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Title: The Power of Movement in Plants

Author: Charles Darwin
Sir Francis Darwin

Release date: May 1, 2004 [eBook #5605]
Most recently updated: September 11, 2022

Language: English

Other information and formats: www.gutenberg.org/ebooks/5605

Credits: Sue Asscher

*** START OF THE PROJECT GUTENBERG EBOOK THE POWER OF
MOVEMENT IN PLANTS ***

THE POWER OF
MOVEMENT IN PLANTS

By Charles Darwin

Assisted By Francis Darwin

CONTENTS

DETAILED TABLE OF CONTENTS.
THE MOVEMENTS OF PLANTS.
INTRODUCTION.
CHAPTER I. THE CIRCUMNUTATING MOVEMENTS OF SEEDLING
PLANTS.
CHAPTER II. GENERAL CONSIDERATIONS ON THE MOVEMENTS
AND GROWTH OF SEEDLING PLANTS.
CHAPTER III. SENSITIVENESS OF THE APEX OF THE RADICLE TO
CONTACT AND TO OTHER IRRITANTS.
CHAPTER IV. THE CIRCUMNUTATING MOVEMENTS OF THE
SEVERAL PARTS OF MATURE PLANTS.
CHAPTER V. MODIFIED CIRCUMNUTATION: CLIMBING PLANTS;
EPINASTIC AND HYPONASTIC MOVEMENTS.
CHAPTER VI. MODIFIED CIRCUMNUTATION: SLEEP OR
NYCTITROPIC MOVEMENTS, THEIR USE: SLEEP OF
COTYLEDONS.
CHAPTER VII. MODIFIED CIRCUMNUTATION: NYCTITROPIC OR
SLEEP MOVEMENTS OF LEAVES.
CHAPTER VIII. MODIFIED CIRCUMNUTATION: MOVEMENTS
EXCITED BY LIGHT.
CHAPTER IX. SENSITIVENESS OF PLANTS TO LIGHT: ITS
TRANSMITTED EFFECTS.
CHAPTER X. MODIFIED CIRCUMNUTATION: MOVEMENTS
EXCITED BY GRAVITATION.
CHAPTER XI. LOCALISED SENSITIVENESS TO GRAVITATION,
AND ITS TRANSMITTED EFFECTS.
CHAPTER XII. CONCLUDING REMARKS.
INDEX

DETAILED TABLE OF CONTENTS.

CHAPTER I.—THE CIRCUMNUTATING MOVEMENTS OF
SEEDLING PLANTS.
Brassica oleracea, circumnutation of the radicle, of the arched hypocotyl
whilst still buried beneath the ground, whilst rising above the ground and
straightening itself, and when erect—Circumnutation of the cotyledons—
Rate of movement—Analogous observations on various organs in species
of Githago, Gossypium, Oxalis, Tropaeolum, Citrus, Æsculus, of several
Leguminous and Cucurbitaceous genera, Opuntia, Helianthus, Primula,
Cyclamen, Stapelia, Cerinthe, Nolana, Solanum, Beta, Ricinus, Quercus,
Corylus, Pinus, Cycas, Canna, Allium, Asparagus, Phalaris, Zea, Avena,
Nephrodium, and Selaginella.

CHAPTER II.—GENERAL CONSIDERATIONS ON THE
MOVEMENTS AND GROWTH OF SEEDLING PLANTS.
Generality of the circumnutating movement—Radicles, their
circumnutation of service—Manner in which they penetrate the ground—
Manner in which hypocotyls and other organs break through the ground by
being arched—Singular manner of germination in Megarrhiza, etc.—
Abortion of cotyledons—Circumnutation of hypocotyls and epicotyls whilst
still buried and arched—Their power of straightening themselves—Bursting
of the seed-coats—Inherited effect of the arching process in hypogean
hypocotyls—Circumnutation of hypocotyls and epicotyls when erect—
Circumnutation of cotyledons—Pulvini or joints of cotyledons, duration of
their activity, rudimentary in Oxalis corniculata, their development—
Sensitiveness of cotyledons to light and consequent disturbance of their
periodic movements—Sensitiveness of cotyledons to contact.

CHAPTER III.—SENSITIVENESS OF THE APEX OF THE RADICLE
TO CONTACT AND TO OTHER IRRITANTS.

Manner in which radicles bend when they encounter an obstacle in the soil
—Vicia faba, tips of radicles highly sensitive to contact and other irritants
—Effects of too high a temperature—Power of discriminating between
objects attached on opposite sides—Tips of secondary radicles sensitive—
Pisum, tips of radicles sensitive—Effects of such sensitiveness in
overcoming geotropism—Secondary radicles—Phaseolus, tips of radicles
hardly sensitive to contact, but highly sensitive to caustic and to the
removal of a slice—Tropaeolum—Gossypium—Cucurbita—Raphanus—
Æsculus, tip not sensitive to slight contact, highly sensitive to caustic—
Quercus, tip highly sensitive to contact—Power of discrimination—Zea, tip
highly sensitive, secondary radicles—Sensitiveness of radicles to moist air
—Summary of chapter.

CHAPTER IV.—THE CIRCUMNUTATING MOVEMENTS OF THE
SEVERAL PARTS OF MATURE PLANTS.
Circumnutation of stems: concluding remarks on—Circumnutation of
stolons: aid thus afforded in winding amongst the stems of surrounding
plants—Circumnutation of flower-stems—Circumnutation of
Dicotyledonous leaves—Singular oscillatory movement of leaves of
Dionaea—Leaves of Cannabis sink at night—Leaves of Gymnosperms—Of
Monocotyledons—Cryptogams—Concluding remarks on the
circumnutation of leaves; generally rise in the evening and sink in the
morning.

CHAPTER V.—MODIFIED CIRCUMNUTATION: CLIMBING PLANTS;
EPINASTIC AND HYPONASTIC MOVEMENTS.
Circumnutation modified through innate causes or through the action of
external conditions—Innate causes—Climbing plants; similarity of their
movements with those of ordinary plants; increased amplitude; occasional
points of difference—Epinastic growth of young leaves—Hyponastic
growth of the hypocotyls and epicotyls of seedlings—Hooked tips of
climbing and other plants due to modified circumnutation—Ampelopsis
tricuspidata—Smithia Pfundii—Straightening of the tip due to hyponasty—
Epinastic growth and circumnutation of the flower-peduncles of Trifolium
repens and Oxalis carnosa.

CHAPTER VI.—MODIFIED CIRCUMNUTATION: SLEEP OR
NYCTITROPIC MOVEMENTS, THEIR USE: SLEEP OF
COTYLEDONS.
Preliminary sketch of the sleep or nyctitropic movements of leaves—
Presence of pulvini—The lessening of radiation the final cause of
nyctitropic movements—Manner of trying experiments on leaves of Oxalis,
Arachis, Cassia, Melilotus, Lotus and Marsilea and on the cotyledons of
Mimosa—Concluding remarks on radiation from leaves—Small differences
in the conditions make a great difference in the result—Description of the
nyctitropic position and movements of the cotyledons of various plants—A
List of species—Concluding remarks—Independence of the nyctitropic
movements of the leaves and cotyledons of the same species—Reasons for
believing that the movements have been acquired for a special purpose.

CHAPTER VII.—MODIFIED CIRCUMNUTATION: NYCTITROPIC OR
SLEEP MOVEMENTS OF LEAVES.
Conditions necessary for these movements—List of Genera and Families,
which include sleeping plants—Description of the movements in the several
Genera—Oxalis: leaflets folded at night—Averrhoa: rapid movements of
the leaflets—Porlieria: leaflets close when plant kept very dry—
Tropaeolum: leaves do not sleep unless well illuminated during day—
Lupinus: various modes of sleeping—Melilotus: singular movements of
terminal leaflet—Trifolium—Desmodium: rudimentary lateral leaflets,
movements of, not developed on young plants, state of their pulvini—
Cassia: complex movements of the leaflets—Bauhinia: leaves folded at
night—Mimosa pudica: compounded movements of leaves, effect of
darkness—Mimosa albida, reduced leaflets of—Schrankia: downward
movement of the pinnae—Marsilea: the only cryptogam known to sleep—
Concluding remarks and summary—Nyctitropism consists of modified
circumnutation, regulated by the alternations of light and darkness—Shape
of first true leaves.

CHAPTER VIII.—MODIFIED CIRCUMNUTATION: MOVEMENTS
EXCITED BY LIGHT.
Distinction between heliotropism and the effects of light on the periodicity
of the movements of leaves—Heliotropic movements of Beta, Solanum,
Zea, and Avena—Heliotropic movements towards an obscure light in Apios,

Brassica, Phalaris, Tropaeolum, and Cassia—Apheliotropic movements of
tendrils of Bignonia—Of flower-peduncles of Cyclamen—Burying of the
pods—Heliotropism and apheliotropism modified forms of circumnutation
—Steps by which one movement is converted into the other—Transversal-
heliotropismus or diaheliotropism influenced by epinasty, the weight of the
part and apogeotropism—Apogeotropism overcome during the middle of
the day by diaheliotropism—Effects of the weight of the blades of
cotyledons—So called diurnal sleep—Chlorophyll injured by intense light
—Movements to avoid intense light.

CHAPTER IX.—SENSITIVENESS OF PLANTS TO LIGHT: ITS
TRANSMITTED EFFECTS.
Uses of heliotropism—Insectivorous and climbing plants not heliotropic—
Same organ heliotropic at one age and not at another—Extraordinary
sensitiveness of some plants to light—The effects of light do not correspond
with its intensity—Effects of previous illumination—Time required for the
action of light—After-effects of light—Apogeotropism acts as soon as light
fails—Accuracy with which plants bend to the light—This dependent on
the illumination of one whole side of the part—Localised sensitiveness to
light and its transmitted effects—Cotyledons of Phalaris, manner of bending
—Results of the exclusion of light from their tips—Effects transmitted
beneath the surface of the ground—Lateral illumination of the tip
determines the direction of the curvature of the base—Cotyledons of Avena,
curvature of basal part due to the illumination of upper part—Similar results
with the hypocotyls of Brassica and Beta—Radicles of Sinapis
apheliotropic, due to the sensitiveness of their tips—Concluding remarks
and summary of chapter—Means by which circumnutation has been
converted into heliotropism or apheliotropism.

CHAPTER X.—MODIFIED CIRCUMNUTATION: MOVEMENTS
EXCITED BY GRAVITATION.
Means of observation—Apogeotropism—Cytisus—Verbena—Beta—
Gradual conversion of the movement of circumnutation into apogeotropism
in Rubus, Lilium, Phalaris, Avena, and Brassica—Apogeotropism retarded
by heliotropism—Effected by the aid of joints or pulvini—Movements of
flower-peduncles of Oxalis—General remarks on apogeotropism—
Geotropism—Movements of radicles—Burying of seed-capsules—Use of

process—Trifolium subterraneum—Arachis—Amphicarpæa—
Diageotropism—Conclusion.

CHAPTER XI.—LOCALISED SENSITIVENESS TO GRAVITATION,
AND ITS TRANSMITTED EFFECTS.
General considerations—Vicia faba, effects of amputating the tips of the
radicles—Regeneration of the tips—Effects of a short exposure of the tips
to geotropic action and their subsequent amputation—Effects of amputating
the tips obliquely—Effects of cauterising the tips—Effects of grease on the
tips—Pisum sativum, tips of radicles cauterised transversely, and on their
upper and lower sides—Phaseolus, cauterisation and grease on the tips—
Gossypium—Cucurbita, tips cauterised transversely, and on their upper and
lower sides—Zea, tips cauterised—Concluding remarks and summary of
chapter—Advantages of the sensibility to geotropism being localised in the
tips of the radicles.

CHAPTER XII.—CONCLUDING REMARKS.
Nature of the circumnutating movement—History of a germinating seed—
The radicle first protrudes and circumnutates—Its tip highly sensitive—
Emergence of the hypocotyl or of the epicotyl from the ground under the
form of an arch—Its circumnutation and that of the cotyledons—The
seedling throws up a leaf-bearing stem—The circumnutation of all the parts
or organs—Modified circumnutation—Epinasty and hyponasty—
Movements of climbing plants—Nyctitropic movements—Movements
excited by light and gravitation—Localised sensitiveness—Resemblance
between the movements of plants and animals—The tip of the radicle acts
like a brain.

THE MOVEMENTS OF PLANTS.

INTRODUCTION.

The chief object of the present work is to describe and connect together
several large classes of movement, common to almost all plants. The most
widely prevalent movement is essentially of the same nature as that of the
stem of a climbing plant, which bends successively to all points of the
compass, so that the tip revolves. This movement has been called by Sachs
“revolving nutation;” but we have found it much more convenient to use the
terms circumnutation and circumnutate. As we shall have to say much about
this movement, it will be useful here briefly to describe its nature. If we
observe a circumnutating stem, which happens at the time to be bent, we
will say towards the north, it will be found gradually to bend more and
more easterly, until it faces the east; and so onwards to the south, then to the
west, and back again to the north. If the movement had been quite regular,
the apex would have described a circle, or rather, as the stem is always
growing upwards, a circular spiral. But it generally describes irregular
elliptical or oval figures; for the apex, after pointing in any one direction,
commonly moves back to the opposite side, not, however, returning along
the same line. Afterwards other irregular ellipses or ovals are successively
described, with their longer axes directed to different points of the compass.
Whilst describing such figures, the apex often travels in a zigzag line, or
makes small subordinate loops or triangles. In the case of leaves the ellipses
are generally narrow.
Until recently the cause of all such bending movements was believed to
be due to the increased growth of the side which becomes for a time
convex; that this side does temporarily grow more quickly than the concave
side has been well established; but De Vries has lately shown that such
increased growth follows a previously increased state of turgescence on the
convex side.[1] In the case of parts provided with a so-called joint, cushion
or pulvinus, which consists of an aggregate of small cells that have ceased
to increase in size from a very early age, we meet with similar movements;

and here, as Pfeffer has shown[2] and as we shall see in the course of this
work, the increased turgescence of the cells on opposite sides is not
followed by increased growth. Wiesner denies in certain cases the accuracy
of De Vries’ conclusion about turgescence, and maintains[3] that the
increased extensibility of the cell-walls is the more important element. That
such extensibility must accompany increased turgescence in order that the
part may bend is manifest, and this has been insisted on by several
botanists; but in the case of unicellular plants it can hardly fail to be the
more important element. On the whole we may at present conclude that
increased growth, first on one side and then on another, is a secondary
effect, and that the increased turgescence of the cells, together with the
extensibility of their walls, is the primary cause of the movement of
circumnutation.[4]
[1] Sachs first showed (‘Lehrbuch,’ etc., 4th edit. p. 452) the intimate connection
between turgescence and growth. For De Vries’ interesting essay,
‘Wachsthumskrümmungen mehrzelliger Organe,’ see ‘Bot. Zeitung,’ Dec. 19,
1879, p. 830.

[2] ‘Die Periodischen Bewegungen der Blattorgane,’ 1875.

[3] ‘Untersuchungen über den Heliotropismus,’ Sitzb. der K. Akad. der
Wissenschaft. (Vienna), Jan. 1880.

[4] See Mr. Vines’ excellent discussion (‘Arbeiten des Bot. Instituts in
Würzburg,’ B. II. pp. 142, 143, 1878) on this intricate subject. Hofmeister’s
observations (‘Jahreschrifte des Vereins für Vaterl. Naturkunde in Würtemberg,’
1874, p. 211) on the curious movements of Spirogyra, a plant consisting of a
single row of cells, are valuable in relation to this subject.

In the course of the present volume it will be shown that apparently every
growing part of every plant is continually circumnutating, though often on a
small scale. Even the stems of seedlings before they have broken through
the ground, as well as their buried radicles, circumnutate, as far as the
pressure of the surrounding earth permits. In this universally present
movement we have the basis or groundwork for the acquirement, according
to the requirements of the plant, of the most diversified movements. Thus,
the great sweeps made by the stems of twining plants, and by the tendrils of
other climbers, result from a mere increase in the amplitude of the ordinary
movement of circumnutation. The position which young leaves and other
organs ultimately assume is acquired by the circumnutating movement
being increased in some one direction. the leaves of various plants are said

to sleep at night, and it will be seen that their blades then assume a vertical
position through modified circumnutation, in order to protect their upper
surfaces from being chilled through radiation. The movements of various
organs to the light, which are so general throughout the vegetable kingdom,
and occasionally from the light, or transversely with respect to it, are all
modified forms of circumnutation; as again are the equally prevalent
movements of stems, etc., towards the zenith, and of roots towards the
centre of the earth. In accordance with these conclusions, a considerable
difficulty in the way of evolution is in part removed, for it might have been
asked, how did all these diversified movements for the most different
purposes first arise? As the case stands, we know that there is always
movement in progress, and its amplitude, or direction, or both, have only to
be modified for the good of the plant in relation with internal or external
stimuli.
Besides describing the several modified forms of circumnutation, some
other subjects will be discussed. The two which have interested us most are,
firstly, the fact that with some seedling plants the uppermost part alone is
sensitive to light, and transmits an influence to the lower part, causing it to
bend. If therefore the upper part be wholly protected from light, the lower
part may be exposed for hours to it, and yet does not become in the least
bent, although this would have occurred quickly if the upper part had been
excited by light. Secondly, with the radicles of seedlings, the tip is sensitive
to various stimuli, especially to very slight pressure, and when thus excited,
transmits an influence to the upper part, causing it to bend from the pressed
side. On the other hand, if the tip is subjected to the vapour of water
proceeding from one side, the upper part of the radicle bends towards this
side. Again it is the tip, as stated by Ciesielski, though denied by others,
which is sensitive to the attraction of gravity, and by transmission causes
the adjoining parts of the radicle to bend towards the centre of the earth.
These several cases of the effects of contact, other irritants, vapour, light,
and the attraction of gravity being transmitted from the excited part for
some little distance along the organ in question, have an important bearing
on the theory of all such movements.

Terminology.—A brief explanation of some terms which will be used,
must here be given. With seedlings, the stem which supports the cotyledons

(i.e. the organs which represent the first leaves) has been called by many
botanists the hypocotyledonous stem, but for brevity sake we will speak of
it merely as the hypocotyl: the stem immediately above the cotyledons will
be called the epicotyl or plumule. The radicle can be distinguished from the
hypocotyl only by the presence of root-hairs and the nature of its covering.
The meaning of the word circumnutation has already been explained.
Authors speak of positive and negative heliotropism,[5]—that is, the bending
of an organ to or from the light; but it is much more convenient to confine
the word heliotropism to bending towards the light, and to designate as
apheliotropism bending from the light. There is another reason for this
change, for writers, as we have observed, occasionally drop the adjectives
positive and negative, and thus introduce confusion into their discussions.
Diaheliotropism may express a position more or less transverse to the light
and induced by it. In like manner positive geotropism, or bending towards
the centre of the earth, will be called by us geotropism; apogeotropism will
mean bending in opposition to gravity or from the centre of the earth; and
diageotropism, a position more or less transverse to the radius of the earth.
The words heliotropism and geotropism properly mean the act of moving in
relation to the light or the earth; but in the same manner as gravitation,
though defined as “the act of tending to the centre,” is often used to express
the cause of a body falling, so it will be found convenient occasionally to
employ heliotropism and geotropism, etc., as the cause of the movements in
question.
[5] The highly useful terms of Heliotropism and Geotropism were first used by
Dr. A. B. Frank: see his remarkable ‘Beiträge zur Pflanzenphysiologie,’ 1868.

The term epinasty is now often used in Germany, and implies that the
upper surface of an organ grows more quickly than the lower surface, and
thus causes it to bend downwards. Hyponasty is the reverse, and implies
increased growth along the lower surface, causing the part to bend upwards.
[6]

[6] These terms are used in the sense given them by De Vries, ‘Würzburg
Arbeiten,’ Heft ii 1872, p. 252.

Methods of Observation.—The movements, sometimes very small and
sometimes considerable in extent, of the various organs observed by us,
were traced in the manner which after many trials we found to be best, and
which must be described. Plants growing in pots were protected wholly

from the light, or had light admitted from above, or on one side as the case
might require, and were covered above by a large horizontal sheet of glass,
and with another vertical sheet on one side. A glass filament, not thicker
than a horsehair, and from a quarter to three-quarters of an inch in length,
was affixed to the part to be observed by means of shellac dissolved in
alcohol. The solution was allowed to evaporate, until it became so thick that
it set hard in two or three seconds, and it never injured the tissues, even the
tips of tender radicles, to which it was applied. To the end of the glass
filament an excessively minute bead of black sealing-wax was cemented,
below or behind which a bit of card with a black dot was fixed to a stick
driven into the ground. The weight of the filament was so slight that even
small leaves were not perceptibly pressed down. another method of
observation, when much magnification of the movement was not required,
will presently be described. The bead and the dot on the card were viewed
through the horizontal or vertical glass-plate (according to the position of
the object), and when one exactly covered the other, a dot was made on the
glass-plate with a sharply pointed stick dipped in thick Indian-ink. Other
dots were made at short intervals of time and these were afterwards joined
by straight lines. The figures thus traced were therefore angular; but if dots
had been made every 1 or 2 minutes, the lines would have been more
curvilinear, as occurred when radicles were allowed to trace their own
courses on smoked glass-plates. To make the dots accurately was the sole
difficulty, and required some practice. Nor could this be done quite
accurately, when the movement was much magnified, such as 30 times and
upwards; yet even in this case the general course may be trusted. To test the
accuracy of the above method of observation, a filament was fixed to an
inanimate object which was made to slide along a straight edge and dots
were repeatedly made on a glass-plate; when these were joined, the result
ought to have been a perfectly straight line, and the line was very nearly
straight. It may be added that when the dot on the card was placed half-an-
inch below or behind the bead of sealing-wax, and when the glass-plate
(supposing it to have been properly curved) stood at a distance of 7 inches
in front (a common distance), then the tracing represented the movement of
the bead magnified 15 times.
Whenever a great increase of the movement was not required, another,
and in some respects better, method of observation was followed. This
consisted in fixing two minute triangles of thin paper, about 1/20 inch in

height, to the two ends of the attached glass filament; and when their tips
were brought into a line so that they covered one another, dots were made
as before on the glass-plate. If we suppose the glass-plate to stand at a
distance of seven inches from the end of the shoot bearing the filament, the
dots when joined, will give nearly the same figure as if a filament seven
inches long, dipped in ink, had been fixed to the moving shoot, and had
inscribed its own course on the plate. The movement is thus considerably
magnified; for instance, if a shoot one inch in length were bending, and the
glass-plate stood at the distance of seven inches, the movement would be
magnified eight times. It would, however, have been very difficult to have
ascertained in each case how great a length of the shoot was bending; and
this is indispensable for ascertaining the degree to which the movement is
magnified.
After dots had been made on the glass-plates by either of the above
methods, they were copied on tracing paper and joined by ruled lines, with
arrows showing the direction of the movement. The nocturnal courses are
represented by straight broken lines. the first dot is always made larger than
the others, so as to catch the eye, as may be seen in the diagrams. The
figures on the glass-plates were often drawn on too large a scale to be
reproduced on the pages of this volume, and the proportion in which they
have been reduced is always given.[7] Whenever it could be approximately
told how much the movement had been magnified, this is stated. We have
perhaps introduced a superfluous number of diagrams; but they take up less
space than a full description of the movements. Almost all the sketches of
plants asleep, etc., were carefully drawn for us by Mr. George Darwin.
[7] We are much indebted to Mr. Cooper for the care with which he has reduced
and engraved our diagrams.

As shoots, leaves, etc., in circumnutating bend more and more, first in
one direction and then in another, they were necessarily viewed at different
times more or less obliquely; and as the dots were made on a flat surface,
the apparent amount of movement is exaggerated according to the degree of
obliquity of the point of view. It would, therefore, have been a much better
plan to have used hemispherical glasses, if we had possessed them of all
sizes, and if the bending part of the shoot had been distinctly hinged and
could have been placed so as to have formed one of the radii of the sphere.
But even in this case it would have been necessary afterwards to have

projected the figures on paper; so that complete accuracy could not have
been attained. From the distortion of our figures, owing to the above causes,
they are of no use to any one who wishes to know the exact amount of
movement, or the exact course pursued; but they serve excellently for
ascertaining whether or not the part moved at all, as well as the general
character of the movement.

In the following chapters, the movements of a considerable number of
plants are described; and the species have been arranged according to the
system adopted by Hooker in Le Maout and Decaisne’s ‘Descriptive
Botany.’ No one who is not investigating the present subject need read all
the details, which, however, we have thought it advisable to give. To save
the reader trouble, the conclusions and most of the more important parts
have been printed in larger type than the other parts. He may, if he thinks
fit, read the last chapter first, as it includes a summary of the whole volume;
and he will thus see what points interest him, and on which he requires the
full evidence.
Finally, we must have the pleasure of returning our sincere thanks to Sir
Joseph Hooker and to Mr. W. Thiselton Dyer for their great kindness, in not
only sending us plants from Kew, but in procuring others from several
sources when they were required for our observations; also, for naming
many species, and giving us information on various points.

CHAPTER I.
THE CIRCUMNUTATING MOVEMENTS OF
SEEDLING PLANTS.

Brassica oleracea, circumnutation of the radicle, of the
arched hypocotyl whilst still buried beneath the ground,
whilst rising above the ground and straightening itself, and
when erect—Circumnutation of the cotyledons—Rate of
movement—Analogous observations on various organs in
species of Githago, Gossypium, Oxalis, Tropaeolum, Citrus,
Æsculus, of several Leguminous and Cucurbitaceous genera,
Opuntia, Helianthus, Primula, Cyclamen, Stapelia, Cerinthe,
Nolana, Solanum, Beta, Ricinus, Quercus, Corylus, Pinus,
Cycas, Canna, Allium, Asparagus, Phalaris, Zea, Avena,
Nephrodium, and Selaginella.

The following chapter is devoted to the circumnutating movements of the
radicles, hypocotyls, and cotyledons of seedling plants; and, when the
cotyledons do not rise above the ground, to the movements of the epicotyl.
But in a future chapter we shall have to recur to the movements of certain
cotyledons which sleep at night.

Brassica oleracea (Cruciferae)’.—Fuller details will be given with respect
to the movements in this case than in any other, as space and time will thus
ultimately be saved.
Radicle.—A seed with the radicle projecting .05 inch was fastened with
shellac to a little plate of zinc, so that the radicle stood up vertically; and a
fine glass filament was then fixed near its base, that is, close to the seed-
coats. The seed was surrounded by little bits of wet sponge, and the

movement of the bead at the end of the filament was traced (Fig. 1) during
sixty hours. In this time the radicle increased in length from .05 to .11 inch.
Had the filament been attached at first close to the apex of the radicle, and
if it could have remained there all the time, the movement exhibited would
have been much greater, for at the close of our observations the tip, instead
of standing vertically upwards, had become bowed downwards through
geotropism, so as almost to touch the zinc plate. As far as we could roughly
ascertain by measurements made with compasses on other seeds, the tip
alone, for a length of only 2/100 to 3/100 of an inch, is acted on by
geotropism. But the tracing shows that the basal part of the radicle
continued to circumnutate irregularly during the whole time. The actual
extreme amount of movement of the bead at the end of the filament was
nearly .05 inch, but to what extent the movement of the radicle was
magnified by the filament, which was nearly 3/4 inch in length, it was
impossible to estimate.
Fig. 1. Brassica oleracea: circumnutation of radicle, traced on horizontal
glass, from 9 A.M. Jan. 31st to 9 P.M. Feb. 2nd. Movement of bead at end
of filament magnified about 40 times.
Another seed was treated and observed in the same manner, but the
radicle in this case protruded .1 inch, and was not fastened so as to project
quite vertically upwards. The filament was affixed close to its base. The
tracing (Fig. 2, reduced by half) shows the movement from 9 A.M. Jan. 31st
to 7 A.M. Feb. 2nd; but it continued to move during the whole of the 2nd in
the same general direction, and in a similar zigzag manner. From the radicle
not being quite perpendicular when the filament was affixed geotropism
came into play at once; but the irregular zigzag course shows that there was
growth (probably preceded by turgescence), sometimes on one and
sometimes on another side. Occasionally the bead remained stationary for
about an hour, and then probably growth occurred on the side opposite to
that which caused the geotropic curvature. In the case previously described
the basal part of the very short radicle from being turned vertically upwards,
was at first very little affected by geotropism. Filaments were affixed in two
other instances to rather longer radicles protruding obliquely from seeds
which had been turned upside down; and in these cases the lines traced on
the horizontal glasses were only slightly zigzag, and the movement was
always in the same general direction, through the action of geotropism. All
these observations are liable to several causes of error, but we believe, from

what will hereafter be shown with respect to the movements of the radicles
of other plants, that they may be largely trusted.
Fig. 2. Brassica oleracea: circumnutating and geotropic movement of
radicle, traced on horizontal glass during 46 hours.
Hypocotyl.—The hypocotyl protrudes through the seed-coats as a
rectangular projection, which grows rapidly into an arch like the letter U
turned upside down; the cotyledons being still enclosed within the seed. In
whatever position the seed may be embedded in the earth or otherwise
fixed, both legs of the arch bend upwards through apogeotropism, and thus
rise vertically above the ground. As soon as this has taken place, or even
earlier, the inner or concave surface of the arch grows more quickly than the
upper or convex surface; and this tends to separate the two legs and aids in
drawing the cotyledons out of the buried seed-coats. By the growth of the
whole arch the cotyledons are ultimately dragged from beneath the ground,
even from a considerable depth; and now the hypocotyl quickly straightens
itself by the increased growth of the concave side.
Even whilst the arched or doubled hypocotyl is still beneath the ground,
it circumnutates as much as the pressure of the surrounding soil will permit;
but this was difficult to observe, because as soon as the arch is freed from
lateral pressure the two legs begin to separate, even at a very early age,
before the arch would naturally have reached the surface. Seeds were
allowed to germinate on the surface of damp earth, and after they had fixed
themselves by their radicles, and after the, as yet, only slightly arched
hypocotyl had become nearly vertical, a glass filament was affixed on two
occasions near to the base of the basal leg (i.e. the one in connection with
the radicle), and its movements were traced in darkness on a horizontal
glass. The result was that long lines were formed running in nearly the
plane of the vertical arch, due to the early separation of the two legs now
freed from pressure; but as the lines were zigzag, showing lateral
movement, the arch must have been circumnutating, whilst it was
straightening itself by growth along its inner or concave surface.
A somewhat different method of observation was next followed: as soon
as the earth with seeds in a pot began to crack, the surface was removed in
parts to the depth of .2 inch; and a filament was fixed to the basal leg of a
buried and arched hypocotyl, just above the summit of the radicle. The
cotyledons were still almost completely enclosed within the much-cracked

seed-coats; and these were again covered up with damp adhesive soil
pressed pretty firmly down. The movement of the filament was traced (Fig.
3) from 11 A.M. Feb. 5th till 8 A.M. Feb. 7th. By this latter period the
cotyledons had been dragged from beneath the pressed-down earth, but the
upper part of the hypocotyl still formed nearly a right angle with the lower
part. The tracing shows that the arched hypocotyl tends at this early age to
circumnutate irregularly. On the first day the greater movement (from right
to left in the figure) was not in the plane of the vertical and arched
hypocotyl, but at right angles to it, or in the plane of the two cotyledons,
which were still in close contact. The basal leg of the arch at the time when
the filament was affixed to it, was already bowed considerably backwards,
or from the cotyledons; had the filament been affixed before this bowing
occurred, the chief movement would have been at right angles to that shown
in the figure. A filament was attached to another buried hypocotyl of the
same age, and it moved in a similar general manner, but the line traced was
not so complex. This hypocotyl became almost straight, and the cotyledons
were dragged from beneath the ground on the evening of the second day.
Fig. 3. Brassica oleracea: circumnutating movement of buried and arched
hypocotyl (dimly illuminated from above), traced on horizontal glass during
45 hours. Movement of bead of filament magnified about 25 times, and
here reduced to one-half of original scale.
Fig. 4. Brassica oleracea: circumnutating movement of buried and arched
hypocotyl, with the two legs of the arch tied together, traced on horizontal
glass during 33½ hours. Movement of the bead of filament magnified about
26 times, and here reduced to one-half original scale.
Before the above observations were made, some arched hypocotyls
buried at the depth of a quarter of an inch were uncovered; and in order to
prevent the two legs of the arch from beginning to separate at once, they
were tied together with fine silk. This was done partly because we wished to
ascertain how long the hypocotyl, in its arched condition, would continue to
move, and whether the movement when not masked and disturbed by the
straightening process, indicated circumnutation. Firstly a filament was fixed
to the basal leg of an arched hypocotyl close above the summit of the
radicle. The cotyledons were still partially enclosed within the seed-coats.
The movement was traced (Fig. 4) from 9.20 A.M. on Dec. 23rd to 6.45
A.M. on Dec. 25th. No doubt the natural movement was much disturbed by

the two legs having been tied together; but we see that it was distinctly
zigzag, first in one direction and then in an almost opposite one. After 3
P.M. on the 24th the arched hypocotyl sometimes remained stationary for a
considerable time, and when moving, moved far slower than before.
Therefore, on the morning of the 25th, the glass filament was removed from
the base of the basal leg, and was fixed horizontally on the summit of the
arch, which, from the legs having been tied, had grown broad and almost
flat. The movement was now traced during 23 hours (Fig. 5), and we see
that the course was still zigzag, which indicates a tendency to
circumnutation. The base of the basal leg by this time had almost
completely ceased to move.
Fig. 5. Brassica oleracea: circumnutating movement of the crown of a
buried and arched hypocotyl, with the two legs tied together, traced on a
horizontal glass during 23 hours. Movement of the bead of the filament
magnified about 58 times, and here reduced to one-half original scale.
As soon as the cotyledons have been naturally dragged from beneath the
ground, and the hypocotyl has straightened itself by growth along the inner
or concave surface, there is nothing to interfere with the free movements of
the parts; and the circumnutation now becomes much more regular and
clearly displayed, as shown in the following cases:—A seedling was placed
in front and near a north-east window with a line joining the two cotyledons
parallel to the window. It was thus left the whole day so as to accommodate
itself to the light. On the following morning a filament was fixed to the
midrib of the larger and taller cotyledon (which enfolds the other and
smaller one, whilst still within the seed), and a mark being placed close
behind, the movement of the whole plant, that is, of the hypocotyl and
cotyledon, was traced greatly magnified on a vertical glass. At first the plant
bent so much towards the light that it was useless to attempt to trace the
movement; but at 10 A.M. heliotropism almost wholly ceased and the first
dot was made on the glass. The last was made at 8.45 P.M.; seventeen dots
being altogether made in this interval of 10 h. 45 m. (see Fig. 6). It should
be noticed that when I looked shortly after 4 P.M. the bead was pointing off
the glass, but it came on again at 5.30 P.M., and the course during this
interval of 1 h. 30 m. has been filled up by imagination, but cannot be far
from correct. The bead moved seven times from side to side, and thus
described 3½ ellipses in 10 3/4 h.; each being completed on an average in 3
h. 4 m.

Fig. 6. Brassica oleracea: conjoint circumnutation of the hypocotyl and
cotyledons during 10 hours 45 minutes. Figure here reduced to one-half
original scale.
On the previous day another seedling had been observed under similar
conditions, excepting that the plant was so placed that a line joining the two
cotyledons pointed towards the window; and the filament was attached to
the smaller cotyledon on the side furthest from the window. Moreover the
plant was now for the first time placed in this position. The cotyledons
bowed themselves greatly towards the light from 8 to 10.50 A.M., when the
first dot was made (Fig. 7). During the next 12 hours the bead swept
obliquely up and down 8 times and described 4 figures representing
ellipses; so that it travelled at nearly the same rate as in the previous case.
during the night it moved upwards, owing to the sleep-movement of the
cotyledons, and continued to move in the same direction till 9 A.M. on the
following morning; but this latter movement would not have occurred with
seedlings under their natural conditions fully exposed to the light.
Fig. 7. Brassica oleracea: conjoint circumnutation of the hypocotyl and
cotyledons, from 10.50 A.M. to 8 A.M. on the following morning. Tracing
made on a vertical glass.
By 9.25 A.M. on this second day the same cotyledon had begun to fall,
and a dot was made on a fresh glass. The movement was traced until 5.30
P.M. as shown in (Fig. 8), which is given, because the course followed was
much more irregular than on the two previous occasions. During these 8
hours the bead changed its course greatly 10 times. The upward movement
of the cotyledon during the afternoon and early part of the night is here
plainly shown.
Fig. 8. Brassica oleracea: conjoint circumnutation of the hypocotyl and
cotyledons during 8 hours. Figure here reduced to one-third of the original
scale, as traced on a vertical glass.
As the filaments were fixed in the three last cases to one of the
cotyledons, and as the hypocotyl was left free, the tracings show the
movement of both organs conjoined; and we now wished to ascertain
whether both circumnutated. Filaments were therefore fixed horizontally to
two hypocotyls close beneath the petioles of their cotyledons. These
seedlings had stood for two days in the same position before a north-east
window. In the morning, up to about 11 A.M., they moved in zigzag lines

towards the light; and at night they again became almost upright through
apogeotropism. After about 11 A.M. they moved a little back from the light,
often crossing and recrossing their former path in zigzag lines. the sky on
this day varied much in brightness, and these observations merely proved
that the hypocotyls were continually moving in a manner resembling
circumnutation. On a previous day which was uniformly cloudy, a
hypocotyl was firmly secured to a little stick, and a filament was fixed to
the larger of the two cotyledons, and its movement was traced on a vertical
glass. It fell greatly from 8.52 A.M., when the first dot was made, till 10.55
A.M.; it then rose greatly until 12.17 P.M. Afterwards it fell a little and
made a loop, but by 2.22 P.M. it had risen a little and continued rising till
9.23 P.M., when it made another loop, and at 10.30 P.M. was again rising.
These observations show that the cotyledons move vertically up and down
all day long, and as there was some slight lateral movement, they
circumnutated.
Fig. 9. Brassica oleracea: circumnutation of hypocotyl, in darkness,
traced on a horizontal glass, by means of a filament with a bead fixed across
its summit, between 9.15 A.M. and 8.30 A.M. on the following morning.
Figure here reduced to one-half of original scale.
The cabbage was one of the first plants, the seedlings of which were
observed by us, and we did not then know how far the circumnutation of the
different parts was affected by light. Young seedlings were therefore kept in
complete darkness except for a minute or two during each observation,
when they were illuminated by a small wax taper held almost vertically
above them. During the first day the hypocotyl of one changed its course 13
times (see Fig. 9); and it deserves notice that the longer axes of the figures
described often cross one another at right or nearly right angles. Another
seedling was observed in the same manner, but it was much older, for it had
formed a true leaf a quarter of an inch in length, and the hypocotyl was 1
3/8 inch in height. The figure traced was a very complex one, though the
movement was not so great in extent as in the last case.
The hypocotyl of another seedling of the same age was secured to a little
stick, and a filament having been fixed to the midrib of one of the
cotyledons, the movement of the bead was traced during 14 h. 15 m. (see
Fig. 10) in darkness. It should be noted that the chief movement of the
cotyledons, namely, up and down, would be shown on a horizontal glass-

plate only by the lines in the direction of the midrib (that is, up and down,
as Fig. 10 here stands) being a little lengthened or shortened; whereas any
lateral movement would be well exhibited. The present tracing shows that
the cotyledon did thus move laterally (that is, from side to side in the
tracing) 12 times in the 14 h. 15 m. of observation. Therefore the cotyledons
certainly circumnutated, though the chief movement was up and down in a
vertical plane.
Fig. 10. Brassica oleracea: circumnutation of a cotyledon, the hypocotyl
having been secured to a stick, traced on a horizontal glass, in darkness,
from 8.15 A.M. to 10.30 P.M. Movement of the bead of the filament
magnified 13 times.
Rate of Movement.—The movements of the hypocotyls and cotyledons
of seedling cabbages of different ages have now been sufficiently
illustrated. With respect to the rate, seedlings were placed under the
microscope with the stage removed, and with a micrometer eye-piece so
adjusted that each division equalled 1/500 inch; the plants were illuminated
by light passing through a solution of bichromate of potassium so as to
eliminate heliotropism. Under these circumstances it was interesting to
observe how rapidly the circumnutating apex of a cotyledon passed across
the divisions of the micrometer. Whilst travelling in any direction the apex
generally oscillated backwards and forwards to the extent of 1/500 and
sometimes of nearly 1/250 of an inch. These oscillations were quite
different from the trembling caused by any disturbance in the same room or
by the shutting of a distant door. The first seedling observed was nearly two
inches in height and had been etiolated by having been grown in darkness.
The tip of the cotyledon passed across 10 divisions of the micrometer, that
is, 1/50 of an inch, in 6 m. 40 s. Short glass filaments were then fixed
vertically to the hypocotyls of several seedlings so as to project a little
above the cotyledons, thus exaggerating the rate of movement; but only a
few of the observations thus made are worth giving. The most remarkable
fact was the oscillatory movement above described, and the difference of
rate at which the point crossed the divisions of the micrometer, after short
intervals of time. For instance, a tall not-etiolated seedling had been kept
for 14 h. in darkness; it was exposed before a north-east window for only
two or three minutes whilst a glass filament was fixed vertically to the
hypocotyl; it was then again placed in darkness for half an hour and
afterwards observed by light passing through bichromate of potassium. The

point, oscillating as usual, crossed five divisions of the micrometer (i.e.
1/100 inch) in 1 m. 30 s. The seedling was then left in darkness for an hour,
and now it required 3 m. 6 s. to cross one division, that is, 15 m. 30 s. to
have crossed five divisions. Another seedling, after being occasionally
observed in the back part of a northern room with a very dull light, and left
in complete darkness for intervals of half an hour, crossed five divisions in
5 m. in the direction of the window, so that we concluded that the
movement was heliotropic. But this was probably not the case, for it was
placed close to a north-east window and left there for 25 m., after which
time, instead of moving still more quickly towards the light, as might have
been expected, it travelled only at the rate of 12 m. 30 s. for five divisions.
It was then again left in complete darkness for 1 h., and the point now
travelled in the same direction as before, but at the rate of 3 m. 18 s. for five
divisions.
We shall have to recur to the cotyledons of the cabbage in a future
chapter, when we treat of their sleep-movements. The circumnutation, also,
of the leaves of fully-developed plants will hereafter be described.
Fig. 11. Githago segetum: circumnutation of hypocotyl, traced on a
horizontal glass, by means of a filament fixed transversely across its
summit, from 8.15 A.M. to 12.15 P.M. on the following day. Movement of
bead of filament magnified about 13 times, here reduced to one-half the
original scale.
Githago segetum (Caryophylleae).—A young seedling was dimly
illuminated from above, and the circumnutation of the hypocotyl was
observed during 28 h., as shown in Fig. 11. It moved in all directions; the
lines from right and to left in the figure being parallel to the blades of the
cotyledons. The actual distance travelled from side to side by the summit of
the hypocotyl was about .2 of an inch; but it was impossible to be accurate
on this head, as the more obliquely the plant was viewed, after it had moved
for some time, the more the distances were exaggerated.
We endeavoured to observe the circumnutation of the cotyledons, but as
they close together unless kept exposed to a moderately bright light, and as
the hypocotyl is extremely heliotropic, the necessary arrangements were too
troublesome. We shall recur to the nocturnal or sleep-movements of the
cotyledons in a future chapter.

Fig. 12. Gossypium: circumnutation of hypocotyl, traced on a horizontal
glass, from 10.30 A.M. to 9.30 A.M. on following morning, by means of a
filament fixed across its summit. Movement of bead of filament magnified
about twice; seedling illuminated from above.
Gossypium (var. Nankin cotton) (Malvaceae).—The circumnutation of a
hypocotyl was observed in the hot-house, but the movement was so much
exaggerated that the bead twice passed for a time out of view. It was,
however, manifest that two somewhat irregular ellipses were nearly
completed in 9 h. Another seedling, 1½ in. in height, was then observed
during 23 h.; but the observations were not made at sufficiently short
intervals, as shown by the few dots in Fig. 12, and the tracing was not now
sufficiently enlarged. Nevertheless there could be no doubt about the
circumnutation of the hypocotyl, which described in 12 h. a figure
representing three irregular ellipses of unequal sizes.
The cotyledons are in constant movement up and down during the whole
day, and as they offer the unusual case of moving downwards late in the
evening and in the early part of the night, many observations were made on
them. A filament was fixed along the middle of one, and its movement
traced on a vertical glass; but the tracing is not given, as the hypocotyl was
not secured, so that it was impossible to distinguish clearly between its
movement and that of the cotyledon. The cotyledons rose from 10.30 A.M.
to about 3 P.M.; they then sank till 10 P.M., rising, however, greatly in the
latter part of the night. The angles above the horizon at which the
cotyledons of another seedling stood at different hours is recorded in the
following short table:—
Oct. 20 2.50 P.M...25° above horizon. Oct. 20 4.20 P.M...22° above
horizon. Oct. 20 5.20 P.M...15° above horizon. Oct. 20 10.40 P.M...8° above
horizon. Oct. 21 8.40 A.M...28° above horizon. Oct. 21 11.15 A.M...35°
above horizon. Oct. 21 9.11 P.M...10° below horizon.
The position of the two cotyledons was roughly sketched at various hours
with the same general result.
In the following summer, the hypocotyl of a fourth seedling was secured
to a little stick, and a glass filament with triangles of paper having been
fixed to one of the cotyledons, its movements were traced on a vertical
glass under a double skylight in the house. The first dot was made at 4.20
P.M. June 20th; and the cotyledon fell till 10.15 P.M. in a nearly straight

line. Just past midnight it was found a little lower and somewhat to one
side. By the early morning, at 3.45 A.M., it had risen greatly, but by 6.20
A.M. had fallen a little. During the whole of this day (21st) it fell in a
slightly zigzag line, but its normal course was disturbed by the want of
sufficient illumination, for during the night it rose only a little, and travelled
irregularly during the whole of the following day and night of June 22nd.
The ascending and descending lines traced during the three days did not
coincide, so that the movement was one of circumnutation. This seedling
was then taken back to the hot-house, and after five days was inspected at
10 P.M., when the cotyledons were found hanging so nearly vertically
down, that they might justly be said to have been asleep. On the following
morning they had resumed their usual horizontal position.
Oxalis rosea (Oxalideae).—The hypocotyl was secured to a little stick,
and an extremely thin glass filament, with two triangles of paper, was
attached to one of the cotyledons, which was .15 inch in length. In this and
the following species the end of the petiole, where united to the blade, is
developed into a pulvinus. The apex of the cotyledon stood only 5 inches
from the vertical glass, so that its movement was not greatly exaggerated as
long as it remained nearly horizontal; but in the course of the day it both
rose considerably above and fell beneath a horizontal position, and then of
course the movement was much exaggerated. In Fig. 13 its course is shown
from 6.45 A.M. on June 17th, to 7.40 A.M. on the following morning; and
we see that during the daytime, in the course of 11 h. 15 m., it travelled
thrice down and twice up. After 5.45 P.M. it moved rapidly downwards, and
in an hour or two depended vertically; it thus remained all night asleep. This
position could not be represented on the vertical glass nor in the figure here
given. By 6.40 A.M. on the following morning (18th) both cotyledons had
risen greatly, and they continued to rise until 8 A.M., when they stood
almost horizontally. Their movement was traced during the whole of this
day and until the next morning; but a tracing is not given, as it was closely
similar to Fig. 13, excepting that the lines were more zigzag. The
cotyledons moved 7 times, either upwards or downwards; and at about 4
P.M. the great nocturnal sinking movement commenced.
Fig. 13. Oxalis rosea: circumnutation of cotyledons, the hypocotyl being
secured to a stick; illuminated from above. Figure here given one-half of
original scale.

Another seedling was observed in a similar manner during nearly 24 h.,
but with the difference that the hypocotyl was left free. The movement also
was less magnified. Between 8.12 A.M. and 5 P.M. on the 18th, the apex of
the cotyledon moved 7 times upwards or downwards (Fig. 14). The
nocturnal sinking movement, which is merely a great increase of one of the
diurnal oscillations, commenced about 4 P.M.
Oxalis Valdiviana.—This species is interesting, as the cotyledons rise
perpendicularly upwards at night so as to come into close contact, instead of
sinking vertically downwards, as in the case of O. rosea. A glass filament
was fixed to a cotyledon, .17 of an inch in length, and the hypocotyl was
left free. On the first day the seedling was placed too far from the vertical
glass; so that the tracing was enormously exaggerated and the movement
could not be traced when the cotyledon either rose or sank much; but it was
clearly seen that the cotyledons rose thrice and fell twice between 8.15
A.M. and 4.15 P.M. Early on the following morning (June 19th) the apex of
a cotyledon was placed only 1 7/8 inch from the vertical glass. At 6.40 A.M.
it stood horizontally; it then fell till 8.35, and then rose. Altogether in the
course of 12 h. it rose thrice and fell thrice, as may be seen in Fig. 15. The
great nocturnal rise of the cotyledons usually commences about 4 or 5 P.M.,
and on the following morning they are expanded or stand horizontally at
about 6.30 A.M. In the present instance, however, the great nocturnal rise
did not commence till 7 P.M.; but this was due to the hypocotyl having from
some unknown cause temporarily bent to the left side, as is shown in the
tracing. To ascertain positively that the hypocotyl circumnutated, a mark
was placed at 8.15 P.M. behind the two now closed and vertical cotyledons;
and the movement of a glass filament fixed upright to the top of the
hypocotyl was traced until 10.40 P.M. During this time it moved from side
to side, as well as backwards and forwards, plainly showing
circumnutation; but the movement was small in extent. Therefore Fig. 15
represents fairly well the movements of the cotyledons alone, with the
exception of the one great afternoon curvature to the left.
Fig. 14. Oxalis rosea: conjoint circumnutation of the cotyledons and
hypocotyl, traced from 8.12 A.M. on June 18th to 7.30 A.M. 19th. The apex
of the cotyledon stood only 3 3/4 inches from the vertical glass. Figure here
given one-half of original scale.

