiful orange or golden yellow.
These lichens, more especially Letharia vulpina, have been used by
Northern peoples to poison wolves. Dead carcasses are stuffed with a
mixture of lichen and powdered glass and exposed in the haunts of wolves
in time of frost. Henneguy[1285], who insists on the non-poisonous character
of all lichens, asserts that the broken glass is the fatal ingredient in the
mixture, but Kobert[1286], who has proved the poisonous nature of vulpinic
acid, says that the wounds caused by the glass render the internal organs
extremely sensitive to the action of the lichen.
Kobert, Neubert[1287] and others have recorded the results of experiments
on living animals with these poisons. They find that Letharia vulpina either
powdered or in solution has an exciting effect on the mucous membrane.
Elementary organisms treated with a solution of the lichen succumbed more
quickly than in a solution of the acid as a salt. Kobert concluded that
vulpinic acid is a poison of protoplasm.
He further tested the effect of the poison on both cold- and warm-blooded
animals. Administered as a sodium salt, 4 mg. proved fatal to frogs. The
effect on warm-blooded animals was similar. A sodium salt, whether
swallowed or administered as subcutaneous or intravenous injections, was
poisonous. Cats were the most sensitive—hedgehogs the least—of all the
animals that were subjected to the experiments. Volkard’s[1288] synthetic
preparation of vulpinic acid gave the same results as the solution directly
extracted from the lichens.
D. Lichens used in Tanning, Brewing and Distilling
The astringent property in Cetraria islandica and in Lobaria pulmonaria
has been made use of in tanning leather. The latter lichen grows commonly
whereas those of fungi are decomposition or degradation waste products of
the albuminoids akin to alkaloids.”
The two outstanding exceptions to this general statement are the two
Alpine species Letharia vulpina and Cetraria pinastri. The former contains
vulpinic acid in the cortical cells, the crystals of which are lemon-yellow in
the mass. Cetraria pinastri produces pinastrinic acid in the hyphae of the
medulla and the crystals are a beautiful orange or golden yellow.
These lichens, more especially Letharia vulpina, have been used by
Northern peoples to poison wolves. Dead carcasses are stuffed with a
mixture of lichen and powdered glass and exposed in the haunts of wolves
in time of frost. Henneguy[1285], who insists on the non-poisonous character
of all lichens, asserts that the broken glass is the fatal ingredient in the
mixture, but Kobert[1286], who has proved the poisonous nature of vulpinic
acid, says that the wounds caused by the glass render the internal organs
extremely sensitive to the action of the lichen.
Kobert, Neubert[1287] and others have recorded the results of experiments
on living animals with these poisons. They find that Letharia vulpina either
powdered or in solution has an exciting effect on the mucous membrane.
Elementary organisms treated with a solution of the lichen succumbed more
quickly than in a solution of the acid as a salt. Kobert concluded that
vulpinic acid is a poison of protoplasm.
He further tested the effect of the poison on both cold- and warm-blooded
animals. Administered as a sodium salt, 4 mg. proved fatal to frogs. The
effect on warm-blooded animals was similar. A sodium salt, whether
swallowed or administered as subcutaneous or intravenous injections, was
poisonous. Cats were the most sensitive—hedgehogs the least—of all the
animals that were subjected to the experiments. Volkard’s[1288] synthetic
preparation of vulpinic acid gave the same results as the solution directly
extracted from the lichens.
D. Lichens used in Tanning, Brewing and Distilling
The astringent property in Cetraria islandica and in Lobaria pulmonaria
has been made use of in tanning leather. The latter lichen grows commonly
Page 522
on oak and could hardly be gathered in sufficient quantity to be of
commercial importance. Like many other lichens it develops very slowly.
Lobaria pulmonaria has also been used to replace hops in the brewing of
beer. Gmelin[1289] in his journey through Siberia visited a monastery at
Ussolka where the monks employed it for this purpose. The beer tasted
exactly like that made with hops, but was more intoxicating. The lichen in
that country grew on pine-trees.
Lichens have in more modern times been used in the preparation of
alcohol. The process of manufacture was discovered by Roy of Tonnerre,
early in the nineteenth century, and was described by Léorier[1290]. It was
further improved by Stenberg[1291], a Professor of Chemistry in Stockholm.
Roy had worked with Physcia ciliaris, Ramalina fraxinea, R. fastigiata, R.
farinacea and Usnea florida, but Stenberg and distillers after his time[1292]
made more use of Cladonia rangiferina (Fig. 127), Cetraria islandica (Fig.
128) and Alectoria jubata.
By treatment with weak sulphuric or nitric acid the lichenin of the thallus
is transformed into glucose which on fermentation forms alcohol. Stenberg
found that 68 per cent. of the weight in Cladonia rangiferina was a “sugar”
from which a good brandy could be prepared: a kilogramme of the lichens
furnished half a litre of alcohol. The Professor followed up his researches
by establishing a distillery near Stockholm. His papers contain full
instructions as to collecting and preparing the plants. Henneguy[1293],
writing in 1883, stated that the fabrication of alcohol from lichens was then
a large and increasing industry in Sweden. The whole industry seems,
however, to have fallen into disuse very soon: Wainio[1294], quoting
Hellbom[1295], states that the various distilleries were already closed in
1884, because of the exhaustion of the lichen in the neighbourhood, and the
impossibility of obtaining sufficient supplies of such slow-growing plants.
E. Dyeing Properties of Lichens
a. Lichens as Dye-plants. Knowledge as to the dyeing properties of
lichens dates back to a remote antiquity. It has been generally accepted that
lichen-colours are indicated by the prophet Ezekiel in his denunciation of
Tyre: “blue and purple from the Isles of Elishah was that which covered
commercial importance. Like many other lichens it develops very slowly.
Lobaria pulmonaria has also been used to replace hops in the brewing of
beer. Gmelin[1289] in his journey through Siberia visited a monastery at
Ussolka where the monks employed it for this purpose. The beer tasted
exactly like that made with hops, but was more intoxicating. The lichen in
that country grew on pine-trees.
Lichens have in more modern times been used in the preparation of
alcohol. The process of manufacture was discovered by Roy of Tonnerre,
early in the nineteenth century, and was described by Léorier[1290]. It was
further improved by Stenberg[1291], a Professor of Chemistry in Stockholm.
Roy had worked with Physcia ciliaris, Ramalina fraxinea, R. fastigiata, R.
farinacea and Usnea florida, but Stenberg and distillers after his time[1292]
made more use of Cladonia rangiferina (Fig. 127), Cetraria islandica (Fig.
128) and Alectoria jubata.
By treatment with weak sulphuric or nitric acid the lichenin of the thallus
is transformed into glucose which on fermentation forms alcohol. Stenberg
found that 68 per cent. of the weight in Cladonia rangiferina was a “sugar”
from which a good brandy could be prepared: a kilogramme of the lichens
furnished half a litre of alcohol. The Professor followed up his researches
by establishing a distillery near Stockholm. His papers contain full
instructions as to collecting and preparing the plants. Henneguy[1293],
writing in 1883, stated that the fabrication of alcohol from lichens was then
a large and increasing industry in Sweden. The whole industry seems,
however, to have fallen into disuse very soon: Wainio[1294], quoting
Hellbom[1295], states that the various distilleries were already closed in
1884, because of the exhaustion of the lichen in the neighbourhood, and the
impossibility of obtaining sufficient supplies of such slow-growing plants.
E. Dyeing Properties of Lichens
a. Lichens as Dye-plants. Knowledge as to the dyeing properties of
lichens dates back to a remote antiquity. It has been generally accepted that
lichen-colours are indicated by the prophet Ezekiel in his denunciation of
Tyre: “blue and purple from the Isles of Elishah was that which covered
Page 523
thee.” Theophrastus describes certain plants as growing in Crete, and being
used to dye wool, etc., and Pliny in his Phycos Thalassion is also
understood as referring to the lichen Roccella, “with crisp leaves, used in
Crete for dyeing garments.”
Information as to the dyeing properties of certain lichens is given in most
of the books or papers dealing with these plants from the herbals onwards.
Hoffmann[1296] devoted a large part of his Commentatio de vario Lichenum
usu to the dye-lichens, and, illustrating his work, are a series of small
rectangular coloured blocks representing samples of woollen cloth dyed
with different lichens. There are seventy-seven of these samples with the
colour names used by French dyers.
An important treatise on the subject translated into French was also
contributed by Westring[1297]. He desired to draw attention to the tinctorial
properties of lichens other than the Roccellae which do not grow in
Sweden. The Swedes, he states, already used four to six lichens as dye-
plants, but only for one colour. He demonstrated by his improved methods
that other colours and of finer tint could be obtained. He describes the best
methods both of extraction and of dyeing, and then follows with an account
of the different lichens likely to be of service. The treatise was subsequently
published at greater length in Swedish[1298] with twenty-four very fine
coloured illustrations of the lichens used, and with sample blocks of the
colours to be obtained.
b. The Orchil Lichen, Roccella. The value of Roccella as a dye-plant
had been lost sight of until it was accidentally rediscovered, early in the
fourteenth century, by a Florentine merchant called Federigo. He introduced
its use into Florence, and as he retained the industry in his own hands he
made a large fortune, and founded the family of the Orcellarii, called later
the Rucellarii or Rucellai, hence the botanical name, Roccella. The product
was called orseille for which the English name is orchil or archil. Another
origin suggested for orchil is the Spanish name of the plant, Orcigilia.
There are a number of different species that vary in the amount of dye-
product. Most of them grow on rocks by the sea-side in crowded bluish-
grey or whitish tufts of strap-shaped or rounded stiff narrow fronds varying
in length up to about six inches or more. The main supply of “weeds” came
from the Levant until the fifteenth century when supplies were obtained
used to dye wool, etc., and Pliny in his Phycos Thalassion is also
understood as referring to the lichen Roccella, “with crisp leaves, used in
Crete for dyeing garments.”
Information as to the dyeing properties of certain lichens is given in most
of the books or papers dealing with these plants from the herbals onwards.
Hoffmann[1296] devoted a large part of his Commentatio de vario Lichenum
usu to the dye-lichens, and, illustrating his work, are a series of small
rectangular coloured blocks representing samples of woollen cloth dyed
with different lichens. There are seventy-seven of these samples with the
colour names used by French dyers.
An important treatise on the subject translated into French was also
contributed by Westring[1297]. He desired to draw attention to the tinctorial
properties of lichens other than the Roccellae which do not grow in
Sweden. The Swedes, he states, already used four to six lichens as dye-
plants, but only for one colour. He demonstrated by his improved methods
that other colours and of finer tint could be obtained. He describes the best
methods both of extraction and of dyeing, and then follows with an account
of the different lichens likely to be of service. The treatise was subsequently
published at greater length in Swedish[1298] with twenty-four very fine
coloured illustrations of the lichens used, and with sample blocks of the
colours to be obtained.
b. The Orchil Lichen, Roccella. The value of Roccella as a dye-plant
had been lost sight of until it was accidentally rediscovered, early in the
fourteenth century, by a Florentine merchant called Federigo. He introduced
its use into Florence, and as he retained the industry in his own hands he
made a large fortune, and founded the family of the Orcellarii, called later
the Rucellarii or Rucellai, hence the botanical name, Roccella. The product
was called orseille for which the English name is orchil or archil. Another
origin suggested for orchil is the Spanish name of the plant, Orcigilia.
There are a number of different species that vary in the amount of dye-
product. Most of them grow on rocks by the sea-side in crowded bluish-
grey or whitish tufts of strap-shaped or rounded stiff narrow fronds varying
in length up to about six inches or more. The main supply of “weeds” came
from the Levant until the fifteenth century when supplies were obtained
Page 524
from the Canaries (long considered to produce the best varieties), Cape
Verd and the African coasts. The geographical distribution of the Roccellae
is very wide: they grow on warm sea-coasts all over the globe, more
particularly in Angola, the Cape, Mozambique, Madagascar, in Asia, in
Australia, and in Chili and Peru.
Zopf[1299] has proved the existence of two different colouring substances
among the Roccellas: in R. fuciformis (Fig. 57) and R. fucoides (both British
species), in R. Montagnei and R. peruensis the acid present is erythrin; in R.
tinctoria, R. portentosa and R. sinuensis it is lecanoric acid. In R. tinctoria
(Fig. 133), according to Ronceray[1300], the acid is located chiefly in the
gonidial layer and the soredia but is absent from the cortex and centre. In R.
portentosa it is abundant in the cortex and central layer, while scarcely to be
detected in the gonidial layer, and it is wanting altogether in the soredia. In
R. Montagnei it is chiefly found in the cortex and the gonidial layer, and is
absent from the soredia and from the medulla.
c. Purple Dyes: Orchil, Cudbear and Litmus. Orseille or orchil is
formed not only from erythrin and lecanoric acid (orseillic acid), but also
from erythrinic, gyrophoric, evernic and ramalic acids[1301] and may be
obtained from any lichen containing these substances. By the action of
ammonia the acids are split up into orcin and carbonic acid. In time, under
the influence of ammonia and the oxygen of the air[1302], orcin becomes
orcein which is the colouring principle of orchil; the perfecting of the
process may take a month. The dye is used for animal fibres such as wool
and silk; it has no effect on cotton.
There are several different preparations on the market, chiefly obtained
from France and Holland; orchil or orseille in the form of a solution,
cudbear (persio of Germany) almost the same, but manufactured into a
violet-reddish powder, and litmus (tournesol of France) which is prepared in
a slightly different manner. At one time the lichen, broken into small pieces,
was soaked in urine; a fermentation process was set up, then lime and
potash with an admixture of alum were added. The mass of material when
ready was pressed into cubes and dried in the air. Commercial litmus
contains three substances, erythrolein, erythrolitmin and azolitmin; the last
named, which is the true litmus, is a dark brown amorphous powder soluble
in water, and forming a blue solution with alkalies.
Verd and the African coasts. The geographical distribution of the Roccellae
is very wide: they grow on warm sea-coasts all over the globe, more
particularly in Angola, the Cape, Mozambique, Madagascar, in Asia, in
Australia, and in Chili and Peru.
Zopf[1299] has proved the existence of two different colouring substances
among the Roccellas: in R. fuciformis (Fig. 57) and R. fucoides (both British
species), in R. Montagnei and R. peruensis the acid present is erythrin; in R.
tinctoria, R. portentosa and R. sinuensis it is lecanoric acid. In R. tinctoria
(Fig. 133), according to Ronceray[1300], the acid is located chiefly in the
gonidial layer and the soredia but is absent from the cortex and centre. In R.
portentosa it is abundant in the cortex and central layer, while scarcely to be
detected in the gonidial layer, and it is wanting altogether in the soredia. In
R. Montagnei it is chiefly found in the cortex and the gonidial layer, and is
absent from the soredia and from the medulla.
c. Purple Dyes: Orchil, Cudbear and Litmus. Orseille or orchil is
formed not only from erythrin and lecanoric acid (orseillic acid), but also
from erythrinic, gyrophoric, evernic and ramalic acids[1301] and may be
obtained from any lichen containing these substances. By the action of
ammonia the acids are split up into orcin and carbonic acid. In time, under
the influence of ammonia and the oxygen of the air[1302], orcin becomes
orcein which is the colouring principle of orchil; the perfecting of the
process may take a month. The dye is used for animal fibres such as wool
and silk; it has no effect on cotton.
There are several different preparations on the market, chiefly obtained
from France and Holland; orchil or orseille in the form of a solution,
cudbear (persio of Germany) almost the same, but manufactured into a
violet-reddish powder, and litmus (tournesol of France) which is prepared in
a slightly different manner. At one time the lichen, broken into small pieces,
was soaked in urine; a fermentation process was set up, then lime and
potash with an admixture of alum were added. The mass of material when
ready was pressed into cubes and dried in the air. Commercial litmus
contains three substances, erythrolein, erythrolitmin and azolitmin; the last
named, which is the true litmus, is a dark brown amorphous powder soluble
in water, and forming a blue solution with alkalies.
Page 525
Fig. 133. Roccella tintoria Ach. From the
Cape of Good Hope.
An aqueous solution of litmus when exactly neutralized by an acid is
violet coloured; it becomes red with the smallest trace of free acid, or blue
with free alkali. Litmus paper is prepared by steeping specially prepared
unsized paper in the dye solution. It is as a ready and sensitive indicator of
acidity or alkalinity that litmus is of so much value. According to Zopf[1303]
it is also used as a blueing agent in washing and as a colouring of wine.
Litmus is chiefly manufactured in Holland. Still another substance
somewhat differently prepared from the same lichens is sold as French
purple, a more brilliant and durable colour than orchil.
Cape of Good Hope.
An aqueous solution of litmus when exactly neutralized by an acid is
violet coloured; it becomes red with the smallest trace of free acid, or blue
with free alkali. Litmus paper is prepared by steeping specially prepared
unsized paper in the dye solution. It is as a ready and sensitive indicator of
acidity or alkalinity that litmus is of so much value. According to Zopf[1303]
it is also used as a blueing agent in washing and as a colouring of wine.
Litmus is chiefly manufactured in Holland. Still another substance
somewhat differently prepared from the same lichens is sold as French
purple, a more brilliant and durable colour than orchil.
Page 526
Fig. 134. Lecanora tartarea Ach. (S. H., Photo.).
d. Other Orchil Lichens. Though species of Roccella rank first in
importance as dye-plants, purple and blue colours are obtained, as indicated
above, from other very different lichens. Lindsay[1304] extracted orchil from
about twenty species. Those most in use in northern countries are on the
whole less rich in colouring substances; they are: Umbilicaria pustulata,
species of Gyrophora, Parmelia and Pertusaria, and above all Lecanora
tartarea (Fig. 134). The last named, one of the hardiest and most abundant
of rock- or soil-lichens, is chiefly used in Scotland and Sweden (hence the
name “Swedish moss”) to furnish a red or crimson dye. In Scotland all dye-
lichens are called “crottles,” but the term “cudbear” was given to Lecanora
tartarea (either the lichen or the dye-product); it was acquired from a
corrupt pronunciation of the Christian name of Dr Cuthbert Gordon, a
chemist, who, according to Bohler[1305], obtained a patent for his process of
producing the dye, or who first employed it on a great scale in Glasgow.
Johnson[1306] remarks that the colour yielded by cudbear, if well prepared,
is a fine, clear, but not very bright purple. It is, he alleges, not permanent.
Like other orchil substances it is without effect on cotton or linen.
d. Other Orchil Lichens. Though species of Roccella rank first in
importance as dye-plants, purple and blue colours are obtained, as indicated
above, from other very different lichens. Lindsay[1304] extracted orchil from
about twenty species. Those most in use in northern countries are on the
whole less rich in colouring substances; they are: Umbilicaria pustulata,
species of Gyrophora, Parmelia and Pertusaria, and above all Lecanora
tartarea (Fig. 134). The last named, one of the hardiest and most abundant
of rock- or soil-lichens, is chiefly used in Scotland and Sweden (hence the
name “Swedish moss”) to furnish a red or crimson dye. In Scotland all dye-
lichens are called “crottles,” but the term “cudbear” was given to Lecanora
tartarea (either the lichen or the dye-product); it was acquired from a
corrupt pronunciation of the Christian name of Dr Cuthbert Gordon, a
chemist, who, according to Bohler[1305], obtained a patent for his process of
producing the dye, or who first employed it on a great scale in Glasgow.
Johnson[1306] remarks that the colour yielded by cudbear, if well prepared,
is a fine, clear, but not very bright purple. It is, he alleges, not permanent.
Like other orchil substances it is without effect on cotton or linen.
Page 527
e. Preparation of Orchil. A general mode of treatment of dye-lichens
recommended by Lauder Lindsay[1307] for home production of orchil,
cudbear and litmus is as follows:
1. Careful washing, drying and cleansing to separate
earthy and other impurities.
2. Pulverization into a coarse or fine pulp with water.
3. Repeated addition of ammoniacal liquor of a certain
strength, obtainable from several sources (e.g. putrid urine,
gas liquor, etc.).
4. Frequent stirring of the fermenting mass so as to ensure
full exposure of every part thereof to the action of
atmospheric oxygen.
5. Addition of alkalies in some cases (e.g. potash or soda),
to heighten or modify colour; and of chalk, gypsum and
other substances to impart consistence.
f. Brown and Yellow Dyes. The extracting of these colours from lichens
is also a very old industry. Linnaeus found during his journey to
Lappland[1308], undertaken when he was quite a young man, that the women
in the northern countries made use of a brown lichen for dyeing which is
evidently Parmelia omphalodes (Fig. 135). He describes it as a “rich
Lichenoides of a brown stercoraceous colour,” and he has stated that it grew
in such abundance in the Island of Aland, that every stone was covered,
especially near the sea. In the Plantae tinctoriae[1309] there is a record of six
other lichens used for dyeing: Lichen Roccella, L. tartareus, L. saxatilis, L.
juniperinus, L. parietinus and L. candelarius. The value of Lichen
omphalodes was also emphasized by Lightfoot; the women of Scotland
evidently appreciated its dyeing properties as much as other northern
peoples.
A series of memoirs on the utility of lichens written by Willemet[1310],
Amoreux and Hoffmann, and jointly published at Lyons towards the end of
the eighteenth century, represents the views as to the economic value of
lichens held by scientific botanists of that time. All of them cite the various
recommended by Lauder Lindsay[1307] for home production of orchil,
cudbear and litmus is as follows:
1. Careful washing, drying and cleansing to separate
earthy and other impurities.
2. Pulverization into a coarse or fine pulp with water.
3. Repeated addition of ammoniacal liquor of a certain
strength, obtainable from several sources (e.g. putrid urine,
gas liquor, etc.).
4. Frequent stirring of the fermenting mass so as to ensure
full exposure of every part thereof to the action of
atmospheric oxygen.
5. Addition of alkalies in some cases (e.g. potash or soda),
to heighten or modify colour; and of chalk, gypsum and
other substances to impart consistence.
f. Brown and Yellow Dyes. The extracting of these colours from lichens
is also a very old industry. Linnaeus found during his journey to
Lappland[1308], undertaken when he was quite a young man, that the women
in the northern countries made use of a brown lichen for dyeing which is
evidently Parmelia omphalodes (Fig. 135). He describes it as a “rich
Lichenoides of a brown stercoraceous colour,” and he has stated that it grew
in such abundance in the Island of Aland, that every stone was covered,
especially near the sea. In the Plantae tinctoriae[1309] there is a record of six
other lichens used for dyeing: Lichen Roccella, L. tartareus, L. saxatilis, L.
juniperinus, L. parietinus and L. candelarius. The value of Lichen
omphalodes was also emphasized by Lightfoot; the women of Scotland
evidently appreciated its dyeing properties as much as other northern
peoples.
A series of memoirs on the utility of lichens written by Willemet[1310],
Amoreux and Hoffmann, and jointly published at Lyons towards the end of
the eighteenth century, represents the views as to the economic value of
lichens held by scientific botanists of that time. All of them cite the various
Page 528
dye-species, and Hoffmann, as already stated, gives illustrations of colours
that can be obtained. It has been once and again affirmed that Parmelia
saxatilis yields a red colour, but Zopf[1311] denies this. It contains saxatillic
acid which is colourless when extracted but on boiling gives a clear
reddish-yellow to reddish-brown solution which dyes wool and silk directly
without the aid of a mordant. Zopf[1311] observed the process of dyeing
followed in South Tyrol: a layer of the lichen was placed in a cooking pot,
above this a layer of the material to be dyed, then lichen and again the
material until the pot was filled. It was covered with water and boiled three
to four hours, resulting in a beautiful rust-brown and peculiarly fast dye.
Fig. 135. Parmelia omphalodes Ach. (S. H.,
Photo.).
Reddish- or rust-brown dye is also obtained from Haematomma
ventosum and H. coccineum, a yellow-brown from Parmelia conspersa
(salazinic acid), and other shades of brown from Parmelia perlata, P.
physodes, Lobaria pulmonaria and Cetraria islandica.
Yellow lichens in general furnish yellow dyes, as for instance Xanthoria
parietina which gives either brown or yellow according to treatment and
that can be obtained. It has been once and again affirmed that Parmelia
saxatilis yields a red colour, but Zopf[1311] denies this. It contains saxatillic
acid which is colourless when extracted but on boiling gives a clear
reddish-yellow to reddish-brown solution which dyes wool and silk directly
without the aid of a mordant. Zopf[1311] observed the process of dyeing
followed in South Tyrol: a layer of the lichen was placed in a cooking pot,
above this a layer of the material to be dyed, then lichen and again the
material until the pot was filled. It was covered with water and boiled three
to four hours, resulting in a beautiful rust-brown and peculiarly fast dye.
Fig. 135. Parmelia omphalodes Ach. (S. H.,
Photo.).
Reddish- or rust-brown dye is also obtained from Haematomma
ventosum and H. coccineum, a yellow-brown from Parmelia conspersa
(salazinic acid), and other shades of brown from Parmelia perlata, P.
physodes, Lobaria pulmonaria and Cetraria islandica.
Yellow lichens in general furnish yellow dyes, as for instance Xanthoria
parietina which gives either brown or yellow according to treatment and
Page 529
Cetraria juniperina which forms a beautiful yellow colouring substance on
boiling. Teloschistes flavicans and Letharia vulpina yield very similar
yellow dyes, and from Lecanora parella (Fig. 39), Pertusaria melaleuca
and Usnea barbata yellow colours have been obtained. Candelariella
vitellina and Xanthoria lychnea both contain yellow colouring agents and
have been employed by the Swedes for dyeing the candles used in religious
ceremonies.
g. Collecting of Dye-lichens. Lauder Lindsay[1312] made exhaustive
studies of dye-lichens both in the field and in the laboratory, and recorded
results he obtained from the micro-chemical examination of 540 different
specimens. He sought to revive and encourage the use of their beautiful
colour products among country people; he has given the following practical
hints to collectors:
1. That crustaceous dwarf pale-coloured species growing on rocks, and
especially on sea-coasts, are most likely to yield red and purple dyes similar
to orchil, cudbear or litmus; while on the other hand the largest, most
handsome foliaceous or fruticose species are least likely.
2. That the colour of the thallus is no indication of colorific power (in
orchil lichens), inasmuch as the red or purple colouring substances are the
result of chemical action on crystalline colorific “principles” previously
devoid of colour.
3. That alterations in physical characters, chemical composition and
consequently in dyeing properties are very liable to be produced by
modification in the following external circumstances:
(i) Degree of moisture.
(ii) Degree of heat.
(iii) Degree of exposure to light and air.
(iv) Climate.
(v) Elevation above the sea.
(vi) Habitat; nature of basis of support.
(vii) Age.
boiling. Teloschistes flavicans and Letharia vulpina yield very similar
yellow dyes, and from Lecanora parella (Fig. 39), Pertusaria melaleuca
and Usnea barbata yellow colours have been obtained. Candelariella
vitellina and Xanthoria lychnea both contain yellow colouring agents and
have been employed by the Swedes for dyeing the candles used in religious
ceremonies.
g. Collecting of Dye-lichens. Lauder Lindsay[1312] made exhaustive
studies of dye-lichens both in the field and in the laboratory, and recorded
results he obtained from the micro-chemical examination of 540 different
specimens. He sought to revive and encourage the use of their beautiful
colour products among country people; he has given the following practical
hints to collectors:
1. That crustaceous dwarf pale-coloured species growing on rocks, and
especially on sea-coasts, are most likely to yield red and purple dyes similar
to orchil, cudbear or litmus; while on the other hand the largest, most
handsome foliaceous or fruticose species are least likely.
2. That the colour of the thallus is no indication of colorific power (in
orchil lichens), inasmuch as the red or purple colouring substances are the
result of chemical action on crystalline colorific “principles” previously
devoid of colour.
3. That alterations in physical characters, chemical composition and
consequently in dyeing properties are very liable to be produced by
modification in the following external circumstances:
(i) Degree of moisture.
(ii) Degree of heat.
(iii) Degree of exposure to light and air.
(iv) Climate.
(v) Elevation above the sea.
(vi) Habitat; nature of basis of support.
(vii) Age.
Page 530
(viii) Seasons and atmospheric vicissitudes, etc.
August has been recommended as the best month for collecting dye-
lichens: i.e. just after the season of greatest light and heat when the
accumulation of acids will be at its maximum.
Some of the acids found useful in dyeing occur in the thalli of a large
number of lichens, many of which are too scantily developed to be of any
economic value. Thus salazinic acid which gives the effective yellow-
brown dye in Parmelia conspersa was found by Zopf in 13 species and
varieties. It has since been located by Lettau[1313] in 72 different lichens,
many of them, however, with poorly developed or scanty thalli, so that no
technical use can be made of them.
h. Lichen Colours and Spectrum Characters. In a comparative study of
vegetable colouring substances, Sorby[1314] extracted yellow colouring
matters from various plants distinguished by certain spectrum characters.
He called them the “lichenoxanthine group” because, as he explains, “these
xanthines occur in a more marked manner in lichens than in plants having
true leaves and fronds.” Orange lichenoxanthine he found in Peltigera
canina, Platysma glaucum, etc., when growing well exposed to the sun.
Lichenoxanthine he obtained from the fungus Clavaria fusiformis; it was
difficult to separate from orange lichenoxanthine. Yet another, which he
terms yellow lichenoxanthine, he obtained most readily from Physcia
(Xanthoria) parietina. The solutions of these substances vary according to
Sorby in giving a slightly different kind of spectrum. He did not experiment
on their dyeing properties.
F. Lichens in Perfumery
a. Lichens as Perfumes. There are a few lichens that find a place in
Gerard’s[1315] Herball and that are praised by him as being serviceable to
man. Among others he writes of a “Moss that partakes of the bark of which
it is engendered. It is to be used in compositions which serve for sweet
perfumes and that take away wearisomeness.” At a much later date we find
Amoreux[1316] recording the fact that Lichen (Evernia) prunastri, known as
“Mousse de Chêne,” was used as a perfume plant.
August has been recommended as the best month for collecting dye-
lichens: i.e. just after the season of greatest light and heat when the
accumulation of acids will be at its maximum.
Some of the acids found useful in dyeing occur in the thalli of a large
number of lichens, many of which are too scantily developed to be of any
economic value. Thus salazinic acid which gives the effective yellow-
brown dye in Parmelia conspersa was found by Zopf in 13 species and
varieties. It has since been located by Lettau[1313] in 72 different lichens,
many of them, however, with poorly developed or scanty thalli, so that no
technical use can be made of them.
h. Lichen Colours and Spectrum Characters. In a comparative study of
vegetable colouring substances, Sorby[1314] extracted yellow colouring
matters from various plants distinguished by certain spectrum characters.
He called them the “lichenoxanthine group” because, as he explains, “these
xanthines occur in a more marked manner in lichens than in plants having
true leaves and fronds.” Orange lichenoxanthine he found in Peltigera
canina, Platysma glaucum, etc., when growing well exposed to the sun.
Lichenoxanthine he obtained from the fungus Clavaria fusiformis; it was
difficult to separate from orange lichenoxanthine. Yet another, which he
terms yellow lichenoxanthine, he obtained most readily from Physcia
(Xanthoria) parietina. The solutions of these substances vary according to
Sorby in giving a slightly different kind of spectrum. He did not experiment
on their dyeing properties.
F. Lichens in Perfumery
a. Lichens as Perfumes. There are a few lichens that find a place in
Gerard’s[1315] Herball and that are praised by him as being serviceable to
man. Among others he writes of a “Moss that partakes of the bark of which
it is engendered. It is to be used in compositions which serve for sweet
perfumes and that take away wearisomeness.” At a much later date we find
Amoreux[1316] recording the fact that Lichen (Evernia) prunastri, known as
“Mousse de Chêne,” was used as a perfume plant.
Page 531
Though lichens are not parasitic, the idea that they owed something of
their quality to the substratum was firmly held by the old herbalists. It
appears again and again in the descriptions of medicinal lichens, and still
persists in this matter of perfumes. Hue[1317] states in some notes to a larger
work, that French perfumers extract an excellent perfume from Evernia
prunastri (Fig. 59) known as “Mousse des Chênes” (Oak moss), and it
appears that the plants which grow on oak contain more perfume than those
which live on other trees. The collectors often gather along with Evernia
prunastri other species such as Ramalina calicaris and R. fraxinea, but
these possess little if any scent. A still finer perfume is extracted[1318] from
Lobaria pulmonaria called “moss from the base of the oaks,” but as it is a
rarer lichen than Evernia it is less used. Most of the Stictaceae, to which
family Lobaria belongs, have a somewhat disagreeable odour, but this one
forms a remarkable exception, which can be tested by macerating the
thallus and soaking it in spirit: it will then be found to exhale a pleasant and
very persistent scent. These lichens are not, however, used alone; they are
combined with other substances in the composition of much appreciated
perfumes. The thallus possesses also the power of retaining scent and, for
this reason, lichens frequently form an ingredient of potpourri.
b. Lichens as Hair-powder. In the days of white-powdered hair, use was
occasionally made of Ramalina calicaris which was ground down and
substituted for the starch that was more commonly employed.
In older books on lichenology constant reference is made to a hair-
powder called “Pulvis Cyprius” or “Cyprus powder” and very celebrated in
the seventeenth century. It was believed to beautify and cleanse the hair by
removing scurf, etc. Evernia prunastri was one of the chief ingredients of
the powder, but it might be replaced by Physcia ciliaris or by Usnea. The
virtue of the lichens lay in their capacity to absorb and retain perfume. The
powder was for long manufactured at Montpellier and was a valuable
monopoly. Its composition was kept secret, but Bauhin[1319] (J.) published
an account of the ingredients and how to mix them. Under the title “Pulvis
Cyprius Pretiosius” a more detailed recipe of the famous powder was given
by Zwelser[1320], a Palatine medical doctor. The lichen employed in his
preparation, as in Bauhin’s, is Usnea, but that may include both Evernia and
Physcia as they are all tree plants. He gives elaborate directions as to the
cleaning of the lichen from all impurities—it is to be beaten with a stick,
their quality to the substratum was firmly held by the old herbalists. It
appears again and again in the descriptions of medicinal lichens, and still
persists in this matter of perfumes. Hue[1317] states in some notes to a larger
work, that French perfumers extract an excellent perfume from Evernia
prunastri (Fig. 59) known as “Mousse des Chênes” (Oak moss), and it
appears that the plants which grow on oak contain more perfume than those
which live on other trees. The collectors often gather along with Evernia
prunastri other species such as Ramalina calicaris and R. fraxinea, but
these possess little if any scent. A still finer perfume is extracted[1318] from
Lobaria pulmonaria called “moss from the base of the oaks,” but as it is a
rarer lichen than Evernia it is less used. Most of the Stictaceae, to which
family Lobaria belongs, have a somewhat disagreeable odour, but this one
forms a remarkable exception, which can be tested by macerating the
thallus and soaking it in spirit: it will then be found to exhale a pleasant and
very persistent scent. These lichens are not, however, used alone; they are
combined with other substances in the composition of much appreciated
perfumes. The thallus possesses also the power of retaining scent and, for
this reason, lichens frequently form an ingredient of potpourri.
b. Lichens as Hair-powder. In the days of white-powdered hair, use was
occasionally made of Ramalina calicaris which was ground down and
substituted for the starch that was more commonly employed.
In older books on lichenology constant reference is made to a hair-
powder called “Pulvis Cyprius” or “Cyprus powder” and very celebrated in
the seventeenth century. It was believed to beautify and cleanse the hair by
removing scurf, etc. Evernia prunastri was one of the chief ingredients of
the powder, but it might be replaced by Physcia ciliaris or by Usnea. The
virtue of the lichens lay in their capacity to absorb and retain perfume. The
powder was for long manufactured at Montpellier and was a valuable
monopoly. Its composition was kept secret, but Bauhin[1319] (J.) published
an account of the ingredients and how to mix them. Under the title “Pulvis
Cyprius Pretiosius” a more detailed recipe of the famous powder was given
by Zwelser[1320], a Palatine medical doctor. The lichen employed in his
preparation, as in Bauhin’s, is Usnea, but that may include both Evernia and
Physcia as they are all tree plants. He gives elaborate directions as to the
cleaning of the lichen from all impurities—it is to be beaten with a stick,
Page 532
washed repeatedly with limpid and pure water, placed in a linen cloth and
dried in the sun till it is completely bleached and deprived of all odour and
taste.
When well dried it was placed in a basket in alternate layers with freshly
gathered, entire flowers of roses and jasmine (or flowers of orange and
citrus when possible). The whole was compressed by a heavy weight, and
each day the flowers were renewed until the “Usnea” was thoroughly
impregnated with a very fragrant odour. It was then reduced to a fine
powder and ready for other ingredients. To each pound should be added:
1-1/2 oz. powdered root of white Iris.
1-1/2 oz. of Cyperus (a sedge).
1 scruple or half drachm of musk reduced to a pulp with fragrant spirit of
roses.
1/2 drachm of ambergris dissolved in a scruple of genuine oil of roses, or
oil of jasmine or oranges as may be preferred.
Zwelser adds:
“This most fragrant royal powder when sprinkled on the head invigorates
by its remarkably pleasant odour; by its astringency and dryness it removes
all impurities, and, since it operates with no viscosity nor sticks firmly
either to skin or hair, it is easily removed from the hair of the head.”
G. Some minor Uses of Lichens
The possibility of extracting gum or mucilage from lichens was
demonstrated by the Russian scientist, Professor Georgi[1321], and later by
Amoreux[1322], the method employed being successive boiling of the plants.
The larger foliose or fruticose forms were specially recommended.
At a later date, during the Napoleonic wars, the “ingenious Lord
Dundonald[1323],” of great fame as an inventor, published an account of the
extraction process and of the application of the gum to calico-printing,
staining and manufacture of paper, dressing and stiffening silks. Lord
Dundonald’s aim was to replace the gum Senegal, then a monopoly of the
French, who were in possession of the Settlement of Senegambia. He took
dried in the sun till it is completely bleached and deprived of all odour and
taste.
When well dried it was placed in a basket in alternate layers with freshly
gathered, entire flowers of roses and jasmine (or flowers of orange and
citrus when possible). The whole was compressed by a heavy weight, and
each day the flowers were renewed until the “Usnea” was thoroughly
impregnated with a very fragrant odour. It was then reduced to a fine
powder and ready for other ingredients. To each pound should be added:
1-1/2 oz. powdered root of white Iris.
1-1/2 oz. of Cyperus (a sedge).
1 scruple or half drachm of musk reduced to a pulp with fragrant spirit of
roses.
1/2 drachm of ambergris dissolved in a scruple of genuine oil of roses, or
oil of jasmine or oranges as may be preferred.
Zwelser adds:
“This most fragrant royal powder when sprinkled on the head invigorates
by its remarkably pleasant odour; by its astringency and dryness it removes
all impurities, and, since it operates with no viscosity nor sticks firmly
either to skin or hair, it is easily removed from the hair of the head.”
G. Some minor Uses of Lichens
The possibility of extracting gum or mucilage from lichens was
demonstrated by the Russian scientist, Professor Georgi[1321], and later by
Amoreux[1322], the method employed being successive boiling of the plants.
The larger foliose or fruticose forms were specially recommended.
At a later date, during the Napoleonic wars, the “ingenious Lord
Dundonald[1323],” of great fame as an inventor, published an account of the
extraction process and of the application of the gum to calico-printing,
staining and manufacture of paper, dressing and stiffening silks. Lord
Dundonald’s aim was to replace the gum Senegal, then a monopoly of the
French, who were in possession of the Settlement of Senegambia. He took
Page 533
out a patent for his invention, but whether the gum was successfully used is
not recorded.
According to Henneguy[1324], lichen mucilage, as a substitute for gum
arabic, has been used at Lyons with advantage in the fabrication of dyed
materials.
not recorded.
According to Henneguy[1324], lichen mucilage, as a substitute for gum
arabic, has been used at Lyons with advantage in the fabrication of dyed
materials.
Page 534
APPENDIX
POSTSCRIPT TO CHAPTER VII[1325]
In a remarkable paper on The Symbiosis of Lichens[1326], Dr A. Henry
Church has presented a new and striking view of the origin and
development of lichens: he has sought to link them up with other classes of
vegetation that, in the great transmigration, passed from sea to land. As we
know from his Thalassiophyta[1327] and the subaerial transmigration, he
holds that primeval algae of advanced form and structure were left exposed
on dry land by the gradually receding waters, and those that successfully
adapted themselves to the changed conditions formed the basis of the land
flora. A certain number of the algae lost their surface tissues containing
chlorophyll and they had perforce to secure from other organic sources the
necessary carbohydrates: they adopted a heterotrophic existence as
saprophytic or parasitic fungi. Fungi are a backward race (deteriorated
according to Dr Church) as regards their soma, but in number, distribution
and variety of spore-production, they are eminently successful plants.
Lichens are similarly regarded by Dr Church as derived from stranded
contemporaneous types of marine algae—crustaceous, foliose and fruticose,
that had also lost their chlorophyll, but by taking into association green
algal units of a lower grade they established a vicarious photosynthesis.
But, to quote his own words[1328], “as the alga-lichen-fungus left the sea, so
it remained: it might deteriorate, but it certainly never advanced, once the
sea factors which produced it were eliminated, it simply stopped along
these lines.”
