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THE
POWER OF MOVEMENT
IN
PLANTS.
THE
POWER OF MOVEMENT
IN PLANTS
BY
CHARLES DARWIN, LL.D., F.R.S.
ASSISTED BY
FRANCIS DARWIN
WITH ILLUSTRATIONS
NEW YORK
D. APPLETON AND COMPANY
1897
Aire
Fuerte &
OK
a
“D3
\347
357 101
Authorized Edition.
CONTENTS.
INTRODUCTION 2... 6k wee ete tee Page 1-9
CHAPTER I.
Tue Crrcumnutatine Movements or SEEDLING PLaNTs,
Brassica oleracea, circumnutation of the radicle, of the arched hypo-
cotyl whilst still buried beneath the ground, whilst rising above
the ground and straightening itself, and when ereet—Circumuu-
tation of the cotyledons—Rate of movement—Analogous obser-
vations on various organs in species of Githago, Gossypium,
Oxalis, Tropzolum, Citrus, Aésculus, 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 .. .. .. «. 10-66—
CHAPTER IL
GENERAL CONSIDERATIONS ON THE MOVEMENTS AND GROWTH OF
SEEDLING Puants.
Generality of the circumnutating movement—Radicles, their cir-
cumnutation 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 ger-
mination in Megarrhiza, &.-—Abortion of cotyledons—Cireum-
nutation of ‘hypocotyls and epicotyls whilst still buried and
arched—Their power of straightening themselves— Bursting of
the seed-ccats—Inherited effect of the arching process in hypo-
vi CONTENTS.
gean hypocotyls—Circumnitation of hypocotyls and epicotyle
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.. .. .. Page-67-128
CHAPTER ITI.
SENSITIVENESS OF THE APEX oF THE RapICcLE To CoNnTACT AND
TO OTHER IkRITANTS.
Manner in which radicles bend when they encounter an obstacle in
the soil—Vicia faba, tips of radicles highly sensitive to con-
tact 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—Tropazolum—Gossy pium—Cucurbita
—Raphanus— Aésculus, 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 ., .. 0. we we wees =~: 1 29-200
CHAPTER IV.
Tue CircumnutTaTing MovEMESTS OF THE SEVERAL PARTS OF
Mature Puants.
Circumnutation of stems: concluding remarks on—Circumnutation
of stolons: aid thus afforded in winding amongst the stems of
surrounding plants—Circumnutation of flower-stems—Circume
nutation of Dicotyledonous leaves—Singular oscillatory move-
ment of leaves of Dionzea—Leaves of Cannabis sink at night—
Leaves of Gymnosperms—Of Monocotyledons—Cryptogams—
Ccncluding remarks on the cireumnutation of leaves: generally
tise in the evening and sink in the morning ., .. 201-262
CONTENTS. vil
CHAPTER V.
Mopirizp CirncUMNUTATION: CLImBina PLants; EPINasTio AND
Hyponastic Movements,
Circumnutation modified through ianate causes or through the action
of external conditions—Innate causes—Climbing plants; simi-
larity of their movements with those of ordinary plants; in-
creased 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
—Swmithia Pfundii—Straightening of the tip due to hyponasty—
Epinastic growth and circumnutation of the flower-peduncles of
Trifolium repens and Oxalis carnosa.. .. .. Page 268-279
CHAPTER VIL.
Mopiriep CrrcumnurtatTion: SLEEP on Nyotirropio 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 nictritropic movements—Manuver of trying experiments on
leaves of Oxalis, Arachis, Cassia, Melilotus, Lotus and Marsilca,
and on the cotyledons of Mimosa—Concluding remarks on radia-~
tion from leaves—Small differences in the conditions make a
great difference in the result—Deseription of the nyctitropic
position and movements of the cotyledons of various plants—
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 fora special purpose .. .. .« « .«. 280-316
CHAPTER VII.
Moviriep CrrcumnutatTion: Nyctirroric on SueEP MovEMENTS
or LravEs.