Fig. 15. Oxalis Valdiviana: conjoint circumnutation of a cotyledon and
the hypocotyl, traced on vertical glass, during 24 hours. Figure here given
one-half of original scale; seedling illuminated from above.
Oxalis corniculata (var. cuprea).—The cotyledons rise at night to a
variable degree above the horizon, generally about 45°: those on some
seedlings between 2 and 5 days old were found to be in continued
movement all day long; but the movements were more simple than in the
last two species. This may have partly resulted from their not being
sufficiently illuminated whilst being observed, as was shown by their not
beginning to rise until very late in the evening.
Oxalis (Biophytum) sensitiva.—The cotyledons are highly remarkable
from the amplitude and rapidity of their movements during the day. The
angles at which they stood above or beneath the horizon were measured at
short intervals of time; and we regret that their course was not traced during
the whole day. We will give only a few of the measurements, which were
made whilst the seedlings were exposed to a temperature of 22½° to 24½°
C. One cotyledon rose 70° in 11 m.; another, on a distinct seedling, fell 80°
in 12 m. Immediately before this latter fall the same cotyledon had risen
from a vertically downward to a vertically upward position in 1 h. 48 m.,
and had therefore passed through 180° in under 2 h. We have met with no
other instance of a circumnutating movement of such great amplitude as
180°; nor of such rapidity of movement as the passage through 80° in 12 m.
The cotyledons of this plant sleep at night by rising vertically and coming
into close contact. This upward movement differs from one of the great
diurnal oscillations above described only by the position being permanent
during the night and by its periodicity, as it always commences late in the
evening.
Tropaeolum minus (?) (var. Tom Thumb) (Tropaeoleae).—The
cotyledons are hypogean, or never rise above the ground. By removing the
soil a buried epicotyl or plumule was found, with its summit arched
abruptly downwards, like the arched hypocotyl of the cabbage previously
described. A glass filament with a bead at its end was affixed to the basal
half or leg, just above the hypogean cotyledons, which were again almost
surrounded by loose earth. The tracing (Fig. 16) shows the course of the
bead during 11 h. After the last dot given in the figure, the bead moved to a
great distance, and finally off the glass, in the direction indicated by the

broken line. This great movement, due to increased growth along the
concave surface of the arch, was caused by the basal leg bending backwards
from the upper part, that is in a direction opposite to the dependent tip, in
the same manner as occurred with the hypocotyl of the cabbage. Another
buried and arched epicotyl was observed in the same manner, excepting that
the two legs of the arch were tied together with fine silk for the sake of
preventing the great movement just mentioned. It moved, however, in the
evening in the same direction as before, but the line followed was not so
straight. During the morning the tied arch moved in an irregularly circular,
strongly zigzag course, and to a greater distance than in the previous case,
as was shown in a tracing, magnified 18 times. The movements of a young
plant bearing a few leaves and of a mature plant, will hereafter be
described.
Fig. 16. Tropaeolum minus (?): circumnutation of buried and arched
epicotyl, traced on a horizontal glass, from 9.20 A.M. to 8.15 P.M.
Movement of bead of filament magnified 27 times.
Citrus aurantium (Orange) (Aurantiaceae).—The cotyledons are
hypogean. The circumnutation of an epicotyl, which at the close of our
observations was .59 of an inch (15 mm.) in height above the ground, is
shown in the annexed figure (Fig. 17), as observed during a period of 44 h.
40 m.
Fig. 17. Citrus aurantium: circumnutation of epicotyl with a filament
fixed transversely near its apex, traced on a horizontal glass, from 12.13
P.M. on Feb. 20th to 8.55 A.M. on 22nd. The movement of the bead of the
filament was at first magnified 21 times, or 10½, in figure here given, and
afterwards 36 times, or 18 as here given; seedling illuminated from above.
Æsculus hippocastanum (Hippocastaneae).—Germinating seeds were
placed in a tin box, kept moist internally, with a sloping bank of damp
argillaceous sand, on which four smoked glass-plates rested, inclined at
angles of 70° and 65° with the horizon. The tips of the radicles were placed
so as just to touch the upper end of the glass-plates, and, as they grew
downwards they pressed lightly, owing to geotropism, on the smoked
surfaces, and left tracks of their course. In the middle part of each track the
glass was swept clean, but the margins were much blurred and irregular.
Copies of two of these tracks (all four being nearly alike) were made on
tracing paper placed over the glass-plates after they had been varnished; and

they are as exact as possible considering the nature of the margins (Fig. 18).
They suffice to show that there was some lateral, almost serpentine
movement, and that the tips in their downward course pressed with unequal
force on the plates, as the tracks varied in breadth. The more perfectly
serpentine tracks made by the radicles of Phaseolus multiflorus and Vicia
faba (presently to be described), render it almost certain that the radicles of
the present plant circumnutated.
Fig. 18. Æsculus hippocastanum: outlines of tracks left on inclined glass-
plates by tips of radicles. In A the plate was inclined at 70° with the horizon,
and the radicle was 1.9 inch in length, and .23 inch in diameter at base. In B
the plate was inclined 65° with the horizon, and the radicle was a trifle
larger.
Phaseolus multiflorus (Leguminosae).—Four smoked glass-plates were
arranged in the same manner as described under Æsculus, and the tracks left
by the tips of four radicles of the present plant, whilst growing downwards,
were photographed as transparent objects. Three of them are here exactly
copied (Fig. 19). Their serpentine courses show that the tips moved
regularly from side to side; they also pressed alternately with greater or less
force on the plates, sometimes rising up and leaving them altogether for a
very short distance; but this was better seen on the original plates than in
the copies. These radicles therefore were continually moving in all
directions—that is, they circumnutated. The distance between the extreme
right and left positions of the radicle A, in its lateral movement, was 2 mm.,
as ascertained by measurement with an eye-piece micrometer.
Fig. 19. Phaseolus multiflorus: tracks left on inclined smoked glass-plates
by tips of radicles in growing downwards. A and C, plates inclined at 60°, B
inclined at 68° with the horizon.
Vicia faba (Common Bean) (Leguminosae).—Radicle.—Some beans
were allowed to germinate on bare sand, and after one had protruded its
radicle to a length of .2 of an inch, it was turned upside down, so that the
radicle, which was kept in damp air, now stood upright. A filament, nearly
an inch in length, was affixed obliquely near its tip; and the movement of
the terminal bead was traced from 8.30 A.M. to 10.30 P.M., as shown in
Fig. 18. The radicle at first changed its course twice abruptly, then made a
small loop and then a larger zigzag curve. During the night and till 11 A.M.
on the following morning, the bead moved to a great distance in a nearly

straight line, in the direction indicated by the broken line in the figure. This
resulted from the tip bending quickly downwards, as it had now become
much declined, and had thus gained a position highly favourable for the
action of geotropism.
Fig. 20. Vicia faba: circumnutation of a radicle, at first pointing vertically
upwards, kept in darkness, traced on a horizontal glass, during 14 hours.
Movement of bead of filament magnified 23 times, here reduced to one-half
of original scale.
Fig. 21. Vicia faba: tracks left on inclined smoked glass-plates, by tips of
radicles in growing downwards. Plate C was inclined at 63°, plates A and D
at 71°, plate B at 75°, and plate E at a few degrees beneath the horizon.
We next experimented on nearly a score of radicles by allowing them to
grow downwards over inclined plates of smoked glass, in exactly the same
manner as with Æsculus and Phaseolus. Some of the plates were inclined
only a few degrees beneath the horizon, but most of them between 60° and
75°. In the latter cases the radicles in growing downwards were deflected
only a little from the direction which they had followed whilst germinating
in sawdust, and they pressed lightly on the glass-plates (Fig. 21). Five of the
most distinct tracks are here copied, and they are all slightly sinuous,
showing circumnutation. Moreover, a close examination of almost every
one of the tracks clearly showed that the tips in their downward course had
alternately pressed with greater or less force on the plates, and had
sometimes risen up so as nearly to leave them for short intervals. The
distance between the extreme right and left positions of the radicle A was
0.7 mm., ascertained in the same manner as in the case of Phaseolus.
Epicotyl.—At the point where the radicle had protruded from a bean laid
on its side, a flattened solid lump projected .1 of an inch, in the same
horizontal plane with the bean. This protuberance consisted of the convex
summit of the arched epicotyl; and as it became developed the two legs of
the arch curved themselves laterally upwards, owing to apogeotropism, at
such a rate that the arch stood highly inclined after 14 h., and vertically in
48 h. A filament was fixed to the crown of the protuberance before any arch
was visible, but the basal half grew so quickly that on the second morning
the end of the filament was bowed greatly downwards. It was therefore
removed and fixed lower down. The line traced during these two days

extended in the same general direction, and was in parts nearly straight, and
in others plainly zigzag, thus giving some evidence of circumnutation.
As the arched epicotyl, in whatever position it may be placed, bends
quickly upwards through apogeotropism, and as the two legs tend at a very
early age to separate from one another, as soon as they are relieved from the
pressure of the surrounding earth, it was difficult to ascertain positively
whether the epicotyl, whilst remaining arched, circumnutated. Therefore
some rather deeply buried beans were uncovered, and the two legs of the
arches were tied together, as had been done with the epicotyl of Tropaeolum
and the hypocotyl of the Cabbage. The movements of the tied arches were
traced in the usual manner on two occasions during three days. But the
tracings made under such unnatural conditions are not worth giving; and it
need only be said that the lines were decidedly zigzag, and that small loops
were occasionally formed. We may therefore conclude that the epicotyl
circumnutates whilst still arched and before it has grown tall enough to
break through the surface of the ground.
In order to observe the movements of the epicotyl at a somewhat more
advanced age, a filament was fixed near the base of one which was no
longer arched, for its upper half now formed a right angle with the lower
half. This bean had germinated on bare damp sand, and the epicotyl began
to straighten itself much sooner than would have occurred if it had been
properly planted. The course pursued during 50 h. (from 9 A.M. Dec. 26th,
to 11 A.M. 28th) is here shown (Fig. 22); and we see that the epicotyl
circumnutated during the whole time. Its basal part grew so much during
the 50 h. that the filament at the end of our observations was attached at the
height of .4 inch above the upper surface of the bean, instead of close to it.
If the bean had been properly planted, this part of the epicotyl would still
have been beneath the soil.
Fig. 22. Vicia faba: circumnutation of young epicotyl, traced in darkness
during 50 hours on a horizontal glass. Movement of bead of filament
magnified 20 times, here reduced to one-half of original scale.
Late in the evening of the 28th, some hours after the above observations
were completed, the epicotyl had grown much straighter, for the upper part
now formed a widely open angle with the lower part. A filament was fixed
to the upright basal part, higher up than before, close beneath the lowest
scale-like process or homologue of a leaf; and its movement was traced

during 38 h. (Fig. 23). We here again have plain evidence of continued
circumnutation. Had the bean been properly planted, the part of the epicotyl
to which the filament was attached, the movement of which is here shown,
would probably have just risen above the surface of the ground.
Fig. 23. Vicia faba: circumnutation of the same epicotyl as in Fig. 22, a
little more advanced in age, traced under similar conditions as before, from
8.40 A.M. Dec. 28th, to 10.50 A.M. 30th. Movement of bead here
magnified 20 times.
Lathyrus nissolia (Leguminosae).—This plant was selected for
observation from being an abnormal form with grass-like leaves. The
cotyledons are hypogean, and the epicotyl breaks through the ground in an
arched form. The movements of a stem, 1.2 inch in height, consisting of
three internodes, the lower one almost wholly subterranean, and the upper
one bearing a short, narrow leaf, is shown during 24 h., in Fig. 24. No glass
filament was employed, but a mark was placed beneath the apex of the leaf.
The actual length of the longer of the two ellipses described by the stem
was about .14 of an inch. On the previous day the chief line of movement
was nearly at right angles to that shown in the present figure, and it was
more simple.
Fig. 24. Lathyrus nissolia: circumnutation of stem of young seedling,
traced in darkness on a horizontal glass, from 6.45 A.M. Nov. 22nd, to 7
A.M. 23rd. Movement of end of leaf magnified about 12 times, here
reduced to one-half of original scale.
Cassia tora[1] (Leguminosae).—A seedling was placed before a north-east
window; it bent very little towards it, as the hypocotyl which was left free
was rather old, and therefore not highly heliotropic. A filament had been
fixed to the midrib of one of the cotyledons, and the movement of the whole
seedling was traced during two days. The circumnutation of the hypocotyl
is quite insignificant compared with that of the cotyledons. These rise up
vertically at night and come into close contact; so that they may be said to
sleep. This seedling was so old that a very small true leaf had been
developed, which at night was completely hidden by the closed cotyledons.
On Sept. 24th, between 8 A.M. and 5 P.M., the cotyledons moved five times
up and five times down; they therefore described five irregular ellipses in
the course of the 9 h. The great nocturnal rise commenced about 4.30 P.M.

[1] Seeds of this plant, which grew near the sea-side, were sent to us by Fritz
Müller from S. Brazil. The seedlings did not flourish or flower well with us; they
were sent to Kew, and were pronounced not to be distinguishable from C. tora.

Fig. 25. Cassia tora: conjoint circumnutation of cotyledons and
hypocotyl, traced on vertical glass, from 7.10 A.M. Sept. 25th to 7.30 A.M.
26th. Figure here given reduced to one-half of original scale.
On the following morning (Sept. 25th) the movement of the same
cotyledon was again traced in the same manner during 24 h.; and a copy of
the tracing is here given (Fig. 25). The morning was cold, and the window
had been accidentally left open for a short time, which must have chilled
the plant; and this probably prevented it from moving quite as freely as on
the previous day; for it rose only four and sank only four times during the
day, one of the oscillations being very small. At 7.10 A.M., when the first
dot was made, the cotyledons were not fully open or awake; they continued
to open till about 9 A.M., by which time they had sunk a little beneath the
horizon: by 9.30 A.M. they had risen, and then they oscillated up and down;
but the upward and downward lines never quite coincided. At about 4.30
P.M. the great nocturnal rise commenced. At 7 A.M. on the following
morning (Sept. 26th) they occupied nearly the same level as on the previous
morning, as shown in the diagram: they then began to open or sink in the
usual manner. The diagram leads to the belief that the great periodical daily
rise and fall does not differ essentially, excepting in amplitude, from the
oscillations during the middle of the day.
Lotus Jacoboeus (Leguminosae).—The cotyledons of this plant, after the
few first days of their life, rise so as to stand almost, though rarely quite,
vertically at night. They continue to act in this manner for a long time even
after the development of some of the true leaves. With seedlings, 3 inches in
height, and bearing five or six leaves, they rose at night about 45°. They
continued to act thus for about an additional fortnight. Subsequently they
remained horizontal at night, though still green and at last dropped off.
Their rising at night so as to stand almost vertically appears to depend
largely on temperature; for when the seedlings were kept in a cool house,
though they still continued to grow, the cotyledons did not become vertical
at night. It is remarkable that the cotyledons do not generally rise at night to
any conspicuous extent during the first four or five days after germination;
but the period was extremely variable with seedlings kept under the same
conditions; and many were observed. Glass filaments with minute triangles

of paper were fixed to the cotyledons (1½ mm. in breadth) of two seedlings,
only 24 h. old, and the hypocotyl was secured to a stick; their movements
greatly magnified were traced, and they certainly circumnutated the whole
time on a small scale, but they did not exhibit any distinct nocturnal and
diurnal movement. The hypocotyls, when left free, circumnutated over a
large space.
Another and much older seedling, bearing a half-developed leaf, had its
movements traced in a similar manner during the three first days and nights
of June; but seedlings at this age appear to be very sensitive to a deficiency
of light; they were observed under a rather dim skylight, at a temperature of
between 16° to 17½° C.’ and apparently, in consequence of these
conditions, the great daily movement of the cotyledons ceased on the third
day. During the first two days they began rising in the early afternoon in a
nearly straight line, until between 6 and 7 P.M., when they stood vertically.
During the latter part of the night, or more probably in the early morning,
they began to fall or open, so that by 6.45 A.M. they stood fully expanded
and horizontal. They continued to fall slowly for some time, and during the
second day described a single small ellipse, between 9 A.M. and 2 P.M., in
addition to the great diurnal movement. The course pursued during the
whole 24 h. was far less complex than in the foregoing case of Cassia. On
the third morning they fell very much, and then circumnutated on a small
scale round the same spot; by 8.20 P.M. they showed no tendency to rise at
night. Nor did the cotyledons of any of the many other seedlings in the
same pot rise; and so it was on the following night of June 5th. The pot was
then taken back into the hot-house, where it was exposed to the sun, and on
the succeeding night all the cotyledons rose again to a high angle, but did
not stand quite vertically. On each of the above days the line representing
the great nocturnal rise did not coincide with that of the great diurnal fall, so
that narrow ellipses were described, as is the usual rule with circumnutating
organs. The cotyledons are provided with a pulvinus, and its development
will hereafter be described.
Mimosa pudica (Leguminosae).—The cotyledons rise up vertically at
night, so as to close together. Two seedlings were observed in the
greenhouse (temp. 16° to 17° C. or 63° to 65° F.). Their hypocotyls were
secured to sticks, and glass filaments bearing little triangles of paper were
affixed to the cotyledons of both. Their movements were traced on a
vertical glass during 24 h. on November 13th. The pot had stood for some

time in the same position, and they were chiefly illuminated through the
glass-roof. The cotyledons of one of these seedlings moved downward in
the morning till 11.30 A.M., and then rose, moving rapidly in the evening
until they stood vertically, so that in this case there was simply a single
great daily fall and rise. The other seedling behaved rather differently, for it
fell in the morning until 11.30 A.M., and then rose, but after 12.10 P.M.
again fell; and the great evening rise did not begin until 1.22 P.M. On the
following morning this cotyledon had fallen greatly from its vertical
position by 8.15 A.M. Two other seedlings (one seven and the other eight
days old) had been previously observed under unfavourable circumstances,
for they had been brought into a room and placed before a north-east
window, where the temperature was between only 56° and 57° F. They had,
moreover, to be protected from lateral light, and perhaps were not
sufficiently illuminated. Under these circumstances the cotyledons moved
simply downwards from 7 A.M. till 2 P.M., after which hour and during a
large part of the night they continued to rise. Between 7 and 8 A.M. on the
following morning they fell again; but on this second and likewise on the
third day the movements became irregular, and between 3 and 10.30 P.M.
they circumnutated to a small extent about the same spot; but they did not
rise at night. Nevertheless, on the following night they rose as usual.
Cytisus fragrans (Leguminosae).—Only a few observations were made
on this plant. The hypocotyl circumnutated to a considerable extent, but in a
simple manner—namely, for two hours in one direction, and then much
more slowly back again in a zigzag course, almost parallel to the first line,
and beyond the starting-point. It moved in the same direction all night, but
next morning began to return. The cotyledons continually move both up and
down and laterally; but they do not rise up at night in a conspicuous
manner.
Lupinus luteus (Leguminosae).—Seedlings of this plant were observed
because the cotyledons are so thick (about .08 of an inch) that it seemed
unlikely that they would move. Our observations were not very successful,
as the seedlings are strongly heliotropic, and their circumnutation could not
be accurately observed near a north-east window, although they had been
kept during the previous day in the same position. A seedling was then
placed in darkness with the hypocotyl secured to a stick; both cotyledons
rose a little at first, and then fell during the rest of the day; in the evening
between 5 and 6 P.M. they moved very slowly; during the night one

continued to fall and the other rose, though only a little. The tracing was not
much magnified, and as the lines were plainly zigzag, the cotyledons must
have moved a little laterally, that is, they must have circumnutated.
The hypocotyl is rather thick, about .12 of inch; nevertheless it
circumnutated in a complex course, though to a small extent. The
movement of an old seedling with two true leaves partially developed, was
observed in the dark. As the movement was magnified about 100 times it is
not trustworthy and is not given; but there could be no doubt that the
hypocotyl moved in all directions during the day, changing its course 19
times. The extreme actual distance from side to side through which the
upper part of the hypocotyl passed in the course of 14½ hours was only
1/60 of an inch; it sometimes travelled at the rate of 1/50 of an inch in an
hour.
Cucurbita ovifera (Cucurbitaceæ).—Radicle: a seed which had
germinated on damp sand was fixed so that the slightly curved radicle,
which was only .07 inch in length, stood almost vertically upwards, in
which position geotropism would act at first with little power. A filament
was attached near to its base, and projected at about an angle of 45° above
the horizon. The general course followed during the 11 hours of observation
and during the following night is shown in the accompanying diagram (Fig.
26), and was plainly due to geotropism; but it was also clear that the radicle
circumnutated. By the next morning the tip had curved so much downwards
that the filament, instead of projecting at 45° above the horizon, was nearly
horizontal. Another germinating seed was turned upside down and covered
with damp sand; and a filament was fastened to the radicle so as to project
at an angle of about 50° above the horizon; this radicle was .35 of an inch in
length and a little curved. The course pursued was mainly governed, as in
the last case, by geotropism, but the line traced during 12 hours and
magnified as before was more strongly zigzag, again showing
circumnutation.
Fig. 26. Cucurbita ovifera: course followed by a radicle in bending
geotropically downwards, traced on a horizontal glass, between 11.25 A.M.
and 10.25 P.M.; the direction during the night is indicated by the broken
line. Movement of bead magnified 14 times.
Four radicles were allowed to grow downwards over plates of smoked
glass, inclined at 70° to the horizon, under the same conditions as in the

cases of Æsculus, Phaseolus, and Vicia. Facsimiles are here given (Fig. 27)
of two of these tracks; and a third short one was almost as plainly
serpentine as that at A. It was also manifest by a greater or less amount of
soot having been swept off the glasses, that the tips had pressed alternately
with greater and less force on them. There must, therefore, have been
movement in at least two planes at right angles to one another. These
radicles were so delicate that they rarely had the power to sweep the glasses
quite clean. One of them had developed some lateral or secondary rootlets,
which projected a few degrees beneath the horizon; and it is an important
fact that three of them left distinctly serpentine tracks on the smoked
surface, showing beyond doubt that they had circumnutated like the main or
primary radicle. But the tracks were so slight that they could not be traced
and copied after the smoked surface had been varnished.
Fig. 27. Cucurbita ovifera: tracks left by tips of radicles in growing
downwards over smoked glass-plates, inclined at 70° to the horizon.
Fig. 28. Cucurbita ovifera: circumnutation of arched hypocotyl at a very
early age, traced in darkness on a horizontal glass, from 8 A.M. to 10.20
A.M. on the following day. The movement of the bead magnified 20 times,
here reduced to one-half of original scale.
Fig. 29. Cucurbita ovifera: circumnutation of straight and vertical
hypocotyl, with filament fastened transversely across its upper end, traced
in darkness on a horizontal glass, from 8.30 A.M. to 8.30 P.M. The
movement of the terminal bead originally magnified about 18 times, here
only 4½ times.
Hypocotyl.—A seed lying on damp sand was firmly fixed by two crossed
wires and by its own growing radicle. The cotyledons were still enclosed
within the seed-coats; and the short hypocotyl, between the summit of the
radicle and the cotyledons, was as yet only slightly arched. A filament (.85
of inch in length) was attached at an angle of 35° above the horizon to the
side of the arch adjoining the cotyledons. This part would ultimately form
the upper end of the hypocotyl, after it had grown straight and vertical. Had
the seed been properly planted, the hypocotyl at this stage of growth would
have been deeply buried beneath the surface. The course followed by the
bead of the filament is shown in Fig. 28. The chief lines of movement from
left to right in the figure were parallel to the plane of the two united
cotyledons and of the flattened seed; and this movement would aid in

dragging them out of the seed-coats, which are held down by a special
structure hereafter to be described. The movement at right angles to the
above lines was due to the arched hypocotyl becoming more arched as it
increased in height. The foregoing observations apply to the leg of the arch
next to the cotyledons, but the other leg adjoining the radicle likewise
circumnutated at an equally early age.
The movement of the same hypocotyl after it had become straight and
vertical, but with the cotyledons only partially expanded, is shown in Fig.
29. The course pursued during 12 h. apparently represents four and a half
ellipses or ovals, with the longer axis of the first at nearly right angles to
that of the others. The longer axes of all were oblique to a line joining the
opposite cotyledons. The actual extreme distance from side to side over
which the summit of the tall hypocotyl passed in the course of 12 h. was .28
of an inch. The original figure was traced on a large scale, and from the
obliquity of the line of view the outer parts of the diagram are much
exaggerated.
Cotyledons.—On two occasions the movements of the cotyledons were
traced on a vertical glass, and as the ascending and descending lines did not
quite coincide, very narrow ellipses were formed; they therefore
circumnutated. Whilst young they rise vertically up at night, but their tips
always remain reflexed; on the following morning they sink down again.
With a seedling kept in complete darkness they moved in the same manner,
for they sank from 8.45 A.M. to 4.30 P.M.; they then began to rise and
remained close together until 10 P.M., when they were last observed. At 7
A.M. on the following morning they were as much expanded as at any hour
on the previous day. The cotyledons of another young seedling, exposed to
the light, were fully open for the first time on a certain day, but were found
completely closed at 7 A.M. on the following morning. They soon began to
expand again, and continued doing so till about 5 P.M.; they then began to
rise, and by 10.30 P.M. stood vertically and were almost closed. At 7 A.M.
on the third morning they were nearly vertical, and again expanded during
the day; on the fourth morning they were not closed, yet they opened a little
in the course of the day and rose a little on the following night. By this time
a minute true leaf had become developed. Another seedling, still older,
bearing a well-developed leaf, had a sharp rigid filament affixed to one of
its cotyledons (85 mm. in length), which recorded its own movements on a
revolving drum with smoked paper. The observations were made in the hot-

house, where the plant had lived, so that there was no change in temperature
or light. The record commenced at 11 A.M. on February 18th; and from this
hour till 3 P.M. the cotyledon fell; it then rose rapidly till 9 P.M., then very
gradually till 3 A.M. February 19th, after which hour it sank gradually till
4.30 P.M.; but the downward movement was interrupted by one slight rise
or oscillation about 1.30 P.M. After 4.30 P.M. (19th) the cotyledon rose till
1 A.M. (in the night of February 20th) and then sank very gradually till 9.30
A.M., when our observations ceased. The amount of movement was greater
on the 18th than on the 19th or on the morning of the 20th.
Cucurbita aurantia.—An arched hypocotyl was found buried a little
beneath the surface of the soil; and in order to prevent it straightening itself
quickly, when relieved from the surrounding pressure of the soil, the two
legs of the arch were tied together. The seed was then lightly covered with
loose damp earth. A filament with a bead at the end was affixed to the basal
leg, the movements of which were observed during two days in the usual
manner. On the first day the arch moved in a zigzag line towards the side of
the basal leg. On the next day, by which time the dependent cotyledons had
been dragged above the surface of the soil, the tied arch changed its course
greatly nine times in the course of 14½ h. It swept a large, extremely
irregular, circular figure, returning at night to nearly the same spot whence
it had started early in the morning. The line was so strongly zigzag that it
apparently represented five ellipses, with their longer axes pointing in
various directions. With respect to the periodical movements of the
cotyledons, those of several young seedlings formed together at 4 P.M. an
angle of about 60°, and at 10 P.M. their lower parts stood vertically and
were in contact; their tips, however, as is usual in the genus, were
permanently reflexed. These cotyledons, at 7 A.M. on the following
morning, were again well expanded.
Lagenaria vulgaris (var. miniature Bottle-gourd) (Cucurbitaceæ).—A
seedling opened its cotyledons, the movements of which were alone
observed, slightly on June 27th and closed them at night: next day, at noon
(28th), they included an angle of 53°, and at 10 P.M. they were in close
contact, so that each had risen 26½°. At noon, on the 29th, they included an
angle of 118°, and at 10 P.M. an angle of 54°, so each had risen 32°. On the
following day they were still more open, and the nocturnal rise was greater,
but the angles were not measured. Two other seedlings were observed, and
behaved during three days in a closely similar manner. The cotyledons,

therefore, open more and more on each succeeding day, and rise each night
about 30°; consequently during the first two nights of their life they stand
vertically and come into contact.
Fig. 30. Lagenaria vulgaris: circumnutation of a cotyledon, 1½ inch in
length, apex only 4 3/4 inches from the vertical glass, on which its
movements were traced from 7.35 A.M. July 11th to 9.5 A.M. on the 14th.
Figure here given reduced to one-third of original scale.
In order to ascertain more accurately the nature of these movements, the
hypocotyl of a seedling, with its cotyledons well expanded, was secured to
a little stick, and a filament with triangles of paper was affixed to one of the
cotyledons. The observations were made under a rather dim skylight, and
the temperature during the whole time was between 17½° to 18° C. (63° to
65° F.). Had the temperature been higher and the light brighter, the
movements would probably have been greater. On July 11th (see Fig. 30),
the cotyledon fell from 7.35 A.M. till 10 A.M.; it then rose (rapidly after 4
P.M.) till it stood quite vertically at 8.40 P.M. During the early morning of
the next day (12th) it fell, and continued to fall till 8 A.M., after which hour
it rose, then fell, and again rose, so that by 10.35 P.M. it stood much higher
than it did in the morning, but was not vertical as on the preceding night.
During the following early morning and whole day (13th) it fell and
circumnutated, but had not risen when observed late in the evening; and this
was probably due to the deficiency of heat or light, or of both. We thus see
that the cotyledons became more widely open at noon on each succeeding
day; and that they rose considerably each night, though not acquiring a
vertical position, except during the first two nights.
Cucumis dudaim (Cucurbitaceæ).—Two seedlings had opened their
cotyledons for the first time during the day,—one to the extent of 90° and
the other rather more; they remained in nearly the same position until 10.40
P.M.; but by 7 A.M. on the following morning the one which had been
previously open to the extent of 90° had its cotyledons vertical and
completely shut; the other seedling had them nearly shut. Later in the
morning they opened in the ordinary manner. It appears therefore that the
cotyledons of this plant close and open at somewhat different periods from
those of the foregoing species of the allied genera of Cucurbita and
Lagenaria.

Fig. 31. Opuntia basilaris: conjoint circumnutation of hypocotyl and
cotyledon; filament fixed longitudinally to cotyledon, and movement traced
during 66 h. on horizontal glass. Movement of the terminal bead magnified
about 30 times, here reduced to one-third scale. Seedling kept in hot-house,
feebly illuminated from above.
Opuntia basilaris (Cacteæ).—A seedling was carefully observed,
because, considering its appearance and the nature of the mature plant, it
seemed very unlikely that either the hypocotyl or cotyledons would
circumnutate to an appreciable extent. The cotyledons were well developed,
being .9 of an inch in length, .22 in breadth, and .15 in thickness. The
almost cylindrical hypocotyl, now bearing a minute spinous bud on its
summit, was only .45 of an inch in height, and .19 in diameter. The tracing
(Fig. 31) shows the combined movement of the hypocotyl and of one of the
cotyledons, from 4.45 P.M. on May 28th to 11 A.M. on the 31st. On the
29th a nearly perfect ellipse was completed. On the 30th the hypocotyl
moved, from some unknown cause, in the same general direction in a
zigzag line; but between 4.30 and 10 P.M. almost completed a second small
ellipse. The cotyledons move only a little up and down: thus at 10.15 P.M.
they stood only 10° higher than at noon. The chief seat of movement
therefore, at least when the cotyledons are rather old as in the present case,
lies in the hypocotyl. The ellipse described on the 29th had its longer axis
directed at nearly right angles to a line joining the two cotyledons. The
actual amount of movement of the bead at the end of the filament was, as
far as could be ascertained, about .14 of an inch.
Fig. 32. Helianthus annuus: circumnutation of hypocotyl, with filament
fixed across its summit, traced on a horizontal glass in darkness, from 8.45
A.M. to 10.45 P.M., and for an hour on following morning. Movement of
bead magnified 21 times, here reduced to one-half of original scale.
Helianthus annuus (Compositæ).—The upper part of the hypocotyl
moved during the day-time in the course shown in the annexed figure (Fig.
32). As the line runs in various directions, crossing itself several times, the
movement may be considered as one of circumnutation. The extreme actual
distance travelled was at least .1 of an inch. The movements of the
cotyledons of two seedlings were observed; one facing a north-east window,
and the other so feebly illuminated from above us as to be almost in
darkness. They continued to sink till about noon, when they began to rise;

but between 5 and 7 or 8 P.M. they either sank a little, or moved laterally,
and then again began to rise. At 7 A.M. on the following morning those on
the plant before the north-east window had opened so little that they stood
at an angle of 73° above the horizon, and were not observed any longer.
Those on the seedling which had been kept in almost complete darkness,
sank during the whole day, without rising about mid-day, but rose during
the night. On the third and fourth days they continued sinking without any
alternate ascending movement; and this, no doubt, was due to the absence
of light.
Primula Sinensis (Primulaceae).—A seedling was placed with the two
cotyledons parallel to a north-east window on a day when the light was
nearly uniform, and a filament was affixed to one of them. From
observations subsequently made on another seedling with the stem secured
to a stick, the greater part of the movement shown in the annexed figure
(Fig. 33), must have been that of the hypocotyl, though the cotyledons
certainly move up and down to a certain extent both during the day and
night. The movements of the same seedling were traced on the following
day with nearly the same result; and there can be no doubt about the
circumnutation of the hypocotyl.
Fig. 33. Primula Sinensis: conjoint circumnutation of hypocotyl and
cotyledon, traced on vertical glass, from 8.40 A.M. to 10.45 P.M.
Movements of bead magnified about 26 times.
Cyclamen Persicum (Primulaceae).—This plant is generally supposed to
produce only a single cotyledon, but Dr. H. Gressner[2] has shown that a
second one is developed after a long interval of time. The hypocotyl is
converted into a globular corm, even before the first cotyledon has broken
through the ground with its blade closely enfolded and with its petiole in the
form of an arch, like the arched hypocotyl or epicotyl of any ordinary
dicotyledonous plant. A glass filament was affixed to a cotyledon, .55 of an
inch in height, the petiole of which had straightened itself and stood nearly
vertical, but with the blade not as yet fully expanded. Its movements were
traced during 24½ h. on a horizontal glass, magnified 50 times; and in this
interval it described two irregular small circles; it therefore circumnutates,
though on an extremely small scale.
[2] ‘Bot. Zeitung,’ 1874, p. 837.

Fig. 34. Stapelia sarpedon: circumnutation of hypocotyl, illuminated
from above, traced on horizontal glass, from 6.45 A.M. June 26th to 8.45
A.M. 28th. Temp. 23–24° C. Movement of bead magnified 21 times.
Stapelia sarpedon (Asclepiadeae).—This plant, when mature, resembles a
cactus. The flattened hypocotyl is fleshy, enlarged in the upper part, and
bears two rudimentary cotyledons. It breaks through the ground in an
arched form, with the rudimentary cotyledons closed or in contact. A
filament was affixed almost vertically to the hypocotyl of a seedling half an
inch high; and its movements were traced during 50 h. on a horizontal glass
(Fig. 34). From some unknown cause it bowed itself to one side, and as this
was effected by a zigzag course, it probably circumnutated; but with hardly
any other seedling observed by us was this movement so obscurely shown.
Ipomœa caerulea vel Pharbitis nil (Convolvulaceae).—Seedlings of this
plant were observed because it is a twiner, the upper internodes of which
circumnutate conspicuously; but like other twining plants, the first few
internodes which rise above the ground are stiff enough to support
themselves, and therefore do not circumnutate in any plainly recognisable
manner.[3] In this particular instance the fifth internode (including the
hypocotyl) was the first which plainly circumnutated and twined round a
stick. We therefore wished to learn whether circumnutation could be
observed in the hypocotyl if carefully observed in our usual manner. Two
seedlings were kept in the dark with filaments fixed to the upper part of
their hypocotyls; but from circumstances not worth explaining their
movements were traced for only a short time. One moved thrice forwards
and twice backwards in nearly opposite directions, in the course of 3 h. 15
m.; and the other twice forwards and twice backwards in 2 h. 22 m. The
hypocotyl therefore circumnutated at a remarkably rapid rate. It may here
be added that a filament was affixed transversely to the summit of the
second internode above the cotyledons of a little plant 3½ inches in height;
and its movements were traced on a horizontal glass. It circumnutated, and
the actual distance travelled from side to side was a quarter of an inch,
which was too small an amount to be perceived without the aid of marks.
[3] ‘Movements and Habits of Climbing Plants,’ p. 33, 1875.

The movements of the cotyledons are interesting from their complexity
and rapidity, and in some other respects. The hypocotyl (2 inches high) of a
vigorous seedling was secured to a stick, and a filament with triangles of

paper was affixed to one of the cotyledons. The plant was kept all day in the
hot-house, and at 4.20 P.M. (June 20th) was placed under a skylight in the
house, and observed occasionally during the evening and night. It fell in a
slightly zigzag line to a moderate extent from 4.20 P.M. till 10.15 P.M.
When looked at shortly after midnight (12.30 P.M.) it had risen a very little,
and considerably by 3.45 A.M. When again looked at, at 6.10 A.M. (21st), it
had fallen largely. A new tracing was now begun (see Fig. 35), and soon
afterwards, at 6.42 A.M., the cotyledon had risen a little. During the
forenoon it was observed about every hour; but between 12.30 and 6 P.M.
every half-hour. If the observations had been made at these short intervals
during the whole day, the figure would have been too intricate to have been
copied. As it was, the cotyledon moved up and down in the course of 16 h.
20 m. (i.e. between 6.10 A.M. and 10.30 P.M.) thirteen times.
Fig. 35. Ipomœa caerulea: circumnutation of cotyledon, traced on vertical
glass, from 6.10 A.M. June 21st to 6.45 A.M. 22nd. Cotyledon with petiole
1.6 inch in length, apex of blade 4.1 inch from the vertical glass; so
movement not greatly magnified; temp. 20° C.
The cotyledons of this seedling sank downwards during both evenings
and the early part of the night, but rose during the latter part. As this is an
unusual movement, the cotyledons of twelve other seedlings were observed;
they stood almost or quite horizontally at mid-day, and at 10 P.M. were all
declined at various angles. The most usual angle was between 30° and 35°;
but three stood at about 50° and one at even 70° beneath the horizon. The
blades of all these cotyledons had attained almost their full size, viz. from 1
to 1½ inches in length, measured along their midribs. It is a remarkable fact
that whilst young—that is, when less than half an inch in length, measured
in the same manner—they do not sink downwards in the evening. Therefore
their weight, which is considerable when almost fully developed, probably
came into play in originally determining the downward movement. The
periodicity of this movement is much influenced by the degree of light to
which the seedlings have been exposed during the day; for three kept in an
obscure place began to sink about noon, instead of late in the evening; and
those of another seedling were almost paralysed by having been similarly
kept during two whole days. The cotyledons of several other species of
Ipomœa likewise sink downwards late in the evening.

Cerinthe major (Boragineae).—The circumnutation of the hypocotyl of a
young seedling with the cotyledons hardly expanded, is shown in the
annexed figure (Fig. 36), which apparently represents four or five irregular
ellipses, described in the course of a little over 12 hours. Two older
seedlings were similarly observed, excepting that one of them was kept in
the dark; their hypocotyls also circumnutated, but in a more simple manner.
The cotyledons on a seedling exposed to the light fell from the early
morning until a little after noon, and then continued to rise until 10.30 P.M.
or later. The cotyledons of this same seedling acted in the same general
manner during the two following days. It had previously been tried in the
dark, and after being thus kept for only 1 h. 40 m. the cotyledons began at
4.30 P.M. to sink, instead of continuing to rise till late at night.
Fig. 36. Cerinthe major: circumnutation of hypocotyl, with filament fixed
across its summit, illuminated from above, traced on horizontal glass, from
9.26 A.M. to 9.53 P.M. on Oct. 25th. Movement of the bead magnified 30
times, here reduced to one-third of original scale.
Nolana prostrata (Nolaneae).—The movements were not traced, but a pot
with seedlings, which had been kept in the dark for an hour, was placed
under the microscope, with the micrometer eye-piece so adjusted that each
division equalled 1/500th of an inch. The apex of one of the cotyledons
crossed rather obliquely four divisions in 13 minutes; it was also sinking, as
shown by getting out of focus. The seedlings were again placed in darkness
for another hour, and the apex now crossed two divisions in 6 m. 18 s.; that
is, at very nearly the same rate as before. After another interval of an hour
in darkness, it crossed two divisions in 4 m. 15 s., therefore at a quicker
rate. In the afternoon, after a longer interval in the dark, the apex was
motionless, but after a time it recommenced moving, though slowly;
perhaps the room was too cold. Judging from previous cases, there can
hardly be a doubt that this seedling was circumnutating.
Solanum lycopersicum (Solaneae).—The movements of the hypocotyls
of two seedling tomatoes were observed during seven hours, and there
could be no doubt that both circumnutated. They were illuminated from
above, but by an accident a little light entered on one side, and in the
accompanying figure (Fig. 37) it may be seen that the hypocotyl moved to
this side (the upper one in the figure), making small loops and zigzagging in
its course. The movements of the cotyledons were also traced both on

vertical and horizontal glasses; their angles with the horizon were likewise
measured at various hours. They fell from 8.30 A.M. (October 17th) to
about noon; then moved laterally in a zigzag line, and at about 4 P.M. began
to rise; they continued to do so until 10.30 P.M., by which hour they stood
vertically and were asleep. At what hour of the night or early morning they
began to fall was not ascertained. Owing to the lateral movement shortly
after mid-day, the descending and ascending lines did not coincide, and
irregular ellipses were described during each 24 h. The regular periodicity
of these movements is destroyed, as we shall hereafter see, if the seedlings
are kept in the dark.
Fig. 37. Solanum lycopersicum: circumnutation of hypocotyl, with
filament fixed across its summit, traced on horizontal glass, from 10 A.M.
to 5 P.M. Oct. 24th. Illuminated obliquely from above. Movement of bead
magnified about 35 times, here reduced to one-third of original scale.
Solanum palinacanthum.—Several arched hypocotyls rising nearly .2 of
an inch above the ground, but with the cotyledons still buried beneath the
surface, were observed, and the tracings showed that they circumnutated.
Moreover, in several cases little open circular spaces or cracks in the
argillaceous sand which surrounded the arched hypocotyls were visible, and
these appeared to have been made by the hypocotyls having bent first to one
and then to another side whilst growing upwards. In two instances the
vertical arches were observed to move to a considerable distance backwards
from the point where the cotyledons lay buried; this movement, which has
been noticed in some other cases, and which seems to aid in extracting the
cotyledons from the buried seed-coats, is due to the commencement of the
straightening of the hypocotyl. In order to prevent this latter movement, the
two legs of an arch, the summit of which was on a level with the surface of
the soil, were tied together; the earth having been previously removed to a
little depth all round. The movement of the arch during 47 hours under
these unnatural circumstances is exhibited in the annexed figure.
Fig. 38. Solanum palinacanthum: circumnutation of an arched hypocotyl,
just emerging from the ground, with the two legs tied together, traced in
darkness on a horizontal glass, from 9.20 A.M. Dec. 17th to 8.30 A.M. 19th.
Movement of bead magnified 13 times; but the filament, which was affixed
obliquely to the crown of the arch, was of unusual length.

The cotyledons of some seedlings in the hot-house were horizontal about
noon on December 13th; and at 10 P.M. had risen to an angle of 27° above
the horizon; at 7 A.M. on the following morning, before it was light, they
had risen to 59° above the horizon; in the afternoon of the same day they
were found again horizontal.
Beta vulgaris (Chenopodeae).—The seedlings are excessively sensitive
to light, so that although on the first day they were uncovered only during
two or three minutes at each observation, they all moved steadily towards
the side of the room whence the light proceeded, and the tracings consisted
only of slightly zigzag lines directed towards the light. On the next day the
plants were placed in a completely darkened room, and at each observation
were illuminated as much as possible from vertically above by a small wax
taper. The annexed figure (Fig. 39) shows the movement of the hypocotyl
during 9 h. under these circumstances. A second seedling was similarly
observed at the same time, and the tracing had the same peculiar character,
due to the hypocotyl often moving and returning in nearly parallel lines.
The movement of a third hypocotyl differed greatly.
Fig. 39. Beta vulgaris: circumnutation of hypocotyl, with filament fixed
obliquely across its summit, traced in darkness on horizontal glass, from
8.25 A.M. to 5.30 P.M. Nov. 4th. Movement of bead magnified 23 times,
here reduced to one-third of original scale.
We endeavoured to trace the movements of the cotyledons, and for this
purpose some seedlings were kept in the dark, but they moved in an
abnormal manner; they continued rising from 8.45 A.M. to 2 P.M., then
moved laterally, and from 3 to 6 P.M. descended; whereas cotyledons which
have been exposed all the day to the light rise in the evening so as to stand
vertically at night; but this statement applies only to young seedlings. For
instance, six seedlings in the greenhouse had their cotyledons partially open
for the first time on the morning of November 15th, and at 8.45 P.M. all
were completely closed, so that they might properly be said to be asleep.
Again, on the morning of November 27th, the cotyledons of four other
seedlings, which were surrounded by a collar of brown paper so that they
received light only from above, were open to the extent of 39°; at 10 P.M.
they were completely closed; next morning (November 28th) at 6.45 A.M.
whilst it was still dark, two of them were partially open and all opened in
the course of the morning; but at 10.20 P.M. all four (not to mention nine

others which had been open in the morning and six others on another
occasion) were again completely closed. On the morning of the 29th they
were open, but at night only one of the four was closed, and this only
partially; the three others had their cotyledons much more raised than
during the day. On the night of the 30th the cotyledons of the four were
only slightly raised.
Ricinus Borboniensis (Euphorbiaceae).—Seeds were purchased under the
above name—probably a variety of the common castor-oil plant. As soon as
an arched hypocotyl had risen clear above the ground, a filament was
attached to the upper leg bearing the cotyledons which were still buried
beneath the surface, and the movement of the bead was traced on a
horizontal glass during a period of 34 h. The lines traced were strongly
zigzag, and as the bead twice returned nearly parallel to its former course in
two different directions, there could be no doubt that the arched hypocotyl
circumnutated. At the close of the 34 h. the upper part began to rise and
straighten itself, dragging the cotyledons out of the ground, so that the
movements of the bead could no longer be traced on the glass.
Quercus (American sp.) (Cupuliferae).—Acorns of an American oak
which had germinated at Kew were planted in a pot in the greenhouse. This
transplantation checked their growth; but after a time one grew to a height
of five inches, measured to the tips of the small partially unfolded leaves on
the summit, and now looked vigorous. It consisted of six very thin
internodes of unequal lengths. Considering these circumstances and the
nature of the plant, we hardly expected that it would circumnutate; but the
annexed figure (Fig. 40) shows that it did so in a conspicuous manner,
changing its course many times and travelling in all directions during the 48
h. of observation. The figure seems to represent 5 or 6 irregular ovals or
ellipses. The actual amount of movement from side to side (excluding one
great bend to the left) was about .2 of an inch; but this was difficult to
estimate, as owing to the rapid growth of the stem, the attached filament
was much further from the mark beneath at the close than at the
commencement of the observations. It deserves notice that the pot was
placed in a north-east room within a deep box, the top of which was not at
first covered up, so that the inside facing the windows was a little more
illuminated than the opposite side; and during the first morning the stem
travelled to a greater distance in this direction (to the left in the figure) than
it did afterwards when the box was completely protected from light.

Fig. 40. Quercus (American sp.): circumnutation of young stem, traced
on horizontal glass, from 12.50 P.M. Feb. 22nd to 12.50 P.M. 24th.
Movement of bead greatly magnified at first, but slightly towards the close
of the observations—about 10 times on an average.
Quercus robur.—Observations were made only on the movements of the
radicles from germinating acorns, which were allowed to grow downwards
in the manner previously described, over plates of smoked glass, inclined at
angles between 65° and 69° to the horizon. In four cases the tracks left were
almost straight, but the tips had pressed sometimes with more and
sometimes with less force on the glass, as shown by the varying thickness
of the tracks and by little bridges of soot left across them. In the fifth case
the track was slightly serpentine, that is, the tip had moved a little from side
to side. In the sixth case (Fig. 41, A) it was plainly serpentine, and the tip
had pressed almost equably on the glass in its whole course. In the seventh
case (B) the tip had moved both laterally and had pressed alternately with
unequal force on the glass; so that it had moved a little in two planes at
right angles to one another. In the eighth and last case (C) it had moved
very little laterally, but had alternately left the glass and come into contact
with it again. There can be no doubt that in the last four cases the radicle of
the oak circumnutated whilst growing downwards.
Fig. 41. Quercus robur: tracks left on inclined smoked glass-plates by tips
of radicles in growing downwards. Plates A and C inclined at 65° and plate
B at 68° to the horizon.
Corylus avellana (Corylaceae).—The epicotyl breaks through the ground
in an arched form; but in the specimen which was first examined, the apex
had become decayed, and the epicotyl grew to some distance through the
soil, in a tortuous, almost horizontal direction, like a root. In consequence
of this injury it had emitted near the hypogean cotyledons two secondary
shoots, and it was remarkable that both of these were arched, like the
normal epicotyl in ordinary cases. The soil was removed from around one
of these arched secondary shoots, and a glass filament was affixed to the
basal leg. The whole was kept damp beneath a metal-box with a glass lid,
and was thus illuminated only from above. Owing apparently to the lateral
pressure of the earth being removed, the terminal and bowed-down part of
the shoot began at once to move upwards, so that after 24 h. it formed a
right angle with the lower part. This lower part, to which the filament was

attached, also straightened itself, and moved a little backwards from the
upper part. Consequently a long line was traced on the horizontal glass; and
this was in parts straight and in parts decidedly zigzag, indicating
circumnutation.
On the following day the other secondary shoot was observed; it was a
little more advanced in age, for the upper part, instead of depending
vertically downwards, stood at an angle of 45° above the horizon. The tip of
the shoot projected obliquely .4 of an inch above the ground, but by the
close of our observations, which lasted 47 h., it had grown, chiefly towards
its base, to a height of .85 of an inch. The filament was fixed transversely to
the basal and almost upright half of the shoot, close beneath the lowest
scale-like appendage. The circumnutating course pursued is shown in the
accompanying figure (Fig. 42). The actual distance traversed from side to
side was about .04 of an inch.
Fig. 42. Corylus avellana: circumnutation of a young shoot emitted from
the epicotyl, the apex of which had been injured, traced on a horizontal
glass, from 9 A.M. Feb. 2nd to 8 A.M. 4th. Movement of bead magnified
about 27 times.
Pinus pinaster (Coniferæ).—A young hypocotyl, with the tips of the
cotyledons still enclosed within the seed-coats, was at first only .35 of an
inch in height; but the upper part grew so rapidly that at the end of our
observations it was .6 in height, and by this time the filament was attached
some way down the little stem. From some unknown cause, the hypocotyl
moved far towards the left, but there could be no doubt (Fig. 43) that it
circumnutated. Another hypocotyl was similarly observed, and it likewise
moved in a strongly zigzag line to the same side. This lateral movement was
not caused by the attachment of the glass filaments, nor by the action of
light; for no light was allowed to enter when each observation was made,
except from vertically above.
Fig. 43. Pinus pinaster: circumnutation of hypocotyl, with filament fixed
across its summit, traced on horizontal glass, from 10 A.M. March 21st to 9
A.M. 23rd. Seedling kept in darkness. Movement of bead magnified about
35 times.
The hypocotyl of a seedling was secured to a little stick; it bore nine in
appearance distinct cotyledons, arranged in a circle. The movements of two
nearly opposite ones were observed. The tip of one was painted white, with

a mark placed below, and the figure described (Fig. 44, A) shows that it
made an irregular circle in the course of about 8 h. during the night it
travelled to a considerable distance in the direction indicated by the broken
line. A glass filament was attached longitudinally to the other cotyledon,
and this nearly completed (Fig, 44, B) an irregular circular figure in about
12 hours. During the night it also moved to a considerable distance, in the
direction indicated by the broken line. The cotyledons therefore
circumnutate independently of the movement of the hypocotyl. Although
they moved much during the night, they did not approach each other so as
to stand more vertically than during the day.
Fig. 44. Pinus pinaster: circumnutation of two opposite cotyledons,
traced on horizontal glass in darkness, from 8.45 A.M. to 8.35 P.M. Nov.
25th. Movement of tip in A magnified about 22 times, here reduced to one-
half of original scale.
Cycas pectinata (Cycadeæ).—The large seeds of this plant in germinating
first protrude a single leaf, which breaks through the ground with the petiole
bowed into an arch and with the leaflets involuted. A leaf in this condition,
which at the close of our observations was 2½ inches in height, had its
movements traced in a warm greenhouse by means of a glass filament
bearing paper triangles attached across its tip. The tracing (Fig. 45) shows
how large, complex, and rapid were the circumnutating movements. The
extreme distance from side to side which it passed over amounted to
between .6 and .7 of an inch.
Fig. 45. Cycas pectinata: circumnutation of young leaf whilst emerging
from the ground, feebly illuminated from above, traced on vertical glass,
from 5 P.M. May 28th to 11 A.M. 31st. Movement magnified 7 times, here
reduced to two-thirds of original scale.
Canna Warscewiczii (Cannaceae).—A seedling with the plumule
projecting one inch above the ground was observed, but not under fair
conditions, as it was brought out of the hot-house and kept in a room not
sufficiently warm. Nevertheless the tracing (Fig. 46) shows that it made two
or three incomplete irregular circles or ellipses in the course of 48 hours.
The plumule is straight; and this was the first instance observed by us of the
part that first breaks through the ground not being arched.
Fig. 46. Canna Warscewiczii: circumnutation of plumule with filament
affixed obliquely to outer sheath-like leaf, traced in darkness on horizontal

glass from 8.45 A.M. Nov. 9th to 8.10 A.M. 11th. Movement of bead
magnified 6 times.
Allium cepa (Liliaceae).—The narrow green leaf, which protrudes from
the seed of the common onion as a cotyledon,[4] breaks through the ground
in the form of an arch, in the same manner as the hypocotyl or epicotyl of a
dicotyledonous plant. Long after the arch has risen above the surface the
apex remains within the seed-coats, evidently absorbing the still abundant
contents. The summit or crown of the arch, when it first protrudes from the
seed and is still buried beneath the ground, is simply rounded; but before it
reaches the surface it is developed into a conical protuberance of a white
colour (owing to the absence of chlorophyll), whilst the adjoining parts are
green, with the epidermis apparently rather thicker and tougher than
elsewhere. We may therefore conclude that this conical protuberance is a
special adaptation for breaking through the ground,[5] and answers the same
end as the knife-like white crest on the summit of the straight cotyledon of
the Gramineæ. After a time the apex is drawn out of the empty seed-coats,
and rises up, forming a right angle, or more commonly a still larger angle
with the lower part, and occasionally the whole becomes nearly straight.
The conical protuberance, which originally formed the crown of the arch, is
now seated on one side, and appears like a joint or knee, which from
acquiring chlorophyll becomes green, and increases in size. In rarely or
never becoming perfectly straight, these cotyledons differ remarkably from
the ultimate condition of the arched hypocotyls or epicotyls of dicotyledons.
It is, also, a singular circumstance that the attenuated extremity of the upper
bent portion invariably withers and dies.
[4] This is the expression used by Sachs in his ‘Text-book of Botany.’

[5] Haberlandt has briefly described (‘Die Schutzeinrichtungen...Keimpflanze,’
1877, p. 77) this curious structure and the purpose which it subserves. He states
that good figures of the cotyledon of the onion have been given by Tittmann and
by Sachs in his ‘Experimental Physiologie,’ p. 93.

A filament, 1.7 inch in length, was affixed nearly upright beneath the
knee to the basal and vertical portion of a cotyledon; and its movements
were traced during 14 h. in the usual manner. The tracing here given (Fig.
47) indicates circumnutation. The movement of the upper part above the
knee of the same cotyledon, which projected at about an angle of 45° above
the horizon, was observed at the same time. A filament was not affixed to it,

but a mark was placed beneath the apex, which was almost white from
beginning to wither, and its movements were thus traced. The figure
described resembled pretty closely that above given; and this shows that the
chief seat of movement is in the lower or basal part of the cotyledon.
Fig. 47. Allium cepa: circumnutation of basal half of arched cotyledon,
traced in darkness on horizontal glass, from 8.15 A.M. to 10 P.M. Oct. 31st.
Movement of bead magnified about 17 times.
Asparagus officinalis (Asparageae).—The tip of a straight plumule or
cotyledon (for we do not know which it should be called) was found at a
depth of .1 inch beneath the surface, and the earth was then removed all
round to the dept of .3 inch. a glass filament was affixed obliquely to it, and
the movement of the bead, magnified 17 times, was traced in darkness.
During the first 1 h. 15 m. the plumule moved to the right, and during the
next two hours it returned in a roughly parallel but strongly zigzag course.
From some unknown cause it had grown up through the soil in an inclined
direction, and now through apogeotropism it moved during nearly 24 h. in
the same general direction, but in a slightly zigzag manner, until it became
upright. On the following morning it changed its course completely. There
can therefore hardly be a doubt that the plumule circumnutates, whilst
buried beneath the ground, as much as the pressure of the surrounding earth
will permit. The surface of the soil in the pot was now covered with a thin
layer of very fine argillaceous sand, which was kept damp; and after the
tapering seedlings had grown a few tenths of an inch in height, each was
found surrounded by a little open space or circular crack; and this could be
accounted for only by their having circumnutated and thus pushed away the
sand on all sides; for there was no vestige of a crack in any other part.
In order to prove that there was circumnutation, the movements of five
seedlings, varying in height from .3 inch to 2 inches, were traced. They
were placed within a box and illuminated from above; but in all five cases
the longer axes of the figures described were directed to nearly the same
point; so that more light seemed to have come through the glass roof of the
greenhouse on one side than on any other. All five tracings resembled each
other to a certain extent, and it will suffice to give two of them. In A (Fig.
48) the seedling was only .45 of an inch in height, and consisted of a single
internode bearing a bud on its summit. The apex described between 8.30
A.M. and 10.20 P.M. (i.e. during nearly 14 hours) a figure which would

probably have consisted of 3½ ellipses, had not the stem been drawn to one
side until 1 P.M., after which hour it moved backwards. On the following
morning it was not far distant from the point whence it had first started. The
actual amount of movement of the apex from side to side was very small,
viz. about 1/18th of an inch. The seedling of which the movements are
shown in Fig. 48, B, was 1 3/4 inch in height, and consisted of three
internodes besides the bud on the summit. The figure, which was described
during 10 h., apparently represents two irregular and unequal ellipses or
circles. The actual amount of movement of the apex, in the line not
influenced by the light, was .11 of an inch, and in that thus influenced .37 of
an inch. With a seedling 2 inches in height it was obvious, even without the
aid of any tracing, that the uppermost part of the stem bent successively to
all points of the compass, like the stem of a twining plant. A little increase
in the power of circumnutating and in the flexibility of the stem, would
convert the common asparagus into a twining plant, as has occurred with
one species in this genus, namely, A. scandens.
Fig. 48. Asparagus officinalis: circumnutation of plumules with tips
whitened and marks placed beneath, traced on a horizontal glass. A, young
plumule; movement traced from 8.30 A.M. Nov. 30th to 7.15 A.M. next
morning; magnified about 35 times. B, older plumule; movement traced
from 10.15 A.M. to 8.10 P.M. Nov. 29th; magnified 9 times, but here
reduced to one-half of original scale.
Phalaris Canariensis (Gramineæ).—With the Gramineæ the part which
first rises above the ground has been called by some authors the pileole; and
various views have been expressed on its homological nature. It is
considered by some great authorities to be a cotyledon, which term we will
use without venturing to express any opinion on the subject.[6] It consists in
the present case of a slightly flattened reddish sheath, terminating upwards
in a sharp white edge; it encloses a true green leaf, which protrudes from
the sheath through a slit-like orifice, close beneath and at right angles to the
sharp edge on the summit. The sheath is not arched when it breaks through
the ground.
[6] We are indebted to the Rev. G. Henslow for an abstract of the views which
have been held on this subject, together with references.