And again[1329]: “Lichens thus present an interesting case of an algal race
deteriorating along the lines of a heterotrophic existence, yet arrested, as it
were, on the somatic down-grade, by the adoption of intrusive algal units of
lower degree to subserve photosynthesis (much in the manner of the marine
worm Convoluta). Thus arrested, they have been enabled to retain more
definite expression of more deeply inherent factors of sea-weed habit and
construction than any other race of fungi; though closely paralleled by such
POSTSCRIPT TO CHAPTER VII[1325]
In a remarkable paper on The Symbiosis of Lichens[1326], Dr A. Henry
Church has presented a new and striking view of the origin and
development of lichens: he has sought to link them up with other classes of
vegetation that, in the great transmigration, passed from sea to land. As we
know from his Thalassiophyta[1327] and the subaerial transmigration, he
holds that primeval algae of advanced form and structure were left exposed
on dry land by the gradually receding waters, and those that successfully
adapted themselves to the changed conditions formed the basis of the land
flora. A certain number of the algae lost their surface tissues containing
chlorophyll and they had perforce to secure from other organic sources the
necessary carbohydrates: they adopted a heterotrophic existence as
saprophytic or parasitic fungi. Fungi are a backward race (deteriorated
according to Dr Church) as regards their soma, but in number, distribution
and variety of spore-production, they are eminently successful plants.
Lichens are similarly regarded by Dr Church as derived from stranded
contemporaneous types of marine algae—crustaceous, foliose and fruticose,
that had also lost their chlorophyll, but by taking into association green
algal units of a lower grade they established a vicarious photosynthesis.
But, to quote his own words[1328], “as the alga-lichen-fungus left the sea, so
it remained: it might deteriorate, but it certainly never advanced, once the
sea factors which produced it were eliminated, it simply stopped along
these lines.”
And again[1329]: “Lichens thus present an interesting case of an algal race
deteriorating along the lines of a heterotrophic existence, yet arrested, as it
were, on the somatic down-grade, by the adoption of intrusive algal units of
lower degree to subserve photosynthesis (much in the manner of the marine
worm Convoluta). Thus arrested, they have been enabled to retain more
definite expression of more deeply inherent factors of sea-weed habit and
construction than any other race of fungi; though closely paralleled by such
Page 535
types as Xylaria (Ascomycete) and Clavaria (Basidiomycete), which have
followed the full fungus progression as holosaprophytic on decaying plant
residues.”
Dr Church’s theory is of vivid interest and might be convincing were
there no possibility and no proof of advance within the symbiotic plant, but
in numbers of crustaceous thalli, there is evident, by normal or
abnormal[1330] development, the first advance to the formation of
rudimentary squamules, a condition diagnosed as subsquamulose.
“Deterioration” of the lichen plant—when it occurs owing to unfavourable
conditions—is a reversion to the leprose early stage of the association; there
is no evidence of reversion from fruticose or foliose to squamulose. A
glance at the table of lichen phyla[1331] shows progression again and again
from the crustaceous forms onwards. In such a phylum as Physciaceae
(with colourless polarilocular spores) there is a clear example of a closely
connected series; the different types of thallus—crustaceous, squamulose,
foliose and fruticose—are all represented and form a natural sequence,
being well delimited by the unusual form of the spore and by the presence
of parietin in thallus or apothecium.
That there has been development seems absolutely certain, and that along
the lines sketched in the chapter on phylogeny. Progress has been mainly in
the thallus, but there has also been change and advance in the reproductive
organs, more especially in the spores which in several families reach a size
and septation unparalleled in fungi. That association with green algal cells
stimulated the fungus to new development is the view taken of the lichen
plant and emphasized in the present volume. But it seems more in
accordance with the polyphyletic origin and recurring parallel development
in the phyla that association began at the elementary crustaceous stage, and
that the lichen soma was gradually evolved within what is after all a very
limited and simple structure.
followed the full fungus progression as holosaprophytic on decaying plant
residues.”
Dr Church’s theory is of vivid interest and might be convincing were
there no possibility and no proof of advance within the symbiotic plant, but
in numbers of crustaceous thalli, there is evident, by normal or
abnormal[1330] development, the first advance to the formation of
rudimentary squamules, a condition diagnosed as subsquamulose.
“Deterioration” of the lichen plant—when it occurs owing to unfavourable
conditions—is a reversion to the leprose early stage of the association; there
is no evidence of reversion from fruticose or foliose to squamulose. A
glance at the table of lichen phyla[1331] shows progression again and again
from the crustaceous forms onwards. In such a phylum as Physciaceae
(with colourless polarilocular spores) there is a clear example of a closely
connected series; the different types of thallus—crustaceous, squamulose,
foliose and fruticose—are all represented and form a natural sequence,
being well delimited by the unusual form of the spore and by the presence
of parietin in thallus or apothecium.
That there has been development seems absolutely certain, and that along
the lines sketched in the chapter on phylogeny. Progress has been mainly in
the thallus, but there has also been change and advance in the reproductive
organs, more especially in the spores which in several families reach a size
and septation unparalleled in fungi. That association with green algal cells
stimulated the fungus to new development is the view taken of the lichen
plant and emphasized in the present volume. But it seems more in
accordance with the polyphyletic origin and recurring parallel development
in the phyla that association began at the elementary crustaceous stage, and
that the lichen soma was gradually evolved within what is after all a very
limited and simple structure.
Page 536
ADDENDUM
Footnote to Page 404
E. M. Holmes[1332] has published recently an account of a substance
which seems in some respects to answer to the description of manna
(Exodus xvi.; Numbers xi.) more nearly than the generally accepted
Lecanora esculenta. The information is quoted from Swann’s book:
Fighting the slave-hunters in Central Africa. The author writes (p. 116): “I
was shown a curious white substance similar to porridge. It was found early
in the morning before the sun rose. On examination it was found to possess
all the characteristics of the manna ... of the Israelites. In appearance it
resembled coriander seed, was white in colour like hoar frost, sweet to the
taste, melted in the sun and if kept over night was full of worms in the
morning. It required to be baked if you intended to keep it for any length of
time. It looked as if it was deposited on the ground in the night.” The writer
has suggested that “the substance might be mushroom spawn as, on the spot
where it melted tiny fungi sprung up the next night.” Swann’s statement has
been confirmed by Dr Wareham, a medical missionary from the same
district, who states, however, that it is of rare occurrence.
Footnote to Page 404
E. M. Holmes[1332] has published recently an account of a substance
which seems in some respects to answer to the description of manna
(Exodus xvi.; Numbers xi.) more nearly than the generally accepted
Lecanora esculenta. The information is quoted from Swann’s book:
Fighting the slave-hunters in Central Africa. The author writes (p. 116): “I
was shown a curious white substance similar to porridge. It was found early
in the morning before the sun rose. On examination it was found to possess
all the characteristics of the manna ... of the Israelites. In appearance it
resembled coriander seed, was white in colour like hoar frost, sweet to the
taste, melted in the sun and if kept over night was full of worms in the
morning. It required to be baked if you intended to keep it for any length of
time. It looked as if it was deposited on the ground in the night.” The writer
has suggested that “the substance might be mushroom spawn as, on the spot
where it melted tiny fungi sprung up the next night.” Swann’s statement has
been confirmed by Dr Wareham, a medical missionary from the same
district, who states, however, that it is of rare occurrence.
Page 537
FOOTNOTES
[1] E. Acton (1909) has described a primitive lichen Botrydina vulgaris, in
which there is no fruiting stage, and in which the fungus seems to show affinity
with a Hyphomycete.
[2] Luyken 1809.
[3] Hornschuch 1819.
[4] Raab 1819.
[5] Dillenius 1741, p. 200.
[6] Wallroth 1825.
[7] Agardh 1820.
[8] See p. 27.
[9] Schwendener 1867.
[10] Fink 1913.
[11] Lindsay 1876.
[12] Nylander 1869.
[13] Crombie 1891.
[14] Nylander 1891.
[15] Crombie 1874.
[16] Crombie 1877.
[17] Crombie 1885.
[18] Fink 1913.
[19] Elfving 1913.
[20] Moreau 1918.
[21] Peirce 1898.
[22] French 1898.
[23] Morison 1699.
[24] Tournefort 1694 and 1700.
[25] Dillenius 1741.
[26] Krempelhuber 1867-1872.
[27] Grete Herball 1526.
[28] Ruel 1536.
[1] E. Acton (1909) has described a primitive lichen Botrydina vulgaris, in
which there is no fruiting stage, and in which the fungus seems to show affinity
with a Hyphomycete.
[2] Luyken 1809.
[3] Hornschuch 1819.
[4] Raab 1819.
[5] Dillenius 1741, p. 200.
[6] Wallroth 1825.
[7] Agardh 1820.
[8] See p. 27.
[9] Schwendener 1867.
[10] Fink 1913.
[11] Lindsay 1876.
[12] Nylander 1869.
[13] Crombie 1891.
[14] Nylander 1891.
[15] Crombie 1874.
[16] Crombie 1877.
[17] Crombie 1885.
[18] Fink 1913.
[19] Elfving 1913.
[20] Moreau 1918.
[21] Peirce 1898.
[22] French 1898.
[23] Morison 1699.
[24] Tournefort 1694 and 1700.
[25] Dillenius 1741.
[26] Krempelhuber 1867-1872.
[27] Grete Herball 1526.
[28] Ruel 1536.
Page 538
[29] Dorstenius 1540.
[30] Camerarius 1586.
[31] Tabernaemontanus 1590.
[32] L’Obel 1576.
[33] Dodoens 1583.
[34] Gerard 1597.
[35] Schwenckfeld 1600.
[36] Colonna 1606.
[37] Bauhin 1623, pp. 360-2.
[38] Parkinson 1640.
[39] How 1650.
[40] Merrett 1666.
[41] Plot 1686.
[42] Morison 1699.
[43] Ray 1670.
[44] Ray 1686.
[45] Ray 1690.
[46] Petiver 1695.
[47] Plukenet 1691-1696.
[48] Malpighi 1686.
[49] Porta 1688.
[50] Tournefort 1694.
[51] Tournefort 1700.
[52] Rupp 1718.
[53] Buxbaum 1721.
[54] Vaillant 1727.
[55] Dillenius 1724 and 1741.
[56] Micheli 1729.
[57] Dillenius 1719.
[58] See Druce and Vines 1907.
[59] Crombie 1880.
[60] Haller 1742.
[61] Linnaeus 1753.
[62] Schneider 1897.
[63] Hill 1751. Hill’s genus Collema is Nostoc, etc.
[30] Camerarius 1586.
[31] Tabernaemontanus 1590.
[32] L’Obel 1576.
[33] Dodoens 1583.
[34] Gerard 1597.
[35] Schwenckfeld 1600.
[36] Colonna 1606.
[37] Bauhin 1623, pp. 360-2.
[38] Parkinson 1640.
[39] How 1650.
[40] Merrett 1666.
[41] Plot 1686.
[42] Morison 1699.
[43] Ray 1670.
[44] Ray 1686.
[45] Ray 1690.
[46] Petiver 1695.
[47] Plukenet 1691-1696.
[48] Malpighi 1686.
[49] Porta 1688.
[50] Tournefort 1694.
[51] Tournefort 1700.
[52] Rupp 1718.
[53] Buxbaum 1721.
[54] Vaillant 1727.
[55] Dillenius 1724 and 1741.
[56] Micheli 1729.
[57] Dillenius 1719.
[58] See Druce and Vines 1907.
[59] Crombie 1880.
[60] Haller 1742.
[61] Linnaeus 1753.
[62] Schneider 1897.
[63] Hill 1751. Hill’s genus Collema is Nostoc, etc.
Page 539
[64] Hill 1760.
[65] Watson 1759.
[66] Scopoli 1760.
[67] Adanson 1763.
[68] Hudson 1762 and 1778.
[69] Withering 1776.
[70] Lightfoot 1777.
[71] Dickson 1785.
[72] Weber 1780.
[73] Sibthorp 1794.
[74] Relhan 1785 and 1820.
[75] Smith 1790.
[76] Hoffmann 1798.
[77] Persoon 1794.
[78] Buxbaum 1728.
[79] Petiver 1712.
[80] Sloane 1796 and 1807.
[81] Swartz 1788 and 1791.
[82] Desfontaines 1798-1800.
[83] Georgi 1797.
[84] Willomet, etc. 1787.
[85] Acharius 1798.
[86] Acharius 1803.
[87] Acharius 1810.
[88] Acharius 1814.
[89] Hue 1908.
[90] De Candolle 1805.
[91] Flörke 1815-1819.
[92] Davies 1813.
[93] Forster 1816.
[94] S. F. Gray 1821.
[95] Carrington 1870.
[96] See List of the Books, etc. by John Edward Gray, p. 3, 1872.
[97] Hooker 1821.
[98] Hooker 1831.
[65] Watson 1759.
[66] Scopoli 1760.
[67] Adanson 1763.
[68] Hudson 1762 and 1778.
[69] Withering 1776.
[70] Lightfoot 1777.
[71] Dickson 1785.
[72] Weber 1780.
[73] Sibthorp 1794.
[74] Relhan 1785 and 1820.
[75] Smith 1790.
[76] Hoffmann 1798.
[77] Persoon 1794.
[78] Buxbaum 1728.
[79] Petiver 1712.
[80] Sloane 1796 and 1807.
[81] Swartz 1788 and 1791.
[82] Desfontaines 1798-1800.
[83] Georgi 1797.
[84] Willomet, etc. 1787.
[85] Acharius 1798.
[86] Acharius 1803.
[87] Acharius 1810.
[88] Acharius 1814.
[89] Hue 1908.
[90] De Candolle 1805.
[91] Flörke 1815-1819.
[92] Davies 1813.
[93] Forster 1816.
[94] S. F. Gray 1821.
[95] Carrington 1870.
[96] See List of the Books, etc. by John Edward Gray, p. 3, 1872.
[97] Hooker 1821.
[98] Hooker 1831.
Page 540
[99] Greville 1823-1827.
[100] Greville 1824.
[101] Hooker 1833.
[102] Taylor 1836.
[103] Fries 1831.
[104] Fée 1824.
[105] Flörke 1828.
[106] Wallroth 1829.
[107] Delise 1822.
[108] Chevalier 1824.
[109] Wallroth 1825.
[110] Meyer 1825.
[111] Holle 1849.
[112] Koerber 1839.
[113] Michaux 1803.
[114] Mühlenberg 1813.
[115] Torrey 1819.
[116] Halsey 1824.
[117] Tuckerman 1839.
[118] Fée 1824.
[119] Martius 1833.
[120] Montagne 1851.
[121] Hooker 1841.
[122] Schaerer 1850.
[123] Eschweiler 1824.
[124] Fée 1824.
[125] De Notaris 1846.
[126] Massalongo 1852.
[127] Norman 1852.
[128] Koerber 1855.
[129] Mudd 1861.
[130] Lindsay 1856.
[131] Leighton 1851, etc.
[132] See Hue 1899.
[133] Nylander 1854 and 1855.
[100] Greville 1824.
[101] Hooker 1833.
[102] Taylor 1836.
[103] Fries 1831.
[104] Fée 1824.
[105] Flörke 1828.
[106] Wallroth 1829.
[107] Delise 1822.
[108] Chevalier 1824.
[109] Wallroth 1825.
[110] Meyer 1825.
[111] Holle 1849.
[112] Koerber 1839.
[113] Michaux 1803.
[114] Mühlenberg 1813.
[115] Torrey 1819.
[116] Halsey 1824.
[117] Tuckerman 1839.
[118] Fée 1824.
[119] Martius 1833.
[120] Montagne 1851.
[121] Hooker 1841.
[122] Schaerer 1850.
[123] Eschweiler 1824.
[124] Fée 1824.
[125] De Notaris 1846.
[126] Massalongo 1852.
[127] Norman 1852.
[128] Koerber 1855.
[129] Mudd 1861.
[130] Lindsay 1856.
[131] Leighton 1851, etc.
[132] See Hue 1899.
[133] Nylander 1854 and 1855.
Page 541
[134] Tulasne 1852.
[135] Lauder Lindsay 1859.
[136] Itzigsohn 1854-1855.
[137] Speerschneider 1853.
[138] Sachs 1855.
[139] Thwaites 1849.
[140] Schwendener 1863-1868.
[141] Leighton 1851.
[142] Leighton 1854.
[143] Leighton 1856.
[144] Mudd 1865.
[145] Th. Fries 1858.
[146] Schwendener 1867.
[147] Nylander 1874.
[148] Crombie 1885.
[149] Lett 1890.
[150] Fünfstück 1898.
[151] Zahlbruckner 1903-1907.
[152] Ventenat 1794, p. 36.
[153] Cassini 1817, p. 395.
[154] Agardh 1820.
[155] Scopoli 1760, p. 79.
[156] Persoon 1794, p. 17.
[157] Sprengel 1804, p. 325.
[158] Wallroth 1825, i.
[159] Wallroth 1825, i., p. 303.
[160] Fries 1831, pp. lvi and lvii.
[161] Kützing 1843.
[162] Thwaites 1849, pp. 219 and 241.
[163] Flotow 1850.
[164] Sachs 1855.
[165] Itzigsohn 1855.
[166] Itzigsohn 1854.
[167] Hicks 1860 and 1861.
[168] Speerschneider 1853.
[135] Lauder Lindsay 1859.
[136] Itzigsohn 1854-1855.
[137] Speerschneider 1853.
[138] Sachs 1855.
[139] Thwaites 1849.
[140] Schwendener 1863-1868.
[141] Leighton 1851.
[142] Leighton 1854.
[143] Leighton 1856.
[144] Mudd 1865.
[145] Th. Fries 1858.
[146] Schwendener 1867.
[147] Nylander 1874.
[148] Crombie 1885.
[149] Lett 1890.
[150] Fünfstück 1898.
[151] Zahlbruckner 1903-1907.
[152] Ventenat 1794, p. 36.
[153] Cassini 1817, p. 395.
[154] Agardh 1820.
[155] Scopoli 1760, p. 79.
[156] Persoon 1794, p. 17.
[157] Sprengel 1804, p. 325.
[158] Wallroth 1825, i.
[159] Wallroth 1825, i., p. 303.
[160] Fries 1831, pp. lvi and lvii.
[161] Kützing 1843.
[162] Thwaites 1849, pp. 219 and 241.
[163] Flotow 1850.
[164] Sachs 1855.
[165] Itzigsohn 1855.
[166] Itzigsohn 1854.
[167] Hicks 1860 and 1861.
[168] Speerschneider 1853.
Page 542
[169] Famintzin and Baranetzky 1867.
[170] Baranetzky 1869.
[171] Itzigsohn 1867.
[172] Bayrhoffer 1851.
[173] Tulasne 1852.
[174] Speerschneider 1854.
[175] de Bary 1866, p. 242.
[176] Schwendener 1860, p. 125.
[177] de Bary 1866, p. 291.
[178] Nylander 1870.
[179] Elfving 1903 and 1913.
[180] See p. 133.
[181] Minks 1878 and 1879.
[182] Müller 1878 and 1884.
[183] Zukal 1884.
[184] Darbishire 1895¹.
[185] Schwendener 1860, etc.
[186] Schwendener 1867.
[187] Schwendener 1868, p. 195.
[188] Schwendener 1869.
[189] Rees 1871.
[190] Bornet 1872.
[191] The authors quoted have been followed in their designation of the
various green algae that form lichen gonidia. It is however now recognized
(Wille 1913) that either Protococcus viridis Ag., Chlorella or other
Protococcaceae may form the universal green coating on trees, etc., and be
incorporated as lichen gonidia. Pleurococcus vulgaris Naeg. and Pleurococcus
Naegeli Chod. are synonyms of Protococcus viridis. In that alga there is no
pyrenoid, and no zoospores are formed.
The genus Cystococcus, according to Chodat (1913), is characterized by the
presence of a pyrenoid and by reproduction with zoospores and is identical with
Pleurococcus vulgaris Menegh. (non Naeg.), though Wille regards Meneghini’s
species as of mixed content. Paulson and Hastings (1920) now find that Chodat’s
pyrenoid is the nucleus of the cell.
[192] Woronin 1872.
[193] Archer 1873, 1874, 1875.
[194] Bornet 1873 and 1874.
[195] Treub 1873.
[170] Baranetzky 1869.
[171] Itzigsohn 1867.
[172] Bayrhoffer 1851.
[173] Tulasne 1852.
[174] Speerschneider 1854.
[175] de Bary 1866, p. 242.
[176] Schwendener 1860, p. 125.
[177] de Bary 1866, p. 291.
[178] Nylander 1870.
[179] Elfving 1903 and 1913.
[180] See p. 133.
[181] Minks 1878 and 1879.
[182] Müller 1878 and 1884.
[183] Zukal 1884.
[184] Darbishire 1895¹.
[185] Schwendener 1860, etc.
[186] Schwendener 1867.
[187] Schwendener 1868, p. 195.
[188] Schwendener 1869.
[189] Rees 1871.
[190] Bornet 1872.
[191] The authors quoted have been followed in their designation of the
various green algae that form lichen gonidia. It is however now recognized
(Wille 1913) that either Protococcus viridis Ag., Chlorella or other
Protococcaceae may form the universal green coating on trees, etc., and be
incorporated as lichen gonidia. Pleurococcus vulgaris Naeg. and Pleurococcus
Naegeli Chod. are synonyms of Protococcus viridis. In that alga there is no
pyrenoid, and no zoospores are formed.
The genus Cystococcus, according to Chodat (1913), is characterized by the
presence of a pyrenoid and by reproduction with zoospores and is identical with
Pleurococcus vulgaris Menegh. (non Naeg.), though Wille regards Meneghini’s
species as of mixed content. Paulson and Hastings (1920) now find that Chodat’s
pyrenoid is the nucleus of the cell.
[192] Woronin 1872.
[193] Archer 1873, 1874, 1875.
[194] Bornet 1873 and 1874.
[195] Treub 1873.
Page 543
[196] Borzi 1875.
[197] Stahl 1877.
[198] Bonnier 1886 and 1889.
[199] Bonnier was probably experimenting with an Arthopyrenia. Verrucaria
species combine with Protococcus or according to Chodat with Coccobotrys
gen. nov.
[200] Nylander 1858.
[201] Fuisting 1868, p. 674.
[202] Winter 1876, p. 264.
[203] Stahl 1877.
[204] See p. 62.
[205] Wainio 1890, 2, p. 29.
[206] Reinke 1872, p. 108.
[207] Reinke 1873¹.
[208] Reinke 1873², p. 98.
[209] Frank 1876.
[210] de Bary 1879.
[211] Bornet 1873.
[212] Hedlund 1892.
[213] Peirce 1899.
[214] Hue 1915.
[215] Lindau 1895¹.
[216] Peirce 1899.
[217] Claassen 1914.
[218] Frank 1876.
[219] Lindau 1895.
[220] Bachmann 1913.
[221] Cunningham 1879.
[222] Ward 1884.
[223] Jennings 1895.
[224] Fitting 1910.
[225] Bornet 1873.
[226] Bonnier 1889².
[227] Schwendener 1867.
[228] Elenkin 1902¹ and 1904¹, 1904².
[229] Elenkin 1906².
[197] Stahl 1877.
[198] Bonnier 1886 and 1889.
[199] Bonnier was probably experimenting with an Arthopyrenia. Verrucaria
species combine with Protococcus or according to Chodat with Coccobotrys
gen. nov.
[200] Nylander 1858.
[201] Fuisting 1868, p. 674.
[202] Winter 1876, p. 264.
[203] Stahl 1877.
[204] See p. 62.
[205] Wainio 1890, 2, p. 29.
[206] Reinke 1872, p. 108.
[207] Reinke 1873¹.
[208] Reinke 1873², p. 98.
[209] Frank 1876.
[210] de Bary 1879.
[211] Bornet 1873.
[212] Hedlund 1892.
[213] Peirce 1899.
[214] Hue 1915.
[215] Lindau 1895¹.
[216] Peirce 1899.
[217] Claassen 1914.
[218] Frank 1876.
[219] Lindau 1895.
[220] Bachmann 1913.
[221] Cunningham 1879.
[222] Ward 1884.
[223] Jennings 1895.
[224] Fitting 1910.
[225] Bornet 1873.
[226] Bonnier 1889².
[227] Schwendener 1867.
[228] Elenkin 1902¹ and 1904¹, 1904².
[229] Elenkin 1906².
Page 544
[230] Danilov 1910.
[231] Paulson and Hastings 1920.
[232] Nienburg 1917.
[233] Zukal 1891.
[234] Sutherland 1915.
[235] Beyerinck 1890.
[236] Artari 1902.
[237] See p. 56.
[238] Artari 1902.
[239] Treboux 1912.
[240] Chodat 1913.
[241] See Paulson and Hastings 1920.
[242] Keeble 1910.
[243] Reinke 1872.
[244] Dufrenoy 1918.
[245] Artari 1899.
[246] Etard and Bouilhac 1898.
[247] Radais 1900.
[248] Artari 1901.
[249] Chodat 1913.
[250] Treboux 1905.
[251] Marshall Ward 1884.
[252] Uhlir 1915.
[253] Tobler 1911.
[254] Zopf 1907.
[255] Chambers 1912.
[256] Chodat 1913.
[257] See note Paulson and Hastings, p. 28.
[258] Chodat 1913.
[259] Gargeaune 1911.
[260] Servettaz 1913.
[261] See p. 65.
[262] Wettstein 1915.
[263] Meyer 1825.
[264] Holle 1849.
[231] Paulson and Hastings 1920.
[232] Nienburg 1917.
[233] Zukal 1891.
[234] Sutherland 1915.
[235] Beyerinck 1890.
[236] Artari 1902.
[237] See p. 56.
[238] Artari 1902.
[239] Treboux 1912.
[240] Chodat 1913.
[241] See Paulson and Hastings 1920.
[242] Keeble 1910.
[243] Reinke 1872.
[244] Dufrenoy 1918.
[245] Artari 1899.
[246] Etard and Bouilhac 1898.
[247] Radais 1900.
[248] Artari 1901.
[249] Chodat 1913.
[250] Treboux 1905.
[251] Marshall Ward 1884.
[252] Uhlir 1915.
[253] Tobler 1911.
[254] Zopf 1907.
[255] Chambers 1912.
[256] Chodat 1913.
[257] See note Paulson and Hastings, p. 28.
[258] Chodat 1913.
[259] Gargeaune 1911.
[260] Servettaz 1913.
[261] See p. 65.
[262] Wettstein 1915.
[263] Meyer 1825.
[264] Holle 1849.
Page 545
[265] Tulasne 1852.
[266] Bonnier 1889².
[267] Term coined by Lindau (1899) to describe the pseudo-cellular tissue of
lichens and fungi now referred to as “plectenchyma.”
[268] Wainio 1897.
[269] Möller 1887.
[270] Tobler 1909.
[271] Wahrlich 1893.
[272] Baur 1898.
[273] Darbishire 1899.
[274] Kienitz-Gerloff 1902.
[275] Meyer 1902.
[276] Salter 1902.
[277] Nylander (1866) gave the term “gonimia” to the blue-green algae of the
Phycolichens, retaining the term “gonidia” for the bright-green algae of the
Archilichens: the distinction is not now maintained.
[278] For further details see also the chapter on Classification.
[279] See p. 133.
[280] Krempelhuber 1873.
[281] Chodat 1913.
[282] Paulson and Hastings 1920.
[283] Paulson in litt.
[284] Acton 1909.
[285] Bialosuknia 1909.
[286] Hue 1905.
[287] Deckenbach 1893.
[288] In a comparative study of leaf algae from Ceylon and Barbadoes, N.
Thomas (1913) came to the conclusion that Marshall Ward’s alga in its early
stages is the same as Phyllactidium tropicum Moebius; and that the Barbadoes
alga with which she was working represented the older stages, it being then
subcuticular in habit, forming rhizoids, barren and sterile aerial hairs and
subcuticular zoosporangia.
[289] De Toni 1889.
[290] Bornet 1873.
[291] Fünfstück 1899.
[292] Hedlund 1892.
[293] Zukal 1895, p. 19.
[294] Moebius 1888.
[266] Bonnier 1889².
[267] Term coined by Lindau (1899) to describe the pseudo-cellular tissue of
lichens and fungi now referred to as “plectenchyma.”
[268] Wainio 1897.
[269] Möller 1887.
[270] Tobler 1909.
[271] Wahrlich 1893.
[272] Baur 1898.
[273] Darbishire 1899.
[274] Kienitz-Gerloff 1902.
[275] Meyer 1902.
[276] Salter 1902.
[277] Nylander (1866) gave the term “gonimia” to the blue-green algae of the
Phycolichens, retaining the term “gonidia” for the bright-green algae of the
Archilichens: the distinction is not now maintained.
[278] For further details see also the chapter on Classification.
[279] See p. 133.
[280] Krempelhuber 1873.
[281] Chodat 1913.
[282] Paulson and Hastings 1920.
[283] Paulson in litt.
[284] Acton 1909.
[285] Bialosuknia 1909.
[286] Hue 1905.
[287] Deckenbach 1893.
[288] In a comparative study of leaf algae from Ceylon and Barbadoes, N.
Thomas (1913) came to the conclusion that Marshall Ward’s alga in its early
stages is the same as Phyllactidium tropicum Moebius; and that the Barbadoes
alga with which she was working represented the older stages, it being then
subcuticular in habit, forming rhizoids, barren and sterile aerial hairs and
subcuticular zoosporangia.
[289] De Toni 1889.
[290] Bornet 1873.
[291] Fünfstück 1899.
[292] Hedlund 1892.
[293] Zukal 1895, p. 19.
[294] Moebius 1888.
Page 546
[295] Frank 1876, p. 158.
[296] Stahl 1877.
[297] Neubner 1893.
[298] Krabbe 1891.
[299] Forssell 1885.
[300] Hue 1910.
[301] Harmand 1913, p. 1050.
[302] Forssell 1886.
[303] See Chap. VII.
[304] Lindau 1895.
[305] Darbishire 1897.
[306] Nienburg 1917.
[307] Bonnier 1888 and 1889².
[308] Bonnier 1889.
[309] Forssell 1884, p. 34.
[310] Zahlbruckner 1902.
[311] Lindau 1899.
[312] Reinke 1895.
[313] Zukal 1895, p. 562.
[314] Zahlbruckner 1907.
[315] Hue 1899.
[316] Wainio has adopted this term for growing hyphae 1897, p. 33.
[317] Tulasne 1852.
[318] Zukal 1895.
[319] Zukal 1895.
[320] Schwendener 1866.
[321] Schwendener 1863.
[322] Hue 1906.
[323] See p. 83.
[324] Malinowski 1911.
[325] Steiner 1881.
[326] Fünfstück 1899.
[327] Bachmann 1913.
[328] See p. 215.
[329] Friedrich 1906.
[296] Stahl 1877.
[297] Neubner 1893.
[298] Krabbe 1891.
[299] Forssell 1885.
[300] Hue 1910.
[301] Harmand 1913, p. 1050.
[302] Forssell 1886.
[303] See Chap. VII.
[304] Lindau 1895.
[305] Darbishire 1897.
[306] Nienburg 1917.
[307] Bonnier 1888 and 1889².
[308] Bonnier 1889.
[309] Forssell 1884, p. 34.
[310] Zahlbruckner 1902.
[311] Lindau 1899.
[312] Reinke 1895.
[313] Zukal 1895, p. 562.
[314] Zahlbruckner 1907.
[315] Hue 1899.
[316] Wainio has adopted this term for growing hyphae 1897, p. 33.
[317] Tulasne 1852.
[318] Zukal 1895.
[319] Zukal 1895.
[320] Schwendener 1866.
[321] Schwendener 1863.
[322] Hue 1906.
[323] See p. 83.
[324] Malinowski 1911.
[325] Steiner 1881.
[326] Fünfstück 1899.
[327] Bachmann 1913.
[328] See p. 215.
[329] Friedrich 1906.
Page 547
[330] Bachmann 1907.
[331] Bachmann 1904.
[332] Bachmann 1904.
[333] Stahlecker 1906.
[334] Lang 1903.
[335] Fünfstück 1899.
[336] Darbishire 1897.
[337] Frank 1876.
[338] Bornet 1873, p. 81.
[339] Lindau 1895.
[340] Bitter 1899.
[341] See p. 83.
[342] Friedrich 1906.
[343] See p. 76.
[344] See p. 126.
[345] Schwendener 1860, 1863 and 1868.
[346] Zukal 1895, p. 1305.
[347] Hue 1906.
[348] Heber Howe 1912.
[349] Hue 1911.
[350] Schwendener 1863, p. 180.
[351] Darbishire 1897.
[352] Rosendahl 1907.
[353] See p. 96.
[354] See p. 133.
[355] Rosendahl 1907.
[356] Meyer 1902.
[357] See p. 52.
[358] Nylander 1858.
[359] Hue 1898.
[360] Rosendahl 1907.
[361] Darbishire 1912.
[362] Porter 1919.
[363] Darbishire 1897.
[364] Schwendener 1860.
[331] Bachmann 1904.
[332] Bachmann 1904.
[333] Stahlecker 1906.
[334] Lang 1903.
[335] Fünfstück 1899.
[336] Darbishire 1897.
[337] Frank 1876.
[338] Bornet 1873, p. 81.
[339] Lindau 1895.
[340] Bitter 1899.
[341] See p. 83.
[342] Friedrich 1906.
[343] See p. 76.
[344] See p. 126.
[345] Schwendener 1860, 1863 and 1868.
[346] Zukal 1895, p. 1305.
[347] Hue 1906.
[348] Heber Howe 1912.
[349] Hue 1911.
[350] Schwendener 1863, p. 180.
[351] Darbishire 1897.
[352] Rosendahl 1907.
[353] See p. 96.
[354] See p. 133.
[355] Rosendahl 1907.
[356] Meyer 1902.
[357] See p. 52.
[358] Nylander 1858.
[359] Hue 1898.
[360] Rosendahl 1907.
[361] Darbishire 1912.
[362] Porter 1919.
[363] Darbishire 1897.
[364] Schwendener 1860.
Page 548
[365] Rosendahl 1907.
[366] Meyer 1902.
[367] Reinke 1895, p. 186.
[368] Bitter 1901.
[369] Sernander 1901.
[370] Parfitt in Leighton 1871, p. 470.
[371] Galløe 1915.
[372] Bitter 1899.
[373] Sturgis 1890.
[374] See p. 108.
[375] Darbishire 1898.
[376] Darbishire 1895.
[377] Brandt 1906.
[378] Hue 1906.
[379] Haberlandt 1896.
[380] Schulte 1904.
[381] See p. 120.
[382] Lutz 1894.
[383] Peirce 1898.
[384] Zopf 1903.
[385] Lindau 1895.
[386] Brandt 1906.
[387] Porter 1916.
[388] Darbishire 1898.
[389] Wainio 1880.
[390] Krabbe 1891.
[391] Wainio 1897.
[392] Wainio 1880.
[393] Krabbe 1891.
[394] Krabbe 1891.
[395] Baur 1904.
[396] Wainio 1880.
[397] Chodat 1913.
[398] Wainio 1897.
[399] Baur 1904.
[366] Meyer 1902.
[367] Reinke 1895, p. 186.
[368] Bitter 1901.
[369] Sernander 1901.
[370] Parfitt in Leighton 1871, p. 470.
[371] Galløe 1915.
[372] Bitter 1899.
[373] Sturgis 1890.
[374] See p. 108.
[375] Darbishire 1898.
[376] Darbishire 1895.
[377] Brandt 1906.
[378] Hue 1906.
[379] Haberlandt 1896.
[380] Schulte 1904.
[381] See p. 120.
[382] Lutz 1894.
[383] Peirce 1898.
[384] Zopf 1903.
[385] Lindau 1895.
[386] Brandt 1906.
[387] Porter 1916.
[388] Darbishire 1898.
[389] Wainio 1880.
[390] Krabbe 1891.
[391] Wainio 1897.
[392] Wainio 1880.
[393] Krabbe 1891.
[394] Krabbe 1891.
[395] Baur 1904.
[396] Wainio 1880.
[397] Chodat 1913.
[398] Wainio 1897.
[399] Baur 1904.
Page 549
[400] Wainio 1897.
[401] Wainio 1897.
[402] Lindsay 1859, p. 171.
[403] Wainio 1897.
[404] Wainio 1897, p. 9.
[405] Wainio 1880.
[406] Krabbe 1891.
[407] Necker 1871.
[408] Persoon 1794.
[409] Acharius 1803.
[410] Wallroth 1829, p. 61.
[411] Tulasne 1852.
[412] Koerber 1855.
[413] Reinke 1894.
[414] Sättler 1914.
[415] Nienburg 1908.
[416] See p. 183.
[417] Wainio 1897.
[418] Baur 1904.
[419] Wolff 1905.
[420] Aigret 1901.
[421] Wainio 1897.
[422] Wainio 1890, p. 67.
[423] Reinke 1895.
[424] Nylander 1858, p. 63.
[425] Acharius 1810, p. 12.
[426] Haller 1768, p. 85.
[427] Schreber 1791, p. 768.
[428] Meyer 1825, p. 148.
[429] Delise 1822.
[430] Nylander 1858, p. 14.
[431] Nylander 1860, p. 333.
[432] Schwendener 1863, p. 169.
[433] Wainio 1890, i. p. 183.
[434] Schwendener 1863, p. 169.
[401] Wainio 1897.
[402] Lindsay 1859, p. 171.
[403] Wainio 1897.
[404] Wainio 1897, p. 9.
[405] Wainio 1880.
[406] Krabbe 1891.
[407] Necker 1871.
[408] Persoon 1794.
[409] Acharius 1803.
[410] Wallroth 1829, p. 61.
[411] Tulasne 1852.
[412] Koerber 1855.
[413] Reinke 1894.
[414] Sättler 1914.
[415] Nienburg 1908.
[416] See p. 183.
[417] Wainio 1897.
[418] Baur 1904.
[419] Wolff 1905.
[420] Aigret 1901.
[421] Wainio 1897.
[422] Wainio 1890, p. 67.
[423] Reinke 1895.
[424] Nylander 1858, p. 63.
[425] Acharius 1810, p. 12.
[426] Haller 1768, p. 85.
[427] Schreber 1791, p. 768.
[428] Meyer 1825, p. 148.
[429] Delise 1822.
[430] Nylander 1858, p. 14.
[431] Nylander 1860, p. 333.
[432] Schwendener 1863, p. 169.
[433] Wainio 1890, i. p. 183.
[434] Schwendener 1863, p. 169.
Page 550
[435] Stizenberger 1895.
[436] Zukal 1895, p. 1355.
[437] Wainio 1909.
[438] Schwendener 1863, p. 169.
[439] Jatta 1889, p. 48.
[440] Zukal 1895, p. 1357.
[441] Rosendahl 1907.
[442] Zukal 1895.
[443] Reinke 1895, p. 183.
[444] Darbishire 1901.
[445] Brandt 1906.
[446] Bitter 1899.
[447] Nylander 1874².
[448] Bitter 1901².
[449] Zukal 1895, p. 1348.
[450] Acharius 1803.
[451] Hue 1904 and 1910.
[452] Flörke 1815, iv. p. 15.
[453] Wallroth 1825, p. 678.
[454] Th. M. Fries 1858.
[455] Forssell 1884.
[456] Leighton 1869.
[457] Nylander 1878.
[458] Schneider 1897.
[459] Hue 1910.
[460] Hue 1910.
[461] Tuckerman 1875.
[462] Schneider 1897, p. 58.
[463] Nylander 1869.
[464] Bornet 1873, p. 72.
[465] Forssell 1885, p. 24.
[466] Riddle 1910.
[467] Babikoff 1878.
[468] Th. M. Fries 1866.
[469] Winter 1877.
[436] Zukal 1895, p. 1355.
[437] Wainio 1909.
[438] Schwendener 1863, p. 169.
[439] Jatta 1889, p. 48.
[440] Zukal 1895, p. 1357.
[441] Rosendahl 1907.
[442] Zukal 1895.
[443] Reinke 1895, p. 183.
[444] Darbishire 1901.
[445] Brandt 1906.
[446] Bitter 1899.
[447] Nylander 1874².
[448] Bitter 1901².
[449] Zukal 1895, p. 1348.
[450] Acharius 1803.
[451] Hue 1904 and 1910.
[452] Flörke 1815, iv. p. 15.
[453] Wallroth 1825, p. 678.
[454] Th. M. Fries 1858.
[455] Forssell 1884.
[456] Leighton 1869.
[457] Nylander 1878.
[458] Schneider 1897.
[459] Hue 1910.
[460] Hue 1910.
[461] Tuckerman 1875.
[462] Schneider 1897, p. 58.
[463] Nylander 1869.
[464] Bornet 1873, p. 72.
[465] Forssell 1885, p. 24.
[466] Riddle 1910.
[467] Babikoff 1878.
[468] Th. M. Fries 1866.
[469] Winter 1877.
Page 551
[470] Schneider 1897.
[471] Etard and Bouilhac 1898.
[472] Hue 1910.
[473] Sernander 1907.
[474] Bitter 1904.
[475] Bitter 1904.
[476] Linkola 1913.
[477] Acharius, 1798, p. xix, and 1810, pp. 8 and 10.
[478] Malpighi, 1686, p. 50, pl. 27, fig. 106.
[479] Micheli 1729, pp. 73, 74.
[480] Linnaeus 1737, p. 325.
[481] Hedwig 1798.
[482] Sprengel 1807, Letter xxiii.
[483] Wallroth 1825, i. p. 595.