Conditions necessary for these movements—List of Genera and
Families, which include sleeping plants—Description of the
movements in the several Gencra—Oxalis: leaflets folded ut
Vu CONTENTS.
night—Averrhoa: rapid movements of the leatlets—Porlieria :
leaflets close when plant kept very dry—Tropevlum: leaves de
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 ycung plants, state of their
palvini—Cassia : complex movements of the leaflets—Bauhinia:
leaves folded at ni.-ht—Mimosa pudica: compounded move-
ments of leaves, effect of darkness—Mimosa albida, reduced
leaflets of—Schrankia: downward movement of the pinna—
Marsilea: the only cryptogam known to sleep—Concluding
remarks and summary—Nyctitropism consists of modified cir-
cumnutation, regulated by the alteruations of light and darkness
—Shape of first true leaves «ove we ee) Page 817-417
CHAPTER VIII.
MopiFIED CIRCUMNUTATION: MOVEMENTS EXCITED BY LIGHT.
Distinction between heliotropism and the effects of light on the
periodicity of the movements of leavcs—Heliotropic movements
of Beta, Solanum, Zea, and Avena—Heliotropic movements
towards an obscure light in Apios, Brassica, Phalaris, Tropso-
lum, and Cassia—Apheliotropic movements of tendrils of Big-
nonia—Of flower-peduncles of Cyclamen—Burying of the pods
—Heliotropism and apheliotropism moditied forms of cireumnu-
tation—Steps by which one movement is converted into the
other—Transversal-heliotropismus or diaheliotropism infinenced
by epinasty, the weight of the part and apogeotropism—A pogeo-
tropism overcome during the middle of the day by diaheliotro-
pism—Effects of the weight of the blades of cotyledons—So-
called diurnal sleep—Chlorophyll injured by intense light—
Movements to avoid intense light.. .. .. .. .. 418-448
CHAPTER IX.
SENSITIVENESS OF PLaANTs TO LiGnt: ITS TRANSMITTED EFFECTS,
Uses of he 'iotropism—lInsectivorous and climbing plants not helic-
tropic—Same organ heliotropic at one age and not at another--
Extraordinary sensitiveness of some plants to light—The effects
CONTENTS. 1x
of light do not correspond with its intensity—Eftccts of previous
illumination—Time required for the action of light—A fter-effects
of light—Apogeotropism acts as soon as light fails—Aceuracy
with which plants bend to the light—This dependent on the
Llumination of one whole side of the part—Localised sensitive-
ness 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 hase—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 aphelio-
tropic, due to the sensitiveness of their tips—Concluding remarks
and summary of chapter—Means by which circumnutation has
been converted into heliotropism or apheliotropism Page 449-492
CHAPTER X.
MopirieD 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—
Gencral remarks on apogeotropism—Geotropism—Movements of
radicles—Burying of seed-capsules—Use of process—T'ifolium
subterraneum — Arachis — Amphicarpaa — Diagcotropism —
Conclusion .. 0 «eee we a a 493-522
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 ex-
posure of the tips to geotrojic action and their subsequent
amputation—Fffects of amputating the tips obliquely—Effects
of cauterising the tips—Effects of grease on the tips—Pisum
x CONTENTS.
sativum, tips of radicles cauterised transversely, and on theit
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—Con-
eluding remarks and summary of chapter—Advantages of the
sensibility to geotropism being localised in the tips of the
radicles 4, 0 .. 4. ue ae we eee Page 28-545
CHAPTER XII
Summary axp Coxctupine Remarks,
Wature 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 grcund under the form of an arch—Its circumnutation
and that of the cotyledons—The seedling throws up a leaf-
bearing stem—'he 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 likea brain... ww ee we we |B 4G+57B
INDEX: os ae kee wi ae a a eye we TEBE
THE MOVEMENTS OF PLANTS.
INTRODUCTION.
Tue chief object of the present work is to describe
and connect together several large classes of move-
ment, 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 cirewmnutation.
and cireumnutate. 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 beer
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 point-
ing 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
2 INTRODUCTION.
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 move-
ments 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.* 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 f
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
lenies in certain cases the accuracy of De Vries’ con-
vlusion about turgescence, and maintains{ 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.
Or: the whole we may at present conclude that in-
“Sachs first showed ‘‘Lehr- 19, 1879, p. 839.
buch, &c., 4th edit. p. 452) the t ‘Dee Perioidisclen Bewegun-
intimate connection b. tween tur- gen der Blattorgane,’ 1X75.
gescence and growth. For De } ‘Untersuchungen iiber den
Wries’ interesting essay,‘ Wachs- Heliotropismus,’ Sitzb. der kh
‘thumskriimmungen mehrzelliger Akad. der Wissenschaft. (Vienna).