The movements of three rather old seedlings, about 1½ inch in height,
shortly before the protrusion of the leaves, were first traced. They were

illuminated exclusively from above; for, as will hereafter be shown, they are
excessively sensitive to the action of light; and if any enters even
temporarily on one side, they merely bend to this side in slightly zigzag
lines. Of the three tracings one alone (Fig. 49) is here given. Had the
observations been more frequent during the 12 h. two oval figures would
have been described with their longer axes at right angles to one another.
The actual amount of movement of the apex from side to side was about .3
of an inch. The figures described by the other two seedlings resembled to a
certain extent the one here given.
Fig. 49. Phalaris Canariensis: circumnutation of a cotyledon, with a mark
placed below the apex, traced on a horizontal glass, from 8.35 A.M. Nov.
26th to 8.45 A.M. 27th. Movement of apex magnified 7 times, here reduced
to one-half scale.
A seedling which had just broken through the ground and projected only
1/20th of an inch above the surface, was next observed in the same manner
as before. It was necessary to clear away the earth all round the seedling to
a little depth in order to place a mark beneath the apex. The figure (Fig. 50)
shows that the apex moved to one side, but changed its course ten times in
the course of the ten hours of observation; so that there can be no doubt
about its circumnutation. The cause of the general movement in one
direction could hardly be attributed to the entrance of lateral light, as this
was carefully guarded against; and we suppose it was in some manner
connected with the removal of the earth round the little seedling.
Fig. 50. Phalaris Canariensis: circumnutation of a very young cotyledon,
with a mark placed below the apex, traced on a horizontal glass, from 11.37
A.M. to 9.30 P.M. Dec. 13th. Movement of apex greatly magnified, here
reduced to one-fourth of original scale.
Lastly, the soil in the same pot was searched with the aid of a lens, and
the white knife-like apex of a seedling was found on an exact level with that
of the surrounding surface. The soil was removed all round the apex to the
depth of a quarter of an inch, the seed itself remaining covered. The pot,
protected from lateral light, was placed under the microscope with a
micrometer eye-piece, so arranged that each division equalled 1/500th of an
inch. After an interval of 30 m. the apex was observed, and it was seen to
cross a little obliquely two divisions of the micrometer in 9 m. 15 s.; and
after a few minutes it crossed the same space in 8 m. 50s. The seedling was

again observed after an interval of three-quarters of an hour, and now the
apex crossed rather obliquely two divisions in 10 m. We may therefore
conclude that it was travelling at about the rate of 1/50th of an inch in 45
minutes. We may also conclude from these and the previous observations,
that the seedlings of Phalaris in breaking through the surface of the soil
circumnutate as much as the surrounding pressure will permit. This fact
accounts (as in the case before given of the asparagus) for a circular,
narrow, open space or crack being distinctly visible round several seedlings
which had risen through very fine argillaceous sand, kept uniformly damp.
Fig. 51. Zea mays: circumnutation of cotyledon, traced on horizontal
glass, from 8.30 A.M. Feb. 4th to 8 A.M. 6th. Movement of bead magnified
on an average about 25 times.
Zea mays (Gramineæ).—A glass filament was fixed obliquely to the
summit of a cotyledon, rising .2 of an inch above the ground; but by the
third morning it had grown to exactly thrice this height, so that the distance
of the bead from the mark below was greatly increased, consequently the
tracing (Fig. 51) was much more magnified on the first than on the second
day. The upper part of the cotyledon changed its course by at least as much
as a rectangle six times on each of the two days. The plant was illuminated
by an obscure light from vertically above. This was a necessary precaution,
as on the previous day we had traced the movements of cotyledons placed
in a deep box, the inner side of which was feebly illuminated on one side
from a distant north-east window, and at each observation by a wax taper
held for a minute or two on the same side; and the result was that the
cotyledons travelled all day long to this side, though making in their course
some conspicuous flexures, from which fact alone we might have
concluded that they were circumnutating; but we thought it advisable to
make the tracing above given.
Radicles.—Glass filaments were fixed to two short radicles, placed so as
to stand almost upright, and whilst bending downwards through geotropism
their courses were strongly zigzag; from this latter circumstance
circumnutation might have been inferred, had not their tips become slightly
withered after the first 24 h., though they were watered and the air kept very
damp. Nine radicles were next arranged in the manner formerly described,
so that in growing downwards they left tracks on smoked glass-plates,
inclined at various angles between 45° and 80° beneath the horizon. Almost

every one of these tracks offered evidence in their greater or less breadth in
different parts, or in little bridges of soot being left, that the apex had come
alternately into more and less close contact with the glass. In the
accompanying figure (Fig. 52) we have an accurate copy of one such track.
In two instances alone (and in these the plates were highly inclined) there
was some evidence of slight lateral movement. We presume therefore that
the friction of the apex on the smoked surface, little as this could have been,
sufficed to check the movement from side to side of these delicate radicles.
Fig. 52. Zea mays: track left on inclined smoked glass-plate by tip of
radicle in growing downwards.
Avena sativa (Gramineæ).—A cotyledon, 1½ inch in height, was placed
in front of a north-east window, and the movement of the apex was traced
on a horizontal glass during two days. It moved towards the light in a
slightly zigzag line from 9 to 11.30 A.M. on October 15th; it then moved a
little backwards and zigzagged much until 5 P.M., after which hour, and
curing the night, it continued to move towards the window. On the
following morning the same movement was continued in a nearly straight
line until 12.40 P.M., when the sky remained until 2.35 extraordinarily dark
from thunder-clouds. During this interval of 1 h. 55 m., whilst the light was
obscure, it was interesting to observe how circumnutation overcame
heliotropism, for the apex, instead of continuing to move towards the
window in a slightly zigzag line, reversed its course four times, making two
small narrow ellipses. A diagram of this case will be given in the chapter on
Heliotropism.
A filament was next fixed to a cotyledon only 1/4 of an inch in height,
which was illuminated exclusively from above, and as it was kept in a
warm greenhouse, it grew rapidly; and now there could be no doubt about
its circumnutation, for it described a figure of 8 as well as two small ellipses
in 5½ hours.
Nephrodium molle (Filices).—A seedling fern of this species came up by
chance in a flowerpot near its parent. The frond, as yet only slightly lobed,
was only .16 of an inch in length and .2 in breadth, and was supported on a
rachis as fine as a hair and .23 of an inch in height. A very thin glass
filament, which projected for a length of .36 of an inch, was fixed to the end
of the frond. The movement was so highly magnified that the figure (Fig.
53) cannot be fully trusted; but the frond was constantly moving in a

complex manner, and the bead greatly changed its course eighteen times in
the 12 hours of observation. Within half an hour it often returned in a line
almost parallel to its former course. The greatest amount of movement
occurred between 4 and 6 P.M. The circumnutation of this plant is
interesting, because the species in the genus Lygodium are well known to
circumnutate conspicuously and to twine round any neighbouring object.
Fig. 53. Nephrodium molle: circumnutation of very young frond, traced
in darkness on horizontal glass, from 9 A.M. to 9 P.M. Oct. 30th. Movement
of bead magnified 48 times.
Selaginella Kraussii (?) (Lycopodiaceæ).—A very young plant, only .4 of
an inch in height, had sprung up in a pot in the hot-house. An extremely fine
glass filament was fixed to the end of the frond-like stem, and the
movement of the bead traced on a horizontal glass. It changed its course
several times, as shown in Fig. 54, whilst observed during 13 h. 15 m., and
returned at night to a point not far distant from that whence it had started in
the morning. There can be no doubt that this little plant circumnutated.
Fig. 54. Selaginella Kraussii (?): circumnutation of young plant, kept in
darkness, traced from 8.45 A.M. to 10 P.M. Oct. 31st.

CHAPTER II.
GENERAL CONSIDERATIONS ON THE
MOVEMENTS AND GROWTH OF SEEDLING
PLANTS.

Generality of the circumnutating movement—Radicles, their
circumnutation of service—Manner in which they penetrate
the ground—Manner in which hypocotyls and other organs
break through the ground by being arched—Singular manner
of germination in Megarrhiza, etc.—Abortion of cotyledons
—Circumnutation of hypocotyls and epicotyls whilst still
buried and arched—Their power of straightening themselves
—Bursting of the seed-coats—Inherited effect of the arching
process in hypogean hypocotyls—Circumnutation of
hypocotyls and epicotyls when erect—Circumnutation of
cotyledons—Pulvini or joints of cotyledons, duration of
their activity, rudimentary in Oxalis corniculata, their
development—Sensitiveness of cotyledons to light and
consequent disturbance of their periodic movements—
Sensitiveness of cotyledons to contact.

The circumnutating movements of the several parts or organs of a
considerable number of seedling plants have been described in the last
chapter. A list is here appended of the Families, Cohorts, Sub-classes, etc.,
to which they belong, arranged and numbered according to the
classification adopted by Hooker.[1] Any one who will consider this list will
see that the young plants selected for observation, fairly represent the whole
vegetable series excepting the lowest cryptogams, and the movements of
some of the latter when mature will hereafter be described. As all the

seedlings which were observed, including Conifers, Cycads and Ferns,
which belong to the most ancient types amongst plants, were continually
circumnutating, we may infer that this kind of movement is common to
every seedling species.
[1] As given in the ‘General System of Botany,’ by Le Maout and Decaisne,
1873.

SUB-KINGDOM I.—Phaenogamous Plants.
Class I.—DICOTYLEDONS.
Sub-class I.—Angiosperms. Family. Cohort. 14. Cruciferae. II.
PARIETALES. 26. Caryophylleae. IV. CARYOPHYLLALES. 36.
Malvaceae. VI MALVALES. 41. Oxalideae. VII. GERANIALES. 49.
Tropaeoleae. DITTO 52. Aurantiaceae. DITTO 70. Hippocastaneae. X.
SAPINDALES. 75. Leguminosae. XI. ROSALES. 106. Cucurbitaceæ. XII.
PASSIFLORALES. 109. Cacteæ. XIV. FICOIDALES. 122. Compositæ.
XVII. ASTRALES. 135. Primulaceae. XX. PRIMULALES. 145.
Asclepiadeae. XXII. GENTIANALES. 151. Convolvulaceae. XXIII.
POLEMONIALES. 154. Boragineae. DITTO 156. Nolaneae. DITTO 157.
Solaneae. XXIV. SOLANALES. 181. Chenopodieae. XXVII.
CHENOPODIALES. 202. Euphorbiaceae. XXXII. EUPHORBIALES. 211.
Cupuliferae. XXXVI. QUERNALES. 212. Corylaceae. DITTO
Sub-class II.—Gymnosperms. 223. Coniferæ. 224. Cycadeæ.
Class II.—MONOCOTYLEDONS. 2. Cannaceae. II. AMOMALES. 34.
Liliaceae. XI. LILIALES. 41. Asparageae. DITTO 55. Gramineæ. XV.
GLUMALES.
SUB-KINGDOM II.—Cryptogamic Plants.
1. Filices. I. FILICALES. 6. Lycopodiaceæ. DITTO
Radicles.—In all the germinating seeds observed by us, the first change
is the protrusion of the radicle, which immediately bends downwards and
endeavours to penetrate the ground. In order to effect this, it is almost
necessary that the seed should be pressed down so as to offer some
resistance, unless indeed the soil is extremely loose; for otherwise the seed
is lifted up, instead of the radicle penetrating the surface. But seeds often
get covered by earth thrown up by burrowing quadrupeds or scratching
birds, by the castings of earth-worms, by heaps of excrement, the decaying
branches of trees, etc., and will thus be pressed down; and they must often

fall into cracks when the ground is dry, or into holes. Even with seeds lying
on the bare surface, the first developed root-hairs, by becoming attached to
stones or other objects on the surface, are able to hold down the upper part
of the radicle, whilst the tip penetrates the ground. Sachs has shown[2] how
well and closely root-hairs adapt themselves by growth to the most irregular
particles in the soil, and become firmly attached to them. This attachment
seems to be effected by the softening or liquefaction of the outer surface of
the wall of the hair and its subsequent consolidation, as will be on some
future occasion more fully described. This intimate union plays an
important part, according to Sachs, in the absorption of water and of the
inorganic matter dissolved in it. The mechanical aid afforded by the root-
hairs in penetrating the ground is probably only a secondary service.
[2] ‘Physiologie Végétale,’ 1868, pp. 199, 205.

The tip of the radicle, as soon as it protrudes from the seed-coats, begins
to circumnutate, and the whole growing part continues to do so, probably
for as long as growth continues. This movement of the radicle has been
described in Brassica, Æsculus, Phaseolus, Vicia, Cucurbita, Quercus and
Zea. The probability of its occurrence was inferred by Sachs,[3] from
radicles placed vertically upwards being acted on by geotropism (which we
likewise found to be the case), for if they had remained absolutely
perpendicular, the attraction of gravity could not have caused them to bend
to any one side. Circumnutation was observed in the above specified cases,
either by means of extremely fine filaments of glass affixed to the radicles
in the manner previously described, or by their being allowed to grow
downwards over inclined smoked glass-plates, on which they left their
tracks. In the latter cases the serpentine course (see Figs. 19, 21, 27, 41)
showed unequivocally that the apex had continually moved from side to
side. This lateral movement was small in extent, being in the case of
Phaseolus at most about 1 mm. from a medial line to both sides. But there
was also movement in a vertical plane at right angles to the inclined glass-
plates. This was shown by the tracks often being alternately a little broader
and narrower, due to the radicles having alternately pressed with greater and
less force on the plates. Occasionally little bridges of soot were left across
the tracks, showing that the apex had at these spots been lifted up. This
latter fact was especially apt to occur xwhen the radicle instead of travelling
straight down the glass made a semicircular bend; but Fig. 52 shows that

this may occur when the track is rectilinear. The apex by thus rising, was in
one instance able to surmount a bristle cemented across an inclined glass-
plate; but slips of wood only 1/40 of an inch in thickness always caused the
radicles to bend rectangularly to one side, so that the apex did not rise to
this small height in opposition to geotropism.
[3] ‘Ueber das Wachsthum der Wurzeln: Arbeiten des bot. Instituts in Würzburg,’
Heft iii. 1873, p. 460. This memoir, besides its intrinsic and great interest,
deserves to be studied as a model of careful investigation, and we shall have
occasion to refer to it repeatedly. Dr. Frank had previously remarked (‘Beiträge
zur Pflanzenphysiologie, 1868, p. 81) on the fact of radicles placed vertically
upwards being acted on by geotropism, and he explained it by the supposition
that their growth was not equal on all sides.

In those cases in which radicles with attached filaments were placed so as
to stand up almost vertically, they curved downwards through the action of
geotropism, circumnutating at the same time, and their courses were
consequently zigzag. Sometimes, however, they made great circular
sweeps, the lines being likewise zigzag.
Radicles closely surrounded by earth, even when this is thoroughly
soaked and softened, may perhaps be quite prevented from circumnutating.
Yet we should remember that the circumnutating sheath-like cotyledons of
Phalaris, the hypocotyls of Solanum, and the epicotyls of Asparagus formed
round themselves little circular cracks or furrows in a superficial layer of
damp argillaceous sand. They were also able, as well as the hypocotyls of
Brassica, to form straight furrows in damp sand, whilst circumnutating and
bending towards a lateral light. In a future chapter it will be shown that the
rocking or circumnutating movement of the flower-heads of Trifolium
subterraneum aids them in burying themselves. It is therefore probable that
the circumnutation of the tip of the radicle aids it slightly in penetrating the
ground; and it may be observed in several of the previously given diagrams,
that the movement is more strongly pronounced in radicles when they first
protrude from the seed than at a rather later period; but whether this is an
accidental or an adaptive coincidence we do not pretend to decide.
Nevertheless, when young radicles of Phaseolus multiflorus were fixed
vertically close over damp sand, in the expectation that as soon as they
reached it they would form circular furrows, this did not occur,—a fact
which may be accounted for, as we believe, by the furrow being filled up as
soon as formed by the rapid increase of thickness in the apex of the radicle.

Whether or not a radicle, when surrounded by softened earth, is aided in
forming a passage for itself by circumnutating, this movement can hardly
fail to be of high importance, by guiding the radicle along a line of least
resistance, as will be seen in the next chapter when we treat of the
sensibility of the tip to contact. If, however, a radicle in its downward
growth breaks obliquely into any crevice, or a hole left by a decayed root,
or one made by the larva of an insect, and more especially by worms, the
circumnutating movement of the tip will materially aid it in following such
open passage; and we have observed that roots commonly run down the old
burrows of worms.[4]
[4] See, also, Prof. Hensen’s statements (‘Zeitschrift für Wissen, Zool.,’ B.
xxviii. p. 354, 1877) to the same effect. He goes so far as to believe that roots are
able to penetrate the ground to a great depth only by means of the burrows made
by worms.

When a radicle is placed in a horizontal or inclined position, the terminal
growing part, as is well known, bends down towards the centre of the earth;
and Sachs[5] has shown that whilst thus bending, the growth of the lower
surface is greatly retarded, whilst that of the upper surface continues at the
normal rate, or may be even somewhat increased. He has further shown by
attaching a thread, running over a pulley, to a horizontal radicle of large
size, namely that of the common bean, that it was able to pull up a weight
of only one gramme, or 15.4 grains. We may therefore conclude that
geotropism does not give a radicle force sufficient to penetrate the ground,
but merely tells it (if such an expression may be used) which course to
pursue. Before we knew of Sachs’ more precise observations we covered a
flat surface of damp sand with the thinnest tin-foil which we could procure
(.02 to .03 mm., or .00012 to .00079 of an inch in thickness), and placed a
radicle close above, in such a position that it grew almost perpendicularly
downwards. When the apex came into contact with the polished level
surface it turned at right angles and glided over it without leaving any
impression; yet the tin-foil was so flexible, that a little stick of soft wood,
pointed to the same degree as the end of the radicle and gently loaded with
a weight of only a quarter of an ounce (120 grains) plainly indented the tin-
foil.
[5] ‘Arbeiten des bot. Inst. Würzburg,’ vol. i. 1873, p. 461. See also p. 397 for
the length of the growing part, and p. 451 on the force of geotropism.

Radicles are able to penetrate the ground by the force due to their
longitudinal and transverse growth; the seeds themselves being held down
by the weight of the superincumbent soil. In the case of the bean the apex,
protected by the root-cap, is sharp, and the growing part, from 8 to 10 mm.
in length, is much more rigid, as Sachs has proved, than the part
immediately above, which has ceased to increase in length. We
endeavoured to ascertain the downward pressure of the growing part, by
placing germinating beans between two small metal plates, the upper one of
which was loaded with a known weight; and the radicle was then allowed to
grow into a narrow hole in wood, 2 or 3 tenths of an inch in depth, and
closed at the bottom. The wood was so cut that the short space of radicle
between the mouth of the hole and the bean could not bend laterally on
three sides; but it was impossible to protect the fourth side, close to the
bean. Consequently, as long as the radicle continued to increase in length
and remained straight, the weighted bean would be lifted up after the tip
had reached the bottom of the shallow hole. Beans thus arranged,
surrounded by damp sand, lifted up a quarter of a pound in 24 h. after the
tip of the radicle had entered the hole. With a greater weight the radicles
themselves always became bent on the one unguarded side; but this
probably would not have occurred if they had been closely surrounded on
all sides by compact earth. There was, however, a possible, but not
probable, source of error in these trials, for it was not ascertained whether
the beans themselves go on swelling for several days after they have
germinated, and after having been treated in the manner in which ours had
been; namely, being first left for 24 h. in water, then allowed to germinate in
very damp air, afterwards placed over the hole and almost surrounded by
damp sand in a closed box.
Fig. 55. Outline of piece of stick (reduced to one-half natural size) with a
hole through which the radicle of a bean grew. Thickness of stick at narrow
end .08 inch, at broad end .16; depth of hole .1 inch.
We succeeded better in ascertaining the force exerted transversely by
these radicles. Two were so placed as to penetrate small holes made in little
sticks, one of which was cut into the shape here exactly copied (Fig. 55).
The short end of the stick beyond the hole was purposely split, but not the
opposite end. As the wood was highly elastic, the split or fissure closed
immediately after being made. After six days the stick and bean were dug
out of the damp sand, and the radicle was found to be much enlarged above

and beneath the hole. The fissure which was at first quite closed, was now
open to a width of 4 mm.; as soon as the radicle was extracted, it
immediately closed to a width of 2 mm. The stick was then suspended
horizontally by a fine wire passing through the hole lately filled by the
radicle, and a little saucer was suspended beneath to receive the weights;
and it required 8 lbs. 8 ozs. to open the fissure to the width of 4 mm.—that
is, the width before the root was extracted. But the part of the radicle (only
.1 of an inch in length) which was embedded in the hole, probably exerted a
greater transverse strain even than 8 lbs. 8 ozs., for it had split the solid
wood for a length of rather more than a quarter of an inch (exactly .275
inch), and this fissure is shown in Fig. 55. A second stick was tried in the
same manner with almost exactly the same result.
Fig. 56. Wooden pincers, kept closed by a spiral brass spring, with a hole
(.14 inch in diameter and .6 inch in depth) bored through the narrow closed
part, through which a radicle of a bean was allowed to grow. Temp. 50°–60°
F.
We then followed a better plan. Holes were bored near the narrow end of
two wooden clips or pincers (Fig. 56), kept closed by brass spiral springs.
Two radicles in damp sand were allowed to grow through these holes. The
pincers rested on glass-plates to lessen the friction from the sand. The holes
were a little larger (viz..14 inch) and considerably deeper (viz..6 inch) than
in the trials with the sticks; so that a greater length of a rather thicker radicle
exerted a transverse strain. After 13 days they were taken up. The distance
of two dots (see the figure) on the longer ends of the pincers was now
carefully measured; the radicles were then extracted from the holes, and the
pincers of course closed. They were then suspended horizontally in the
same manner as were the bits of sticks, and a weight of 1500 grams (or 3
pounds 4 ounces) was necessary with one of the pincers to open them to the
same extent as had been effected by the transverse growth of the radicle. As
soon as this radicle had slightly opened the pincers, it had grown into a
flattened form and had escaped a little beyond the hole; its diameter in one
direction being 4.2 mm., and at rightangles 3.5 mm. If this escape and
flattening could have been prevented, the radicle would probably have
exerted a greater strain than the 3 pounds 4 ounces. With the other pincers
the radicle escaped still further out of the hole; and the weight required to
open them to the same extent as had been effected by the radicle, was only
600 grams.

With these facts before us, there seems little difficulty in understanding
how a radicle penetrates the ground. The apex is pointed and is protected by
the root-cap; the terminal growing part is rigid, and increases in length with
a force equal, as far as our observations can be trusted, to the pressure of at
least a quarter of a pound, probably with a much greater force when
prevented from bending to any side by the surrounding earth. Whilst thus
increasing in length it increases in thickness, pushing away the damp earth
on all sides, with a force of above 8 pounds in one case, of 3 pounds in
another case. It was impossible to decide whether the actual apex exerts,
relatively to its diameter, the same transverse strain as the parts a little
higher up; but there seems no reason to doubt that this would be the case.
The growing part therefore does not act like a nail when hammered into a
board, but more like a wedge of wood, which whilst slowly driven into a
crevice continually expands at the same time by the absorption of water;
and a wedge thus acting will split even a mass of rock.
Manner in which Hypocotyls, Epicotyls, etc., rise up and break through
the ground.—After the radicle has penetrated the ground and fixed the seed,
the hypocotyls of all the dicotyledonous seedlings observed by us, which
lift their cotyledons above the surface, break through the ground in the form
of an arch. When the cotyledons are hypogean, that is, remain buried in the
soil, the hypocotyl is hardly developed, and the epicotyl or plumule rises in
like manner as an arch through the ground. In all, or at least in most of such
cases, the downwardly bent apex remains for a time enclosed within the
seed-coats. With Corylus avellena the cotyledons are hypogean, and the
epicotyl is arched; but in the particular case described in the last chapter its
apex had been injured, and it grew laterally through the soil like a root; and
in consequence of this it had emitted two secondary shoots, which likewise
broke through the ground as arches.
Cyclamen does not produce any distinct stem, and only a single
cotyledon appears at first;[6] its petiole breaks through the ground as an arch
(Fig. 57). Abronia has only a single fully developed cotyledon, but in this
case it is the hypocotyl which first emerges and is arched. Abronia
umbellata, however, presents this peculiarity, that the enfolded blade of the
one developed cotyledon (with the enclosed endosperm) whilst still beneath
the surface has its apex upturned and parallel to the descending leg of the
arched hypocotyl; but it is dragged out of the ground by the continued
growth of the hypocotyl, with the apex pointing downward. With Cycas

pectinata the cotyledons are hypogean, and a true leaf first breaks through
the ground with its petiole forming an arch.
[6] This is the conclusion arrived at by Dr. H. Gressner (‘Bot. Zeitung,’ 1874, p.
837), who maintains that what has been considered by other botanists as the first
true leaf is really the second cotyledon, which is greatly delayed in its
development.

Fig. 57. Cyclamen Persicum: seedling, figure enlarged: c, blade of
cotyledon, not yet expanded, with arched petiole beginning to straighten
itself; h, hypocotyl developed into a corm; r, secondary radicles.
Fig. 58. Acanthus mollis: seedling with the hypogean cotyledon on the
near side removed and the radicles cut off; a, blade of first leaf beginning to
expand, with petiole still partially arched; b, second and opposite leaf, as
yet very imperfectly developed; c, hypogean cotyledon on the opposite side.
In the genus Acanthus the cotyledons are likewise hypogean. In A.
mollis, a single leaf first breaks through the ground with its petiole arched,
and with the opposite leaf much less developed, short, straight, of a
yellowish colour, and with the petiole at first not half as thick as that of the
other. The undeveloped leaf is protected by standing beneath its arched
fellow; and it is an instrucive fact that it is not arched, as it has not to force
for itself a passage through the ground. In the accompanying sketch (Fig.
58) the petiole of the first leaf has already partially straightened itself, and
the blade is beginning to unfold. The small second leaf ultimately grows to
an equal size with the first, but this process is effected at very different rates
in different individuals: in one instance the second leaf did not appear fully
above the ground until six weeks after the first leaf. As the leaves in the
whole family of the Acanthaceae stand either opposite one another or in
whorls, and as these are of equal size, the great inequality between the first
two leaves is a singular fact. We can see how this inequality of development
and the arching of the petiole could have been gradually acquired, if they
were beneficial to the seedlings by favouring their emergence; for with A.
candelabrum, spinosus, and latifolius there was a great variability in the
inequality between the two first leaves and in the arching of their petioles.
In one seedling of A. candelabrum the first leaf was arched and nine times
as long as the second, which latter consisted of a mere little, yellowish-
white, straight, hairy style. In other seedlings the difference in length
between the two leaves was as 3 to 2, or as 4 to 3, or as only .76 to .62 inch.

In these latter cases the first and taller leaf was not properly arched. Lastly,
in another seedling there was not the least difference in size between the
two first leaves, and both of them had their petioles straight; their laminae
were enfolded and pressed against each other, forming a lance or wedge, by
which means they had broken through the ground. Therefore in different
individuals of this same species of Acanthus the first pair of leaves breaks
through the ground by two widely different methods; and if either had
proved decidedly advantageous or disadvantageous, one of them no doubt
would soon have prevailed.
Asa Gray has described[7] the peculiar manner of germination of three
widely different plants, in which the hypocotyl is hardly at all developed.
These were therefore observed by us in relation to our present subject.
[7] ‘Botanical Text-Book,’ 1879, p. 22.

Delphinium nudicaule.—The elongated petioles of the two cotyledons
are confluent (as are sometimes their blades at the base), and they break
through the ground as an arch. They thus resemble in a most deceptive
manner a hypocotyl. At first they are solid, but after a time become tubular;
and the basal part beneath the ground is enlarged into a hollow chamber,
within which the young leaves are developed without any prominent
plumule. Externally root-hairs are formed on the confluent petioles, either a
little above, or on a level with, the plumule. The first leaf at an early period
of its growth and whilst within the chamber is quite straight, but the petiole
soon becomes arched; and the swelling of this part (and probably of the
blade) splits open one side of the chamber, and the leaf then emerges. The
slit was found in one case to be 3.2 mm. in length, and it is seated on the
line of confluence of the two petioles. The leaf when it first escapes from
the chamber is buried beneath the ground, and now an upper part of the
petiole near the blade becomes arched in the usual manner. The second leaf
comes out of the slit either straight or somewhat arched, but afterwards the
upper part of the petiole,—certainly in some, and we believe in all cases,—
arches itself whilst forcing a passage through the soil.
Megarrhiza Californica.—The cotyledons of this Gourd never free
themselves from the seed-coats and are hypogean. Their petioles are
completely confluent, forming a tube which terminates downwards in a
little solid point, consisting of a minute radicle and hypocotyl, with the
likewise minute plumule enclosed within the base of the tube. This structure

was well exhibited in an abnormal specimen, in which one of the two
cotyledons failed to produce a petiole, whilst the other produced one
consisting of an open semicylinder ending in a sharp point, formed of the
parts just described. As soon as the confluent petioles protrude from the
seed they bend down, as they are strongly geotropic, and penetrate the
ground. The seed itself retains its original position, either on the surface or
buried at some depth, as the case may be. If, however, the point of the
confluent petioles meets with some obstacle in the soil, as appears to have
occurred with the seedlings described and figured by Asa Gray,[8] the
cotyledons are lifted up above the ground. The petioles are clothed with
root-hairs like those on a true radicle, and they likewise resemble radicles in
becoming brown when immersed in a solution of permanganate of
potassium. Our seeds were subjected to a high temperature, and in the
course of three or four days the petioles penetrated the soil perpendicularly
to a depth of from 2 to 2½ inches; and not until then did the true radicle
begin to grow. In one specimen which was closely observed, the petioles in
7 days after their first protrusion attained a length of 2½ inches, and the
radicle by this time had also become well developed. The plumule, still
enclosed within the tube, was now .3 inch in length, and was quite straight;
but from having increased in thickness it had just begun to split open the
lower part of the petioles on one side, along the line of their confluence. By
the following morning the upper part of the plumule had arched itself into a
right angle, and the convex side or elbow had thus been forced out through
the slit. Here then the arching of the plumule plays the same part as in the
case of the petioles of the Delphinium. As the plumule continued to grow,
the tip became more arched, and in the course of six days it emerged
through the 2½ inches of superincumbent soil, still retaining its arched
form. After reaching the surface it straightened itself in the usual manner. In
the accompanying figure (Fig. 58, A) we have a sketch of a seedling in this
advanced state of development; the surface of the ground being represented
by the line G...........G.
[8] ‘American Journal of Science,’ vol. xiv. 1877, p. 21.

Fig. 58, A. Megarrhiza Californica: sketch of seedling, copied from Asa
Gray, reduced to one-half scale: c, cotyledons within seed-coats; p, the two
confluent petioles; h and r, hypocotyl and radicle; p1, plumule; G..........G,
surface of soil.

The germination of the seeds in their native Californian home proceeds in
a rather different manner, as we infer from an interesting letter from Mr.
Rattan, sent to us by Prof. Asa Gray. The petioles protrude from the seeds
soon after the autumnal rains, and penetrate the ground, generally in a
vertical direction, to a depth of from 4 to even 6 inches. they were found in
this state by Mr. Rattan during the Christmas vacation, with the plumules
still enclosed within the tubes; and he remarks that if the plumules had been
at once developed and had reached the surface (as occurred with our seeds
which were exposed to a high temperature), they would surely have been
killed by the frost. As it is, they lie dormant at some depth beneath the
surface, and are thus protected from the cold; and the root-hairs on the
petioles would supply them with sufficient moisture. We shall hereafter see
that many seedlings are protected from frost, but by a widely different
process, namely, by being drawn beneath the surface by the contraction of
their radicles. We may, however, believe that the extraordinary manner of
germination of Megarrhiza has another and secondary advantage. The
radicle begins in a few weeks to enlarge into a little tuber, which then
abounds with starch and is only slightly bitter. It would therefore be very
liable to be devoured by animals, were it not protected by being buried
whilst young and tender, at a depth of some inches beneath the surface.
Ultimately it grows to a huge size.
Ipomœa leptophylla.—In most of the species of this genus the hypocotyl
is well developed, and breaks through the ground as an arch. But the seeds
of the present species in germinating behave like those of Megarrhiza,
excepting that the elongated petioles of the cotyledons are not confluent.
After they have protruded from the seed, they are united at their lower ends
with the undeveloped hypocotyl and undeveloped radicle, which together
form a point only about .1 inch in length. They are at first highly geotropic,
and penetrate the ground to a depth of rather above half an inch. The radicle
then begins to grow. On four occasions after the petioles had grown for a
short distance vertically downwards, they were placed in a horizontal
position in damp air in the dark, and in the course of 4 hours they again
became curved vertically downwards, having passed through 90° in this
time. But their sensitiveness to geotropism lasts for only 2 or 3 days; and
the terminal part alone, for a length of between .2 and .4 inch, is thus
sensitive. Although the petioles of our specimens did not penetrate the
ground to a greater depth than about ½ inch, yet they continued for some

time to grow rapidly, and finally attained the great length of about 3 inches.
The upper part is apogeotropic, and therefore grows vertically upwards,
excepting a short portion close to the blades, which at an early period bends
downwards and becomes arched, and thus breaks through the ground.
Afterwards this portion straightens itself, and the cotyledons then free
themselves from the seed-coats. Thus we here have in different parts of the
same organ widely different kinds of movement and of sensitiveness; for
the basal part is geotropic, the upper part apogeotropic, and a portion near
the blades temporarily and spontaneously arches itself. The plumule is not
developed for some little time; and as it rises between the bases of the
parallel and closely approximate petioles of the cotyledons, which in
breaking through the ground have formed an almost open passage, it does
not require to be arched and is consequently always straight. Whether the
plumule remains buried and dormant for a time in its native country, and is
thus protected from the cold of winter, we do not know. The radicle, like
that of the Megarrhiza, grows into a tuber-like mass, which ultimately
attains a great size. So it is with Ipomœa pandurata, the germination of
which, as Asa Gray informs us, resembles that of I. leptophylla.
The following case is interesting in connection with the root-like nature
of the petioles. The radicle of a seedling was cut off, as it was completely
decayed, and the two now separated cotyledons were planted. They emitted
roots from their bases, and continued green and healthy for two months.
The blades of both then withered, and on removing the earth the bases of
the petioles (instead of the radicle) were found enlarged into little tubers.
Whether these would have had the power of producing two independent
plants in the following summer, we do not know.
In Quercus virens, according to Dr. Engelmann,[9] both the cotyledons
and their petioles are confluent. The latter grow to a length “of an inch or
even more;” and, if we understand rightly, penetrate the ground, so that they
must be geotropic. The nutriment within the cotyledons is then quickly
transferred to the hypocotyl or radicle, which thus becomes developed into
a fusiform tuber. The fact of tubers being formed by the foregoing three
widely distinct plants, makes us believe that their protection from animals
at an early age and whilst tender, is one at least of the advantages gained by
the remarkable elongation of the petioles of the cotyledons, together with
their power of penetrating the ground like roots under the guidance of
geotropism.

[9] ‘Transact. St. Louis Acad. Science,’ vol. iv. p. 190.

The following cases may be here given, as they bear on our present
subject, though not relating to seedlings. The flower-stem of the parasitic
Lathraea squamaria, which is destitute of true leaves, breaks through the
ground as an arch;[10] so does the flower-stem of the parasitic and leafless
Monotropa hypopitys. With Helleborus niger, the flower-stems, which rise
up independently of the leaves, likewise break through the ground as
arches. This is also the case with the greatly elongated flower-stems, as well
as with the petioles of Epimedium pinnatum. So it is with the petioles of
Ranunculus ficaria, when they have to break through the ground, but when
they arise from the summit of the bulb above ground, they are from the first
quite straight; and this is a fact which deserves notice. The rachis of the
bracken fern (Pteris aquilina), and of some, probably many, other ferns,
likewise rises above ground under the form of an arch. No doubt other
analogous instances could be found by careful search. In all ordinary cases
of bulbs, rhizomes, root-stocks, etc., buried beneath the ground, the surface
is broken by a cone formed by the young imbricated leaves, the combined
growth of which gives them force sufficient for the purpose.
[10] The passage of the flower-stem of the Lathraea through the ground cannot
fail to be greatly facilitated by the extraordinary quantity of water secreted at this
period of the year by the subterranean scale-like leaves; not that there is any
reason to suppose that the secretion is a special adaptation for this purpose: it
probably follows from the great quantity of sap absorbed in the early spring by
the parasitic roots. After a long period without any rain, the earth had become
light-coloured and very dry, but it was dark-coloured and damp, even in parts
quite wet, for a distance of at least six inches all round each flower-stem. The
water is secreted by glands (described by Cohn, ‘Bericht. Bot. Sect. der
Schlesischen Gesell.,’ 1876, p. 113) which line the longitudinal channels running
through each scale-like leaf. A large plant was dug up, washed so as to remove
the earth, left for some time to drain, and then placed in the evening on a dry
glass-plate, covered with a bell-glass, and by next morning it had secreted a large
pool of water. The plate was wiped dry, and in the course of the succeeding 7 or
8 hours another little pool was secreted, and after 16 additional hours several
large drops. A smaller plant was washed and placed in a large jar, which was left
inclined for an hour, by which time no more water drained off. The jar was then
placed upright and closed: after 23 hours two drachms of water were collected
from the bottom, and a little more after 25 additional hours. The flower-stems
were now cut off, for they do not secrete, and the subterranean part of the plant
was found to weigh 106.8 grams (1611 grains), and the water secreted during the
48 hours weighed 11.9 grams (183 grains),—that is, one-ninth of the whole
weight of the plant, excluding the flower-stems. We should remember that plants
in a state of nature would probably secrete in 48 hours much more than the

above large amount, for their roots would continue all the time absorbing sap
from the plant on which they were parasitic.

With germinating monocotyledonous seeds, of which, however, we did
not observe a large number, the plumules, for instance, those of Asparagus
and Canna, are straight whilst breaking through the ground. With the
Gramineæ, the sheath-like cotyledons are likewise straight; they, however,
terminate in a sharp crest, which is white and somewhat indurated; and this
structure obviously facilitates their emergence from the soil: the first true
leaves escape from the sheath through a slit beneath the chisel-like apex and
at right angles to it. In the case of the onion (Allium cepa) we again meet
with an arch; the leaf-like cotyledon being abruptly bowed, when it breaks
through the ground, with the apex still enclosed within the seed-coats. The
crown of the arch, as previously described, is developed into a white
conical protuberance, which we may safely believe to be a special
adaptation for this office.
The fact of so many organs of different kinds—hypocotyls and epicotyls,
the petioles of some cotyledons and of some first leaves, the cotyledons of
the onion, the rachis of some ferns, and some flower-stems—being all
arched whilst they break through the ground, shows how just are Dr.
Haberlandt’s[11] remarks on the importance of the arch to seedling plants. He
attributes its chief importance to the upper, young, and more tender parts of
the hypocotyl or epicotyl, being thus saved from abrasion and pressure
whilst breaking through the ground. But we think that some importance
may be attributed to the increased force gained by the hypocotyl, epicotyl,
or other organ by being at first arched; for both legs of the arch increase in
length, and both have points of resistance as long as the tip remains
enclosed within the seed-coats; and thus the crown of the arch is pushed up
through the earth with twice as much force as that which a straight
hypocotyl, etc., could exert. As soon, however, as the upper end has freed
itself, all the work has to be done by the basal leg. In the case of the
epicotyl of the common bean, the basal leg (the apex having freed itself
from the seed-coats) grew upwards with a force sufficient to lift a thin plate
of zinc, loaded with 12 ounces. Two more ounces were added, and the 14
ounces were lifted up to a very little height, and then the epicotyl yielded
and bent to one side.
[11] ‘Die Schutzeinrichtungen in der Entwickelung der Keimpflanze,’ 1877. We
have learned much from this interesting essay, though our observations lead us to

differ on some points from the author.

With respect to the primary cause of the arching process, we long thought
in the case of many seedlings that this might be attributed to the manner in
which the hypocotyl or epicotyl was packed and curved within the seed-
coats; and that the arched shape thus acquired was merely retained until the
parts in question reached the surface of the ground. But it is doubtful
whether this is the whole of the truth in any case. For instance, with the
common bean, the epicotyl or plumule is bowed into an arch whilst
breaking through the seed-coats, as shown in Fig. 59 (p. 92). The plumule
first protrudes as a solid knob (e in A), which after twenty-four hours’
growth is seen (e in B) to be the crown of an arch. Nevertheless, with
several beans which germinated in damp air, and had otherwise been treated
in an unnatural manner, little plumules were developed in the axils of the
petioles of both cotyledons, and these were as perfectly arched as the
normal plumule; yet they had not been subjected to any confinement or
pressure, for the seed-coats were completely ruptured, and they grew in the
open air. This proves that the plumule has an innate or spontaneous
tendency to arch itself.
In some other cases the hypocotyl or epicotyl protrudes from the seed at
first only slightly bowed; but the bowing afterwards increases
independently of any constraint. The arch is thus made narrow, with the two
legs, which are sometimes much elongated, parallel and close together, and
thus it becomes well fitted for breaking through the ground.
With many kinds of plants, the radicle, whilst still enclosed within the
seed and likewise after its first protrusion, lies in a straight line with the
future hypocotyl and with the longitudinal axis of the cotyledons. This is
the case with Cucurbita ovifera: nevertheless, in whatever position the seeds
were buried, the hypocotyl always came up arched in one particular
direction. Seeds were planted in friable peat at a depth of about an inch in a
vertical position, with the end from which the radicle protrudes downwards.
Therefore all the parts occupied the same relative positions which they
would ultimately hold after the seedlings had risen clear above the surface.
Notwithstanding this fact, the hypocotyl arched itself; and as the arch grew
upwards through the peat, the buried seeds were turned either upside down,
or were laid horizontally, being afterwards dragged above the ground.
Ultimately the hypocotyl straightened itself in the usual manner; and now

after all these movements the several parts occupied the same position
relatively to one another and to the centre of the earth, which they had done
when the seeds were first buried. But it may be argued in this and other
such cases that, as the hypocotyl grows up through the soil, the seed will
almost certainly be tilted to one side; and then from the resistance which it
must offer during its further elevation, the upper part of the hypocotyl will
be doubled down and thus become arched. This view seems the more
probable, because with Ranunculus ficaria only the petioles of the leaves
which forced a passage through the earth were arched; and not those which
arose from the summits of the bulbs above the ground. Nevertheless, this
explanation does not apply to the Cucurbita, for when germinating seeds
were suspended in damp air in various positions by pins passing through the
cotyledons, fixed to the inside of the lids of jars, in which case the
hypocotyls were not subjected to any friction or constraint, yet the upper
part became spontaneously arched. This fact, moreover, proves that it is not
the weight of the cotyledons which causes the arching. Seeds of Helianthus
annuus and of two species of Ipomœa (those of ‘I. bona nox’ being for the
genus large and heavy) were pinned in the same manner, and the hypocotyls
became spontaneously arched; the radicles, which had been vertically
dependent, assumed in consequence a horizontal position. In the case of
Ipomœa leptophylla it is the petioles of the cotyledons which become
arched whilst rising through the ground; and this occurred spontaneously
when the seeds were fixed to the lids of jars.
It may, however, be suggested with some degree of probability that the
arching was aboriginally caused by mechanical compulsion, owing to the
confinement of the parts in question within the seed-coats, or to friction
whilst they were being dragged upwards. But if this is so, we must admit
from the cases just given, that a tendency in the upper part of the several
specified organs to bend downwards and thus to become arched, has now
become with many plants firmly inherited. The arching, to whatever cause
it may be due, is the result of modified circumnutation, through increased
growth along the convex side of the part; such growth being only
temporary, for the part always straightens itself subsequently by increased
growth along the concave side, as will hereafter be described.
It is a curious fact that the hypocotyls of some plants, which are but little
developed and which never raise their cotyledons above the ground,
nevertheless inherit a slight tendency to arch themselves, although this

movement is not of the least use to them. We refer to a movement observed
by Sachs in the hypocotyls of the bean and some other Leguminosae, and
which is shown in the accompanying figure (Fig. 59), copied from his
Essay.[12] The hypocotyl and radicle at first grow perpendicularly
downwards, as at A, and then bend, often in the course of 24 hours, into the
position shown at B. As we shall hereafter often have to recur to this
movement, we will, for brevity sake, call it “Sachs’ curvature.” At first sight
it might be thought that the altered position of the radicle in B was wholly
due to the outgrowth of the epicotyl (e), the petiole (p) serving as a hinge;
and it is probable that this is partly the cause; but the hypocotyl and upper
part of the radicle themselves become slightly curved.
[12] ‘Arbeiten des bot. Instit. Würzburg,’ vol. i. 1873, p. 403.

The above movement in the bean was repeatedly seen by us; but our
observations were made chiefly on Phaseolus multiflorus, the cotyledons of
which are likewise hypogean. Some seedlings with well-developed radicles
were first immersed in a solution of permanganate of potassium; and,
judging from the changes of colour (though these were not very clearly
defined), the hypocotyl is about .3 inch in length. Straight, thin, black lines
of this length were now drawn from the bases of the short petioles along the
hypocotyls of 23 germinating seeds, which were pinned to the lids of jars,
generally with the hilum downwards, and with their radicles pointing to the
centre of the earth. After an interval of from 24 to 48 hours the black lines
on the hypocotyls of 16 out of the 23 seedlings became distinctly curved,
but in very various degrees (namely, with radii between 20 and 80 mm. on
Sachs’ cyclometer) in the same relative direction as shown at B in Fig. 59.
As geotropism will obviously tend to check this curvature, seven seeds
were allowed to germinate with proper precautions for their growth in a
klinostat,[13] by which means geotropism was eliminated. The position of the
hypocotyls was observed during four successive days, and they continued to
bend towards the hilum and lower surface of the seed. On the fourth day
they were deflected by an average angle of 63° from a line perpendicular to
the lower surface, and were therefore considerably more curved than the
hypocotyl and radicle in the bean at B (Fig. 59), though in the same relative
direction.
[13] An instrument devised by Sachs, consisting essentially of a slowly revolving
horizontal axis, on which the plant under observation is supported: see

‘Würzburg Arbeiten,’ 1879, p. 209.

Fig. 59. Vicia faba: germinating seeds, suspended in damp air: A, with
radicle growing perpendicularly downwards; B, the same bean after 24
hours and after the radicle has curved itself; r. radicle; h, short hypocotyl; e,
epicotyl appearing as a knob in A and as an arch in B; p, petiole of the
cotyledon, the latter enclosed within the seed-coats.
It will, we presume, be admitted that all leguminous plants with
hypogean cotyledons are descended from forms which once raised their
cotyledons above the ground in the ordinary manner; and in doing so, it is
certain that their hypocotyls would have been abruptly arched, as in the case
of every other dicotyledonous plant. This is especially clear in the case of
Phaseolus, for out of five species, the seedlings of which we observed,
namely, P. multiflorus, caracalla, vulgaris, Hernandesii and Roxburghii
(inhabitants of the Old and New Worlds), the three last-named species have
well-developed hypocotyls which break through the ground as arches. Now,
if we imagine a seedling of the common bean or of P. multiflorus, to behave
as its progenitors once did, the hypocotyl (h, Fig. 59), in whatever position
the seed may have been buried, would become so much arched that the
upper part would be doubled down parallel to the lower part; and this is
exactly the kind of curvature which actually occurs in these two plants,
though to a much less degree. Therefore we can hardly doubt that their short
hypocotyls have retained by inheritance a tendency to curve themselves in
the same manner as they did at a former period, when this movement was
highly important to them for breaking through the ground, though now
rendered useless by the cotyledons being hypogean. Rudimentary structures
are in most cases highly variable, and we might expect that rudimentary or
obsolete actions would be equally so; and Sachs’ curvature varies extremely
in amount, and sometimes altogether fails. This is the sole instance known
to us of the inheritance, though in a feeble degree, of movements which
have become superfluous from changes which the species has undergone.
Rudimentary Cotyledons.—A few remarks on this subject may be here
interpolated. It is well known that some dicotyledonous plants produce only
a single cotyledon; for instance, certain species of Ranunculus, Corydalis,
Chaerophyllum; and we will here endeavour to show that the loss of one or
both cotyledons is apparently due to a store of nutriment being laid up in
some other part, as in the hypocotyl or one of the two cotyledons, or one of

the secondary radicles. With the orange (Citrus aurantium) the cotyledons
are hypogean, and one is larger than the other, as may be seen in A (Fig.
60). In B the inequality is rather greater, and the stem has grown between
the points of insertion of the two petioles, so that they do not stand opposite
to one another; in another case the separation amounted to one-fifth of an
inch. The smaller cotyledon of one seedling was extremely thin, and not
half the length of the larger one, so that it was clearly becoming
rudimentary[14] In all these seedlings the hypocotyl was enlarged or swollen.
Fig. 60. Citrus aurantium: two young seedlings: c, larger cotyledon; c’,
smaller cotyledon; h, thickened hypocotyl; r, radicle. In A the epicotyl is
still arched, in B it has become erect.
Fig. 61. Abronia umbellata: seedling twice natural size: c cotyledon; c’,
rudimentary cotyledon; h, enlarged hypocotyl, with a heel or projection (h’)
at the lower end; r, radicle.
[14] In Pachira aquatica, as described by Mr. R. I. Lynch (‘Journal Linn. Soc.
Bot.’ vol. xvii. 1878, p. 147), one of the hypogean cotyledons is of immense size;
the other is small and soon falls off; the pair do not always stand opposite. In
another and very different water-plant, ‘Trapa natans’, one of the cotyledons,
filled with farinaceous matter, is much larger than the other, which is scarcely
visible, as is stated by Aug. de Candolle, ‘Physiologie Veg.’ tom. ii. p. 834, 1832.

With Abronia umbellata one of the cotyledons is quite rudimentary, as
may be seen (c’) in Fig. 61. In this specimen it consisted of a little green
flap, 1/84th inch in length, destitute of a petiole and covered with glands
like those on the fully developed cotyledon (c). At first it stood opposite to
the larger cotyledon; but as the petiole of the latter increased in length and
grew in the same line with the hypocotyl (h), the rudiment appeared in older
seedlings as if seated some way down the hypocotyl. With Abronia arenaria
there is a similar rudiment, which in one specimen was only 1/100th and in
another 1/60th inch in length; it ultimately appeared as if seated halfway
down the hypocotyl. In both these species the hypocotyl is so much
enlarged, especially at a very early age, that it might almost be called a
corm. The lower end forms a heel or projection, the use of which will
hereafter be described.
In Cyclamen Persicum the hypocotyl, even whilst still within the seed, is
enlarged into a regular corm,[15] and only a single cotyledon is at first
developed (see former Fig. 57). With Ranunculus ficaria two cotyledons are
never produced, and here one of the secondary radicles is developed at an

early age into a so-called bulb.[16] Again, certain species of Chaerophyllum
and Corydalis produce only a single cotyledon;[17] in the former the
hypocotyl, and in the latter the radicle is enlarged, according to Irmisch,
into a bulb.
[15] Dr. H. Gressner, ‘Bot. Zeitung,’ 1874, p. 824.

[16] Irmisch, ‘Beiträge zur Morphologie der Pflanzen,’ 1854, pp. 11, 12; ‘Bot.
Zeitung,’ 1874, p. 805.

[17] Delpino, ‘Rivista Botanica,’ 1877, p. 21. It is evident from Vaucher’s
account (‘Hist. Phys. des Plantes d’Europe,’ tom. i. 1841, p. 149) of the
germination of the seeds of several species of Corydalis, that the bulb or
tubercule begins to be formed at an extremely early age.

In the several foregoing cases one of the cotyledons is delayed in its
development, or reduced in size, or rendered rudimentary, or quite aborted;
but in other cases both cotyledons are represented by mere rudiments. With
Opuntia basilaris this is not the case, for both cotyledons are thick and
large, and the hypocotyl shows at first no signs of enlargement; but
afterwards, when the cotyledons have withered and disarticulated
themselves, it becomes thickened, and from its tapering form, together with
its smooth, tough, brown skin, appears, when ultimately drawn down to
some depth into the soil, like a root. On the other hand, with several other
Cacteæ, the hypocotyl is from the first much enlarged, and both cotyledons
are almost or quite rudimentary. Thus with Cereus Landbeckii two little
triangular projections, representing the cotyledons, are narrower than the
hypocotyl, which is pear-shaped, with the point downwards. In Rhipsalis
cassytha the cotyledons are represented by mere points on the enlarged
hypocotyl. In Echinocactus viridescens the hypocotyl is globular, with two
little prominences on its summit. In Pilocereus Houlletii the hypocotyl,
much swollen in the upper part, is merely notched on the summit; and each
side of the notch evidently represents a cotyledon. Stapelia sarpedon, a
member of the very distinct family of the Asclepiadeae, is fleshy like a
cactus; and here again the upper part of the flattened hypocotyl is much
thickened and bears two minute cotyledons, which, measured internally,
were only .15 inch in length, and in breadth not equal to one-fourth of the
diameter of the hypocotyl in its narrow axis; yet these minute cotyledons
are probably not quite useless, for when the hypocotyl breaks through the

ground in the form of an arch, they are closed or pressed against one
another, and thus protect the plumule. They afterwards open.
From the several cases now given, which refer to widely distinct plants,
we may infer that there is some close connection between the reduced size
of one or both cotyledons and the formation, by the enlargement of the
hypocotyl or of the radicle, of a so-called bulb. But it may be asked, did the
cotyledons first tend to abort, or did a bulb first begin to be formed? As all
dicotyledons naturally produce two well-developed cotyledons, whilst the
thickness of the hypocotyl and of the radicle differs much in different
plants, it seems probable that these latter organs first became from some
cause thickened—in several instances apparently in correlation with the
fleshy nature of the mature plant—so as to contain a store of nutriment
sufficient for the seedling, and then that one or both cotyledons, from being
superfluous, decreased in size. It is not surprising that one cotyledon alone
should sometimes have been thus affected, for with certain plants, for
instance the cabbage, the cotyledons are at first of unequal size, owing
apparently to the manner in which they are packed within the seed. It does
not, however, follow from the above connection, that whenever a bulb is
formed at an early age, one or both cotyledons will necessarily become
superfluous, and consequently more or less rudimentary. Finally, these cases
offer a good illustration of the principle of compensation or balancement of
growth, or, as Goethe expresses it, “in order to spend on one side, Nature is
forced to economise on the other side.”
Circumnutation and other movements of Hypocotyls and Epicotyls,
whilst still arched and buried beneath the ground, and whilst breaking
through it.—According to the position in which a seed may chance to have
been buried, the arched hypocotyl or epicotyl will begin to protrude in a
horizontal, a more or less inclined, or in a vertical plane. Except when
already standing vertically upwards, both legs of the arch are acted on from
the earliest period by apogeotropism. Consequently they both bend upwards
until the arch becomes vertical. During the whole of this process, even
before the arch has broken through the ground, it is continually trying to
circumnutate to a slight extent; as it likewise does if it happens at first to
stand vertically up,—all which cases have been observed and described,
more or less fully, in the last chapter. After the arch has grown to some
height upwards the basal part ceases to circumnutate, whilst the upper part
continues to do so.