[484] Koerber 1841.
[485] Schwendener 1860.
[486] Meyer 1825, p. 170.
[487] Krabbe 1891.
[488] Bitter 1901.
[489] Schwendener 1860, p. 137.
[490] Wainio 1897, p. 32.
[491] Reinke 1895, p. 380.
[492] Bitter 1901.
[493] Lesdain 1910.
[494] Schwendener 1860.
[495] Nilson 1903.
[496] Darbishire 1897.
[497] Bitter 1901, p. 191.
[498] Krabbe 1891.
[499] Darbishire 1907.
[500] Tobler 1911², 11.
[501] Bitter 1901².
[502] Lindau 1895.
[503] Nilson 1903.
[504] Bitter 1904.
[471] Etard and Bouilhac 1898.
[472] Hue 1910.
[473] Sernander 1907.
[474] Bitter 1904.
[475] Bitter 1904.
[476] Linkola 1913.
[477] Acharius, 1798, p. xix, and 1810, pp. 8 and 10.
[478] Malpighi, 1686, p. 50, pl. 27, fig. 106.
[479] Micheli 1729, pp. 73, 74.
[480] Linnaeus 1737, p. 325.
[481] Hedwig 1798.
[482] Sprengel 1807, Letter xxiii.
[483] Wallroth 1825, i. p. 595.
[484] Koerber 1841.
[485] Schwendener 1860.
[486] Meyer 1825, p. 170.
[487] Krabbe 1891.
[488] Bitter 1901.
[489] Schwendener 1860, p. 137.
[490] Wainio 1897, p. 32.
[491] Reinke 1895, p. 380.
[492] Bitter 1901.
[493] Lesdain 1910.
[494] Schwendener 1860.
[495] Nilson 1903.
[496] Darbishire 1897.
[497] Bitter 1901, p. 191.
[498] Krabbe 1891.
[499] Darbishire 1907.
[500] Tobler 1911², 11.
[501] Bitter 1901².
[502] Lindau 1895.
[503] Nilson 1903.
[504] Bitter 1904.
Page 552
[505] Acharius 1798, pp. 2, 87.
[506] Fries 1825.
[507] Hooker 1833.
[508] Taylor 1836.
[509] Rosendahl 1907.
[510] Bitter 1899.
[511] Nilson 1903.
[512] Kajanus (Nilson) 1911.
[513] Zopf 1903.
[514] Zopf 1905².
[515] Bitter 1899.
[516] Swartz 1788.
[517] Gmelin 1791.
[518] Woodward 1797.
[519] Fries 1825.
[520] Nylander 1855.
[521] Mattirolo 1881.
[522] Johow 1884.
[523] Wainio 1890.
[524] Möller 1893.
[525] Malpighi 1686.
[526] Tournefort 1694.
[527] Morison 1699.
[528] Micheli 1729.
[529] Micheli, Pls. 52 and 56.
[530] Dillenius 1741.
[531] Linnaeus 1737.
[532] Necker 1771, p. 257.
[533] Scopoli 1772.
[534] Koelreuter 1777.
[535] Hoffmann 1784.
[536] Hedwig 1784.
[537] Acharius 1810.
[538] Hornschuch 1821.
[539] Wallroth 1825.
[506] Fries 1825.
[507] Hooker 1833.
[508] Taylor 1836.
[509] Rosendahl 1907.
[510] Bitter 1899.
[511] Nilson 1903.
[512] Kajanus (Nilson) 1911.
[513] Zopf 1903.
[514] Zopf 1905².
[515] Bitter 1899.
[516] Swartz 1788.
[517] Gmelin 1791.
[518] Woodward 1797.
[519] Fries 1825.
[520] Nylander 1855.
[521] Mattirolo 1881.
[522] Johow 1884.
[523] Wainio 1890.
[524] Möller 1893.
[525] Malpighi 1686.
[526] Tournefort 1694.
[527] Morison 1699.
[528] Micheli 1729.
[529] Micheli, Pls. 52 and 56.
[530] Dillenius 1741.
[531] Linnaeus 1737.
[532] Necker 1771, p. 257.
[533] Scopoli 1772.
[534] Koelreuter 1777.
[535] Hoffmann 1784.
[536] Hedwig 1784.
[537] Acharius 1810.
[538] Hornschuch 1821.
[539] Wallroth 1825.
Page 553
[540] Meyer 1825.
[541] Sprengel 1804.
[542] Luyken 1809.
[543] Persoon 1801.
[544] See also p. 166.
[545] Wainio 1890.
[546] Tulasne 1852.
[547] Fuisting 1868.
[548] Stahl 1877.
[549] Borzi 1878.
[550] Baur 1898.
[551] Fünfstück (1902) suggests that the lichen worked at by Baur is Collema
cheileum Ach.
[552] Krabbe 1883.
[553] Mäule 1891.
[554] F. Bachmann 1912.
[555] This species of Collema has been described as Collemodes
Bachmannianum by Bruce Fink 1918.
[556] F. Bachmann 1913.
[557] Wainio i. 1890.
[558] Wolff 1905.
[559] Stahl 1877.
[560] Forssell 1885².
[561] Zukal 1887, p. 42.
[562] Borzi 1878.
[563] Lindau 1888.
[564] Mäule 1891.
[565] Darbishire 1900.
[566] Baur 1904.
[567] Lindau 1888.
[568] Darbishire 1900.
[569] See also p. 180.
[570] Nienburg 1908.
[571] Wainio i. 1890.
[572] Darbishire 1900.
[541] Sprengel 1804.
[542] Luyken 1809.
[543] Persoon 1801.
[544] See also p. 166.
[545] Wainio 1890.
[546] Tulasne 1852.
[547] Fuisting 1868.
[548] Stahl 1877.
[549] Borzi 1878.
[550] Baur 1898.
[551] Fünfstück (1902) suggests that the lichen worked at by Baur is Collema
cheileum Ach.
[552] Krabbe 1883.
[553] Mäule 1891.
[554] F. Bachmann 1912.
[555] This species of Collema has been described as Collemodes
Bachmannianum by Bruce Fink 1918.
[556] F. Bachmann 1913.
[557] Wainio i. 1890.
[558] Wolff 1905.
[559] Stahl 1877.
[560] Forssell 1885².
[561] Zukal 1887, p. 42.
[562] Borzi 1878.
[563] Lindau 1888.
[564] Mäule 1891.
[565] Darbishire 1900.
[566] Baur 1904.
[567] Lindau 1888.
[568] Darbishire 1900.
[569] See also p. 180.
[570] Nienburg 1908.
[571] Wainio i. 1890.
[572] Darbishire 1900.
Page 554
[573] Baur 1901.
[574] Baur 1904.
[575] Nienburg 1908.
[576] Harper 1900.
[577] Guilliermond 1904, p. 60.
[578] Baur 1899.
[579] Sturgis 1890.
[580] Nienburg 1908.
[581] Schwendener 1864.
[582] Wahlberg 1902.
[583] Baur 1904.
[584] Brown 1911.
[585] Moreau 1916.
[586] Lindau 1888.
[587] Fünfstück 1884.
[588] Baur 1904.
[589] Nienburg 1908.
[590] Rosendahl 1907.
[591] Lindau 1888.
[592] Baur 1904.
[593] Wolff 1905.
[594] Fünfstück 1902.
[595] Krabbe 1882.
[596] Baur 1901.
[597] Fünfstück 1902.
[598] Darbishire 1897.
[599] See also p. 147.
[600] Wolff 1905.
[601] See Chap. VII.
[602] Krabbe 1883 and 1891.
[603] Baur 1904.
[604] Sättler 1914.
[605] See Chap. VII.
[606] Fuisting 1868.
[574] Baur 1904.
[575] Nienburg 1908.
[576] Harper 1900.
[577] Guilliermond 1904, p. 60.
[578] Baur 1899.
[579] Sturgis 1890.
[580] Nienburg 1908.
[581] Schwendener 1864.
[582] Wahlberg 1902.
[583] Baur 1904.
[584] Brown 1911.
[585] Moreau 1916.
[586] Lindau 1888.
[587] Fünfstück 1884.
[588] Baur 1904.
[589] Nienburg 1908.
[590] Rosendahl 1907.
[591] Lindau 1888.
[592] Baur 1904.
[593] Wolff 1905.
[594] Fünfstück 1902.
[595] Krabbe 1882.
[596] Baur 1901.
[597] Fünfstück 1902.
[598] Darbishire 1897.
[599] See also p. 147.
[600] Wolff 1905.
[601] See Chap. VII.
[602] Krabbe 1883 and 1891.
[603] Baur 1904.
[604] Sättler 1914.
[605] See Chap. VII.
[606] Fuisting 1868.
Page 555
[607] Stahl 1877.
[608] Baur 1904.
[609] Baur 1901.
[610] Krabbe 1882.
[611] Forssell 1883.
[612] Wainio 1890, p. x.
[613] Neubner 1893.
[614] Fünfstück 1884.
[615] Darbishire 1913.
[616] Moreau 1915.
[617] Sturgis 1890.
[618] Metzger 1903.
[619] Baur 1904.
[620] Moreau 1916.
[621] Krabbe 1882.
[622] Lindau 1899.
[623] Wolff 1905.
[624] Rosendahl 1907.
[625] Bitter 1901².
[626] Baur 1904.
[627] Nienburg 1908.
[628] Krabbe 1882.
[629] Schulte 1904.
[630] Wainio 1890.
[631] Schikorra 1909.
[632] Harper 1900.
[633] Fraser 1907.
[634] Thaxter 1912.
[635] Faull 1911.
[636] Dawson 1900.
[637] Brooks 1910.
[638] Blackman and Welsford 1912.
[639] Lindau 1899.
[640] Van Tieghem 1891.
[641] Zukal 1895.
[608] Baur 1904.
[609] Baur 1901.
[610] Krabbe 1882.
[611] Forssell 1883.
[612] Wainio 1890, p. x.
[613] Neubner 1893.
[614] Fünfstück 1884.
[615] Darbishire 1913.
[616] Moreau 1915.
[617] Sturgis 1890.
[618] Metzger 1903.
[619] Baur 1904.
[620] Moreau 1916.
[621] Krabbe 1882.
[622] Lindau 1899.
[623] Wolff 1905.
[624] Rosendahl 1907.
[625] Bitter 1901².
[626] Baur 1904.
[627] Nienburg 1908.
[628] Krabbe 1882.
[629] Schulte 1904.
[630] Wainio 1890.
[631] Schikorra 1909.
[632] Harper 1900.
[633] Fraser 1907.
[634] Thaxter 1912.
[635] Faull 1911.
[636] Dawson 1900.
[637] Brooks 1910.
[638] Blackman and Welsford 1912.
[639] Lindau 1899.
[640] Van Tieghem 1891.
[641] Zukal 1895.
Page 556
[642] Wainio 1890.
[643] Steiner 1901.
[644] See also Chap. VII.
[645] F. Bachmann 1913.
[646] Cutting 1909.
[647] Darbishire 1900.
[648] Baur 1904.
[649] See p. 161.
[650] Stahl 1877.
[651] Baur 1898.
[652] F. Bachmann 1912 and 1913.
[653] Darbishire 1900.
[654] Fitzpatrick 1918.
[655] Harper 1900.
[656] Fünfstück 1902.
[657] Schwendener 1864.
[658] Hue 1906.
[659] Lindau 1899.
[660] Hedwig 1784.
[661] Acharius 1803.
[662] Sprengel 1807.
[663] Luyken 1809.
[664] Eschweiler 1824.
[665] Fée 1824.
[666] Mohl 1833.
[667] Dangeard 1894.
[668] Baur 1904.
[669] Nienburg 1908.
[670] Maire 1903.
[671] Bachmann 1913.
[672] Mohl 1833.
[673] Zukal 1895.
[674] Fée 1824.
[675] Meyer 1825.
[676] Holle 1849.
[643] Steiner 1901.
[644] See also Chap. VII.
[645] F. Bachmann 1913.
[646] Cutting 1909.
[647] Darbishire 1900.
[648] Baur 1904.
[649] See p. 161.
[650] Stahl 1877.
[651] Baur 1898.
[652] F. Bachmann 1912 and 1913.
[653] Darbishire 1900.
[654] Fitzpatrick 1918.
[655] Harper 1900.
[656] Fünfstück 1902.
[657] Schwendener 1864.
[658] Hue 1906.
[659] Lindau 1899.
[660] Hedwig 1784.
[661] Acharius 1803.
[662] Sprengel 1807.
[663] Luyken 1809.
[664] Eschweiler 1824.
[665] Fée 1824.
[666] Mohl 1833.
[667] Dangeard 1894.
[668] Baur 1904.
[669] Nienburg 1908.
[670] Maire 1903.
[671] Bachmann 1913.
[672] Mohl 1833.
[673] Zukal 1895.
[674] Fée 1824.
[675] Meyer 1825.
[676] Holle 1849.
Page 557
[677] Tulasne 1852.
[678] De Bary 1866-1867.
[679] Haberlandt 1887.
[680] Zopf 1905.
[681] Massalongo 1852.
[682] Koerber 1855.
[683] Wainio 1. 1890, p. 113.
[684] Harper 1899.
[685] Hue 1911².
[686] Tulasne 1852.
[687] Bornet 1873.
[688] Bonnier 1889².
[689] Maire 1905.
[690] Neubner 1893.
[691] Brefeld 1889.
[692] See p. 143.
[693] Bornet 1873.
[694] Bornet’s observations have not been repeated, and it is possible that he
may have been dealing with a parasitic hyphomycetous fungus.
[695] Steiner 1901.
[696] Müller 1881.
[697] Wainio 1890, ii. p. 27.
[698] Fée 1873.
[699] Müller 1890.
[700] Tulasne 1851.
[701] Dillenius 1741.
[702] Hedwig 1784 and 1789.
[703] Acharius 1810.
[704] Fries 1831.
[705] Wallroth 1825.
[706] Schaerer 1823-1842.
[707] Flotow 1850.
[708] Itzigsohn 1850.
[709] Tulasne 1851.
[710] Tulasne 1852.
[678] De Bary 1866-1867.
[679] Haberlandt 1887.
[680] Zopf 1905.
[681] Massalongo 1852.
[682] Koerber 1855.
[683] Wainio 1. 1890, p. 113.
[684] Harper 1899.
[685] Hue 1911².
[686] Tulasne 1852.
[687] Bornet 1873.
[688] Bonnier 1889².
[689] Maire 1905.
[690] Neubner 1893.
[691] Brefeld 1889.
[692] See p. 143.
[693] Bornet 1873.
[694] Bornet’s observations have not been repeated, and it is possible that he
may have been dealing with a parasitic hyphomycetous fungus.
[695] Steiner 1901.
[696] Müller 1881.
[697] Wainio 1890, ii. p. 27.
[698] Fée 1873.
[699] Müller 1890.
[700] Tulasne 1851.
[701] Dillenius 1741.
[702] Hedwig 1784 and 1789.
[703] Acharius 1810.
[704] Fries 1831.
[705] Wallroth 1825.
[706] Schaerer 1823-1842.
[707] Flotow 1850.
[708] Itzigsohn 1850.
[709] Tulasne 1851.
[710] Tulasne 1852.
Page 558
[711] Lindsay 1859 and 1872.
[712] Forssell 1885.
[713] Nienburg 1908.
[714] Möller 1887.
[715] Sturgis 1890.
[716] Nylander 1858, pp. 34, 35.
[717] Nylander, Crombie and others apply the term “sterigma” to the whole
spermatiophore. In the more usual restricted sense, it refers only to the short
process from which the spermatium is abstricted.
[718] Glück 1899.
[719] Steiner 1901.
[720] Gibelli 1866.
[721] Tulasne 1852.
[722] Nylander 1858.
[723] Corda 1839.
[724] Allescher 1901-3.
[725] Keiszler 1911.
[726] Nylander 1858, p. 37.
[727] Möller 1887.
[728] Istvanffi 1895.
[729] Möller 1888.
[730] Hedlund 1892.
[731] Tulasne 1852.
[732] Müller 1885.
[733] Lindsay 1859 and 1872.
[734] Laubert 1911.
[735] Blackman 1904.
[736] Istvanffi 1895.
[737] Plowright 1889.
[738] Sappin-Trouffy 1896.
[739] Brefeld 1891.
[740] De Bary 1866, p. 7.
[741] Gilson 1893.
[742] Winterstein 1893.
[743] Gilson 1894.
[712] Forssell 1885.
[713] Nienburg 1908.
[714] Möller 1887.
[715] Sturgis 1890.
[716] Nylander 1858, pp. 34, 35.
[717] Nylander, Crombie and others apply the term “sterigma” to the whole
spermatiophore. In the more usual restricted sense, it refers only to the short
process from which the spermatium is abstricted.
[718] Glück 1899.
[719] Steiner 1901.
[720] Gibelli 1866.
[721] Tulasne 1852.
[722] Nylander 1858.
[723] Corda 1839.
[724] Allescher 1901-3.
[725] Keiszler 1911.
[726] Nylander 1858, p. 37.
[727] Möller 1887.
[728] Istvanffi 1895.
[729] Möller 1888.
[730] Hedlund 1892.
[731] Tulasne 1852.
[732] Müller 1885.
[733] Lindsay 1859 and 1872.
[734] Laubert 1911.
[735] Blackman 1904.
[736] Istvanffi 1895.
[737] Plowright 1889.
[738] Sappin-Trouffy 1896.
[739] Brefeld 1891.
[740] De Bary 1866, p. 7.
[741] Gilson 1893.
[742] Winterstein 1893.
[743] Gilson 1894.
Page 559
[744] The chemical formula of chitin is given as C₆₀H₁₀₀N₈O₃₈, that of
chitosan as C₁₄H₂₆N₂O₁₀.
[745] Escombe 1896.
[746] Wisselingh 1898.
[747] Wester 1909.
[748] Berzelius 1813.
[749] Guérin-Varry 1834.
[750] Mulder 1838.
[751] Berg 1873.
[752] Beilstein ex Errera 1882, p. 16 (note).
[753] Escombe 1896.
[754] Wiesner 1900.
[755] Lacour 1880.
[756] Wisselingh 1898.
[757] Stüde 1864.
[758] Czapek 1905, i. p. 515.
[759] Ulander 1905.
[760] Müller 1905.
[761] Stüde 1864.
[762] Wisselingh 1898.
[763] Schellenberg 1896.
[764] Escombe 1896.
[765] Wester 1909.
[766] Czapek 1905, i. p. 515.
[767] Moreau 1916.
[768] Errera 1882.
[769] Schwendener 1862, p. 231.
[770] De Bary 1866-1867, p. 211.
[771] Gautier 1899.
[772] Herissey 1898.
[773] Czapek 1905, ii. p. 257.
[774] Ronceray 1904.
[775] Zopf in Schenk 1890, p. 448.
[776] Knop 1872.
[777] Zopf 1907.
chitosan as C₁₄H₂₆N₂O₁₀.
[745] Escombe 1896.
[746] Wisselingh 1898.
[747] Wester 1909.
[748] Berzelius 1813.
[749] Guérin-Varry 1834.
[750] Mulder 1838.
[751] Berg 1873.
[752] Beilstein ex Errera 1882, p. 16 (note).
[753] Escombe 1896.
[754] Wiesner 1900.
[755] Lacour 1880.
[756] Wisselingh 1898.
[757] Stüde 1864.
[758] Czapek 1905, i. p. 515.
[759] Ulander 1905.
[760] Müller 1905.
[761] Stüde 1864.
[762] Wisselingh 1898.
[763] Schellenberg 1896.
[764] Escombe 1896.
[765] Wester 1909.
[766] Czapek 1905, i. p. 515.
[767] Moreau 1916.
[768] Errera 1882.
[769] Schwendener 1862, p. 231.
[770] De Bary 1866-1867, p. 211.
[771] Gautier 1899.
[772] Herissey 1898.
[773] Czapek 1905, ii. p. 257.
[774] Ronceray 1904.
[775] Zopf in Schenk 1890, p. 448.
[776] Knop 1872.
[777] Zopf 1907.
Page 560
[778] Hamlet and Plowright 1877.
[779] Braconnot 1825.
[780] Zopf 1907.
[781] Errera 1893.
[782] Euler 1908, p. 7.
[783] Rosendahl 1907.
[784] Knop 1872.
[785] Kratzmann 1913.
[786] Zukal 1895, p. 1311.
[787] Kerner and Oliver 1894, p. 235.
[788] Steiner 1881.
[789] Zukal 1884.
[790] Zukal 1886.
[791] Hulth 1891.
[792] Bachmann 1892.
[793] Fünfstück 1895.
[794] Fünfstück 1899.
[795] Bachmann 1904¹.
[796] Lang 1906.
[797] Lang 1906, p. 171.
[798] Bachmann 1892.
[799] Bachmann 1904¹.
[800] Bachmann 1904².
[801] Fünfstück 1895.
[802] Zukal 1895, p. 1372.
[803] Rosendahl 1907.
[804] Zukal 1895.
[805] Fünfstück 1896.
[806] Fünfstück 1899.
[807] Lang 1906.
[808] Beijerinck 1904.
[809] Wehmer 1891.
[810] Stahel 1911.
[811] See p. 218.
[812] Pfeffer 1877.
[779] Braconnot 1825.
[780] Zopf 1907.
[781] Errera 1893.
[782] Euler 1908, p. 7.
[783] Rosendahl 1907.
[784] Knop 1872.
[785] Kratzmann 1913.
[786] Zukal 1895, p. 1311.
[787] Kerner and Oliver 1894, p. 235.
[788] Steiner 1881.
[789] Zukal 1884.
[790] Zukal 1886.
[791] Hulth 1891.
[792] Bachmann 1892.
[793] Fünfstück 1895.
[794] Fünfstück 1899.
[795] Bachmann 1904¹.
[796] Lang 1906.
[797] Lang 1906, p. 171.
[798] Bachmann 1892.
[799] Bachmann 1904¹.
[800] Bachmann 1904².
[801] Fünfstück 1895.
[802] Zukal 1895, p. 1372.
[803] Rosendahl 1907.
[804] Zukal 1895.
[805] Fünfstück 1896.
[806] Fünfstück 1899.
[807] Lang 1906.
[808] Beijerinck 1904.
[809] Wehmer 1891.
[810] Stahel 1911.
[811] See p. 218.
[812] Pfeffer 1877.
Page 561
[813] Pfaff 1826.
[814] Herberger 1830.
[815] Knop and Schnederman 1846.
[816] Hesse 1904.
[817] Zopf 1907, p. 179.
[818] Zopf 1907.
[819] Senft 1907.
[820] Tobler 1909.
[821] Keegan 1907.
[822] Schwarz 1880, p. 264.
[823] Schwendener 1863, p. 180.
[824] Fünfstück 1902.
[825] Heber Howe 1913.
[826] Knowles 1913.
[827] West, W. 1905.
[828] Lettau 1914.
[829] Lettau 1914.
[830] Parietin differs chemically from chrysophanic acid of Rheum, etc.
[831] Stenhouse and Groves 1877.
[832] Volkard 1894.
[833] Nylander 1866.
[834] Jumelle 1892.
[835] Sievers 1908.
[836] Zukal 1895.
[837] Beckmann 1907.
[838] Herre 1911².
[839] Sievers 1908.
[840] Jumelle 1892.
[841] Schrenk 1898.
[842] Bonnier 1889².
[843] West 1905.
[844] Sandstede 1904.
[845] Friedrich 1906.
[846] Lindau 1895².
[847] See p. 109.
[814] Herberger 1830.
[815] Knop and Schnederman 1846.
[816] Hesse 1904.
[817] Zopf 1907, p. 179.
[818] Zopf 1907.
[819] Senft 1907.
[820] Tobler 1909.
[821] Keegan 1907.
[822] Schwarz 1880, p. 264.
[823] Schwendener 1863, p. 180.
[824] Fünfstück 1902.
[825] Heber Howe 1913.
[826] Knowles 1913.
[827] West, W. 1905.
[828] Lettau 1914.
[829] Lettau 1914.
[830] Parietin differs chemically from chrysophanic acid of Rheum, etc.
[831] Stenhouse and Groves 1877.
[832] Volkard 1894.
[833] Nylander 1866.
[834] Jumelle 1892.
[835] Sievers 1908.
[836] Zukal 1895.
[837] Beckmann 1907.
[838] Herre 1911².
[839] Sievers 1908.
[840] Jumelle 1892.
[841] Schrenk 1898.
[842] Bonnier 1889².
[843] West 1905.
[844] Sandstede 1904.
[845] Friedrich 1906.
[846] Lindau 1895².
[847] See p. 109.
Page 562
[848] Uloth 1861.
[849] Zopf 1903.
[850] Zopf 1907.
[851] Ohlert 1871.
[852] See p. 75.
[853] Uloth 1861.
[854] Egeling 1881.
[855] Buchet 1890.
[856] Bachmann 1904.
[857] Bachmann 1911.
[858] Lang 1903.
[859] Stahlecker 1906.
[860] Bitter 1899.
[861] Zukal 1879.
[862] Kihlman 1890.
[863] Jumelle 1892.
[864] Zopf 1890, p. 489.
[865] Jumelle 1892.
[866] Weir 1919.
[867] Wainio 1897, p. 16.
[868] Nienburg 1908.
[869] Metzger 1903.
[870] Bitter 1899.
[871] Wiesner 1895.
[872] Bitter 1901, p. 465.
[873] Fink 1909.
[874] Galløe 1908.
[875] Zukal 1896.
[876] Bitter 1901.
[877] Maheu 1906.
[878] Wiesner 1895.
[879] R. Paulson, ined.
[880] Krempelhuber 1861.
[881] Zukal 1896, p. 111.
[882] Zukal 1896.
[849] Zopf 1903.
[850] Zopf 1907.
[851] Ohlert 1871.
[852] See p. 75.
[853] Uloth 1861.
[854] Egeling 1881.
[855] Buchet 1890.
[856] Bachmann 1904.
[857] Bachmann 1911.
[858] Lang 1903.
[859] Stahlecker 1906.
[860] Bitter 1899.
[861] Zukal 1879.
[862] Kihlman 1890.
[863] Jumelle 1892.
[864] Zopf 1890, p. 489.
[865] Jumelle 1892.
[866] Weir 1919.
[867] Wainio 1897, p. 16.
[868] Nienburg 1908.
[869] Metzger 1903.
[870] Bitter 1899.
[871] Wiesner 1895.
[872] Bitter 1901, p. 465.
[873] Fink 1909.
[874] Galløe 1908.
[875] Zukal 1896.
[876] Bitter 1901.
[877] Maheu 1906.
[878] Wiesner 1895.
[879] R. Paulson, ined.
[880] Krempelhuber 1861.
[881] Zukal 1896, p. 111.
[882] Zukal 1896.
Page 563
[883] Hedlund 1892, p. 22.
[884] Zopf 1893.
[885] Zopf 1907.
[886] Zopf 1892.
[887] Knop 1872.
[888] Bachmann 1890.
[889] A similar reaction with nitric acid is produced on the blue hypothalline
hyphae of Placynthium nigrum.
[890] Knowles 1915.
[891] Rosendahl 1907.
[892] John 1819.
[893] Grimbel 1856.
[894] Molisch 1892.
[895] Nilson 1907.
[896] Meyer 1825, p. 44.
[897] Lindsay 1856.
[898] Berkeley 1857.
[899] Weddell 1869.
[900] Phillips 1878.
[901] Scott Elliot 1907.
[902] Vallot 1896.
[903] Bitter 1901.
[904] Heere 1904.
[905] Krabbe 1891, p. 131.
[906] Reinke 1894, p. 18.
[907] Bonnier, see p. 29.
[908] Darbishire, see p. 148.
[909] Tobler, see p. 148.
[910] Stahl 1877, p. 34.
[911] Paulson 1918.
[912] Paulson and Thompson 1913.
[913] Fink 1917.
[914] Baur 1901.
[915] Miyoshi 1901.
[916] Darbishire 1897, p. 657.
[884] Zopf 1893.
[885] Zopf 1907.
[886] Zopf 1892.
[887] Knop 1872.
[888] Bachmann 1890.
[889] A similar reaction with nitric acid is produced on the blue hypothalline
hyphae of Placynthium nigrum.
[890] Knowles 1915.
[891] Rosendahl 1907.
[892] John 1819.
[893] Grimbel 1856.
[894] Molisch 1892.
[895] Nilson 1907.
[896] Meyer 1825, p. 44.
[897] Lindsay 1856.
[898] Berkeley 1857.
[899] Weddell 1869.
[900] Phillips 1878.
[901] Scott Elliot 1907.
[902] Vallot 1896.
[903] Bitter 1901.
[904] Heere 1904.
[905] Krabbe 1891, p. 131.
[906] Reinke 1894, p. 18.
[907] Bonnier, see p. 29.
[908] Darbishire, see p. 148.
[909] Tobler, see p. 148.
[910] Stahl 1877, p. 34.
[911] Paulson 1918.
[912] Paulson and Thompson 1913.
[913] Fink 1917.
[914] Baur 1901.
[915] Miyoshi 1901.
[916] Darbishire 1897, p. 657.
Page 564
[917] Beckmann 1907.
[918] Bitter 1899.
[919] Peirce 1898.
[920] Schrenk 1898.
[921] Elenkin 1901.
[922] See Chap. X.
[923] Mereschkovsky 1918.
[924] Meyer 1825, p. 44.
[925] Paulson and Somerville Hastings 1914.
[926] Crombie 1872.
[927] See p. 35.
[928] Dufrenoy 1918.
[929] Arnold 1874.
[930] Kupfer 1894.
[931] See p. 236.
[932] Malme 1895.
[933] Bitter 1899.
[934] Hofmann 1906.
[935] Almquist 1880.
[936] Bitter 1899.
[937] See p. 237.
[938] Arnold 1874.
[939] Nylander 1852.
[940] Hue 1915.
[941] Th. Fries 1874, p. 343.
[942] Tobler 1911².
[943] Lindsay 1869².
[944] Winter 1877.
[945] Abrothallus has been included in the lichen genus Buellia.
[946] Tulasne 1852.
[947] Lindsay 1856.
[948] Crombie 1894.
[949] Kotte 1910.
[950] Zopf 1896.
[951] Zopf 1898, p. 249.
[918] Bitter 1899.
[919] Peirce 1898.
[920] Schrenk 1898.
[921] Elenkin 1901.
[922] See Chap. X.
[923] Mereschkovsky 1918.
[924] Meyer 1825, p. 44.
[925] Paulson and Somerville Hastings 1914.
[926] Crombie 1872.
[927] See p. 35.
[928] Dufrenoy 1918.
[929] Arnold 1874.
[930] Kupfer 1894.
[931] See p. 236.
[932] Malme 1895.
[933] Bitter 1899.
[934] Hofmann 1906.
[935] Almquist 1880.
[936] Bitter 1899.
[937] See p. 237.
[938] Arnold 1874.
[939] Nylander 1852.
[940] Hue 1915.
[941] Th. Fries 1874, p. 343.
[942] Tobler 1911².
[943] Lindsay 1869².
[944] Winter 1877.
[945] Abrothallus has been included in the lichen genus Buellia.
[946] Tulasne 1852.
[947] Lindsay 1856.
[948] Crombie 1894.
[949] Kotte 1910.
[950] Zopf 1896.
[951] Zopf 1898, p. 249.
Page 565
[952] Tobler 1911².
[953] See p. 276.
[954] Elenkin 1901².
[955] Stahl 1904.
[956] Lindsay 1859, 1869, 1871.
[957] Zopf 1896.
[958] Zopf 1898.
[959] Moreau 1916³.
[960] Vouaux 1912, etc.
[961] Bitter 1904.
[962] Zukal 1893.
[963] Lister 1911.
[964] Zopf 1897.
[965] Zukal 1896, p. 258.
[966] Zukal 1896, p. 255.
[967] Cunningham 1879.
[968] Friedrich 1906, p. 401.
[969] See p. 78.
[970] Gleditsch 1775, p. 31.
[971] Lindau 1895, p. 53.
[972] Dufrenoy 1881.
[973] Porter 1917.
[974] Friedrich 1906.
[975] Waite 1893.
[976] Lesdain 1912.
[977] Zopf 1907.
[978] Lesdain 1910.
[979] Zukal 1896, p. 258.
[980] See p. 51.
[981] See p. 177 et seq.
[982] Zahlbruckner 1903.
[983] Steiner 1896.
[984] Müller-Argau 1880.
[985] Wainio 1890, p. xxiii.
[986] Lloyd 1917.
[953] See p. 276.
[954] Elenkin 1901².
[955] Stahl 1904.
[956] Lindsay 1859, 1869, 1871.
[957] Zopf 1896.
[958] Zopf 1898.
[959] Moreau 1916³.
[960] Vouaux 1912, etc.
[961] Bitter 1904.
[962] Zukal 1893.
[963] Lister 1911.
[964] Zopf 1897.
[965] Zukal 1896, p. 258.
[966] Zukal 1896, p. 255.
[967] Cunningham 1879.
[968] Friedrich 1906, p. 401.
[969] See p. 78.
[970] Gleditsch 1775, p. 31.
[971] Lindau 1895, p. 53.
[972] Dufrenoy 1881.
[973] Porter 1917.
[974] Friedrich 1906.
[975] Waite 1893.
[976] Lesdain 1912.
[977] Zopf 1907.
[978] Lesdain 1910.
[979] Zukal 1896, p. 258.
[980] See p. 51.
[981] See p. 177 et seq.
[982] Zahlbruckner 1903.
[983] Steiner 1896.
[984] Müller-Argau 1880.
[985] Wainio 1890, p. xxiii.
[986] Lloyd 1917.
Page 566
[987] Rehm 1890.
[988] Reinke 1894.
[989] See p. 260.
[990] Wainio 1890.
[991] Müller-Argau 1862.
[992] Rehm 1890.
[993] Rehm 1890.
[994] Tobler 1911², p. 407.
[995] Lightfoot 1777, p. 965.
[996] See Chap. III.
[997] Forssell 1885.
[998] Hue 1911¹.
[999] See p. 133.
[1000] Zahlbruckner 1907.
[1001] Reinke 1895.
[1002] See p. 126.
[1003] Reinke 1895.
[1004] Neubner 1893.
[1005] Reinke 1895, p. 110.
[1006] Wainio 1890.
[1007] See Chap. III.
[1008] Wainio 1897.
[1009] See Chap. III.
[1010] Sättler 1914.
[1011] See p. 90.
[1012] Darbishire 1912.
[1013] See p. 101.
[1014] See p. 188.
[1015] Dr Church (1920) has published a new conception of the origin of
lichens. See postscript at the end of the volume, p. 421.
[1016] Tournefort 1694.
[1017] Morison 1699.
[1018] Dillenius 1741.
[1019] Linnaeus 1753.
[1020] Acharius 1803.
[988] Reinke 1894.
[989] See p. 260.
[990] Wainio 1890.
[991] Müller-Argau 1862.
[992] Rehm 1890.
[993] Rehm 1890.
[994] Tobler 1911², p. 407.
[995] Lightfoot 1777, p. 965.
[996] See Chap. III.
[997] Forssell 1885.
[998] Hue 1911¹.
[999] See p. 133.
[1000] Zahlbruckner 1907.
[1001] Reinke 1895.
[1002] See p. 126.
[1003] Reinke 1895.
[1004] Neubner 1893.
[1005] Reinke 1895, p. 110.
[1006] Wainio 1890.
[1007] See Chap. III.
[1008] Wainio 1897.
[1009] See Chap. III.
[1010] Sättler 1914.
[1011] See p. 90.
[1012] Darbishire 1912.
[1013] See p. 101.
[1014] See p. 188.
[1015] Dr Church (1920) has published a new conception of the origin of
lichens. See postscript at the end of the volume, p. 421.
[1016] Tournefort 1694.
[1017] Morison 1699.
[1018] Dillenius 1741.
[1019] Linnaeus 1753.
[1020] Acharius 1803.
Page 567
[1021] Acharius 1810.
[1022] Acharius 1814.
[1023] Wallroth 1825.
[1024] Meyer 1825.
[1025] Nylander 1854.
[1026] Reinke 1894, ’95, ’96.
[1027] Darbishire and Fischer-Benzon 1901.
[1028] Wainio 1887, ’94, ’97.
[1029] Wainio 1890.
[1030] Zahlbruckner 1907.
[1031] Massee 1887.
[1032] Fischer 1890.
[1033] Linnaeus 1753.
[1034] Steiner 1901.
[1035] See p. 56.
[1036] Norman 1872 and ’74.
[1037] Genera marked with an asterisk have not been found in the British
Isles.
[1038] Zukal 1890.
[1039] Hue 1914.
[1040] Hue 1909.
[1041] Hue 1905.
[1042] Zahlbr., in Hedwigia, lix. p. 301, 1917.
[1043] Riddle 1917.
[1044] Bioret 1914.
[1045] Reinke 1895.
[1046] Darbishire 1898.
[1047] Hue 1909.
[1048] Nylander 1855.
[1049] Nylander 1883.
[1050] Lorrain Smith 1906.
[1051] Neophyllis Wils. is synonymous with Gymnoderma.
[1052] Lindau 1899.
[1053] Stirton 1877, p. 164.
[1054] A. Zahlbruckner, in Oesterr. bot. Zeitschr. 1919, p. 163.
[1022] Acharius 1814.
[1023] Wallroth 1825.
[1024] Meyer 1825.
[1025] Nylander 1854.
[1026] Reinke 1894, ’95, ’96.
[1027] Darbishire and Fischer-Benzon 1901.
[1028] Wainio 1887, ’94, ’97.
[1029] Wainio 1890.
[1030] Zahlbruckner 1907.
[1031] Massee 1887.
[1032] Fischer 1890.
[1033] Linnaeus 1753.
[1034] Steiner 1901.
[1035] See p. 56.
[1036] Norman 1872 and ’74.
[1037] Genera marked with an asterisk have not been found in the British
Isles.
[1038] Zukal 1890.
[1039] Hue 1914.
[1040] Hue 1909.
[1041] Hue 1905.
[1042] Zahlbr., in Hedwigia, lix. p. 301, 1917.
[1043] Riddle 1917.
[1044] Bioret 1914.
[1045] Reinke 1895.
[1046] Darbishire 1898.
[1047] Hue 1909.
[1048] Nylander 1855.
[1049] Nylander 1883.
[1050] Lorrain Smith 1906.
[1051] Neophyllis Wils. is synonymous with Gymnoderma.
[1052] Lindau 1899.
[1053] Stirton 1877, p. 164.
[1054] A. Zahlbruckner, in Oesterr. bot. Zeitschr. 1919, p. 163.
Page 568
[1055] Bitter 1904².
[1056] Hue 1892.
[1057] Hue 1914.
[1058] Tuckerman 1872, p. 107.
[1059] See p. 188.
[1060] Hue 1908.
[1061] See p. 152.
[1062] Olivier 1907.
[1063] Th. Fries 1867.
[1064] Darbishire 1909.
[1065] Hue 1892.
[1066] Arnold 1890.
[1067] These genera are associated with Trentepohlia algae which are
numerous and abundant in tropical climates, and their presence there may
possibly account for these particular lichens.
[1068] Wainio 1897.
[1069] Wainio 1909.
[1070] Elenkin 1906.
[1071] Darbishire 1905.
[1072] Hue 1915.
[1073] Darbishire 1912.
[1074] Lindsay 1870.
[1075] Calkins 1896.
[1076] Hue 1898.
[1077] Fink 1903.
[1078] Wainio 1896.
[1079] Comm. Heber Howe.
[1080] Herre 1910.
[1081] Nylander 1890.
[1082] Müller 1879.
[1083] Nylander and Crombie 1884.
[1084] Babington 1855.
[1085] Stirton 1875.
[1086] Nylander 1888.
[1087] Hellbom 1896.
[1088] Wilson 1892.
[1056] Hue 1892.
[1057] Hue 1914.
[1058] Tuckerman 1872, p. 107.
[1059] See p. 188.
[1060] Hue 1908.
[1061] See p. 152.
[1062] Olivier 1907.
[1063] Th. Fries 1867.
[1064] Darbishire 1909.
[1065] Hue 1892.
[1066] Arnold 1890.
[1067] These genera are associated with Trentepohlia algae which are
numerous and abundant in tropical climates, and their presence there may
possibly account for these particular lichens.
[1068] Wainio 1897.
[1069] Wainio 1909.
[1070] Elenkin 1906.
[1071] Darbishire 1905.
[1072] Hue 1915.
[1073] Darbishire 1912.
[1074] Lindsay 1870.
[1075] Calkins 1896.
[1076] Hue 1898.
[1077] Fink 1903.
[1078] Wainio 1896.
[1079] Comm. Heber Howe.
[1080] Herre 1910.
[1081] Nylander 1890.
[1082] Müller 1879.
[1083] Nylander and Crombie 1884.
[1084] Babington 1855.
[1085] Stirton 1875.
[1086] Nylander 1888.
[1087] Hellbom 1896.
[1088] Wilson 1892.
Page 569
[1089] Müller-Argau 1884.
[1090] Stizenberger 1888-1895.
[1091] Steiner 1895.
[1092] Flagey 1892.
[1093] Wainio 1890.
[1094] Wainio 1890, ii. p. 27 (recorded under Lecidea).
[1095] Elenkin and Woronichin 1908.
[1096] Jaczewski 1904.
[1097] Steiner 1919.
[1098] Müller 1892.