That an arched hypocotyl or epicotyl, with the two legs fixed in the
ground, should be able to circumnutate, seemed to us, until we had read
Prof. Wiesner’s observations, an inexplicable fact. He has shown[18] in the
case of certain seedlings, whose tips are bent downwards (or which nutate),
that whilst the posterior side of the upper or dependent portion grows
quickest, the anterior and opposite side of the basal portion of the same
internode grows quickest; these two portions being separated by an
indifferent zone, where the growth is equal on all sides. There may be even
more than one indifferent zone in the same internode; and the opposite sides
of the parts above and below each such zone grow quickest. This peculiar
manner of growth is called by Wiesner “undulatory nutation.”
Circumnutation depends on one side of an organ growing quickest
(probably preceded by increased turgescence), and then another side,
generally almost the opposite one, growing quickest. Now if we look at an
arch like this [upside down U] and suppose the whole of one side—we will
say the whole convex side of both legs—to increase in length, this would
not cause the arch to bend to either side. But if the outer side or surface of
the left leg were to increase in length the arch would be pushed over to the
right, and this would be aided by the inner side of the right leg increasing in
length. If afterwards the process were reversed, the arch would be pushed
over to the opposite or left side, and so on alternately,—that is, it would
circumnutate. As an arched hypocotyl, with the two legs fixed in the
ground, certainly circumnutates, and as it consists of a single internode, we
may conclude that it grows in the manner described by Wiesner. It may be
added, that the crown of the arch does not grow, or grows very slowly, for it
does not increase much in breadth, whilst the arch itself increases greatly in
height.
[18] ‘Die undulirende Nutation der Internodien,’ Akad. der Wissench. (Vienna),
Jan. 17th, 1878. Also published separately, see p. 32.

The circumnutating movements of arched hypocotyls and epicotyls can
hardly fail to aid them in breaking through the ground, if this be damp and
soft; though no doubt their emergence depends mainly on the force exerted
by their longitudinal growth. Although the arch circumnutates only to a
slight extent and probably with little force, yet it is able to move the soil
near the surface, though it may not be able to do so at a moderate depth. A
pot with seeds of Solanum palinacanthum, the tall arched hypocotyls of

which had emerged and were growing rather slowly, was covered with fine
argillaceous sand kept damp, and this at first closely surrounded the bases
of the arches; but soon a narrow open crack was formed round each of
them, which could be accounted for only by their having pushed away the
sand on all sides; for no such cracks surrounded some little sticks and pins
which had been driven into the sand. It has already been stated that the
cotyledons of Phalaris and Avena, the plumules of Asparagus and the
hypocotyls of Brassica, were likewise able to displace the same kind of
sand, either whilst simply circumnutating or whilst bending towards a
lateral light.
As long as an arched hypocotyl or epicotyl remains buried beneath the
ground, the two legs cannot separate from one another, except to a slight
extent from the yielding of the soil; but as soon as the arch rises above the
ground, or at an earlier period if the pressure of the surrounding earth be
artificially removed, the arch immediately begins to straighten itself. This
no doubt is due to growth along the whole inner surface of both legs of the
arch; such growth being checked or prevented, as long as the two legs of the
arch are firmly pressed together. When the earth is removed all round an
arch and the two legs are tied together at their bases, the growth on the
under side of the crown causes it after a time to become much flatter and
broader than naturally occurs. The straightening process consists of a
modified form of circumnutation, for the lines described during this process
(as with the hypocotyl of Brassica, and the epicotyls of Vicia and Corylus)
were often plainly zigzag and sometimes looped. After hypocotyls or
epicotyls have emerged from the ground, they quickly become perfectly
straight. No trace is left of their former abrupt curvature, excepting in the
case of Allium cepa, in which the cotyledon rarely becomes quite straight,
owing to the protuberance developed on the crown of the arch.
The increased growth along the inner surface of the arch which renders it
straight, apparently begins in the basal leg or that which is united to the
radicle; for this leg, as we often observed, is first bowed backwards from
the other leg. This movement facilitates the withdrawal of the tip of the
epicotyl or of the cotyledons, as the case may be, from within the seed-coats
and from the ground. But the cotyledons often emerge from the ground still
tightly enclosed within the seed-coats, which apparently serve to protect
them. The seed-coats are afterwards ruptured and cast off by the swelling of

the closely conjoined cotyledons, and not by any movement or their
separation from one another.
Nevertheless, in some few cases, especially with the Cucurbitaceæ, the
seed-coats are ruptured by a curious contrivance, described by M. Flahault.
[19]
A heel or peg is developed on one side of the summit of the radicle or
base of the hypocotyl; and this holds down the lower half of the seed-coats
(the radicle being fixed into the ground) whilst the continued growth of the
arched hypocotyl forced upwards the upper half, and tears asunder the seed-
coats at one end, and the cotyledons are then easily withdrawn.
[19] ‘Bull. Soc. Bot. de France,’ tom. xxiv. 1877, p. 201.

The accompanying figure (Fig. 62) will render this description
intelligible. Forty-one seeds of Cucurbita ovifera were laid on friable peat
and were covered by a layer about an inch in thickness, not much pressed
down, so that the cotyledons in being dragged up were subjected to very
little friction, yet forty of them came up naked, the seed-coats being left
buried in the peat. This was certainly due to the action of the peg, for when
it was prevented from acting, the cotyledons, as we shall presently see, were
lifted up still enclosed in their seed-coats. They were, however, cast off in
the course of two or three days by the swelling of the cotyledons. Until this
occurs light is excluded, and the cotyledons cannot decompose carbonic
acid; but no one probably would have thought that the advantage thus
gained by a little earlier casting off of the seed-coats would be sufficient to
account for the development of the peg. Yet according to M. Flahault,
seedlings which have been prevented from casting their seed-coats whilst
beneath the ground, are inferior to those which have emerged with their
cotyledons naked and ready to act.
Fig. 62. Cucurbita ovifera: germinating seed, showing the heel or peg
projecting on one side from summit of radicle and holding down lower tip
of seed-coats, which have been partially ruptured by the growth of the
arched hypocotyl.
The peg is developed with extraordinary rapidity; for it could only just be
distinguished in two seedlings, having radicles .35 inch in length, but after
an interval of only 24 hours was well developed in both. It is formed,
according to Flahault, by the enlargement of the layers of the cortical
parenchyma at the base of the hypocotyl. If, however, we judge by the

effects of a solution of permanganate of potassium, it is developed on the
exact line of junction between the hypocotyl and radicle; for the flat lower
surface, as well as the edges, were coloured brown like the radicle; whilst
the upper slightly inclined surface was left uncoloured like the hypocotyl,
excepting indeed in one out of 33 immersed seedlings in which a large part
of the upper surface was coloured brown. Secondary roots sometimes
spring from the lower surface of the peg, which thus seems in all respects to
partake of the nature of the radicle. The peg is always developed on the side
which becomes concave by the arching of the hypocotyl; and it would be of
no service if it were formed on any other side. It is also always developed
with the flat lower side, which, as just stated, forms a part of the radicle, at
right angles to it, and in a horizontal plane. This fact was clearly shown by
burying some of the thin flat seeds in the same position as in Fig. 62,
excepting that they were not laid on their flat broad sides, but with one edge
downwards. Nine seeds were thus planted, and the peg was developed in
the same position, relatively to the radicle, as in the figure; consequently it
did not rest on the flat tip of the lower half of the seed-coats, but was
inserted like a wedge between the two tips. As the arched hypocotyl grew
upwards it tended to draw up the whole seed, and the peg necessarily
rubbed against both tips, but did not hold either down. The result was, that
the cotyledons of five out of the nine seeds thus placed were raised above
the ground still enclosed within their seed-coats. Four seeds were buried
with the end from which the radicle protrudes pointing vertically
downwards, and owing to the peg being always developed in the same
position, its apex alone came into contact with, and rubbed against the tip
on one side; the result was, that the cotyledons of all four emerged still
within their seed-coats. These cases show us how the peg acts in co-
ordination with the position which the flat, thin, broad seeds would almost
always occupy when naturally sown. When the tip of the lower half of the
seed-coats was cut off, Flahault found (as we did likewise) that the peg
could not act, since it had nothing to press on, and the cotyledons were
raised above the ground with their seed-coats not cast off. Lastly, nature
shows us the use of the peg; for in the one Cucurbitaceous genus known to
us, in which the cotyledons are hypogean and do not cast their seed-coats,
namely, Megarrhiza, there is no vestige of a peg. This structure seems to be
present in most of the other genera in the family, judging from Flahault’s
statements’ we found it well-developed and properly acting in

Trichosanthes anguina, in which we hardly expected to find it, as the
cotyledons are somewhat thick and fleshy. Few cases can be advanced of a
structure better adapted for a special purpose than the present one.
With Mimosa pudica the radicle protrudes from a small hole in the sharp
edge of the seed; and on its summit, where united with the hypocotyl, a
transverse ridge is developed at an early age, which clearly aids in splitting
the tough seed-coats; but it does not aid in casting them off, as this is
subsequently effected by the swelling of the cotyledons after they have been
raised above the ground. The ridge or heel therefore acts rather differently
from that of Cucurbita. Its lower surface and the edges were coloured
brown by the permanganate of potassium, but not the upper surface. It is a
singular fact that after the ridge has done its work and has escaped from the
seed-coats, it is developed into a frill all round the summit of the radicle.[20]
[20] Our attention was called to this case by a brief statement by Nobbe in his
‘Handbuch der Samenkunde,’ 1876, p. 215, where a figure is also given of a
seedling of Martynia with a heel or ridge at the junction of the radicle and
hypocotyl. This seed possesses a very hard and tough coat, and would be likely
to require aid in bursting and freeing the cotyledons.

At the base of the enlarged hypocotyl of Abronia umbellata, where it
blends into the radicle, there is a projection or heel which varies in shape,
but its outline is too angular in our former figure (Fig. 61). The radicle first
protrudes from a small hole at one end of the tough, leathery, winged fruit.
At this period the upper part of the radicle is packed within the fruit parallel
to the hypocotyl, and the single cotyledon is doubled back parallel to the
latter. The swelling of these three parts, and especially the rapid
development of the thick heel between the hypocotyl and radicle at the
point where they are doubled, ruptures the tough fruit at the upper end and
allows the arched hypocotyl to emerge; and this seems to be the function of
the heel. A seed was cut out of the fruit and allowed to germinate in damp
air, and now a thin flat disc was developed all round the base of the
hypocotyl and grew to an extraordinary breadth, like the frill described
under Mimosa, but somewhat broader. Flahault says that with Mirabilis, a
member of the same family with Abronia, a heel or collar is developed all
round the base of the hypocotyl, but more on one side than on the other; and
that it frees the cotyledons from their seed-coats. We observed only old
seeds, and these were ruptured by the absorption of moisture, independently
of any aid from the heel and before the protrusion of the radicle; but it does

not follow from our experience that fresh and tough fruits would behave in
a like manner.

In concluding this section of the present chapter it may be convenient to
summarise, under the form of an illustration, the usual movements of the
hypocotyls and epicotyls of seedlings, whilst breaking through the ground
and immediately afterwards. We may suppose a man to be thrown down on
his hands and knees, and at the same time to one side, by a load of hay
falling on him. He would first endeavour to get his arched back upright,
wriggling at the same time in all directions to free himself a little from the
surrounding pressure; and this may represent the combined effects of
apogeotropism and circumnutation, when a seed is so buried that the arched
hypocotyl or epicotyl protrudes at first in a horizontal or inclined plane. The
man, still wriggling, would then raise his arched back as high as he could;
and this may represent the growth and continued circumnutation of an
arched hypocotyl or epicotyl, before it has reached the surface of the
ground. As soon as the man felt himself at all free, he would raise the upper
part of his body, whilst still on his knees and still wriggling; and this may
represent the bowing backwards of the basal leg of the arch, which in most
cases aids in the withdrawal of the cotyledons from the buried and ruptured
seed-coats, and the subsequent straightening of the whole hypocotyl or
epicotyl—circumnutation still continuing.
Circumnutation of Hypocotyls and Epicotyls, when erect.—The
hypocotyls, epicotyls, and first shoots of the many seedlings observed by
us, after they had become straight and erect, circumnutated continuously.
The diversified figures described by them, often during two successive
days, have been shown in the woodcuts in the last chapter. It should be
recollected that the dots were joined by straight lines, so that the figures are
angular; but if the observations had been made every few minutes the lines
would have been more or less curvilinear, and irregular ellipses or ovals, or
perhaps occasionally circles, would have been formed. The direction of the
longer axes of the ellipses made during the same day or on successive days
generally changed completely, so as to stand at right angles to one another.
The number of irregular ellipses or circles made within a given time differs
much with different species. Thus with Brassica oleracea, Cerinthe major,
and Cucurbita ovifera about four such figures were completed in 12 h.;

whereas with Solanum palinacanthum and Opuntia basilaris, scarcely more
than one. The figures likewise differ greatly in size; thus they were very
small and in some degree doubtful in Stapelia, and large in Brassica, etc.
The ellipses described by Lathyrus nissolia and Brassica were narrow,
whilst those made by the Oak were broad. The figures are often
complicated by small loops and zigzag lines.
As most seedling plants before the development of true leaves are of low,
sometimes very low stature, the extreme amount of movement from side to
side of their circumnutating stems was small; that of the hypocotyl of
Githago segetum was about .2 of an inch, and that of Cucurbita ovifera
about .28. A very young shoot of Lathyrus nissolia moved about .14, that of
an American oak .2, that of the common nut only .04, and a rather tall shoot
of the Asparagus .11 of an inch. The extreme amount of movement of the
sheath-like cotyledon of Phalaris Canariensis was .3 of an inch; but it did
not move very quickly, the tip crossing on one occasion five divisions of the
micrometer, that is, 1/100th of an inch, in 22 m. 5 s. A seedling Nolana
prostrata travelled the same distance in 10 m. 38 s. Seedling cabbages
circumnutate much more quickly, for the tip of a cotyledon crossed 1/100th
of an inch on the micrometer in 3 m. 20 s.; and this rapid movement,
accompanied by incessant oscillations, was a wonderful spectacle when
beheld under the microscope.
The absence of light, for at least a day, does not interfere in the least with
the circumnutation of the hypocotyls, epicotyls, or young shoots of the
various dicotyledonous seedlings observed by us; nor with that of the young
shoots of some monocotyledons. The circumnutation was indeed much
plainer in darkness than in light, for if the light was at all lateral the stem
bent towards it in a more or less zigzag course.
Finally, the hypocotyls of many seedlings are drawn during the winter
into the ground, or even beneath it so that they disappear. This remarkable
process, which apparently serves for their protection, has been fully
described by De Vries.[21] He shows that it is effected by the contraction of
the parenchyma-cells of the root. But the hypocotyl itself in some cases
contracts greatly, and although at first smooth becomes covered with zigzag
ridges, as we observed with Githago segetum. How much of the drawing
down and burying of the hypocotyl of Opuntia basilaris was due to the

contraction of this part and how much to that of the radicle, we did not
observe.
[21] ‘Bot. Zeitung,’ 1879, p. 649. See also Winkler in ‘Verhandl. des Bot. Vereins
der P. Brandenburg,’ Jahrg. xvi. p. 16, as quoted by Haberlandt,
‘Schutzeinrichungen der Keimpflanze,’ 1877, p. 52.

Circumnutation of Cotyledons.—With all the dicotyledonous seedlings
described in the last chapter, the cotyledons were in constant movement,
chiefly in a vertical plane, and commonly once up and once down in the
course of the 24 hours. But there were many exceptions to such simplicity
of movement; thus the cotyledons of Ipomœa caerulea moved 13 times
either upwards or downwards in the course of 16 h.. 18 m. Those of Oxalis
rosea moved in the same manner 7 times in the course of 24 h.; and those of
Cassia tora described 5 irregular ellipses in 9 h. The cotyledons of some
individuals of Mimosa pudica and of Lotus Jacobæus moved only once up
and down in 24 h., whilst those of others performed within the same period
an additional small oscillation. Thus with different species, and with
different individuals of the same species, there were many gradations from
a single diurnal movement to oscillations as complex as those of the
Ipomœa and Cassia. The opposite cotyledons on the same seedling move to
a certain extent independently of one another. This was conspicuous with
those of Oxalis sensitiva, in which one cotyledon might be seen during the
daytime rising up until it stood vertically, whilst the opposite one was
sinking down.
Although the movements of cotyledons were generally in nearly the same
vertical plane, yet their upward and downward courses never exactly
coincided; so that ellipses, more or less narrow, were described, and the
cotyledons may safely be said to have circumnutated. Nor could this fact be
accounted for by the mere increase in length of the cotyledons through
growth, for this by itself would not induce any lateral movement. That there
was lateral movement in some instances, as with the cotyledons of the
cabbage, was evident; for these, besides moving up and down, changed
their course from right to left 12 times in 14 h. 15 m. With Solanum
lycopersicum the cotyledons, after falling in the forenoon, zigzagged from
side to side between 12 and 4 P.M., and then commenced rising. The
cotyledons of Lupinus luteus are so thick (about .08 of an inch) and fleshy,
[22]
that they seemed little likely to move, and were therefore observed with

especial interest; they certainly moved largely up and down, and as the line
traced was zigzag there was some lateral movement. The nine cotyledons of
a seedling Pinus pinaster plainly circumnutated; and the figures described
approached more nearly to irregular circles than to irregular ovals or
ellipses. The sheath-like cotyledons of the Gramineæ circumnutate, that is,
move to all sides, as plainly as do the hypocotyls or epicotyls of any
dicotyledonous plants. Lastly, the very young fronds of a Fern and of a
Selaginella circumnutated.
[22] The cotyledons, though bright green, resemble to a certain extent hypogean
ones; see the interesting discussion by Haberlandt (‘Die Schutzeinrichtungen,’
etc., 1877, p. 95), on the gradations in the Leguminosae between subaërial and
subterranean cotyledons.

In a large majority of the cases which were carefully observed, the
cotyledons sink a little downwards in the forenoon, and rise a little in the
afternoon or evening. They thus stand rather more highly inclined during
the night than during the mid-day, at which time they are expanded almost
horizontally. The circumnutating movement is thus at least partially
periodic, no doubt in connection, as we shall hereafter see, with the daily
alternations of light and darkness. The cotyledons of several plants move up
so much at night as to stand nearly or quite vertically; and in this latter case
they come into close contact with one another. On the other hand, the
cotyledons of a few plants sink almost or quite vertically down at night; and
in this latter case they clasp the upper part of the hypocotyl. In the same
genus Oxalis the cotyledons of certain species stand vertically up, and those
of other species vertically down, at night. In all such cases the cotyledons
may be said to sleep, for they act in the same manner as do the leaves of
many sleeping plants. This is a movement for a special purpose, and will
therefore be considered in a future chapter devoted to this subject.
In order to gain some rude notion of the proportional number of cases in
which the cotyledons of dicotyledonous plants (hypogean ones being of
course excluded) changed their position in a conspicuous manner at night,
one or more species in several genera were cursorily observed, besides
those described in the last chapter. Altogether 153 genera, included in as
many families as could be procured, were thus observed by us. The
cotyledons were looked at in the middle of the day and again at night; and
those were noted as sleeping which stood either vertically or at an angle of
at least 60° above or beneath the horizon. Of such genera there were 26; and

in 21 of them the cotyledons of some of the species rose, and in only 6 sank
at night; and some of these latter cases are rather doubtful from causes to be
explained in the chapter on the sleep of cotyledons. When cotyledons which
at noon were nearly horizontal, stood at night at more than 20° and less than
60° above the horizon, they were recorded as “plainly raised;” and of such
genera there were 38. We did not meet with any distinct instances of
cotyledons periodically sinking only a few degrees at night, although no
doubt such occur. We have now accounted for 64 genera out of the 153, and
there remain 89 in which the cotyledons did not change their position at
night by as much as 20°—that is, in a conspicuous manner which could
easily be detected by the unaided eye and by memory; but it must not be
inferred from this statement that these cotyledons did not move at all, for in
several cases a rise of a few degrees was recorded, when they were
carefully observed. The number 89 might have been a little increased, for
the cotyledons remained almost horizontal at night in some species in a few
genera, for instance, Trifolium and Geranium, which are included amongst
the sleepers, such genera might therefore have been added to the 89. Again,
one species of Oxalis generally raised its cotyledons at night more than 20°
and less than 60° above the horizon; so that this genus might have been
included under two heads. But as several species in the same genus were
not often observed, such double entries have been avoided.
In a future chapter it will be shown that the leaves of many plants which
do not sleep, rise a few degrees in the evening and during the early part of
the night; and it will be convenient to defer until then the consideration of
the periodicity of the movements of cotyledons.
On the Pulvini or Joints of Cotyledons.—With several of the seedlings
described in this and the last chapter, the summit of the petiole is developed
into a pulvinus, cushion, or joint (as this organ has been variously called),
like that with which many leaves are provided. It consists of a mass of small
cells usually of a pale colour from the absence of chlorophyll, and with its
outline more or less convex, as shown in the annexed figure. In the case of
Oxalis sensitiva two-thirds of the petiole, and in that of Mimosa pudica,
apparently the whole of the short sub-petioles of the leaflets have been
converted into pulvini. With pulvinated leaves (i.e. those provided with a
pulvinus) their periodical movements depend, according to Pfeffer,[23] on the
cells of the pulvinus alternately expanding more quickly on one side than
on the other; whereas the similar movements of leaves not provided with

pulvini, depend on their growth being alternately more rapid on one side
than on the other.[24] As long as a leaf provided with a pulvinus is young and
continues to grow, its movement depends on both these causes combined;[25]
and if the view now held by many botanists be sound, namely, that growth
is always preceded by the expansion of the growing cells, then the
difference between the movements induced by the aid of pulvini and
without such aid, is reduced to the expansion of the cells not being followed
by growth in the first case, and being so followed in the second case.
[23] ‘Die Periodische Bewegungen der Blattorgane,’ 1875.

[24] Batalin, ‘Flora,’ Oct. 1st, 1873

[25] Pfeffer, ibid. p. 5.

Fig. 63. Oxalis rosea: longitudinal section of a pulvinus on the summit of
the petiole of a cotyledon, drawn with the camera lucida, magnified 75
times: p, p, petiole; f, fibro-vascular bundle: b, b, commencement of blade
of cotyledon.
Dots were made with Indian ink along the midrib of both pulvinated
cotyledons of a rather old seedling of Oxalis Valdiviana; their distances
were repeatedly measured with an eye-piece micrometer during 8 3/4 days,
and they did not exhibit the least trace of increase. It is therefore almost
certain that the pulvinus itself was not then growing. Nevertheless, during
this whole time and for ten days afterwards, these cotyledons rose vertically
every night. In the case of some seedlings raised from seeds purchased
under the name of Oxalis floribunda, the cotyledons continued for a long
time to move vertically down at night, and the movement apparently
depended exclusively on the pulvini, for their petioles were of nearly the
same length in young, and in old seedlings which had produced true leaves.
With some species of Cassia, on the other hand, it was obvious without any
measurement that the pulvinated cotyledons continued to increase greatly in
length during some weeks; so that here the expansion of the cells of the
pulvini and the growth of the petiole were probably combined in causing
their prolonged periodic movements. It was equally evident that the
cotyledons of many plants, not provided with pulvini, increased rapidly in
length; and their periodic movements no doubt were exclusively due to
growth.

In accordance with the view that the periodic movements of all
cotyledons depend primarily on the expansion of the cells, whether or not
followed by growth, we can understand the fact that there is but little
difference in the kind or form of movement in the two sets of cases. This
may be seen by comparing the diagrams given in the last chapter. Thus the
movements of the cotyledons of Brassica oleracea and of Ipomœa caerulea,
which are not provided with pulvini, are as complex as those of Oxalis and
Cassia which are thus provided. The pulvinated cotyledons of some
individuals of Mimosa pudica and Lotus Jacobæus made only a single
oscillation, whilst those of other individuals moved twice up and down in
the course of 24 hours; so it was occasionally with the cotyledons of
Cucurbita ovifera, which are destitute of a pulvinus. The movements of
pulvinated cotyledons are generally larger in extent than those without a
pulvinus; nevertheless some of the latter moved through an angle of 90°.
There is, however, one important difference in the two sets of cases; the
nocturnal movements of cotyledons without pulvini, for instance, those in
the Cruciferae, Cucurbitaceæ, Githago, and Beta, never last even for a
week, to any conspicuous degree. Pulvinated cotyledons, on the other hand,
continue to rise at night for a much longer period, even for more than a
month, as we shall now show. But the period no doubt depends largely on
the temperature to which the seedlings are exposed and their consequent
rate of development.

Oxalis Valdiviana.—Some cotyledons which had lately opened and were
horizontal on March 6th at noon, stood at night vertically up; on the 13th
the first true leaf was formed, and was embraced at night by the cotyledons;
on April 9th, after an interval of 35 days, six leaves were developed, and yet
the cotyledons rose almost vertically at night. The cotyledons of another
seedling, which when first observed had already produced a leaf, stood
vertically at night and continued to do so for 11 additional days. After 16
days from the first observation two leaves were developed, and the
cotyledons were still greatly raised at night. After 21 days the cotyledons
during the day were deflected beneath the horizon, but at night were raised
45° above it. After 24 days from the first observation (begun after a true leaf
had been developed) the cotyledons ceased to rise at night.

Oxalis (Biophytum) sensitiva.—The cotyledons of several seedlings, 45
days after their first expansion, stood nearly vertical at night, and closely
embraced either one or two true leaves which by this time had been formed.
These seedlings had been kept in a very warm house, and their development
had been rapid.
Oxalis corniculata.—The cotyledons do not stand vertical at night, but
generally rise to an angle of about 45° above the horizon. They continued
thus to act for 23 days after their first expansion, by which time two leaves
had been formed; even after 29 days they still rose moderately above their
horizontal or downwardly deflected diurnal position.
Mimosa pudica.—The cotyledons were expanded for the first time on
Nov. 2nd, and stood vertical at night. On the 15th the first leaf was formed,
and at night the cotyledons were vertical. On the 28th they behaved in the
same manner. On Dec. 15th, that is after 44 days, the cotyledons were still
considerably raised at night; but those of another seedling, only one day
older, were raised very little.
Mimosa albida.—A seedling was observed during only 12 days, by
which time a leaf had been formed, and the cotyledons were then quite
vertical at night.
Trifolium subterraneum.—A seedling, 8 days old, had its cotyledons
horizontal at 10.30 A.M. and vertical at 9.15 P.M. After an interval of two
months, by which time the first and second true leaves had been developed,
the cotyledons still performed the same movement. They had now increased
greatly in size, and had become oval; and their petioles were actually .8 of
an inch in length!
Trifolium strictum.—After 17 days the cotyledons still rose at night, but
were not afterwards observed.
Lotus Jacoboeus.—The cotyledons of some seedlings having well-
developed leaves rose to an angle of about 45° at night; and even after 3 or
4 whorls of leaves had been formed, the cotyledons rose at night
considerably above their diurnal horizontal position.
Cassia mimosoides.—The cotyledons of this Indian species, 14 days after
their first expansion, and when a leaf had been formed, stood during the day
horizontal, and at night vertical.

Cassia sp? (a large S. Brazilian tree raised from seeds sent us by F.
Müller).—The cotyledons, after 16 days from their first expansion, had
increased greatly in size with two leaves just formed. They stood
horizontally during the day and vertically at night, but were not afterwards
observed.
Cassia neglecta (likewise a S. Brazilian species).—A seedling, 34 days
after the first expansion of its cotyledons, was between 3 and 4 inches in
height, with 3 well-developed leaves; and the cotyledons, which during the
day were nearly horizontal, at night stood vertical, closely embracing the
young stem. The cotyledons of another seedling of the same age, 5 inches in
height, with 4 well-developed leaves, behaved at night in exactly the same
manner.

It is known[26] that there is no difference in structure between the upper
and lower halves of the pulvini of leaves, sufficient to account for their
upward or downward movements. In this respect cotyledons offer an
unusually good opportunity for comparing the structure of the two halves;
for the cotyledons of Oxalis Valdiviana rise vertically at night, whilst those
of O. rosea sink vertically; yet when sections of their pulvini were made, no
clear difference could be detected between the corresponding halves of this
organ in the two species which move so differently. With O. rosea, however,
there were rather more cells in the lower than in the upper half, but this was
likewise the case in one specimen of O. Valdiviana. the cotyledons of both
species (3½ mm. in length) were examined in the morning whilst extended
horizontally, and the upper surface of the pulvinus of O. rosea was then
wrinkled transversely, showing that it was in a state of compression, and
this might have been expected, as the cotyledons sink at night; with O.
Valdiviana it was the lower surface which was wrinkled, and its cotyledons
rise at night.
[26] Pfeffer, ‘Die Period. Bewegungen,’ 1875, p. 157.

Trifolium is a natural genus, and the leaves of all the species seen by us
are pulvinated; so it is with the cotyledons of T. subterraneum and strictum,
which stand vertically at night; whereas those of T. resupinatum exhibit not
a trace of a pulvinus, nor of any nocturnal movement. This was ascertained
by measuring the distance between the tips of the cotyledons of four

seedlings at mid-day and at night. In this species, however, as in the others,
the first-formed leaf, which is simple or not trifoliate, rises up and sleeps
like the terminal leaflet on a mature plant.
In another natural genus, Oxalis, the cotyledons of O. Valdiviana, rosea,
floribunda, articulata, and sensitiva are pulvinated, and all move at night
into an upward or downward vertical position. In these several species the
pulvinus is seated close to the blade of the cotyledon, as is the usual rule
with most plants. Oxalis corniculata (var. Atro-purpurea) differs in several
respects; the cotyledons rise at night to a very variable amount, rarely more
than 45°; and in one lot of seedlings (purchased under the name of O.
tropaeoloides, but certainly belonging to the above variety) they rose only
from 5° to 15° above the horizon. The pulvinus is developed imperfectly
and to an extremely variable degree, so that apparently it is tending towards
abortion. No such case has hitherto, we believe, been described. It is
coloured green from its cells containing chlorophyll; and it is seated nearly
in the middle of the petiole, instead of at the upper end as in all the other
species. The nocturnal movement is effected partly by its aid, and partly by
the growth of the upper part of the petiole as in the case of plants destitute
of a pulvinus. From these several reasons and from our having partially
traced the development of the pulvinus from an early age, the case seems
worth describing in some detail.
When the cotyledons of O. corniculata were dissected out of a seed from
which they would soon have naturally emerged, no trace of a pulvinus
could be detected; and all the cells forming the short petiole, 7 in number in
a longitudinal row, were of nearly equal size. In seedlings one or two days
old, the pulvinus was so indistinct that we thought at first that it did not
exist; but in the middle of the petiole an ill-defined transverse zone of cells
could be seen, which were much shorter than those both above and below,
although of the same breadth with them. They presented the appearance of
having been just formed by the transverse division of longer cells; and there
can be little doubt that this had occurred, for the cells in the petiole which
had been dissected out of the seed averaged in length 7 divisions of the
micrometer (each division equalling .003 mm.), and were a little longer
than those forming a well-developed pulvinus, which varied between 4 and
6 of these same divisions. After a few additional days the ill-defined zone of
cells becomes distinct, and although it does not extend across the whole
width of the petiole, and although the cells are of a green colour from

containing chlorophyll, yet they certainly constitute a pulvinus, which as we
shall presently see, acts as one. These small cells were arranged in
longitudinal rows, and varied from 4 to 7 in number; and the cells
themselves varied in length in different parts of the same pulvinus and in
different individuals. In the accompanying figures, A and B (Fig. 64), we
have views of the epidermis[27] in the middle part of the petioles of two
seedlings, in which the pulvinus was for this species well developed. They
offer a striking contrast with the pulvinus of O. rosea (see former Fig. 63),
or of O. Valdiviana. With the seedlings, falsely called O. tropaeoloides, the
cotyledons of which rise very little at night, the small cells were still fewer
in number and in parts formed a single transverse row, and in other parts
short longitudinal rows of only two or three. Nevertheless they sufficed to
attract the eye, when the whole petiole was viewed as a transparent object
beneath the microscope. In these seedlings there could hardly be a doubt
that the pulvinus was becoming rudimentary and tending to disappear; and
this accounts for its great variability in structure and function.
[27] Longitudinal sections show that the forms of the epidermic cells may be
taken as a fair representation of those constituting the pulvinus.

Fig. 64. Oxalis corniculata: A and B the almost rudimentary pulvini of
the cotyledons of two rather old seedlings, viewed as transparent objects.
Magnified 50 times.
In the following Table some measurements of the cells in fairly well-
developed pulvini of O. corniculata are given:—
Seedling 1 day old, with cotyledon 2.3 mm. in length. Divisions of
Micrometer.[28] Average length of cells of
pulvinus..................................................6 to 7 Length of longest cell below
the pulvinus..................................... 13 Length of longest cell above the
pulvinus...................................... 20
Seedling 5 days old, cotyledon 3.1 mm. in length, with the pulvinus quite
distinct. Average length of cells of pulvinus..................................................
6 Length of longest cell below the pulvinus..................................... 22
Length of longest cell above the pulvinus...................................... 40
Seedling 8 days old, cotyledon 5 mm. in length, with a true leaf formed
but not yet expanded. Average length of cells of
pulvinus.................................................. 9 Length of longest cell below the

pulvinus..................................... 44 Length of longest cell above the
pulvinus...................................... 70
Seedling 13 days old, cotyledon 4.5 mm. in length, with a small true leaf
fully developed. Average length of cells of
pulvinus.................................................. 7 Length of longest cell below the
pulvinus..................................... 30 Length of longest cell above the
pulvinus...................................... 60

[28] Each division equalled .003 mm.

We here see that the cells of the pulvinus increase but little in length with
advancing age, in comparison with those of the petiole both above and
below it; but they continue to grow in width, and keep equal in this respect
with the other cells of the petiole. The rate of growth, however, varies in all
parts of the cotyledons, as may be observed in the measurements of the 8-
days’ old seedling.
The cotyledons of seedlings only a day old rise at night considerably,
sometimes as much as afterwards; but there was much variation in this
respect. As the pulvinus is so indistinct at first, the movement probably does
not then depend on the expansion of its cells, but on periodically unequal
growth in the petiole. By the comparison of seedlings of different known
ages, it was evident that the chief seat of growth of the petiole was in the
upper part between the pulvinus and the blade; and this agrees with the fact
(shown in the measurements above given) that the cells grow to a greater
length in the upper than in the lower part. With a seedling 11 days old, the
nocturnal rise was found to depend largely on the action of the pulvinus, for
the petiole at night was curved upwards at this point; and during the day,
whilst the petiole was horizontal, the lower surface of the pulvinus was
wrinkled with the upper surface tense. Although the cotyledons at an
advanced age do not rise at night to a higher inclination than whilst young,
yet they have to pass through a larger angle (in one instance amounting to
63°) to gain their nocturnal position, as they are generally deflected beneath
the horizon during the day. Even with the 11-days’ old seedling the
movement did not depend exclusively on the pulvinus, for the blade where
joined to the petiole was curved upwards, and this must be attributed to

unequal growth. Therefore the periodic movements of the cotyledons of ‘O.
corniculata’ depend on two distinct but conjoint actions, namely, the
expansion of the cells of the pulvinus and on the growth of the upper part of
the petiole, including the base of the blade.
Lotus Jacoboeus.—The seedlings of this plant present a case parallel to
that of Oxalis corniculata in some respects, and in others unique, as far as
we have seen. The cotyledons during the first 4 or 5 days of their life do not
exhibit any plain nocturnal movement; but afterwards they stand vertically
or almost vertically up at night. There is, however, some degree of
variability in this respect, apparently dependent on the season and on the
degree to which they have been illuminated during the day. With older
seedlings, having cotyledons 4 mm. in length, which rise considerably at
night, there is a well-developed pulvinus close to the blade, colourless, and
rather narrower than the rest of the petiole, from which it is abruptly
separated. It is formed of a mass of small cells of an average length of .021
mm.; whereas the cells in the lower part of the petiole are about .06 mm.,
and those in the blade from .034 to .04 mm. in length. The epidermic cells
in the lower part of the petiole project conically, and thus differ in shape
from those over the pulvinus.
Turning now to very young seedlings, the cotyledons of which do not rise
at night and are only from 2 to 2½ mm. in length, their petioles do not
exhibit any defined zone of small cells, destitute of chlorophyll and
differing in shape exteriorly from the lower ones. Nevertheless, the cells at
the place where a pulvinus will afterwards be developed are smaller (being
on an average .015 mm. in length) than those in the lower parts of the same
petiole, which gradually become larger in proceeding downwards, the
largest being .030 mm. in length. At this early age the cells of the blade are
about .027 mm. in length. We thus see that the pulvinus is formed by the
cells in the uppermost part of the petiole, continuing for only a short time to
increase in length, then being arrested in their growth, accompanied by the
loss of their chlorophyll grains; whilst the cells in the lower part of the
petiole continue for a long time to increase in length, those of the epidermis
becoming more conical. The singular fact of the cotyledons of this plant not
sleeping at first is therefore due to the pulvinus not being developed at an
early age.

We learn from these two cases of Lotus and Oxalis, that the development
of a pulvinus follows from the growth of the cells over a small defined
space of the petiole being almost arrested at an early age. With Lotus
Jacobæus the cells at first increase a little in length; in Oxalis corniculata
they decrease a little, owing to self-division. A mass of such small cells
forming a pulvinus, might therefore be either acquired or lost without any
special difficulty, by different species in the same natural genus: and we
know that with seedlings of Trifolium, Lotus, and Oxalis some of the
species have a well-developed pulvinus, and others have none, or one in a
rudimentary condition. As the movements caused by the alternate
turgescence of the cells in the two halves of a pulvinus, must be largely
determined by the extensibility and subsequent contraction of their walls,
we can perhaps understand why a large number of small cells will be more
efficient than a small number of large cells occupying the same space. As a
pulvinus is formed by the arrestment of the growth of its cells, movements
dependent on their action may be long-continued without any increase in
length of the part thus provided; and such long-continued movements seem
to be one chief end gained by the development of a pulvinus. Long-
continued movement would be impossible in any part, without an inordinate
increase in its length, if the turgescence of the cells was always followed by
growth.
Disturbance of the Periodic Movements of Cotyledons by Light.—The
hypocotyls and cotyledons of most seedling plants are, as is well known,
extremely heliotropic; but cotyledons, besides being heliotropic, are
affected paratonically (to use Sachs’ expression) by light; that is, their daily
periodic movements are greatly and quickly disturbed by changes in its
intensity or by its absence. It is not that they cease to circumnutate in
darkness, for in all the many cases observed by us they continued to do so;
but the normal order of their movements in relation to the alternations of
day and night is much disturbed or quite annulled. This holds good with
species the cotyledons of which rise or sink so much at night that they may
be said to sleep, as well as with others which rise only a little. But different
species are affected in very different degrees by changes in the light.
For instance, the cotyledons of Beta vulgaris, Solanum lycopersicum,
Cerinthe major, and Lupinus luteus, when placed in darkness, moved down
during the afternoon and early night, instead of rising as they would have
done if they had been exposed to the light. All the individuals of the

Solanum did not behave in the same manner, for the cotyledons of one
circumnutated about the same spot between 2.30 and 10 P.M. The
cotyledons of a seedling of Oxalis corniculata, which was feebly
illuminated from above, moved downwards during the first morning in the
normal manner, but on the second morning it moved upwards. The
cotyledons of Lotus Jacoboeus were not affected by 4 h. of complete
darkness, but when placed under a double skylight and thus feebly
illuminated, they quite lost their periodical movements on the third
morning. On the other hand, the cotyledons of Cucurbita ovifera moved in
the normal manner during a whole day in darkness.
Seedlings of Githago segetum were feebly illuminated from above in the
morning before their cotyledons had expanded, and they remained closed
for the next 40 h. Other seedlings were placed in the dark after their
cotyledons had opened in the morning and these did not begin to close until
about 4 h. had elapsed. The cotyledons of Oxalis rosea sank vertically
downwards after being left for 1 h. 20 m. in darkness; but those of some
other species of Oxalis were not affected by several hours of darkness. The
cotyledons of several species of Cassia are eminently susceptible to changes
in the degree of light to which they are exposed: thus seedlings of an
unnamed S. Brazilian species (a large and beautiful tree) were brought out
of the hot-house and placed on a table in the middle of a room with two
north-east and one north-west window, so that they were fairly well
illuminated, though of course less so than in the hot-house, the day being
moderately bright; and after 36 m. the cotyledons which had been
horizontal rose up vertically and closed together as when asleep; after thus
remaining on the table for 1 h. 13 m. they began to open. The cotyledons of
young seedlings of another Brazilian species and of C. neglecta, treated in
the same manner, behaved similarly, excepting that they did not rise up
quite so much: they again became horizontal after about an hour.
Here is a more interesting case: seedlings of Cassia tora in two pots,
which had stood for some time on the table in the room just described, had
their cotyledons horizontal. One pot was now exposed for 2 h. to dull
sunshine, and the cotyledons remained horizontal; it was then brought back
to the table, and after 50 m. the cotyledons had risen 68° above the horizon.
The other pot was placed during the same 2 h. behind a screen in the room,
where the light was very obscure, and the cotyledons rose 63° above the
horizon; the pot was then replaced on the table, and after 50 m. the

cotyledons had fallen 33°. These two pots with seedlings of the same age
stood close together, and were exposed to exactly the same amount of light,
yet the cotyledons in the one pot were rising, whilst those in the other pot
were at the same time sinking. This fact illustrates in a striking manner that
their movements are not governed by the actual amount, but by a change in
the intensity or degree of the light. A similar experiment was tried with two
sets of seedlings, both exposed to a dull light, but different in degree, and
the result was the same. The movements of the cotyledons of this Cassia
are, however, determined (as in many other cases) largely by habit or
inheritance, independently of light; for seedlings which had been
moderately illuminated during the day, were kept all night and on the
following morning in complete darkness; yet the cotyledons were partially
open in the morning and remained open in the dark for about 6 h. The
cotyledons in another pot, similarly treated on another occasion, were open
at 7 A.M. and remained open in the dark for 4 h. 30 m., after which time
they began to close. Yet these same seedlings, when brought in the middle
of the day from a moderately bright into only a moderately dull light raised,
as we have seen, their cotyledons high above the horizon.
Sensitiveness of Cotyledons to contact.—This subject does not possess
much interest, as it is not known that sensitiveness of this kind is of any
service to seedling plants. We have observed cases in only four genera,
though we have vainly observed the cotyledons of many others. The genus
cassia seems to be pre-eminent in this respect: thus, the cotyledons of C.
tora, when extended horizontally, were both lightly tapped with a very thin
twig for 3 m. and in the course of a few minutes they formed together an
angle of 90°, so that each had risen 45°. A single cotyledon of another
seedling was tapped in a like manner for 1 m., and it rose 27° in 9 m.; and
after eight additional minutes it had risen 10° more; the opposite cotyledon,
which was not tapped, hardly moved at all. The cotyledons in all these cases
became horizontal again in less than half an hour. The pulvinus is the most
sensitive part, for on slightly pricking three cotyledons with a pin in this
part, they rose up vertically; but the blade was found also to be sensitive,
care having been taken that the pulvinus was not touched. Drops of water
placed quietly on these cotyledons produced no effect, but an extremely fine
stream of water, ejected from a syringe, caused them to move upwards.
When a pot of seedlings was rapidly hit with a stick and thus jarred, the
cotyledons rose slightly. When a minute drop of nitric acid was placed on

both pulvini of a seedling, the cotyledons rose so quickly that they could
easily be seen to move, and almost immediately afterwards they began to
fall; but the pulvini had been killed and became brown.
The cotyledons of an unnamed species of Cassia (a large tree from S.
Brazil) rose 31° in the course of 26 m. after the pulvini and the blades had
both been rubbed during 1 m. with a twig; but when the blade alone was
similarly rubbed the cotyledons rose only 8°. The remarkably long and
narrow cotyledons, of a third unnamed species from S. Brazil, did not move
when their blades were rubbed on six occasions with a pointed stick for 30
s. or for 1 m.; but when the pulvinus was rubbed and slightly pricked with a
pin, the cotyledons rose in the course of a few minutes through an angle of
6°o. Several cotyledons of C. neglecta (likewise from S. Brazil) rose in
from 5 m. to 15 m. to various angles between 16v and 34°, after being
rubbed during 1 m. with a twig. Their sensitiveness is retained to a
somewhat advanced age, for the cotyledons of a little plant of C. neglecta,
34 days old and bearing three true leaves, rose when lightly pinched
between the finger and thumb. Some seedlings were exposed for 30 m. to a
wind (temp. 50° F.) sufficiently strong to keep the cotyledons vibrating, but
this to our surprise did not cause any movement. The cotyledons of four
seedlings of the Indian C. glauca were either rubbed with a thin twig for 2
m. or were lightly pinched: one rose 34°; a second only 6°; a third 13°; and
a fourth 17°. A cotyledon of C. florida similarly treated rose 9°; one of C.
corymbosa rose 7½°, and one of the very distinct C. mimosoides only 6°.
Those of C. pubescens did not appear to be in the least sensitive; nor were
those of C. nodosa, but these latter are rather thick and fleshy, and do not
rise at night or go to sleep.
Smithia sensitiva.—This plant belongs to a distinct sub-order of the
Leguminosae from Cassia. Both cotyledons of an oldish seedling, with the
first true leaf partially unfolded, were rubbed for 1 m. with a fine twig, and
in 5 m. each rose 32°; they remained in this position for 15 m., but when
looked at again 40 m. after the rubbing, each had fallen 14°. Both
cotyledons of another and younger seedling were lightly rubbed in the same
manner for 1 m., and after an interval of 32 m. each had risen 30°. They
were hardly at all sensitive to a fine jet of water. The cotyledons of S.
Pfundii, an African water plant, are thick and fleshy; they are not sensitive
and do not go to sleep.

Mimosa pudica and albida.—The blades of several cotyledons of both
these plants were rubbed or slightly scratched with a needle during 1 m. or
2 m.; but they did not move in the least. When, however, the pulvini of six
cotyledons of M. pudica were thus scratched, two of them were slightly
raised. In these two cases perhaps the pulvinus was accidentally pricked, for
on pricking the pulvinus of another cotyledon it rose a little. It thus appears
that the cotyledons of Mimosa are less sensitive than those of the previously
mentioned plants.[29]
[29] The sole notice which we have met with on the sensitiveness of cotyledons,
relates to Mimosa; for Aug. P. De Candolle says (‘Phys. Vég.,’ 1832, tom. ii. p.
865), “les cotyledons du M. pudica tendent à se raprocher par leurs faces
supérieures lorsqu’on les irrite.”

Oxalis sensitiva.—The blades and pulvini of two cotyledons, standing
horizontally, were rubbed or rather tickled for 30 s. with a fine split bristle,
and in 10 m. each had risen 48°; when looked at again in 35 m. after being
rubbed they had risen 4° more; after 30 additional minutes they were again
horizontal. On hitting a pot rapidly with a stick for 1 m., the cotyledons of
two seedlings were considerably raised in the course of 11 m. A pot was
carried a little distance on a tray and thus jolted; and the cotyledons of four
seedlings were all raised in 10 m.; after 17 m. one had risen 56°, a second
45°, a third almost 90°, and a fourth 90°. After an additional interval of 40
m. three of them had re-expanded to a considerable extent. These
observations were made before we were aware at what an extraordinarily
rapid rate the cotyledons circumnutate, and are therefore liable to error.
Nevertheless it is extremely improbable that the cotyledons in the eight
cases given, should all have been rising at the time when they were irritated.
The cotyledons of Oxalis Valdiviana and rosea were rubbed and did not
exhibit any sensitiveness.
Finally, there seems to exist some relation between the habit of
cotyledons rising vertically at night or going to sleep, and their
sensitiveness, especially that of their pulvini, to a touch; for all the above-
named plants sleep at night. On the other hand, there are many plants the
cotyledons of which sleep, and are not in the least sensitive. As the
cotyledons of several species of Cassia are easily affected both by slightly
diminished light and by contact, we thought that these two kinds of
sensitiveness might be connected; but this is not necessarily the case, for the
cotyledons of Oxalis sensitiva did not rise when kept on one occasion for

1½ h., and on a second occasion for nearly 4 h., in a dark closet. Some other
cotyledons, as those of Githago segetum, are much affected by a feeble
light, but do not move when scratched by a needle. That with the same plant
there is some relation between the sensitiveness of its cotyledons and leaves
seems highly probable, for the above described Smithia and Oxalis have
been called sensitiva, owing to their leaves being sensitive; and though the
leaves of the several species of Cassia are not sensitive to a touch, yet if a
branch be shaken or syringed with water, they partially assume their
nocturnal dependent position. But the relation between the sensitiveness to
contact of the cotyledons and of the leaves of the same plant is not very
close, as may be inferred from the cotyledons of Mimosa pudica being only
slightly sensitive, whilst the leaves are well known to be so in the highest
degree. Again, the leaves of Neptunia oleracea are very sensitive to a touch,
whilst the cotyledons do not appear to be so in any degree.

CHAPTER III.
SENSITIVENESS OF THE APEX OF THE
RADICLE TO CONTACT AND TO OTHER
IRRITANTS.

Manner in which radicles bend when they encounter an
obstacle in the soil—Vicia faba, tips of radicles highly
sensitive to contact and other irritants—Effects of too high a
temperature—Power of discriminating between objects
attached on opposite sides—Tips of secondary radicles
sensitive—Pisum, tips of radicles sensitive—Effects of such
sensitiveness in overcoming geotropism—Secondary
radicles—Phaseolus, tips of radicles hardly sensitive to
contact, but highly sensitive to caustic and to the removal of
a slice—Tropaeolum—Gossypium—Cucurbita—Raphanus
—Æsculus, tip not sensitive to slight contact, highly
sensitive to caustic—Quercus, tip highly sensitive to contact
—Power of discrimination—Zea, tip highly sensitive,
secondary radicles—Sensitiveness of radicles to moist air—
Summary of chapter.

In order to see how the radicles of seedlings would pass over stones,
roots, and other obstacles, which they must incessantly encounter in the
soil, germinating beans (Vicia faba) were so placed that the tips of the
radicles came into contact, almost rectangularly or at a high angle, with
underlying plates of glass. In other cases the beans were turned about whilst
their radicles were growing, so that they descended nearly vertically on
their own smooth, almost flat, broad upper surfaces. The delicate root-cap,
when it first touched any directly opposing surface, was a little flattened

transversely; the flattening soon became oblique, and in a few hours quite
disappeared, the apex now pointing at right angles, or at nearly right angles,
to its former course. The radicle then seemed to glide in its new direction
over the surface which had opposed it, pressing on it with very little force.
How far such abrupt changes in its former course are aided by the
circumnutation of the tip must be left doubtful. Thin slips of wood were
cemented on more or less steeply inclined glass-plates, at right angles to the
radicles which were gliding down them. Straight lines had been painted
along the growing terminal part of some of these radicles, before they met
the opposing slip of wood; and the lines became sensibly curved in 2 h.
after the apex had come into contact with the slips. In one case of a radicle,
which was growing rather slowly, the root-cap, after encountering a rough
slip of wood at right angles, was at first slightly flattened transversely: after
an interval of 2 h. 30 m. the flattening became oblique; and after an
additional 3 hours the flattening had wholly disappeared, and the apex now
pointed at right angles to its former course. It then continued to grow in its
new direction alongside the slip of wood, until it came to the end of it,
round which it bent rectangularly. Soon afterwards when coming to the
edge of the plate of glass, it was again bent at a large angle, and descended
perpendicularly into the damp sand.
When, as in the above cases, radicles encountered an obstacle at right
angles to their course, the terminal growing part became curved for a length
of between .3 and .4 of an inch (8–10 mm.), measured from the apex. This
was well shown by the black lines which had been previously painted on
them. The first and most obvious explanation of the curvature is, that it
results merely from the mechanical resistance to the growth of the radicle in
its original direction. Nevertheless, this explanation did not seem to us
satisfactory. The radicles did not present the appearance of having been
subjected to a sufficient pressure to account for their curvature; and Sachs
has shown[1] that the growing part is more rigid than the part immediately
above which has ceased to grow, so that the latter might have been expected
to yield and become curved as soon as the apex encountered an unyielding
object; whereas it was the stiff growing part which became curved.
Moreover, an object which yields with the greatest ease will deflect a
radicle: thus, as we have seen, when the apex of the radicle of the bean
encountered the polished surface of extremely thin tin-foil laid on soft sand,
no impression was left on it, yet the radicle became deflected at right

angles. A second explanation occurred to us, namely, that even the gentlest
pressure might check the growth of the apex, and in this case growth could
continue only on one side, and thus the radicle would assume a rectangular
form; but this view leaves wholly unexplained the curvature of the upper
part, extending for a length of 8–10 mm.
[1] ‘Arbeiten Bot. Inst. Würzburg,’ Heft iii. 1873, p. 398.

We were therefore led to suspect that the apex was sensitive to contact,
and that an effect was transmitted from it to the upper part of the radicle,
which was thus excited to bend away from the touching object. As a little
loop of fine thread hung on a tendril or on the petiole of a leaf-climbing
plant, causes it to bend, we thought that any small hard object affixed to the
tip of a radicle, freely suspended and growing in damp air, might cause it to
bend, if it were sensitive, and yet would not offer any mechanical resistance
to its growth. Full details will be given of the experiments which were tried,
as the result proved remarkable. The fact of the apex of a radicle being
sensitive to contact has never been observed, though, as we shall hereafter
see, Sachs discovered that the radicle a little above the apex is sensitive, and
bends like a tendril towards the touching object. But when one side of the
apex is pressed by any object, the growing part bends away from the object;
and this seems a beautiful adaptation for avoiding obstacles in the soil, and,
as we shall see, for following the lines of least resistance. Many organs,
when touched, bend in one fixed direction, such as the stamens of Berberis,
the lobes of Dionaea, etc.; and many organs, such as tendrils, whether
modified leaves or flower-peduncles, and some few stems, bend towards a
touching object; but no case, we believe, is known of an organ bending
away from a touching object.