[1099] Nylander 1867.
[1100] Leighton 1869.
[1101] Nylander 1900.
[1102] Nylander 1891.
[1103] Schimper 1869, p. 145.
[1104] Lindsay 1879.
[1105] Braun 1840.
[1106] Muenster 1846, p. 26.
[1107] Eltingshausen and Debey 1857.
[1108] Engelhardt 1870 (Pl. I. figs. 1 and 2).
[1109] Goeppert 1845, p. 195.
[1110] See Schimper 1869, pp. 145, etc.
[1111] Goeppert and Menge 1883, t. 1, fig. 3.
[1112] Ludwig 1859, p. 61 (t. 9, figs. 1-4), 1859-61.
[1113] Schimper in Zittel 1890.
[1114] Goeppert and Menge 1883.
[1115] Sernander 1918.
[1116] See p. 392.
[1117] Moss 1913.
[1118] Macmillan 1894.
[1119] See p. 240 et seq.
[1120] See p. 238.
[1121] West 1915.
[1122] Fink 1894.
[1123] Kihlman 1890.
[1090] Stizenberger 1888-1895.
[1091] Steiner 1895.
[1092] Flagey 1892.
[1093] Wainio 1890.
[1094] Wainio 1890, ii. p. 27 (recorded under Lecidea).
[1095] Elenkin and Woronichin 1908.
[1096] Jaczewski 1904.
[1097] Steiner 1919.
[1098] Müller 1892.
[1099] Nylander 1867.
[1100] Leighton 1869.
[1101] Nylander 1900.
[1102] Nylander 1891.
[1103] Schimper 1869, p. 145.
[1104] Lindsay 1879.
[1105] Braun 1840.
[1106] Muenster 1846, p. 26.
[1107] Eltingshausen and Debey 1857.
[1108] Engelhardt 1870 (Pl. I. figs. 1 and 2).
[1109] Goeppert 1845, p. 195.
[1110] See Schimper 1869, pp. 145, etc.
[1111] Goeppert and Menge 1883, t. 1, fig. 3.
[1112] Ludwig 1859, p. 61 (t. 9, figs. 1-4), 1859-61.
[1113] Schimper in Zittel 1890.
[1114] Goeppert and Menge 1883.
[1115] Sernander 1918.
[1116] See p. 392.
[1117] Moss 1913.
[1118] Macmillan 1894.
[1119] See p. 240 et seq.
[1120] See p. 238.
[1121] West 1915.
[1122] Fink 1894.
[1123] Kihlman 1890.
Page 570
[1124] Nilson 1907.
[1125] Lindsay 1869.
[1126] Sättler 1914.
[1127] Peirce 1898.
[1128] Schrenk 1898.
[1129] Nylander 1866.
[1130] Hue 1898.
[1131] Wheldon and Wilson 1915.
[1132] Paulson and Thompson 1911.
[1133] Paulson and Thompson 1912.
[1134] Chodat 1912.
[1135] Fée 1824.
[1136] Fries 1831.
[1137] Krempelhuber 1861.
[1138] Arnold 1891, etc.
[1139] Fink 1902.
[1140] Watson 1909.
[1141] Paulson 1919.
[1142] Lesdain 1912.
[1143] Fink 1896, etc.
[1144] Stahl 1877.
[1125] Lindsay 1869.
[1126] Sättler 1914.
[1127] Peirce 1898.
[1128] Schrenk 1898.
[1129] Nylander 1866.
[1130] Hue 1898.
[1131] Wheldon and Wilson 1915.
[1132] Paulson and Thompson 1911.
[1133] Paulson and Thompson 1912.
[1134] Chodat 1912.
[1135] Fée 1824.
[1136] Fries 1831.
[1137] Krempelhuber 1861.
[1138] Arnold 1891, etc.
[1139] Fink 1902.
[1140] Watson 1909.
[1141] Paulson 1919.
[1142] Lesdain 1912.
[1143] Fink 1896, etc.
[1144] Stahl 1877.
Page 571
[1145] Fink 1902, etc.
[1146] Arnold 1891.
[1147] Mayfield 1916.
[1148] Paulson and Thompson 1913.
[1149] Lesdain 1910².
[1150] Lettau 1911.
[1151] Fink 1903.
[1152] Wheldon and Wilson 1907.
[1153] Arnold 1892, p. 34.
[1154] Wheldon and Wilson 1915.
[1155] See p. 358.
[1156] Aigret 1901.
[1157] Kieffer 1894.
[1158] Stahlecker 1906.
[1159] Link 1795.
[1160] Malinowski 1911.
[1161] See also p. 254.
[1162] Fink 1904.
[1163] Link 1789.
[1164] Watson 1918².
[1165] Wheldon and Wilson 1907.
[1166] Flagey 1901.
[1167] Bruce Fink 1902².
[1168] Forssell 1885.
[1169] Servit 1910.
[1170] Malinowski 1911.
[1171] Bachmann 1914.
[1172] West 1912.
[1173] Wheldon and Wilson 1913.
[1174] Stahlecker 1906.
[1175] Malinowski 1911.
[1176] Wheldon and Wilson 1915.
[1177] Wheldon and Wilson 1907.
[1178] Schade 1916.
[1146] Arnold 1891.
[1147] Mayfield 1916.
[1148] Paulson and Thompson 1913.
[1149] Lesdain 1910².
[1150] Lettau 1911.
[1151] Fink 1903.
[1152] Wheldon and Wilson 1907.
[1153] Arnold 1892, p. 34.
[1154] Wheldon and Wilson 1915.
[1155] See p. 358.
[1156] Aigret 1901.
[1157] Kieffer 1894.
[1158] Stahlecker 1906.
[1159] Link 1795.
[1160] Malinowski 1911.
[1161] See also p. 254.
[1162] Fink 1904.
[1163] Link 1789.
[1164] Watson 1918².
[1165] Wheldon and Wilson 1907.
[1166] Flagey 1901.
[1167] Bruce Fink 1902².
[1168] Forssell 1885.
[1169] Servit 1910.
[1170] Malinowski 1911.
[1171] Bachmann 1914.
[1172] West 1912.
[1173] Wheldon and Wilson 1913.
[1174] Stahlecker 1906.
[1175] Malinowski 1911.
[1176] Wheldon and Wilson 1915.
[1177] Wheldon and Wilson 1907.
[1178] Schade 1916.
Page 572
[1179] Lesdain 1910.
[1180] Arnold 1858.
[1181] Richard 1877.
[1182] Darbishire 1909.
[1183] Cf. p. 234.
[1184] Paulson and Thompson 1913.
[1185] Wheldon and Wilson 1913.
[1186] Weddell 1875.
[1187] Knowles 1913.
[1188] The two morphologically similar plants Ramalina cuspidata and R.
scopulorum are here united under the older name R. siliquosa. The distinction
between the two is based on reaction tests with potash, which give very
uncertain results.
[1189] Nylander 1861.
[1190] Knowles 1915.
[1191] Wheldon and Wilson 1913.
[1192] Sandstede 1904.
[1193] Aigret 1901.
[1194] Wheldon and Wilson 1915.
[1195] Watson 1918¹.
[1196] Sandstede 1904.
[1197] McLean 1915.
[1198] Wheldon and Wilson 1915.
[1199] Wheldon and Wilson 1914.
[1200] Maheu 1887.
[1201] Leighton 1867.
[1202] Kihlman 1890.
[1203] Nilson 1907.
[1204] Darbishire 1909.
[1205] Flagey 1901.
[1206] Patouillard 1897.
[1207] Steiner 1895.
[1208] Bruce Fink 1909.
[1209] Herre 1911².
[1210] See p. 97.
[1211] Lindsay 1856.
[1180] Arnold 1858.
[1181] Richard 1877.
[1182] Darbishire 1909.
[1183] Cf. p. 234.
[1184] Paulson and Thompson 1913.
[1185] Wheldon and Wilson 1913.
[1186] Weddell 1875.
[1187] Knowles 1913.
[1188] The two morphologically similar plants Ramalina cuspidata and R.
scopulorum are here united under the older name R. siliquosa. The distinction
between the two is based on reaction tests with potash, which give very
uncertain results.
[1189] Nylander 1861.
[1190] Knowles 1915.
[1191] Wheldon and Wilson 1913.
[1192] Sandstede 1904.
[1193] Aigret 1901.
[1194] Wheldon and Wilson 1915.
[1195] Watson 1918¹.
[1196] Sandstede 1904.
[1197] McLean 1915.
[1198] Wheldon and Wilson 1915.
[1199] Wheldon and Wilson 1914.
[1200] Maheu 1887.
[1201] Leighton 1867.
[1202] Kihlman 1890.
[1203] Nilson 1907.
[1204] Darbishire 1909.
[1205] Flagey 1901.
[1206] Patouillard 1897.
[1207] Steiner 1895.
[1208] Bruce Fink 1909.
[1209] Herre 1911².
[1210] See p. 97.
[1211] Lindsay 1856.
Page 573
[1212] Macmillan 1894.
[1213] Knowles in litt.
[1214] Bruce Fink 1903.
[1215] Lettau 1911.
[1216] Wheldon and Wilson 1915.
[1217] Wheldon and Wilson 1913.
[1218] Linnaeus 1762.
[1219] Guembel 1856.
[1220] Goeppert 1860.
[1221] Salter 1856.
[1222] Bachmann 1911.
[1223] Bachmann 1913.
[1224] Braun 1917.
[1225] Treub 1888.
[1226] Brez 1791.
[1227] Persoon 1794.
[1228] Zukal 1895, p. 1317 (note).
[1229] Zukal 1895, p. 1315.
[1230] Zopf 1896.
[1231] Stahl 1904.
[1232] Hue 1915.
[1233] Zopf 1907.
[1234] Bitter 1899.
[1235] Petch 1913.
[1236] Paulson and Thompson 1913.
[1237] Michael 1884.
[1238] Zopf 1907.
[1239] Lesdain 1910.
[1240] Wheldon 1914.
[1241] See also p. 267.
[1242] Paulson and Thompson 1913.
[1243] Stone 1896.
[1244] Tutt 1900, p. 107.
[1245] Zopf 1907, p. 372.
[1246] Kihlman 1890.
[1213] Knowles in litt.
[1214] Bruce Fink 1903.
[1215] Lettau 1911.
[1216] Wheldon and Wilson 1915.
[1217] Wheldon and Wilson 1913.
[1218] Linnaeus 1762.
[1219] Guembel 1856.
[1220] Goeppert 1860.
[1221] Salter 1856.
[1222] Bachmann 1911.
[1223] Bachmann 1913.
[1224] Braun 1917.
[1225] Treub 1888.
[1226] Brez 1791.
[1227] Persoon 1794.
[1228] Zukal 1895, p. 1317 (note).
[1229] Zukal 1895, p. 1315.
[1230] Zopf 1896.
[1231] Stahl 1904.
[1232] Hue 1915.
[1233] Zopf 1907.
[1234] Bitter 1899.
[1235] Petch 1913.
[1236] Paulson and Thompson 1913.
[1237] Michael 1884.
[1238] Zopf 1907.
[1239] Lesdain 1910.
[1240] Wheldon 1914.
[1241] See also p. 267.
[1242] Paulson and Thompson 1913.
[1243] Stone 1896.
[1244] Tutt 1900, p. 107.
[1245] Zopf 1907, p. 372.
[1246] Kihlman 1890.
Page 574
[1247] Linnaeus 1762.
[1248] Johnson 1861.
[1249] Lindsay 1856.
[1250] Willemet 1787.
[1251] Keller 1866.
[1252] Proust 1906.
[1253] Johnson 1861.
[1254] Church 1880.
[1255] Brown 1898.
[1256] Hutchinson 1916.
[1257] Forskål 1875, p. 193.
[1258] Watt 1890.
[1259] Calkins 1892.
[1260] Miyoshi 1893.
[1261] See p. 422.
[1262] Eversmann 1825.
[1263] Berkeley 1849.
[1264] Visiani 1867.
[1265] Errera 1893.
[1266] Müller-Argau 1881, p. 526.
[1267] See p. 138.
[1268] From an examination of old figures of the Muscus cranii, Arnold
(1892, p. 53) has decided that several kinds of lichens or hepatics are included in
this designation.
[1269] Parkinson 1640, p. 1313.
[1270] Ray 1686, p. 117.
[1271] Amoreux 1787, p. 46.
[1272] Dillenius 1741, p. 202.
[1273] Lightfoot 1777, ii. p. 846.
[1274] Dorstenius 1540.
[1275] Culpepper 1652.
[1276] Hill 1751.
[1277] Cordus 1561.
[1278] Sibbald 1684.
[1279] Ray 1686.
[1280] Linnaeus 1737.
[1248] Johnson 1861.
[1249] Lindsay 1856.
[1250] Willemet 1787.
[1251] Keller 1866.
[1252] Proust 1906.
[1253] Johnson 1861.
[1254] Church 1880.
[1255] Brown 1898.
[1256] Hutchinson 1916.
[1257] Forskål 1875, p. 193.
[1258] Watt 1890.
[1259] Calkins 1892.
[1260] Miyoshi 1893.
[1261] See p. 422.
[1262] Eversmann 1825.
[1263] Berkeley 1849.
[1264] Visiani 1867.
[1265] Errera 1893.
[1266] Müller-Argau 1881, p. 526.
[1267] See p. 138.
[1268] From an examination of old figures of the Muscus cranii, Arnold
(1892, p. 53) has decided that several kinds of lichens or hepatics are included in
this designation.
[1269] Parkinson 1640, p. 1313.
[1270] Ray 1686, p. 117.
[1271] Amoreux 1787, p. 46.
[1272] Dillenius 1741, p. 202.
[1273] Lightfoot 1777, ii. p. 846.
[1274] Dorstenius 1540.
[1275] Culpepper 1652.
[1276] Hill 1751.
[1277] Cordus 1561.
[1278] Sibbald 1684.
[1279] Ray 1686.
[1280] Linnaeus 1737.
Page 575
[1281] Scopoli 1760.
[1282] Cramer 1880.
[1283] Kobert 1895.
[1284] Keegan 1905.
[1285] Henneguy 1883.
[1286] Kobert 1895.
[1287] Neubert 1893.
[1288] See p. 228.
[1289] Gmelin 1752, p. 425.
[1290] Léorier 1825.
[1291] Stenberg 1868.
[1292] Richard 1877.
[1293] Henneguy 1883.
[1294] Wainio 1887, p. 47.
[1295] Hellbom 1886, p. 72.
[1296] Hoffmann 1787.
[1297] Westring 1792 and 1793.
[1298] Westring 1805-1809.
[1299] Zopf 1907.
[1300] Ronceray 1904.
[1301] Zopf 1907.
[1302] Zahlbruckner (1905, p. 109) quotes from Czapek a statement that
orchil fermentation is brought about by an obligate aerobic bacillus.
[1303] Zopf 1907, p. 393.
[1304] Lindsay 1855.
[1305] Bohler 1835, N. 10.
[1306] Johnson 1861.
[1307] Lindsay 1855.
[1308] Linnaeus 1711.
[1309] Linnaeus 1760.
[1310] Willemet etc. 1787.
[1311] Zopf 1907.
[1312] Lindsay 1855.
[1313] Lettau 1914.
[1314] Sorby 1873.
[1282] Cramer 1880.
[1283] Kobert 1895.
[1284] Keegan 1905.
[1285] Henneguy 1883.
[1286] Kobert 1895.
[1287] Neubert 1893.
[1288] See p. 228.
[1289] Gmelin 1752, p. 425.
[1290] Léorier 1825.
[1291] Stenberg 1868.
[1292] Richard 1877.
[1293] Henneguy 1883.
[1294] Wainio 1887, p. 47.
[1295] Hellbom 1886, p. 72.
[1296] Hoffmann 1787.
[1297] Westring 1792 and 1793.
[1298] Westring 1805-1809.
[1299] Zopf 1907.
[1300] Ronceray 1904.
[1301] Zopf 1907.
[1302] Zahlbruckner (1905, p. 109) quotes from Czapek a statement that
orchil fermentation is brought about by an obligate aerobic bacillus.
[1303] Zopf 1907, p. 393.
[1304] Lindsay 1855.
[1305] Bohler 1835, N. 10.
[1306] Johnson 1861.
[1307] Lindsay 1855.
[1308] Linnaeus 1711.
[1309] Linnaeus 1760.
[1310] Willemet etc. 1787.
[1311] Zopf 1907.
[1312] Lindsay 1855.
[1313] Lettau 1914.
[1314] Sorby 1873.
Page 576
[1315] Gerard 1597.
[1316] Amoreux 1787.
[1317] Hue 1889.
[1318] Hue 1900.
[1319] Bauhin 1650, p. 88.
[1320] Zwelser 1672.
[1321] Georgi 1779.
[1322] Amoreux 1787.
[1323] Dundonald 1801.
[1324] Henneguy 1883.
[1325] See p. 302.
[1326] Journ. Bot. lviii. pp. 213-9; 262-7, 1920.
[1327] Bot. Memoirs, 3, Oxford, 1919.
[1328] Church in litt.
[1329] Journ. Bot. l.c.
[1330] See p. 271 ante.
[1331] See p. 302 ante.
[1332] Chemist and Druggist, xcii. pp. 25-26, 1920; Bot. Abstracts, N. 903, p.
135, 1920.
[1316] Amoreux 1787.
[1317] Hue 1889.
[1318] Hue 1900.
[1319] Bauhin 1650, p. 88.
[1320] Zwelser 1672.
[1321] Georgi 1779.
[1322] Amoreux 1787.
[1323] Dundonald 1801.
[1324] Henneguy 1883.
[1325] See p. 302.
[1326] Journ. Bot. lviii. pp. 213-9; 262-7, 1920.
[1327] Bot. Memoirs, 3, Oxford, 1919.
[1328] Church in litt.
[1329] Journ. Bot. l.c.
[1330] See p. 271 ante.
[1331] See p. 302 ante.
[1332] Chemist and Druggist, xcii. pp. 25-26, 1920; Bot. Abstracts, N. 903, p.
135, 1920.
Page 577
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Waite, M. B. Experiments with Fungicides in the removal of Lichens from
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Wallroth, F. W. Naturgeschichte der Flechten. 2 vols. Frankfurt am Main,
1825-1827.
—— Naturgeschichte der Säulchen-Flechten. Naumburg, 1829.
Ward, Marshall. On the structure, development and life-history of a
tropical epiphyllous lichen (Strigula complanata Fée, fide Rev. J. M.
Crombie). Trans. Linn. Soc., Ser. 2, ii. pp. 87-119 (4 pls.), 1884.
Watson, Sir W. An Historical Memoir concerning a Genus of Plants called
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Watson, W. The Distribution of Bryophytes in the woodlands of Somerset.
New Phytologist, viii. pp. 60-96, 1909.
—— Cryptogamic Vegetation of the Sand-Dunes of the West coast of
England. Journ. Ecol. vi. pp. 126-143, 1918¹.
—— The Bryophytes and Lichens of calcareous soil. Tom. cit. pp. 189-198,
1918².
Watt, George. A Dictionary of the Economic Products of India, iv. pp. 635-
639, 1890.
Weber, G. H. Wiggers’ Primitiae Florae Holsaticae. Kiel, 1780.
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1869.
—— Les Lichens du massif granitique de Ligugé, etc. Bull. Soc. Bot. Fr.
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—— Excursion lichénologique dans l’ile d’Yeu sur la côte de la Vendée.
Mém. Soc. Sci. Nat. Cherb. xix. pp. 251-316, 1875¹.
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—— Lichenes ... Pitlekai in Sibiria septentrionali a E. Almquist collecti.
Arkiv Bot. viii. n. 4, 175 pp., 1909.
Waite, M. B. Experiments with Fungicides in the removal of Lichens from
Pear trees. Journ. Mycol. VII. pp. 264-268 (2 pls.), 1893.
Wallroth, F. W. Naturgeschichte der Flechten. 2 vols. Frankfurt am Main,
1825-1827.
—— Naturgeschichte der Säulchen-Flechten. Naumburg, 1829.
Ward, Marshall. On the structure, development and life-history of a
tropical epiphyllous lichen (Strigula complanata Fée, fide Rev. J. M.
Crombie). Trans. Linn. Soc., Ser. 2, ii. pp. 87-119 (4 pls.), 1884.
Watson, Sir W. An Historical Memoir concerning a Genus of Plants called
Lichen, etc. Phil. Trans. l. 2 [1758], pp. 652-688. London, 1759.
Watson, W. The Distribution of Bryophytes in the woodlands of Somerset.
New Phytologist, viii. pp. 60-96, 1909.
—— Cryptogamic Vegetation of the Sand-Dunes of the West coast of
England. Journ. Ecol. vi. pp. 126-143, 1918¹.
—— The Bryophytes and Lichens of calcareous soil. Tom. cit. pp. 189-198,
1918².
Watt, George. A Dictionary of the Economic Products of India, iv. pp. 635-
639, 1890.
Weber, G. H. Wiggers’ Primitiae Florae Holsaticae. Kiel, 1780.
Weddell, H. A. Les Lichens des promenades publiques et, en particulier, du
Jardin de Blossac, à Poitiers. Bull. Soc. Bot. Fr. xvi. pp. 194-203.
1869.
—— Les Lichens du massif granitique de Ligugé, etc. Bull. Soc. Bot. Fr.
xx. pp. 142-155, 1873.
—— Excursion lichénologique dans l’ile d’Yeu sur la côte de la Vendée.
Mém. Soc. Sci. Nat. Cherb. xix. pp. 251-316, 1875¹.
Page 622
—— Remarques complémentaires sur le rôle du substratum, etc. Comptes
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—— Remarques sur le rôle du substratum dans la distribution des Lichens
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Wehmer, Carl. Entstehung und physiologische Bedeutung der Oxalsäure
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Wester, D. A. Studien über das Chitin. Arch. Pharm. ccxlvii. pp. 282-307,
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—— Svenska Lafvarnes Farghistoria. Stockholm (24 col. pls.), 1805-1809.
Wettstein, F. V. Geosiphon Fr. Wettst., eine neue interessante Siphonee.
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—— Remarques sur le rôle du substratum dans la distribution des Lichens
saxicoles. Ann. Sci. Nat. Sér. 6, i. pp. 394-398, 1875⁴.
Wehmer, Carl. Entstehung und physiologische Bedeutung der Oxalsäure
im Stoffwechsel einiger Pilze. Bot. Zeit. xlix. pp. 611-620 and 630-
638, 1891.
Weir, James R. Concerning the introduction into the United States of extra-
limital wood-destroying fungi. Mycologia, xi. pp. 58-65, 1919.
West, G. S. A Treatise on the British Freshwater Algae. Cambridge, 1904.
—— Cambridge Botanical Handbooks. Algae, vol. i. Cambridge, 1916.
West, W. Physcia parietina. Journ. Bot. xliii. p. 31, 1905.
—— Ecological Notes; chiefly Cryptogamic. Journ. Linn. Soc. xliii. pp. 57-
85, 1915.
Wester, D. A. Studien über das Chitin. Arch. Pharm. ccxlvii. pp. 282-307,
1909. (Bot. Zeit. lxvii. pp. 293-294, 1909.)
Westring, J. P. Sur la propriété tinctoriale des Lichens. Ann. Chimie, xv.
pp. 267-297, 1792; xvii. pp. 67-84, 1793.
—— Svenska Lafvarnes Farghistoria. Stockholm (24 col. pls.), 1805-1809.
Wettstein, F. V. Geosiphon Fr. Wettst., eine neue interessante Siphonee.
Oesterr. Bot. Zeitschr. pp. 145-156 (2 pls.), 1915. See also Bot.
Centralbl. cxxxi. pp. 131-132, 1916.
Wheldon, J. A. Stone Mites in West Lancashire. Lancashire and Cheshire
Naturalist. pp. 31-32 (4 figs.), 1914.
Wheldon, J. A. and Travis, W. G. The Lichens of South Lancashire. Journ.
Linn. Soc. xliii. pp. 87-136, 1915.
Wheldon, J. A. and Wilson, A. The Flora of West Lancashire. Eastbourne,
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Page 623
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Winterstein, E. Zur Kenntniss der Pilzcellulose. Ber. Deutsch. Bot. Ges. xi.
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Withering, W. A Botanical Arrangement, etc. ed. i. Birmingham, 1776.
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Wiesner, J. Untersuchungen über den Lichtgenuss der Pflanzen, etc.
Sitzungsb. K. Akad. Wiss. Wien, Math.-Naturw. Cl. civ. pp. 606-711,
1895.
—— Die Rohstoffe des Pflanzenreichs. i. pp. 668-671, 1900.
Wille, N. Algologische Notizen. xxii. Nyt. Magazin. Naturv. li. i. pp. 1-26
(1 pl.), 1913.
Willemet, M. Lichenographie Économique ou Histoire des Lichens utiles.
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Wilson, A. and Wheldon, J. A. Alpine Vegetation of Ben-y-Gloe,
Perthshire. Journ. Bot. lii. pp. 227-235, 1914.
Wilson, F. R. M. The Climate of Eastern Tasmania indicated by its lichen
flora. Papers and Proc. Roy. Soc. Tasmania for 1892, p. 131, 1893.
Winter, Georg. Ueber die Gattung Sphaeromphale und Verwandte. Ein
Beitrag zur Anatomie der Krustenflechten. Pringsh. Jahrb. Wiss. Bot.
x. pp. 245-274 (3 pls.), 1876.
—— Lichenologische Notizen. i. Cephalodien von Sticta und Solorina.
Flora, lx. pp. 177-184, 193-203, 1877¹. ii. Flechtenparasiten, tom. cit.
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Winterstein, E. Zur Kenntniss der Pilzcellulose. Ber. Deutsch. Bot. Ges. xi.
pp. 441-445, 1893.
Wisselingh, C. van. Mikrochemische Untersuchungen über die Zellwände
der Fungi. Pringsh. Jahrb. Wiss. Bot. xxxi. pp. 618-687 (pl.), 1898.
Withering, W. A Botanical Arrangement, etc. ed. i. Birmingham, 1776.
Wolff, Gertr. P. Beiträge zur Entwicklungsgeschichte der
Flechtenapothecien. Flora, xcv. pp. 31-57 (figs.), 1905.
Woodward, T. J. Observations upon the Generic Characters of Ulva with
Descriptions of some new species. Trans. Linn. Soc. iii. pp. 46-58,
Page 624
1797.
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—— Zur biologischen Bedeutung der Flechtensäuren. Biol. Centralbl. xvi.
No. 16, pp. 593-610, 1896.
—— Untersuchungen über die durch parasitische Pilze hervorgerufene
Krankheiten der Flechten. Nova Acta Acad. Caes. Leop.-Carol. lxx.
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—— Vergleichende Untersuchungen über Flechten in Bezug auf ihre
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—— Biologische und morphologische Beobachtungen an Flechten. Ber.
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Woronin, M. Recherches sur les gonidies du Lichen Parmelia pulverulenta
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Zahlbruckner, A. Studien über brasilianische Flechten. Sitzungsb. K.
Akad. Wiss. Wien, Math.-Naturw. Cl. cxi. pp. 357-432 (2 pls.), 1902.
—— Lichenes (Specieller Teil). Engler and Prantl, Die Natürlichen
Pflanzenfamilien, li*. pp. 49-249, 1903-1907.
Zittel, A. Handbuch der Palaeontologie. Abt. ii. von W. Ph. Schimper und
A. Schenk. München und Leipzig, 1890.
Zopf, W. Die Pilze. Schenk’s Handbuch der Botanik, iv. pp. 271-775, 1890.
—— Beitr. Phys. Morph. niederer Organismen. Leipzig, 1892.
—— Die Weissfärbung von Thamnolia vermicularis, etc. Hedwigia, xxxii.
pp. 66-69, 1893.
—— Uebersicht der auf Flechten schmarotzenden Pilze. Hedwigia, xxxv.
pp. 312-366, 1896.
—— Ueber Nebensymbiose (Parasymbiose). Ber. Deutsch. Bot. Ges. xv.
pp. 90-92, 1897.
—— Zur biologischen Bedeutung der Flechtensäuren. Biol. Centralbl. xvi.
No. 16, pp. 593-610, 1896.
—— Untersuchungen über die durch parasitische Pilze hervorgerufene
Krankheiten der Flechten. Nova Acta Acad. Caes. Leop.-Carol. lxx.
No. 2, pp. 97-190 (pl.), 1897, and tom. cit. No. 4, pp. 243-288 (fig.),
1898.
—— Vergleichende Untersuchungen über Flechten in Bezug auf ihre
Stoffwechselprodukte. Beih. Bot. Centralbl. xiv. pp. 95-126 (4 pls.),
1903.
—— Biologische und morphologische Beobachtungen an Flechten. Ber.
Deutsch. Bot. Ges. xxiii. pp. 497-504 (1 pl.), 1905.
—— Zur Kenntniss der Flechtenstoffe. Lieb. Ann. Chemie, cclxxxiv.-
ccclii., 1895-1907.
Page 625
—— Die Flechtenstoffe in chemischer botanischer pharmakologischer und
technischer Beziehung. Jena, 1907.
—— Biologische und morphologische Beobachtungen an Flechten. Ber.
Deutsch. Bot. Ges. xxv. pp. 233-238 (1 pl.), 1907.
—— Beiträge zu einer chemischen Monographie der Cladoniaceen. Ber.
Deutsch. Bot. Ges. xxvi. pp. 51-113 (4 pls.), 1908.
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xlviii. ii. pp. 249-292 (1 pl.), 1884.
—— Ueber das Vorkommen von Reservestoffbehältern bei Kalkflechten.
Bot. Zeit. xliv. pp. 761-770, 1886.
—— Ueber einige neue Ascomyceten. Verh. K. K. Zool.-Bot. Ges. Wien,
xxxvii. pp. 39-46 (1 pl.), 1887.
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and 133-137 (1 pl.), 1893.
—— Morphologische und biologische Untersuchungen über die Flechten.
Sitzungsb. K. Akad. Wiss. Math.-Naturw. Cl. Wien, civ. pp. 529-574
and 1303-1395 (2 pls.), 1895; op. cit. cv. pp. 197-264, 1896.
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etc. (p. 578), 1672.
technischer Beziehung. Jena, 1907.
—— Biologische und morphologische Beobachtungen an Flechten. Ber.
Deutsch. Bot. Ges. xxv. pp. 233-238 (1 pl.), 1907.
—— Beiträge zu einer chemischen Monographie der Cladoniaceen. Ber.
Deutsch. Bot. Ges. xxvi. pp. 51-113 (4 pls.), 1908.
—— Die Flechtenstoffe. Liebig’s Ann. Chemie, ccclxiv. pp. 273-313,
1909.
Zschacke, H. Ein Beitrag zur Flechtenflora des unteren Saaletales. Zeitschr.
Naturwiss. lxxx. pp. 231-253, 1908.
Zukal, H. Das Zusammenleben von Moos und Flechten. Oesterr. Bot.
Zeitschr. xxix. pp. 189-191, 1879.
—— Flechtenstudien. Denkschr. K. Akad. Wiss. Math.-Nat. Cl. Wien,
xlviii. ii. pp. 249-292 (1 pl.), 1884.
—— Ueber das Vorkommen von Reservestoffbehältern bei Kalkflechten.
Bot. Zeit. xliv. pp. 761-770, 1886.
—— Ueber einige neue Ascomyceten. Verh. K. K. Zool.-Bot. Ges. Wien,
xxxvii. pp. 39-46 (1 pl.), 1887.
—— Epigloea bactrospora. Verh. K. K. Zool.-Bot. Ges. Wien, xxxix. p. 78,
1889 and Österr. Bot. Zeitschr. xl. pp. 323-328 (1 pl.), 1889.
—— Halbflechten. Flora, lxxiv. pp. 92-107 (1 pl.), 1891.
—— Ueber zwei neue Myxomyceten. Oesterr. Bot. Zeitschr. xliii. pp. 73-77
and 133-137 (1 pl.), 1893.
—— Morphologische und biologische Untersuchungen über die Flechten.
Sitzungsb. K. Akad. Wiss. Math.-Naturw. Cl. Wien, civ. pp. 529-574
and 1303-1395 (2 pls.), 1895; op. cit. cv. pp. 197-264, 1896.
Zwelser, Joanne. Pharmacopæa augustana reformata cum ejus mantissa,
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Page 626
INDEX
Abrothallus De Not., 267
A. Cetrariae Kotte, 264
A. oxysporus Tul., 263
A. Peyritschii Kotte, 264
A. Smithii Tul., 263
Acanthothecium Wain., 322
Acarinae, 271, 397
Acarospora Massal., 183, 331, 390
A. chlorophana Massal., 374, 375, 390
A. glaucocarpa Koerb., 176
A. Heppii Koerb., 377
A. pruinosa (Sm.), 377
A. smaragdula Massal., 388, 393
A. xanthophana (Nyl.), 242
Acarosporaceae, 310, 331
Acarus, 395
Acharius, 1, 10, 123, 126, 133, 141, 149, 156, 185, 192, 304
Acolium, S. F. Gray, 277
Acrocordia gemmata Koerb., 152 (Fig. 90 b)
Acroscyphus, Lév., 320
A. sphaerophoroides Lév., 289
Actinoplaca Müll.-Arg., 327
Abrothallus De Not., 267
A. Cetrariae Kotte, 264
A. oxysporus Tul., 263
A. Peyritschii Kotte, 264
A. Smithii Tul., 263
Acanthothecium Wain., 322
Acarinae, 271, 397
Acarospora Massal., 183, 331, 390
A. chlorophana Massal., 374, 375, 390
A. glaucocarpa Koerb., 176
A. Heppii Koerb., 377
A. pruinosa (Sm.), 377
A. smaragdula Massal., 388, 393
A. xanthophana (Nyl.), 242
Acarosporaceae, 310, 331
Acarus, 395
Acharius, 1, 10, 123, 126, 133, 141, 149, 156, 185, 192, 304
Acolium, S. F. Gray, 277
Acrocordia gemmata Koerb., 152 (Fig. 90 b)
Acroscyphus, Lév., 320
A. sphaerophoroides Lév., 289
Actinoplaca Müll.-Arg., 327
Page 627
Acton, xix, 57
Adanson, 9
Aesculus, 253
Agardh, C. A., xx, 21
Agyrium flavescens Rehm, 266
Aigret, 125, 371, 384
Alectoria Ach., 85, 94, 101, 103, 200, 257, 300, 340, 346, 350, 352
A. implexa Nyl., 227
A. jubata Ach., 3, 111, 401, 411
A. nigricans Nyl., 346, 389
A. ochroleuca Ach., 227, 389
A. thrausta Ach., 105 (Fig. 60)
Alectoriaceae, 339
Allarthonia Nyl., 321
Allarthothelium Wain., 321
Allescher, 201
Almquist, 262
Ambergris, 419
Amoreux, 10, 407, 415, 418, 420
Amphidium Nyl., 335
Amphiloma Koerb., 325
Anabæna Bory, 41
Anaptychia Koerb., 341 (see Physcia)
Anapyrenium Müll.-Arg., 315
Anema Nyl., 333, 373
Angiocarpeae, 156
Adanson, 9
Aesculus, 253
Agardh, C. A., xx, 21
Agyrium flavescens Rehm, 266
Aigret, 125, 371, 384
Alectoria Ach., 85, 94, 101, 103, 200, 257, 300, 340, 346, 350, 352
A. implexa Nyl., 227
A. jubata Ach., 3, 111, 401, 411
A. nigricans Nyl., 346, 389
A. ochroleuca Ach., 227, 389
A. thrausta Ach., 105 (Fig. 60)
Alectoriaceae, 339
Allarthonia Nyl., 321
Allarthothelium Wain., 321
Allescher, 201
Almquist, 262
Ambergris, 419
Amoreux, 10, 407, 415, 418, 420
Amphidium Nyl., 335
Amphiloma Koerb., 325
Anabæna Bory, 41
Anaptychia Koerb., 341 (see Physcia)
Anapyrenium Müll.-Arg., 315
Anema Nyl., 333, 373
Angiocarpeae, 156
Page 628
Anthoceros L., 41
Anthracothecium Massal., 316, 350
Anzia Stiz., 90, 299, 339
A. colpodes Stiz., 90
A. japonica Müll.-Arg., 90
Archer, 28
Arctomia Th. Fr., 334
Argopsis Th. Fr., 105, 135, 297, 330
Arnold, 18, 261, 342, 343, 364, 368, 370, 407
Arnoldia minutula Born., 190 (Fig. 108)
Arnott, Walker, 15
Artari, 39, 42
Arthonia Ach., 158, 203, 278, 305, 321, 343, 361
A. astroidea Ach., 202
A. cinnabarina Wallr. (see A. gregaria), 349
A. dispersa Nyl., 365
A. gregaria Koerb., 247, 248
A. lecideella Nyl., 365
A. pruinosa Ach., 145
A. radiata Ach., 78, 365
A. subvarians Nyl., 262
Arthoniaceae, 59, 278, 309, 321
Arthoniopsis Müll.-Arg., 321
Arthopyrenia Massal., 30, 316
A. fallax Arn., 365
A. halizoa A. L. Sm., 383
Anthracothecium Massal., 316, 350
Anzia Stiz., 90, 299, 339
A. colpodes Stiz., 90
A. japonica Müll.-Arg., 90
Archer, 28
Arctomia Th. Fr., 334
Argopsis Th. Fr., 105, 135, 297, 330
Arnold, 18, 261, 342, 343, 364, 368, 370, 407
Arnoldia minutula Born., 190 (Fig. 108)
Arnott, Walker, 15
Artari, 39, 42
Arthonia Ach., 158, 203, 278, 305, 321, 343, 361
A. astroidea Ach., 202
A. cinnabarina Wallr. (see A. gregaria), 349
A. dispersa Nyl., 365
A. gregaria Koerb., 247, 248
A. lecideella Nyl., 365
A. pruinosa Ach., 145
A. radiata Ach., 78, 365
A. subvarians Nyl., 262
Arthoniaceae, 59, 278, 309, 321
Arthoniopsis Müll.-Arg., 321
Arthopyrenia Massal., 30, 316
A. fallax Arn., 365
A. halizoa A. L. Sm., 383
Page 629
A. halodytes Oliv., 383
A. leptotera A. L. Sm., 383
A. macrospora Fink, 365
A. marina A. L. Sm., 383
A. punctiformis Arn., 346, 365
A. quinqueseptata Fink, 365
Arthotheliopsis Wain., 327
Arthothelium Massal., 321
Ascolichens, 272, 273, 281, 308, 311
Ascomycetes xix, 178 et passim
Ascophanus carneus Boud., 180
Aspergillus Micheli, 220
Aspicilia Massal., 133, 136, 140 (see Lecanora)
A. atroviolacea (Flot.) Hue, 158
A. flavida (Hepp), 248
Aspidoferae, 9
Aspidopyrenium Wain., 314
Aspidothelium Wain., 314
Asteristion Leight., 337
Asteroporum Müll.-Arg., 316
Asterothyrium Müll.-Arg., 327
Astrotheliaceae, 309, 317, 352
Astrothelium Trev., 317
Athalami, 305
Aulaxina Fée, 322
Azolla Laur., 41
A. leptotera A. L. Sm., 383
A. macrospora Fink, 365
A. marina A. L. Sm., 383
A. punctiformis Arn., 346, 365
A. quinqueseptata Fink, 365
Arthotheliopsis Wain., 327
Arthothelium Massal., 321
Ascolichens, 272, 273, 281, 308, 311
Ascomycetes xix, 178 et passim
Ascophanus carneus Boud., 180
Aspergillus Micheli, 220
Aspicilia Massal., 133, 136, 140 (see Lecanora)
A. atroviolacea (Flot.) Hue, 158
A. flavida (Hepp), 248
Aspidoferae, 9
Aspidopyrenium Wain., 314
Aspidothelium Wain., 314
Asteristion Leight., 337
Asteroporum Müll.-Arg., 316
Asterothyrium Müll.-Arg., 327
Astrotheliaceae, 309, 317, 352
Astrothelium Trev., 317
Athalami, 305
Aulaxina Fée, 322
Azolla Laur., 41
Page 630
Babikoff, 138
Babington, 18, 350
Bachmann, E., 35, 75, 76, 215, 216, 235, 247, 347, 393
Bachmann, Freda, 162, 179, 181, 186
Bacidia, De Not., 329
B. acclinis (Flot.), 248
B. Beckhausii Koerb., 262
B. flavovirescens Anzi, 280
B. fuscorubella Arn., 249, 365
B. inundata Koerb., 372, 373, 377, 391, 392
B. muscorum Mudd, 248, 368, 370, 377
B. rubella Massal., 365
Bacotia sepium, 399
Baeomyces Pers., 123, 293, 294, 330
B. paeminosus Krempelh., 55
B. placophyllus Ach., 293, 368
B. roseus Pers., 123, 167, 195, 218, 247, 362, 367, 368, 369
B. rufus, DC., 123, 167, 177, 218, 237, 240, 362, 368, 369
Baranetzky, 24
Bary, de, 24, 31, 187, 209, 213
Bauhin, J., 419
Bauhin, K., 3
Baur, 51, 115, 118, 124, 161, 165, 167, 168, 169, 170, 172, 173, 174,
176, 177, 180, 181, 185, 255
Beckmann, 230, 257
Beechey, 15
Babington, 18, 350
Bachmann, E., 35, 75, 76, 215, 216, 235, 247, 347, 393
Bachmann, Freda, 162, 179, 181, 186
Bacidia, De Not., 329
B. acclinis (Flot.), 248
B. Beckhausii Koerb., 262
B. flavovirescens Anzi, 280
B. fuscorubella Arn., 249, 365
B. inundata Koerb., 372, 373, 377, 391, 392
B. muscorum Mudd, 248, 368, 370, 377
B. rubella Massal., 365
Bacotia sepium, 399
Baeomyces Pers., 123, 293, 294, 330
B. paeminosus Krempelh., 55
B. placophyllus Ach., 293, 368
B. roseus Pers., 123, 167, 195, 218, 247, 362, 367, 368, 369
B. rufus, DC., 123, 167, 177, 218, 237, 240, 362, 368, 369
Baranetzky, 24
Bary, de, 24, 31, 187, 209, 213
Bauhin, J., 419
Bauhin, K., 3
Baur, 51, 115, 118, 124, 161, 165, 167, 168, 169, 170, 172, 173, 174,
176, 177, 180, 181, 185, 255
Beckmann, 230, 257
Beechey, 15
Page 631
Beetle-mites, 397
Beijerinck, 39, 220
Beilstein, 211
Belonia Koerb., 316
Berg, 211
Berkeley, 252, 404
Berzelius, 210
Betula nana L., 95
Bialosuknia, 57
Biatora Koerb., 158, 279, 293 (see also Lecidea), 391
Biatorella Th. Fr., 331
B. cinerea Th. Fr., 375
B. pruinosa Mudd, 217 (Fig. 119)
B. resinae Th. Fr., 355
B. simplex Br. and Rostr., 217 (Fig. 118)
B. testudinea Massal., 375
Biatorina Massal., 245, 291
B. Bouteillei Arn., 363
B. chalybeia Mudd, 386
B. coeruleonigricans A. L. Sm., 367
B. globulosa Koerb., 378
B. lenticularis Koerb., 383
B. prasina Syd., 33, 61
B. (denigrata) synothea Koerb., 33, 204
Bilimbia, aromatica Jatta, 349
B. incana A. L. Sm., 343
Beijerinck, 39, 220
Beilstein, 211
Belonia Koerb., 316
Berg, 211
Berkeley, 252, 404
Berzelius, 210
Betula nana L., 95
Bialosuknia, 57
Biatora Koerb., 158, 279, 293 (see also Lecidea), 391
Biatorella Th. Fr., 331
B. cinerea Th. Fr., 375
B. pruinosa Mudd, 217 (Fig. 119)
B. resinae Th. Fr., 355
B. simplex Br. and Rostr., 217 (Fig. 118)
B. testudinea Massal., 375
Biatorina Massal., 245, 291
B. Bouteillei Arn., 363
B. chalybeia Mudd, 386
B. coeruleonigricans A. L. Sm., 367
B. globulosa Koerb., 378
B. lenticularis Koerb., 383
B. prasina Syd., 33, 61
B. (denigrata) synothea Koerb., 33, 204
Bilimbia, aromatica Jatta, 349
B. incana A. L. Sm., 343
Page 632
B. microcarpa Th. Fr., 262
B. obscurata Th. Fr., 262
B. sabulosa Massal., 370
B. sphaeroides Koerb., 385
Bioret, 320
Birger, see Nilson
Bitter, 64, 79, 94, 97, 131, 140, 143, 147, 148, 149, 151, 176, 240, 242,
253, 257, 261, 267, 337, 397
Blackman, 206
Blackman and Welsford, 179
Blastenia Th. Fr., 340
Blastodesmia Massal., 316
Bohler, 415
Bombyliospora De Not., 329
Bonnier, 29, 36, 47, 65, 189, 232, 253
Bornet, 27, 28, 32, 36, 61, 78, 136, 189
Borrer, 12, 14
Borrera, see Physcia
Borzi, 28, 161, 164
Botrydina vulgaris Bréb., xix, 57
Botrydium pyriforme Kütz., 45
Bottaria Massal., 317
Bouilhac, 42, 140
Braconnot, 214
Brandt, 103, 130
Braun, Fr., 354
B. obscurata Th. Fr., 262
B. sabulosa Massal., 370
B. sphaeroides Koerb., 385
Bioret, 320
Birger, see Nilson
Bitter, 64, 79, 94, 97, 131, 140, 143, 147, 148, 149, 151, 176, 240, 242,
253, 257, 261, 267, 337, 397
Blackman, 206
Blackman and Welsford, 179
Blastenia Th. Fr., 340
Blastodesmia Massal., 316
Bohler, 415
Bombyliospora De Not., 329
Bonnier, 29, 36, 47, 65, 189, 232, 253
Bornet, 27, 28, 32, 36, 61, 78, 136, 189
Borrer, 12, 14
Borrera, see Physcia
Borzi, 28, 161, 164
Botrydina vulgaris Bréb., xix, 57
Botrydium pyriforme Kütz., 45
Bottaria Massal., 317
Bouilhac, 42, 140
Braconnot, 214
Brandt, 103, 130
Braun, Fr., 354
Page 633
Braun, L., 393
Brefeld, 189, 207
Brez, 395
Brooks, F. T., 64, 179
Brown, E. W., 402
Brown, W. H., 168
Bryopogon, see Oropogon
Bryum L., 392
Buchet, 90
Buddle, 4
Buellia, De Not., 263, 280, 291, 302, 308, 341, 347
B. aethalea Th. Fr., 261
B. atrata Mudd, 245, 375
B. canescens De Not., 80, 366, 377, 380, 399
B. colludens Tuck., 382, 386
B. coracina Koerb., 375
B. discolor Koerb., 388
B. leptocline Koerb., 374
B. myriocarpa Mudd, 50, 346, 366, 369
B. parasema Th. Fr., 365, 367, 377
B. Parmeliarum Oliv., 263
B. punctiformis, 50, 202, 207 (Fig. 118)
B. ryssolea A. L. Sm., 380, 382 (Fig. 125)
B. stellulata Mudd, 382, 388
B. triphragmia Th. Fr., 390
B. turgescens Tuck., 367
Brefeld, 189, 207
Brez, 395
Brooks, F. T., 64, 179
Brown, E. W., 402
Brown, W. H., 168
Bryopogon, see Oropogon
Bryum L., 392
Buchet, 90
Buddle, 4
Buellia, De Not., 263, 280, 291, 302, 308, 341, 347
B. aethalea Th. Fr., 261
B. atrata Mudd, 245, 375
B. canescens De Not., 80, 366, 377, 380, 399
B. colludens Tuck., 382, 386
B. coracina Koerb., 375
B. discolor Koerb., 388
B. leptocline Koerb., 374
B. myriocarpa Mudd, 50, 346, 366, 369
B. parasema Th. Fr., 365, 367, 377
B. Parmeliarum Oliv., 263
B. punctiformis, 50, 202, 207 (Fig. 118)
B. ryssolea A. L. Sm., 380, 382 (Fig. 125)
B. stellulata Mudd, 382, 388
B. triphragmia Th. Fr., 390
B. turgescens Tuck., 367
Page 634
B. verruculosa Mudd, 261
Buelliaceae, 311, 341
Buxbaum, 6, 10
Buxus sempervirens L., 353
Cactus, 325, 353
Calenia Müll.-Arg., 338
Caliciaceae, 62, 115, 175, 189, 244, 288, 309, 319, 353, 366
Calicium De Not., 184, 201, 277, 319, 361
C. arenarium Nyl., 376
C. corynellum Ach., 376
C. hyperellum Ach., 349, 365
C. parietinum Ach., 202, 367
C. trachelinum Ach., 196, 202, 204
Calkins, 348, 403
Callopisma, see Placodium
Calluna Salisb., 95, 355
Caloplaca Th. Fr. (see Placodium), 340
C. aurantia, var. callopisma Stein., 190
C. gilvella (Nyl.), 276
C. interveniens Müll.-Arg., 276
C. pyracea Th. Fr., 34, 388
Caloplacaceae, 311, 340
Calothricopsis Wain., 333
Calycidium Stirt., 289, 320
C. cuneatum Stirt., 350
Buelliaceae, 311, 341
Buxbaum, 6, 10
Buxus sempervirens L., 353
Cactus, 325, 353
Calenia Müll.-Arg., 338
Caliciaceae, 62, 115, 175, 189, 244, 288, 309, 319, 353, 366
Calicium De Not., 184, 201, 277, 319, 361
C. arenarium Nyl., 376
C. corynellum Ach., 376
C. hyperellum Ach., 349, 365
C. parietinum Ach., 202, 367
C. trachelinum Ach., 196, 202, 204
Calkins, 348, 403
Callopisma, see Placodium
Calluna Salisb., 95, 355
Caloplaca Th. Fr. (see Placodium), 340
C. aurantia, var. callopisma Stein., 190
C. gilvella (Nyl.), 276
C. interveniens Müll.-Arg., 276
C. pyracea Th. Fr., 34, 388
Caloplacaceae, 311, 340
Calothricopsis Wain., 333
Calycidium Stirt., 289, 320
C. cuneatum Stirt., 350
Page 635
Camellia L., 269
Camerarius, 1
Camillea Fr., 276
Campylidium, 191
Campylothelium Müll.-Arg., 317
Candelaria Massal., 339
C. concolor Wain., 365, 388, 399
Candelariella Müll.-Arg., 338
C. cerinella A. Zahlbr., 390
C. vitellina Müll.-Arg., 233, 237, 369, 377, 393, 417
Capnodium Mont., 179
Carpinus Tournef., 240
Carrington, 12
Carroll, 19
Cassini, 21
Catillaria Th. Fr. (see Biatorina), 329
C. Hochstetteri Koerb., 375
Celidiaceae, 265
Cellidium stictarum Tul., 267
Cenomyce Th. Fr., 295
Cephaleuros Kunze (see Mycoidea), 59, 288
Cephaloidei, 303
Cepteus ocellatus, 397
Cerania S. F. Gray, 340
C. vermicularis S. F. Gray, 194, 387
Camerarius, 1
Camillea Fr., 276
Campylidium, 191
Campylothelium Müll.-Arg., 317
Candelaria Massal., 339
C. concolor Wain., 365, 388, 399
Candelariella Müll.-Arg., 338
C. cerinella A. Zahlbr., 390
C. vitellina Müll.-Arg., 233, 237, 369, 377, 393, 417
Capnodium Mont., 179
Carpinus Tournef., 240
Carrington, 12
Carroll, 19
Cassini, 21
Catillaria Th. Fr. (see Biatorina), 329
C. Hochstetteri Koerb., 375
Celidiaceae, 265
Cellidium stictarum Tul., 267
Cenomyce Th. Fr., 295
Cephaleuros Kunze (see Mycoidea), 59, 288
Cephaloidei, 303
Cepteus ocellatus, 397
Cerania S. F. Gray, 340
C. vermicularis S. F. Gray, 194, 387
Page 636
Cetraria Ach., 84, 94, 200, 210, 213, 225, 241, 264, 299, 346, 350,
357, 358, 370, 388, 399
C. aculeata Fr., 211, 241, 262, 299, 300, 355, 369, 384, 385, 386,
387
C. caperata Wain., 264
C. crispa Lamy, 387, 388
C. cucullata Ach., 201, 244, 389
C. diffusa A. L. Sm., 366
C. glauca Ach., 201, 231, 259, 264, 347, 388, 418
C. islandica Ach., 2, 94, 128, 195 (Fig. 112), 210, 212, 221, 227,
231, 241, 338, 355, 387, 401 (Fig. 128), 406, 408, 409, 411,
416
C. juniperina Ach., 201, 246, 416
C. Laureri Kremp., 364
C. nivalis Ach., 201, 210, 389
C. pinastri S. F. Gray, 145, 246, 410
C. tristis, see Parmelia
Chaenotheca Th. Fr., 201, 319
C. chrysocephala Th. Fr., 265, 277, 288
Chalice-Moss, 3
Chambers, 43
Chasmariae, 295
Chevalier, 13
Chiodecton Müll.-Arg., 276, 320, 323, 351, 364
Chiodectonaceae, 59, 278, 309, 323
Chlorella Beij., 56
Ch. Cladoniae Chod., 56
357, 358, 370, 388, 399
C. aculeata Fr., 211, 241, 262, 299, 300, 355, 369, 384, 385, 386,
387
C. caperata Wain., 264
C. crispa Lamy, 387, 388
C. cucullata Ach., 201, 244, 389
C. diffusa A. L. Sm., 366
C. glauca Ach., 201, 231, 259, 264, 347, 388, 418
C. islandica Ach., 2, 94, 128, 195 (Fig. 112), 210, 212, 221, 227,
231, 241, 338, 355, 387, 401 (Fig. 128), 406, 408, 409, 411,
416
C. juniperina Ach., 201, 246, 416
C. Laureri Kremp., 364
C. nivalis Ach., 201, 210, 389
C. pinastri S. F. Gray, 145, 246, 410
C. tristis, see Parmelia
Chaenotheca Th. Fr., 201, 319
C. chrysocephala Th. Fr., 265, 277, 288
Chalice-Moss, 3
Chambers, 43
Chasmariae, 295
Chevalier, 13
Chiodecton Müll.-Arg., 276, 320, 323, 351, 364
Chiodectonaceae, 59, 278, 309, 323
Chlorella Beij., 56
Ch. Cladoniae Chod., 56
Page 637
Ch. faginea Wille, 56 (Fig. 23 a)
Ch. lichina Chod., 56
Ch. miniata Wille, 56 (Fig. 23 a)
Ch. viscosa Chod., 56
Ch. vulgaris Beyer., 42, 56
Chlorococcus (?Chlorococcum Fr.), 24
Chlorophyceae, xix, 51, 55-60, 61, 272, 324
Chodat, 28, 30, 43, 44, 55, 115, 329
Chroococcaceae, 25
Chroococcus Naeg., 24, 52, 82, 136, 153, 284, 311, 332, 373
Ch. giganteus West, 52 (Fig. 16)
Ch. Schizodermaticus West, 52 (Fig. 16)
Ch. turgidus Naeg., 52 (Fig. 16), 136
Chroolepus Ag., see Trentepohlia
C. ebeneus Ag., 22
Chrysothricaceae, 57, 310, 325
Chrysothrix Mont., 325, 353
C. noli tangere Mont., 325
Church, A. Henry, 421
Church, A. Herbert, 402
Cicinnobolus Ehrenb., 261
Cinchona L., 364
C. cordaminea Humb., 364
C. cordifolia Mutis, 364
C. oblongifolia Mutis, 364
Claassen, 34
Ch. lichina Chod., 56
Ch. miniata Wille, 56 (Fig. 23 a)
Ch. viscosa Chod., 56
Ch. vulgaris Beyer., 42, 56
Chlorococcus (?Chlorococcum Fr.), 24
Chlorophyceae, xix, 51, 55-60, 61, 272, 324
Chodat, 28, 30, 43, 44, 55, 115, 329
Chroococcaceae, 25
Chroococcus Naeg., 24, 52, 82, 136, 153, 284, 311, 332, 373
Ch. giganteus West, 52 (Fig. 16)
Ch. Schizodermaticus West, 52 (Fig. 16)
Ch. turgidus Naeg., 52 (Fig. 16), 136
Chroolepus Ag., see Trentepohlia
C. ebeneus Ag., 22
Chrysothricaceae, 57, 310, 325
Chrysothrix Mont., 325, 353
C. noli tangere Mont., 325
Church, A. Henry, 421
Church, A. Herbert, 402
Cicinnobolus Ehrenb., 261
Cinchona L., 364
C. cordaminea Humb., 364
C. cordifolia Mutis, 364
C. oblongifolia Mutis, 364
Claassen, 34
Page 638
Cladina Leight., 112, 122, 253, 292
Cladonia Hill, 9, 13, 23, 38, 44, 55, 56, 80, 81, 95, 104, 106, 172, 213,
237, 241, 242, 257, 262, 329, 344, 346, 347, 355, 358, 372, 375,
385, 391, 399, 408
Cl. agariciformis Wulf., 368
Cl. aggregata Ach., 120
Cl. alcicornis Floerk., 385, 386
Cl. alpestris Rabenh., 125, 211, 349, 369
Cl. alpicola Wain., 122
Cl. amaurocrea Schaer., 118
Cl. bellidiflora Schaer., 119
Cl. botrytes Willd., 173
Cl. caespiticia Floerk., 115, 124, 294, 296
Cl. cariosa Spreng., 113, 120, 295, 296, 368
Cl. cartilaginea Müll.-Arg., 122
Cl. ceratophylla Spreng., 122
Cl. cervicornis Schaer., 113, 120, 122, 243, 384, 387
Cl. coccifera Willd., 113, 118, 368, 369, 370, 387
Cl. cristatella Tuck., 367, 369
Cl. decorticata Spreng., 172 (Fig. 98)
Cl. deformis Hoffm., 226
Cl. degenerans Floerk., 114, 117, 124
Cl. destricta Nyl., 387
Cl. digitata Hoffm., 113, 122, 371
Cl. divaricata Meng. and Goepp., 355
Cl. enantia f. dilatala Wain., 112
Cl. endiviaefolia Fr., 384
Cladonia Hill, 9, 13, 23, 38, 44, 55, 56, 80, 81, 95, 104, 106, 172, 213,
237, 241, 242, 257, 262, 329, 344, 346, 347, 355, 358, 372, 375,
385, 391, 399, 408
Cl. agariciformis Wulf., 368
Cl. aggregata Ach., 120
Cl. alcicornis Floerk., 385, 386
Cl. alpestris Rabenh., 125, 211, 349, 369
Cl. alpicola Wain., 122
Cl. amaurocrea Schaer., 118
Cl. bellidiflora Schaer., 119
Cl. botrytes Willd., 173
Cl. caespiticia Floerk., 115, 124, 294, 296
Cl. cariosa Spreng., 113, 120, 295, 296, 368
Cl. cartilaginea Müll.-Arg., 122
Cl. ceratophylla Spreng., 122
Cl. cervicornis Schaer., 113, 120, 122, 243, 384, 387
Cl. coccifera Willd., 113, 118, 368, 369, 370, 387
Cl. cristatella Tuck., 367, 369
Cl. decorticata Spreng., 172 (Fig. 98)
Cl. deformis Hoffm., 226
Cl. degenerans Floerk., 114, 117, 124
Cl. destricta Nyl., 387
Cl. digitata Hoffm., 113, 122, 371
Cl. divaricata Meng. and Goepp., 355
Cl. enantia f. dilatala Wain., 112
Cl. endiviaefolia Fr., 384
Page 639
Cl. fimbriata Fr., 51, 117, 120, 295, 296, 349, 367, 368, 370, 377;
Subsp. fibula Nyl., 119, 369
Cl. flabelliformis Wain., 371
Cl Floerkeana Fr., 173, 296, 362, 370
Cl. foliacea Willd., 112, 113, 120, 122, 240, 295, 296
Cl. furcata Schrad., 117 (Fig. 70), 118, 124, 194 (Fig. 109), 212,
295, 297, 355, 368, 369, 377, 386
Cl. gracilis Hoffm., 115 (Fig. 68), 122, 124, 210, 297, 367, 369,
387
Cl. leptophylla Floerk., 295, 296
Cl. macilenta Hoffm., 362, 366, 367, 369, 378
Cl. miniata Mey., 112, 122
Cl. nana Wain., 112
Cl. Neo-Zelandica Wain., 112
Cl. papillaria Hoffm., 195, 296, 344
Cl. pityrea Floerk., 255, 366
Cl. pungens Floerk. (see Cl. rangiformis)
Cl. pycnoclada Nyl., 345
Cl. pyxidata Hoffm., 2, 44, 110, 111 (Fig. 66), 113, 114, 117 (Fig.
69), 118, 120, 124, 172, 227, 295, 346, 349, 362, 366, 368,
370, 371, 377, 408
Cl. racemosa Hoffm., 387
Cl. rangiferina Web., 56, 95, 117, 119, 120, 210, 211, 215, 227,
231, 237, 238, 253, 267, 293, 297, 349, 355, 357, 369, 386,
388, 400, 411
Cl. rangiformis Hoffm., 271, 295, 366, 368, 386
Cl. retepora Fr., 117, 120 (Fig. 71), 231, 351
Cl. rosea Ludw., 354
Subsp. fibula Nyl., 119, 369
Cl. flabelliformis Wain., 371
Cl Floerkeana Fr., 173, 296, 362, 370
Cl. foliacea Willd., 112, 113, 120, 122, 240, 295, 296
Cl. furcata Schrad., 117 (Fig. 70), 118, 124, 194 (Fig. 109), 212,
295, 297, 355, 368, 369, 377, 386
Cl. gracilis Hoffm., 115 (Fig. 68), 122, 124, 210, 297, 367, 369,
387
Cl. leptophylla Floerk., 295, 296
Cl. macilenta Hoffm., 362, 366, 367, 369, 378
Cl. miniata Mey., 112, 122
Cl. nana Wain., 112
Cl. Neo-Zelandica Wain., 112
Cl. papillaria Hoffm., 195, 296, 344
Cl. pityrea Floerk., 255, 366
Cl. pungens Floerk. (see Cl. rangiformis)
Cl. pycnoclada Nyl., 345
Cl. pyxidata Hoffm., 2, 44, 110, 111 (Fig. 66), 113, 114, 117 (Fig.
69), 118, 120, 124, 172, 227, 295, 346, 349, 362, 366, 368,
370, 371, 377, 408
Cl. racemosa Hoffm., 387
Cl. rangiferina Web., 56, 95, 117, 119, 120, 210, 211, 215, 227,
231, 237, 238, 253, 267, 293, 297, 349, 355, 357, 369, 386,
388, 400, 411
Cl. rangiformis Hoffm., 271, 295, 366, 368, 386
Cl. retepora Fr., 117, 120 (Fig. 71), 231, 351
Cl. rosea Ludw., 354
Page 640
Cl. solida Wain., 114
Cl. squamosa Hoffm., 113, 115 (Fig. 67), 118, 210, 243, 295, 366,
368
Cl. sylvatica Hoffm., 95, 112, 117, 119, 271, 349, 366, 368, 369,
385, 400
Cl. symphicarpia Tuck., 367
Cl. tophacea Hill, 8
Cl. turgida Hoffm., 369
Cl. uncialis Web., 112, 120, 369, 387, 389
Cl. verticillaris Fr., 122
Cl. verticillata Floerk., 114, 119, 120, 124, 349, 367, 369
Cladoniaceae, 135, 292, 310, 329, 366, 370
Cladoniodei, 306
Cladophora Kütz., 35, 59, 188
C. glomerata Kütz., 58 (Fig. 30)
Cladophoraceae, 59
Clathrinae, 117, 120
Clathroporina Müll.-Arg., 316
Clausae, 295
Clavaria Vaill., 421
Cleora lichenaria, 399
Cocciferae, 295
Coccobotrys Chod., 30, 40, 56, 315
C. Verrucariae Chod., 57 (Fig. 24)
Coccocarpia Pers., 335
C. molybdaea Pers., 61
C. pellita Müll.-Arg., 166
Cl. squamosa Hoffm., 113, 115 (Fig. 67), 118, 210, 243, 295, 366,
368
Cl. sylvatica Hoffm., 95, 112, 117, 119, 271, 349, 366, 368, 369,
385, 400
Cl. symphicarpia Tuck., 367
Cl. tophacea Hill, 8
Cl. turgida Hoffm., 369
Cl. uncialis Web., 112, 120, 369, 387, 389
Cl. verticillaris Fr., 122
Cl. verticillata Floerk., 114, 119, 120, 124, 349, 367, 369
Cladoniaceae, 135, 292, 310, 329, 366, 370
Cladoniodei, 306
Cladophora Kütz., 35, 59, 188
C. glomerata Kütz., 58 (Fig. 30)
Cladophoraceae, 59
Clathrinae, 117, 120
Clathroporina Müll.-Arg., 316
Clausae, 295
Clavaria Vaill., 421
Cleora lichenaria, 399
Cocciferae, 295
Coccobotrys Chod., 30, 40, 56, 315
C. Verrucariae Chod., 57 (Fig. 24)
Coccocarpia Pers., 335
C. molybdaea Pers., 61
C. pellita Müll.-Arg., 166
Page 641
Coccomyxa Schmidle, 56
C. Solorinae croceae Chod., 56
C. Solorinae saccatae Chod., 56
C. subellipsoidea Acton, 57 (Fig. 25)
Coccotrema Müll.-Arg., 316
Coenogoniaceae, 59, 291, 310, 328
Coenogonium Ehrenb., 23, 35, 69, 182, 246, 291, 328, 351
C. ebeneum A. L. Sm., 22 (Fig. 3), 34, 59, 328, 350, 352, 363
C. implexum Nyl., 352
C. Linkii Ehrenb., 213
Coenothalami, 303
Coleochaete Bréb., 178
Collema Wigg., 6, 9, 21, 23, 25, 30, 48, 69, 87, 132, 165, 173, 200,
230, 284, 305, 334, 367, 392
C. ceranoides Borr., 385
C. cheileum Ach., 161
C. crispum Ach., 161, 180
C. flaccidum Ach., 365
C. fluviatile Sm., 392
C. granulatum Ach., 368
C. granuliferum Nyl., 69, 232, 243
C. Hildenbrandii Garov., 202 (see Leptogium)
C. limosum Ach., xx, 21, 349
C. microphyllum Ach., 160 (Fig. 91), 161 (Fig. 92), 202
C. nigrescens Ach., 20 (Fig. 2), 161, 243, 245, 364
C. plicatile, 409
C. Solorinae croceae Chod., 56
C. Solorinae saccatae Chod., 56
C. subellipsoidea Acton, 57 (Fig. 25)
Coccotrema Müll.-Arg., 316
Coenogoniaceae, 59, 291, 310, 328
Coenogonium Ehrenb., 23, 35, 69, 182, 246, 291, 328, 351
C. ebeneum A. L. Sm., 22 (Fig. 3), 34, 59, 328, 350, 352, 363
C. implexum Nyl., 352
C. Linkii Ehrenb., 213
Coenothalami, 303
Coleochaete Bréb., 178
Collema Wigg., 6, 9, 21, 23, 25, 30, 48, 69, 87, 132, 165, 173, 200,
230, 284, 305, 334, 367, 392
C. ceranoides Borr., 385
C. cheileum Ach., 161
C. crispum Ach., 161, 180
C. flaccidum Ach., 365
C. fluviatile Sm., 392
C. granulatum Ach., 368
C. granuliferum Nyl., 69, 232, 243
C. Hildenbrandii Garov., 202 (see Leptogium)
C. limosum Ach., xx, 21, 349
C. microphyllum Ach., 160 (Fig. 91), 161 (Fig. 92), 202
C. nigrescens Ach., 20 (Fig. 2), 161, 243, 245, 364
C. plicatile, 409
Page 642
C. pulposum Ach., 24, 162, 179, 186, 202, 266, 368, 385
C. pustulatum Ach., 373
C. pycnocarpum Nyl., 365
C. tenax Sm., 368
Collemaceae, 27, 53, 69, 160, 241, 244, 266, 284, 306, 310, 334, 364,
384, 396
Collemodes Fink, 162
C. Bachmannianum Fink, 162
Collemodium, see Leptogium
Collemopsidium Nyl., 333, 374
Collybia, Quél., 105
Colonna, 3
Combea De Not., 83
Conida Massal., 265, 267
C. rubescens, Arn., 265
Conidella urceolata Elenk., 265
Coniocarpi, 307
Coniocarpineae, 267, 273, 274, 276, 288, 309, 319
Coniocarpon DC., 305
Coniocybe Ach., 277, 319, 366
C. furfuracea Ach., 246, 376
Conotrema Tuck., 326
C. urceolatum Tuck., 343
Convoluta roscoffensis, 40
Cora Fr., 53, 246, 281, 311, 342, 352
C. Pavonia Fr., 88, 152 (Figs. 86, 87)
C. pustulatum Ach., 373
C. pycnocarpum Nyl., 365
C. tenax Sm., 368
Collemaceae, 27, 53, 69, 160, 241, 244, 266, 284, 306, 310, 334, 364,
384, 396
Collemodes Fink, 162
C. Bachmannianum Fink, 162
Collemodium, see Leptogium
Collemopsidium Nyl., 333, 374
Collybia, Quél., 105
Colonna, 3
Combea De Not., 83
Conida Massal., 265, 267
C. rubescens, Arn., 265
Conidella urceolata Elenk., 265
Coniocarpi, 307
Coniocarpineae, 267, 273, 274, 276, 288, 309, 319
Coniocarpon DC., 305
Coniocybe Ach., 277, 319, 366
C. furfuracea Ach., 246, 376
Conotrema Tuck., 326
C. urceolatum Tuck., 343
Convoluta roscoffensis, 40
Cora Fr., 53, 246, 281, 311, 342, 352
C. Pavonia Fr., 88, 152 (Figs. 86, 87)
Page 643
Coralloides, 5, 6, 7, 303
Corda, 200
Cordus, 409
Cordyceps Fr., 261
Corella Wain., 153, 311, 342, 352
C. brasiliensis Wain., 154
Coriscium Wain., 285, 288, 319
Cornicularia (Cetraria) Schreb., 388
C. ochroleuca Ach., 355
C. subpubescens Goepp., 355
C. succinea Goepp., 355
Corylus Tournef., 240
Cramer, 409
Croall, 19
Crocynia Nyl., 325
C. gossypina Nyl., 325
C. lanuginosa Hue, 325, 373
Crombie, xxi, 7, 18, 19, 197, 260, 262, 264, 306, 361
Crottles, 415
Cruoria Fr., 73
Cryptothecia Stirton, 331
Cryptothele Nyl., 333
Cudbear, 413, 415
Culpepper, 409
Cunningham, 35, 269
Cuppe-Moss, 3
Corda, 200
Cordus, 409
Cordyceps Fr., 261
Corella Wain., 153, 311, 342, 352
C. brasiliensis Wain., 154
Coriscium Wain., 285, 288, 319
Cornicularia (Cetraria) Schreb., 388
C. ochroleuca Ach., 355
C. subpubescens Goepp., 355
C. succinea Goepp., 355
Corylus Tournef., 240
Cramer, 409
Croall, 19
Crocynia Nyl., 325
C. gossypina Nyl., 325
C. lanuginosa Hue, 325, 373
Crombie, xxi, 7, 18, 19, 197, 260, 262, 264, 306, 361
Crottles, 415
Cruoria Fr., 73
Cryptothecia Stirton, 331
Cryptothele Nyl., 333
Cudbear, 413, 415
Culpepper, 409
Cunningham, 35, 269
Cuppe-Moss, 3
Page 644
Cupthongs, 9
Curnow, 19
Cutting, 180
Cyanophili, 308, 310
Cyanophyceae, 309; see Myxophyceae
Cycas L., 40
Cyclocarpineae, 273, 279, 290, 309, 324
Cyperus, 419
Cypheliaceae, 309, 320
Cyphelium Th. Fr., 276, 277, 288, 320
Cyphella aeruginascens Karst., 191
Cystococcus Chod., 55, 56
C. Cladoniae fimbriatae Chod., 56
C. Cladoniae pixidatae Chod., 56 (Fig. 56)
Cystococcus Naeg., 24, 26, 28, 34, 115, 229
C. humicola Naeg., 24, 27, 40, 55
Cystocoleus Thwaites, 23
Cytospora Ehrenb., 204
Czapek, 211, 413
Dacampia Massal., 315
Dactylina Nyl., 340
D. arctica Nyl., 339, 346
Dangeard, 185
Danilov, 37
Curnow, 19
Cutting, 180
Cyanophili, 308, 310
Cyanophyceae, 309; see Myxophyceae
Cycas L., 40
Cyclocarpineae, 273, 279, 290, 309, 324
Cyperus, 419
Cypheliaceae, 309, 320
Cyphelium Th. Fr., 276, 277, 288, 320
Cyphella aeruginascens Karst., 191
Cystococcus Chod., 55, 56
C. Cladoniae fimbriatae Chod., 56
C. Cladoniae pixidatae Chod., 56 (Fig. 56)
Cystococcus Naeg., 24, 26, 28, 34, 115, 229
C. humicola Naeg., 24, 27, 40, 55
Cystocoleus Thwaites, 23
Cytospora Ehrenb., 204
Czapek, 211, 413
Dacampia Massal., 315
Dactylina Nyl., 340
D. arctica Nyl., 339, 346
Dangeard, 185
Danilov, 37
Page 645
Darbishire, 18, 26, 51, 64, 77, 86, 90, 92, 101, 103, 110, 130, 147, 148,
166, 167, 171, 175, 180, 181, 253, 256, 299, 324, 342, 346, 347,
377, 389
Darbishire and Fischer-Benzon, 307
Darbishirella A. Zahlbr., 324
Davies, 12, 14
Dawson, 178
De Candolle, 12
Deckenbach, 59
Deer, 401
Delise, 13, 126
Dendrographa Darbish., 324
D. leucophaea Darbish., 103, 213
Dermatiscum Nyl., 331
Dermatocarpaceae, 309, 314
Dermatocarpon Eschw., 80, 81, 276, 288, 315
D. aquaticum A. Zahlbr., 391, 392
D. cinereum Th. Fr., 368
D. hepaticum Th. Fr., 368, 388
D. lachneum A. L. Sm., 88, 368
D. miniatum Th. Fr., 56, 96 (Fig. 56), 173 (Fig. 99), 185, 241,
261, 373, 391, 392, 403
Desfontaines, 10
Diatoms, 220
Dichodium Nyl., 334
Dickson, 9
Dictyographa Müll.-Arg., 322
166, 167, 171, 175, 180, 181, 253, 256, 299, 324, 342, 346, 347,
377, 389
Darbishire and Fischer-Benzon, 307
Darbishirella A. Zahlbr., 324
Davies, 12, 14
Dawson, 178
De Candolle, 12
Deckenbach, 59
Deer, 401
Delise, 13, 126
Dendrographa Darbish., 324
D. leucophaea Darbish., 103, 213
Dermatiscum Nyl., 331
Dermatocarpaceae, 309, 314
Dermatocarpon Eschw., 80, 81, 276, 288, 315
D. aquaticum A. Zahlbr., 391, 392
D. cinereum Th. Fr., 368
D. hepaticum Th. Fr., 368, 388
D. lachneum A. L. Sm., 88, 368
D. miniatum Th. Fr., 56, 96 (Fig. 56), 173 (Fig. 99), 185, 241,
261, 373, 391, 392, 403
Desfontaines, 10
Diatoms, 220
Dichodium Nyl., 334
Dickson, 9
Dictyographa Müll.-Arg., 322
Page 646
Dictyonema A. Zahlbr., 54, 153, 311, 342, 352
Didymella Sacc., 276
Didymosphaeria pulposi Zopf, 266
Dillenius, xx, 1, 6, 155, 192, 262, 304, 407
Dioscorides, 2
Diplogramma Müll.-Arg., 322
Diplopodon, 270
Diploschistaceae, 310, 326
Diploschistes Norm., 326
D. bryophilus Zahlbr., 374
D. ocellatus Norm., 247, 248, 374
D. scruposus Norm., 195, 214, 241, 243, 262, 368
Diplosphaera Bial., 57
D. Chodati Bial., 57
Dirina Fr., 73, 83, 290, 323
Dirinaceae, 290, 309, 323
Dirinastrum Müll.-Arg., 290, 323
Discocarpi, 307
Discomycetes, 267, 273
Dodoens, 3
Dog-lichen, 408
Domestic animals (Oxen, horses, etc.), 401
Don, 14
Doody, 4
Dorstenius, 2, 408
Dothidea Fr., 317
Didymella Sacc., 276
Didymosphaeria pulposi Zopf, 266
Dillenius, xx, 1, 6, 155, 192, 262, 304, 407
Dioscorides, 2
Diplogramma Müll.-Arg., 322
Diplopodon, 270
Diploschistaceae, 310, 326
Diploschistes Norm., 326
D. bryophilus Zahlbr., 374
D. ocellatus Norm., 247, 248, 374
D. scruposus Norm., 195, 214, 241, 243, 262, 368
Diplosphaera Bial., 57
D. Chodati Bial., 57
Dirina Fr., 73, 83, 290, 323
Dirinaceae, 290, 309, 323
Dirinastrum Müll.-Arg., 290, 323
Discocarpi, 307
Discomycetes, 267, 273
Dodoens, 3
Dog-lichen, 408
Domestic animals (Oxen, horses, etc.), 401
Don, 14
Doody, 4
Dorstenius, 2, 408
Dothidea Fr., 317
Page 647
Dufour, 11
Dufourea Nyl., 340
Dufrenoy, 42, 260, 269
Dumontia Lamour., 111
Dundonald, Lord, 420
Ectolechiaceae, 69, 310, 327, 352, 363
Egeling, 234
Elaphomyces Nees, 261
Elenkin, 36, 37, 258, 265, 347