Sensitiveness of the Apex of the Radicle of Vicia faba.—Common beans,
after being soaked in water for 24 h., were pinned with the hilum
downwards (in the manner followed by Sachs), inside the cork lids of glass-
vessels, which were half filled with water; the sides and the cork were well
moistened, and light was excluded. As soon as the beans had protruded
radicles, some to a length of less than a tenth of an inch, and others to a
length of several tenths, little squares or oblongs of card were affixed to the
short sloping sides of their conical tips. The squares therefore adhered

obliquely with reference to the longitudinal axis of the radicle; and this is a
very necessary precaution, for if the bits of card accidentally became
displaced, or were drawn by the viscid matter employed so as to adhere
parallel to the side of the radicle, although only a little way above the
conical apex, the radicle did not bend in the peculiar manner which we are
here considering. Squares of about the 1/20th of an inch (i.e. about 1½
mm.), or oblong bits of nearly the same size, were found to be the most
convenient and effective. We employed at first ordinary thin card, such as
visiting cards, or bits of very thin glass, and various other objects; but
afterwards sand-paper was chiefly employed, for it was almost as stiff as
thin card, and the roughened surface favoured its adhesion. At first we
generally used very thick gum-water; and this of course, under the
circumstances, never dried in the least; on the contrary, it sometimes
seemed to absorb vapour, so that the bits of card became separated by a
layer of fluid from the tip. When there was no such absorption and the card
was not displaced, it acted well and caused the radicle to bend to the
opposite side. I should state that thick gum-water by itself induces no
action. In most cases the bits of card were touched with an extremely small
quantity of a solution of shellac in spirits of wine, which had been left to
evaporate until it was thick; it then set hard in a few seconds, and fixed the
bits of card well. When small drops of the shellac were placed on the tips
without any card, they set into hard little beads, and these acted like any
other hard object, causing the radicles to bend to the opposite side. Even
extremely minute beads of the shellac occasionally acted in a slight degree,
as will hereafter be described. But that it was the cards which chiefly acted
in our many trials, was proved by coating one side of the tip with a little bit
of goldbeaters’ skin (which by itself hardly acts), and then fixing a bit of
card to the skin with shellac which never came into contact with the radicle:
nevertheless the radicle bent away from the attached card in the ordinary
manner.
Some preliminary trials were made, presently to be described, by which
the proper temperature was determined, and then the following experiments
were made. It should be premised that the beans were always fixed to the
cork-lids, for the convenience of manipulation, with the edge from which
the radicle and plumule protrudes, outwards; and it must be remembered
that owing to what we have called Sachs’ curvature, the radicles, instead of
growing perpendicularly downwards, often bend somewhat, even as much

as about 45° inwards, or under the suspended bean. Therefore when a
square of card was fixed to the apex in front, the bowing induced by it
coincided with Sachs’ curvature, and could be distinguished from it only by
being more strongly pronounced or by occurring more quickly. To avoid
this source of doubt, the squares were fixed either behind, causing a
curvature in direct opposition to that of Sachs’, or more commonly to the
right or left sides. For the sake of brevity, we will speak of the bits of card,
etc., as fixed in front, or behind, or laterally. As the chief curvature of the
radicle is at a little distance from the apex, and as the extreme terminal and
basal portions are nearly straight, it is possible to estimate in a rough
manner the amount of curvature by an angle; and when it is said that the
radicle became deflected at any angle from the perpendicular, this implies
that the apex was turned upwards by so many degrees from the downward
direction which it would naturally have followed, and to the side opposite to
that to which the card was affixed. That the reader may have a clear idea of
the kind of movement excited by the bits of attached card, we append here
accurate sketches of three germinating beans thus treated, and selected out
of several specimens to show the gradations in the degrees of curvature. We
will now give in detail a series of experiments, and afterwards a summary
of the results.
Fig. 65. Vicia faba: A, radicle beginning to bend from the attached little
square of card; B, bent at a rectangle; C, bent into a circle or loop, with the
tip beginning to bend downwards through the action of geotropism.

In the first 12 trials, little squares or oblongs of sanded card, 1.8 mm. in
length, and 1.5 or only 0.9 mm. in breadth (i.e. .071 of an inch in length and
.059 or .035 of an inch in breadth) were fixed with shellac to the tips of the
radicles. In the subsequent trials the little squares were only occasionally
measured, but were of about the same size.
(1.) A young radicle, 4 mm. in length, had a card fixed behind: after 9 h.
deflected in the plane in which the bean is flattened, 50° from the
perpendicular and from the card, and in opposition to Sachs’ curvature: no
change next morning, 23 h. from the time of attachment.
(2.) Radicle 5.5 mm. in length, card fixed behind: after 9 h. deflected in
the plane of the bean 20° from the perpendicular and from the card, and in
opposition to Sachs’ curvature: after 23 h. no change.

(3.) Radicle 11 mm. in length, card fixed behind: after 9 h. deflected in
the plane of the bean 40° from the perpendicular and from the card, and in
opposition to Sachs’ curvature. The tip of the radicle more curved than the
upper part, but in the same plane. After 23 h. the extreme tip was slightly
bent towards the card; the general curvature of the radicle remaining the
same.
(4.) Radicle 9 mm. long, card fixed behind and a little laterally: after 9 h.
deflected in the plane of the bean only about 7° or 8° from the
perpendicular and from the card, in opposition to Sachs’ curvature. There
was in addition a slight lateral curvature directed partly from the card. After
23 h. no change.
(5.) Radicle 8 mm. long, card affixed almost laterally: after 9 h. deflected
30° from the perpendicular, in the plane of the bean and in opposition to
Sachs’ curvature; also deflected in a plane at right angles to the above one,
20° from the perpendicular: after 23 h. no change.
(6.) Radicle 9 mm. long, card affixed in front: after 9 h. deflected in the
plane of the bean about 40° from the vertical, away from the card and in the
direction of Sachs’ curvature. Here therefore we have no evidence of the
card being the cause of the deflection, except that a radicle never moves
spontaneously, as far as we have seen, as much as 40° in the course of 9 h.
After 23 h. no change.
(7.) Radicle 7 mm. long, card affixed to the back: after 9 h. the terminal
part of the radicle deflected in the plane of the bean 20° from the vertical,
away from the card and in opposition to Sachs’ curvature. After 22 h. 30 m.
this part of the radicle had become straight.
(8.) Radicle 12 mm. long, card affixed almost laterally: after 9 h.
deflected laterally in a plane at right angles to that of the bean between 40°
and 50° from the vertical and from the card. In the plane of the bean itself
the deflection amounted to 8° or 9° from the vertical and from the card, in
opposition to Sachs’ curvature. After 22 h. 30 m. the extreme tip had
become slightly curved towards the card.
(9.) Card fixed laterally: after 11 h. 30 m. no effect, the radicle being still
almost vertical.
(10.) Card fixed almost laterally: after 11 h. 30 m. deflected 90° from the
vertical and from the card, in a plane intermediate between that of the bean

itself and one at right angles to it. Radicle consequently partially deflected
from Sachs’ curvature.
(11.) Tip of radicle protected with goldbeaters’ skin, with a square of card
of the usual dimensions affixed with shellac: after 11 h. greatly deflected in
the plane of the bean, in the direction of Sachs’ curvature, but to a much
greater degree and in less time than ever occurs spontaneously.
(12.) Tip of radicle protected as in last case: after 11 h. no effect, but after
24 h. 40 m. radicle clearly deflected from the card. This slow action was
probably due to a portion of the goldbeaters’ skin having curled round and
lightly touched the opposite side of the tip and thus irritated it.
(13.) A radicle of considerable length had a small square of card fixed
with shellac to its apex laterally: after only 7 h. 15 m. a length of .4 of an
inch from the apex, measured along the middle, was considerably curved
from the side bearing the card.
(14.) Case like the last in all respects, except that a length of only .25 of
an inch of the radicle was thus deflected.
(15.) A small square of card fixed with shellac to the apex of a young
radicle; after 9 h. 15 m. deflected through 90° from the perpendicular and
from the card. After 24 h. deflection much decreased, and after an
additional day, reduced to 23° from the perpendicular.
(16.) Square of card fixed with shellac behind the apex of a radicle,
which from its position having been changed during growth had become
very crooked; but the terminal portion was straight, and this became
deflected to about 45° from the perpendicular and from the card, in
opposition to Sachs’ curvature.
(17.) Square of card affixed with shellac: after 8 h. radicle curved at right
angles from the perpendicular and from the card. After 15 additional hours
curvature much decreased.
(18.) Square of card affixed with shellac: after 8 h. no effect; after 23 h. 3
m. from time of affixing, radicle much curved from the square. (19.) Square
of card affixed with shellac: after 24 h. no effect, but the radicle had not
grown well and seemed sickly.
(20.) Square of card affixed with shellac: after 24 h. no effect.
(21, 22.) Squares of card affixed with shellac: after 24 h. radicles of both
curved at about 45° from the perpendicular and from the cards.

(23.) Square of card fixed with shellac to young radicle: after 9 h. very
slightly curved from the card; after 24 h. tip curved towards card. Refixed
new square laterally, after 9 h. distinctly curved from the card, and after 24
h. curved at right angles from the perpendicular and from the card.
(24.) A rather large oblong piece of card fixed with shellac to apex: after
24 h. no effect, but the card was found not to be touching the apex. A small
square was now refixed with shellac; after 16 h. slight deflection from the
perpendicular and from the card. After an additional day the radicle became
almost straight.
(25.) Square of card fixed laterally to apex of young radicle; after 9 h.
deflection from the perpendicular considerable; after 24 h. deflection
reduced. Refixed a fresh square with shellac: after 24 h. deflection about
40° from the perpendicular and from the card.
(26.) A very small square of card fixed with shellac to apex of young
radicle: after 9 h. the deflection from the perpendicular and from the card
amounted to nearly a right angle; after 24 h. deflection much reduced; after
an additional 24 h. radicle almost straight.
(27.) Square of card fixed with shellac to apex of young radicle: after 9 h.
deflection from the card and from the perpendicular a right angle; next
morning quite straight. Refixed a square laterally with shellac; after 9 h. a
little deflection, which after 24 h. increased to nearly 20° from the
perpendicular and from the card.
(28.) Square of card fixed with shellac; after 9 h. some deflection; next
morning the card dropped off; refixed it with shellac; it again became loose
and was refixed; and now on the third trial the radicle was deflected after 14
h. at right angles from the card.
(29.) A small square of card was first fixed with thick gum-water to the
apex. It produced a slight effect but soon fell off. A similar square was now
affixed laterally with shellac: after 9 h. the radicle was deflected nearly 45°
from the perpendicular and from the card. After 36 additional hours angle of
deflection reduced to about 30°.
(30.) A very small piece, less than 1/20th of an inch square, of thin tin-
foil fixed with shellac to the apex of a young radicle; after 24 h. no effect.
Tin-foil removed, and a small square of sanded card fixed with shellac;
after 9 h. deflection at nearly right angles from the perpendicular and from

the card. Next morning deflection reduced to about 40° from the
perpendicular.
(31.) A splinter of thin glass gummed to apex, after 9 h. no effect, but it
was then found not to be touching the apex of the radicle. Next morning a
square of card was fixed with shellac to it, and after 9 h. radicle greatly
deflected from the card. After two additional days the deflection had
decreased and was only 35° from the perpendicular.
(32.) Small square of sanded card, attached with thick gum-water
laterally to the apex of a long straight radicle: after 9 h. greatly deflected
from the perpendicular and from the card. Curvature extended for a length
of .22 of an inch from the apex. After 3 additional hours terminal portion
deflected at right angles from the perpendicular. Next morning the curved
portion was .36 in length.
(33.) Square of card gummed to apex: after 15 h. deflected at nearly 90°
from the perpendicular and from the card.
(34.) Small oblong of sanded card gummed to apex: after 15 h. deflected
90° from the perpendicular and from the card: in the course of the three
following days the terminal portion became much contorted and ultimately
coiled into a helix.
(35.) Square of card gummed to apex: after 9 h. deflected from card: after
24 h. from time of attachment greatly deflected obliquely and partly in
opposition to Sachs’ curvature.
(36.) Small piece of card, rather less than 1/20th of an inch square,
gummed to apex: in 9 h. considerably deflected from card and in opposition
to Sachs’ curvature; after 24 h. greatly deflected in the same direction. After
an additional day the extreme tip was curved towards the card.
(37.) Square of card, gummed to apex in front, caused after 8 h. 30 m.
hardly any effect; refixed fresh square laterally, after 15 h. deflected almost
90° from the perpendicular and from the card. After 2 additional days
deflection much reduced.
(38.) Square of card gummed to apex: after 9 h. much deflection, which
after 24 h. from time of fixing increased to nearly 90°. After an additional
day terminal portion was curled into a loop, and on the following day into a
helix.

(39.) Small oblong piece of card gummed to apex, nearly in front, but a
little to one side; in 9 h. slightly deflected in the direction of Sachs’
curvature, but rather obliquely, and to side opposite to card. Next day more
curved in the same direction, and after 2 additional days coiled into a ring.
(40.) Square of card gummed to apex: after 9 h. slightly curved from
card; next morning radicle straight, and apex had grown beyond the card.
Refixed another square laterally with shellac; in 9 h. deflected laterally, but
also in the direction of Sachs’ curvature. After 2 additional days’ curvature
considerably increased in the same direction.
(41.) Little square of tin-foil fixed with gum to one side of apex of a
young and short radicle: after 15 h. no effect, but tin-foil had become
displaced. A little square of card was now gummed to one side of apex,
which after 8 h. 40 m. was slightly deflected; in 24 h. from the time of
attachment deflected at 90° from the perpendicular and from the card; after
9 additional hours became hooked, with the apex pointing to the zenith. In 3
days from the time of attachment the terminal portion of the radicle formed
a ring or circle.
(42.) A little square of thick letter-paper gummed to the apex of a radicle,
which after 9 h. was deflected from it. In 24 h. from time when the paper
was affixed the deflection much increased, and after 2 additional days it
amounted to 50° from the perpendicular and from the paper.
(43.) A narrow chip of a quill was fixed with shellac to the apex of a
radicle. After 9 h. no effect; after 24 h. moderate deflection, but now the
quill had ceased to touch the apex. Removed quill and gummed a little
square of card to apex, which after 8 h. caused slight deflection. On the
fourth day from the first attachment of any object, the extreme tip was
curved towards the card.
(44.) A rather long and narrow splinter of extremely thin glass, fixed with
shellac to apex, it caused in 9 h. slight deflection, which disappeared in 24
h.; the splinter was then found not touching the apex. It was twice refixed,
with nearly similar results, that is, it caused slight deflection, which soon
disappeared. On the fourth day from the time of first attachment the tip was
bent towards the splinter.

From these experiments it is clear that the apex of the radicle of the bean
is sensitive to contact, and that it causes the upper part to bend away from
the touching object. But before giving a summary of the results, it will be
convenient briefly to give a few other observations. Bits of very thin glass
and little squares of common card were affixed with thick gum-water to the
tips of the radicles of seven beans, as a preliminary trial. Six of these were
plainly acted on, and in two cases the radicles became coiled up into
complete loops. One radicle was curved into a semi-circle in so short a
period as 6 h. 10 m. The seventh radicle which was not affected was
apparently sickly, as it became brown on the following day; so that it
formed no real exception. Some of these trials were made in the early
spring during cold weather in a sitting-room, and others in a greenhouse,
but the temperature was not recorded. These six striking cases almost
convinced us that the apex was sensitive, but of course we determined to
make many more trials. As we had noticed that the radicles grew much
more quickly when subjected to considerable heat, and as we imagined that
heat would increase their sensitiveness, vessels with germinating beans
suspended in damp air were placed on a chimney-piece, where they were
subjected during the greater part of the day to a temperature of between 69°
and 72° F.; some, however, were placed in the hot-house where the
temperature was rather higher. Above two dozen beans were thus tried; and
when a square of glass or card did not act, it was removed, and a fresh one
affixed, this being often done thrice to the same radicle. Therefore between
five and six dozen trials were altogether made. But there was moderately
distinct deflection from the perpendicular and from the attached object in
only one radicle out of this large number of cases. In five other cases there
was very slight and doubtful deflection. We were astonished at this result,
and concluded that we had made some inexplicable mistake in the first six
experiments. But before finally relinquishing the subject, we resolved to
make one other trial for it occurred to us that sensitiveness is easily affected
by external conditions, and that radicles growing naturally in the earth in
the early spring would not be subjected to a temperature nearly so high as
70° F. We therefore allowed the radicles of 12 beans to grow at a
temperature of between 55° and 60° F. The result was that in every one of
these cases (included in the above-described experiments) the radicle was
deflected in the course of a few hours from the attached object. All the
above recorded successful trials, and some others presently to be given,

were made in a sitting-room at the temperatures just specified. It therefore
appears that a temperature of about, or rather above, 70° F. destroys the
sensitiveness of the radicles, either directly, or indirectly through
abnormally accelerated growth; and this curious fact probably explains why
Sachs, who expressly states that his beans were kept at a high temperature,
failed to detect the sensitiveness of the apex of the radicle.
But other causes interfere with this sensibility. Eighteen radicles were
tried with little squares of sanded card, some affixed with shellac and some
with gum-water, during the few last days of 1878, and few first days of the
next year. They were kept in a room at the proper temperature during the
day, but were probably too cold at night, as there was a hard frost at the
time. The radicles looked healthy but grew very slowly. The result was that
only 6 out of the 18 were deflected from the attached cards, and this only to
a slight degree and at a very slow rate. These radicles therefore presented a
striking contrast with the 44 above described. On March 6th and 7th, when
the temperature of the room varied between 53° and 59° F., eleven
germinating beans were tried in the same manner, and now every one of the
radicles became curved away from the cards, though one was only slightly
deflected. Some horticulturists believe that certain kinds of seeds will not
germinate properly in the middle of the winter, although kept at a right
temperature. If there really is any proper period for the germination of the
bean, the feeble degree of sensibility of the above radicles may have
resulted from the trial having been made in the middle of the winter, and not
simply from the nights being too cold. Lastly, the radicles of four beans,
which from some innate cause germinated later than all the others of the
same lot, and which grew slowly though appearing healthy, were similarly
tried, and even after 24 h. they were hardly at all deflected from the
attached cards. We may therefore infer that any cause which renders the
growth of the radicles either slower or more rapid than the normal rate,
lessens or annuls the sensibility of their tips to contact. It deserves particular
attention that when the attached objects failed to act, there was no bending
of any kind, excepting Sachs’ curvature. The force of our evidence would
have been greatly weakened if occasionally, though rarely, the radicles had
become curved in any direction independently of the attached objects. In
the foregoing numbered paragraphs, however, it may be observed that the
extreme tip sometimes becomes, after a considerable interval of time,

abruptly curved towards the bit of card; but this is a totally distinct
phenomenon, as will presently be explained.
A Summary of the Results of the foregoing Experiments on the Radicles
of Vicia faba.—Altogether little squares (about 1/20th of an inch), generally
of sanded paper as stiff as thin card (between .15 and .20 mm. in thickness),
sometimes of ordinary card, or little fragments of very thin glass etc., were
affixed at different times to one side of the conical tips of 55 radicles. The
11 last-mentioned cases, but not the preliminary ones, are here included.
The squares, etc., were most commonly affixed with shellac, but in 19 cases
with thick gum-water. When the latter was used, the squares were
sometimes found, as previously stated, to be separated from the apex by a
layer of thick fluid, so that there was no contact, and consequently no
bending of the radicle; and such few cases were not recorded. But in every
instance in which shellac was employed, unless the square fell off very
soon, the result was recorded. In several instances when the squares became
displaced, so as to stand parallel to the radicle, or were separated by fluid
from the apex, or soon fell off, fresh squares were attached, and these cases
(described under the numbered paragraphs) are here included. Out of 55
radicles experimented on under the proper temperature, 52 became bent,
generally to a considerable extent from the perpendicular, and away from
the side to which the object was attached. Of the three failures, one can be
accounted for, as the radicle became sickly on the following day; and a
second was observed only during 11 h. 30 m. As in several cases the
terminal growing part of the radicle continued for some time to bend from
the attached object, it formed itself into a hook, with the apex pointing to
the zenith, or even into a ring, and occasionally into a spire or helix. It is
remarkable that these latter cases occurred more frequently when objects
were attached with thick gum-water, which never became dry, than when
shellac was employed. The curvature was often well-marked in from 7 h. to
11 h.; and in one instance a semicircle was formed in 6 h. 10 m, from the
time of attachment. But in order to see the phenomenon as well displayed as
in the above described cases, it is indispensable that the bits of card, etc.,
should be made to adhere closely to one side of the conical apex; that
healthy radicles should be selected and kept at not too high or too low a
temperature, and apparently that the trials should not be made in the middle
of the winter.

In ten instances, radicles which had curved away from a square of card or
other object attached to their tips, straightened themselves to a certain
extent, or even completely, in the course of from one to two days from the
time of attachment. This was more especially apt to occur when the
curvature was slight. But in one instance (No. 27) a radicle which in 9 h.
had been deflected about 90° from the perpendicular, became quite straight
in 24 h. from the period of attachment. With No. 26, the radicle was almost
straight in 48 h. We at first attributed the straightening process to the
radicles becoming accustomed to a slight stimulus, in the same manner as a
tendril or sensitive petiole becomes accustomed to a very light loop of
thread, and unbends itself though the loop remains still suspended; but
Sachs states[2] that radicles of the bean placed horizontally in damp air after
curving downwards through geotropism, straighten themselves a little by
growth along their lower or concave sides. Why this should occur is not
clear: but perhaps it likewise occurred in the above ten cases. There is
another occasional movement which must not be passed over: the tip of the
radicle, for a length of from 2 to 3 mm., was found in six instances, after an
interval of about 24 or more hours, bent towards the bit of still attached
card,—that is, in a direction exactly opposite to the previously induced
curvature of the whole growing part for a length of from 7 to 8 mm. This
occurred chiefly when the first curvature was small, and when an object had
been affixed more than once to the apex of the same radicle. The attachment
of a bit of card by shellac to one side of the tender apex may sometimes
mechanically prevent its growth; or the application of thick gum-water
more than once to the same side may injure it; and then checked growth on
this side with continued growth on the opposite and unaffected side would
account for the reversed curvature of the apex.
[2] ‘Arbeiten Bot. Instit., Würzburg,’ Heft iii. p. 456.

Various trials were made for ascertaining, as far as we could, the nature
and degree of irritation to which the apex must be subjected, in order that
the terminal growing part should bend away, as if to avoid the cause of
irritation. We have seen in the numbered experiments, that a little square of
rather thick letter-paper gummed to the apex induced, though slowly,
considerable deflection. Judging from several cases in which various
objects had been affixed with gum, and had soon become separated from
the apex by a layer of fluid, as well as from some trials in which drops of

thick gum-water alone had been applied, this fluid never causes bending.
We have also seen in the numbered experiments that narrow splinters of
quill and of very thin glass, affixed with shellac, caused only a slight degree
of deflection, and this may perhaps have been due to the shellac itself. Little
squares of goldbeaters’ skin, which is excessively thin, were damped, and
thus made to adhere to one side of the tips of two radicles; one of these,
after 24 h., produced no effect; nor did the other in 8 h., within which time
squares of card usually act; but after 24 h. there was slight deflection.
An oval bead, or rather cake, of dried shellac, 1.01 mm. in length and
0.63 in breadth, caused a radicle to become deflected at nearly right angles
in the course of only 6 h.; but after 23 h. it had nearly straightened itself. A
very small quantity of dissolved shellac was spread over a bit of card, and
the tips of 9 radicles were touched laterally with it; only two of them
became slightly deflected to the side opposite to that bearing the speck of
dried shellac, and they afterwards straightened themselves. These specks
were removed, and both together weighed less than 1/100th of a grain; so
that a weight of rather less than 1/200th of a grain (0.32 mg.) sufficed to
excite movement in two out of the nine radicles. Here then we have
apparently reached nearly the minimum weight which will act.
A moderately thick bristle (which on measurement was found rather
flattened, being 0.33 mm. in one diameter, and 0.20 mm. in the other) was
cut into lengths of about 1/20th of an inch. These after being touched with
thick gum-water, were placed on the tips of eleven radicles. Three of them
were affected; one being deflected in 8 h. 15 m. to an angle of about 90°
from the perpendicular; a second to the same amount when looked at after 9
h.; but after 24 h. from the time of first attachment the deflection had
decreased to only 19°; the third was only slightly deflected after 9 h., and
the bit of bristle was then found not touching the apex; it was replaced, and
after 15 additional hours the deflection amounted to 26° from the
perpendicular. The remaining eight radicles were not at all acted on by the
bits of bristle, so that we here appear to have nearly reached the minimum
of size of an object which will act on the radicle of the bean. But it is
remarkable that when the bits of bristle did act, that they should have acted
so quickly and efficiently.
As the apex of a radicle in penetrating the ground must be pressed on all
sides, we wished to learn whether it could distinguish between harder or

more resisting, and softer substances. A square of the sanded paper, almost
as stiff as card, and a square of extremely thin paper (too thin for writing
on), of exactly the same size (about 1/20th of an inch), were fixed with
shellac on opposite sides of the apices of 12 suspended radicles. The sanded
card was between 0.15 and 0.20 mm. (or between 0.0059 and 0.0079 of an
inch), and the thin paper only 0.045 mm. (or 0.00176 of an inch) in
thickness. In 8 out of the 12 cases there could be no doubt that the radicle
was deflected from the side to which the card-like paper was attached, and
towards the opposite side, bearing the very thin paper. This occurred in
some instances in 9 h., but in others not until 24 h. had elapsed. Moreover,
some of the four failures can hardly be considered as really failures: thus, in
one of them, in which the radicle remained quite straight, the square of thin
paper was found, when both were removed from the apex, to have been so
thickly coated with shellac that it was almost as stiff as the card: in the
second case, the radicle was bent upwards into a semicircle, but the
deflection was not directly from the side bearing the card, and this was
explained by the two squares having become cemented laterally together,
forming a sort of stiff gable, from which the radicle was deflected: in the
third case, the square of card had been fixed by mistake in front, and though
there was deflection from it, this might have been due to Sachs’ curvature:
in the fourth case alone no reason could be assigned why the radicle had not
been at all deflected. These experiments suffice to prove that the apex of the
radicle possesses the extraordinary power of discriminating between thin
card and very thin paper, and is deflected from the side pressed by the more
resisting or harder substance.
Some trials were next made by irritating the tips without any object being
left in contact with them. Nine radicles, suspended over water, had their tips
rubbed, each six times with a needle, with sufficient force to shake the
whole bean; the temperature was favourable, viz. about 63° F. In 7 out of
these cases no effect whatever was produced; in the eighth case the radicle
became slightly deflected from, and in the ninth case slightly deflected
towards, the rubbed side; but these two latter opposed curvatures were
probably accidental, as radicles do not always grow perfectly straight
downwards. The tips of two other radicles were rubbed in the same manner
for 15 seconds with a little round twig, two others for 30 seconds, and two
others for 1 minute, but without any effect being produced. We may
therefore conclude from these 15 trials that the radicles are not sensitive to

temporary contact, but are acted on only by prolonged, though very slight,
pressure.
We then tried the effects of cutting off a very thin slice parallel to one of
the sloping sides of the apex, as we thought that the wound would cause
prolonged irritation, which might induce bending towards the opposite side,
as in the case of an attached object. Two preliminary trials were made:
firstly, slices were cut from the radicles of 6 beans suspended in damp air,
with a pair of scissors, which, though sharp, probably caused considerable
crushing, and no curvature followed. Secondly, thin slices were cut with a
razor obliquely off the tips of three radicles similarly suspended; and after
44 h. two were found plainly bent from the sliced surface; and the third, the
whole apex of which had been cut off obliquely by accident, was curled
upwards over the bean, but it was not clearly ascertained whether the
curvature had been at first directed from the cut surface. These results led us
to pursue the experiment, and 18 radicles, which had grown vertically
downwards in damp air, had one side of their conical tips sliced off with a
razor. The tips were allowed just to enter the water in the jars, and they
were exposed to a temperature 14°–16° C. (57°–61° F.). The observations
were made at different times. Three were examined 12 h. after being sliced,
and were all slightly curved from the cut surface; and the curvature
increased considerably after an additional 12 h. Eight were examined after
19 h.; four after 22 h. 30 m.; and three after 25 h. The final result was that
out of the 18 radicles thus tried, 13 were plainly bent from the cut surface
after the above intervals of time; and one other became so after an
additional interval of 13 h. 30 m. So that only 4 out of the 18 radicles were
not acted on. To these 18 cases the 3 previously mentioned ones should be
added. It may, therefore, be concluded that a thin slice removed by a razor
from one side of the conical apex of the radicle causes irritation, like that
from an attached object, and induces curvature from the injured surface.
Lastly, dry caustic (nitrate of silver) was employed to irritate one side of
the apex. If one side of the apex or of the whole terminal growing part of a
radicle, is by any means killed or badly injured, the other side continues to
grow; and this causes the part to bend over towards the injured side.[3] But
in the following experiments we endeavoured, generally with success, to
irritate the tips on one side, without badly injuring them. This was effected
by first drying the tip as far as possible with blotting-paper, though it still
remained somewhat damp, and then touching it once with quite dry caustic.

Seventeen radicles were thus treated, and were suspended in moist air over
water at a temperature of 58° F. They were examined after an interval of 21
h. or 24h. The tips of two were found blackened equally all round, so that
they could tell nothing and were rejected, 15 being left. Of these, 10 were
curved from the side which had been touched, where there was a minute
brown or blackish mark. Five of these radicles, three of which were already
slightly deflected, were allowed to enter the water in the jar, and were re-
examined after an additional interval of 27 h. (i.e. in 48 h. after the
application of the caustic), and now four of them had become hooked, being
bent from the discoloured side, with their points directed to the zenith; the
fifth remained unaffected and straight. Thus 11 radicles out of the 15 were
acted on. But the curvature of the four just described was so plain, that they
alone would have sufficed to show that the radicles of the bean bend away
from that side of the apex which has been slightly irritated by caustic.
[3] Ciesielski found this to be the case (‘Untersuchungen über die
Abwartskrümmung der Wurzel,’ 1871, p. 28) after burning with heated platinum
one side of a radicle. So did we when we painted longitudinally half of the whole
length of 7 radicles, suspended over water, with a thick layer of grease, which is
very injurious or even fatal to growing parts; for after 48 hours five of these
radicles were curved towards the greased side, two remaining straight.

The Power of an Irritant on the apex of the Radicle of the Bean,
compared with that of Geotropism.—We know that when a little square of
card or other object is fixed to one side of the tip of a vertically dependent
radicle, the growing part bends from it often into a semicircle, in opposition
to geotropism, which force is conquered by the effect of the irritation from
the attached object. Radicles were therefore extended horizontally in damp
air, kept at the proper low temperature for full sensitiveness, and squares of
card were affixed with shellac on the lower sides of their tips, so that if the
squares acted, the terminal growing part would curve upwards. Firstly, eight
beans were so placed that their short, young, horizontally extended radicles
would be simultaneously acted on both by geotropism and by Sachs’
curvature, if the latter came into play; and they all eight became bowed
downwards to the centre of the earth in 20 h., excepting one which was only
slightly acted on. Two of them were a little bowed downwards in only 5 h.!
Therefore the cards, affixed to the lower sides of their tips, seemed to
produce no effect; and geotropism easily conquered the effects of the
irritation thus caused. Secondly, 5 oldish radicles, 1½ inch in length, and

therefore less sensitive than the above-mentioned young ones, were
similarly placed and similarly treated. From what has been seen on many
other occasions, it may be safely inferred that if they had been suspended
vertically they would have bent away from the cards; and if they had been
extended horizontally, without cards attached to them, they would have
quickly bent vertically downwards through geotropism; but the result was
that two of these radicles were still horizontal after 23 h.; two were curved
only slightly, and the fifth as much as 40° beneath the horizon. Thirdly, 5
beans were fastened with their flat surfaces parallel to the cork-lid, so that
Sachs’ curvature would not tend to make the horizontally extended radicles
turn either upwards or downwards, and little squares of card were affixed as
before, to the lower sides of their tips. The result was that all five radicles
were bent down, or towards the centre of the earth, after only 8 h. 20 m. At
the same time and within the same jars, 3 radicles of the same age, with
squares affixed to one side, were suspended vertically; and after 8 h. 20 m.
they were considerably deflected from the cards, and therefore curved
upwards in opposition to geotropism. In these latter cases the irritation from
the squares had over-powered geotropism; whilst in the former cases, in
which the radicles were extended horizontally, geotropism had overpowered
the irritation. Thus within the same jars, some of the radicles were curving
upwards and others downwards at the same time—these opposite
movements depending on whether the radicles, when the squares were first
attached to them, projected vertically down, or were extended horizontally.
This difference in their behaviour seems at first inexplicable, but can, we
believe, be simply explained by the difference between the initial power of
the two forces under the above circumstances, combined with the well-
known principle of the after-effects of a stimulus. When a young and
sensitive radicle is extended horizontally, with a square attached to the
lower side of the tip, geotropism acts on it at right angles, and, as we have
seen, is then evidently more efficient than the irritation from the square; and
the power of geotropism will be strengthened at each successive period by
its previous action—that is, by its after-effects. On the other hand, when a
square is affixed to a vertically dependent radicle, and the apex begins to
curve upwards, this movement will be opposed by geotropism acting only
at a very oblique angle, and the irritation from the card will be strengthened
by its previous action. We may therefore conclude that the initial power of
an irritant on the apex of the radicle of the bean, is less than that of

geotropism when acting at right angles, but greater than that of geotropism
when acting obliquely on it.
Sensitiveness of the tips of the Secondary Radicles of the Bean to
contact.—All the previous observations relate to the main or primary
radicle. Some beans suspended to cork-lids, with their radicles dipping into
water, had developed secondary or lateral radicles, which were afterwards
kept in very damp air, at the proper low temperature for full sensitiveness.
They projected, as usual, almost horizontally, with only a slight downward
curvature, and retained this position during several days. Sachs has shown[4]
that these secondary roots are acted on in a peculiar manner by geotropism,
so that if displaced they reassume their former sub-horizontal position, and
do not bend vertically downwards like the primary radicle. Minute squares
of the stiff sanded paper were affixed by means of shellac (but in some
instances with thick gum-water) to the tips of 39 secondary radicles of
different ages, generally the uppermost ones. Most of the squares were
fixed to the lower sides of the apex, so that if they acted the radicle would
bend upwards; but some were fixed laterally, and a few on the upper side.
Owing to the extreme tenuity of these radicles, it was very difficult to attach
the square to the actual apex. Whether owing to this or some other
circumstance, only nine of the squares induced any curvature. The curvature
amounted in some cases to about 45° above the horizon, in others to 90°,
and then the tip pointed to the zenith. In one instance a distinct upward
curvature was observed in 8 h. 15 m., but usually not until 24 h. had
elapsed. Although only 9 out of 39 radicles were affected, yet the curvature
was so distinct in several of them, that there could be no doubt that the tip is
sensitive to slight contact, and that the growing part bends away from the
touching object. It is possible that some secondary radicles are more
sensitive than others; for Sachs has proved[5] the interesting fact that each
individual secondary radicle possesses its own peculiar constitution.
[4] ‘Arbeiten Bot. Inst., Würzburg,’ Heft iv. 1874, p. 605–617.

[5] ‘Arbeiten Bot. Instit., Würzburg,’ Heft, iv. 1874, p. 620.

Sensitiveness to contact of the Primary Radicle, a little above the apex, in
the Bean (Vicia faba) and Pea (Pisum sativum).—The sensitiveness of the
apex of the radicle in the previously described cases, and the consequent
curvature of the upper part from the touching object or other source of

irritation, is the more remarkable, because Sachs[6] has shown that pressure
at the distance of a few millimeters above the apex causes the radicle to
bend, like a tendril, towards the touching object. By fixing pins so that they
pressed against the radicles of beans suspended vertically in damp air, we
saw this kind of curvature; but rubbing the part with a twig or needle for a
few minutes produced no effect. Haberlandt remarks,[7] that these radicles in
breaking through the seed-coats often rub and press against the ruptured
edges, and consequently bend round them. As little squares of the card-like
paper affixed with shellac to the tips were highly efficient in causing the
radicles to bend away from them, similar pieces (of about 1/20th inch
square, or rather less) were attached in the same manner to one side of the
radicle at a distance of 3 or 4 mm. above the apex. In our first trial on 15
radicles no effect was produced. In a second trial on the same number, three
became abruptly curved (but only one strongly) towards the card within 24
h. From these cases we may infer that the pressure from a bit of card affixed
with shellac to one side above the apex, is hardly a sufficient irritant; but
that it occasionally causes the radicle to bend like a tendril towards this
side.
[6] Ibid. Heft iii. 1873, p. 437.

[7] ‘Die Schutzeinrichtungen der Keimpflanze,’ 1877, p. 25.

We next tried the effect of rubbing several radicles at a distance of 4 mm.
from the apex for a few seconds with lunar caustic (nitrate of silver); and
although the radicles had been wiped dry and the stick of caustic was dry,
yet the part rubbed was much injured and a slight permanent depression
was left. In such cases the opposite side continues to grow, and the radicle
necessarily becomes bent towards the injured side. But when a point 4 mm.
from the apex was momentarily touched with dry caustic, it was only faintly
discoloured, and no permanent injury was caused. This was shown by
several radicles thus treated straightening themselves after one or two days;
yet at first they became curved towards the touched side, as if they had been
there subjected to slight continued pressure. These cases deserve notice,
because when one side of the apex was just touched with caustic, the
radicle, as we have seen, curved itself in an opposite direction, that is, away
from the touched side.

The radicle of the common pea at a point a little above the apex is rather
more sensitive to continued pressure than that of the bean, and bends
towards the pressed side.[8] We experimented on a variety (Yorkshire Hero)
which has a much wrinkled tough skin, too large for the included
cotyledons; so that out of 30 peas which had been soaked for 24 h. and
allowed to germinate on damp sand, the radicles of three were unable to
escape, and were crumpled up in a strange manner within the skin; four
other radicles were abruptly bent round the edges of the ruptured skin
against which they had pressed. Such abnormalities would probably never,
or very rarely, occur with forms developed in a state of nature and subjected
to natural selection. One of the four radicles just mentioned in doubling
backwards came into contact with the pin by which the pea was fixed to the
cork-lid; and now it bent at right angles round the pin, in a direction quite
different from that of the first curvature due to contact with the ruptured
skin; and it thus afforded a good illustration of the tendril-like sensitiveness
of the radicle a little above the apex.
[8] Sachs, ‘Arbeiten Bot. Institut., Würzburg,’ Heft iii. p. 438.

Little squares of the card-like paper were next affixed to radicles of the
pea at 4 mm. above the apex, in the same manner as with the bean. Twenty-
eight radicles suspended vertically over water were thus treated on different
occasions, and 13 of them became curved towards the cards. The greatest
degree of curvature amounted to 62° from the perpendicular; but so large an
angle was only once formed. On one occasion a slight curvature was
perceptible after 5 h. 45 m., and it was generally well-marked after 14 h.
There can therefore be no doubt that with the pea, irritation from a bit of
card attached to one side of the radicle above the apex suffices to induce
curvature.
Squares of card were attached to one side of the tips of 11 radicles within
the same jars in which the above trials were made, and five of them became
plainly, and one slightly, curved away from this side. Other analogous cases
will be immediately described. The fact is here mentioned because it was a
striking spectacle, showing the difference in the sensitiveness of the radicle
in different parts, to behold in the same jar one set of radicles curved away
from the squares on their tips, and another set curved towards the squares
attached a little higher up. Moreover, the kind of curvature in the two cases
is different. The squares attached above the apex cause the radicle to bend

abruptly, the part above and beneath remaining nearly straight; so that here
there is little or no transmitted effect. On the other hand, the squares
attached to the apex affect the radicle for a length of from about 4 to even 8
mm., inducing in most cases a symmetrical curvature; so that here some
influence is transmitted from the apex for this distance along the radicle.
Pisum sativum (var. Yorkshire Hero): Sensitiveness of the apex of the
Radicle.—Little squares of the same card-like paper were affixed (April
24th) with shellac to one side of the apex of 10 vertically suspended
radicles: the temperature of the water in the bottom of the jars was 60°–61°
F. Most of these radicles were acted on in 8 h. 30 m.; and eight of them
became in the course of 24 h. conspicuously, and the remaining two
slightly, deflected from the perpendicular and from the side bearing the
attached squares. Thus all were acted on; but it will suffice to describe two
conspicuous cases. In one the terminal portion of the radicle was bent at
right angles (A, Fig. 66) after 24h.; and in the other (B) it had by this time
become hooked, with the apex pointing to the zenith. The two bits of card
here used were .07 inch in length and .04 inch in breadth. Two other
radicles, which after 8 h. 30 m. were moderately deflected, became straight
again after 24h. Another trial was made in the same manner with 15
radicles; but from circumstances, not worth explaining, they were only once
and briefly examined after the short interval of 5 h. 30 m.; and we merely
record in our notes “almost all bent slightly from the perpendicular, and
away from the squares; the deflection amounting in one or two instances to
nearly a rectangle.” These two sets of cases, especially the first one, prove
that the apex of the radicle is sensitive to slight contact and that the upper
part bends from the touching object. Nevertheless, on June 1st and 4th, 8
other radicles were tried in the same manner at a temperature of 58°–60° F.,
and after 24 h. only 1 was decidedly bent from the card, 4 slightly, 2
doubtfully, and 1 not in the least. The amount of curvature was
unaccountably small; but all the radicles which were at all bent, were bent
away from the cards.
Fig. 66. Pisum sativum: deflection produced within 24 hours in the
growth of vertically dependent radicles, by little squares of card affixed
with shellac to one side of apex: A, bent at right angles; B, hooked.
We now tried the effects of widely different temperatures on the
sensitiveness of these radicles with squares of card attached to their tips.

Firstly, 13 peas, most of them having very short and young radicles, were
placed in an ice-box, in which the temperature rose during three days from
44° to 47° F. They grew slowly, but 10 out of the 13 became in the course
of the three days very slightly curved from the squares; the other 3 were not
affected; so that this temperature was too low for any high degree of
sensitiveness or for much movement. Jars with 13 other radicles were next
placed on a chimney-piece, where they were subjected to a temperature of
between 68° and 72° F., and after 24 h., 4 were conspicuously curved from
the cards, 2 slightly, and 7 not at all; so that this temperature was rather too
high. Lastly 12 radicles were subjected to a temperature varying between
72° and 85° F., and none of them were in the least affected by the squares.
The above several trials, especially the first recorded one, indicate that the
most favourable temperature for the sensitiveness of the radicle of the pea is
about 60° F.
The tips of 6 vertically dependent radicles were touched once with dry
caustic, in the manner described under Vicia faba. After 24 h. four of them
were bent from the side bearing a minute black mark; and the curvature
increased in one case after 38 h., and in another case after 48 h., until the
terminal part projected almost horizontally. The two remaining radicles
were not affected.
With radicles of the bean, when extended horizontally in damp air,
geotropism always conquered the effects of the irritation caused by squares
of card attached to the lower sides of their tips. A similar experiment was
tried on 13 radicles of the pea; the squares being attached with shellac, and
the temperature between 58°–60° F. The result was somewhat different; for
these radicles are either less strongly acted on by geotropism, or, what is
more probable, are more sensitive to contact. After a time geotropism
always prevailed, but its action was often delayed; and in three instances
there was a most curious struggle between geotropism and the irritation
caused by the cards. Four of the 13 radicles were a little curved downwards
within 6 or 8 h., always reckoning from the time when the squares were
first attached, and after 23 h. three of them pointed vertically downwards,
and the fourth at an angle of 45° beneath the horizon. These four radicles
therefore did not seem to have been at all affected by the attached squares.
Four others were not acted on by geotropism within the first 6 or 8 h., but
after 23 h. were much bowed down. Two others remained almost horizontal
for 23 h., but afterwards were acted on. So that in these latter six cases the

action of geotropism was much delayed. The eleventh radicle was slightly
curved down after 8 h., but when looked at again after 23 h. the terminal
portion was curved upwards; if it had been longer observed, the tip no
doubt would have been found again curved down, and it would have formed
a loop as in the following case. The twelfth radicle after 6 h. was slightly
curved downwards; but when looked at again after 21 h., this curvature had
disappeared and the apex pointed upwards; after 30 h. the radicle formed a
hook, as shown at A (Fig. 67); which hook after 45 h. was converted into a
loop (B). The thirteenth radicle after 6 h. was slightly curved downwards,
but within 21 h. had curved considerably up, and then down again at an
angle of 45° beneath the horizon, afterwards becoming perpendicular. In
these three last cases geotropism and the irritation caused by the attached
squares alternately prevailed in a highly remarkable manner; geotropism
being ultimately victorious.
Fig. 67. Pisum sativum: a radicle extended horizontally in damp air with
a little square of card affixed to the lower side of its tip, causing it to bend
upwards in opposition to geotropism. The deflection of the radicle after 21
hours is shown at A, and of the same radicle after 45 hours at B, now
forming a loop.
Similar experiments were not always quite so successful as in the above
cases. Thus 6 radicles, horizontally extended with attached squares, were
tried on June 8th at a proper temperature, and after 7 h. 30 m. none were in
the least curved upwards and none were distinctly geotropic; whereas of 6
radicles without any attached squares, which served as standards of
comparison or controls, 3 became slightly and 3 almost rectangularly
geotropic within the 7 h. 30 m.; but after 23 h. the two lots were equally
geotropic. On July 10th another trial was made with 6 horizontally extended
radicles, with squares attached in the same manner beneath their tips; and
after 7 h. 30 m., 4 were slightly geotropic, 1 remained horizontal, and 1 was
curved upwards in opposition to gravity or geotropism. This latter radicle
after 48 h. formed a loop, like that at B (Fig. 67).
An analogous trial was now made, but instead of attaching squares of
card to the lower sides of the tips, these were touched with dry caustic. The
details of the experiment will be given in the chapter on Geotropism, and it
will suffice here to say that 10 peas, with radicles extended horizontally and
not cauterised, were laid on and under damp friable peat; these, which

served as standards or controls, as well as 10 others which had been
touched on the upper side with the caustic, all became strongly geotropic in
24 h. Nine radicles, similarly placed, had their tips touched on the lower
side with the caustic; and after 24 h., 3 were slightly geotropic, 2 remained
horizontal, and 4 were bowed upwards in opposition to gravity and to
geotropism. This upward curvature was distinctly visible in 8 h. 45m. after
the lower sides of the tips had been cauterised.
Little squares of card were affixed with shellac on two occasions to the
tips of 22 young and short secondary radicles, which had been emitted from
the primary radicle whilst growing in water, but were now suspended in
damp air. Besides the difficulty of attaching the squares to such finely
pointed objects as were these radicles, the temperature was too high,—
varying on the first occasion from 72° to 77° F., and on the second being
almost steadily 78° F.; and this probably lessened the sensitiveness of the
tips. The result was that after an interval of 8 h. 30 m., 6 of the 22 radicles
were bowed upwards (one of them greatly) in opposition to gravity, and 2
laterally; the remaining 14 were not affected. Considering the unfavourable
circumstances, and bearing in mind the case of the bean, the evidence
appears sufficient to show that the tips of the secondary radicles of the pea
are sensitive to slight contact.
Phaseolus multiflorus: Sensitiveness of the apex of the Radicle.—Fifty-
nine radicles were tried with squares of various sizes of the same card-like
paper, also with bits of thin glass and rough cinders, affixed with shellac to
one side of the apex. Rather large drops of the dissolved shellac were also
placed on them and allowed to set into hard beads. The specimens were
subjected to various temperatures between 60° and 72° F., more commonly
at about the latter. But out of this considerable number of trials only 5
radicles were plainly bent, and 8 others slightly or even doubtfully, from the
attached objects; the remaining 46 not being at all affected. It is therefore
clear that the tips of the radicles of this Phaseolus are much less sensitive to
contact than are those of the bean or pea. We thought that they might be
sensitive to harder pressure, but after several trials we could not devise any
method for pressing harder on one side of the apex than on the other,
without at the same time offering mechanical resistance to its growth. We
therefore tried other irritants.

The tips of 13 radicles, dried with blotting-paper, were thrice touched or
just rubbed on one side with dry nitrate of silver. They were rubbed thrice,
because we supposed from the foregoing trials, that the tips were not highly
sensitive. After 24 h. the tips were found greatly blackened; 6 were
blackened equally all round, so that no curvature to any one side could be
expected; 6 were much blackened on one side for a length of about 1/10th
of an inch, and this length became curved at right angles towards the
blackened surface, the curvature afterwards increasing in several instances
until little hooks were formed. It was manifest that the blackened side was
so much injured that it could not grow, whilst the opposite side continued to
grow. One alone out of these 13 radicles became curved from the blackened
side, the curvature extending for some little distance above the apex.
After the experience thus gained, the tips of six almost dry radicles were
once touched with the dry caustic on one side; and after an interval of 10 m.
were allowed to enter water, which was kept at a temperature of 65°–67° F.
The result was that after an interval of 8 h. a minute blackish speck could
just be distinguished on one side of the apex of five of these radicles, all of
which became curved towards the opposite side—in two cases at about an
angle of 45°—in two other cases at nearly a rectangle—and in the fifth case
at above a rectangle, so that the apex was a little hooked; in this latter case
the black mark was rather larger than in the others. After 24 h. from the
application of the caustic, the curvature of three of these radicles (including
the hooked one) had diminished; in the fourth it remained the same, and in
the fifth it had increased, the tip being now hooked. It has been said that
after 8 h. black specks could be seen on one side of the apex of five of the
six radicles; on the sixth the speck, which was extremely minute, was on the
actual apex and therefore central; and this radicle alone did not become
curved. It was therefore again touched on one side with caustic, and after 15
h. 30 m. was found curved from the perpendicular and from the blackened
side at an angle of 34°, which increased in nine additional hours to 54°.
It is therefore certain that the apex of the radicle of this Phaseolus is
extremely sensitive to caustic, more so than that of the bean, though the
latter is far more sensitive to pressure. In the experiments just given, the
curvature from the slightly cauterised side of the tip, extended along the
radicle for a length of nearly 10 mm.; whereas in the first set of
experiments, when the tips of several were greatly blackened and injured on
one side, so that their growth was arrested, a length of less than 3 mm.

became curved towards the much blackened side, owing to the continued
growth of the opposite side. This difference in the results is interesting, for
it shows that too strong an irritant does not induce any transmitted effect,
and does not cause the adjoining, upper and growing part of the radicle to
bend. We have analogous cases with Drosera, for a strong solution of
carbonate of ammonia when absorbed by the glands, or too great heat
suddenly applied to them, or crushing them, does not cause the basal part of
the tentacles to bend, whilst a weak solution of the carbonate, or a moderate
heat, or slight pressure always induced such bending. Similar results were
observed with Dionaea and Pinguicula.
The effect of cutting off with a razor a thin slice from one side of the
conical apex of 14 young and short radicles was next tried. Six of them after
being operated on were suspended in damp air; the tips of the other eight,
similarly suspended, were allowed to enter water at a temperature of about
65° F. It was recorded in each case which side of the apex had been sliced
off, and when they were afterwards examined the direction of the curvature
was noted, before the record was consulted. Of the six radicles in damp air,
three had their tips curved after an interval of 10 h. 15 m. directly away
from the sliced surface, whilst the other three were not affected and
remained straight; nevertheless, one of them after 13 additional hours
became slightly curved from the sliced surface. Of the eight radicles with
their tips immersed in water, seven were plainly curved away from the
sliced surfaces after 10 h. 15 m.; and with respect to the eighth which
remained quite straight, too thick a slice had been accidentally removed, so
that it hardly formed a real exception to the general result. When the seven
radicles were looked at again, after an interval of 23 h. from the time of
slicing, two had become distorted; four were deflected at an angle of about
70° from the perpendicular and from the cut surface; and one was deflected
at nearly 90°, so that it projected almost horizontally, but with the extreme
tip now beginning to bend downwards through the action of geotropism. It
is therefore manifest that a thin slice cut off one side of the conical apex,
causes the upper growing part of the radicle of this Phaseolus to bend,
through the transmitted effects of the irritation, away from the sliced
surface.
Tropaeolum majus: Sensitiveness of the apex of the Radicle to contact.—
Little squares of card were attached with shellac to one side of the tips of 19
radicles, some of which were subjected to 78° F., and others to a much

lower temperature. Only 3 became plainly curved from the squares, 5
slightly, 4 doubtfully, and 7 not at all. These seeds were, as we believed,
old, so we procured a fresh lot, and now the results were widely different.
Twenty-three were tried in the same manner; five of the squares produced
no effect, but three of these cases were no real exceptions, for in two of
them the squares had slipped and were parallel to the apex, and in the third
the shellac was in excess and had spread equally all round the apex. One
radicle was deflected only slightly from the perpendicular and from the
card; whilst seventeen were plainly deflected. The angles in several of these
latter cases varied between 40° and 65° from the perpendicular; and in two
of them it amounted after 15 h. or 16 h. to about 90°. In one instance a loop
was nearly completed in 16 h. There can, therefore, be no doubt that the
apex is highly sensitive to slight contact, and that the upper part of the
radicle bends away from the touching object.
Gossypium herbaceum: Sensitiveness of the apex of the Radicle.—
Radicles were experimented on in the same manner as before, but they
proved ill-fitted for our purpose, as they soon became unhealthy when
suspended in damp air. Of 38 radicles thus suspended, at temperatures
varying from 66° to 69° F., with squares of card attached to their tips, 9
were plainly and 7 slightly or even doubtfully deflected from the squares
and from the perpendicular; 22 not being affected. We thought that perhaps
the above temperature was not high enough, so 19 radicles with attached
squares, likewise suspended in damp air, were subjected to a temperature of
from 74° to 79° F., but not one of them was acted on, and they soon became
unhealthy. Lastly, 19 radicles were suspended in water at a temperature
from 70° to 75° F., with bits of glass or squares of the card attached to their
tips by means of Canada-balsam or asphalte, which adhered rather better
than shellac beneath the water. The radicles did not keep healthy for long.
The result was that 6 were plainly and 2 doubtfully deflected from the
attached objects and the perpendicular; 11 not being affected. The evidence
consequently is hardly conclusive, though from the two sets of cases tried
under a moderate temperature, it is probable that the radicles are sensitive to
contact; and would be more so under favourable conditions.
Fifteen radicles which had germinated in friable peat were suspended
vertically over water. Seven of them served as controls, and they remained
quite straight during 24 h. The tips of the other eight radicles were just
touched with dry caustic on one side. After only 5 h. 10 m. five of them

were slightly curved from the perpendicular and from the side bearing the
little blackish marks. After 8 h. 40 m., 4 out of these 5 were deflected at
angles between 15° and 65° from the perpendicular. On the other hand, one
which had been slightly curved after 5 h. 10 m., now became straight. After
24 h. the curvature in two cases had considerably increased; also in four
other cases, but these latter radicles had now become so contorted, some
being turned upwards, that it could no longer be ascertained whether they
were still curved from the cauterised side. The control specimens exhibited
no such irregular growth, and the two sets presented a striking contrast. Out
of the 8 radicles which had been touched with caustic, two alone were not
affected, and the marks left on their tips by the caustic were extremely
minute. These marks in all cases were oval or elongated; they were
measured in three instances, and found to be of nearly the same size, viz.
2/3 of a mm. in length. Bearing this fact in mind, it should be observed that
the length of the curved part of the radicle, which had become deflected
from the cauterised side in the course of 8 h. 40 m. was found to be in three
cases 6, 7, and 9 mm.