Elenkin and Woronichin, 353
Elfving, xxi, 25
Encephalographa Massal., 322
Enchylium Massal., see Forssellia
Endocarpon Hedw., 62, 88, 89, 197, 200, 261, 288, 315, 351, 389
E. monstrosum Massal., 373
E. pusillum Hedw., 28 (Figs. 5, 6)
Endocena Cromb., 339, 340
Endomyces scytonemata Zuk., 38
Englehardt, 354
Enterodictyon Müll.-Arg., 323
Enterographa Fée, 320
E. crassa Fée, 350
Enterostigma Müll.-Arg., 323
Erioderma Fée, 335
Eolichen Zuk., 285, 319
Dufourea Nyl., 340
Dufrenoy, 42, 260, 269
Dumontia Lamour., 111
Dundonald, Lord, 420
Ectolechiaceae, 69, 310, 327, 352, 363
Egeling, 234
Elaphomyces Nees, 261
Elenkin, 36, 37, 258, 265, 347
Elenkin and Woronichin, 353
Elfving, xxi, 25
Encephalographa Massal., 322
Enchylium Massal., see Forssellia
Endocarpon Hedw., 62, 88, 89, 197, 200, 261, 288, 315, 351, 389
E. monstrosum Massal., 373
E. pusillum Hedw., 28 (Figs. 5, 6)
Endocena Cromb., 339, 340
Endomyces scytonemata Zuk., 38
Englehardt, 354
Enterodictyon Müll.-Arg., 323
Enterographa Fée, 320
E. crassa Fée, 350
Enterostigma Müll.-Arg., 323
Erioderma Fée, 335
Eolichen Zuk., 285, 319
Page 648
E. Heppii Zuk., 319
Ephebaceae, 54, 284, 310, 331
Ephebe Fr., 23, 25, 27, 30, 38, 68, 201, 284, 322
E. lanata Wain., see E. pubescens
E. pubescens Nyl., 23 (Fig. 3)
Ephebeia Nyl., 332
Epiconiaceae, 307
Epiconiodei, 306
Epigloea Zuk., 313
E. bactrospora Zuk., 313
Epigloeaceae, 57, 309, 313
Erica tetralix L., 95
Errera, 213, 214, 405
Erysiphe Link, 188
Eschweiler, 15, 184
Escombe, 210
Etard and Bouilhac, 42, 140
Ettingshausen and Debey, 354
Euler, 214
Eunephroma Stiz., 337
Euopsis granatina Nyl., 282, 387
Evernia Ach., 84, 95, 99, 200, 213, 340
E. furfuracea Mann, 24, 38, 94, 99, 108, 142 (Fig. 81), 151, 227,
231, 233, 300, 366, 376, 403, 405
E. prunastri Ach., 2, 100 (Fig. 59), 108, 210, 211, 212, 227, 233,
234, 238, 269, 300, 364, 384, 385, 396, 400, 403, 418, 419
Everniopsis Nyl., 339, 340
Ephebaceae, 54, 284, 310, 331
Ephebe Fr., 23, 25, 27, 30, 38, 68, 201, 284, 322
E. lanata Wain., see E. pubescens
E. pubescens Nyl., 23 (Fig. 3)
Ephebeia Nyl., 332
Epiconiaceae, 307
Epiconiodei, 306
Epigloea Zuk., 313
E. bactrospora Zuk., 313
Epigloeaceae, 57, 309, 313
Erica tetralix L., 95
Errera, 213, 214, 405
Erysiphe Link, 188
Eschweiler, 15, 184
Escombe, 210
Etard and Bouilhac, 42, 140
Ettingshausen and Debey, 354
Euler, 214
Eunephroma Stiz., 337
Euopsis granatina Nyl., 282, 387
Evernia Ach., 84, 95, 99, 200, 213, 340
E. furfuracea Mann, 24, 38, 94, 99, 108, 142 (Fig. 81), 151, 227,
231, 233, 300, 366, 376, 403, 405
E. prunastri Ach., 2, 100 (Fig. 59), 108, 210, 211, 212, 227, 233,
234, 238, 269, 300, 364, 384, 385, 396, 400, 403, 418, 419
Everniopsis Nyl., 339, 340
Page 649
Eversman, 404
Famintzin, 24
Farriolla Norm., 319
Faull, 178
Fée, 13, 15, 184, 187, 192, 364
Fink, Bruce, xx, 242, 254, 348, 358, 365, 367, 368, 369, 373, 389, 391
Fischer, 308
Fitting, 36
Fitzpatrick, 181
Flagey, 373, 389
Florideae, 160, 177, 273
Flörke, 12, 13, 133
Flotow, 23, 192
Fontinalis L., 391
Forficula auricularia, 396
Forskål, 403
Forssell, 63, 65, 133, 136, 163, 175, 282, 373
Forssellia A. Zahlbr., 284, 333, 373
Forster, 12, 14
Fossil Lichens, 353-355
Frank, 31, 62, 78
Fraser, 178
French, xxiii
Friedrich, 75, 233, 269, 270
Fries, E., 13, 22, 149, 364
Famintzin, 24
Farriolla Norm., 319
Faull, 178
Fée, 13, 15, 184, 187, 192, 364
Fink, Bruce, xx, 242, 254, 348, 358, 365, 367, 368, 369, 373, 389, 391
Fischer, 308
Fitting, 36
Fitzpatrick, 181
Flagey, 373, 389
Florideae, 160, 177, 273
Flörke, 12, 13, 133
Flotow, 23, 192
Fontinalis L., 391
Forficula auricularia, 396
Forskål, 403
Forssell, 63, 65, 133, 136, 163, 175, 282, 373
Forssellia A. Zahlbr., 284, 333, 373
Forster, 12, 14
Fossil Lichens, 353-355
Frank, 31, 62, 78
Fraser, 178
French, xxiii
Friedrich, 75, 233, 269, 270
Fries, E., 13, 22, 149, 364
Page 650
Fries, Th. M., 17, 18, 133, 138, 152, 192, 263, 342
Fucus L., 281
F. spiralis L., 383
Fuisting, 30, 159, 173
Fünfstück, 18, 19, 61, 75, 76, 161, 169, 170, 171, 175, 181, 216, 218,
219, 224, 342
Gage, 14
Galløe, 95, 242
Gargeaune, 45
Gasterolichens, 308
Gautier, 213
Geisleria Nitschke, 314
G. sychnogonioides Nitschke, 370
Georgi, 10, 420
Geosiphon Wettst., 45
Gerard, John, 3, 418
Gibelli, 200
Gilson, 209
Gleditsch, 269
Gloeocapsa Kütz., 23, 32, 55, 61, 68, 136, 195, 232, 284, 292, 332,
373
G. magma Kütz., 52 (Fig. 17), 60, 136
G. polydermatica Kütz., 53
Gloeocystis Naeg., 33, 57 (Fig. 28), 61, 133, 318
Gloeolichens, 175, 282, 284, 373, 389
Glossodium Nyl., 330
Fucus L., 281
F. spiralis L., 383
Fuisting, 30, 159, 173
Fünfstück, 18, 19, 61, 75, 76, 161, 169, 170, 171, 175, 181, 216, 218,
219, 224, 342
Gage, 14
Galløe, 95, 242
Gargeaune, 45
Gasterolichens, 308
Gautier, 213
Geisleria Nitschke, 314
G. sychnogonioides Nitschke, 370
Georgi, 10, 420
Geosiphon Wettst., 45
Gerard, John, 3, 418
Gibelli, 200
Gilson, 209
Gleditsch, 269
Gloeocapsa Kütz., 23, 32, 55, 61, 68, 136, 195, 232, 284, 292, 332,
373
G. magma Kütz., 52 (Fig. 17), 60, 136
G. polydermatica Kütz., 53
Gloeocystis Naeg., 33, 57 (Fig. 28), 61, 133, 318
Gloeolichens, 175, 282, 284, 373, 389
Glossodium Nyl., 330
Page 651
G. aversum Nyl., 294
Glück, 198
Glyphis Fée, 276, 323
Glypholecia Nyl., 331
Gmelin, J. F., 152
Gmelin, J. G., 411
Gnomonia erythrostoma Auersw., 178
Goeppert, 354, 393
Goeppert and Menge, 354
Gomphillus Nyl., 293, 330
Gongrosira Kütz., xxi
Gongylia Koerb., 314
G. viridis A. L. Sm., 368, 388
Gonohymenia Stein., 333
Gonothecium Wain., 31, 327
Gordon, Cuthbert, 415
Gossypina Ulmi, 399
Grammophori, 307
Graphidaceae, 59, 158, 309, 321, 351, 352, 364
Graphideae, 13, 17, 27, 34, 62, 78, 79, 172, 348, 349, 351, 353, 364
Graphidineae, 273, 278, 289, 309, 320, 365
Graphina Müll.-Arg., 322
Graphis Adans., 9, 211, 321, 322, 343, 349, 351, 355, 361, 364
G. elegans Ach., 30, 158 (Fig. 89), 172, 180, 397
G. scripta Ach., 50, 349, 354, 365, 366
G. scripta succinea Goepp., 355
Glück, 198
Glyphis Fée, 276, 323
Glypholecia Nyl., 331
Gmelin, J. F., 152
Gmelin, J. G., 411
Gnomonia erythrostoma Auersw., 178
Goeppert, 354, 393
Goeppert and Menge, 354
Gomphillus Nyl., 293, 330
Gongrosira Kütz., xxi
Gongylia Koerb., 314
G. viridis A. L. Sm., 368, 388
Gonohymenia Stein., 333
Gonothecium Wain., 31, 327
Gordon, Cuthbert, 415
Gossypina Ulmi, 399
Grammophori, 307
Graphidaceae, 59, 158, 309, 321, 351, 352, 364
Graphideae, 13, 17, 27, 34, 62, 78, 79, 172, 348, 349, 351, 353, 364
Graphidineae, 273, 278, 289, 309, 320, 365
Graphina Müll.-Arg., 322
Graphis Adans., 9, 211, 321, 322, 343, 349, 351, 355, 361, 364
G. elegans Ach., 30, 158 (Fig. 89), 172, 180, 397
G. scripta Ach., 50, 349, 354, 365, 366
G. scripta succinea Goepp., 355
Page 652
Gray, J. E., 12, 305
Grete Herball, 2
Greville, 12
Grimbel, 250
Grimmia pulvinata Sm., 393
G. apocarpa Hedw., 393
Guembel, 392
Guérin-Varry, 210
Guillermond, 167
Gunnera L., 31, 41
Gyalecta Ach., 191, 328
G. cupularis Schaer., 244
G. Flotovii Koerb., 244
G. geoica Ach., 254
G. rubra Massal., 249
Gyalectaceae, 54, 59, 69, 310, 327
Gyalolechia Massal., 201
G. subsimilis (Th. Fr.) Darb., 378
Gymnocarpeae, 156, 308, 318
Gymnoderma Nyl., 330
G. coccocarpum Nyl., 293
Gymnographa Müll.-Arg., 322
Gyrophora Ach., 88, 96, 184, 200, 227, 231, 241, 249, 268, 304, 331,
346, 350, 376, 390, 393, 414
G. cylindrica Ach., 176, 184 (Fig. 103), 375, 387
G. erosa Ach., 330, 387
Grete Herball, 2
Greville, 12
Grimbel, 250
Grimmia pulvinata Sm., 393
G. apocarpa Hedw., 393
Guembel, 392
Guérin-Varry, 210
Guillermond, 167
Gunnera L., 31, 41
Gyalecta Ach., 191, 328
G. cupularis Schaer., 244
G. Flotovii Koerb., 244
G. geoica Ach., 254
G. rubra Massal., 249
Gyalectaceae, 54, 59, 69, 310, 327
Gyalolechia Massal., 201
G. subsimilis (Th. Fr.) Darb., 378
Gymnocarpeae, 156, 308, 318
Gymnoderma Nyl., 330
G. coccocarpum Nyl., 293
Gymnographa Müll.-Arg., 322
Gyrophora Ach., 88, 96, 184, 200, 227, 231, 241, 249, 268, 304, 331,
346, 350, 376, 390, 393, 414
G. cylindrica Ach., 176, 184 (Fig. 103), 375, 387
G. erosa Ach., 330, 387
Page 653
G. esculenta Miyosh., 403
G. flocculosa Turn. and Borr., 375
G. murina Ach., 94
G. polyphylla Hook., 387
G. polyrhiza Koerb., 94, 349, 404 (Fig. 129)
G. proboscidea Ach., 192, 346, 375
G. spodochroa Ach., 94
G. tonefacta Cromb., 375, 387
G. vellea Ach., 74, 176
Gyrophoraceae, 291, 310, 330
Gyrostomum Fr., 326
Haberlandt, 106, 188
Haematomma Massal., 230, 236, 338
H. coccineum Koerb., 214, 223, 226
H. elatinum Koerb., 201
H. ventosum Massal., 214, 225, 241, 252, 298, 375, 376, 388, 393
Hagenia ciliaris, 24
Haller, 7, 126
Halopyrenula Müll.-Arg., 318
Halsey, 14
Hamlet and Plowright, 213
Harmand, 63
Harper, 167, 178, 181, 188
Harpidium Koerb., 298, 338
H. rutilans Koerb., 298
G. flocculosa Turn. and Borr., 375
G. murina Ach., 94
G. polyphylla Hook., 387
G. polyrhiza Koerb., 94, 349, 404 (Fig. 129)
G. proboscidea Ach., 192, 346, 375
G. spodochroa Ach., 94
G. tonefacta Cromb., 375, 387
G. vellea Ach., 74, 176
Gyrophoraceae, 291, 310, 330
Gyrostomum Fr., 326
Haberlandt, 106, 188
Haematomma Massal., 230, 236, 338
H. coccineum Koerb., 214, 223, 226
H. elatinum Koerb., 201
H. ventosum Massal., 214, 225, 241, 252, 298, 375, 376, 388, 393
Hagenia ciliaris, 24
Haller, 7, 126
Halopyrenula Müll.-Arg., 318
Halsey, 14
Hamlet and Plowright, 213
Harmand, 63
Harper, 167, 178, 181, 188
Harpidium Koerb., 298, 338
H. rutilans Koerb., 298
Page 654
Harriman, 14
Hassea A. Zahlbr., 319
Hedlund, 32, 61, 204, 245
Hedwig, 142, 156, 184, 192
Helix hortensis, 396
H. cingulata, 396
Hellbom, 350, 411
Helminthocarpon Fée, 322
Henneguy, 410, 411, 420
Heppia Naeg., 81, 175, 285, 335, 348, 351, 389
H. Depreauxii Tuck., 368
H. Guepini Nyl., 80, 88, 96
H. virescens Nyl., 368
Heppiaceae, 54, 285, 310
Herberger, 221
Herissey, 213
Herre, 230, 253, 349
Hesse, 12, 221, 224
Heterocarpon Müll.-Arg., 315
Heterodea Nyl., 339
H. Mülleri Nyl., 128, 299, 339, 350
Heterogenei, 303
Heteromyces Müll.-Arg., 293, 330
Heufleria Trev., 317
Hicks, 24
Hildenbrandtia Nardo, 73
Hassea A. Zahlbr., 319
Hedlund, 32, 61, 204, 245
Hedwig, 142, 156, 184, 192
Helix hortensis, 396
H. cingulata, 396
Hellbom, 350, 411
Helminthocarpon Fée, 322
Henneguy, 410, 411, 420
Heppia Naeg., 81, 175, 285, 335, 348, 351, 389
H. Depreauxii Tuck., 368
H. Guepini Nyl., 80, 88, 96
H. virescens Nyl., 368
Heppiaceae, 54, 285, 310
Herberger, 221
Herissey, 213
Herre, 230, 253, 349
Hesse, 12, 221, 224
Heterocarpon Müll.-Arg., 315
Heterodea Nyl., 339
H. Mülleri Nyl., 128, 299, 339, 350
Heterogenei, 303
Heteromyces Müll.-Arg., 293, 330
Heufleria Trev., 317
Hicks, 24
Hildenbrandtia Nardo, 73
Page 655
Hill, Sir John, 8, 409
Hoffmann, 10, 154, 412, 415
Hofmann, 261
Holl, 19
Holle, 14, 46, 187
Holmes, 19, 422
Homogenei, 303
Homopsella Nyl., 334
Homothalami, 305
Homothecium Mont., 334
Hooker, 12, 15, 149
Hornschuch, xx, 156
How, 3
Howe, Heber, 85, 224, 348
Hudson, 7, 9, 303
Hue, 11, 16, 18, 33, 57, 63, 69, 73, 82, 85, 103, 133, 135, 136, 140,
188, 262, 283, 315, 325, 339, 340, 342, 347, 348, 360, 396, 418
Hulth, 215
Hutchins, 14
Hutchinson, 403
Hydrothyria Russ., 336
H. venosa Russ., 97, 175, 233, 286, 348, 390
Hymenobolina parasitica Zuk., 267, 399
Hymenolichens, xix, 54, 152-154, 273, 281, 308, 311, 335, 342
Hymenomycetes, xix, 153 et passim
Hyphomycetes, xix, 191
Hoffmann, 10, 154, 412, 415
Hofmann, 261
Holl, 19
Holle, 14, 46, 187
Holmes, 19, 422
Homogenei, 303
Homopsella Nyl., 334
Homothalami, 305
Homothecium Mont., 334
Hooker, 12, 15, 149
Hornschuch, xx, 156
How, 3
Howe, Heber, 85, 224, 348
Hudson, 7, 9, 303
Hue, 11, 16, 18, 33, 57, 63, 69, 73, 82, 85, 103, 133, 135, 136, 140,
188, 262, 283, 315, 325, 339, 340, 342, 347, 348, 360, 396, 418
Hulth, 215
Hutchins, 14
Hutchinson, 403
Hydrothyria Russ., 336
H. venosa Russ., 97, 175, 233, 286, 348, 390
Hymenobolina parasitica Zuk., 267, 399
Hymenolichens, xix, 54, 152-154, 273, 281, 308, 311, 335, 342
Hymenomycetes, xix, 153 et passim
Hyphomycetes, xix, 191
Page 656
Hypnum L., 392
H. cupressiforme L., 385
Hypogymnia Nyl., 94, 176
Hypoxylon Bull., 12
Hysteriaceae, 273, 307
Hysterium Tode, 12
Iceland Moss, 210, 401 et passim
Icmadophila Massal., 166, 338
I. aeruginosa Mudd, see I. ericetorum
I. ericetorum A. Zahlbr., 196, 244, 370
Illosporium carneum Fr., 268
Ingaderia Darbish., 324
Iris, white, 419
Isidium Ach., 149
I. corallinum Ach., 149
I. Westringii Ach., 149
Istvanffi, 202, 206
Itzigsohn, 17, 23, 24, 193
Jaczewski, 353
Jasmine, oil of, 419
Jatta, 129
Jenmania Wächt., 333, 352
Jennings, Vaughan, 60
Jesuit’s bark, 10
H. cupressiforme L., 385
Hypogymnia Nyl., 94, 176
Hypoxylon Bull., 12
Hysteriaceae, 273, 307
Hysterium Tode, 12
Iceland Moss, 210, 401 et passim
Icmadophila Massal., 166, 338
I. aeruginosa Mudd, see I. ericetorum
I. ericetorum A. Zahlbr., 196, 244, 370
Illosporium carneum Fr., 268
Ingaderia Darbish., 324
Iris, white, 419
Isidium Ach., 149
I. corallinum Ach., 149
I. Westringii Ach., 149
Istvanffi, 202, 206
Itzigsohn, 17, 23, 24, 193
Jaczewski, 353
Jasmine, oil of, 419
Jatta, 129
Jenmania Wächt., 333, 352
Jennings, Vaughan, 60
Jesuit’s bark, 10
Page 657
John, 250
Johnson, C. P., 401, 402
Johnson, W., 19
Johow, 153
Jonaspis Th. Fr., 328
Joshua, 19
Jumelle, 230, 238
Kajanus (Nilson), 151
Karschia Koerb., 280
K. destructans Tobl., 265
K. lignyota Sacc., 280
Keeble, 41
Keegan, 224, 410
Keiszler, 201
Keller, 402
Kerner and Oliver, 215
Kieffer, 371
Kienitz-Gerloff, 51
Kihlman, 237, 358, 388, 401
Knop, 213, 247
Knop and Schnederman, 221
Knowles, 224, 249, 379, 384, 391
Kobert, 409, 410
Koelreuter, 155
Koerber, 14, 123, 142, 188, 305
Johnson, C. P., 401, 402
Johnson, W., 19
Johow, 153
Jonaspis Th. Fr., 328
Joshua, 19
Jumelle, 230, 238
Kajanus (Nilson), 151
Karschia Koerb., 280
K. destructans Tobl., 265
K. lignyota Sacc., 280
Keeble, 41
Keegan, 224, 410
Keiszler, 201
Keller, 402
Kerner and Oliver, 215
Kieffer, 371
Kienitz-Gerloff, 51
Kihlman, 237, 358, 388, 401
Knop, 213, 247
Knop and Schnederman, 221
Knowles, 224, 249, 379, 384, 391
Kobert, 409, 410
Koelreuter, 155
Koerber, 14, 123, 142, 188, 305
Page 658
Koerberia Massal., 334
Kotte, 264
Krabbe, 63, 113, 114, 119, 122, 123, 124, 143, 147, 162, 170, 172,
174, 176, 177, 253
Kratzmann, 214
Krempelhuber, 1, 55, 244, 364
Kupfer, 261
Kützing, 22
Laboulbenia Mont. and Robin, 178
Laboulbeniaceae, 178, 274
Lachnea scutellata Gill., 168
L. stercorea Gill., 178
Lacour, 211
Lang, 76, 216, 235
Larbalestier, 19
Laubert, 206
Laudatea Joh., 154
Laurera Reichenb., 317
Lecanactidaceae, 310, 325
Lecanactis Eschw., 204, 325
Lecania Massal., 136, 338
L. candicans A. Zahlbr., 80 (Fig. 43)
L. cyrtella Oliv., 377
L. erysibe Mudd, 377
L. holophaea A. L. Sm., 350
Kotte, 264
Krabbe, 63, 113, 114, 119, 122, 123, 124, 143, 147, 162, 170, 172,
174, 176, 177, 253
Kratzmann, 214
Krempelhuber, 1, 55, 244, 364
Kupfer, 261
Kützing, 22
Laboulbenia Mont. and Robin, 178
Laboulbeniaceae, 178, 274
Lachnea scutellata Gill., 168
L. stercorea Gill., 178
Lacour, 211
Lang, 76, 216, 235
Larbalestier, 19
Laubert, 206
Laudatea Joh., 154
Laurera Reichenb., 317
Lecanactidaceae, 310, 325
Lecanactis Eschw., 204, 325
Lecania Massal., 136, 338
L. candicans A. Zahlbr., 80 (Fig. 43)
L. cyrtella Oliv., 377
L. erysibe Mudd, 377
L. holophaea A. L. Sm., 350
Page 659
Lecaniella Wain., 327
Lecanora Ach., 78, 88, 200, 298, 305, 338, 347, 349, 351, 353, 364,
365, 372, 390
L. aquatica Koerb., 391
L. aspidophora f. errabunda Hue, 262
L. atra Ach., 63, 225, 249, 375, 380, 382 (Fig. 125), 384, 386,
393
L. atriseda Nyl., 261
L. atroflava, see Placodium
L. aurella (Hoffm.), 262
L. badia Ach., 79, 375, 386
L. caesiocinerea Nyl., 218, 384
L. calcarea Somm., 218 (Fig. 120), 373, 396
L. campestris B. de Lesd., 361, 384
L. cenisia Ach., 375
L. cinerea Somm., 229, 349, 375
L. citrina Ach., see Placodium
L. coilocarpa Nyl., 30
L. crassa Ach., 79, 81, 201, 218, 367, 368, 373, 389
L. crenulata Hook., 361, 377
L. Dicksonii Nyl., 250, 375
L. dispersa Nyl., 261, 369, 377, 384
L. effusa Ach., 204
L. epanora Ach., 246
L. epibryon Ach., 378, 389
L. epulotica Nyl., 392
Lecanora Ach., 78, 88, 200, 298, 305, 338, 347, 349, 351, 353, 364,
365, 372, 390
L. aquatica Koerb., 391
L. aspidophora f. errabunda Hue, 262
L. atra Ach., 63, 225, 249, 375, 380, 382 (Fig. 125), 384, 386,
393
L. atriseda Nyl., 261
L. atroflava, see Placodium
L. aurella (Hoffm.), 262
L. badia Ach., 79, 375, 386
L. caesiocinerea Nyl., 218, 384
L. calcarea Somm., 218 (Fig. 120), 373, 396
L. campestris B. de Lesd., 361, 384
L. cenisia Ach., 375
L. cinerea Somm., 229, 349, 375
L. citrina Ach., see Placodium
L. coilocarpa Nyl., 30
L. crassa Ach., 79, 81, 201, 218, 367, 368, 373, 389
L. crenulata Hook., 361, 377
L. Dicksonii Nyl., 250, 375
L. dispersa Nyl., 261, 369, 377, 384
L. effusa Ach., 204
L. epanora Ach., 246
L. epibryon Ach., 378, 389
L. epulotica Nyl., 392
Page 660
L. esculenta Eversm., 211, 257, 265, 298, 389, 404 (Fig. 130),
422
L. exigua, see Rinodina
L. ferruginea Nyl., 30
L. galactina Ach., 254, 262, 360, 369, 377, 384, 386
L. gelida Ach., 135, 136, 137 (Fig. 77), 140, 375
L. gibbosa Nyl., 375, 384, 386
L. glaucoma Ach., see L. sordida; var. corrugata Nyl., 84 (Fig.
46)
L. Hageni Ach., 366, 367, 369, 377, 383
L. hypnorum Ach., see Psoroma
L. lacustris Th. Fr., 233, 250, 391, 392
L. lentigera Ach., 81, 90, 298, 367
L. muralis Schaer., 242
L. ochracea Nyl., 373
L. pallescens Mudd, 213
L. pallida Schaer., 78
L. parella Ach., 72, 375, 382, 384, 417
L. peliocypha Nyl., 375
L. picea Nyl., 374
L. piniperda Koerb., 204
L. polytropa Schaer., 237, 376, 394
L. prosechoides Nyl., 383, 384
L. rubina Wain., 390
L. rugosa Nyl., 366
L. Sambuci Nyl., 204
422
L. exigua, see Rinodina
L. ferruginea Nyl., 30
L. galactina Ach., 254, 262, 360, 369, 377, 384, 386
L. gelida Ach., 135, 136, 137 (Fig. 77), 140, 375
L. gibbosa Nyl., 375, 384, 386
L. glaucoma Ach., see L. sordida; var. corrugata Nyl., 84 (Fig.
46)
L. Hageni Ach., 366, 367, 369, 377, 383
L. hypnorum Ach., see Psoroma
L. lacustris Th. Fr., 233, 250, 391, 392
L. lentigera Ach., 81, 90, 298, 367
L. muralis Schaer., 242
L. ochracea Nyl., 373
L. pallescens Mudd, 213
L. pallida Schaer., 78
L. parella Ach., 72, 375, 382, 384, 417
L. peliocypha Nyl., 375
L. picea Nyl., 374
L. piniperda Koerb., 204
L. polytropa Schaer., 237, 376, 394
L. prosechoides Nyl., 383, 384
L. rubina Wain., 390
L. rugosa Nyl., 366
L. Sambuci Nyl., 204
Page 661
L. saxicola Ach., 79, 80, 81, 233, 252, 349, 369, 384, 386, 393,
396
L. simplex Nyl. (see Biatorella), 75, 77, 382
L. smaragdula Nyl., 382
L. sophodes Ach., 30; see Rinodina
L. sordida Th. Fr., 194, 236, 261, 374, 375, 380, 382
L. squamulosa Nyl., 374
L. subfusca Ach., 22, 30, 49, 65 (Fig. 34), 70 (Fig. 57), 157 (Fig.
88), 164, 166, 167, 168, 236, 347, 365, 366
L. sulphurea Ach., 226, 238, 376, 384
L. tartarea Ach., 57, 147, 183 (Fig. 102), 224, 225, 227, 237, 262,
346, 358, 359, 371, 375, 387, 389, 414 (Fig. 134)
L. umbrina Massal., 377, 385
L. upsaliensis Nyl., 387
L. urbana Nyl., 361
L. varia Ach., 227, 346, 360, 361, 362, 366, 367, 377
L. ventosa, see Haematomma
L. verrucosa Laur., 378
L. xantholyta Nyl., 373
Lecanoraceae, 136, 311, 337, 353
Lecanorales, 297
Lecidea Ach., 78, 184, 261, 279, 292, 304, 308, 328, 346, 347, 349,
351, 353, 364, 365, 372, 373, 385, 390
L. aglaea Somm., 375
L. albocoerulescens Ach., 392
L. alpestris Somm., 387
L. arctica Somm., 387
396
L. simplex Nyl. (see Biatorella), 75, 77, 382
L. smaragdula Nyl., 382
L. sophodes Ach., 30; see Rinodina
L. sordida Th. Fr., 194, 236, 261, 374, 375, 380, 382
L. squamulosa Nyl., 374
L. subfusca Ach., 22, 30, 49, 65 (Fig. 34), 70 (Fig. 57), 157 (Fig.
88), 164, 166, 167, 168, 236, 347, 365, 366
L. sulphurea Ach., 226, 238, 376, 384
L. tartarea Ach., 57, 147, 183 (Fig. 102), 224, 225, 227, 237, 262,
346, 358, 359, 371, 375, 387, 389, 414 (Fig. 134)
L. umbrina Massal., 377, 385
L. upsaliensis Nyl., 387
L. urbana Nyl., 361
L. varia Ach., 227, 346, 360, 361, 362, 366, 367, 377
L. ventosa, see Haematomma
L. verrucosa Laur., 378
L. xantholyta Nyl., 373
Lecanoraceae, 136, 311, 337, 353
Lecanorales, 297
Lecidea Ach., 78, 184, 261, 279, 292, 304, 308, 328, 346, 347, 349,
351, 353, 364, 365, 372, 373, 385, 390
L. aglaea Somm., 375
L. albocoerulescens Ach., 392
L. alpestris Somm., 387
L. arctica Somm., 387
Page 662
L. aromatica (see Bilimbia)
L. atrofusca Nyl., 248, 387
L. auriculata Th. Fr., 375
L. Berengeriana Th. Fr., 387
L. coarctata Nyl., 247
L. coeruleonigricans Schaer., 373
L. colludens Nyl., 384; see Buellia
L. confluens Ach., 375, 388; f. oxydata Leight., 250
L. consentiens Nyl., 134, 135
L. contigua Fr., 375, 376, 388, 392; var. flavicunda Nyl., 250
L. crustulata Koerb., 369
L. (Bilimbia) cuprea Somm., 387
L. cupreiformis Nyl., 387
L. decipiens Ach., 291, 367, 368
L. decolorans Floerk, see L. granulosa
L. demissa Th. Fr., 369, 387
L. diducens Nyl., 375
L. enteroleuca Nyl., 164, 168, 365
L. fumosa Ach., 159
L. fuscoatra Ach., 200 (Fig. 114), 375
L. gelatinosa Floerk., 368
L. granulosa Schaer., 218, 237, 269, 291, 362, 369, 370, 377
L. grisella Floerk., 243
L. helvola Th. Fr., 245
L. herbidula Nyl., xxi
L. illita Nyl., 136
L. atrofusca Nyl., 248, 387
L. auriculata Th. Fr., 375
L. Berengeriana Th. Fr., 387
L. coarctata Nyl., 247
L. coeruleonigricans Schaer., 373
L. colludens Nyl., 384; see Buellia
L. confluens Ach., 375, 388; f. oxydata Leight., 250
L. consentiens Nyl., 134, 135
L. contigua Fr., 375, 376, 388, 392; var. flavicunda Nyl., 250
L. crustulata Koerb., 369
L. (Bilimbia) cuprea Somm., 387
L. cupreiformis Nyl., 387
L. decipiens Ach., 291, 367, 368
L. decolorans Floerk, see L. granulosa
L. demissa Th. Fr., 369, 387
L. diducens Nyl., 375
L. enteroleuca Nyl., 164, 168, 365
L. fumosa Ach., 159
L. fuscoatra Ach., 200 (Fig. 114), 375
L. gelatinosa Floerk., 368
L. granulosa Schaer., 218, 237, 269, 291, 362, 369, 370, 377
L. grisella Floerk., 243
L. helvola Th. Fr., 245
L. herbidula Nyl., xxi
L. illita Nyl., 136
Page 663
L. immersa Ach., 217 (Fig. 117), 398
L. inserena Nyl., 375
L. insularis Nyl., 236, 261
L. irregularis Fée, 192
L. Kochiana Hepp, 375
L. lapicida Ach., 375
L. lavata Nyl., 384
L. limosa Ach., 387
L. lucida Ach., 246, 376
L. lurida Ach., 79, 195, 241, 367
L. mesotropa Nyl., 375
L. Metzleri Th. Fr., 398
L. nigroclavata Nyl., 384
L. ostreata Schaer., 79, 145, 291, 366
L. pallida Th. Fr., 135
L. panaeola Ach., 134, 135, 136, 375
L. parasema Ach., 183 (Fig. 101), 366
L. pelobotrya Somm., 135, 136
L. phylliscocarpa Nyl., 31
L. phyllocaris Wain., 31, 327
L. plana Nyl., 375
L. platycarpa Ach., 375
L. pycnocarpa Koerb., 375
L. quernea Ach., 236, 349, 386
L. rivulosa Ach., 374, 375, 376
L. sanguinaria Ach., 187 (Fig. 105), 248
L. inserena Nyl., 375
L. insularis Nyl., 236, 261
L. irregularis Fée, 192
L. Kochiana Hepp, 375
L. lapicida Ach., 375
L. lavata Nyl., 384
L. limosa Ach., 387
L. lucida Ach., 246, 376
L. lurida Ach., 79, 195, 241, 367
L. mesotropa Nyl., 375
L. Metzleri Th. Fr., 398
L. nigroclavata Nyl., 384
L. ostreata Schaer., 79, 145, 291, 366
L. pallida Th. Fr., 135
L. panaeola Ach., 134, 135, 136, 375
L. parasema Ach., 183 (Fig. 101), 366
L. pelobotrya Somm., 135, 136
L. phylliscocarpa Nyl., 31
L. phyllocaris Wain., 31, 327
L. plana Nyl., 375
L. platycarpa Ach., 375
L. pycnocarpa Koerb., 375
L. quernea Ach., 236, 349, 386
L. rivulosa Ach., 374, 375, 376
L. sanguinaria Ach., 187 (Fig. 105), 248
Page 664
L. sanguineoatra Ach., 370
L. stellulata Tayl., 376
L. sulphurella Hedl., 242
L. sylvicola Flot., 372
L. testacea Ach., 195 (Fig. 111)
L. tricolor Nyl. (Biatorina Griffithii), 362
L. tumida Massal., 375
L. uliginosa Ach., 254, 291, 370, 385, 387
L. vernalis Ach., 66 (Fig. 35)
Lecideaceae, 135, 241, 279, 291, 298, 310, 327, 328, 341, 346, 353
Lecideales, 290, 308
Leciophysma Th. Fr., 334
Leighton, 16, 17, 18, 19, 134, 306, 342, 353, 388
Leiosoma palmicinctum, 397
Lemming rats, 401
Lemmopsis A. Zahlbr., 334
Lenzites Fr., 261, 371
Léorier, 411
Lepidocollema Wain., 81, 336
Lepidoptera, 399
Lepolichen Trevis., 318
L. coccophora Hue, 57, 318
L. granulatus Müll.-Arg., 318
Lepra Hall., 143
L. viridis Humb., 23
Lepraria Ach., 143, 237, 305
L. stellulata Tayl., 376
L. sulphurella Hedl., 242
L. sylvicola Flot., 372
L. testacea Ach., 195 (Fig. 111)
L. tricolor Nyl. (Biatorina Griffithii), 362
L. tumida Massal., 375
L. uliginosa Ach., 254, 291, 370, 385, 387
L. vernalis Ach., 66 (Fig. 35)
Lecideaceae, 135, 241, 279, 291, 298, 310, 327, 328, 341, 346, 353
Lecideales, 290, 308
Leciophysma Th. Fr., 334
Leighton, 16, 17, 18, 19, 134, 306, 342, 353, 388
Leiosoma palmicinctum, 397
Lemming rats, 401
Lemmopsis A. Zahlbr., 334
Lenzites Fr., 261, 371
Léorier, 411
Lepidocollema Wain., 81, 336
Lepidoptera, 399
Lepolichen Trevis., 318
L. coccophora Hue, 57, 318
L. granulatus Müll.-Arg., 318
Lepra Hall., 143
L. viridis Humb., 23
Lepraria Ach., 143, 237, 305
Page 665
L. botryoides, xx
L. chlorina, 376
Leprieur, 15
Leprocollema Wain., 285, 354
Leproloma Nyl., 325
Leptodendriscum Wain., 284, 332
Leptogidium Nyl., 284, 332, 350
L. dendriscum Nyl., 332
Leptogium S. F. Gray, 69, 84, 87, 232, 285, 335, 370
L. Burgessii Mont., 245
L. byssinum Nyl., 368
L. Hildenbrandii Nyl., 364
L. lacerum S. F. Gray, 243, 254, 373
L. myochroum Nyl., 365
L. scotinum Fr., 385
L. turgidum Nyl., 385
Leptorhaphis Koerb., 263, 316
Lesdain, Bouly de, 140, 270, 271, 366, 369, 376, 398
Letharia A. Zahlbr., 84, 340
L. vulpina Wain., 95, 105, 226, 228, 246, 265, 349, 364, 410, 417
Lett, 19
Lettau, 225, 227, 369, 391, 417
Lichen, xxvi, 1, 5, 9, 303
Lichen albineus Ludw., 354
Lichen candelarius L., 371, 415
Lichen cinereus terrestris, 407
L. chlorina, 376
Leprieur, 15
Leprocollema Wain., 285, 354
Leproloma Nyl., 325
Leptodendriscum Wain., 284, 332
Leptogidium Nyl., 284, 332, 350
L. dendriscum Nyl., 332
Leptogium S. F. Gray, 69, 84, 87, 232, 285, 335, 370
L. Burgessii Mont., 245
L. byssinum Nyl., 368
L. Hildenbrandii Nyl., 364
L. lacerum S. F. Gray, 243, 254, 373
L. myochroum Nyl., 365
L. scotinum Fr., 385
L. turgidum Nyl., 385
Leptorhaphis Koerb., 263, 316
Lesdain, Bouly de, 140, 270, 271, 366, 369, 376, 398
Letharia A. Zahlbr., 84, 340
L. vulpina Wain., 95, 105, 226, 228, 246, 265, 349, 364, 410, 417
Lett, 19
Lettau, 225, 227, 369, 391, 417
Lichen, xxvi, 1, 5, 9, 303
Lichen albineus Ludw., 354
Lichen candelarius L., 371, 415
Lichen cinereus terrestris, 407
Page 666
Lichen dichotomus Engelh., 354
Lichen diffusus Ludw., 354
Lichen gelatinosus Rupp, 6
Lichen juniperinus L., 415
Lichen orbiculatus Ludw., 354
Lichen parietinus L., 371, 415
Lichen Roccella L., 415
Lichen saxatilis L., 415
Lichen tartareus L., 415
Lichen tenellus Scop., 371
Lichenacei, 306
Lichenes Coralloidei etc. Hall., 7
Lichenodium Nyl., 334
Lichenoides, 1, 6, 7, 304, 415
Lichenophoma Keisz., 201
Lichenoxanthine, 418
Lichina Ag., 163, 195, 201, 233, 281, 284, 334, 383
L. confinis Ag., 383, 384
L. pygmaea Ag., 195, 201, 383
Lichinaceae, 55, 99, 310, 333
Lichinella Nyl., 354
Lightfoot, 9, 280, 303, 407, 415
Limax, 396
Lindau, 18, 34, 36, 48, 64, 67, 78, 108, 149, 164, 168, 170, 176, 178,
184, 233, 269, 330
Lindsay, xx, 16, 17, 19, 120, 193, 203, 252, 262, 266, 348, 354, 358,
391, 401, 415, 417
Lichen diffusus Ludw., 354
Lichen gelatinosus Rupp, 6
Lichen juniperinus L., 415
Lichen orbiculatus Ludw., 354
Lichen parietinus L., 371, 415
Lichen Roccella L., 415
Lichen saxatilis L., 415
Lichen tartareus L., 415
Lichen tenellus Scop., 371
Lichenacei, 306
Lichenes Coralloidei etc. Hall., 7
Lichenodium Nyl., 334
Lichenoides, 1, 6, 7, 304, 415
Lichenophoma Keisz., 201
Lichenoxanthine, 418
Lichina Ag., 163, 195, 201, 233, 281, 284, 334, 383
L. confinis Ag., 383, 384
L. pygmaea Ag., 195, 201, 383
Lichinaceae, 55, 99, 310, 333
Lichinella Nyl., 354
Lightfoot, 9, 280, 303, 407, 415
Limax, 396
Lindau, 18, 34, 36, 48, 64, 67, 78, 108, 149, 164, 168, 170, 176, 178,
184, 233, 269, 330
Lindsay, xx, 16, 17, 19, 120, 193, 203, 252, 262, 266, 348, 354, 358,
391, 401, 415, 417
Page 667
Link, 371
Linkola, 141
Linnaeus, 7, 142, 154, 304, 312, 392, 401, 409, 415
Lister, 267
Listerella paradoxa Jahn, 267
Lithographa Nyl., 322
Lithoicea Massal., see Verrucaria
L. lecideoides Massal., 373
Lithothelium Müll.-Arg., 317
Litmus, 413
Lobaria Schreb., 136, 182, 287, 336
L. laciniata Wain., 133, 134
L. laetevirens A. Zahlbr., 2, 196
L. pulmonaria Hoffm., 2, 3, 10, 90, 96, 126 (Fig. 127), 130, 195,
252, 267, 336, 400, 406, 408, 411, 416, 418
L. scrobiculata DC., 130, 143
L’Obel, 2
Lopadiopsis Wain., 327
Lopadium Koerb., 191, 329
Lophothelium Stirt., 319
Loxa (Cinchona), 364
Ludwig, 354
Luffia lapidella, 399
Lung-wort, 406, 409
Lutz, 108
Luyken, xx, 156, 184
Linkola, 141
Linnaeus, 7, 142, 154, 304, 312, 392, 401, 409, 415
Lister, 267
Listerella paradoxa Jahn, 267
Lithographa Nyl., 322
Lithoicea Massal., see Verrucaria
L. lecideoides Massal., 373
Lithothelium Müll.-Arg., 317
Litmus, 413
Lobaria Schreb., 136, 182, 287, 336
L. laciniata Wain., 133, 134
L. laetevirens A. Zahlbr., 2, 196
L. pulmonaria Hoffm., 2, 3, 10, 90, 96, 126 (Fig. 127), 130, 195,
252, 267, 336, 400, 406, 408, 411, 416, 418
L. scrobiculata DC., 130, 143
L’Obel, 2
Lopadiopsis Wain., 327
Lopadium Koerb., 191, 329
Lophothelium Stirt., 319
Loxa (Cinchona), 364
Ludwig, 354
Luffia lapidella, 399
Lung-wort, 406, 409
Lutz, 108
Luyken, xx, 156, 184
Page 668
Lycoperdaceae, 307
Lyell, 14
Lyngbya Ag., 136
Mackay, 13
McLean, 385
Macmillan, 357, 391
Maheu, 243, 387
Maire, 185, 186, 189
Malinowski, 74, 371, 374
Malme, 261
Malpighi, 5, 142, 155
Manna, 404, 422
Marchantia L., 1, 5
Maronea Massal., 331
Martindale, 19
Martius, 15
Massalongia Koerb., 287, 335
Massalongo, 16, 188, 305
Massee, 308
Mastoidea Hook. and Harv., 315
Mastoidiaceae, 60, 309, 315
Mattirolo, 152
Mäule, 162, 164
Mayfield, 368
Mazosia Massal., 59, 323
Lyell, 14
Lyngbya Ag., 136
Mackay, 13
McLean, 385
Macmillan, 357, 391
Maheu, 243, 387
Maire, 185, 186, 189
Malinowski, 74, 371, 374
Malme, 261
Malpighi, 5, 142, 155
Manna, 404, 422
Marchantia L., 1, 5
Maronea Massal., 331
Martindale, 19
Martius, 15
Massalongia Koerb., 287, 335
Massalongo, 16, 188, 305
Massee, 308
Mastoidea Hook. and Harv., 315
Mastoidiaceae, 60, 309, 315
Mattirolo, 152
Mäule, 162, 164
Mayfield, 368
Mazosia Massal., 59, 323
Page 669
Mead, Richard, 407
Megalospora Mey. and Flot., 329
Melampydium Müll.-Arg., 325
Melanotheca Müll.-Arg., 317
Melaspilea Nyl., 321, 322
Mereschkovsky, 258
Merrett, 3
Metzger, 176, 240
Meyer, 13, 46, 51, 126, 143, 156, 187, 252, 258, 305
Micarea Fr., see Biatorina Massal.
Michael, 397
Michaux, 14
Micheli, 1, 6, 142, 155
Microcystis Kütz., 52, 319
Microglaena Lönnr., 314
Micrographa Müll.-Arg., 322
Microphiale A. Zahlbr., 328
Microthelia Koerb., 316
Microtheliopsis Müll.-Arg., 318
Minks, 26
Minksia Müll.-Arg., 323
Mites, 395, 397
Miyoshi, 256, 403
Mnium hornum L., 65 (Fig. 35)
Moebius, 62
Mohl, 185, 186
Megalospora Mey. and Flot., 329
Melampydium Müll.-Arg., 325
Melanotheca Müll.-Arg., 317
Melaspilea Nyl., 321, 322
Mereschkovsky, 258
Merrett, 3
Metzger, 176, 240
Meyer, 13, 46, 51, 126, 143, 156, 187, 252, 258, 305
Micarea Fr., see Biatorina Massal.