Cucurbita ovifera: Sensitiveness of the apex of the Radicle.—The tips
proved ill-fitted for the attachment of cards, as they are extremely fine and
flexible. Moreover, owing to the hypocotyls being soon developed and
becoming arched, the whole radicle is quickly displaced and confusion is
thus caused. A large number of trials were made, but without any definite
result, excepting on two occasions, when out of 23 radicles 10 were
deflected from the attached squares of card, and 13 were not acted on.
Rather large squares, though difficult to affix, seemed more efficient than
very small ones.
We were much more successful with caustic; but in our first trial, 15
radicles were too much cauterised, and only two became curved from the
blackened side; the others being either killed on one side, or blackened
equally all round. In our next trial the dried tips of 11 radicles were touched
momentarily with dry caustic, and after a few minutes were immersed in
water. The elongated marks thus caused were never black, only brown, and
about ½ mm. in length, or even less. In 4 h. 30 m. after the cauterisation, 6
of them were plainly curved from the side with the brown mark, 4 slightly,
and 1 not at all. The latter proved unhealthy, and never grew; and the marks

on 2 of the 4 slightly curved radicles were excessively minute, one being
distinguishable only with the aid of a lens. Of 10 control specimens tried in
the same jars at the same time, not one was in the least curved. In 8 h. 40 m.
after the cauterisation, 5 of the radicles out of the 10 (the one unhealthy one
being omitted) were deflected at about 90°, and 3 at about 45° from the
perpendicular and from the side bearing the brown mark. After 24 h. all 10
radicles had increased immensely in length; in 5 of them the curvature was
nearly the same, in 2 it had increased, and in 3 it had decreased. The
contrast presented by the 10 controls, after both the 8 h. 40 m. and the 24 h.
intervals, was very great; for they had continued to grow vertically
downwards, excepting two which, from some unknown cause, had become
somewhat tortuous.
In the chapter on Geotropism we shall see that 10 radicles of this plant
were extended horizontally on and beneath damp friable peat, under which
conditions they grow better and more naturally than in damp air; and their
tips were slightly cauterised on the lower side, brown marks about ½ mm.
in length being thus caused. Uncauterised specimens similarly placed
became much bent downwards through geotropism in the course of 5 or 6
hours. After 8 h. only 3 of the cauterised ones were bowed downwards, and
this in a slight degree; 4 remained horizontal; and 3 were curved upwards in
opposition to geotropism and from the side bearing the brown mark. Ten
other specimens had their tips cauterised at the same time and in the same
degree, on the upper side; and this, if it produced any effect, would tend to
increase the power of geotropism; and all these radicles were strongly
bowed downwards after 8 h. From the several foregoing facts, there can be
no doubt that the cauterisation of the tip of the radicle of this Cucurbita on
one side, if done lightly enough, causes the whole growing part to bend to
the opposite side. Raphanus sativus: Sensitiveness of the apex of the
Radicle.—We here encountered many difficulties in our trials, both with
squares of card and with caustic; for when seeds were pinned to a cork-lid,
many of the radicles, to which nothing had been done, grew irregularly,
often curving upwards, as if attracted by the damp surface above; and when
they were immersed in water they likewise often grew irregularly. We did
not therefore dare to trust our experiments with attached squares of card;
nevertheless some of them seemed to indicate that the tips were sensitive to
contact. Our trials with caustic generally failed from the difficulty of not
injuring too greatly the extremely fine tips. Out of 7 radicles thus tried, one

became bowed after 22 h. at an angle of 60°, a second at 40°, and a third
very slightly from the perpendicular and from the cauterised side.
Æsculus hippocastanum: Sensitiveness of the apex of the Radicle.—Bits
of glass and squares of card were affixed with shellac or gum-water to the
tips of 12 radicles of the horse-chestnut; and when these objects fell off,
they were refixed; but not in a single instance was any curvature thus
caused. These massive radicles, one of which was above 2 inches in length
and .3 inch in diameter at its base, seemed insensible to so slight a stimulus
as any small attached object. Nevertheless, when the apex encountered an
obstacle in its downward course, the growing part became so uniformly and
symmetrically curved, that its appearance indicated not mere mechanical
bending, but increased growth along the whole convex side, due to the
irritation of the apex.
That this is the correct view may be inferred from the effects of the more
powerful stimulus of caustic. The bending from the cauterised side occurred
much slower than in the previously described species, and it will perhaps be
worth while to give our trials in detail.
The seeds germinated in sawdust, and one side of the tips of the radicles
were slightly rubbed once with dry nitrate of silver; and after a few minutes
were allowed to dip into water. They were subjected to a rather varying
temperature, generally between 52° and 58° F. A few cases have not been
thought worth recording, in which the whole tip was blackened, or in which
the seedling soon became unhealthy.
(1.) The radicle was slightly deflected from the cauterised side in one day
(i.e. 24 h.); in three days it stood at 60° from the perpendicular; in four days
at 90°; on the fifth day it was curved up about 40° above the horizon; so
that it had passed through an angle of 130° in the five days, and this was the
greatest amount of curvature observed.
(2.) In two days radicle slightly deflected; after seven days deflected 69°
from the perpendicular and from the cauterised side; after eight days the
angle amounted to nearly 90°.
(3.) After one day slight deflection, but the cauterised mark was so faint
that the same side was again touched with caustic. In four days from the
first touch deflection amounted to 78°, which in an additional day increased
to 90°.

(4.) After two days slight deflection, which during the next three days
certainly increased but never became great; the radicle did not grow well
and died on the eighth day.
(5.) After two days very slight deflection; but this on the fourth day
amounted to 56° from the perpendicular and from the cauterised side.
(6.) After three days doubtfully, but after four days certainly deflected
from the cauterised side. On the fifth day deflection amounted to 45° from
the perpendicular, and this on the seventh day increased to about 90°.
(7.) After two days slightly deflected; on the third day the deflection
amounted to 25° from the perpendicular, and this did not afterwards
increase.
(8.) After one day deflection distinct; on the third day it amounted to 44°,
and on the fourth day to 72° from the perpendicular and the cauterised side.
(9.) After two days deflection slight, yet distinct; on the third day the tip
was again touched on the same side with caustic and thus killed.
(10.) After one day slight deflection, which after six days increased to
50° from the perpendicular and the cauterised side.
(11.) After one day decided deflection, which after six days increased to
62° from the perpendicular and from the cauterised side.
(12.) After one day slight deflection, which on the second day amounted
to 35°, on the fourth day to 50°, and the sixth day to 63° from the
perpendicular and the cauterised side.
(13.) Whole tip blackened, but more on one side than the other; on the
fourth day slightly, and on the sixth day greatly deflected from the more
blackened side; the deflection on the ninth day amounted to 90° from the
perpendicular.
(14.) Whole tip blackened in the same manner as in the last case: on the
second day decided deflection from the more blackened side, which
increased on the seventh day to nearly 90°; on the following day the radicle
appeared unhealthy.
(15.) Here we had the anomalous case of a radicle bending slightly
towards the cauterised side on the first day, and continuing to do so for the
next three days, when the deflection amounted to about 90° from the
perpendicular. The cause appeared to lie in the tendril-like sensitiveness of
the upper part of the radicle, against which the point of a large triangular

flap of the seed-coats pressed with considerable force; and this irritation
apparently conquered that from the cauterised apex.

These several cases show beyond doubt that the irritation of one side of
the apex, excites the upper part of the radicle to bend slowly towards the
opposite side. This fact was well exhibited in one lot of five seeds pinned to
the cork-lid of a jar; for when after 6 days the lid was turned upside down
and viewed from directly above, the little black marks made by the caustic
were now all distinctly visible on the upper sides of the tips of the laterally
bowed radicles. A thin slice was shaved off with a razor from one side of
the tips of 22 radicles, in the manner described under the common bean; but
this kind of irritation did not prove very effective. Only 7 out of the 22
radicles became moderately deflected in from 3 to 5 days from the sliced
surface, and several of the others grew irregularly. The evidence, therefore,
is far from conclusive.
Quercus robur: Sensitiveness of the apex of the Radicle.—The tips of the
radicles of the common oak are fully as sensitive to slight contact as are
those of any plant examined by us. They remained healthy in damp air for
10 days, but grew slowly. Squares of the card-like paper were fixed with
shellac to the tips of 15 radicles, and ten of these became conspicuously
bowed from the perpendicular and from the squares; two slightly, and three
not at all. But two of the latter were not real exceptions, as they were at first
very short, and hardly grew afterwards. Some of the more remarkable cases
are worth describing. The radicles were examined on each successive
morning, at nearly the same hour, that is, after intervals of 24 h.

No. 1. This radicle suffered from a series of accidents, and acted in an
anomalous manner, for the apex appeared at first insensible and afterwards
sensitive to contact. The first square was attached on Oct 19th; on the 21st
the radicle was not at all curved, and the square was accidentally knocked
off; it was refixed on the 22nd, and the radicle became slightly curved from
the square, but the curvature disappeared on the 23rd, when the square was
removed and refixed. No curvature ensued, and the square was again
accidentally knocked off, and refixed. On the morning of the 27th it was
washed off by having reached the water in the bottom of the jar. The square

was refixed, and on the 29th, that is, ten days after the first square had been
attached, and two days after the attachment of the last square, the radicle
had grown to the great length of 3.2 inches, and now the terminal growing
part had become bent away from the square into a hook (see Fig. 68).
Fig. 68. Quercus robur: radicle with square of card attached to one side of
apex, causing it to become hooked. Drawing one-half natural scale.
No. 2. Square attached on the 19th; on the 20th radicle slightly deflected
from it and from the perpendicular; on the 21st deflected at nearly right
angles; it remained during the next two days in this position, but on the 25th
the upward curvature was lessened through the action of geotropism, and
still more so on the 26th.
No. 3. Square attached on the 19th; on the 21st a trace of curvature from
the square, which amounted on the 22nd to about 40°, and on the 23rd to
53° from the perpendicular.
No. 4. Square attached on the 21st; on the 22nd trace of curvature from
the square; on the 23rd completely hooked with the point turned up to the
zenith. Three days afterwards (i.e. 26th) the curvature had wholly
disappeared and the apex pointed perpendicularly downwards.
No. 5. Square attached on the 21st; on the 22nd decided though slight
curvature from the square; on the 23rd the tip had curved up above the
horizon, and on the 24th was hooked with the apex pointing almost to the
zenith, as in Fig. 68.
No. 6. Square attached on the 21st; on the 22nd slightly curved from the
square; 23rd more curved; 25th considerably curved; 27th all curvature lost,
and the radicle was now directed perpendicularly downwards.
No. 7. Square attached on the 21st; on the 22nd a trace of curvature from
the square, which increased next day, and on the 24th amounted to a right
angle.
It is, therefore, manifest that the apex of the radicle of the oak is highly
sensitive to contact, and retains its sensitiveness during several days. The
movement thus induced was, however, slower than in any of the previous
cases, with the exception of that of Æsculus. As with the bean, the terminal
growing part, after bending, sometimes straightened itself through the
action of geotropism, although the object still remained attached to the tip.

The same remarkable experiment was next tried, as in the case of the
bean; namely, little squares of exactly the same size of the card-like sanded
paper and of very thin paper (the thicknesses of which have been given
under Vicia faba) were attached with shellac on opposite sides (as
accurately as could be done) of the tips of 13 radicles, suspended in damp
air, at a temperature of 65°–66° F. The result was striking, for 9 out of these
13 radicles became plainly, and 1 very slightly, curved from the thick paper
towards the side bearing the thin paper. In two of these cases the apex
became completely hooked after two days; in four cases the deflection from
the perpendicular and from the side bearing the thick paper, amounted in
from two to four days to angles of 90°, 72°, 60°, and 49°, but in two other
cases to only 18° and 15°. It should, however, be stated that in the case in
which the deflection was 49°, the two squares had accidentally come into
contact on one side of the apex, and thus formed a lateral gable; and the
deflection was directed in part from this gable and in part from the thick
paper. In three cases alone the radicles were not affected by the difference
in thickness of the squares of paper attached to their tips, and consequently
did not bend away from the side bearing the stiffer paper.
Zea mays: Sensitiveness of the apex of the Radicle to contact.—A large
number of trials were made on this plant, as it was the only monocotyledon
on which we experimented. An abstract of the results will suffice. In the
first place, 22 germinating seeds were pinned to cork-lids without any
object being attached to their radicles, some being exposed to a temperature
of 65°–66° F., and others to between 74° and 79°; and none of them became
curved, though some were a little inclined to one side. A few were selected,
which from having germinated on sand were crooked, but when suspended
in damp air the terminal part grew straight downwards. This fact having
been ascertained, little squares of the card-like paper were affixed with
shellac, on several occasions, to the tips of 68 radicles. Of these the
terminal growing part of 39 became within 24 h. conspicuously curved
away from the attached squares and from the perpendicular; 13 out of the
39 forming hooks with their points directed towards the zenith, and 8
forming loops. Moreover, 7 other radicles out of the 68, were slightly and
two doubtfully deflected from the cards. There remain 20 which were not
affected; but 10 of these ought not to be counted; for one was diseased, two
had their tips quite surrounded by shellac, and the squares on 7 had slipped
so as to stand parallel to the apex, instead of obliquely on it. There were

therefore only 10 out of the 68 which certainly were not acted on. Some of
the radicles which were experimented on were young and short, most of
them of moderate length, and two or three exceeded three inches in length.
The curvature in the above cases occurred within 24 h., but it was often
conspicuous within a much shorter period. For instance, the terminal
growing part of one radicle was bent upwards into a rectangle in 8 h. 15 m.,
and of another in 9 h. On one occasion a hook was formed in 9 h. Six of the
radicles in a jar containing nine seeds, which stood on a sand-bath, raised to
a temperature varying from 76° to 82° F., became hooked, and a seventh
formed a complete loop, when first looked at after 15 hours.
The accompanying figures of four germinating seeds (Fig. 69) show,
firstly, a radicle (A) the apex of which has become so much bent away from
the attached square as to form a hook. Secondly (B), a hook converted
through the continued irritation of the card, aided perhaps by geotropism,
into an almost complete circle or loop. The tip in the act of forming a loop
generally rubs against the upper part of the radicle, and pushes off the
attached square; the loop then contracts or closes, but never disappears; and
the apex afterwards grows vertically downwards, being no longer irritated
by any attached object. This frequently occurred, and is represented at C.
The jar above mentioned with the six hooked radicles and another jar were
kept for two additional days, for the sake of observing how the hooks would
be modified. Most of them became converted into simple loops, like that
figured at C; but in one case the apex did not rub against the upper part of
the radicle and thus remove the card; and it consequently made, owing to
the continued irritation from the card, two complete loops, that is, a helix of
two spires; which afterwards became pressed closely together. Then
geotropism prevailed and caused the apex to grow perpendicularly
downwards. In another case, shown at (D), the apex in making a second
turn or spire, passed through the first loop, which was at first widely open,
and in doing so knocked off the card; it then grew perpendicularly
downwards, and thus tied itself into a knot, which soon became tight!
Fig. 69. Zea mays: radicles excited to bend away from the little squares
of card attached to one side of their tips.
Secondary Radicles of Zea.—A short time after the first radicle has
appeared, others protrude from the seed, but not laterally from the primary
one. Ten of these secondary radicles, which were directed obliquely

downwards, were experimented on with very small squares of card attached
with shellac to the lower sides of their tips. If therefore the squares acted,
the radicles would bend upwards in opposition to gravity. The jar stood
(protected from light) on a sand-bath, which varied between 76° and 82° F.
After only 5 h. one appeared to be a little deflected from the square, and
after 20 h. formed a loop. Four others were considerably curved from the
squares after 20 h., and three of them became hooked, with their tips
pointing to the zenith,—one after 29 h. and the two others after 44 h. By
this latter time a sixth radicle had become bent at a right angle from the side
bearing the square. Thus altogether six out of the ten secondary radicles
were acted on, four not being affected. There can, therefore, be no doubt
that the tips of these secondary radicles are sensitive to slight contact, and
that when thus excited they cause the upper part to bend from the touching
object; but generally, as it appears, not in so short a time as in the case of
the first-formed radicle.

SENSITIVENESS OF THE TIP OF THE RADICLE
TO MOIST AIR.
Sachs made the interesting discovery, a few years ago, that the radicles of
many seedling plants bend towards an adjoining damp surface.[9] We shall
here endeavour to show that this peculiar form of sensitiveness resides in
their tips. The movement is directly the reverse of that excited by the
irritants hitherto considered, which cause the growing part of the radicle to
bend away from the source of irritation. In our experiments we followed
Sachs’ plan, and sieves with seeds germinating in damp sawdust were
suspended so that the bottom was generally inclined at 40° with the horizon.
If the radicles had been acted on solely by geotropism, they would have
grown out of the bottom of the sieve perpendicularly downwards; but as
they were attracted by the adjoining damp surface they bent towards it and
were deflected 50° from the perpendicular. For the sake of ascertaining
whether the tip or the whole growing part of the radicle was sensitive to the
moist air, a length of from 1 to 2 mm. was coated in a certain number of
cases with a mixture of olive-oil and lamp-black. This mixture was made in
order to give consistence to the oil, so that a thick layer could be applied,
which would exclude, at least to a large extent, the moist air, and would be

easily visible. A greater number of experiments than those which were
actually tried would have been necessary, had not it been clearly established
that the tip of the radicle is the part which is sensitive to various other
irritants.
[9] ‘Arbeiten des Bot. Institut., in Würzburg,’ vol. i. 1872, p. 209.

Phaseolus multiflorus.—Twenty-nine radicles, to which nothing had been
done, growing out of a sieve, were observed at the same time with those
which had their tips greased, and for an equal length of time. Of the 29, 24
curved themselves so as to come into close contact with the bottom of the
sieve. The place of chief curvature was generally at a distance of 5 or 6 mm.
from the apex. Eight radicles had their tips greased for a length of 2 mm.,
and two others for a length of 1½ mm.; they were kept at a temperature of
15°–16° C. After intervals of from 19 h. to 24 h. all were still vertically or
almost vertically dependent, for some of them had moved towards the
adjoining damp surface by about 10°. They had therefore not been acted on,
or only slightly acted on, by the damper air on one side, although the whole
upper part was freely exposed. After 48 h. three of these radicles became
considerably curved towards the sieve; and the absence of curvature in
some of the others might perhaps be accounted for by their not having
grown very well. But it should be observed that during the first 19 h. to 24
h. all grew well; two of them having increased 2 and 3 mm. in length in 11
h.; five others increased 5 to 8 mm. in 19 h.; and two, which had been at
first 4 and 6 mm. in length, increased in 24 h. to 15 and 20 mm.
The tips of 10 radicles, which likewise grew well, were coated with the
grease for a length of only 1 mm., and now the result was somewhat
different; for of these 4 curved themselves to the sieve in from 21 h. to 24h.,
whilst 6 did not do so. Five of the latter were observed for an additional
day, and now all excepting one became curved to the sieve.
The tips of 5 radicles were cauterised with nitrate of silver, and about 1
mm. in length was thus destroyed. They were observed for periods varying
between 11 h. and 24h., and were found to have grown well. One of them
had curved until it came into contact with the sieve; another was curving
towards it; whilst the remaining three were still vertically dependent. Of 7
not cauterised radicles observed at the same time, all had come into contact
with the sieve.

The tips of 11 radicles were protected by moistened gold-beaters’ skin,
which adheres closely, for a length varying from 1½ to 2½ mm. After 22 h.
to 24 h., 6 of these radicles were clearly bent towards or had come into
contact with the sieve; 2 were slightly curved in this direction, and 3 not at
all. All had grown well. Of 14 control specimens observed at the same time,
all excepting one had closely approached the sieve. It appears from these
cases that a cap of goldbeaters’ skin checks, though only to a slight degree,
the bending of the radicles to an adjoining damp surface. Whether an
extremely thin sheet of this substance when moistened allows moisture
from the air to pass through it, we do not know. One case indicated that the
caps were sometimes more efficient than appears from the above results; for
a radicle, which after 23 h. had only slightly approached the sieve, had its
cap (1½ mm. in length) removed, and during the next 15½ h. it curved itself
abruptly towards the source of moisture, the chief seat of curvature being at
a distance of 2 to 3 mm. from the apex.
Vicia faba.—The tips of 13 radicles were coated with the grease for a
length of 2 mm.; and it should be remembered that with these radicles the
seat of chief curvature is about 4 or 5 mm. from the apex. Four of them
were examined after 22h., three after 26 h., and six after 36 h., and none had
been attracted towards the damp lower surface of the sieve. In another trial
7 radicles were similarly treated, and 5 of them still pointed perpendicularly
downwards after 11 h., whilst 2 were a little curved towards the sieve; by an
accident they were not subsequently observed. In both these trials the
radicles grew well; 7 of them, which were at first from 4 to 11 mm. in
length, were after 11 h. between 7 and 16 mm.; 3 which were at first from 6
to 8 mm. after 26 h. were 11.5 to 18 mm. in length; and lastly, 4 radicles
which were at first 5 to 8 mm. after 46 h. were 18 to 23 mm. in length. The
control or ungreased radicles were not invariably attracted towards the
bottom of the sieve. But on one occasion 12 out of 13, which were observed
for periods between 22 h. and 36 h., were thus attracted. On two other
occasions taken together, 38 out of 40 were similarly attracted. On another
occasion only 7 out of 14 behaved in this manner, but after two more days
the proportion of the curved increased to 17 out of 23. On a last occasion
only 11 out of 20 were thus attracted. If we add up these numbers, we find
that 78 out of 96 of the control specimens curved themselves towards the
bottom of the sieve. Of the specimens with greased tips, 2 alone out of the
20 (but 7 of these were not observed for a sufficiently long time) thus

curved themselves. We can, therefore, hardly doubt that the tip for a length
of 2 mm. is the part which is sensitive to a moist atmosphere, and causes the
upper part to bend towards its source.
The tips of 15 radicles were cauterised with nitrate of silver, and they
grew as well as those above described with greased tips. After an interval of
24 h., 9 of them were not at all curved towards the bottom of the sieve; 2
were curved towards it at angles of 20° and 12° from their former vertical
position, and 4 had come into close contact with it. Thus the destruction of
the tip for a length of about 1 mm. prevented the curvature of the greater
number of these radicles to the adjoining damp surface. Of 24 control
specimens, 23 were bent to the sieve, and on a second occasion 15 out of 16
were similarly curved in a greater or less degree. These control trials are
included in those given in the foregoing paragraph.
Avena sativa.—The tips of 13 radicles, which projected between 2 and 4
mm. from the bottom of the sieve, many of them not quite perpendicularly
downwards, were coated with the black grease for a length of from 1 to 1½
mm. The sieves were inclined at 30° with the horizon. The greater number
of these radicles were examined after 22 h., and a few after 25 h., and
within these intervals they had grown so quickly as to have nearly doubled
their lengths. With the ungreased radicles the chief seat of curvature is at a
distance of not less than between 3.5 and 5.5 mm., and not more than
between 7 and 10 mm. from the apex. Out of the 13 radicles with greased
tips, 4 had not moved at all towards the sieve; 6 were deflected towards it
and from the perpendicular by angles varying between 10° and 35°; and 3
had come into close contact with it. It appears, therefore, at first sight that
greasing the tips of these radicles had checked but little their bending to the
adjoining damp surface. But the inspection of the sieves on two occasions
produced a widely different impression on the mind; for it was impossible
to behold the radicles with the black greased tips projecting from the
bottom, and all those with ungreased tips, at least 40 to 50 in number,
clinging closely to it, and feel any doubt that the greasing had produced a
great effect. On close examination only a single ungreased radicle could be
found which had not become curved towards the sieve. It is probable that if
the tips had been protected by grease for a length of 2 mm. instead of from
1 to 1½ mm., they would not have been affected by the moist air and none
would have become curved.

Triticum vulgare.—Analogous trials were made on 8 radicles of the
common wheat; and greasing their tips produced much less effect than in
the case of the oats. After 22 h., 5 of them had come into contact with the
bottom of the sieve; 2 had moved towards it 10° and 15°, and one alone
remained perpendicular. Not one of the very numerous ungreased radicles
failed to come into close contact with the sieve. These trials were made on
Nov. 28th, when the temperature was only 4.8° C. at 10 A.M. We should
hardly have thought this case worth notice, had it not been for the following
circumstance. In the beginning of October, when the temperature was
considerably higher, viz., 12° to 13° C., we found that only a few of the
ungreased radicles became bent towards the sieve; and this indicates that
sensitiveness to moisture in the air is increased by a low temperature, as we
have seen with the radicles of Vicia faba relatively to objects attached to
their tips. But in the present instance it is possible that a difference in the
dryness of the air may have caused the difference in the results at the two
periods.

Finally, the facts just given with respect to Phaseolus multiflorus, Vicia
faba, and Avena sativa show, as it seems to us, that a layer of grease spread
for a length of 1½ to 2 mm. over the tip of the radicle, or the destruction of
the tip by caustic, greatly lessens or quite annuls in the upper and exposed
part the power of bending towards a neighbouring source of moisture. We
should bear in mind that the part which bends most, lies at some little
distance above the greased or cauterised tip; and that the rapid growth of
this part, proves that it has not been injured by the tips having been thus
treated. In those cases in which the radicles with greased tips became
curved, it is possible that the layer of grease was not sufficiently thick
wholly to exclude moisture, or that a sufficient length was not thus
protected, or, in the case of the caustic, not destroyed. When radicles with
greased tips are left to grow for several days in damp air, the grease is
drawn out into the finest reticulated threads and dots, with narrow portions
of the surface left clean. Such portions would, it is probable, be able to
absorb moisture, and thus we can account for several of the radicles with
greased tips having become curved towards the sieve after an interval of
one or two days. On the whole, we may infer that sensitiveness to a
difference in the amount of moisture in the air on the two sides of a radicle

resides in the tip, which transmits some influence to the upper part, causing
it to bend towards the source of moisture. Consequently, the movement is
the reverse of that caused by objects attached to one side of the tip, or by a
thin slice being cut off, or by being slightly cauterised. In a future chapter it
will be shown that sensitiveness to the attraction of gravity likewise resides
in the tip; so that it is the tip which excites the adjoining parts of a
horizontally extended radicle to bend towards the centre of the earth.

SECONDARY RADICLES BECOMING VERTICALLY GEOTROPIC
BY THE DESTRUCTION OR INJURY OF THE TERMINAL PART OF
THE PRIMARY RADICLE.

Sachs has shown that the lateral or secondary radicles of the bean, and
probably of other plants, are acted on by geotropism in so peculiar a
manner, that they grow out horizontally or a little inclined downwards; and
he has further shown[10] the interesting fact, that if the end of the primary
radicle be cut off, one of the nearest secondary radicles changes its nature
and grows perpendicularly downwards, thus replacing the primary radicle.
We repeated this experiment, and planted beans with amputated radicles in
friable peat, and saw the result described by Sachs; but generally two or
three of the secondary radicles grew perpendicularly downwards. We also
modified the experiment, by pinching young radicles a little way above
their tips, between the arms of a U-shaped piece of thick leaden wire. The
part pinched was thus flattened, and was afterwards prevented from
growing thicker. Five radicles had their ends cut off, and served as controls
or standards. Eight were pinched; of these 2 were pinched too severely and
their ends died and dropped off; 2 were not pinched enough and were not
sensibly affected; the remaining 4 were pinched sufficiently to check the
growth of the terminal part, but did not appear otherwise injured. When the
U-shaped wires were removed, after an interval of 15 days, the part beneath
the wire was found to be very thin and easily broken, whilst the part above
was thickened. Now in these four cases, one or more of the secondary
radicles, arising from the thickened part just above the wire, had grown
perpendicularly downwards. In the best case the primary radicle (the part
below the wire being 1½ inch in length) was somewhat distorted, and was
not half as long as three adjoining secondary radicles, which had grown
vertically, or almost vertically, downwards. Some of these secondary

radicles adhered together or had become confluent. We learn from these
four cases that it is not necessary, in order that a secondary radicle should
assume the nature of a primary one, that the latter should be actually
amputated; it is sufficient that the flow of sap into it should be checked, and
consequently should be directed into the adjoining secondary radicles; for
this seems to be the most obvious result of the primary radicle being
pinched between the arms of a U-shaped wire.
[10] ‘Arbeiten Bot. Institut., Würzburg,’ Heft iv. 1874, p. 622.

This change in the nature of secondary radicles is clearly analogous, as
Sachs has remarked, to that which occurs with the shoots of trees, when the
leading one is destroyed and is afterwards replaced by one or more of the
lateral shoots; for these now grow upright instead of sub-horizontally. But
in this latter case the lateral shoots are rendered apogeotropic, whereas with
radicles the lateral ones are rendered geotropic. We are naturally led to
suspect that the same cause acts with shoots as with roots, namely, an
increased flow of sap into the lateral ones. We made some trials with Abies
communis and pectinata, by pinching with wire the leading and all the
lateral shoots excepting one. But we believe that they were too old when
experimented on; and some were pinched too severely, and some not
enough. Only one case succeeded, namely, with the spruce-fir. The leading
shoot was not killed, but its growth was checked; at its base there were
three lateral shoots in a whorl, two of which were pinched, one being thus
killed; the third was left untouched. These lateral shoots, when operated on
(July 14th) stood at an angle of 8° above the horizon; by Sept. 8th the
unpinched one had risen 35°; by Oct. 4th it had risen 46°, and by Jan. 26th
48°, and it had now become a little curved inwards. Part of this rise of 48°
may be attributed to ordinary growth, for the pinched shoot rose 12° within
the same period. It thus follows that the unpinched shoot stood, on Jan.
26th, 56° above the horizon, or 34° from the vertical; and it was thus
obviously almost ready to replace the slowly growing, pinched, leading
shoot. Nevertheless, we feel some doubt about this experiment, for we have
since observed with spruce-firs growing rather unhealthily, that the lateral
shoots near the summit sometimes become highly inclined, whilst the
leading shoot remains apparently sound.
A widely different agency not rarely causes shoots which naturally would
have brown out horizontally to grow up vertically. The lateral branches of

the Silver Fir (A. pectinata) are often affected by a fungus, Æcidium
elatinum, which causes the branch to enlarge into an oval knob formed of
hard wood, in one of which we counted 24 rings of growth. According to
De Bary[11], when the mycelium penetrates a bud beginning to elongate, the
shoot developed from it grows vertically upwards. Such upright shoots
afterwards produce lateral and horizontal branches; and they then present a
curious appearance, as if a young fir-tree had grown out of a ball of clay
surrounding the branch. These upright shoots have manifestly changed their
nature and become apogeotropic; for if they had not been affected by the
Æcidium, they would have grown out horizontally like all the other twigs
on the same branches. This change can hardly be due to an increased flow
of sap into the part; but the presence of the mycelium will have greatly
disturbed its natural constitution.
[11] See his valuable article in ‘Bot. Zeitung,’ 1867, p. 257, on these monstrous
growths, which are called in German “Hexenbesen,” or “witch-brooms.”

According to Mr. Meehan,[12] the stems of three species of Euphorbia and
of Portulaca oleracea are “normally prostrate or procumbent;” but when
they are attacked by an Æcidium, they “assume an erect habit.” Dr. Stahl
informs us that he knows of several analogous cases; and these seem to be
closely related to that of the Abies. The rhizomes of Sparganium ramosum
grow out horizontally in the soil to a considerable length, or are
diageotropic; but F. Elfving found that when they were cultivated in water
their tips turned upwards, and they became apogeotropic. The same result
followed when the stem of the plant was bent until it cracked or was merely
much bowed.[13]
[12] ‘Proc. Acad. Nat. Sc. Philadelphia,’ June 16th, 1874, and July 23rd, 1875.

[13] See F. Elfving’s interesting paper in ‘Arbeiten Bot. Institut., in Würzburg,’
vol. ii. 1880, p. 489. Carl Kraus (Triesdorf) had previously observed (‘Flora,’
1878, p. 324) that the underground shoots of Triticum repens bend vertically up
when the parts above ground are removed, and when the rhizomes are kept partly
immersed in water.

No explanation has hitherto been attempted of such cases as the
foregoing,—namely, of secondary radicles growing vertically downwards,
and of lateral shoots growing vertically upwards, after the amputation of the
primary radicle or of the leading shoot. The following considerations give
us, as we believe, the clue. Firstly, any cause which disturbs the

constitution[14] is apt to induce reversion; such as the crossing of two distinct
races, or a change of conditions, as when domestic animals become feral.
But the case which most concerns us, is the frequent appearance of peloric
flowers on the summit of a stem, or in the centre of the inflorescence,—
parts which, it is believed, receive the most sap; for when an irregular
flower becomes perfectly regular or peloric, this may be attributed, at least
partly, to reversion to a primitive and normal type. Even the position of a
seed at the end of the capsule sometimes gives to the seedling developed
from it a tendency to revert. Secondly, reversions often occur by means of
buds, independently of reproduction by seed; so that a bud may revert to the
character of a former state many bud-generations ago. In the case of
animals, reversions may occur in the individual with advancing age. Thirdly
and lastly, radicles when they first protrude from the seed are always
geotropic, and plumules or shoots almost always apogeotropic. If then any
cause, such as an increased flow of sap or the presence of mycelium,
disturbs the constitution of a lateral shoot or of a secondary radicle, it is apt
to revert to its primordial state; and it becomes either apogeotropic or
geotropic, as the case may be, and consequently grows either vertically
upwards or downwards. It is indeed possible, or even probable, that this
tendency to reversion may have been increased, as it is manifestly of
service to the plant.
[14] The facts on which the following conclusions are founded are given in ‘The
Variation of Animals and Plants under Domestication,’ 2nd edit. 1875. On the
causes leading to reversion see chap. xii. vol. ii. and p. 59, chap. xiv. On peloric
flowers, chap. xiii. p. 32; and see p. 337 on their position on the plant. With
respect to seeds, p. 340. On reversion by means of buds, p. 438, chap. xi. vol. i.

A SUMMARY OF CHAPTER.
A part or organ may be called sensitive, when its irritation excites
movement in an adjoining part. Now it has been shown in this chapter, that
the tip of the radicle of the bean is in this sense sensitive to the contact of
any small object attached to one side by shellac or gum-water; also to a
slight touch with dry caustic, and to a thin slice cut off one side. The
radicles of the pea were tried with attached objects and caustic, both of
which acted. With Phaseolus multiflorus the tip was hardly sensitive to
small squares of attached card, but was sensitive to caustic and to slicing.

The radicles of Tropaeolum were highly sensitive to contact; and so, as far
as we could judge, were those of Gossypium herbaceum, and they were
certainly sensitive to caustic. The tips of the radicles of Cucurbita ovifera
were likewise highly sensitive to caustic, though only moderately so to
contact. Raphanus sativus offered a somewhat doubtful case. With Æsculus
the tips were quite indifferent to bodies attached to them, though sensitive
to caustic. Those of Quercus robur and Zea mays were highly sensitive to
contact, as were the radicles of the latter to caustic. In several of these cases
the difference in sensitiveness of the tip to contact and to caustic was, as we
believe, merely apparent; for with Gossypium, Raphanus, and Cucurbita,
the tip was so fine and flexible that it was very difficult to attach any object
to one of its sides. With the radicles of Æsculus, the tips were not at all
sensitive to small bodies attached to them; but it does not follow from this
fact that they would not have been sensitive to somewhat greater continued
pressure, if this could have been applied.
The peculiar form of sensitiveness which we are here considering, is
confined to the tip of the radicle for a length of from 1 mm. to 1.5 mm.
When this part is irritated by contact with any object, by caustic, or by a
thin slice being cut off, the upper adjoining part of the radicle, for a length
of from 6 or 7 to even 12 mm., is excited to bend away from the side which
has been irritated. Some influence must therefore be transmitted from the
tip along the radicle for this length. The curvature thus caused is generally
symmetrical. The part which bends most apparently coincides with that of
the most rapid growth. The tip and the basal part grow very slowly and they
bend very little.
Considering the widely separated position in the vegetable series of the
several above-named genera, we may conclude that the tips of the radicles
of all, or almost all, plants are similarly sensitive, and transmit an influence
causing the upper part to bend. With respect to the tips of the secondary
radicles, those of Vicia faba, Pisum sativum, and Zea mays were alone
observed, and they were found similarly sensitive.
In order that these movements should be properly displayed, it appears
necessary that the radicles should grow at their normal rate. If subjected to a
high temperature and made to grow rapidly, the tips seem either to lose their
sensitiveness, or the upper part to lose the power of bending. So it appears
to be if they grow very slowly from not being vigorous, or from being kept

at too low a temperature; also when they are forced to germinate in the
middle of the winter.
The curvature of the radicle sometimes occurs within from 6 to 8 hours
after the tip has been irritated, and almost always within 24 h., excepting in
the case of the massive radicles of Æsculus. The curvature often amounts to
a rectangle,—that is, the terminal part bends upwards until the tip, which is
but little curved, projects almost horizontally. Occasionally the tip, from the
continued irritation of the attached object, continues to bend up until it
forms a hook with the point directed towards the zenith, or a loop, or even a
spire. After a time the radicle apparently becomes accustomed to the
irritation, as occurs in the case of tendrils, for it again grows downwards,
although the bit of card or other object may remain attached to the tip. It is
evident that a small object attached to the free point of a vertically
suspended radicle can offer no mechanical resistance to its growth as a
whole, for the object is carried downwards as the radicle elongates, or
upwards as the radicle curves upwards. Nor can the growth of the tip itself
be mechanically checked by an object attached to it by gum-water, which
remains all the time perfectly soft. The weight of the object, though quite
insignificant, is opposed to the upward curvature. We may therefore
conclude that it is the irritation due to contact which excites the movement.
The contact, however, must be prolonged, for the tips of 15 radicles were
rubbed for a short time, and this did not cause them to bend. Here then we
have a case of specialised sensibility, like that of the glands of Drosera; for
these are exquisitely sensitive to the slightest pressure if prolonged, but not
to two or three rough touches.
When the tip of a radicle is lightly touched on one side with dry nitrate of
silver, the injury caused is very slight, and the adjoining upper part bends
away from the cauterised point, with more certainty in most cases than from
an object attached on one side. Here it obviously is not the mere touch, but
the effect produced by the caustic, which induces the tip to transmit some
influence to the adjoining part, causing it to bend away. If one side of the tip
is badly injured or killed by the caustic, it ceases to grow, whilst the
opposite side continues growing; and the result is that the tip itself bends
towards the injured side and often becomes completely hooked; and it is
remarkable that in this case the adjoining upper part does not bend. The
stimulus is too powerful or the shock too great for the proper influence to
be transmitted from the tip. We have strictly analogous cases with Drosera,

Dionaea and Pinguicula, with which plants a too powerful stimulus does not
excite the tentacles to become incurved, or the lobes to close, or the margin
to be folded inwards.
With respect to the degree of sensitiveness of the apex to contact under
favourable conditions, we have seen that with Vicia faba a little square of
writing-paper affixed with shellac sufficed to cause movement; as did on
one occasion a square of merely damped goldbeaters’ skin, but it acted very
slowly. Short bits of moderately thick bristle (of which measurements have
been given) affixed with gum-water acted in only three out of eleven trials,
and beads of dried shellac under 1/200th of a grain in weight acted only
twice in nine cases; so that here we have nearly reached the minimum of
necessary irritation. The apex, therefore, is much less sensitive to pressure
than the glands of Drosera, for these are affected by far thinner objects than
bits of bristle, and by a very much less weight than 1/200th of a grain. But
the most interesting evidence of the delicate sensitiveness of the tip of the
radicle, was afforded by its power of discriminating between equal-sized
squares of card-like and very thin paper, when these were attached on
opposite sides, as was observed with the radicles of the bean and oak.
When radicles of the bean are extended horizontally with squares of card
attached to the lower sides of their tips, the irritation thus caused was
always conquered by geotropism, which then acts under the most
favourable conditions at right angles to the radicle. But when objects were
attached to the radicles of any of the above-named genera, suspended
vertically, the irritation conquered geotropism, which latter power at first
acted obliquely on the radicle; so that the immediate irritation from the
attached object, aided by its after-effects, prevailed and caused the radicle to
bend upwards, until sometimes the point was directed to the zenith. We
must, however, assume that the after-effects of the irritation of the tip by an
attached object come into play, only after movement has been excited. The
tips of the radicles of the pea seem to be more sensitive to contact than
those of the bean, for when they were extended horizontally with squares of
card adhering to their lower sides, a most curious struggle occasionally
arose, sometimes one and sometimes the other force prevailing, but
ultimately geotropism was always victorious; nevertheless, in two instances
the terminal part became so much curved upwards that loops were
subsequently formed. With the pea, therefore, the irritation from an attached
object, and from geotropism when acting at right angles to the radicle, are

nearly balanced forces. Closely similar results were observed with the
horizontally extended radicles of Cucurbita ovifera, when their tips were
slightly cauterised on the lower side.
Finally, the several co-ordinated movements by which radicles are
enabled to perform their proper functions are admirably perfect. In
whatever direction the primary radicle first protrudes from the seed,
geotropism guides it perpendicularly downwards; and the capacity to be
acted on by the attraction of gravity resides in the tip. But Sachs has
proved[15] that the secondary radicles, or those emitted by the primary one,
are acted on by geotropism in such a manner that they tend to bend only
obliquely downwards. If they had been acted on like the primary radicle, all
the radicles would have penetrated the ground in a close bundle. We have
seen that if the end of the primary radicle is cut off or injured, the adjoining
secondary radicles become geotropic and grow vertically downwards. This
power must often be of great service to the plant, when the primary radicle
has been destroyed by the larvae of insects, burrowing animals, or any other
accident. The tertiary radicles, or those emitted by the secondary ones, are
not influenced, at least in the case of the bean, by geotropism; so they grow
out freely in all directions. From this manner of growth of the various kinds
of radicles, they are distributed, together with their absorbent hairs,
throughout the surrounding soil, as Sachs has remarked, in the most
advantageous manner; for the whole soil is thus closely searched.
[15] ‘Arbeiten Bot. Institut, Würzburg,’ Heft iv. 1874, pp. 605–631.

Geotropism, as was shown in the last chapter, excites the primary radicle
to bend downwards with very little force, quite insufficient to penetrate the
ground. Such penetration is effected by the pointed apex (protected by the
root-cap) being pressed down by the longitudinal expansion or growth of
the terminal rigid portion, aided by its transverse expansion, both of which
forces act powerfully. It is, however, indispensable that the seeds should be
at first held down in some manner. When they lie on the bare surface they
are held down by the attachment of the root-hairs to any adjoining objects;
and this apparently is effected by the conversion of their outer surfaces into
a cement. But many seeds get covered up by various accidents, or they fall
into crevices or holes. With some seeds their own weight suffices. The
circumnutating movement of the terminal growing part both of the primary
and secondary radicles is so feeble that it can aid them very little in

penetrating the ground, excepting when the superficial layer is very soft and
damp. But it must aid them materially when they happen to break obliquely
into cracks, or into burrows made by earth-worms or larvae. This
movement, moreover, combined with the sensitiveness of the tip to contact,
can hardly fail to be of the highest importance; for as the tip is always
endeavouring to bend to all sides it will press on all sides, and will thus be
able to discriminate between the harder and softer adjoining surfaces, in the
same manner as it discriminated between the attached squares of card-like
and thin paper. Consequently it will tend to bend from the harder soil, and
will thus follow the lines of least resistance. So it will be if it meets with a
stone or the root of another plant in the soil, as must incessantly occur. If
the tip were not sensitive, and if it did not excite the upper part of the root
to bend away, whenever it encountered at right angles some obstacle in the
ground, it would be liable to be doubled up into a contorted mass. But we
have seen with radicles growing down inclined plates of glass, that as soon
as the tip merely touched a slip of wood cemented across the plate, the
whole terminal growing part curved away, so that the tip soon stood at right
angles to its former direction; and thus it would be with an obstacle
encountered in the ground, as far as the pressure of the surrounding soil
would permit. We can also understand why thick and strong radicles, like
those of Æsculus, should be endowed with less sensitiveness than more
delicate ones; for the former would be able by the force of their growth to
overcome any slight obstacle.
After a radicle, which has been deflected by some stone or root from its
natural downward course, reaches the edge of the obstacle, geotropism will
direct it to grow again straight downward; but we know that geotropism
acts with very little force, and here another excellent adaptation, as Sachs
has remarked,[16] comes into play. For the upper part of the radicle, a little
above the apex, is, as we have seen, likewise sensitive; and this
sensitiveness causes the radicle to bend like a tendril towards the touching
object, so that as it rubs over the edge of an obstacle, it will bend
downwards; and the curvature thus induced is abrupt, in which respect it
differs from that caused by the irritation of one side of the tip. This
downward bending coincides with that due to geotropism, and both will
cause the root to resume its original course.
[16] ‘Arbeiten Bot. Inst., Würzburg,’ Heft iii. p. 456.

As radicles perceive an excess of moisture in the air on one side and bend
towards this side, we may infer that they will act in the same manner with
respect to moisture in the earth. The sensitiveness to moisture resides in the
tip, which determines the bending of the upper part. This capacity perhaps
partly accounts for the extent to which drain-pipes often become choked
with roots.
Considering the several facts given in this chapter, we see that the course
followed by a root through the soil is governed by extraordinarily complex
and diversified agencies,—by geotropism acting in a different manner on
the primary, secondary, and tertiary radicles,—by sensitiveness to contact,
different in kind in the apex and in the part immediately above the apex,
and apparently by sensitiveness to the varying dampness of different parts
of the soil. These several stimuli to movement are all more powerful than
geotropism, when this acts obliquely on a radicle, which has been deflected
from its perpendicular downward course. The roots, moreover, of most
plants are excited by light to bend either to or from it; but as roots are not
naturally exposed to the light it is doubtful whether this sensitiveness,
which is perhaps only the indirect result of the radicles being highly
sensitive to other stimuli, is of any service to the plant. The direction which
the apex takes at each successive period of the growth of a root, ultimately
determines its whole course; it is therefore highly important that the apex
should pursue from the first the most advantageous direction; and we can
thus understand why sensitiveness to geotropism, to contact and to
moisture, all reside in the tip, and why the tip determines the upper growing
part to bend either from or to the exciting cause. A radicle may be compared
with a burrowing animal such as a mole, which wishes to penetrate
perpendicularly down into the ground. By continually moving his head
from side to side, or circumnutating, he will feel any stone or other
obstacle, as well as any difference in the hardness of the soil, and he will
turn from that side; if the earth is damper on one than on the other side he
will turn thitherward as a better hunting-ground. Nevertheless, after each
interruption, guided by the sense of gravity, he will be able to recover his
downward course and to burrow to a greater depth.

CHAPTER IV.
THE CIRCUMNUTATING MOVEMENTS OF THE
SEVERAL PARTS OF MATURE PLANTS.

Circumnutation of stems: concluding remarks on—
Circumnutation of stolons: aid thus afforded in winding
amongst the stems of surrounding plants—Circumnutation
of flower-stems—Circumnutation of Dicotyledonous leaves
—Singular oscillatory movement of leaves of Dionaea—
Leaves of Cannabis sink at night—Leaves of Gymnosperms
—Of Monocotyledons—Cryptogams—Concluding remarks
on the circumnutation of leaves; generally rise in the
evening and sink in the morning.

We have seen in the first chapter that the stems of all seedlings, whether
hypocotyls or epicotyls, as well as the cotyledons and the radicles, are
continually circumnutating—that is they grow first on one side and then on
another, such growth being probably preceded by increased turgescence of
the cells. As it was unlikely that plants should change their manner of
growth with advancing age, it seemed probable that the various organs of
all plants at all ages, as long as they continued to grow, would be found to
circumnutate, though perhaps to an extremely small extent. As it was
important for us to discover whether this was the case, we determined to
observe carefully a certain number of plants which were growing
vigorously, and which were not known to move in any manner. We
commenced with stems. Observations of this kind are tedious, and it
appeared to us that it would be sufficient to observe the stems in about a
score of genera, belonging to widely distinct families and inhabitants of
various countries. Several plants were selected which, from being woody, or
for other reasons, seemed the least likely to circumnutate. The observations

and the diagrams were made in the manner described in the Introduction.
Plants in pots were subjected to a proper temperature, and whilst being
observed, were kept either in darkness or were feebly illuminated from
above. They are arranged in the order adopted by Hooker in Le Maout and
Decaisne’s ‘System of Botany.’ The number of the family to which each
genus belongs is appended, as this serves to show the place of each in the
series.