Michael, 397
Michaux, 14
Micheli, 1, 6, 142, 155
Microcystis Kütz., 52, 319
Microglaena Lönnr., 314
Micrographa Müll.-Arg., 322
Microphiale A. Zahlbr., 328
Microthelia Koerb., 316
Microtheliopsis Müll.-Arg., 318
Minks, 26
Minksia Müll.-Arg., 323
Mites, 395, 397
Miyoshi, 256, 403
Mnium hornum L., 65 (Fig. 35)
Moebius, 62
Mohl, 185, 186
Page 670
Molisch, 250
Möller, 49, 154, 196, 202, 203
Moma orion, 399
Monas Lens, xx
Monascus, Van Teigh., 178
Montagne, 15
Moreau, xxi, 168, 175, 176, 212, 266
Moriola Norm., 313
Moriolaceae, 309, 313
Morison, 1, 4, 5, 155, 304
Moss, 356
Mousse des Chênes, 418
Mudd, 16, 17, 19
Muenster, 354
Mühlenberg, 14
Mulder, 210
Müller(-Argau), 18, 26, 191, 192, 205, 278, 307, 353, 405
Müller, K., 212
Müllerella Hepp, 275
Musco-fungus, 1
Muscus, 1
Muscus cranii humani, 413
Musk, 419
Mycetozoon on Lichens, 267
Mycoblastus Norm., 329
M. sanguinarius Th. Fr., 188; see Lecidea
Möller, 49, 154, 196, 202, 203
Moma orion, 399
Monas Lens, xx
Monascus, Van Teigh., 178
Montagne, 15
Moreau, xxi, 168, 175, 176, 212, 266
Moriola Norm., 313
Moriolaceae, 309, 313
Morison, 1, 4, 5, 155, 304
Moss, 356
Mousse des Chênes, 418
Mudd, 16, 17, 19
Muenster, 354
Mühlenberg, 14
Mulder, 210
Müller(-Argau), 18, 26, 191, 192, 205, 278, 307, 353, 405
Müller, K., 212
Müllerella Hepp, 275
Musco-fungus, 1
Muscus, 1
Muscus cranii humani, 413
Musk, 419
Mycetozoon on Lichens, 267
Mycoblastus Norm., 329
M. sanguinarius Th. Fr., 188; see Lecidea
Page 671
Mycocalicium Rehm, 277
M. parietinum Rehm, 277
Mycoconiocybe Rehm, 277
Mycoidea Cunningh., 35, 59, 309, 318, 352, 363
M. parasitica Cunningh., 36, 59 (Fig. 31), 60
Mycoideaceae, 59
Mycoporaceae, 309, 318, 352
Mycoporellum Zahlbr., 159, 318
Mycoporum Flot., 159, 276, 318
Mycosphaerella Johans., 39
Mycosphaerellaceae, 275
Myriangiacei, 306
Myxodictyon Massal., 338
Myxophyceae, xix, 51, 52-55, 60, 68, 272, 324, 385
Narcyria monilifera, 399
Necker, 123, 154
Nees von Esenbeck, xxiv
Neophyllis Wils., 330, 351
Nephroma Ach., 63, 135, 136, 169, 244, 286, 337, 348
N. expallidum Nyl., 139 (Fig. 79)
Nephromium Nyl., 63, 158, 175, 200, 222, 244, 283, 286, 337, 349,
351
N. laevigatum Nyl., 195
N. lusitanicum Nyl., 228, 246
N. tomentosum Nyl., 87, 128, 169
M. parietinum Rehm, 277
Mycoconiocybe Rehm, 277
Mycoidea Cunningh., 35, 59, 309, 318, 352, 363
M. parasitica Cunningh., 36, 59 (Fig. 31), 60
Mycoideaceae, 59
Mycoporaceae, 309, 318, 352
Mycoporellum Zahlbr., 159, 318
Mycoporum Flot., 159, 276, 318
Mycosphaerella Johans., 39
Mycosphaerellaceae, 275
Myriangiacei, 306
Myxodictyon Massal., 338
Myxophyceae, xix, 51, 52-55, 60, 68, 272, 324, 385
Narcyria monilifera, 399
Necker, 123, 154
Nees von Esenbeck, xxiv
Neophyllis Wils., 330, 351
Nephroma Ach., 63, 135, 136, 169, 244, 286, 337, 348
N. expallidum Nyl., 139 (Fig. 79)
Nephromium Nyl., 63, 158, 175, 200, 222, 244, 283, 286, 337, 349,
351
N. laevigatum Nyl., 195
N. lusitanicum Nyl., 228, 246
N. tomentosum Nyl., 87, 128, 169
Page 672
Nephromopsis Müll.-Arg., 158, 244, 339
Neubert, 410
Neubner, 62, 175, 189, 288
Neuropogon Flot. and Nees, 346
Nienburg, 38, 64, 123, 166, 167, 168, 169, 177, 185, 196, 240
Nilson, 147, 151, 250, 358, 389
Norman, 16, 313
Normandina Nyl., see Coriscium
Normandina Wain., 315
Nostoc Vauch., 20, 21, 23, 24, 26, 27, 32, 42, 53, 61, 63, 69, 136, 138,
232, 246, 266, 285, 309 et seq., 396
N. coerulescens Lyngb., 53 (Fig. 18)
N. lichenoides Kütz., xx, 54
N. Linckia Born., 53 (Fig. 18)
N. sphaericum Vauch., 54
N. symbioticum, 45
Nostocaceae, 25, 53
Notaris, De, 1, 15, 16
Notaspis lutorum, 397
Nyctalis Fr., 261
Nylander, xxi, 7, 8, 16, 18, 25, 30, 52, 126, 131, 135, 136, 152, 197,
228, 262, 306, 325, 350, 353, 360, 383
Nylanderiella Hue, 315
Obryzum Wallr., 263
Ocellularia Spreng., 326
Ochrolechia Massal., 338
Neubert, 410
Neubner, 62, 175, 189, 288
Neuropogon Flot. and Nees, 346
Nienburg, 38, 64, 123, 166, 167, 168, 169, 177, 185, 196, 240
Nilson, 147, 151, 250, 358, 389
Norman, 16, 313
Normandina Nyl., see Coriscium
Normandina Wain., 315
Nostoc Vauch., 20, 21, 23, 24, 26, 27, 32, 42, 53, 61, 63, 69, 136, 138,
232, 246, 266, 285, 309 et seq., 396
N. coerulescens Lyngb., 53 (Fig. 18)
N. lichenoides Kütz., xx, 54
N. Linckia Born., 53 (Fig. 18)
N. sphaericum Vauch., 54
N. symbioticum, 45
Nostocaceae, 25, 53
Notaris, De, 1, 15, 16
Notaspis lutorum, 397
Nyctalis Fr., 261
Nylander, xxi, 7, 8, 16, 18, 25, 30, 52, 126, 131, 135, 136, 152, 197,
228, 262, 306, 325, 350, 353, 360, 383
Nylanderiella Hue, 315
Obryzum Wallr., 263
Ocellularia Spreng., 326
Ochrolechia Massal., 338
Page 673
O. pallescens Koerb., 187 (Fig. 106), 213
Ochrophaeae Wain., 295
Officinal barks, 15
Ohlert, 234
Oidia, 189
Olivier, 342
Omphalaria Dur. and Mont., 348, 373, 393
O. Heppii Müll., 63
O. pulvinata Nyl., 373
Oniscus, 396
Oospora Wallr., 45
Opegrapha Ach., 11, 13, 35, 184, 304, 321, 322, 353, 354, 361
O. atra Pers., 15, 202
O. calcarea Turn., 383
O. endoleuca Nyl., 243
O. hapalea Ach., 243
O. saxicola Ach., 216, 219
O. subsiderella Nyl., 50, 202, 349
O. Thomasiana Goepp., 354
O. varia Pers., 354, 365
O. vulgata Ach., 30
O. zonata Koerb., 392
Opegraphella Müll.-Arg., 322
Orbilia coccinella Karst., 261
Orchil lichen, 412, 416
Oribata Parmeliae, 397
Ochrophaeae Wain., 295
Officinal barks, 15
Ohlert, 234
Oidia, 189
Olivier, 342
Omphalaria Dur. and Mont., 348, 373, 393
O. Heppii Müll., 63
O. pulvinata Nyl., 373
Oniscus, 396
Oospora Wallr., 45
Opegrapha Ach., 11, 13, 35, 184, 304, 321, 322, 353, 354, 361
O. atra Pers., 15, 202
O. calcarea Turn., 383
O. endoleuca Nyl., 243
O. hapalea Ach., 243
O. saxicola Ach., 216, 219
O. subsiderella Nyl., 50, 202, 349
O. Thomasiana Goepp., 354
O. varia Pers., 354, 365
O. vulgata Ach., 30
O. zonata Koerb., 392
Opegraphella Müll.-Arg., 322
Orbilia coccinella Karst., 261
Orchil lichen, 412, 416
Oribata Parmeliae, 397
Page 674
Oribatidae, 397
Oropogon Fr., 340
O. loxensis Th. Fr., 130, 210, 352
Orphniospora Koerb., 329
Orthidium, 191
Orthoptera, 397
Oscillaria Bosc., 24
Pachyphiale Lönnr., 328
Padina Pavonia Gaillon, 153
Palmella Lyngb., 24, 57, 232, 278, 282, 289, 309, 321, 338, 353
P. botryoides Kütz., 313
Pannaria Del., 61, 79, 81, 135, 168, 175, 336, 392
P. brunnea Massal., 244, 370
P. microphylla Massal., 81, 244
P. pezizoides Leight., 63
P. rubiginosa Del., 283
P. triptophylla Nyl., 244
Pannariaceae, 54, 135, 285, 287, 311, 335
Pannoparmelia Darbish., 338
P. anzioides Darbish., 90 (Fig. 51)
Paracelsus, 407
Paratheliaceae, 309, 316, 352
Parathelium Müll.-Arg., 317
Parfitt, 95
Parkinson, 3, 407
Oropogon Fr., 340
O. loxensis Th. Fr., 130, 210, 352
Orphniospora Koerb., 329
Orthidium, 191
Orthoptera, 397
Oscillaria Bosc., 24
Pachyphiale Lönnr., 328
Padina Pavonia Gaillon, 153
Palmella Lyngb., 24, 57, 232, 278, 282, 289, 309, 321, 338, 353
P. botryoides Kütz., 313
Pannaria Del., 61, 79, 81, 135, 168, 175, 336, 392
P. brunnea Massal., 244, 370
P. microphylla Massal., 81, 244
P. pezizoides Leight., 63
P. rubiginosa Del., 283
P. triptophylla Nyl., 244
Pannariaceae, 54, 135, 285, 287, 311, 335
Pannoparmelia Darbish., 338
P. anzioides Darbish., 90 (Fig. 51)
Paracelsus, 407
Paratheliaceae, 309, 316, 352
Parathelium Müll.-Arg., 317
Parfitt, 95
Parkinson, 3, 407
Page 675
Parmelei, 353
Parmelia Ach., 84, 86, 93, 94, 95, 133, 200, 213, 227, 231, 238, 241,
242, 249, 260, 264, 267, 269, 299, 300, 305, 346, 347, 348, 349,
351, 354, 364, 372, 414
P. acetabulum Dub., 30, 167, 169 (Fig. 96), 170, 180, 195 (Fig.
111), 231, 255, 259, 360
P. adglutinata Floerk., 365
P. aleurites Ach., 364
P. alpicola Fr., 18, 350, 387
P. aspidota Rosend. (see P. exasperata), 92 (Fig. 53), 170, 338
P. Borreri Turn., 265; see P. dubia
P. caperata Ach., 88 (Fig. 49), 253, 255, 365, 366, 395
P. cetrata Ach., 92
P. conspersa Ach., 194, 241, 242, 355, 369, 376, 416, 417
P. crinita Nyl., 365
P. dubia Schaer., 377
P. encausta Ach., 268, 388, 393
P. enteromorpha Ach., 131
P. exasperata Carroll, 62, 129 (Fig. 74), 132, 196
P. farinacea Bitt., 131, 143
P. fuliginosa Nyl., 247, 361, 376, 386
P. glabra Nyl., 87, 170, 176
P. glabratula Lamy, 170
P. glomellifera Nyl., 249, 251
P. hyperopta Ach., 261
P. isidiophora A. Zahlbr., 66
P. Kamtschadalis Eschw., 300
Parmelia Ach., 84, 86, 93, 94, 95, 133, 200, 213, 227, 231, 238, 241,
242, 249, 260, 264, 267, 269, 299, 300, 305, 346, 347, 348, 349,
351, 354, 364, 372, 414
P. acetabulum Dub., 30, 167, 169 (Fig. 96), 170, 180, 195 (Fig.
111), 231, 255, 259, 360
P. adglutinata Floerk., 365
P. aleurites Ach., 364
P. alpicola Fr., 18, 350, 387
P. aspidota Rosend. (see P. exasperata), 92 (Fig. 53), 170, 338
P. Borreri Turn., 265; see P. dubia
P. caperata Ach., 88 (Fig. 49), 253, 255, 365, 366, 395
P. cetrata Ach., 92
P. conspersa Ach., 194, 241, 242, 355, 369, 376, 416, 417
P. crinita Nyl., 365
P. dubia Schaer., 377
P. encausta Ach., 268, 388, 393
P. enteromorpha Ach., 131
P. exasperata Carroll, 62, 129 (Fig. 74), 132, 196
P. farinacea Bitt., 131, 143
P. fuliginosa Nyl., 247, 361, 376, 386
P. glabra Nyl., 87, 170, 176
P. glabratula Lamy, 170
P. glomellifera Nyl., 249, 251
P. hyperopta Ach., 261
P. isidiophora A. Zahlbr., 66
P. Kamtschadalis Eschw., 300
Page 676
P. lacunosa Meng. and Goepp., 355
P. lanata Wallr., see P. pubescens
P. locarensis Zopf., 249
P. molliuscula Ach., 265
P. Mougeotii Schaer., 375
P. obscurata DC., 64, 131, 176, 242
P. olivacea Ach., 247, 365
P. omphalodes Ach., 3, 260, 375, 387, 415 (Fig. 135)
P. papulosa Rosend., 150, 214, 219
P. perforata Hook. (?), 365
P. perlata Ach., 92, 114, 213, 237, 243, 262, 353, 363, 403, 416
P. pertusa Schaer., 131
P. physodes Ach., 64, 91, 144 (Fig. 83), 146 (Fig. 84), 156, 194,
234, 237, 242, 253, 262, 299, 355, 361, 363, 366, 384, 385,
416
P. pilosella Hue, 92
P. proboscidea Tayl., 92, 150
P. prolixa Carroll, 241, 249, 382
P. pubescens Wain., 85, 299, 300, 350, 375, 387
P. revoluta Floerk., 247, 259 (Fig. 121)
P. saxatilis Ach., 169, 170, 242, 243, 253, 260, 355, 361, 365,
366, 375, 386, 387, 393, 407 (Fig. 131), 416
P. scortea Ach., 150, 366
P. stygia Ach., 130, 299, 350, 375, 387, 393
P. subaurifera Nyl., 143, 226, 246, 377
P. sulcata Tayl., 144, 361
P. tiliacea Ach., 164, 170, 252, 365
P. lanata Wallr., see P. pubescens
P. locarensis Zopf., 249
P. molliuscula Ach., 265
P. Mougeotii Schaer., 375
P. obscurata DC., 64, 131, 176, 242
P. olivacea Ach., 247, 365
P. omphalodes Ach., 3, 260, 375, 387, 415 (Fig. 135)
P. papulosa Rosend., 150, 214, 219
P. perforata Hook. (?), 365
P. perlata Ach., 92, 114, 213, 237, 243, 262, 353, 363, 403, 416
P. pertusa Schaer., 131
P. physodes Ach., 64, 91, 144 (Fig. 83), 146 (Fig. 84), 156, 194,
234, 237, 242, 253, 262, 299, 355, 361, 363, 366, 384, 385,
416
P. pilosella Hue, 92
P. proboscidea Tayl., 92, 150
P. prolixa Carroll, 241, 249, 382
P. pubescens Wain., 85, 299, 300, 350, 375, 387
P. revoluta Floerk., 247, 259 (Fig. 121)
P. saxatilis Ach., 169, 170, 242, 243, 253, 260, 355, 361, 365,
366, 375, 386, 387, 393, 407 (Fig. 131), 416
P. scortea Ach., 150, 366
P. stygia Ach., 130, 299, 350, 375, 387, 393
P. subaurifera Nyl., 143, 226, 246, 377
P. sulcata Tayl., 144, 361
P. tiliacea Ach., 164, 170, 252, 365
Page 677
P. tristis Wallr., 88, 130, 247, 375, 387
P. verruculifera Nyl., 87, 143, 214
P. vittata Nyl., 131, 143
Parmeliaceae, 200, 287, 298, 311
Parmeliales, 308
Parmeliella Müll.-Arg., 81, 286, 336
Parmeliopsis Nyl., 339
Parmentaria Fée, 317
Patellaria Fr., 280
Patellariaceae, 278
Patinella Sacc., 279
P. atroviridis Rehm, 278
Patouillard, 389
Paulia Fée, 284, 333, 352
Paulson, 244, 254, 366
Paulson and Hastings, 28, 38, 44, 56, 260
Paulson and Thompson, 254, 361, 369, 377, 397
Peccania Forss., 284, 333, 373
Peirce, xxiii, 33, 34, 108, 258, 359
Peltati, 305
Peltidea Ach., 63, 286; see Peltigera
Peltigera Willd., 3, 42, 53, 61, 63, 88, 135, 136, 137, 168, 175, 186,
204, 212, 213, 222, 232, 242, 257, 266, 283, 286, 337, 346, 349,
355, 367, 384, 385, 392
P. americana Wain., 351
P. aphthosa Willd., 26, 87, 133, 138 (Fig. 78 a, b), 141, 211, 262,
347, 359, 370, 406
P. verruculifera Nyl., 87, 143, 214
P. vittata Nyl., 131, 143
Parmeliaceae, 200, 287, 298, 311
Parmeliales, 308
Parmeliella Müll.-Arg., 81, 286, 336
Parmeliopsis Nyl., 339
Parmentaria Fée, 317
Patellaria Fr., 280
Patellariaceae, 278
Patinella Sacc., 279
P. atroviridis Rehm, 278
Patouillard, 389
Paulia Fée, 284, 333, 352
Paulson, 244, 254, 366
Paulson and Hastings, 28, 38, 44, 56, 260
Paulson and Thompson, 254, 361, 369, 377, 397
Peccania Forss., 284, 333, 373
Peirce, xxiii, 33, 34, 108, 258, 359
Peltati, 305
Peltidea Ach., 63, 286; see Peltigera
Peltigera Willd., 3, 42, 53, 61, 63, 88, 135, 136, 137, 168, 175, 186,
204, 212, 213, 222, 232, 242, 257, 266, 283, 286, 337, 346, 349,
355, 367, 384, 385, 392
P. americana Wain., 351
P. aphthosa Willd., 26, 87, 133, 138 (Fig. 78 a, b), 141, 211, 262,
347, 359, 370, 406
Page 678
P. canina Willd., 24, 51, 84 (Fig. 47), 87, 89 (Fig. 50), 93 (Figs.
54, 55), 97, 185, 213, 254, 262, 359, 367, 370, 394, 396,
407, 418
P. horizontalis Hoffm., 169, 244
P. lepidophora (Nyl.) Bitt., 140
P. leptoderma Nyl., 351
P. malacea Fr., 169, 370
P. polydactyla Hoffm., 51, 244, 266, 368
P. rufescens Hoffm., 169, 386
P. spuria Leight., 268, 369
P. spuriella Wain., 351
P. venosa Hoffm., 244, 347
Peltigeraceae, 54, 135, 283, 286, 287, 311, 336
Pelvetia canaliculata Dec. and Thur., 39
Pentagenella Darbish., 83, 324
Perforaria Müll.-Arg., 337
Persio, 413
Persoon, 10, 21, 123, 156, 395
Pertusaria DC., 34, 73, 85, 86, 88, 170, 180, 186, 213, 246, 253, 337,
414
P. amara Ach., 148, 236, 243, 349, 361, 366, 408 (Fig. 132)
P. communis DC., 50, 202, 214 (Fig. 116), 255, 269, 366, 393
P. concreta Nyl., 382
P. corallina (Ach.) Bachm., 374
P. dactylina Nyl., 387
P. dealbata Cromb., 215, 375, 376
P. faginea Leight., 396
54, 55), 97, 185, 213, 254, 262, 359, 367, 370, 394, 396,
407, 418
P. horizontalis Hoffm., 169, 244
P. lepidophora (Nyl.) Bitt., 140
P. leptoderma Nyl., 351
P. malacea Fr., 169, 370
P. polydactyla Hoffm., 51, 244, 266, 368
P. rufescens Hoffm., 169, 386
P. spuria Leight., 268, 369
P. spuriella Wain., 351
P. venosa Hoffm., 244, 347
Peltigeraceae, 54, 135, 283, 286, 287, 311, 336
Pelvetia canaliculata Dec. and Thur., 39
Pentagenella Darbish., 83, 324
Perforaria Müll.-Arg., 337
Persio, 413
Persoon, 10, 21, 123, 156, 395
Pertusaria DC., 34, 73, 85, 86, 88, 170, 180, 186, 213, 246, 253, 337,
414
P. amara Ach., 148, 236, 243, 349, 361, 366, 408 (Fig. 132)
P. communis DC., 50, 202, 214 (Fig. 116), 255, 269, 366, 393
P. concreta Nyl., 382
P. corallina (Ach.) Bachm., 374
P. dactylina Nyl., 387
P. dealbata Cromb., 215, 375, 376
P. faginea Leight., 396
Page 679
P. globulifera Nyl., 33 (Fig. 12), 236, 237, 262, 357, 366
P. glomerata Schaer., 387
P. lactea Nyl., 374, 376
P. leioplaca Schaer., 365
P. lutescens Lamy, 226
P. melaleuca Dub., 417
P. oculata Th. Fr., 387
P. velata Nyl., 265
P. Wulfenii DC., 226, 366
Pertusariaceae, 147, 311
Petch, 397
Petiver, 4, 10
Petractis Fr., 327
P. exanthematica Fr., 61, 75, 215, 216
Peziza Dill., 157, 213, 307
P. resinae Fr., 355
Pfaff, 221
Pfeffer, 220
Phacopsis vulpina Tobl., 265
Phaeographina Müll.-Arg., 322
Phaeographis Müll.-Arg., 322
Ph. Lyellii A. Zahlbr., 350
Phaeotrema Müll.-Arg., 326
Phalena, 395
Phascum cuspidatum Schreb., 45
Phialopsis rubra Koerb., 174, 249; see Gyalecta
P. glomerata Schaer., 387
P. lactea Nyl., 374, 376
P. leioplaca Schaer., 365
P. lutescens Lamy, 226
P. melaleuca Dub., 417
P. oculata Th. Fr., 387
P. velata Nyl., 265
P. Wulfenii DC., 226, 366
Pertusariaceae, 147, 311
Petch, 397
Petiver, 4, 10
Petractis Fr., 327
P. exanthematica Fr., 61, 75, 215, 216
Peziza Dill., 157, 213, 307
P. resinae Fr., 355
Pfaff, 221
Pfeffer, 220
Phacopsis vulpina Tobl., 265
Phaeographina Müll.-Arg., 322
Phaeographis Müll.-Arg., 322
Ph. Lyellii A. Zahlbr., 350
Phaeotrema Müll.-Arg., 326
Phalena, 395
Phascum cuspidatum Schreb., 45
Phialopsis rubra Koerb., 174, 249; see Gyalecta
Page 680
Phillips, 252
Phleopeccania Stein., 284, 333, 352
Phlyctella Müll.-Arg., 338
Phlyctidia Müll.-Arg., 338
Phlyctis Wallr., 338
P. agelaea Koerb., 174
Phycolichens, 22, 282, 283, 285
Phycopeltis Millard., 59, 278, 318, 321, 322, 323, 327, 352, 363
P. expansa Jenn., 35 (Fig. 13), 60 (Fig. 32)
Phyllactidium Moeb., 59, 62, 288, 309, 310, 318, 327, 363
P. tropicum Moeb., 59
Phylliscidium Forss., 333
Phylliscum Nyl., 286, 333
Phyllobathelium Müll.-Arg., 318
Phyllophora Grev., 111
Phyllophthalmaria A. Zahlbr., 326, 352
Ph. coccinea A. Zahlbr., 352
Phylloporina Müll.-Arg., 318
Phyllopsora Müll.-Arg., 329
P. furfuracea A. Zahlbr., 329
Phyllopsoraceae, 310, 329
Phyllopyreniaceae, 309, 318
Phymaloidei, 304
Physcia Schreb., 90, 94, 166, 186, 238, 301, 351, 372, 399
P. aipolia Nyl., 20 (Fig. 1), 249
P. aquila Nyl., 380, 382, 384
Phleopeccania Stein., 284, 333, 352
Phlyctella Müll.-Arg., 338
Phlyctidia Müll.-Arg., 338
Phlyctis Wallr., 338
P. agelaea Koerb., 174
Phycolichens, 22, 282, 283, 285
Phycopeltis Millard., 59, 278, 318, 321, 322, 323, 327, 352, 363
P. expansa Jenn., 35 (Fig. 13), 60 (Fig. 32)
Phyllactidium Moeb., 59, 62, 288, 309, 310, 318, 327, 363
P. tropicum Moeb., 59
Phylliscidium Forss., 333
Phylliscum Nyl., 286, 333
Phyllobathelium Müll.-Arg., 318
Phyllophora Grev., 111
Phyllophthalmaria A. Zahlbr., 326, 352
Ph. coccinea A. Zahlbr., 352
Phylloporina Müll.-Arg., 318
Phyllopsora Müll.-Arg., 329
P. furfuracea A. Zahlbr., 329
Phyllopsoraceae, 310, 329
Phyllopyreniaceae, 309, 318
Phymaloidei, 304
Physcia Schreb., 90, 94, 166, 186, 238, 301, 351, 372, 399
P. aipolia Nyl., 20 (Fig. 1), 249
P. aquila Nyl., 380, 382, 384
Page 681
P. ascendens Bitt., 270, 369, 377
P. caesia Nyl., 226, 369, 384
P. chrysophthalma, see Teloschistes
P. ciliaris DC., 3, 46, 84 (Fig. 48), 92, 94, 99, 103, 155, 165 (Fig.
94), 166, 167, 182 (Fig. 100), 184, 185 (Fig. 104), 187, 189,
192, 243, 246, 247, 355, 360, 411, 419
P. granulifera Nyl., 365
P. hispida Tuck., 29, 92, 146, 164, 166, 169, 194 (Fig. 110), 241,
271, 360, 366
P. hypoleuca Tuck., 399
P. intricata Schaer., 301
P. leucomelas Mich., 99
P. obscura Nyl., 243, 360, 365, 369, 377
P. parietina (see Xanthoria), 29 (Figs. 7, 8)
P. picta Nyl., 349, 353
P. pulverulenta Nyl., 28, 164 (Fig. 93), 166, 181, 248, 360, 365,
366, 377, 399
P. puncticulata Hue, 33
P. sciastrella Hann., 369
P. stellaris Nyl., 29, 365, 384
P. stellaris var. tenella Cromb., see P. hispida Tuck.
P. subobscura A. L. Sm., 384
P. tenella Bitt., 366, 384, 386
P. tribacia Nyl., 365
P. villosa Dub., 268
Physciaceae, 136, 200, 267, 300, 308, 311, 341
Physcidia Tuck., 299, 339
P. caesia Nyl., 226, 369, 384
P. chrysophthalma, see Teloschistes
P. ciliaris DC., 3, 46, 84 (Fig. 48), 92, 94, 99, 103, 155, 165 (Fig.
94), 166, 167, 182 (Fig. 100), 184, 185 (Fig. 104), 187, 189,
192, 243, 246, 247, 355, 360, 411, 419
P. granulifera Nyl., 365
P. hispida Tuck., 29, 92, 146, 164, 166, 169, 194 (Fig. 110), 241,
271, 360, 366
P. hypoleuca Tuck., 399
P. intricata Schaer., 301
P. leucomelas Mich., 99
P. obscura Nyl., 243, 360, 365, 369, 377
P. parietina (see Xanthoria), 29 (Figs. 7, 8)
P. picta Nyl., 349, 353
P. pulverulenta Nyl., 28, 164 (Fig. 93), 166, 181, 248, 360, 365,
366, 377, 399
P. puncticulata Hue, 33
P. sciastrella Hann., 369
P. stellaris Nyl., 29, 365, 384
P. stellaris var. tenella Cromb., see P. hispida Tuck.
P. subobscura A. L. Sm., 384
P. tenella Bitt., 366, 384, 386
P. tribacia Nyl., 365
P. villosa Dub., 268
Physciaceae, 136, 200, 267, 300, 308, 311, 341
Physcidia Tuck., 299, 339
Page 682
Ph. Wrightii Nyl., 352
Physma Massal., 163, 284, 334, 341
P. chalazanum Arn., 32 (Fig. 9)
P. compactum Koerb., 163, 266
P. franconicum Massal., 263
Pilocarpaceae, 310, 325
Pilocarpon Wain., 325, 353; see Pilophorus
P. leucoblepharum Wain., 325, 363
Pilophorus Th. Fr., 17, 125, 133, 135, 201, 292, 294, 297, 330
P. robustus Th. Fr., 136
Pinus sylvestris L., 94, 271
Piptocephalis De Bary, 261
Placidiopsis Beltr., 288
Placodium DC., 80, 339, 340, 346, 360, 372
P. atroflavum A. L. Sm., 386
P. aurantiacum Hepp, 365
P. bicolor Tuck., 136
P. callopismum Mér., 349
P. cerinum Hepp, 262, 365, 366, 367
P. citrinum Hepp, 224, 271, 349, 373, 377, 386, 393
P. decipiens Leight., 218, 369, 383
P. elegans DC., 225, 241, 347, 369, 390
P. ferrugineum Hepp, 346, 384
P. flavescens A. L. Sm., 377
P. fruticulosum Darbish., 347
P. fulgens S. F. Gray, 367
Physma Massal., 163, 284, 334, 341
P. chalazanum Arn., 32 (Fig. 9)
P. compactum Koerb., 163, 266
P. franconicum Massal., 263
Pilocarpaceae, 310, 325
Pilocarpon Wain., 325, 353; see Pilophorus
P. leucoblepharum Wain., 325, 363
Pilophorus Th. Fr., 17, 125, 133, 135, 201, 292, 294, 297, 330
P. robustus Th. Fr., 136
Pinus sylvestris L., 94, 271
Piptocephalis De Bary, 261
Placidiopsis Beltr., 288
Placodium DC., 80, 339, 340, 346, 360, 372
P. atroflavum A. L. Sm., 386
P. aurantiacum Hepp, 365
P. bicolor Tuck., 136
P. callopismum Mér., 349
P. cerinum Hepp, 262, 365, 366, 367
P. citrinum Hepp, 224, 271, 349, 373, 377, 386, 393
P. decipiens Leight., 218, 369, 383
P. elegans DC., 225, 241, 347, 369, 390
P. ferrugineum Hepp, 346, 384
P. flavescens A. L. Sm., 377
P. fruticulosum Darbish., 347
P. fulgens S. F. Gray, 367
Page 683
P. lacteum Lesd., 377
P. lobulatum A. L. Sm., 379, 382, 384
P. luteoalbum Hepp, 301
P. murorum DC., 42, 80 (Fig. 42), 227, 241, 243, 347, 369, 380
P. nivale Tuck., 301
P. pyraceum Anzi, 369, 377
P. rupestre Br. and Rostr., 301
P. subfruticulosum Elenk., 347
P. sympageum, see P. flavescens
P. tegularis (Ehrh.) Darbish., 379, 384
P. teicholytum DC., 369
Placodium Hill (non DC.), 8
Placodium Web. (non DC.), 9
P. Garovagli (Koerb.) Fried., 81
P. saxicolum S. F. Gray, 146, 168; see Lecanora
Placolecania Zahlbr., 338
Placothelium Müll.-Arg., 285, 319
Placynthium Ach., 336
P. nigrum S. F. Gray, 248, 373
Plagiothecium sylvaticum Buch. and Schimp., 237
Plagiotrema Müll.-Arg., 317
Platygrapha Nyl., 325
Platysma Nyl., 8, 200, 257; see Cetraria
P. commixtum Nyl., 375
P. corniculatum Hill, 8
P. Fahlunense Nyl., 375
P. lobulatum A. L. Sm., 379, 382, 384
P. luteoalbum Hepp, 301
P. murorum DC., 42, 80 (Fig. 42), 227, 241, 243, 347, 369, 380
P. nivale Tuck., 301
P. pyraceum Anzi, 369, 377
P. rupestre Br. and Rostr., 301
P. subfruticulosum Elenk., 347
P. sympageum, see P. flavescens
P. tegularis (Ehrh.) Darbish., 379, 384
P. teicholytum DC., 369
Placodium Hill (non DC.), 8
Placodium Web. (non DC.), 9
P. Garovagli (Koerb.) Fried., 81
P. saxicolum S. F. Gray, 146, 168; see Lecanora
Placolecania Zahlbr., 338
Placothelium Müll.-Arg., 285, 319
Placynthium Ach., 336
P. nigrum S. F. Gray, 248, 373
Plagiothecium sylvaticum Buch. and Schimp., 237
Plagiotrema Müll.-Arg., 317
Platygrapha Nyl., 325
Platysma Nyl., 8, 200, 257; see Cetraria
P. commixtum Nyl., 375
P. corniculatum Hill, 8
P. Fahlunense Nyl., 375
Page 684
P. glaucum Nyl., 10, 375, 376, 418
P. lacunosa Nyl., 375
Pleospora collematum Zuk., 163, 266
Pleurococcus Menegh. (?), 22, 29, 62
P. Naegeli Chod., 28
P. vulgaris Menegh., 28, 55 (Fig. 22), 223
P. vulgaris Naeg., 28
Pleurocybe Müll.-Arg., 320
P. madagascarea A. Zahlbr., 289
Pleurothelium Müll.-Arg., 317
Pleurotrema Müll.-Arg., 317
Plot, 4
Plowright, 207
Plukenet, 5
Poa compressa L., 393
Poduridae, 256
Polyblastia Massal., 48, 314
P. catalepta (Ach.) Fuist., 30
P. Vouauxi Lesd., 378
Polyblastiopsis Nyl., 316
Polycauliona Hue, 339, 340, 346
P. regale Hue, 339, 346
Polycaulionaceae, 339
Polychidium A. Zahlbr., 284, 332
Polycoccus Kütz., 24
P. punctiformis Kütz., 24, 54, 61
P. lacunosa Nyl., 375
Pleospora collematum Zuk., 163, 266
Pleurococcus Menegh. (?), 22, 29, 62
P. Naegeli Chod., 28
P. vulgaris Menegh., 28, 55 (Fig. 22), 223
P. vulgaris Naeg., 28
Pleurocybe Müll.-Arg., 320
P. madagascarea A. Zahlbr., 289
Pleurothelium Müll.-Arg., 317
Pleurotrema Müll.-Arg., 317
Plot, 4
Plowright, 207
Plukenet, 5
Poa compressa L., 393
Poduridae, 256
Polyblastia Massal., 48, 314
P. catalepta (Ach.) Fuist., 30
P. Vouauxi Lesd., 378
Polyblastiopsis Nyl., 316
Polycauliona Hue, 339, 340, 346
P. regale Hue, 339, 346
Polycaulionaceae, 339
Polychidium A. Zahlbr., 284, 332
Polycoccus Kütz., 24
P. punctiformis Kütz., 24, 54, 61
Page 685
Polyporus Mich., 261
Polystictus versicolor (Fr.), 152
Polystigma rubrum DC., 178, 207
Polystroma Clem., 326
P. Ferdinandezii Clem., 326
Polytrichum L., 392
P. commune L., 237
Polyxenus, 270
Porina Ach., 204, 316
P. lectissima A. Zahlbr., 249, 251, 392
P. olivacea A. L. Sm., 159 (Fig. 90 a)
Porocyphus Koerb., 332
Poronia Willd., 13, 178
Porta, 5
Porter, 109, 270
Prasiola Ag., 60, 309, 315
P. parietina Wille, 60 (Fig. 33)
Prasiolaceae, 60
Propagula, 11
Protocaliceaceae, 277
Protococcaceae, 55, 288, 291, 309, 310, 313 et seq., 353, 363
Protococcus Ag., xx, 28, 56, 62, 63, 65, 287
P. botryoides Kirchn., 65
P. viridis Ag., 22, 28, 44, 48 (Fig. 15), 55 (Fig. 22), 65, 313
Pseudopyrenula Müll.-Arg., 316
Psocus, 397
Polystictus versicolor (Fr.), 152
Polystigma rubrum DC., 178, 207
Polystroma Clem., 326
P. Ferdinandezii Clem., 326
Polytrichum L., 392
P. commune L., 237
Polyxenus, 270
Porina Ach., 204, 316
P. lectissima A. Zahlbr., 249, 251, 392
P. olivacea A. L. Sm., 159 (Fig. 90 a)
Porocyphus Koerb., 332
Poronia Willd., 13, 178
Porta, 5
Porter, 109, 270
Prasiola Ag., 60, 309, 315
P. parietina Wille, 60 (Fig. 33)
Prasiolaceae, 60
Propagula, 11
Protocaliceaceae, 277
Protococcaceae, 55, 288, 291, 309, 310, 313 et seq., 353, 363
Protococcus Ag., xx, 28, 56, 62, 63, 65, 287
P. botryoides Kirchn., 65
P. viridis Ag., 22, 28, 44, 48 (Fig. 15), 55 (Fig. 22), 65, 313
Pseudopyrenula Müll.-Arg., 316
Psocus, 397
Page 686
Psora (Lecidea) decipiens Hook., 388
Psorella Müll.-Arg., 329
Psoroglaena Müll.-Arg., 315
Psoroma S. F. Gray, 136, 285, 286, 335
P. hypnorum S. F. Gray, 63, 81, 88, 89, 135, 246, 283, 370
Psoromaria Nyl., 285, 286, 335
Psorotichia Massal., 68, 163, 333, 373
Ps. lugubris Dal. Tor. and Sarnth., 375
Ps. lutophila Arn., 368
Psychides, 399
Pterygiopsis Wain., 332
Pterygium Nyl., 333
Pt. Kenmorensis A. L. Sm., 392
Ptychographa Nyl., 321, 322
Pulteney, 4, 14
Pulvis antilyssus, 407
Pulvis Cyprius, 419
Pycnothelia (Cladonia) papillaria Duf., 369
Pyrenastrum Eschw., 317
Pyrenidiaceae, 53, 54, 275, 285, 309, 319
Pyrenidium Nyl., 285, 319
P. actinellum Nyl., 99
Pyrenocarpeae, 158, 273, 308
Pyrenocarpei, 306, 307, 353
Pyrenocarpineae, 273, 275, 288, 308
Pyrenocollema Reinke, 334
Psorella Müll.-Arg., 329
Psoroglaena Müll.-Arg., 315
Psoroma S. F. Gray, 136, 285, 286, 335
P. hypnorum S. F. Gray, 63, 81, 88, 89, 135, 246, 283, 370
Psoromaria Nyl., 285, 286, 335
Psorotichia Massal., 68, 163, 333, 373
Ps. lugubris Dal. Tor. and Sarnth., 375
Ps. lutophila Arn., 368
Psychides, 399
Pterygiopsis Wain., 332
Pterygium Nyl., 333
Pt. Kenmorensis A. L. Sm., 392
Ptychographa Nyl., 321, 322
Pulteney, 4, 14
Pulvis antilyssus, 407
Pulvis Cyprius, 419
Pycnothelia (Cladonia) papillaria Duf., 369
Pyrenastrum Eschw., 317
Pyrenidiaceae, 53, 54, 275, 285, 309, 319
Pyrenidium Nyl., 285, 319
P. actinellum Nyl., 99
Pyrenocarpeae, 158, 273, 308
Pyrenocarpei, 306, 307, 353
Pyrenocarpineae, 273, 275, 288, 308
Pyrenocollema Reinke, 334
Page 687
Pyrenographa Müll.-Arg., 323
Pyrenolichens 159, 241, 276, 352, 391
Pyrenomycetes 158, 267, 273
Pyrenopsidaceae, 282, 284, 310, 352
Pyrenopsidium Forss., 333
Pyrenopsis Nyl., 60, 68, 163, 175, 333
P. haematopis Th. Fr., 195
P. impolita Forss., 175
P. phaeococca Tuck., 175
Pyrenothamnia Tuck., 99, 315
P. Spraguei Tuck., 288
Pyrenothamniaceae, 309, 315
Pyrenothea Ach., 192
Pyrenothrix Riddle, 319
Pyrenula Ach., 200, 316
P. cinerella Fink, 365
P. leucoplaca Koerb., 365
P. nitida Ach., 174, 194, 240, 255, 350, 354, 364, 365
P. thelena Fink, 365
Pyrenulaceae, 50, 276, 309, 316, 365
Pyrgidium Nyl., 319
P. bengalense Nyl., 353
Pyrgillus Nyl., 289, 320
Pyronema Carus., 167
P. confluens Tul., 178
Pyxidium Hill, 8
Pyrenolichens 159, 241, 276, 352, 391
Pyrenomycetes 158, 267, 273
Pyrenopsidaceae, 282, 284, 310, 352
Pyrenopsidium Forss., 333
Pyrenopsis Nyl., 60, 68, 163, 175, 333
P. haematopis Th. Fr., 195
P. impolita Forss., 175
P. phaeococca Tuck., 175
Pyrenothamnia Tuck., 99, 315
P. Spraguei Tuck., 288
Pyrenothamniaceae, 309, 315
Pyrenothea Ach., 192
Pyrenothrix Riddle, 319
Pyrenula Ach., 200, 316
P. cinerella Fink, 365
P. leucoplaca Koerb., 365
P. nitida Ach., 174, 194, 240, 255, 350, 354, 364, 365
P. thelena Fink, 365
Pyrenulaceae, 50, 276, 309, 316, 365
Pyrgidium Nyl., 319
P. bengalense Nyl., 353
Pyrgillus Nyl., 289, 320
Pyronema Carus., 167
P. confluens Tul., 178
Pyxidium Hill, 8
Page 688
Pyxine Nyl., 301, 341
P. Cocoës Nyl., 353
P. Meissnerii Tuck., 353
Quercus alba, 359
Q. chrysolepis, 359
Q. Douglasii, 359
Racodium Pers., 35, 328
R. rupestre Pers., 291, 328
Radais, 42
Ramalina Ach., 3, 84, 103, 110, 195, 213, 238, 244, 257, 270, 305,
340, 347, 348, 351, 359, 361, 363
R. calicaris Fr., 3, 104, 147, 210, 353, 355, 365, 366, 418, 419
R. ceruchis De Not., 103
R. Curnowii Cromb., 104, 109
R. cuspidata Nyl., 225, 271 (see R. siliquosa), 384
R. dilacerata Hoffm., 106, 130
R. Eckloni Mont., 130
R. evernioides Nyl., 103, 300
R. farinacea Ach., 10, 239, 269, 271, 353, 366, 400, 411
R. fastigiata Ach., 109, 365, 366, 400, 411
R. fraxinea Ach., 104, 106, 130 (Fig. 75 a), 155, 164, 170, 195,
200, 212, 215, 300, 355, 365, 366, 400, 411, 418
R. gracilenta Ach., 349
R. homalea Ach., 103
R. Landroensis Zopf, 109, 130
P. Cocoës Nyl., 353
P. Meissnerii Tuck., 353
Quercus alba, 359
Q. chrysolepis, 359
Q. Douglasii, 359
Racodium Pers., 35, 328
R. rupestre Pers., 291, 328
Radais, 42
Ramalina Ach., 3, 84, 103, 110, 195, 213, 238, 244, 257, 270, 305,
340, 347, 348, 351, 359, 361, 363
R. calicaris Fr., 3, 104, 147, 210, 353, 355, 365, 366, 418, 419
R. ceruchis De Not., 103
R. Curnowii Cromb., 104, 109
R. cuspidata Nyl., 225, 271 (see R. siliquosa), 384
R. dilacerata Hoffm., 106, 130
R. Eckloni Mont., 130
R. evernioides Nyl., 103, 300
R. farinacea Ach., 10, 239, 269, 271, 353, 366, 400, 411
R. fastigiata Ach., 109, 365, 366, 400, 411
R. fraxinea Ach., 104, 106, 130 (Fig. 75 a), 155, 164, 170, 195,
200, 212, 215, 300, 355, 365, 366, 400, 411, 418
R. gracilenta Ach., 349
R. homalea Ach., 103
R. Landroensis Zopf, 109, 130
Page 689
R. minuscula Nyl., 103 (Fig. 62), 147
R. pollinaria Ach., 109, 227, 349, 366
R. reticulata Krempelh., 33 (Fig. 11), 99, 106 (Fig. 64), 253, 257,
359
R. scopulorum Ach., see R. siliquosa
R. siliquosa A. L. Sm., 104, 109 (Fig. 65), 130, 224, 225, 271,
300, 379 (Fig. 122), 381 (Figs. 123, 124)
R. strepsilis Zahlbr., 104, 130 (Fig. 75 b)
R. subfarinacea Nyl., 380
R. tertiaria Engelh., 354
Ramalinaceae, 339
Ramalinites lacerus Braun, 354
Ramalodei, 306
Ramonia Stizenb., 328
Rathapu, 403
Ray, 4, 407, 409
Rees, 27
Rehm, 277
Reindeer, 401
Reindeer moss, 400 et passim
Reinke, 18, 31, 41, 68, 123, 125, 130, 144, 253, 277, 284, 291, 307,
324
Reinkella Darbish., 83, 324
Relhan, 9
Rhabdopsora Müll.-Arg., 319
Rhizina undulata Fr., 181
Rhizocarpon Ramond, 248, 302, 329, 341
R. pollinaria Ach., 109, 227, 349, 366
R. reticulata Krempelh., 33 (Fig. 11), 99, 106 (Fig. 64), 253, 257,
359
R. scopulorum Ach., see R. siliquosa
R. siliquosa A. L. Sm., 104, 109 (Fig. 65), 130, 224, 225, 271,
300, 379 (Fig. 122), 381 (Figs. 123, 124)
R. strepsilis Zahlbr., 104, 130 (Fig. 75 b)
R. subfarinacea Nyl., 380
R. tertiaria Engelh., 354
Ramalinaceae, 339
Ramalinites lacerus Braun, 354
Ramalodei, 306
Ramonia Stizenb., 328
Rathapu, 403
Ray, 4, 407, 409
Rees, 27
Rehm, 277
Reindeer, 401
Reindeer moss, 400 et passim
Reinke, 18, 31, 41, 68, 123, 125, 130, 144, 253, 277, 284, 291, 307,
324
Reinkella Darbish., 83, 324
Relhan, 9
Rhabdopsora Müll.-Arg., 319
Rhizina undulata Fr., 181
Rhizocarpon Ramond, 248, 302, 329, 341
Page 690
R. alboatrum Th. Fr., 365, 369, 373, 383
R. concentricum, see R. petraeum
R. confervoides DC., 71 (Fig. 38 a, b), 369, 386
R. distinctum Th. Fr., 261
R. epipolium (Ach.), 265
R. geographicum DC., 73, 74 (Figs. 40, 41), 226, 236, 243, 246,
249, 252, 261, 264, 291, 346, 372, 374, 376, 380
R. obscuratum Massal., 392
R. Oederi Koerb., 375
R. petraeum Koerb. (?), 374
R. petraeum Massal., 171 (Fig. 97), 375, 392
R. viridiatrum Koerb., 249, 375, 376
Rhizomorpha Roth, 12
Rhymbocarpus punctiformis Zopf, 264
Ricasolia De Not., 94 (see Lobaria), 168, 175
R. amplissima De Not., 133, 134 (Fig. 76), 195, 197, 357
R. laetevirens Leight., 357
Richard, 377, 411
Richardson, Dr, 6
Richardson, Sir John, 388
Riddle, 137
Rinodina S. F. Gray, 301, 302, 341, 372
R. archaea Wain., 346
R. Conradi Koerb., 370
R. exigua S. F. Gray, 366, 367, 377, 383, 384
R. isidioides Oliv., 301
R. concentricum, see R. petraeum
R. confervoides DC., 71 (Fig. 38 a, b), 369, 386
R. distinctum Th. Fr., 261
R. epipolium (Ach.), 265
R. geographicum DC., 73, 74 (Figs. 40, 41), 226, 236, 243, 246,
249, 252, 261, 264, 291, 346, 372, 374, 376, 380
R. obscuratum Massal., 392
R. Oederi Koerb., 375
R. petraeum Koerb. (?), 374
R. petraeum Massal., 171 (Fig. 97), 375, 392
R. viridiatrum Koerb., 249, 375, 376
Rhizomorpha Roth, 12
Rhymbocarpus punctiformis Zopf, 264
Ricasolia De Not., 94 (see Lobaria), 168, 175
R. amplissima De Not., 133, 134 (Fig. 76), 195, 197, 357
R. laetevirens Leight., 357
Richard, 377, 411
Richardson, Dr, 6
Richardson, Sir John, 388
Riddle, 137
Rinodina S. F. Gray, 301, 302, 341, 372
R. archaea Wain., 346
R. Conradi Koerb., 370
R. exigua S. F. Gray, 366, 367, 377, 383, 384
R. isidioides Oliv., 301
Page 691
R. oreina Wain., 301, 374, 390
R. sophodes Th. Fr., 367
R. turfacea Th. Fr., 262, 377
Rivularia, 55, 136, 138, 284, 333
R. Biasolettiana, 54 (Fig. 21)
R. minutula Born. and Fl., 54 (Fig. 21)
R. nitida Ag., 55
Rivulariaceae, 54
Roccella DC., 3, 34, 35, 83, 103, 200, 225, 233, 242, 278, 292, 324,
351, 359, 363
R. fuciformis DC., 83 (Fig. 45), 98 (Fig. 57), 101, 110, 227, 228,
349, 350, 412
R. fucoides Wain., 349, 350
R. Montagnei Bél., 213, 413
R. peruensis Kremp., 413
R. phycopsis Ach., 110; see R. fucoides
R. portentosa Mont., 413
R. sinuensis Nyl., 413
R. tinctoria DC., 213, 215, 227, 349, 350, 413 (Fig. 133)
Roccellaceae, 59, 83, 110, 279, 290, 309, 323
Roccellaria Darbish., 323, 324
Roccellina Darbish., 83, 290, 323, 324
Roccellographa Stein., 83, 290, 323, 324
Rock tripe, 404
Roebuck, 401
Ronceray, 213, 413
Rosendahl, 86, 90, 93, 129, 170, 176, 214, 218, 249
R. sophodes Th. Fr., 367
R. turfacea Th. Fr., 262, 377
Rivularia, 55, 136, 138, 284, 333
R. Biasolettiana, 54 (Fig. 21)
R. minutula Born. and Fl., 54 (Fig. 21)
R. nitida Ag., 55
Rivulariaceae, 54
Roccella DC., 3, 34, 35, 83, 103, 200, 225, 233, 242, 278, 292, 324,
351, 359, 363
R. fuciformis DC., 83 (Fig. 45), 98 (Fig. 57), 101, 110, 227, 228,
349, 350, 412
R. fucoides Wain., 349, 350
R. Montagnei Bél., 213, 413
R. peruensis Kremp., 413
R. phycopsis Ach., 110; see R. fucoides
R. portentosa Mont., 413
R. sinuensis Nyl., 413
R. tinctoria DC., 213, 215, 227, 349, 350, 413 (Fig. 133)
Roccellaceae, 59, 83, 110, 279, 290, 309, 323
Roccellaria Darbish., 323, 324
Roccellina Darbish., 83, 290, 323, 324
Roccellographa Stein., 83, 290, 323, 324
Rock tripe, 404
Roebuck, 401
Ronceray, 213, 413
Rosendahl, 86, 90, 93, 129, 170, 176, 214, 218, 249
Page 692
Roses, spirit of, 419
Roy, 411
Ruel, 2
Rupp, 5
Russula Pers., 161
Sachs, 17, 23
Sagedia, see Verrucaria
S. declivum Am., 251
Sagiolechia Massal., 328
Salix repens L., 357
Salter, 51, 393
Sandstede, 233, 384, 385
Sappin-Trouffy, 207
Sarcographa Fée, 323
Sarcographina Müll.-Arg., 323
Sarcogyne (= Biatorella) latericola Stein., 76
Sarcopyrenia Nyl., 314
Sättler, 123, 173, 296, 358
Schade, 376
Schaerer, 15, 192
Schellenberg, 212
Schenk, 213
Schikorra, 178
Schimper, 354, 355
Schismatomma Flot., 325
Roy, 411
Ruel, 2
Rupp, 5
Russula Pers., 161
Sachs, 17, 23
Sagedia, see Verrucaria
S. declivum Am., 251
Sagiolechia Massal., 328
Salix repens L., 357
Salter, 51, 393
Sandstede, 233, 384, 385
Sappin-Trouffy, 207
Sarcographa Fée, 323
Sarcographina Müll.-Arg., 323
Sarcogyne (= Biatorella) latericola Stein., 76
Sarcopyrenia Nyl., 314
Sättler, 123, 173, 296, 358
Schade, 376
Schaerer, 15, 192
Schellenberg, 212
Schenk, 213
Schikorra, 178
Schimper, 354, 355
Schismatomma Flot., 325
Page 693
Schizopelte Th. Fr., 83, 324
Schneider, 7, 135, 136, 139
Schreber, 126
Schrenk, 231, 258, 359
Schulte, 104, 105, 106, 177
Schwarz, 224
Schweinfurth, 405
Schweinitz, 15
Schwenckfeld, 3
Schwendener, xx, 2, 16, 17, 18, 25, 27, 36, 71, 82, 86, 92, 126, 128,
129, 142, 147, 168, 213, 224, 307
Sclerophyton Eschw., 323
S. circumscriptum A. Zahlbr., 322
Scopoli, 8, 21, 154, 409
Scott-Elliot, 253
Scutellati, 305
Scutovertes maculatus, 397
Scytonema Ag., 54, 57, 61, 68, 75, 136, 153, 216, 232, 281, 284, 309 et
seq., 318
S. mirabile Thur., 53 (Fig. 19)
Scytonemaceae, 54
Secoliga (Gyalecta) bryophaga Koerb., 368
Segestria, see Porina
Senft, 223
Septoria Fr., 204
Sernander, 94, 140, 355
Servettaz, 45
Schneider, 7, 135, 136, 139
Schreber, 126
Schrenk, 231, 258, 359
Schulte, 104, 105, 106, 177
Schwarz, 224
Schweinfurth, 405
Schweinitz, 15
Schwenckfeld, 3
Schwendener, xx, 2, 16, 17, 18, 25, 27, 36, 71, 82, 86, 92, 126, 128,
129, 142, 147, 168, 213, 224, 307
Sclerophyton Eschw., 323
S. circumscriptum A. Zahlbr., 322
Scopoli, 8, 21, 154, 409
Scott-Elliot, 253
Scutellati, 305
Scutovertes maculatus, 397
Scytonema Ag., 54, 57, 61, 68, 75, 136, 153, 216, 232, 281, 284, 309 et
seq., 318
S. mirabile Thur., 53 (Fig. 19)
Scytonemaceae, 54
Secoliga (Gyalecta) bryophaga Koerb., 368
Segestria, see Porina
Senft, 223
Septoria Fr., 204
Sernander, 94, 140, 355
Servettaz, 45
Page 694
Servit, 374
Sherard, 4, 6, 7
Sibbald, 409
Sibthorp, 9
Sievers, 230
Simonyella Steiner, 324
Siphula Fr., 340
Sirosiphon pulvinatus Bréb., 54
Sloane, 10
Smith, Lorrain, 328
Smith, Sir J. E., 10
Solorina Ach., 56, 63, 85, 94, 135, 136, 168, 175, 176, 183, 287, 337,
392
S. bispora Nyl., 135
S. crocea Ach., 63, 88, 140, 210, 228, 246, 287, 346, 388
S. octospora Arn., 85
S. saccata Ach., 155, 244, 388
S. spongiosa Carroll, 135, 186, 368
Solorinella Anzi, 337
Sorby, 418
Sowerby, James, 10
Speerschneider, 17, 25
Sphaeria Hall., 192, 213
Sphaeriaceae, 307
Sphaerocephalum Web., 9
Sphaerophoraceae, 135, 309, 320
Sherard, 4, 6, 7
Sibbald, 409
Sibthorp, 9
Sievers, 230
Simonyella Steiner, 324
Siphula Fr., 340
Sirosiphon pulvinatus Bréb., 54
Sloane, 10
Smith, Lorrain, 328
Smith, Sir J. E., 10
Solorina Ach., 56, 63, 85, 94, 135, 136, 168, 175, 176, 183, 287, 337,
392
S. bispora Nyl., 135
S. crocea Ach., 63, 88, 140, 210, 228, 246, 287, 346, 388
S. octospora Arn., 85
S. saccata Ach., 155, 244, 388
S. spongiosa Carroll, 135, 186, 368
Solorinella Anzi, 337
Sorby, 418
Sowerby, James, 10
Speerschneider, 17, 25
Sphaeria Hall., 192, 213
Sphaeriaceae, 307
Sphaerocephalum Web., 9
Sphaerophoraceae, 135, 309, 320
Page 695
Sphaerophoropsis Wain., 291, 329
S. stereocauloides Wain., 292
Sphaerophorus Pers., 83, 105, 184, 277, 289, 320, 361, 375, 387, 393
S. coralloides Pers., 83 (Fig. 44) (see S. globosus), 355, 375, 387,
388, 389
S. fragilis Pers., 375, 387
S. globosus A. L. Sm., 346
S. stereocauloides Nyl., 135
Sphagnum Dill., 231, 355
Spheconisca Norm., 313
Sphinctrina Fr., 277, 319, 353
Sphyridium byssoides, 177
S. fungiforme Koerb., 177
Spilonema Born., 68, 333
Spirographa A. Zahlbr., 322
Spirogyra Link, 188
Splachnum L., 5
Sporocladus lichenicola Corda, 200
Sporodinia Link, 188
Sporopodium Mont., 327, 352
S. Caucasium Elenk. and Woron., 353
Sprengel, 21, 142, 156, 184
Squamaria DC., 200, 298
S. saxicola, see Lecanora
Stahel, 220
Stahl, 28, 30, 62, 160, 163, 173, 266, 395
S. stereocauloides Wain., 292
Sphaerophorus Pers., 83, 105, 184, 277, 289, 320, 361, 375, 387, 393
S. coralloides Pers., 83 (Fig. 44) (see S. globosus), 355, 375, 387,
388, 389
S. fragilis Pers., 375, 387
S. globosus A. L. Sm., 346
S. stereocauloides Nyl., 135
Sphagnum Dill., 231, 355
Spheconisca Norm., 313
Sphinctrina Fr., 277, 319, 353
Sphyridium byssoides, 177
S. fungiforme Koerb., 177
Spilonema Born., 68, 333
Spirographa A. Zahlbr., 322
Spirogyra Link, 188
Splachnum L., 5
Sporocladus lichenicola Corda, 200
Sporodinia Link, 188
Sporopodium Mont., 327, 352
S. Caucasium Elenk. and Woron., 353
Sprengel, 21, 142, 156, 184
Squamaria DC., 200, 298
S. saxicola, see Lecanora
Stahel, 220
Stahl, 28, 30, 62, 160, 163, 173, 266, 395
Page 696
Stahlecker, 76, 235, 371, 374
Staurothele Norm., 31, 62, 76, 314
S. clopima Th. Fr., 391
S. clopismoides Anzi, 249
S. hymenogonia A. Zahlbr., 361
S. umbrinum A. L. Sm., 373, 393
Steganosporium cellulosum Corda, 201
Steiner, 75, 179, 190, 198, 215, 276, 312, 353, 389
Steinera A. Zahlbr., 333
Stenberg, 411
Stenhouse and Groves, 228
Stenocybe Nyl., 177, 319
Stereocaulon Schreb., 17, 23, 83, 105, 125, 133, 135, 176, 201, 283,
292, 294, 297, 330, 346, 358, 361, 387
S. alpinum Laur., 137, 346, 387
S. condensatum Hoffm., 319, 388
S. coralloides Fr., 125, 375
S. Delisei Borg., 375
S. denudatum Floerk., 137, 375, 387
S. evolutum Graewe, 375
S. paschale Fr., 211, 372, 385, 391, 401
S. ramulosum Ach., 125, 136
S. salazinum Borg., 227
S. tomentosum Fr., 125, 136, 387
Stereochlamys Müll.-Arg., 316
Stichococcus Naeg., 62
Staurothele Norm., 31, 62, 76, 314
S. clopima Th. Fr., 391
S. clopismoides Anzi, 249
S. hymenogonia A. Zahlbr., 361
S. umbrinum A. L. Sm., 373, 393
Steganosporium cellulosum Corda, 201
Steiner, 75, 179, 190, 198, 215, 276, 312, 353, 389
Steinera A. Zahlbr., 333
Stenberg, 411
Stenhouse and Groves, 228
Stenocybe Nyl., 177, 319
Stereocaulon Schreb., 17, 23, 83, 105, 125, 133, 135, 176, 201, 283,
292, 294, 297, 330, 346, 358, 361, 387
S. alpinum Laur., 137, 346, 387
S. condensatum Hoffm., 319, 388
S. coralloides Fr., 125, 375
S. Delisei Borg., 375
S. denudatum Floerk., 137, 375, 387
S. evolutum Graewe, 375
S. paschale Fr., 211, 372, 385, 391, 401
S. ramulosum Ach., 125, 136
S. salazinum Borg., 227
S. tomentosum Fr., 125, 136, 387
Stereochlamys Müll.-Arg., 316
Stichococcus Naeg., 62
Page 697
S. bacillaris Naeg., 42
Sticta Schreb., 13, 63, 85, 86, 94, 136, 138, 200, 283, 287, 336, 350,
351, 364, 392
St. aurata Ach., 126, 128, 223, 226, 246, 350
St. crocata Ach., 128, 246
St. damaecornis Nyl., 127 (Fig. 73), 128, 210, 350
St. Dufourei Del., 128
St. fuliginosa Ach., 126, 128, 223
St. intricata Del., 128
St. limbata Ach., 128
St. oregana Tuck., 136, 139
St. sylvatica Ach., 128
St. Wrightii Nyl., 349
Stictaceae, 96, 136, 286, 311, 336, 347, 350, 418
Stictidaceae, 278
Stictina Nyl., 63, 168, 175, 287
Stictis Pers., 278
Stigmatea Fr., 275
Stigonema Ag., 23, 26, 54 (Fig. 20), 68, 136, 283, 284, 310 et seq., 317
S. panniforme Kirchn., 54
Stigonemaceae, 54
Stirton, 331, 350
Stizenberger, 18, 128
Stone, 399
Streptothrix Cohn, 45
Strigula Fr., 60, 65, 288, 318, 353, 363
Sticta Schreb., 13, 63, 85, 86, 94, 136, 138, 200, 283, 287, 336, 350,
351, 364, 392
St. aurata Ach., 126, 128, 223, 226, 246, 350
St. crocata Ach., 128, 246
St. damaecornis Nyl., 127 (Fig. 73), 128, 210, 350
St. Dufourei Del., 128
St. fuliginosa Ach., 126, 128, 223
St. intricata Del., 128
St. limbata Ach., 128
St. oregana Tuck., 136, 139
St. sylvatica Ach., 128
St. Wrightii Nyl., 349
Stictaceae, 96, 136, 286, 311, 336, 347, 350, 418
Stictidaceae, 278
Stictina Nyl., 63, 168, 175, 287
Stictis Pers., 278
Stigmatea Fr., 275
Stigonema Ag., 23, 26, 54 (Fig. 20), 68, 136, 283, 284, 310 et seq., 317
S. panniforme Kirchn., 54
Stigonemaceae, 54
Stirton, 331, 350
Stizenberger, 18, 128
Stone, 399
Streptothrix Cohn, 45
Strigula Fr., 60, 65, 288, 318, 353, 363
Page 698
S. Buxi Chod., 363
S. complanata Mont., 35, 42, 59, 205, 260, 269
S. elegans Müll.-Arg., 205
Strigulaceae, 59, 60, 204, 309, 318, 363
Stüde, 211
Sturgis, 97, 168, 175, 197, 289
Suaeda fruticosa Forsk., 387
Swartz, 10, 152
Swedish moss, 415
Symbiosis, 31
Synalissa Fr., 32, 33, 61, 284, 333, 373
S. symphorea Nyl., 33 (Fig. 10)
Synarthonia Müll.-Arg., 321
Tabernaemontanus, 2
Tapellaria Müll.-Arg., 327
Taylor, 13, 149
Tegeocranus labyrinthicus, 328
Teloschistaceae, 311, 341
Teloschistes Norm., 85, 301, 341
T. chrysophthalmus Th. Fr., 92, 365, 367
T. flavicans Norm., 3, 301, 341, 417
Teras literana, 399
Termes monoceros, 397
Termites, 397
Tetranychus lapidus, 398 (Fig. 126)
S. complanata Mont., 35, 42, 59, 205, 260, 269
S. elegans Müll.-Arg., 205
Strigulaceae, 59, 60, 204, 309, 318, 363
Stüde, 211
Sturgis, 97, 168, 175, 197, 289
Suaeda fruticosa Forsk., 387
Swartz, 10, 152
Swedish moss, 415
Symbiosis, 31
Synalissa Fr., 32, 33, 61, 284, 333, 373
S. symphorea Nyl., 33 (Fig. 10)
Synarthonia Müll.-Arg., 321
Tabernaemontanus, 2
Tapellaria Müll.-Arg., 327
Taylor, 13, 149
Tegeocranus labyrinthicus, 328
Teloschistaceae, 311, 341
Teloschistes Norm., 85, 301, 341
T. chrysophthalmus Th. Fr., 92, 365, 367
T. flavicans Norm., 3, 301, 341, 417
Teras literana, 399
Termes monoceros, 397
Termites, 397
Tetranychus lapidus, 398 (Fig. 126)
Page 699
Tetrasporaceae, 57
Thamnolia Ach., 83, 101 (see Cerania), 246, 340, 389
Th. vermicularis Schaer., 346, 377
Thamnonia Tuck., 339
Thaxter, 178
Thelenidia Nyl., 314
Thelephora Ehrh., 281, 342
Thelephoraceae, 152, 273
Thelidea Hue, 335
Th. corrugata Hue, 335
Thelidium Massal., 314
Th. microcarpum A. L. Sm., 361
Th. minutulum Koerb., 253, 367
Thelocarpon Nyl., 331
Th. prasinellum Nyl., 367
Th. turficolum Arn., 370
Thelopsis Nyl., 316
Thelotrema Ach., 326, 343
Th. lepadinum Ach., 397
Thelotremaceae, 59, 302, 310, 326, 351, 352
Thelotremei, 353
Theophrastus, 1, 2, 411
Thermutis Fr., 68, 284, 332
Tholurna Norm., 320
Th. dissimilis Norm., 289
Thomas, N., 59
Thamnolia Ach., 83, 101 (see Cerania), 246, 340, 389
Th. vermicularis Schaer., 346, 377
Thamnonia Tuck., 339
Thaxter, 178
Thelenidia Nyl., 314
Thelephora Ehrh., 281, 342
Thelephoraceae, 152, 273
Thelidea Hue, 335
Th. corrugata Hue, 335
Thelidium Massal., 314
Th. microcarpum A. L. Sm., 361
Th. minutulum Koerb., 253, 367
Thelocarpon Nyl., 331
Th. prasinellum Nyl., 367
Th. turficolum Arn., 370
Thelopsis Nyl., 316
Thelotrema Ach., 326, 343
Th. lepadinum Ach., 397
Thelotremaceae, 59, 302, 310, 326, 351, 352
Thelotremei, 353
Theophrastus, 1, 2, 411
Thermutis Fr., 68, 284, 332
Tholurna Norm., 320
Th. dissimilis Norm., 289
Thomas, N., 59
Page 700
Thrambium Wallr., 192, 314
T. epigaeum Wallr., 254, 367, 368
Thwaites, 17
Thyrea Massal., 284, 333
Thysanothecium Berk. and Mont., 330
T. Hookeri Berk. and Mont., 294
Ticothecium Flot., 275, 319
T. pygmaeum Koerb., 267
Tieghem, Van, 179
Tobler, 43, 50, 148, 224, 253, 263, 265, 280
Tomasiella Müll.-Arg., 317
Toni, De, 60
Toninia Th. Fr., 329
Torrey, 14
Tournefort, 1, 5, 155, 304
Tournesol, 413
Treboux, 40, 42
Trematosphaeropsis Elenk., 266
Tremotylium Nyl., 326
Trentepohlia Born., 26, 30, 34, 59, 75, 78, 232, 246, 276, 278, 287,
289, 291, 309, 316 etc., 343, 352, 365
T. abietina Hansg., 65, 66
T. aurea Mart., 34, 35, 58 (Fig. 29 a), 59
T. jolithus, 223
T. umbrina Born., 22, 34, 58 (Fig. 29 b), 59, 62, 216
Trentepohliaceae, 59, 288, 289
T. epigaeum Wallr., 254, 367, 368
Thwaites, 17
Thyrea Massal., 284, 333
Thysanothecium Berk. and Mont., 330
T. Hookeri Berk. and Mont., 294
Ticothecium Flot., 275, 319
T. pygmaeum Koerb., 267
Tieghem, Van, 179
Tobler, 43, 50, 148, 224, 253, 263, 265, 280
Tomasiella Müll.-Arg., 317
Toni, De, 60
Toninia Th. Fr., 329
Torrey, 14
Tournefort, 1, 5, 155, 304
Tournesol, 413
Treboux, 40, 42
Trematosphaeropsis Elenk., 266
Tremotylium Nyl., 326
Trentepohlia Born., 26, 30, 34, 59, 75, 78, 232, 246, 276, 278, 287,
289, 291, 309, 316 etc., 343, 352, 365
T. abietina Hansg., 65, 66
T. aurea Mart., 34, 35, 58 (Fig. 29 a), 59
T. jolithus, 223
T. umbrina Born., 22, 34, 58 (Fig. 29 b), 59, 62, 216
Trentepohliaceae, 59, 288, 289
Page 701
Treub, 28, 394
Treveris, Peter, 2
Tricothelium Müll.-Arg., 318
Trimmatothele Norm., 314
Tripe de Roche, 404
Trypetheliaceae, 309, 317
Trypethelium Spreng., 276, 317, 351, 364
Tubercularia Web., 9
Tuckerman, 15, 136, 339
Tulasne, 17, 25, 46, 70, 123, 159, 187, 189, 192, 193, 200, 204, 263
Turner, Dawson, 14
Tutt, 399
Tylophorella Wain., 320
Tylophoron Nyl., 289, 320
Uhlir, 43
Ulander, 211
Uloth, 233
Umbilicaria, 17, 82, 200, 241, 262, 268, 331
U. pustulata Hoffm., 86, 96, 150, 195, 214, 240, 257, 414
Unguentum Armarium, 407
Unguentum sympatheticum, 407
Urceolaria Ach., 48; see Diploschistes
Urococcus Kütz., 57, 133, 318
Usnea Dill., 1, 3, 7, 9, 83, 111, 195, 213, 233, 257, 268, 269, 300, 304,
305, 340, 347, 348, 351, 361, 408, 419
Treveris, Peter, 2
Tricothelium Müll.-Arg., 318
Trimmatothele Norm., 314
Tripe de Roche, 404
Trypetheliaceae, 309, 317
Trypethelium Spreng., 276, 317, 351, 364
Tubercularia Web., 9
Tuckerman, 15, 136, 339
Tulasne, 17, 25, 46, 70, 123, 159, 187, 189, 192, 193, 200, 204, 263
Turner, Dawson, 14
Tutt, 399
Tylophorella Wain., 320
Tylophoron Nyl., 289, 320
Uhlir, 43
Ulander, 211
Uloth, 233
Umbilicaria, 17, 82, 200, 241, 262, 268, 331
U. pustulata Hoffm., 86, 96, 150, 195, 214, 240, 257, 414
Unguentum Armarium, 407
Unguentum sympatheticum, 407
Urceolaria Ach., 48; see Diploschistes
Urococcus Kütz., 57, 133, 318
Usnea Dill., 1, 3, 7, 9, 83, 111, 195, 213, 233, 257, 268, 269, 300, 304,
305, 340, 347, 348, 351, 361, 408, 419
Page 702
U. articulata Hoffm., 210, 268
U. barbata Web., 25, 99 (Fig. 58), 104 (Fig. 63 a), 130, 143 (Fig.
82), 167 (Fig. 95), 168, 177, 200, 211, 215, 226, 234, 239,
246, 339, 348, 364, 417
U. ceratina Ach., 227
U. compressa Hill, 8
U. dasypoga Stiz., 359
U. florida Web., 91 (Fig. 52), 92, 210, 213, 348, 363, 411
U. hirta Hoffm., 348, 355, 366
U. laevis Nyl., 177
U. longissima Ach., 85, 99, 102 (Fig. 61), 105 (Fig. 63 b), 106,
215, 348
U. macrocarpa Arn., 177
U. melaxantha Ach., 346
U. plicata Web., 359
U. Taylori Hook., 104
Usneaceae, 299, 311, 339
Vaillant, 6
Vallot, 253
Valsa Fr., 317
Varicellaria Nyl., 337
V. microsticta Nyl., 77, 92, 187 (Fig. 126)
Variolaria Ach. (see Pertusaria), 64, 171, 237
Vaucheria sessilis DC., 65 (Fig. 34)
Ventenat, 21
Verrucaria Web. (non Pers.), 9, 174, 200, 275, 314, 364
U. barbata Web., 25, 99 (Fig. 58), 104 (Fig. 63 a), 130, 143 (Fig.
82), 167 (Fig. 95), 168, 177, 200, 211, 215, 226, 234, 239,
246, 339, 348, 364, 417
U. ceratina Ach., 227
U. compressa Hill, 8
U. dasypoga Stiz., 359
U. florida Web., 91 (Fig. 52), 92, 210, 213, 348, 363, 411
U. hirta Hoffm., 348, 355, 366
U. laevis Nyl., 177
U. longissima Ach., 85, 99, 102 (Fig. 61), 105 (Fig. 63 b), 106,
215, 348
U. macrocarpa Arn., 177
U. melaxantha Ach., 346
U. plicata Web., 359
U. Taylori Hook., 104
Usneaceae, 299, 311, 339
Vaillant, 6
Vallot, 253
Valsa Fr., 317
Varicellaria Nyl., 337
V. microsticta Nyl., 77, 92, 187 (Fig. 126)
Variolaria Ach. (see Pertusaria), 64, 171, 237
Vaucheria sessilis DC., 65 (Fig. 34)
Ventenat, 21
Verrucaria Web. (non Pers.), 9, 174, 200, 275, 314, 364
Page 703
V. aethiobola Wahlenb., 391, 392
V. anceps Koerb., 377
V. aquatilis Mudd, 383
V. calciseda DC., 176, 215, 219, 241, 373, 398
V. Dufourii DC., 173
V. fuscella Ach., 373
V. Hoffmanni Hepp; f. purpurascens Arn., 251
V. hydrela Ach., 391, 392
V. lecideoides Koerb., 373
V. maculiformis Krempelh., 379
V. margacea Wahlenb., 391, 392
V. maura Wahlenb., 245, 383, 384, 386
V. memnonia Flot., 383
V. microspora Nyl., 256, 383, 386
V. mucosa Wahlenb., 73, 383
V. muralis Ach., 30, 46 (Fig. 14), 70, 243, 255, 361, 393
V. nigrescens Pers., 56, 254, 369, 377, 392
V. papillosa Ach., 377
V. prominula Nyl., 383
V. rupestris Schrad., 215, 243, 361
V. scotina Wedd., 383
V. striatula Wahlenb., 383
V. viridula Ach., 391
Verrucariaceae, 249, 309, 314, 353, 367
Verrucarites geanthricis Goepp., 354
Verrucula Stein., 265, 276
V. anceps Koerb., 377
V. aquatilis Mudd, 383
V. calciseda DC., 176, 215, 219, 241, 373, 398
V. Dufourii DC., 173
V. fuscella Ach., 373
V. Hoffmanni Hepp; f. purpurascens Arn., 251
V. hydrela Ach., 391, 392
V. lecideoides Koerb., 373
V. maculiformis Krempelh., 379
V. margacea Wahlenb., 391, 392
V. maura Wahlenb., 245, 383, 384, 386
V. memnonia Flot., 383
V. microspora Nyl., 256, 383, 386
V. mucosa Wahlenb., 73, 383
V. muralis Ach., 30, 46 (Fig. 14), 70, 243, 255, 361, 393
V. nigrescens Pers., 56, 254, 369, 377, 392
V. papillosa Ach., 377
V. prominula Nyl., 383
V. rupestris Schrad., 215, 243, 361
V. scotina Wedd., 383
V. striatula Wahlenb., 383
V. viridula Ach., 391
Verrucariaceae, 249, 309, 314, 353, 367
Verrucarites geanthricis Goepp., 354
Verrucula Stein., 265, 276
Page 704
V. aegyptica Stein., 276
V. cahirensis Stein., 276
Visiani, 405
Volkard, 228, 410
Vouaux, 267
Wahlberg, 11, 168
Wahrlich, 51
Wainio, 31, 48, 70, 112, 114, 118, 120, 122, 123, 124, 125, 126, 128,
144, 153, 159, 163, 166, 175, 177, 179, 188, 191, 240, 276, 277,
292, 294, 308, 344, 346, 348, 411
Waite, 270
Wallroth, xx, 13, 21, 22, 123, 133, 142, 156, 192, 305
Ward, Marshall, 35, 42, 59
Watson, Sir W., 8
Watson, 365, 373, 385
Watt, 403
Weber, 1, 9
Weddell, 252, 379
Wehmer, 220
Weir, 239
West, G. F., 52, 54, 55, 56
West, W., 225, 233, 357, 374
Wester, 211
Westring, 412
Wettstein, 45
Wheldon, 398
V. cahirensis Stein., 276
Visiani, 405
Volkard, 228, 410
Vouaux, 267
Wahlberg, 11, 168
Wahrlich, 51
Wainio, 31, 48, 70, 112, 114, 118, 120, 122, 123, 124, 125, 126, 128,
144, 153, 159, 163, 166, 175, 177, 179, 188, 191, 240, 276, 277,
292, 294, 308, 344, 346, 348, 411
Waite, 270
Wallroth, xx, 13, 21, 22, 123, 133, 142, 156, 192, 305
Ward, Marshall, 35, 42, 59
Watson, Sir W., 8
Watson, 365, 373, 385
Watt, 403
Weber, 1, 9
Weddell, 252, 379
Wehmer, 220
Weir, 239
West, G. F., 52, 54, 55, 56
West, W., 225, 233, 357, 374
Wester, 211
Westring, 412
Wettstein, 45
Wheldon, 398
Page 705
Wheldon and Wilson, 360, 370, 373, 374, 379, 384, 385, 387, 391, 392
Wiesner, 211, 241, 244
Wilde, 395
Wille, 28
Willemet, 10, 401, 415
Wilson, 350
Winter, 30, 138, 263
Winterstein, 209
Wisselingh, 211
Withering, 9
Wolff, 124, 163, 170, 172, 176
Woodward, 152
Woronin, 28
Woronina Cornu, 261
Xanthocapsa (Sect. of gloeocapsa), 52, 63, 284, 332, 373
Xanthoria Th. Fr., 166, 246
X. lychnea Th. Fr., 233, 252, 365, 417
X. parietina Th. Fr., 3, 22, 24, 27, 28, 38, 42, 48 (Fig. 15), 50, 56,
65, 67 (Fig. 36), 86, 164, 176, 189, 195, 200, 224, 225, 227,
231, 232, 241, 242, 253, 269, 270, 301, 341, 348, 351, 360,
369, 373, 376, 380, 383, 384, 386, 397, 406, 416, 418
X. polycarpa Oliv., 365, 390
Xylaria Hill, 12, 421
Xylographa Fr., 278, 322
X. spilomatica Th. Fr., 145
Xyloschistes Wain., 322
Wiesner, 211, 241, 244
Wilde, 395
Wille, 28
Willemet, 10, 401, 415
Wilson, 350
Winter, 30, 138, 263
Winterstein, 209
Wisselingh, 211
Withering, 9
Wolff, 124, 163, 170, 172, 176
Woodward, 152
Woronin, 28
Woronina Cornu, 261
Xanthocapsa (Sect. of gloeocapsa), 52, 63, 284, 332, 373
Xanthoria Th. Fr., 166, 246
X. lychnea Th. Fr., 233, 252, 365, 417
X. parietina Th. Fr., 3, 22, 24, 27, 28, 38, 42, 48 (Fig. 15), 50, 56,
65, 67 (Fig. 36), 86, 164, 176, 189, 195, 200, 224, 225, 227,
231, 232, 241, 242, 253, 269, 270, 301, 341, 348, 351, 360,
369, 373, 376, 380, 383, 384, 386, 397, 406, 416, 418
X. polycarpa Oliv., 365, 390
Xylaria Hill, 12, 421
Xylographa Fr., 278, 322
X. spilomatica Th. Fr., 145
Xyloschistes Wain., 322
Page 706
Zahlbruckner, A., 19, 59, 60, 66, 69, 275, 284, 308, 335, 413
Zopf, 19, 43, 108, 151, 188, 213, 221, 233, 238, 246, 264, 265, 266,
268, 270, 395, 396, 398, 400, 412, 417
Zukal, 18, 26, 38, 61, 68, 70, 82, 128, 129, 130, 163, 179, 187, 215,
219, 230, 237, 244, 267, 268, 271, 313, 395
Zwelser, 419
Zopf, 19, 43, 108, 151, 188, 213, 221, 233, 238, 246, 264, 265, 266,
268, 270, 395, 396, 398, 400, 412, 417
Zukal, 18, 26, 38, 61, 68, 70, 82, 128, 129, 130, 163, 179, 187, 215,
219, 230, 237, 244, 267, 268, 271, 313, 395
Zwelser, 419
Page 707
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