(1.) Iberis umbellata (Cruciferae, Fam. 14).—The movement of the stem
of a young plant, 4 inches in height, consisting of four internodes (the
hypocotyl included) besides a large bud on the summit, was traced, as here
shown, during 24 h. (Fig. 70). As far as we could judge the uppermost inch
alone of the stem circumnutated, and this in a simple manner. The
movement was slow, and the rate very unequal at different times. In part of
its course an irregular ellipse, or rather triangle, was completed in 6 h. 30
m.
Fig. 70. Iberis umbellata: circumnutation of stem of young plant, traced
from 8.30 A.M. Sept. 13th to same hour on following morning. Distance of
summit of stem beneath the horizontal glass 7.6 inches. Diagram reduced to
half of original size. Movement as here shown magnified between 4 and 5
times.
(2.) Brassica oleracea (Cruciferae).—A very young plant, bearing three
leaves, of which the longest was only three-quarters of an inch in length,
was placed under a microscope, furnished with an eye-piece micrometer,
and the tip of the largest leaf was found to be in constant movement. It
crossed five divisions of the micrometer, that is, 1/100th of an inch, in 6 m.
20 s. There could hardly be a doubt that it was the stem which chiefly
moved, for the tip did not get quickly out of focus; and this would have
occurred had the movement been confined to the leaf, which moves up or
down in nearly the same vertical plane.
(3.) Linum usitatissimum (Lineae, Fam. 39).—The stems of this plant,
shortly before the flowering period, are stated by Fritz Müller (‘Jenaische
Zeitschrift,’ B. v. p. 137) to revolve, or circumnutate.
(4.) Pelargonium zonale (Geraniaceae, Fam. 47).—A young plant, 7½
inches in height, was observed in the usual manner; but, in order to see the

bead at the end of the glass filament and at the same time the mark beneath,
it was necessary to cut off three leaves on one side. We do not know
whether it was owing to this cause, or to the plant having previously
become bent to one side through heliotropism, but from the morning of the
7th of March to 10.30 P.M. on the 8th, the stem moved a considerable
distance in a zigzag line in the same general direction. During the night of
the 8th it moved to some distance at right angles to its former course, and
next morning (9th) stood for a time almost still. At noon on the 9th a new
tracing was begun (see Fig. 71), which was continued till 8 A.M. on the
11th. Between noon on the 9th and 5 P.M. on the 10th (i.e. in the course of
29 h.), the stem described a circle. This plant therefore circumnutates, but at
a very slow rate, and to a small extent.
Fig. 71. Pelargonium zonale: circumnutation of stem of young plant,
feebly illuminated from above. Movement of bead magnified about 11
times; traced on a horizontal glass from noon on March 9th to 8 A.M. on the
11th.
(5.) Tropaeolum majus (?) (dwarfed var. called Tom Thumb);
(Geraniaceae, Fam. 47).—The species of this genus climb by the aid of
their sensitive petioles, but some of them also twine round supports; but
even these latter species do not begin to circumnutate in a conspicuous
manner whilst young. The variety here treated of has a rather thick stem,
and is so dwarf that apparently it does not climb in any manner. We
therefore wished to ascertain whether the stem of a young plant, consisting
of two internodes, together 3.2 inches in height, circumnutated. It was
observed during 25 h., and we see in Fig. 72 that the stem moved in a
zigzag course, indicating circumnutation.
Fig. 72. Tropaeolum majus (?): circumnutation of stem of young plant,
traced on a horizontal glass from 9 A.M. Dec. 26th to 10 A.M. on 27th.
Movement of bead magnified about 5 times, and here reduced to half of
original scale.
Fig. 73. Trifolium resupinatum: circumnutation of stem, traced on
vertical glass from 9.30 A.M. to 4.30 P.M. Nov. 3rd. Tracing not greatly
magnified, reduced to half of original size. Plant feebly illuminated from
above.
(6.) Trifolium resupinatum (Leguminosae, Fam. 75).—When we treat of
the sleep of plants, we shall see that the stems in several Leguminous

genera, for instance, those of Hedysarum, Mimosa, Melilotus, etc., which
are not climbers, circumnutate in a conspicuous manner. We will here give
only a single instance (Fig. 73), showing the circumnutation of the stem of a
large plant of a clover, Trifolium resupinatum. In the course of 7 h. the stem
changed its course greatly eight times and completed three irregular circles
or ellipses. It therefore circumnutated rapidly. Some of the lines run at right
angles to one another.
Fig. 74. Rubus (hybrid): circumnutation of stem, traced on horizontal
glass, from 4 P.M. March 14th to 8.30 A.M. 16th. Tracing much magnified,
reduced to half of original size. Plant illuminated feebly from above.
(7.) Rubus idæus (hybrid) (Rosaceae, Fam. 76).—As we happened to
have a young plant, 11 inches in height and growing vigorously, which had
been raised from a cross between the raspberry (Rubus idæus) and a North
American Rubus, it was observed in the usual manner. During the morning
of March 14th the stem almost completed a circle, and then moved far to
the right. At 4 P.M. it reversed its course, and now a fresh tracing was
begun, which was continued during 40½ h., and is given in Fig. 74. We here
have well-marked circumnutation.
(8.) Deutzia gracilis (Saxifrageae, Fam. 77).—A shoot on a bush about 18
inches in height was observed. The bead changed its course greatly eleven
times in the course of 10 h. 30 m. (Fig. 75), and there could be no doubt
about the circumnutation of the stem.
Fig. 75. Deutzia gracilis: circumnutation of stem, kept in darkness, traced
on horizontal glass, from 8.30 A.M. to 7 P.M. March 20th. Movement of
bead originally magnified about 20 times, here reduced to half scale.
(9.) Fuchsia (greenhouse var., with large flowers, probably a hybrid)
(Onagrarieae, Fam. 100).—A young plant, 15 inches in height, was
observed during nearly 48 h. The accompanying figure (Fig. 76) gives the
necessary particulars, and shows that the stem circumnutated, though rather
slowly.
Fig. 76. Fuchsia (garden var.): circumnutation of stem, kept in darkness,
traced on horizontal glass, from 8.30 A.M. to 7 P.M. March 20th.
Movement of bead originally magnified about 40 times, here reduced to
half scale.
(10.) Cereus speciocissimus (garden var., sometimes called Phyllocactus
multiflorus) (Cacteæ, Fam. 109).—This plant, which was growing

vigorously from having been removed a few days before from the
greenhouse to the hot-house, was observed with especial interest, as it
seemed so little probable that the stem would circumnutate. The branches
are flat, or flabelliform; but some of them are triangular in section, with the
three sides hollowed out. A branch of this latter shape, 9 inches in length
and 1½ in diameter, was chosen for observation, as less likely to
circumnutate than a flabelliform branch. The movement of the bead at the
end of the glass filament, affixed to the summit of the branch, was traced
(A, Fig. 77) from 9.23 A.M. to 4.30 P.M. on Nov. 23rd, during which time it
changed its course greatly six times. On the 24th another tracing was made
(see B), and the bead on this day changed its course oftener, making in 8 h.
what may be considered as four ellipses, with their longer axes differently
directed. The position of the stem and its commencing course on the
following morning are likewise shown. There can be no doubt that this
branch, though appearing quite rigid, circumnutated; but the extreme
amount of movement during the time was very small, probably rather less
than the 1/20th of an inch.
Fig 77. Cereus speciocissimus: circumnutation of stem, illuminated from
above, traced on a horizontal glass, in A from 9 A.M. to 4.30 P.M. on Nov.
23rd; and in B from 8.30 A.M. on the 24th to 8 A.M. on the 25th.
Movement of the bead in B magnified about 38 times.
(11.) Hedera helix (Araliaceae, Fam. 114).—The stem is known to be
apheliotropic, and several seedlings growing in a pot in the greenhouse
became bent in the middle of the summer at right angles from the light. On
Sept. 2nd some of these stems were tied up so as to stand vertically, and
were placed before a north-east window; but to our surprise they were now
decidedly heliotropic, for during 4 days they curved themselves towards the
light, and their course being traced on a horizontal glass, was strongly
zigzag. During the 6 succeeding days they circumnutated over the same
small space at a slow rate, but there could be no doubt about their
circumnutation. The plants were kept exactly in the same place before the
window, and after an interval of 15 days the stems were again observed
during 2 days and their movements traced, and they were found to be still
circumnutating, but on a yet smaller scale.
(12.) Gazania ringens (Compositæ, Fam. 122).—The circumnutation of
the stem of a young plant, 7 inches in height, as measured to the tip of the

highest leaf, was traced during 33 h., and is shown in the accompanying
figure (Fig. 78). Two main lines may be observed running at nearly right
angles to two other main lines; but these are interrupted by small loops.
Fig. 78. Gazania ringens: circumnutation of stem traced from 9 A.M.
March 21st to 6 P.M. on 22nd; plant kept in darkness. Movement of bead at
the close of the observations magnified 34 times, here reduced to half the
original scale.
(13.) Azalea Indica (Ericineae, Fam. 128).—A bush 21 inches in height
was selected for observation, and the circumnutation of its leading shoot
was traced during 26 h. 40 m., as shown in the following figure (Fig. 79).
(14.) Plumbago Capensis (Plumbagineae, Fam. 134).—A small lateral
branch which projected from a tall freely growing bush, at an angle of 35°
above the horizon, was selected for observation. For the first 11 h. it moved
to a considerable distance in a nearly straight line to one side, owing
probably to its having been previously deflected by the light whilst standing
in the greenhouse. At 7.20 P.M. on March 7th a fresh tracing was begun and
continued for the next 43 h. 40 m. (see Fig. 80). During the first 2 h. it
followed nearly the same direction as before, and then changed it a little;
during the night it moved at nearly right angles to its previous course. Next
day (8th) it zigzagged greatly, and on the 9th moved irregularly round and
round a small circular space. By 3 P.M. on the 9th the figure had become so
complicated that no more dots could be made; but the shoot continued
during the evening of the 9th, the whole of the 10th, and the morning of the
11th to circumnutate over the same small space, which was only about the
1/26th of an inch (.97 mm.) in diameter. Although this branch
circumnutated to a very small extent, yet it changed its course frequently.
The movements ought to have been more magnified.
Fig. 79. Azalea Indica: circumnutation of stem, illuminated from above,
traced on horizontal glass, from 9.30 A.M. March 9th to 12.10 P.M. on the
10th. But on the morning of the 10th only four dots were made between
8.30 A.M. and 12.10 P.M., both hours included, so that the circumnutation
is not fairly represented in this part of the diagram. Movement of the bead
here magnified about 30 times.
Fig. 80. Plumbago Capensis: circumnutation of tip of a lateral branch,
traced on horizontal glass, from 7.20 P.M. on March 7th to 3 P.M. on the

9th. Movement of bead magnified 13 times. Plant feebly illuminated from
above.
(15.) Aloysia citriodora (Verbenaceae, Fam. 173).—The following figure
(Fig. 81) gives the movements of a shoot during 31 h. 40 m., and shows that
it circumnutated. The bush was 15 inches in height.
Fig. 81. Aloysia citriodora: circumnutation of stem, traced from 8.20
A.M. on March 22nd to 4 P.M. on 23rd. Plant kept in darkness. Movement
magnified about 40 times.
(16.) Verbena melindres (?) (a scarlet-flowered herbaceous var.)
(Verbenaceae).—A shoot 8 inches in height had been laid horizontally, for
the sake of observing its apogeotropism, and the terminal portion had
grown vertically upwards for a length of 1½ inch. A glass filament, with a
bead at the end, was fixed upright to the tip, and its movements were traced
during 41 h. 30 m. on a vertical glass (Fig. 82). Under these circumstances
the lateral movements were chiefly shown; but as the lines from side to side
are not on the same level, the shoot must have moved in a plane at right
angles to that of the lateral movement, that is, it must have circumnutated.
On the next day (6th) the shoot moved in the course of 16 h. four times to
the right, and four times to the left; and this apparently represents the
formation of four ellipses, so that each was completed in 4 h. (17.)
Ceratophyllum demersum (Ceratophylleae, Fam. 220).—An interesting
account of the movements of the stem of this water-plant has been
published by M. E. Rodier.[1] The movements are confined to the young
internodes, becoming less and less lower down the stem; and they are
extraordinary from their amplitude. The stems sometimes moved through an
angle of above 200° in 6 h., and in one instance through 220° in 3 h. They
generally bent from right to left in the morning, and in an opposite direction
in the afternoon; but the movement was sometimes temporarily reversed or
quite arrested. It was not affected by light. It does not appear that M. Rodier
made any diagram on a horizontal plane representing the actual course
pursued by the apex, but he speaks of the “branches executing round their
axes of growth a movement of torsion.” From the particulars above given,
and remembering in the case of twining plants and of tendrils, how difficult
it is not to mistake their bending to all points of the compass for true
torsion, we are led to believe that the stems of this Ceratophyllum
circumnutate, probably in the shape of narrow ellipses, each completed in

about 26 h. The following statement, however, seems to indicate something
different from ordinary circumnutation, but we cannot fully understand it.
M. Rodier says: “Il est alors facile de voir que le mouvement de flexion se
produit d’abord dans les mérithalles supérieurs, qu’il se propage ensuite, en
s’amoindrissant du haut en bas; tandis qu’au contraire le movement de
redressement commence par la partie inférieur pour se terminer a la partie
supérieure qui, quelquefois, peu de temps avant de se relever tout à fait,
forme avec l’axe un angle très aigu.”
[1] ‘Comptes Rendus,’ April 30th, 1877. Also a second notice published
separately in Bourdeaux, Nov. 12th, 1877.

Fig. 82. Verbena melindres: circumnutation of stem in darkness, traced
on vertical glass, from 5.30 P.M. on June 5th to 11 A.M. June 7th.
Movement of bead magnified 9 times.
(18.) Coniferæ.—Dr. Maxwell Masters states (‘Journal Linn. Soc.,’ Dec.
2nd, 1879) that the leading shoots of many Coniferæ during the season of
their active growth exhibit very remarkable movements of revolving
nutation, that is, they circumnutate. We may feel sure that the lateral shoots
whilst growing would exhibit the same movement if carefully observed.
(19.) Lilium auratum (Fam. Liliaceae).—The circumnutation of the stem
of a plant 24 inches in height is represented in the above figure (Fig. 83).
Fig. 83. Lilium auratum: circumnutation of a stem in darkness, traced on
a horizontal glass, from 8 A.M. on March 14th to 8.35 A.M. on 16th. But it
should be noted that our observations were interrupted between 6 P.M. on
the 14th and 12.15 P.M. on the 15th, and the movements during this interval
of 18 h. 15 m. are represented by a long broken line. Diagram reduced to
half original scale.
Fig. 84. Cyperus alternifolius: circumnutation of stem, illuminated from
above, traced on horizontal glass, from 9.45 A.M. March 9th to 9 P.M. on
10th. The stem grew so rapidly whilst being observed, that it was not
possible to estimate how much its movements were magnified in the
tracing.
(20.) Cyperus alternifolius (Fam. Cyperaceae.)—A glass filament, with a
bead at the end, was fixed across the summit of a young stem 10 inches in
height, close beneath the crown of elongated leaves. On March 8th,
between 12.20 and 7.20 P.M. the stem described an ellipse, open at one end.

On the following day a new tracing was begun (Fig. 84), which plainly
shows that the stem completed three irregular figures in the course of 35 h.
15 m.

Concluding Remarks on the Circumnutation of Stems.—Any one who
will inspect the diagrams now given, and will bear in mind the widely
separated position of the plants described in the series,—remembering that
we have good grounds for the belief that the hypocotyls and epicotyls of all
seedlings circumnutate,—not forgetting the number of plants distributed in
the most distinct families which climb by a similar movement,—will
probably admit that the growing stems of all plants, if carefully observed,
would be found to circumnutate to a greater or less extent. When we treat of
the sleep and other movements of plants, many other cases of
circumnutating stems will be incidentally given. In looking at the diagrams,
we should remember that the stems were always growing, so that in each
case the circumnutating apex as it rose will have described a spire of some
kind. The dots were made on the glasses generally at intervals of an hour, or
hour and a half, and were then joined by straight lines. If they had been
made at intervals of 2 or 3 minutes, the lines would have been more
curvilinear, as in the case of the tracks left on the smoked glass-plates by
the tips of the circumnutating radicles of seedling plants. The diagrams
generally approach in form to a succession of more or less irregular ellipses
or ovals, with their longer axes directed to different points of the compass
during the same day or on succeeding days. The stems therefore, sooner or
later, bend to all sides; but after a stem has bent in any one direction, it
commonly bends back at first in nearly, though not quite, the opposite
direction; and this gives the tendency to the formation of ellipses, which are
generally narrow, but not so narrow as those described by stolons and
leaves. On the other hand, the figures sometimes approach in shape to
circles. Whatever the figure may be, the course pursued is often interrupted
by zigzags, small triangles, loops, or ellipses. A stem may describe a single
large ellipse one day, and two on the next. With different plants the
complexity, rate, and amount of movement differ much. The stems, for
instance, of Iberis and Azalea described only a single large ellipse in 24 h.;
whereas those of the Deutzia made four or five deep zigzags or narrow

ellipses in 11½ h., and those of the Trifolium three triangular or
quadrilateral figures in 7 h.

CIRCUMNUTATION OF STOLONS OR
RUNNERS.
Stolons consist of much elongated, flexible branches, which run along
the surface of the ground and form roots at a distance from the parent-plant.
They are therefore of the same homological nature as stems; and the three
following cases may be added to the twenty previously given cases.

Fragaria (cultivated garden var.): Rosaceae.—A plant growing in a pot
had emitted a long stolon; this was supported by a stick, so that it projected
for the length of several inches horizontally. A glass filament bearing two
minute triangles of paper was affixed to the terminal bud, which was a little
upturned; and its movements were traced during 21 h., as shown in Fig. 85.
In the course of the first 12 h. it moved twice up and twice down in
somewhat zigzag lines, and no doubt travelled in the same manner during
the night. On the following morning after an interval of 20 h. the apex stood
a little higher than it did at first, and this shows that the stolon had not been
acted on within this time by geotropism;[2] nor had its own weight caused it
to bend downwards.
[2] Dr. A. B. Frank states (‘Die Naturliche wagerechte Richtung von
Pflanzentheilen,’ 1870, p. 20) that the stolons of this plant are acted on by
geotropism, but only after a considerable interval of time.

Fig. 85. Fragaria: circumnutation of stolon, kept in darkness, traced on
vertical glass, from 10.45 A.M. May 18th to 7.45 A.M. on 19th.
On the following morning (19th) the glass filament was detached and
refixed close behind the bud, as it appeared possible that the circumnutation
of the terminal bud and of the adjoining part of the stolon might be
different. The movement was now traced during two consecutive days (Fig.
86). During the first day the filament travelled in the course of 14 h. 30 m.
five times up and four times down, besides some lateral movement. On the
20th the course was even more complicated, and can hardly be followed in

the figure; but the filament moved in 16 h. at least five times up and five
times down, with very little lateral deflection. The first and last dots made
on this second day, viz., at 7 A.M. and 11 P.M., were close together,
showing that the stolon had not fallen or risen. Nevertheless, by comparing
its position on the morning of the 19th and 21st, it is obvious that the stolon
had sunk; and this may be attributed to slow bending down either from its
own weight or from geotropism.
Fig. 86. Fragaria: circumnutation of the same stolon as in the last figure,
observed in the same manner, and traced from 8 A.M. May 19th to 8 A.M.
21st.
During a part of the 20th an orthogonal tracing was made by applying a
cube of wood to the vertical glass and bringing the apex of the stolon at
successive periods into a line with one edge; a dot being made each time on
the glass. This tracing therefore represented very nearly the actual amount
of movement of the apex; and in the course of 9 h. the distance of the
extreme dots from one another was .45 inch. By the same method it was
ascertained that the apex moved between 7 A.M. on the 20th and 8 A.M. on
the 21st a distance of .82 inch.
A younger and shorter stolon was supported so that it projected at about
45° above the horizon, and its movement was traced by the same orthogonal
method. On the first day the apex soon rose above the field of vision. By the
next morning it had sunk, and the course pursued was now traced during 14
h. 30 m. (Fig. 87). The amount of movement was almost the same, from
side to side as up and down; and differed in this respect remarkably from
the movement in the previous cases. During the latter part of the day, viz.,
between 3 and 10.30 P.M., the actual distance travelled by the apex
amounted to 1.15 inch; and in the course of the whole day to at least 2.67
inches. This is an amount of movement almost comparable with that of
some climbing plants. The same stolon was observed on the following day,
and now it moved in a somewhat less complex manner, in a plane not far
from vertical. The extreme amount of actual movement was 1.55 inch in
one direction, and .6 inch in another direction at right angles. During neither
of these days did the stolon bend downwards through geotropism or its own
weight.
Fig. 87. Fragaria: circumnutation of another and younger stolon, traced
from 8 A.M. to 10.30 P.M. Figure reduced to one-half of original scale.

Four stolons still attached to the plant were laid on damp sand in the back
of a room, with their tips facing the north-east windows. They were thus
placed because De Vries says[3] that they are apheliotropic when exposed to
the light of the sun; but we could not perceive any effect from the above
feeble degree of illumination. We may add that on another occasion, late in
the summer, some stolons, placed upright before a south-west window on a
cloudy day, became distinctly curved towards the light, and were therefore
heliotropic. Close in front of the tips of the prostrate stolons, a crowd of
very thin sticks and the dried haulms of grasses were driven into the sand,
to represent the crowded stems of surrounding plants in a state of nature.
This was done for the sake of observing how the growing stolons would
pass through them. They did so easily in the course of 6 days, and their
circumnutation apparently facilitated their passage. When the tips
encountered sticks so close together that they could not pass between them,
they rose up and passed over them. The sticks and haulms were removed
after the passage of the four stolons, two of which were found to have
assumed a permanently sinuous shape, and two were still straight. But to
this subject we shall recur under Saxifraga.
[3] ‘Arbeiten Bot Inst., Würzburg,’ 1872, p. 434.

Saxifraga sarmentosa (Saxifrageae).—A plant in a suspended pot had
emitted long branched stolons, which depended like threads on all sides.
Two were tied up so as to stand vertically, and their upper ends became
gradually bent downwards, but so slowly in the course of several days, that
the bending was probably due to their weight and not to geotropism. A glass
filament with little triangles of paper was fixed to the end of one of these
stolons, which was 17½ inches in length, and had already become much
bent down, but still projected at a considerable angle above the horizon. It
moved only slightly three times from side to side and then upwards; on the
following day the movement was even less. As this stolon was so long we
thought that its growth was nearly completed, so we tried another which
was thicker and shorter, viz., 10 1/4 inches in length. It moved greatly,
chiefly upwards, and changed its course five times in the course of the day.
During the night it curved so much upwards in opposition to gravity, that
the movement could no longer be traced on the vertical glass, and a
horizontal one had to be used. The movement was followed during the next
25 h., as shown in Fig. 88. Three irregular ellipses, with their longer axes

somewhat differently directed, were almost completed in the first 15 h. The
extreme actual amount of movement of the tip during the 25 h. was .75
inch. Several stolons were laid on a flat surface of damp sand, in the same
manner as with those of the strawberry. The friction of the sand did not
interfere with their circumnutation; nor could we detect any evidence of
their being sensitive to contact. In order to see how in a state of nature they
would act, when encountering a stone or other obstacle on the ground, short
pieces of smoked glass, an inch in height, were stuck upright into the sand
in front of two thin lateral branches. Their tips scratched the smoked surface
in various directions; one made three upward and two downward lines,
besides a nearly horizontal one; the other curled quite away from the glass;
but ultimately both surmounted the glass and pursued their original course.
The apex of a third thick stolon swept up the glass in a curved line, recoiled
and again came into contact with it; it then moved to the right, and after
ascending, descended vertically; ultimately it passed round one end of the
glass instead of over it.
Fig. 88. Saxifraga sarmentosa: circumnutation of an inclined stolon,
traced in darkness on a horizontal glass, from 7.45 A.M. April 18th to 9
A.M. on 19th. Movement of end of stolon magnified 2.2 times.
Many long pins were next driven rather close together into the sand, so as
to form a crowd in front of the same two thin lateral branches; but these
easily wound their way through the crowd. A thick stolon was much
delayed in its passage; at one place it was forced to turn at right angles to its
former course; at another place it could not pass through the pins, and the
hinder part became bowed; it then curved upwards and passed through an
opening between the upper part of some pins which happened to diverge; it
then descended and finally emerged through the crowd. This stolon was
rendered permanently sinuous to a slight degree, and was thicker where
sinuous than elsewhere, apparently from its longitudinal growth having
been checked.
Cotyledon umbilicus (Crassulaceæ).—A plant growing in a pan of damp
moss had emitted 2 stolons, 22 and 20 inches in length. One of these was
supported, so that a length of 4½ inches projected in a straight and
horizontal line, and the movement of the apex was traced. The first dot was
made at 9.10 A.M.; the terminal portion soon began to bend downwards and
continued to do so until noon. Therefore a straight line, very nearly as long

as the whole figure here given (Fig. 89), was first traced on the glass; but
the upper part of this line has not been copied in the diagram. The curvature
occurred in the middle of the penultimate internode; and its chief seat was
at the distance of 1 1/4 inch from the apex; it appeared due to the weight of
the terminal portion, acting on the more flexible part of the internode, and
not to geotropism. The apex after thus sinking down from 9.10 A.M. to
noon, moved a little to the left; it then rose up and circumnutated in a nearly
vertical plane until 10.35 P.M. On the following day (26th) it was observed
from 6.40 A.M. to 5.20 P.M., and within this time it moved twice up and
twice down. On the morning of the 27th the apex stood as high as it did at
11.30 A.M. on the 25th. Nor did it sink down during the 28th, but continued
to circumnutate about the same place.
Fig. 89. Cotyledon umbilicus: circumnutation of stolon, traced from
11.15 A.M. Aug. 25th to 11 A.M. 27th. Plant illuminated from above. The
terminal internode was .25 inch in length, the penultimate 2.25 and the third
3.0 inches in length. Apex of stolon stood at a distance of 5.75 inches from
the vertical glass; but it was not possible to ascertain how much the tracing
was magnified, as it was not known how great a length of the internode
circumnutated.
Another stolon, which resembled the last in almost every respect, was
observed during the same two days, but only two inches of the terminal
portion was allowed to project freely and horizontally. On the 25th it
continued from 9.10 A.M. to 1.30 P.M. to bend straight downwards,
apparently owing to its weight (Fig. 90); but after this hour until 10.35 P.M.
it zigzagged. This fact deserves notice, for we here probably see the
combined effects of the bending down from weight and of circumnutation.
The stolon, however, did not circumnutate when it first began to bend
down, as may be observed in the present diagram, and as was still more
evident in the last case, when a longer portion of the stolon was left
unsupported. On the following day (26th) the stolon moved twice up and
twice down, but still continued to fall; in the evening and during the night it
travelled from some unknown cause in an oblique direction.
Fig. 90. Cotyledon umbilicus: circumnutation and downward movement
of another stolon, traced on vertical glass, from 9.11 A.M. Aug. 25th to 11
A.M. 27th. Apex close to glass, so that figure but little magnified, and here
reduced to two-thirds of original size.

We see from these three cases that stolons or runners circumnutate in a
very complex manner. The lines generally extend in a vertical plane, and
this may probably be attributed to the effect of the weight of the
unsupported end of the stolon; but there is always some, and occasionally a
considerable, amount of lateral movement. The circumnutation is so great in
amplitude that it may almost be compared with that of climbing plants. That
the stolons are thus aided in passing over obstacles and in winding between
the stems of the surrounding plants, the observations above given render
almost certain. If they had not circumnutated, their tips would have been
liable to have been doubled up, as often as they met with obstacles in their
path; but as it is, they easily avoid them. This must be a considerable
advantage to the plant in spreading from its parent-stock; but we are far
from supposing that the power has been gained by the stolons for this
purpose, for circumnutation seems to be of universal occurrence with all
growing parts; but it is not improbable that the amplitude of the movement
may have been specially increased for this purpose.

CIRCUMNUTATION OF FLOWER-STEMS.
We did not think it necessary to make any special observations on the
circumnutation of flower-stems, these being axial in their nature, like stems
or stolons; but some were incidentally made whilst attending to other
subjects, and these we will here briefly give. A few observations have also
been made by other botanists. These taken together suffice to render it
probable that all peduncles and sub-peduncles circumnutate whilst growing.

Oxalis carnosa.—The peduncle which springs from the thick and woody
stem of this plant bears three or four sub-peduncles. A filament with little
triangles of paper was fixed within the calyx of a flower which stood
upright. Its movements were observed for 48 h.; during the first half of this
time the flower was fully expanded, and during the second half withered.
The figure here given (Fig. 91) represents 8 or 9 ellipses. Although the main
peduncle circumnutated, and described one large and two smaller ellipses in
the course of 24 h., yet the chief seat of movement lies in the sub-
peduncles, which ultimately bend vertically downwards, as will be
described in a future chapter. The peduncles of Oxalis acetosella likewise

bend downwards, and afterwards, when the pods are nearly mature,
upwards; and this is effected by a circumnutating movement.
Fig. 91. Oxalis carnosa: flower-stem, feebly illuminated from above, its
circumnutation traced from 9 A.M. April 13th to 9 A.M. 15th. Summit of
flower 8 inches beneath the horizontal glass. Movement probably magnified
about 6 times.
It may be seen in the above figure that the flower-stem of O. carnosa
circumnutated during two days about the same spot. On the other hand, the
flower-stem of O. sensitiva undergoes a strongly marked, daily, periodical
change of position, when kept at a proper temperature. In the middle of the
day it stands vertically up, or at a high angle; in the afternoon it sinks, and
in the evening projects horizontally, or almost horizontally, rising again
during the night. This movement continues from the period when the
flowers are in bud to when, as we believe, the pods are mature: and it ought
perhaps to have been included amongst the so-called sleep-movements of
plants. A tracing was not made, but the angles were measured at successive
periods during one whole day; and these showed that the movement was not
continuous, but that the peduncle oscillated up and down. We may therefore
conclude that it circumnutated. At the base of the peduncle there is a mass
of small cells, forming a well-developed pulvinus, which is exteriorly
coloured purple and hairy. In no other genus, as far as we know, is the
peduncle furnished with a pulvinus. The peduncle of O. Ortegesii behaved
differently from that of O. sensitiva, for it stood at a less angle above the
horizon in the middle of the day, then in the morning or evening. By 10.20
P.M. it had risen greatly. During the middle of the day it oscillated much up
and down.
Trifolium subterraneum.—A filament was fixed vertically to the
uppermost part of the peduncle of a young and upright flower-head (the
stem of the plant having been secured to a stick); and its movements were
traced during 36 h. Within this time it described (see Fig. 92) a figure which
represents four ellipses; but during the latter part of the time the peduncle
began to bend downwards, and after 10.30 P.M. on the 24th it curved so
rapidly down, that by 6.45 A.M. on the 25th it stood only 19° above the
horizon. It went on circumnutating in nearly the same position for two days.
Even after the flower-heads have buried themselves in the ground they
continue, as will hereafter be shown, to circumnutate. It will also be seen in

the next chapter that the sub-peduncles of the separate flowers of Trifolium
repens circumnutate in a complicated course during several days. I may add
that the gynophore of Arachis hypogoea, which looks exactly like a
peduncle, circumnutates whilst growing vertically downwards, in order to
bury the young pod in the ground.
Fig. 92. Trifolium subterraneum: main flower-peduncle, illuminated from
above, circumnutation traced on horizontal glass, from 8.40 A.M. July 23rd
to 10.30 P.M. 24th.
The movements of the flowers of Cyclamen Persicum were not observed;
but the peduncle, whilst the pod is forming, increases much in length, and
bows itself down by a circumnutating movement. A young peduncle of
Maurandia semperflorens, 1½ inch in length, was carefully observed during
a whole day, and it made 4½ narrow, vertical, irregular and short ellipses,
each at an average rate of about 2 h. 25 m. An adjoining peduncle described
during the same time similar, though fewer, ellipses.[4] According to Sachs[5]
the flower-stems, whilst growing, of many plants, for instance, those of
Brassica napus, revolve or circumnutate; those of Allium porrum bend from
side to side, and, if this movement had been traced on a horizontal glass, no
doubt ellipses would have been formed. Fritz Müller has described[6] the
spontaneous revolving movements of the flower-stems of an Alisma, which
he compares with those of a climbing plant.
[4] ‘The Movements and Habits of Climbing Plants,’ 2nd edit., 1875, p. 68.

[5] ‘Text-Book of Botany,’ 1875, p. 766. Linnæus and Treviranus (according to
Pfeffer, ‘Die Periodischen Bewegungen,’ etc., p. 162) state that the flower-stalks
of many plants occupy different positions by night and day, and we shall see in
the chapter on the Sleep of Plants that this implies circumnutation.

[6] ‘Jenaische Zeitsch.,’ B. v. p. 133.

We made no observations on the movements of the different parts of
flowers. Morren, however, has observed[7] in the stamens of Sparmannia
and Cereus a “fremissement spontané,” which, it may be suspected, is a
circumnutating movement. The circumnutation of the gynostemium of
Stylidium, as described by Gad,[8] is highly remarkable, and apparently aids
in the fertilisation of the flowers. The gynostemium, whilst spontaneously
moving, comes into contact with the viscid labellum, to which it adheres,
until freed by the increasing tension of the parts or by being touched.

[7] ‘N. Mem. de l’Acad. R. de Bruxelles,’ tom. xiv. 1841, p. 3.

[8] ‘Sitzungbericht des bot. Vereins der P. Brandenburg,’ xxi. p. 84.

We have now seen that the flower-stems of plants belonging to such
widely different families as the Cruciferae, Oxalidæ, Leguminosae,
Primulaceae, Scrophularineae, Alismaceae, and Liliaceae, circumnutate;
and that there are indications of this movement in many other families. With
these facts before us, bearing also in mind that the tendrils of not a few
plants consist of modified peduncles, we may admit without much doubt
that all growing flower-stems circumnutate.

CIRCUMNUTATION OF LEAVES:
DICOTYLEDONS.
Several distinguished botanists, Hofmeister, Sachs, Pfeffer, De Vries,
Batalin, Millardet, etc., have observed, and some of them with the greatest
care, the periodical movements of leaves; but their attention has been
chiefly, though not exclusively, directed to those which move largely and
are commonly said to sleep at night. From considerations hereafter to be
given, plants of this nature are here excluded, and will be treated of
separately. As we wished to ascertain whether all young and growing leaves
circumnutated, we thought that it would be sufficient if we observed
between 30 and 40 genera, widely distributed throughout the vegetable
series, selecting some unusual forms and others on woody plants. All the
plants were healthy and grew in pots. They were illuminated from above,
but the light perhaps was not always sufficiently bright, as many of them
were observed under a skylight of ground-glass. Except in a few specified
cases, a fine glass filament with two minute triangles of paper was fixed to
the leaves, and their movements were traced on a vertical glass (when not
stated to the contrary) in the manner already described. I may repeat that the
broken lines represent the nocturnal course. The stem was always secured to
a stick, close to the base of the leaf under observation. The arrangement of
the species, with the number of the Family appended, is the same as in the
case of stems.
Fig. 93. Sarracenia purpurea: circumnutation of young pitcher, traced
from 8 A.M. July 3rd to 10.15 A.M. 4th. Temp. 17°–18° C. Apex of pitcher

20 inches from glass, so movement greatly magnified.
(1.) Sarracenia purpurea (Sarraceneae, Fam. 11).—A young leaf, or
pitcher, 8½ inches in height, with the bladder swollen but with the hood not
as yet open, had a filament fixed transversely across its apex; it was
observed for 48 h., and during the whole of this time it circumnutated in a
nearly similar manner, but to a very small extent. The tracing given (Fig.
93) relates only to the movement during the first 26 h.
(2) Glaucium luteum (Papaveraceae, Fam. 12).—A young plant, bearing
only 8 leaves, had a filament attached to the youngest leaf but one, which
was 3 inches in length, including the petiole. The circumnutating movement
was traced during 47 h. On both days the leaf descended from before 7
A.M. until about 11 A.M., and then ascended slightly during the rest of the
day and the early part of the night. During the latter part of the night it fell
greatly. It did not ascend so much during the second as during the first day,
and it descended considerably lower on the second night than on the first.
This difference was probably due to the illumination from above having
been insufficient during the two days of observation. Its course during the
two days is shown in Fig. 94.
Fig. 94. Glaucium luteum: circumnutation of young leaf, traced from
9.30 A.M. June 14th to 8.30 A.M. 16th. Tracing not much magnified, as
apex of leaf stood only 5½ inches from the glass.
(3.) Crambe maritima (Cruciferae, Fam. 14).—A leaf 9½ inches in length
on a plant not growing vigorously was first observed. Its apex was in
constant movement, but this could hardly be traced, from being so small in
extent. The apex, however, certainly changed its course at least 6 times in
the course of 14 h. A more vigorous young plant, bearing only 4 leaves, was
then selected, and a filament was affixed to the midrib of the third leaf from
the base, which, with the petiole, was 5 inches in length. The leaf stood up
almost vertically, but the tip was deflected, so that the filament projected
almost horizontally, and its movements were traced during 48 h. on a
vertical glass as shown in the accompanying figure (Fig. 95). We here
plainly see that the leaf was continually circumnutating; but the proper
periodicity of its movements was disturbed by its being only dimly
illuminated from above through a double skylight. We infer that this was the
case, because two leaves on plants growing out of doors, had their angles
above the horizon measured in the middle of the day and at 9 to about 10

P.M. on successive nights, and they were found at this latter hour to have
risen by an average angle of 9° above their mid-day position: on the
following morning they fell to their former position. Now it may be
observed in the diagram that the leaf rose during the second night, so that it
stood at 6.40 A.M. higher than at 10.20 P.M. on the preceding night; and
this may be attributed to the leaf adjusting itself to the dim light, coming
exclusively from above.
Fig. 95. Crambe maritima: circumnutation of leaf, disturbed by being
insufficiently illuminated from above, traced from 7.50 A.M. June 23rd to 8
A.M. 25th. Apex of leaf 15 1/4 inches from the vertical glass, so that the
tracing was much magnified, but is here reduced to one-fourth of original
scale.
(4.) Brassica oleracea (Cruciferae).—Hofmeister and Batalin[9] state that
the leaves of the cabbage rise at night, and fall by day. We covered a young
plant, bearing 8 leaves, under a large bell-glass, placing it in the same
position with respect to the light in which it had long remained, and a
filament was fixed at the distance of .4 of an inch from the apex of a young
leaf nearly 4 inches in length. Its movements were then traced during three
days, but the tracing is not worth giving. The leaf fell during the whole
morning, and rose in the evening and during the early part of the night. The
ascending and descending lines did not coincide, so that an irregular ellipse
was formed each 24 h. The basal part of the midrib did not move, as was
ascertained by measuring at successive periods the angle which it formed
with the horizon, so that the movement was confined to the terminal portion
of the leaf, which moved through an angle of 11° in the course of 24 h., and
the distance travelled by the apex, up and down, was between .8 and .9 of
an inch.
[9] ‘Flora,’ 1873, p. 437.

In order to ascertain the effect of darkness, a filament was fixed to a leaf
5½ inches in length, borne by a plant which after forming a head had
produced a stem. The leaf was inclined 44° above the horizon, and its
movements were traced on a vertical glass every hour by the aid of a taper.
During the first day the leaf rose from 8 A.M. to 10.40 P.M. in a slightly
zigzag course, the actual distance travelled by the apex being .67 of an inch.
During the night the leaf fell, whereas it ought to have risen; and by 7 A.M.
on the following morning it had fallen .23 of an inch, and it continued

falling until 9.40 A.M. It then rose until 10.50 P.M., but the rise was
interrupted by one considerable oscillation, that is, by a fall and re-ascent.
During the second night it again fell, but only to a very short distance, and
on the following morning re-ascended to a very short distance. Thus the
normal course of the leaf was greatly disturbed, or rather completely
inverted, by the absence of light; and the movements were likewise greatly
diminished in amplitude.
We may add that, according to Mr. A. Stephen Wilson,[10] the young
leaves of the Swedish turnip, which is a hybrid between B. oleracea and
rapa, draw together in the evening so much “that the horizontal breadth
diminishes about 30 per cent. of the daylight breadth.” Therefore the leaves
must rise considerably at night.
[10] ‘Trans. Bot. Soc. Edinburgh,’ vol. xiii. p. 32. With respect to the origin of
the Swedish turnip, see Darwin, ‘Animals and Plants under Domestication,’ 2nd
edit. vol. i. p. 344.

(5.) Dianthus caryophyllus (Caryophylleae, Fam. 26).—The terminal
shoot of a young plant, growing very vigorously, was selected for
observation. The young leaves at first stand up vertically and close together,
but they soon bend outwards and downwards, so as to become horizontal,
and often at the same time a little to one side. A filament was fixed to the tip
of a young leaf whilst still highly inclined, and the first dot was made on the
vertical glass at 8.30 A.M. June 13th, but it curved downwards so quickly
that by 6.40 A.M. on the following morning it stood only a little above the
horizon. In Fig. 96 the long, slightly zigzag line representing this rapid
downward course, which was somewhat inclined to the left, is not given;
but the figure shows the highly tortuous and zigzag course, together with
some loops, pursued during the next 2½ days. As the leaf continued to
move all the time to the left, it is evident that the zigzag line represents
many circumnutations.
Fig. 96. Dianthus caryophyllus: circumnutation of young leaf, traced
from 10.15 P.M. June 13th to 10.35 P.M. 16th. Apex of leaf stood, at the
close of our observations, 8 3/4 inches from the vertical glass, so tracing not
greatly magnified. The leaf was 5 1/4 inches long. Temp. 15½°–17½° C.
(6.) Camellia Japonica (Camelliaceae, Fam. 32).—A youngish leaf,
which together with its petiole was 2 3/4 inches in length and which arose
from a side branch on a tall bush, had a filament attached to its apex. This

leaf sloped downwards at an angle of 40° beneath the horizon. As it was
thick and rigid, and its petiole very short, much movement could not be
expected. Nevertheless, the apex changed its course completely seven times
in the course of 11½ h., but moved to only a very small distance. On the
next day the movement of the apex was traced during 26 h. 20 m. (as shown
in Fig. 97), and was nearly of the same nature, but rather less complex. The
movement seems to be periodical, for on both days the leaf circumnutated
in the forenoon, fell in the afternoon (on the first day until between 3 and 4
P.M., and on the second day until 6 P.M.), and then rose, falling again
during the night or early morning.
Fig. 97. Camellia Japonica: circumnutation of leaf, traced from 6.40
A.M. June 14th to 6.50 A.M. 15th. Apex of leaf 12 inches from the vertical
glass, so figure considerably magnified. Temp. 16°–16½° C.
In the chapter on the Sleep of Plants we shall see that the leaves in
several Malvaceous genera sink
Fig. 98. Pelargonium zonale: circumnutation and downward movement
of young leaf, traced from 9.30 A.M. June 14th to 6.30 P.M. 16th. Apex of
leaf 9 1.4 inches from the vertical glass, so figure moderately magnified.
Temp. 15°–16½° C.
at night; and as they often do not then occupy a vertical position,
especially if they have not been well illuminated during the day, it is
doubtful whether some of these cases ought not to have been included in the
present chapter.
(7.) Pelargonium zonale (Geraniaceae, Fam. 47).—A young leaf, 1 1/4
inch in breadth, with its petiole 1 inch long, borne on a young plant, was
observed in the usual manner during 61 h.; and its course is shown in the
preceding figure (Fig. 98). During the first day and night the leaf moved
downwards, but circumnutated between 10 A.M. and 4.30 P.M. On the
second day it sank and rose again, but between 10 A.M. and 6 P.M. it
circumnutated on an extremely small scale. On the third day the
circumnutation was more plainly marked.
(8.) Cissus discolor (Ampelideae, Fam. 67).—A leaf, not nearly full-
grown, the third from the apex of a shoot on a cut-down plant, was
observed during 31 h. 30 m. (see Fig. 99). The day was cold (15°–16° C.),
and if the plant had been observed in the hot-house, the circumnutation,

though plain enough as it was, would probably have been far more
conspicuous.
Fig. 99. Cissus discolor: circumnutation of leaf, traced from 10.35 A.M.
May 28th to 6 P.M. 29th. Apex of leaf 8 3/4 inches from the vertical glass.
(9.) Vicia faba (Leguminosae, Fam. 75).—A young leaf, 3.1 inches in
length, measured from base of petiole to end of leaflets, had a filament
affixed to the midrib of one of the two terminal leaflets, and its movements
were traced during 51½ h. The filament fell all morning (July 2nd) till 3
P.M., and then rose greatly till 10.35 P.M.; but the rise this day was so great,
compared with that which subsequently occurred, that it was probably due
in part to the plant being illuminated from above. The latter part of the
course on July 2nd is alone given in the following figure (Fig. 100). On the
next day (July 3rd) the leaf again fell in the morning, then circumnutated in
a conspicuous manner, and rose till late at night; but the movement was not
traced after 7.15 P.M., as by that time the filament pointed towards the
upper edge of the glass. During the latter part of the night or early morning
it again fell in the same manner as before.
As the evening rise and the early morning fall were unusually large, the
angle of the petiole above the horizon was measured at the two periods, and
the leaf was found to have risen 19° between 12.20 P.M. and 10.45 P.M.,
and to have fallen 23° 30 seconds between the latter hour and 10.20 A.M.
on the following morning.
Fig. 100. Vicia faba: circumnutation of leaf, traced from 7.15 P.M. July
2nd to 10.15 A.M. 4th. Apex of the two terminal leaflets 7 1/4 inches from
the vertical glass. Figure here reduced to two-thirds of original scale. Temp.
17°–18° C.
The main petiole was now secured to a stick close to the base of the two
terminal leaflets, which were 1.4 inch in length; and the movements of one
of them were traced during 48 h. (see Fig. 101). The course pursued is
closely analogous to that of the whole leaf. The zigzag line between 8.30
A.M. and 3.30 P.M. on the second day represents 5 very small ellipses, with
their longer axes differently directed. From these observations it follows
that both the whole leaf and the terminal leaflets undergo a well-marked
daily periodical movement, rising in the evening and falling during the
latter part of the night or early morning; whilst in the middle of the day they
generally circumnutate round the same small space.

Fig 101. Vicia faba: circumnutation of one of the two terminal leaflets,
the main petiole having been secured, traced from 10.40 A.M. July 4th to
10.30 A.M. 6th. Apex of leaflet 6 5/8 inches from the vertical glass. Tracing
here reduced to one-half of original scale. Temp. 16°–18° C.
(10.) Acacia retinoides (Leguminosae).—The movement of a young
phyllode, 2 3/8 inches in length, and inclined at a considerable angle above
the horizon, was traced during 45 h. 30 m.; but in the figure here given (Fig.
102), its circumnutation is shown during only 21 h. 30 m. During part of
this time (viz., 14 h. 30 m.) the phyllode described a figure representing 5
or 6 small ellipses. The actual amount of movement in a vertical direction
was .3 inch. The phyllode rose considerably between 1.30 P.M. and 4 P.M.,
but there was no evidence on either day of a regular periodic movement.
Fig. 102. Acacia retinoides: circumnutation of a young phyllode, traced
from 10.45 A.M. July 18th to 8.15 A.M. 19th. Apex of phyllode 9 inches
from the vertical glass; temp. 16½°–17½° C.
(11.) Lupinus speciosus (Leguminosae).—Plants were raised from seed
purchased under this name. This is one of the species in this large genus, the
leaves of which do not sleep at night. The petioles rise direct from the
ground, and are from 5 to 7 inches in length. A filament was fixed to the
midrib of one of the longer leaflets, and the movement of the whole leaf
was traced, as shown in Fig. 103. In the course of 6 h. 30 m. the filament
went four times up and three times down. A new tracing was then begun
(not here given), and during 12½ h. the leaf moved eight times up and seven
times down; so that it described 7½ ellipses in this time, and this is an
extraordinary rate of movement. The summit of the petiole was then
secured to a stick, and the separate leaflets were found to be continually
circumnutating.
Fig. 103. Lupinus speciosus: circumnutation of leaf, traced on vertical
glass, from 10.15 A.M. to 5.45 P.M.; i.e., during 6 h. 30 m.
(12.) Echeveria stolonifera (Crassulaceæ, Fam. 84).—The older leaves of
this plant are so thick and fleshy, and the young ones so short and broad,
that it seemed very improbable that any circumnutation could be detected.
A filament was fixed to a young upwardly inclined leaf, .75 inch in length
and .28 in breadth, which stood on the outside of a terminal rosette of
leaves, produced by a plant growing very vigorously. Its movement was
traced during 3 days, as here shown (Fig. 104). The course was chiefly in an

upward direction, and this may be attributed to the elongation of the leaf
through growth; but we see that the lines are strongly zigzag, and that
occasionally there was distinct circumnutation, though on a very small
scale.
Fig. 104. Echeveria stolonifera: circumnutation of leaf, traced from 8.20
A.M. June 25th to 8.45 A.M. 28th. Apex of leaf 12 1/4 inches from the
glass, so that the movement was much magnified; temp. 23°–24½° C.
(13.) Bryophyllum (vel Calanchæ) calycinum (Crassulaceæ).—Duval-
Jouve (‘Bull. Soc. Bot. de France,’ Feb. 14th, 1868) measured the distance
between the tips of the upper pair of leaves on this plant, with the result
shown in the following Table. It should be noted that the measurements on
Dec. 2nd were made on a different pair of leaves:—
8 A.M. 2 P.M. 7 P.M. Nov. 16. . . . . . . . . . . . . . . . . . .15 mm.. . . . . .25
mm. . . .. . . .(?) ” 19. . . . . . . . . . . . . . . . . . .48 ” . . . . . . . 60 ”. . . . . . . 48
mm. Dec. 2. . . . . . . . . . . . . . . . . . .22 ”. . . . . . . . 43 ”. . . . . . . .28 ”
We see from this Table that the leaves stood considerably further apart at 2
P.M. than at either 8 A.M. or 7 P.M.; and this shows that they rise a little in
the evening and fall or open in the forenoon.
(14.) Drosera rotundifolia (Droseraceae, Fam. 85).—The movements of a
young leaf, having a long petiole but with its tentacles (or gland-bearing
hairs) as yet unfolded, were traced during 47 h. 15 m. The figure (Fig. 105)
shows that it circumnutated largely, chiefly in a vertical direction, making
two ellipses each day. On both days the leaf began to descend after 12 or 1
o’clock, and continued to do so all night, though to a very unequal distance
on the two occasions. We therefore thought that the movement was
periodic; but on observing three other leaves during several successive days
and nights, we found this to be an error; and the case is given merely as a
caution. On the third morning the above leaf occupied almost exactly the
same position as on the first morning; and the tentacles by this time had
unfolded sufficiently to project at right angles to the blade or disc.
Fig. 105. Drosera rotundifolia: circumnutation of young leaf, with
filament fixed to back of blade, traced from 9.15 A.M. June 7th to 8.30
A.M. June 9th. Figure here reduced to one-half original scale.
The leaves as they grow older generally sink more and more downwards.
The movement of an oldish leaf, the glands of which were still secreting
freely, was traced for 24 h., during which time it continued to sink a little in

a slightly zigzag line. On the following morning, at 7 A.M., a drop of a
solution of carbonate of ammonia (2 gr. to 1 oz. of water) was placed on the
disc, and this blackened the glands and induced inflection of many of the
tentacles. The weight of the drop caused the leaf at first to sink a little; but
immediately afterwards it began to rise in a somewhat zigzag course, and
continued to do so till 3 P.M. It then circumnutated about the same spot on a
very small scale for 21 h.; and during the next 21 h. it sank in a zigzag line
to nearly the same level which it had held when the ammonia was first
administered. By this time the tentacles had re-expanded, and the glands
had recovered their proper colour. We thus learn that an old leaf
circumnutates on a small scale, at least whilst absorbing carbonate of
ammonia; for it is probable that this absorption may stimulate growth and
thus re-excite circumnutation. Whether the rising of the glass filament
which was attached to the back of the leaf, resulted from its margin
becoming slightly inflected (as generally occurs), or from the rising of the
petiole, was not ascertained.
In order to learn whether the tentacles or gland-bearing hairs
circumnutate, the back of a young leaf, with the innermost tentacles as yet
incurved, was firmly cemented with shellac to a flat stick driven into
compact damp argillaceous sand. The plant was placed under a microscope
with the stage removed and with an eye-piece micrometer, of which each
division equalled 1/500 of an inch. It should be stated that as the leaves
grow older the tentacles of the exterior rows bend outwards and
downwards, so as ultimately to become deflected considerably beneath the
horizon. A tentacle in the second row from the margin was selected for
observation, and was found to be moving outwards at a rate of 1/500 of an
inch in 20 m., or 1/100 of inch in 1 h. 40 m.; but as it likewise moved from
side to side to an extent of above 1/500 of inch, the movement was probably
one of modified circumnutation. A tentacle on an old leaf was next observed
in the same manner. In 15 m. after being placed under the microscope it had
moved about 1/1000 of an inch. During the next 7½ h. it was looked at
repeatedly, and during this whole time it moved only another 1/1000 of an
inch; and this small movement may have been due to the settling of the
damp sand (on which the plant rested), though the sand had been firmly
pressed down. We may therefore conclude that the tentacles when old do
not circumnutate; yet this tentacle was so sensitive, that in 23 seconds after
its gland had been merely touched with a bit of raw meat, it began to curl

inwards. This fact is of some importance, as it apparently shows that the
inflection of the tentacles from the stimulus of absorbed animal matter (and
no doubt from that of contact with any object) is not due to modified
circumnutation.
(15.) Dionoea muscipula (Droseraceae).—It should be premised that the
leaves at an early stage of their development have the two lobes pressed
closely together. These are at first directed back towards the centre of the
plant; but they gradually rise up and soon stand at right angles to the
petiole, and ultimately in nearly a straight line with it. A young leaf, which
with the petiole was only 1.2 inch in length, had a filament fixed externally
along the midrib of the still closed lobes, which projected at right angles to
the petiole. In the evening this leaf completed an ellipse in the course of 2 h.
On the following day (Sept. 25th) its movements were traced during 22 h.;
and we see in Fig. 106 that it moved in the same general direction, due to
the straightening of the leaf, but in an extremely zigzag line. This line
represents several drawn-out or modified ellipses. There can therefore be no
doubt that this young leaf circumnutated.
Fig. 106. Dionaea muscipula: circumnutation of a young and expanding
leaf, traced on a horizontal glass in darkness, from noon Sept. 24th to 10
A.M. 25th. Apex of leaf 13½ inches from the glass, so tracing considerably
magnified.
A rather old, horizontally extended leaf, with a filament attached along
the under side of the midrib, was next observed during 7 h. It hardly moved,
but when one of its sensitive hairs was touched, the blades closed, though
not very quickly. A new dot was now made on the glass, but in the course of
14 h. 20 m. there was hardly any change in the position of the filament. We
may therefore infer that an old and only moderately sensitive leaf does not
circumnutate plainly; but we shall soon see that it by no means follows that
such a leaf is absolutely motionless. We may further infer that the stimulus
from a touch does not re-excite plain circumnutation.
Another full-grown leaf had a filament attached externally along one side
of the midrib and parallel to it, so that the filament would move if the lobes
closed. It should be first stated that, although a touch on one of the sensitive
hairs of a vigorous leaf causes it to close quickly, often almost instantly, yet
when a bit of damp meat or some solution of carbonate of ammonia is
placed on the lobes, they close so slowly that generally 24 h. is required for

the completion of the act. The above leaf was first observed for 2 h. 30 m.,
and did not circumnutate, but it ought to have been observed for a longer
period; although, as we have seen, a young leaf completed a fairly large
ellipse in 2 h. A drop of an infusion of raw meat was then placed on the leaf,
and within 2 h. the glass filament rose a little; and this implies that the lobes
had begun to close, and perhaps the petiole to rise. It continued to rise with
extreme slowness for the next 8 h. 30 m. The position of the pot was then
(7.15 P.M., Sept. 24th) slightly changed and an additional drop of the
infusion given, and a new tracing was begun (Fig. 107). By 10.50 P.M. the
filament had risen only a little more, and it fell during the night. On the
following morning the lobes were closing more quickly, and by 5 P.M. it
was evident to the eye that they had closed considerably; by 8.48. P.M. this
was still plainer, and by 10.45 P.M. the marginal spikes were interlocked.
The leaf fell a little during the night, and next morning (25th) at 7 A.M. the
lobes were completely shut. The course pursued, as may be seen in the
figure, was strongly zigzag, and this indicates that the closing of the lobes
was combined with the circumnutation of the whole leaf; and there cannot
be much doubt, considering how motionless the leaf was during 2 h. 30 m.
before it received the infusion, that the absorption of the animal matter had
excited it to circumnutate. The leaf was occasionally observed for the next
four days, but was kept in rather too cool a place; nevertheless, it continued
to circumnutate to a small extent, and the lobes remained closed.
Fig. 107. Dionoea muscipula: closure of the lobes and circumnutation of
a full-grown leaf, whilst absorbing an infusion of raw meat, traced in
darkness, from 7.15 P.M. Sept. 24th to 9 A.M. 26th. Apex of leaf 8½ inches
from the vertical glass. Figure here reduced to two-thirds of original scale.
It is sometimes stated in botanical works that the lobes close or sleep at
night; but this is an error. To test the statement, very long glass filaments
were fixed inside the two lobes of three leaves, and the distances between
their tips were measured in the middle of the day and at night; but no
difference could be detected.
The previous observations relate to the movements of the whole leaf, but
the lobes move independently of the petiole, and seem to be continually
opening and shutting to a very small extent. A nearly full-grown leaf
(afterwards proved to be highly sensitive to contact) stood almost
horizontally, so that by driving a long thin pin through the foliaceous petiole

close to the blade, it was rendered motionless. The plant, with a little
triangle of paper attached to one of the marginal spikes, was placed under a
microscope with an eye-piece micrometer, each division of which equalled
1/500 of an inch. The apex of the paper-triangle was now seen to be in
constant slight movement; for in 4 h. it crossed nine divisions, or 9/500 of
an inch, and after ten additional hours it moved back and had crossed 5/500
in an opposite direction. The plant was kept in rather too cool a place, and
on the following day it moved rather less, namely, 1/500 in 3 h., and 2/500
in an opposite direction during the next 6 h. The two lobes, therefore, seem
to be constantly closing or opening, though to a very small distance; for we
must remember that the little triangle of paper affixed to the marginal spike
increased its length, and thus exaggerated somewhat the movement. Similar
observations, with the important difference that the petiole was left free and
the plant kept under a high temperature, were made on a leaf, which was
healthy, but so old that it did not close when its sensitive hairs were
repeatedly touched, though judging from other cases it would have slowly
closed if it had been stimulated by animal matter. The apex of the triangle
was in almost, though not quite, constant movement, sometimes in one
direction and sometimes in an opposite one; and it thrice crossed five
divisions of the micrometer (i.e. 1/100 of an inch) in 30 m. This movement
on so small a scale is hardly comparable with ordinary circumnutation; but
it may perhaps be compared with the zigzag lines and little loops, by which
the larger ellipses made by other plants are often interrupted.
In the first chapter of this volume, the remarkable oscillatory movements
of the circumnutating hypocotyl of the cabbage have been described. The
leaves of Dionaea present the same phenomenon, which is a wonderful one,
as viewed under a low power (2-inch object-glass), with an eye-piece
micrometer of which each division (1/500 of an inch) appeared as a rather
wide space. The young unexpanded leaf, of which the circumnutating
movements were traced (Fig. 106), had a glass filament fixed
perpendicularly to it; and the movement of the apex was observed in the
hot-house (temp. 84° to 86° F.), with light admitted only from above, and
with any lateral currents of air excluded. The apex sometimes crossed one
or two divisions of the micrometer at an imperceptibly slow rate, but
generally it moved onwards by rapid starts or jerks of 2/1000 or 3/1000, and
in one instance of 4/1000 of an inch. After each jerk forwards, the apex
drew itself backwards with comparative slowness for part of the distance

which had just been gained; and then after a very short time made another
jerk forwards. Four conspicuous jerks forwards, with slower retreats, were
seen on one occasion to occur in exactly one minute, besides some minor
oscillations. As far as we could judge, the advancing and retreating lines did
not coincide, and if so, extremely minute ellipses were each time described.
Sometimes the apex remained quite motionless for a short period. Its
general course during the several hours of observation was in two opposite
directions, so that the leaf was probably circumnutating.
An older leaf with the lobes fully expanded, and which was afterwards
proved to be highly sensitive to contact, was next observed in a similar
manner, except that the plant was exposed to a lower temperature in a room.
The apex oscillated forwards and backwards in the same manner as before;
but the jerks forward were less in extent, viz. about 1/1000 inch; and there
were longer motionless periods. As it appeared possible that the movements
might be due to currents of air, a wax taper was held close to the leaf during
one of the motionless periods, but no oscillations were thus caused. After 10
m., however, vigorous oscillations commenced, perhaps owing to the plant
having been warmed and thus stimulated. The candle was then removed and
before long the oscillations ceased; nevertheless, when looked at again after
an interval of 1 h. 30 m., it was again oscillating. The plant was taken back
into the hot-house, and on the following morning was seen to be oscillating,
though not very vigorously. Another old but healthy leaf, which was not in
the least sensitive to a touch, was likewise observed during two days in the
hot-house, and the attached filament made many little jerks forwards of
about 2/1000 or only 1/1000 of an inch.
Finally, to ascertain whether the lobes independently of the petiole
oscillated, the petiole of an old leaf was cemented close to the blade with
shellac to the top of a little stick driven into the soil. But before this was
done the leaf was observed, and found to be vigorously oscillating or
jerking; and after it had been cemented to the stick, the oscillations of about
2/1000 of an inch still continued. On the following day a little infusion of
raw meat was placed on the leaf, which caused the lobes to close together
very slowly in the course of two days; and the oscillations continued during
this whole time and for the next two days. After nine additional days the
leaf began to open and the margins were a little everted, and now the apex
of the glass filament remained for long periods motionless, and then moved
backwards and forwards for a distance of about 1/1000 of an inch slowly,

without any jerks. Nevertheless, after warming the leaf with a taper held
close to it, the jerking movement recommenced.
This same leaf had been observed 2½ months previously, and was then
found to be oscillating or jerking. We may therefore infer that this kind of
movement goes on night and day for a very long period; and it is common
to young unexpanded leaves and to leaves so old as to have lost their
sensitiveness to a touch, but which were still capable of absorbing
nitrogenous matter. The phenomenon when well displayed, as in the young
leaf just described, is a very interesting one. It often brought before our
minds the idea of effort, or of a small animal struggling to escape from
some constraint.
(16.) Eucalyptus resinifera (Myrtaceae, Fam. 94).—A young leaf, two
inches in length together with the petiole, produced by a lateral shoot from
a cut-down tree, was observed in the usual manner. The blade had not as yet
assumed its vertical position. On June 7th only a few observations were
made, and the tracing merely showed that the leaf had moved three times
upwards and three downwards. On the following day it was observed more
frequently; and two tracings were made (see A and B, Fig. 108), as a single
one would have been too complicated. The apex changed its course 13
times in the course of 16 h., chiefly up and down, but with some lateral
movement. The actual amount of movement in any one direction was small.
Fig. 108. Eucalyptus resinifera: circumnutation of a leaf, traced, A, from
6.40 A.M. to 1 P.M. June 8th; B, from 1 P.M. 8th to 8.30 A.M. 9th. Apex of
leaf 14½ inches from the horizontal glass, so figures considerably
magnified.
(17.) Dahlia (garden var.) (Compositæ, Fam. 122).—A fine young leaf 5
3/4 inches in length, produced by a young plant 2 feet high, growing
vigorously in a large pot, was directed at an angle of about 45° beneath the
horizon. On June 18th the leaf descended from 10 A.M. till 11.35 A.M. (see
Fig. 109); it then ascended greatly till 6 P.M., this ascent being probably due
to the light coming only from above. It zigzagged between 6 P.M. and 10.35
P.M., and ascended a little during the night. It should be remarked that the
vertical distances in the lower part of the diagram are much exaggerated, as
the leaf was at first deflected beneath the horizon, and after it had sunk
downwards, the filament pointed in a very oblique line towards the glass.
Next day the leaf descended from 8.20 A.M. till 7.15 P.M., then zigzagged

and ascended greatly during the night. On the morning of the 20th the leaf
was probably beginning to descend, though the short line in the diagram is
horizontal. The actual distances travelled by the apex of the leaf were
considerable, but could not be calculated with safety. From the course
pursued on the second day, when the plant had accommodated itself to the
light from above, there cannot be much doubt that the leaves undergo a
daily periodic movement, sinking during the day and rising at night.
Fig. 109. Dahlia: circumnutation of leaf, traced from 10 A.M. June 18th
to 8.10 A.M. 20th, but with a break of 1 h. 40 m. on the morning of the
19th, as, owing to the glass filament pointing too much to one side, the pot
had to be slightly moved; therefore the relative position of the two tracings
is somewhat arbitrary. The figure here given is reduced to one-fifth of the
original scale. Apex of leaf 9 inches from the glass in the line of its
inclination, and 4 3/4 in a horizontal line.
(18.) Mutisia clematis (Compositæ).—The leaves terminate in tendrils
and circumnutate like those of other tendril-bearers; but this plant is here
mentioned, on account of an erroneous statement[11] which has been
published, namely, that the leaves sink at night and rise during the day. The
leaves which behaved in this manner had been kept for some days in a
northern room and had not been sufficiently illuminated. A plant therefore
was left undisturbed in the hot-house, and three leaves had their angles
measured at noon and at 10 P.M. All three were inclined a little beneath the
horizon at noon, but one stood at night 2°, the second 21°, and the third 10°
higher than in the middle of the day; so that instead of sinking they rise a
little at night.
[11] ‘The Movements and Habits of Climbing Plants,’ 1875, p. 118.

(19.) Cyclamen Persicum (Primulaceae, Fam. 135).—A young leaf, 1.8
of an inch in length, petiole included, produced by an old root-stock, was
observed during three days in the usual manner (Fig. 110). On the first day
the leaf fell more than afterwards, apparently from adjusting itself to the
light from above. On all three days it fell from the early morning to about 7
P.M., and from that hour rose during the night, the course being slightly
zigzag. The movement therefore is strictly periodic. It should be noted that
the leaf would have sunk each evening a little lower down than it did, had
not the glass filament rested between 5 and 6 P.M. on the rim of the pot.
The amount of movement was considerable; for if we assume that the

whole leaf to the base of the petiole became bent, the tracing would be
magnified rather less than five times, and this would give to the apex a rise
and fall of half an inch, with some lateral movement. This amount,
however, would not attract attention without the aid of a tracing or
measurement of some kind.
(20.) Allamanda Schottii (Apocyneae, Fam. 144).—The young leaves of
this shrub are elongated, with the blade bowed so much downwards as
almost to form a semicircle. The chord—that is, a line drawn from the apex
of the blade to the base of the petiole—of a young leaf, 4 3/4 inches in
length, stood at 2.50 P.M. on Dec. 5th at an angle of 13° beneath the
horizon, but by 9.30 P.M. the blade had straightened itself so much, which
implies the raising of the apex, that the chord now stood at 37° above the
horizon, and had therefore risen 50°. On the next day similar angular
measurements of the same leaf were made; and at noon the chord stood 36°
beneath the horizon, and 9.30 P.M. 3½° above it, so had risen 39½°. The
chief cause of the rising movement lies in the straightening of the blade, but
the short petiole rises between 4° and 5°. On the third night the chord stood
at 35° above the horizon, and if the leaf occupied the same position at noon,
as on the previous day, it had risen 71°. With older leaves no such change of
curvature could be detected. The plant was then brought into the house and
kept in a north-east room, but at night there was no change in the curvature
of the young leaves; so that previous exposure to a strong light is apparently
requisite for the periodical change of curvature in the blade, and for the
slight rising of the petiole.
Fig. 110. Cyclamen Persicum: circumnutation of leaf, traced from 6.45
A.M. June 2nd to 6.40 A.M. 5th. Apex of leaf 7 inches from the vertical
glass.
(21.) Wigandia (Hydroleaceae, Fam. 149).—Professor Pfeffer informs us
that the leaves of this plant rise in the evening; but as we do not know
whether or not the rising is great, this species ought perhaps to be classed
amongst sleeping plants.
Fig. 111. Petunia violacea: downward movement and circumnutation of a
very young leaf, traced from 10 A.M. June 2nd to 9.20 A.M. June 6th. N.B.
—At 6.40 A.M. on the 5th it was necessary to move the pot a little, and a
new tracing was begun at the point where two dots are not joined in the

diagram. Apex of leaf 7 inches from the vertical glass. Temp. generally
17½° C.
(22.) Petunia violacea (Solaneae, Fam. 157).—A very young leaf, only
3/4 inch in length, highly inclined upwards, was observed for four days.
During the whole of this time it bent outwards and downwards, so as to
become more and more nearly horizontal. The strongly marked zigzag line
in the figure on p. 248 (Fig. 111), shows that this was effected by modified
circumnutation; and during the latter part of the time there was much
ordinary circumnutation on a small scale. The movement in the diagram is
magnified between 10 and 11 times. It exhibits a clear trace of periodicity,
as the leaf rose a little each evening; but this upward tendency appeared to
be almost conquered by the leaf striving to become more and more
horizontal as it grew older. The angles which two older leaves formed
together, were measured in the evening and about noon on 3 successive
days, and each night the angle decreased a little, though irregularly.
Fig. 112. Acanthus mollis: circumnutation of young leaf, traced from
9.20 A.M. June 14th to 8.30 A.M. 16th. Apex of leaf 11 inches from the
vertical glass, so movement considerably magnified. Figure here reduced to
one-half of original scale. Temp. 15°–16½° C.
(23.) Acanthus mollis (Acanthaceae, Fam. 168).—The younger of two
leaves, 2 1/4 inches in length, petiole included, produced by a seedling
plant, was observed during 47 h. Early on each of the three mornings, the
apex of the leaf fell; and it continued to fall till 3 P.M., on the two
afternoons when observed. After 3 P.M. it rose considerably, and continued
to rise on the second night until the early morning. But on the first night it
fell instead of rising, and we have little doubt that this was owing to the leaf
being very young and becoming through epinastic growth more and more
horizontal; for it may be seen in the diagram (Fig. 112), that the leaf stood
on a higher level on the first than on the second day. The leaves of an allied
species (‘A. spinosus’) certainly rose every night; and the rise between
noon and 10.15 P.M., when measured on one occasion, was 10°. This rise
was chiefly or exclusively due to the straightening of the blade, and not to
the movement of the petiole. We may therefore conclude that the leaves of
Acanthus circumnutate periodically, falling in the morning and rising in the
afternoon and night.

(24.) Cannabis sativa (Cannabineae, Fam. 195).—We have here the rare
case of leaves moving downwards in the evening, but not to a sufficient
degree to be called sleep.[12] In the early morning, or in the latter part of the
night, they move upwards. For instance, all the young leaves near the
summits of several stems stood almost horizontally at 8 A.M. May 29th and
at 10.30 P.M. were considerably declined. On a subsequent day two leaves
stood at 2 P.M. at 21° and 12° beneath the horizon, and at 10 P.M. at 38°
beneath it. Two other leaves on a younger plant were horizontal at 2 P.M.,
and at 10 P.M. had sunk to 36° beneath the horizon. With respect to this
downward movement of the leaves, Kraus believes that it is due to their
epinastic growth. He adds, that the leaves are relaxed during the day, and
tense at night, both in sunny and rainy weather.
[12] We were led to observe this plant by Dr. Carl Kraus’ paper, ‘Beiträge zur
Kentniss der Bewegungen Wachsender Laubblätter,’ Flora, 1879, p. 66. We
regret that we cannot fully understand parts of this paper.

(25.) Pinus pinaster (Coniferæ, Fam. 223).—The leaves on the summits
of the terminal shoots stand at first in a bundle almost upright, but they soon
diverge and ultimately become almost horizontal. The movements of a
young leaf, nearly one inch in length, on the summit of a seedling plant
only 3 inches high, were traced from the early morning of June 2nd to the
evening of the 7th. During these five days the leaf diverged, and its apex
descended at first in an almost straight line; but during the two latter days it
zigzagged so much that it was evidently circumnutating. The same little
plant, when grown to a height of 5 inches, was again observed during four
days. A filament was fixed transversely to the apex of a leaf, one inch in
length, and which had already diverged considerably from its originally
upright position. It continued to diverge (see A, Fig. 113), and to descend
from 11.45 A.M. July 31st to 6.40 A.M. Aug. 1st. On August 1st it
circumnutated about the same small space, and again descended at night.
Next morning the pot was moved nearly one inch to the right, and a new
tracing was begun (B). From this time, viz., 7 A.M. August 2nd to 8.20
A.M. on the 4th, the leaf manifestly circumnutated. It does not appear from
the diagram that the leaves move periodically, for the descending course
during the first two nights, was clearly due to epinastic growth, and at the
close of our observations the leaf was not nearly so horizontal as it would
ultimately become.

Fig. 113. Pinus pinaster: circumnutation of young leaf, traced from 11.45
A.M. July 31st to 8.20 A.M. Aug. 4th. At 7 A.M. Aug. 2nd the pot was
moved an inch to one side, so that the tracing consists of two figures. Apex
of leaf 14½ inches from the vertical glass, so movements much magnified.
Pinus austriaca.—Two leaves, 3 inches in length, but not quite fully
grown, produced by a lateral shoot, on a young tree 3 feet in height, were
observed during 29 h. (July 31st), in the same manner as the leaves of the
previous species. Both these leaves certainly circumnutated, making within
the above period two, or two and a half, small, irregular ellipses.
(26.) Cycas pectinata (Cycadeæ, Fam. 224).—A young leaf, 11½ inches
in length, of which the leaflets had only recently become uncurled, was
observed during 47 h. 30 m. The main petiole was secured to a stick at the
base of the two terminal leaflets. To one of the latter, 3 3/4 inches in length,
a filament was fixed; the leaflet was much bowed downward, but as the
terminal part was upturned, the filament projected almost horizontally. The
leaflet moved (see Fig. 114) largely and periodically, for it fell until about 7
P.M. and rose during the night, falling again next morning after 6.40 A.M.
The descending lines are in a marked manner zigzag, and so probably
would have been the ascending lines, if they had been traced throughout the
night.
Fig. 114. Cycas pectinata: circumnutation of one of the terminal leaflets,
traced from 8.30 A.M. June 22nd to 8 A.M. June 24th. Apex of leaflet 7 3/4
inches from the vertical glass, so tracing not greatly magnified, and here
reduced to one-third of original scale; temp. 19°–21° C.

CIRCUMNUTATION OF LEAVES:
MONOCOTYLEDONS.
(27.) Canna Warscewiczii (Cannaceae, Fam. 2).—The movements of a
young leaf, 8 inches in length and 3½ in breadth, produced by a vigorous
young plant, were observed during 45 h. 50 m., as shown in Fig. 115. The
pot was slided about an inch to the right on the morning of the 11th, as a
single figure would have been too complicated; but the two figures are
continuous in time. The movement is periodical, as the leaf descended from
the early morning until about 5 P.M., and ascended during the rest of the

evening and part of the night. On the evening of the 11th it circumnutated
on a small scale for some time about the same spot.
Fig. 115. Canna Warscewiczii: circumnutation of leaf, traced (A) from
11.30 A.M. June 10th to 6.40 A.M. 11th; and (B) from 6.40 A.M. 11th to
8.40 A.M. 12th. Apex of leaf 9 inches from the vertical glass.
(28.) Iris pseudo-acorus (Irideae, Fam. 10).—The movements of a young
leaf, rising 13 inches above the water in which the plant grew, were traced
as shown in the figure (Fig. 116), during 27 h. 30 m. It manifestly
circumnutated, though only to a small extent. On the second morning,
between 6.40 A.M. and 2 P.M. (at which latter hour the figure here given
ends), the apex changed its course five times. During the next 8 h. 40 m. it
zigzagged much, and descended as far as the lowest dot in the figure,
making in its course two very small ellipses; but if these lines had been
added to the diagram it would have been too complex.
Fig. 116. Iris pseudo-acorus: circumnutation of leaf, traced from 10.30
A.M. May 28th to 2 P.M. 29th. Tracing continued to 11 P.M., but not here
copied. Apex of leaf 12 inches beneath the horizontal glass, so figure
considerably magnified. Temp. 15°–16° C.
(29.) Crinum Capense (Amaryllideae, Fam. 11).—The leaves of this
plant are remarkable for their great length and narrowness: one was
measured and found to be 53 inches long and only 1.4 broad at the base.
Whilst quite young they stand up almost vertically to the height of about a
foot; afterwards their tips begin to bend over, and subsequently hang
vertically down, and thus continue to grow. A rather young leaf was
selected, of which the dependent tapering point was as yet only 5½ inches
in length, the upright basal part being 20 inches high, though this part
would ultimately become shorter by being more bent over. A large bell-
glass was placed over the plant, with a black dot on one side; and by
bringing the dependent apex of the leaf into a line with this dot, the
accompanying figure (Fig. 117) was traced on the other side of the bell,
during 2½ days. During the first day (22nd) the tip travelled laterally far to
the left, perhaps in consequence of the plant having been disturbed; and the
last dot made at 10.30 P.M. on this day is alone here given. As we see in the
figure, there can be no doubt that the apex of this leaf circumnutated.
Fig. 117. Crinum Capense: circumnutation of dependent tip of young
leaf, traced on a bell-glass, from 10.30 P.M. May 22nd to 10.15 A.M. 25th.

Figure not greatly magnified.
A glass filament with little triangles of paper was at the same time fixed
obliquely across the tip of a still younger leaf, which stood vertically up and
was as yet straight. Its movements were traced from 3 P.M. May 22nd to
10.15 A.M. 25th. The leaf was growing rapidly, so that the apex ascended
greatly during this period; as it zigzagged much it was clearly
circumnutating, and it apparently tended to form one ellipse each day. The
lines traced during the night were much more vertical than those traced
during the day; and this indicates that the tracing would have exhibited a
nocturnal rise and a diurnal fall, if the leaf had not grown so quickly. The
movement of this same leaf after an interval of six days (May 31st), by
which time the tip had curved outwards into a horizontal position, and had
thus made the first step towards becoming dependent, was traced
orthogonically by the aid of a cube of wood (in the manner before
explained); and it was thus ascertained that the actual distance travelled by
the apex, and due to circumnutation, was 3 1/8 inches in the course of 20½
h. During the next 24 h. it travelled 2½ inches. The circumnutating
movement, therefore, of this young leaf was strongly marked.
(30.) Pancratium littorale (Amaryllideae).—The movements, much
magnified, of a leaf, 9 inches in length and inclined at about 45° above the
horizon, were traced during two days. On the first day it changed its course
completely, upwards and downwards and laterally, 9 times in 12 h.; and the
figure traced apparently represented five ellipses. On the second day it was
observed seldomer, and was therefore not seen to change its course so often,
viz., only 6 times, but in the same complex manner as before. The
movements were small in extent, but there could be no doubt about the
circumnutation of the leaf.
(31.) Imatophyllum vel Clivia (sp.?) (Amaryllideae).—A long glass
filament was fixed to a leaf, and the angle formed by it with the horizon
was measured occasionally during three successive days. It fell each
morning until between 3 and 4 P.M., and rose at night. The smallest angle at
any time above the horizon was 48°, and the largest 50°; so that it rose only
2° at night; but as this was observed each day, and as similar observations
were nightly made on another leaf on a distinct plant, there can be no doubt
that the leaves move periodically, though to a very small extent. The

position of the apex when it stood highest was .8 of an inch above its lowest
point.
(32.) Pistia stratiotes (Aroideae, Fam. 30).—Hofmeister remarks that the
leaves of this floating water-plant are more highly inclined at night than by
day.[13] We therefore fastened a fine glass filament to the midrib of a
moderately young leaf, and on Sept. 19th measured the angle which it
formed with the horizon 14 times between 9 A.M. and 11.50 P.M. The
temperature of the hot-house varied during the two days of observation
between 18½° and 23½° C. At 9 A.M. the filament stood at 32° above the
horizon; at 3.34 P.M. at 10° and at 11.50 P.M. at 55°; these two latter angles
being the highest and the lowest observed during the day, showing a
difference of 45°. The rising did not become strongly marked until between
5 and 6 P.M. On the next day the leaf stood at only 10° above the horizon at
8.25 A.M., and it remained at about 15° till past 3 P.M.; at 5.40 P.M. it was
23°, and at 9.30 P.M. 58°; so that the rise was more sudden this evening
than on the previous one, and the difference in the angle amounted to 48°.
The movement is obviously periodical, and as the leaf stood on the first
night at 55°, and on the second night at 58° above the horizon, it appeared
very steeply inclined. This case, as we shall see in a future chapter, ought
perhaps to have been included under the head of sleeping plants.
[13] ‘Die Lehre von der Pflanzenzelle,’ 1867, p. 327.

(33.) Pontederia (sp.?) (from the highlands of St. Catharina, Brazil)
(Pontederiaceae, Fam. 46).—A filament was fixed across the apex of a
moderately young leaf, 7½ inches in height, and its movements were traced
during 42½ h. (see Fig. 118). On the first evening, when the tracing was
begun, and during the night, the leaf descended considerably. On the next
morning it ascended in a strongly marked zigzag line, and descended again
in the evening and during the night. The movement, therefore, seems to be
periodic, but some doubt is thrown on this conclusion, because another leaf,
8 inches in height, appearing older and standing more highly inclined,
behaved differently. During the first 12 h. it circumnutated over a small
space, but during the night and the whole following day it ascended in the
same general direction; the ascent being effected by repeated up and down
well-pronounced oscillations.
Fig. 118. Pontederia (sp.?): circumnutation of leaf, traced from 4.50 P.M.
July 2nd to 10.15 A.M. 4th. Apex of leaf 16½ inches from the vertical glass,

so tracing greatly magnified. Temp. about 17° C., and therefore rather too
low.

CRYPTOGAMS.
(34.) Nephrodium molle (Filices, Fam. 1).—A filament was fixed near
the apex of a young frond of this Fern, 17 inches in height, which was not
as yet fully uncurled; and its movements were traced during 24 h. We see in
Fig. 119 that it plainly circumnutated. The movement was not greatly
magnified as the frond was placed near to the vertical glass, and would
probably have been greater and more rapid had the day been warmer. For
the plant was brought out of a warm greenhouse and observed under a
skylight, where the temperature was between 15° and 16° C. We have seen
in Chap. I. that a frond of this Fern, as yet only slightly lobed and with a
rachis only .23 inch in height, plainly circumnutated.[14]
[14] Mr. Loomis and Prof. Asa Gray have described (‘Botanical Gazette,’ 1880,
pp. 27, 43), an extremely curious case of movement in the fronds, but only in the
fruiting fronds, of Asplenium trichomanes. They move almost as rapidly as the
little leaflets of Desmodium gyrans, alternately backwards and forwards through
from 20 to 40 degrees, in a plane at right angles to that of the frond. The apex of
the frond describes “a long and very narrow ellipse,” so that it circumnutates.
But the movement differs from ordinary circumnutation as it occurs only when
the plant is exposed to the light; even artificial light “is sufficient to excite
motion for a few minutes.”

Fig. 119. Nephrodium molle: circumnutation of rachis, traced from 9.15
A.M. May 28th to 9 A.M. 29th. Figure here given two-thirds of original
scale.
In the chapter on the Sleep of Plants the conspicuous circumnutation of
Marsilea quadrifoliata (Marsileaceae, Fam. 4) will be described.
It has also been shown in Chap. I. that a very young Selaginella
(Lycopodiaceæ, Fam. 6), only .4 inch in height, plainly circumnutated; we
may therefore conclude that older plants, whilst growing, would do the
same.
(35.) Lunularia vulgaris (Hepaticae, Fam. 11, Muscales).—The earth in
an old flower-pot was coated with this plant, bearing gemmae. A highly
inclined frond, which projected .3 inch above the soil and was .4 inch in
breadth, was selected for observation. A glass hair of extreme tenuity, .75

inch in length, with its end whitened, was cemented with shellac to the
frond at right angles to its breadth; and a white stick with a minute black
spot was driven into the soil close behind the end of the hair. The white end
could be accurately brought into a line with the black spot, and dots could
thus be successively made on the vertical glass-plate in front. Any
movement of the frond would of course be exhibited and increased by the
long glass hair; and the black spot was placed so close behind the end of the
hair, relatively to the distance of the glass-plate in front, that the movement
of the end was magnified about 40 times. Nevertheless, we are convinced
that our tracing gives a fairly faithful representation of the movements of
the frond. In the intervals between each observation, the plant was covered
by a small bell-glass. The frond, as already stated, was highly inclined, and
the pot stood in front of a north-east window. During the five first days the
frond moved downwards or became less inclined; and the long line which
was traced was strongly zigzag, with loops occasionally formed or nearly
formed; and this indicated circumnutation. Whether the sinking was due to
epinastic growth, or apheliotropism, we do not know. As the sinking was
slight on the fifth day, a new tracing was begun on the sixth day (Oct. 25th),
and was continued for 47 h.; it is here given (Fig. 120). Another tracing was
made on the next day (27th) and the frond was found to be still
circumnutating, for during 14 h. 30 m. it changed its course completely
(besides minor changes) 10 times. It was casually observed for two more
days, and was seen to be continually moving.
Fig. 120. Lunularia vulgaris: circumnutation of a frond, traced from 9
A.M. Oct 25th to 8 A.M. 27th.
The lowest members of the vegetable series, the Thallogens, apparently
circumnutate. If an Oscillaria be watched under the microscope, it may be
seen to describe circles about every 40 seconds. After it has bent to one
side, the tip first begins to bend back to the opposite side and then the
whole filament curves over in the same direction. Hofmeister[15] has given a
minute account of the curious, but less regular though constant, movements
of Spirogyra: during 2½ h. the filament moved 4 times to the left and 3
times to the right, and he refers to a movement at right angles to the above.
The tip moved at the rate of about 0.1 mm. in five minutes. He compares
the movement with the nutation of the higher plants.[16] We shall hereafter
see that heliotropic movements result from modified circumnutation, and as

unicellular Moulds bend to the light we may infer that they also
circumnutate.
[15] ‘Ueber die Bewegungen der Faden der Spirogyra princeps: Jahreshefte des
Vereins für vaterländische Naturkunde in Württemberg,’ 1874, p. 211.

[16] Zukal also remarks (as quoted in ‘Journal R. Microscop. Soc.,’ 1880, vol.
iii. p. 320) that the movements of Spirulina, a member of the Oscillatorieae, are
closely analogous “to the well-known rotation of growing shoots and tendrils.”

CONCLUDING REMARKS ON THE
CIRCUMNUTATION OF LEAVES.
The circumnutating movements of young leaves in 33 genera, belonging
to 25 families, widely distributed amongst ordinary and gymnospermous
Dicotyledons and amongst Monocotyledons, together with several
Cryptogams, have now been described. It would, therefore, not be rash to
assume that the growing leaves of all plants circumnutate, as we have seen
reason to conclude is the case with cotyledons. The seat of movement
generally lies in the petiole, but sometimes both in the petiole and blade, or
in the blade alone. The extent of the movement differed much in different
plants; but the distance passed over was never great, except with Pistia,
which ought perhaps to have been included amongst sleeping plants. The
angular movement of the leaves was only occasionally measured; it
commonly varied from only 2° (and probably even less in some instances)
to about 10°; but it amounted to 23° in the common bean. The movement is
chiefly in a vertical plane, but as the ascending and descending lines never
coincided, there was always some lateral movement, and thus irregular
ellipses were formed. The movement, therefore, deserves to be called one of
circumnutation; for all circumnutating organs tend to describe ellipses,—
that is, growth on one side is succeeded by growth on nearly but not quite
the opposite side. The ellipses, or the zigzag lines representing drawn-out
ellipses, are generally very narrow; yet with the Camellia, their minor axes
were half as long, and with the Eucalyptus more than half as long as their
major axes. In the case of Cissus, parts of the figure more nearly
represented circles than ellipses. The amount of lateral movement is
therefore sometimes considerable. Moreover, the longer axes of the
successively formed ellipses (as with the Bean, Cissus, and Sea-kale), and

in several instances the zigzag lines representing ellipses, were extended in
very different directions during the same day or on the next day. The course
followed was curvilinear or straight, or slightly or strongly zigzag, and little
loops or triangles were often formed. A single large irregular ellipse may be
described on one day, and two smaller ones by the same plant on the next
day. With Drosera two, and with Lupinus, Eucalyptus and Pancratium,
several were formed each day.
The oscillatory and jerking movements of the leaves of Dionaea, which
resemble those of the hypocotyl of the cabbage, are highly remarkable, as
seen under the microscope. They continue night and day for some months,
and are displayed by young unexpanded leaves, and by old ones which have
lost their sensibility to a touch, but which, after absorbing animal matter,
close their lobes. We shall hereafter meet with the same kind of movement
in the joints of certain Gramineæ, and it is probably common to many
plants while circumnutating. It is, therefore, a strange fact that no such
movement could be detected in the tentacles of Drosera rotundifolia, though
a member of the same family with Dionaea; yet the tentacle which was
observed was so sensitive, that it began to curl inwards in 23 seconds after
being touched by a bit of raw meat.
One of the most interesting facts with respect to the circumnutation of
leaves is the periodicity of their movements; for they often, or even
generally, rise a little in the evening and early part of the night, and sink
again on the following morning. Exactly the same phenomenon was
observed in the case of cotyledons. The leaves in 16 genera out of the 33
which were observed behaved in this manner, as did probably 2 others. Nor
must it be supposed that in the remaining 15 genera there was no periodicity
in their movements; for 6 of them were observed during too short a period
for any judgment to be formed on this head, and 3 were so young that their
epinastic growth, which serves to bring them down into a horizontal
position, overpowered every other kind of movement. In only one genus,
Cannabis, did the leaves sink in the evening, and Kraus attributes this
movement to the prepotency of their epinastic growth. That the periodicity
is determined by the daily alternations of light and darkness there can
hardly be a doubt, as will hereafter be shown. Insectivorous plants are very
little affected, as far as their movements are concerned, by light; and hence
probably it is that their leaves, at least in the cases of Sarracenia, Drosera,
and Dionaea, do not move periodically. The upward movement in the

evening is at first slow, and with different plants begins at very different
hours;—with Glaucium as early as 11 A.M., commonly between 3 and 5
P.M., but sometimes as late as 7 P.M. It should be observed that none of the
leaves described in this chapter (except, as we believe, those of Lupinus
speciosus) possess a pulvinus; for the periodical movements of leaves thus
provided have generally been amplified into so-called sleep-movements,
with which we are not here concerned. The fact of leaves and cotyledons
frequently, or even generally, rising a little in the evening and sinking in the
morning, is of interest as giving the foundation from which the specialised
sleep-movements of many leaves and cotyledons, not provided with a
pulvinus, have been developed. the above periodicity should be kept in
mind, by any one considering the problem of the horizontal position of
leaves and cotyledons during the day, whilst illuminated from above.

CHAPTER V.
MODIFIED CIRCUMNUTATION: CLIMBING
PLANTS; EPINASTIC AND HYPONASTIC
MOVEMENTS.

Circumnutation modified through innate causes or through
the action of external conditions—Innate causes—Climbing
plants; similarity of their movements with those of ordinary
plants; increased amplitude; occasional points of difference
—Epinastic growth of young leaves—Hyponastic growth of
the hypocotyls and epicotyls of seedlings—Hooked tips of
climbing and other plants due to modified circumnutation—
Ampelopsis tricuspidata—Smithia Pfundii—Straightening
of the tip due to hyponasty—Epinastic growth and
circumnutation of the flower-peduncles of Trifolium repens
and Oxalis carnosa.

The radicles, hypocotyls and epicotyls of seedling plants, even before
they emerge from the ground, and afterwards the cotyledons, are all
continually circumnutating. So it is with the stems, stolons, flower-
peduncles, and leaves of older plants. We may, therefore, infer with a
considerable degree of safety that all the growing parts of all plants
circumnutate. Although this movement, in its ordinary or unmodified state,
appears in some cases to be of service to plants, either directly or indirectly
—for instance, the circumnutation of the radicle in penetrating the ground,
or that of the arched hypocotyl and epicotyl in breaking through the surface
—yet circumnutation is so general, or rather so universal a phenomenon,
that we cannot suppose it to have been gained for any special purpose. We

must believe that it follows in some unknown way from the manner in
which vegetable tissues grow.
We shall now consider the many cases in which circumnutation has been
modified for various special purposes; that is, a movement already in
progress is temporarily increased in some one direction, and temporarily
diminished or quite arrested in other directions. These cases may be divided
in two sub-classes; in one of which the modification depends on innate or
constitutional causes, and is independent of external conditions, excepting
in so far that the proper ones for growth must be present. In the second sub-
class the modification depends to a large extent on external agencies, such
as the daily alternations of light and darkness, or light alone, temperature, or
the attraction of gravity. The first small sub-class will be considered in the
present chapter, and the second sub-class in the remainder of this volume.

THE CIRCUMNUTATION OF CLIMBING
PLANTS.
The simplest case of modified circumnutation is that offered by climbing
plants, with the exception of those which climb by the aid of motionless
hooks or of rootlets: for the modification consists chiefly in the greatly
increased amplitude of the movement. This would follow either from
greatly increased growth over a small length, or more probably from
moderately increased growth spread over a considerable length of the
moving organ, preceded by turgescence, and acting successively on all
sides. The circumnutation of climbers is more regular than that of ordinary
plants; but in almost every other respect there is a close similarity between
their movements, namely, in their tendency to describe ellipses directed
successively to all points of the compass—in their courses being often
interrupted by zigzag lines, triangles, loops, or small ellipses—in the rate of
movement, and in different species revolving once or several times within
the same length of time. In the same internode, the movements cease first in
the lower part and then slowly upwards. In both sets of cases the movement
may be modified in a closely analogous manner by geotropism and by
heliotropism; though few climbing plants are heliotropic. Other points of
similarity might be pointed out.

That the movements of climbing plants consist of ordinary
circumnutation, modified by being increased in amplitude, is well exhibited
whilst the plants are very young; for at this early age they move like other
seedlings, but as they grow older their movements gradually increase
without undergoing any other change. That this power is innate, and is not
excited by any external agencies, beyond those necessary for growth and
vigour, is obvious. No one doubts that this power has been gained for the
sake of enabling climbing plants to ascend to a height, and thus to reach the
light. This is effected by two very different methods; first, by twining
spirally round a support, but to do so their stems must be long and flexible;
and, secondly, in the case of leaf-climbers and tendril-bearers, by bringing
these organs into contact with a support, which is then seized by the aid of
their sensitiveness. It may be here remarked that these latter movements
have no relation, as far as we can judge, with circumnutation. In other cases
the tips of tendrils, after having been brought into contact with a support,
become developed into little discs which adhere firmly to it.
We have said that the circumnutation of climbing plants differs from that
of ordinary plants chiefly by its greater amplitude. But most leaves
circumnutate in an almost vertical plane, and therefore describe very narrow
ellipses, whereas the many kinds of tendrils which consist of
metamorphosed leaves, make much broader ellipses or nearly circular
figures; and thus they have a far better chance of catching hold of a support
on any side. The movements of climbing plants have also been modified in
some few other special ways. Thus the circumnutating stems of Solnanum
dulcamara can twine round a support only when this is as thin and flexible
as a string or thread. The twining stems of several British plants cannot
twine round a support when it is more than a few inches in thickness; whilst
in tropical forests some can embrace thick trunks;[1] and this great difference
in power depends on some unknown difference in their manner of
circumnutation. The most remarkable special modification of this
movement which we have observed is in the tendrils of Echinocystis lobata;
these are usually inclined at about 45° above the horizon, but they stiffen
and straighten themselves so as to stand upright in a part of their circular
course, namely, when they approach and have to pass over the summit or
the shoot from which they arise. If they had not possessed and exercised
this curious power, they would infallibly have struck against the summit of
the shoot and been arrested in their course. As soon as one of these tendrils

with its three branches begins to stiffen itself and rise up vertically, the
revolving motion becomes more rapid; and as soon as it has passed over the
point of difficulty, its motion coinciding with that from its own weight,
causes it to fall into its previously inclined position so quickly, that the apex
can be seen travelling like the hand of a gigantic clock.
[1] ‘The Movements and Habits of Climbing Plants,’ p. 36.

A large number of ordinary leaves and leaflets and a few flower-
peduncles are provided with pulvini; but this is not the case with a single
tendril at present known. The cause of this difference probably lies in the
fact, that the chief service of a pulvinus is to prolong the movement of the
part thus provided after growth has ceased; and as tendrils or other
climbing-organs are of use only whilst the plant is increasing in height or
growing, a pulvinus which served to prolong their movements would be
useless.

It was shown in the last chapter that the stolons or runners of certain
plants circumnutate largely, and that this movement apparently aids them in
finding a passage between the crowded stems of adjoining plants. If it could
be proved that their movements had been modified and increased for this
special purpose, they ought to have been included in the present chapter;
but as the amplitude of their revolutions is not so conspicuously different
from that of ordinary plants, as in the case of climbers, we have no evidence
on this head. We encounter the same doubt in the case of some plants which
bury their pods in the ground. This burying process is certainly favoured by
the circumnutation of the flower-peduncle; but we do not know whether it
has been increased for this special purpose.

EPINASTY—HYPONASTY.
The term epinasty is used by De Vries[2] to express greater longitudinal
growth along the upper than along the lower side of a part, which is thus
caused to bend downwards; and hyponasty is used for the reversed process,
by which the part is made to bend upwards. These actions come into play so
frequently that the use of the above two terms is highly convenient. The
movements thus induced result from a modified form of circumnutation;

for, as we shall immediately see, an organ under the influence of epinasty
does not generally move in a straight line downwards, or under that of
hyponasty upwards, but oscillates up and down with some lateral
movement: it moves, however, in a preponderant manner in one direction.
This shows that there is some growth on all sides of the part, but more on
the upper side in the case of epinasty, and more on the lower side in that of
hyponasty, than on the other sides. At the same time there may be in
addition, as De Vries insists, increased growth on one side due to
geotropism, and on another side due to heliotropism; and thus the effects of
epinasty or of hyponasty may be either increased or lessened.
[2] ‘Arbeiten des Bot. Inst., in Würzburg,’ Heft ii. 1872, p. 223. De Vries has
slightly modified (p. 252) the meaning of the above two terms as first used by
Schimper, and they have been adopted in this sense by Sachs.

He who likes, may speak of ordinary circumnutation as being combined
with epinasty, hyponasty, the effects of gravitation, light, etc.; but it seems
to us, from reasons hereafter to be given, to be more correct to say that
circumnutation is modified by these several agencies. We will therefore
speak of circumnutation, which is always in progress, as modified by
epinasty, hyponasty, geotropism, or other agencies, whether internal or
external.

One of the commonest and simplest cases of epinasty is that offered by
leaves, which at an early age are crowded together round the buds, and
diverge as they grow older. Sachs first remarked that this was due to
increased growth along the upper side of the petiole and blade; and De
Vries has now shown in more detail that the movement is thus caused, aided
slightly by the weight of the leaf, and resisted as he believes by
apogeotropism, at least after the leaf has somewhat diverged. In our
observations on the circumnutation of leaves, some were selected which
were rather too young, so that they continued to diverge or sink downwards
whilst their movements were being traced. This may be seen in the
diagrams (Figs. 98 and 112, pp. 232 and 249) representing the
circumnutation of the young leaves of Acanthus mollis and Pelargonium
zonale. Similar cases were observed with Drosera. The movements of a
young leaf, only 3/4 inch in length, of Petunia violacea were traced during
four days, and offers a better instance (Fig. 111, p. 248) as it diverged

during the whole of this time in a curiously zigzag line with some of the
angles sharply acute, and during the latter days plainly circumnutated.
Some young leaves of about the same age on a plant of this Petunia, which
had been laid horizontally, and on another plant which was left upright,
both being kept in complete darkness, diverged in the same manner for 48
h., and apparently were not affected by apogeotropism; though their stems
were in a state of high tension, for when freed from the sticks to which they
had been tied, they instantly curled upwards.
The leaves, whilst very young, on the leading shoots of the Carnation
(Dianthus caryophyllus) are highly inclined or vertical; and if the plant is
growing vigorously they diverge so quickly that they become almost
horizontal in a day. But they move downwards in a rather oblique line and
continue for some time afterwards to move in the same direction, in
connection, we presume, with their spiral arrangement on the stem. The
course pursued by a young leaf whilst thus obliquely descending was
traced, and the line was distinctly yet not strongly zigzag; the larger angles
formed by the successive lines amounting only to 135°, 154°, and 163°. The
subsequent lateral movement (shown in Fig. 96, p. 231) was strongly zigzag
with occasional circumnutations. The divergence and sinking of the young
leaves of this plant seem to be very little affected by geotropism or
heliotropism; for a plant, the leaves of which were growing rather slowly
(as ascertained by measurement) was laid horizontally, and the opposite
young leaves diverged from one another symmetrically in the usual manner,
without any upturning in the direction of gravitation or towards the light.
The needle-like leaves of Pinus pinaster form a bundle whilst young;
afterwards they slowly diverge, so that those on the upright shoots become
horizontal. The movements of one such young leaf was traced during 4½
days, and the tracing here given (Fig. 121) shows that it descended at first
in a nearly straight line, but afterwards zigzagged, making one or two little
loops. The diverging and descending movements of a rather older leaf were
also traced (see former Fig. 113, p. 251): it descended during the first day
and night in a somewhat zigzag line; it then circumnutated round a small
space and again descended. By this time the leaf had nearly assumed its
final position, and now plainly circumnutated. As in the case of the
Carnation, the leaves, whilst very young, do not seem to be much affected
by geotropism or heliotropism, for those on a young plant laid horizontally,

and those on another plant left upright, both kept in the dark, continued to
diverge in the usual manner without bending to either side.
Fig. 121. Pinus pinaster: epinastic downward movement of a young leaf,
produced by a young plant in a pot, traced on a vertical glass under a
skylight, from 6.45 A.M. June 2nd to 10.40 P.M. 6th.
With Cobœa scandens, the young leaves, as they successively diverge
from the leading shoot which is bent to one side, rise up so as to project
vertically, and they retain this position for some time whilst the tendril is
revolving. The diverging and ascending movements of the petiole of one
such a leaf, were traced on a vertical glass under a skylight; and the course
pursued was in most parts nearly straight, but there were two well-marked
zigzags (one of them forming an angle of 112°), and this indicates
circumnutation.
The still closed lobes of a young leaf of Dionaea projected at right angles
to the petiole, and were in the act of slowly rising. A glass filament was
attached to the under side of the midrib, and its movements were traced on a
vertical glass. It circumnutated once in the evening, and on the next day
rose, as already described (see Fig. 106, p. 240), by a number of acutely
zigzag lines, closely approaching in character to ellipses. This movement no
doubt was due to epinasty, aided by apogeotropism, for the closed lobes of a
very young leaf on a plant which had been placed horizontally, moved into
nearly the same line with the petiole, as if the plant had stood upright; but at
the same time the lobes curved laterally upwards, and thus occupied an
unnatural position, obliquely to the plane of the foliaceous petiole.
As the hypocotyls and epicotyls of some plants protrude from the seed-
coats in an arched form, it is doubtful whether the arching of these parts,
which is invariably present when they break through the ground, ought
always to be attributed to epinasty; but when they are at first straight and
afterwards become arched, as often happens, the arching is certainly due to
epinasty. As long as the arch is surrounded by compact earth it must retain
its form; but as soon as it rises above the surface, or even before this period
if artificially freed from the surrounding pressure, it begins to straighten
itself, and this no doubt is mainly due to hyponasty. The movement of the
upper and lower half of the arch, and of the crown, was occasionally traced;
and the course was more or less zigzag, showing modified circumnutation.

With not a few plants, especially climbers, the summit of the shoot is
hooked, so that the apex points vertically downwards. In seven genera of
twining plants[3] the hooking, or as it has been called by Sachs, the nutation
of the tip, is mainly due to an exaggerated form of circumnutation. That is,
the growth is so great along one side that it bends the shoot completely over
to the opposite side, thus forming a hook; the longitudinal line or zone of
growth then travels a little laterally round the shoot, and the hook points in
a slightly different direction, and so onwards until the hook is completely
reversed. Ultimately it comes back to the point whence it started. This was
ascertained by painting narrow lines with Indian ink along the convex
surface of several hooks, and the line was found slowly to become at first
lateral, then to appear along the concave surface, and ultimately back again
on the convex surface. In the case of Lonicera brachypoda the hooked
terminal part of the revolving shoot straightens itself periodically, but is
never reversed; that is, the periodically increased growth of the concave
side of the hook is sufficient only to straighten it, and not to bend it over to
the opposite side. The hooking of the tip is of service to twining plants by
aiding them to catch hold of a support, and afterwards by enabling this part
to embrace the support much more closely than it could otherwise have
done at first, thus preventing it, as we often observed, from being blown
away by a strong wind. Whether the advantage thus gained by twining
plants accounts for their summits being so frequently hooked, we do not
know, as this structure is not very rare with plants which do not climb, and
with some climbers (for instance, Vitis, Ampelopsis, Cissus, etc.) to whom
it does not afford any assistance in climbing.
[3] ‘The Movements and Habits of Climbing Plants,’ 2nd edit. p. 13.

With respect to those cases in which the tip remains always bent or
hooked towards the same side, as in the genera just named, the most
obvious explanation is that the bending is due to continued growth in excess
along the convex side. Wiesner, however, maintains[4] that in all cases the
hooking of the tip is the result of its plasticity and weight,—a conclusion
which from what we have already seen with several climbing plants is
certainly erroneous. Nevertheless, we fully admit that the weight of the part,
as well as geotropism, etc., sometimes come into play.
[4] ‘Sitzb. der k. Akad. der Wissensch.,’ Vienna, Jan. 1880, p. 16.

Ampelopsis tricuspidata.—This plant climbs by the aid of adhesive
tendrils, and the hooked tips of the shoots do not appear to be of any service
to it. The hooking depends chiefly, as far as we could ascertain, on the tip
being affected by epinasty and geotropism; the lower and older parts
continually straightening themselves through hyponasty and apogeotropism.
We believe that the weight of the apex is an unimportant element, because
on horizontal or inclined shoots the hook is often extended horizontally or
even faces upwards. Moreover shoots frequently form loops instead of
hooks; and in this case the extreme part, instead of hanging vertically down
as would follow if weight was the efficient cause, extends horizontally or
even points upwards. A shoot, which terminated in a rather open hook, was
fastened in a highly inclined downward position, so that the concave side
faced upwards, and the result was that the apex at first curved upwards.
This apparently was due to epinasty and not to apogeotropism, for the apex,
soon after passing the perpendicular, curved so rapidly downwards that we
could not doubt that the movement was at least aided by geotropism. In the
course of a few hours the hook was thus converted into a loop with the apex
of the shoot pointing straight downwards. The longer axis of the loop was at
first horizontal, but afterwards became vertical. During this same time the
basal part of the hook (and subsequently of the loop) curved itself slowly
upwards; and this must have been wholly due to apogeotropism in
opposition to hyponasty. The loop was then fastened upside down, so that
its basal half would be simultaneously acted on by hyponasty (if present)
and by apogeotropism; and now it curved itself so greatly upwards in the
course of only 4 h. that there could hardly be a doubt that both forces were
acting together. At the same time the loop became open and was thus
reconverted into a hook, and this apparently was effected by the geotropic
movement of the apex in opposition to epinasty. In the case of Ampelopsis
hederacea, weight plays, as far as we could judge, a more important part in
the hooking of the tip.
Fig. 122. Ampelopsis tricuspidata: hyponastic movement of hooked tip of
leading shoot, traced from 8.10 A.M. July 13th to 8 A.M. 15th. Apex of
shoot 5½ inches from the vertical glass. Plant illuminated through a
skylight. Temp. 17½°–19° C. Diagram reduced to one-third of original
scale.
Fig. 123. Smithia Pfundii: hyponastic movement of the curved summit of
a stem, whilst straightening itself, traced from 9 A.M. July 10th to 3 P.M.

13th. Apex 9½ inches from the vertical glass. Diagram reduced to one-fifth
of original scale. Plant illuminated through skylight; temp. 17½°–19° C.
In order to ascertain whether the shoots of A. tricuspidata in straightening
themselves under the combined action of hyponasty and apogeotropism
moved in a simple straight course, or whether they circumnutated, glass
filaments were fixed to the crowns of four hooked tips standing in their
natural position; and the movements of the filaments were traced on a
vertical glass. All four tracings resembled each other in a general manner;
but we will give only one (see Fig. 122, p. 273). The filament rose at first,
which shows that the hook was straightening itself; it then zigzagged,
moving a little to the left between 9.25 A.M. and 9 P.M. From this latter
hour on the 13th to 10.50 A.M. on the following morning (14th) the hook
continued to straighten itself, and then zigzagged a short distance to the
right. But from 1 P.M. to 10.40 P.M. on the 14th the movement was
reversed and the shoot became more hooked. During the night, after 10.40
P.M. to 8.15 A.M. on the 15th, the hook again opened or straightened itself.
By this time the glass filament had become so highly inclined that its
movements could no longer be traced with accuracy; and by 1.30 P.M. on
this same day, the crown of the former arch or hook had become perfectly
straight and vertical. There can therefore be no doubt that the straightening
of the hooked shoot of this plant is effected by the circumnutation of the
arched portion—that is, by growth alternating between the upper and lower
surface, but preponderant on the lower surface, with some little lateral
movement.
We were enabled to trace the movement of another straightening shoot
for a longer period (owing to its slower growth and to its having been
placed further from the vertical glass), namely, from the early morning on
July 13th to late in the evening of the 16th. During the whole daytime of the
14th, the hook straightened itself very little, but zigzagged and plainly
circumnutated about nearly the same spot. By the 16th it had become nearly
straight, and the tracing was no longer accurate, yet it was manifest that
there was still a considerable amount of movement both up and down and
laterally; for the crown whilst continuing to straighten itself occasionally
became for a short time more curved, causing the filament to descend twice
during the day.

Smithia Pfundii.—The stiff terminal shoots of this Leguminous water-
plant from Africa project so as to make a rectangle with the stem below; but
this occurs only when the plants are growing vigorously, for when kept in a
cool place, the summits of the stems become straight, as they likewise did at
the close of the growing season. The direction of the rectangularly bent part
is independent of the chief source of light. But from observing the effects of
placing plants in the dark, in which case several shoots became in two or
three days upright or nearly upright, and when brought back into the light
again became rectangularly curved, we believe that the bending is in part
due to apheliotropism, apparently somewhat opposed by apogeotropism. On
the other hand, from observing the effects of tying a shoot downwards, so
that the rectangle faced upwards, we are led to believe that the curvature is
partly due to epinasty. As the rectangularly bent portion of an upright stem
grows older, the lower part straightens itself; and this is effected through
hyponasty. He who has read Sachs’ recent Essay on the vertical and inclined
positions of the parts of plants[5] will see how difficult a subject this is, and
will feel no surprise at our expressing ourselves doubtfully in this and other
such cases.
[5] ‘Ueber Orthotrope und Plagiotrope Pflanzentheile;’ ‘Arbeiten des Bot. Inst.,
in Würzburg,’ Heft ii. 1879, p. 226.

A plant, 20 inches in height, was secured to a stick close beneath the
curved summit, which formed rather less than a rectangle with the stem
below. The shoot pointed away from the observer; and a glass filament
pointing towards the vertical glass on which the tracing was made, was
fixed to the convex surface of the curved portion. Therefore the descending
lines in the figure represent the straightening of the curved portion as it
grew older. The tracing (Fig. 123, p. 274) was begun at 9 A.M. on July
10th; the filament at first moved but little in a zigzag line, but at 2 P.M. it
began rising and continued to do so till 9 P.M.; and this proves that the
terminal portion was being more bent downwards. After 9 P.M. on the 10th
an opposite movement commenced, and the curved portion began to
straighten itself, and this continued till 11.10 A.M. on the 12th, but was
interrupted by some small oscillations and zigzags, showing movement in
different directions. After 11.10 A.M. on the 12th this part of the stem, still
considerably curved, circumnutated in a conspicuous manner until nearly 3
P.M. on the 13th; but during all this time a downward movement of the

filament prevailed, caused by the continued straightening of the stem. By
the afternoon of the 13th, the summit, which had originally been deflected
more than a right angle from the perpendicular, had grown so nearly straight
that the tracing could no longer be continued on the vertical glass. There
can therefore be no doubt that the straightening of the abruptly curved
portion of the growing stem of this plant, which appears to be wholly due to
hyponasty, is the result of modified circumnutation. We will only add that a
filament was fixed in a different manner across the curved summit of
another plant, and the same general kind of movement was observed.
Trifolium repens.—In many, but not in all the species of Trifolium, as the
separate little flowers wither, the sub-peduncles bend downwards, so as to
depend parallel to the upper part of the main peduncle. In Tr. subterraneum
the main peduncle curves downwards for the sake of burying its capsules,
and in this species the sub-peduncles of the separate flowers bend upwards,
so as to occupy the same position relatively to the upper part of the main
peduncle as in Tr. repens. This fact alone would render it probable that the
movements of the sub-peduncles in Tr. repens were independent of
geotropism. Nevertheless, to make sure, some flower-heads were tied to
little sticks upside down and others in a horizontal position; their sub-
peduncles, however, all quickly curved upwards through the action of
heliotropism. We therefore protected some flower-heads, similarly secured
to sticks, from the light, and although some of them rotted, many of their
sub-peduncles turned very slowly from their reversed or from their
horizontal positions, so as to stand in the normal manner parallel to the
upper part of the main peduncle. These facts show that the movement is
independent of geotropism or apheliotropism; it must there[fore] be
attributed to epinasty, which however is checked, at least as long as the
flowers are young, by heliotropism. Most of the above flowers were never
fertilised owing to the exclusion of bees; they consequently withered very
slowly, and the movements of the sub-peduncles were in like manner much
retarded.
Fig. 124. Trifolium repens: circumnutating and epinastic movements of
the sub-peduncle of a single flower, traced on a vertical glass under a
skylight, in A from 11.30 A.M. Aug. 27th to 7 A.M. 30th; in B from 7 A.M.
Aug. 30th to a little after 6 P.M. Sept. 8th.

To ascertain the nature of the movement of the sub-peduncle, whilst
bending downwards, a filament was fixed across the summit of the calyx of
a not fully expanded and almost upright flower, nearly in the centre of the
head. The main peduncle was secured to a stick close beneath the head. In
order to see the marks on the glass filament, a few flowers had to be cut
away on the lower side of the head. The flower under observation at first
diverged a little from its upright position, so as to occupy the open space
caused by the removal of the adjoining flowers. This required two days,
after which time a new tracing was begun (Fig. 124). In A we see the
complex circumnutating course pursued from 11.30 A.M. Aug. 26th to 7
A.M. on the 30th. The pot was then moved a very little to the right, and the
tracing (B) was continued without interruption from 7 A.M. Aug. 30th to
after 6 P.M. Sept. 8th. It should be observed that on most of these days, only
a single dot was made each morning at the same hour. Whenever the flower
was observed carefully, as on Aug. 30th and Sept. 5th and 6th, it was found
to be circumnutating over a small space. At last, on Sept. 7th, it began to
bend downwards, and continued to do so until after 6 P.M. on the 8th, and
indeed until the morning of the 9th, when its movements could no longer be
traced on the vertical glass. It was carefully observed during the whole of
the 8th, and by 10.30 P.M. it had descended to a point lower down by two-
thirds of the length of the figure as here given; but from want of space the
tracing has been copied in B, only to a little after 6 P.M. On the morning of
the 9th the flower was withered, and the sub-peduncle now stood at an
angle of 57° beneath the horizon. If the flower had been fertilised it would
have withered much sooner, and have moved much more quickly. We thus
see that the sub-peduncle oscillated up and down, or circumnutated, during
its whole downward epinastic course.
The sub-peduncles of the fertilised and withered flowers of Oxalis
carnosa likewise bend downwards through epinasty, as will be shown in a
future chapter; and their downward course is strongly zigzag, indicating
circumnutation.

The number of instances in which various organs move through epinasty
or hyponasty, often in combination with other forces, for the most
diversified purposes, seems to be inexhaustibly great; and from the several