Organe,’ see ‘ Bot. Zeitung,’ Dec. Jan. 1880.
INTRODUCTION. 3
creased growth, first ov one side and then on another,
is a secondary effect, and that the increased tur-
gescence of the cells, together with the extensibility
of their walls, is the primary cause of the movement of
circumnutation.*
In the course of the present volume it wil] 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 pre-
sent 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, aud occasionally from the light,
or transversely with respect to it, are all modified
* See Mr. Vines’ excellent dis. Naturkunde in Wiirtemberg,’
cussion (‘ Arbeitcn des Bot. Insti- 1874, p. 211) on the curious move-
tuts in Wiirzburg? B. II. pp 142, ments of Spirogyra, a plant con-
143, 1878) on thisintricate subject. _ sisting of a single row of cells,.ara
Hofmeister’s observations (‘Jul- valuable in relation to this subject.
reschrifte des Vereins fir Vaterl.
4 INTRODUCTION.
forms of circumnutation; as again are the equally
prevalent movements of stems, &c., towards the zenith,
and of roots towards the centre of the earth. In
accordance with these conclusions, a considerable diffi-
culty in the way of evolution is in part removed, fur
it might have been asked, how did all their diversificd
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 direc-
tion, 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 influ-
ence to the lower part, causing it to bend. If there-
fore 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 seed-
lings, the tip is sensitive to various stimuli, espe-
cially 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
INTRODUCTION. 5
attraction of gravity being transmitted from the ex-
cited 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 circumnu-
tation has already been explained. Authors speak of positive
and negative heliotropism,*—that is, the bending of an organ
to or from the light; but it is much more convenient to confine
the word helivtropism to bending towards the light, and to
designate as a;helivtropism 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. Déiahelio-
tropism may express a position more or less transverse to
the light and induced by it. In like manner positive geotro-
pism, 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 dia-
jeotropism, 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, &c., as the cause of the
movements in question.
The term epinusty is now often used in Germany, and implies
that the upper surface of an organ grows more quickly than the
* The highly useful terms of Frank; see his remarkable ‘ Bei-
Heliotropism and Geotropism triage zur Pflanzenphysiologie,
were first used by Dr. A. B. 1868.
6 INTRODUCTION.
lower surface, and thus causes it to bend downwards. Hypo
nasty is the reverse, and implies increased growth along the
lower surface, causing the part to bend upwards.*
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 obser-
vation, 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 after-
wards 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
* These terms are usedinthe ‘ Wiirzburg Arbeiten” Heft ii
sense given them by De Vries, 1872, p. 252, :
INTRODUCTION. v4
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 5); 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 dis-
tance 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 move-
ment 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.*
Whenever it could be approximately told how much the move-
ment had been magnified, this is stated. We have perhaps
* We are much indebted to he has reduced and engraved our
Mr. Cooper for the care with which diagrams.
2
8 INTRODUCTION.
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, &c., were carefully drawn
for us by Mr. George Darwin.
As shoots, leaves, &c., 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 con-
siderable number of plants are described; and the
species have been arranged according to the system
adopted by Hooker in Le Maout and Decaisne’s ‘ De-
scriptive 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 om
INTRODUCTION. 9
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.
10 OIRCUMNUTATION OF SEEDLINGS. Caar. L
CHAPTER I.
THE CrrocmnuTaTinec Movements or SEEDLING PLANTS.
Brassica oleracea, circumnutation of the radicle, of the arched hypo-
cotyl 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, Osxalis, Tro-
peolum, Citrus, Asculus, of several Leguminous and Cucurbita-
ceous genera, Opuntia, Helianthus, Primula, Cyclamen. Stapel‘a,
Cerinthe, Nolana, Solanum, Beta, Ricinus, Quercus, Corylus, Pinus,
Cycas, Canna, Allium, Asparagus, Phalaris, Zea, Aveua, Nephro-
dium, and Selaginella,
THE following chapter is devoted to the circum-
nutating movements of the radicles, hypocotyls, and
cotyledons of seedling plants; and, when the coty-
ledons do not rise above the ground, to the movements
of the epi.otyl. But in a future chapter we shall have
to recur to the movements of certain cotyledons which
sleep at night.
Brassica oleracea (Crucifere).—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 move-
ment 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 "ll inch. Had the filament been attached at
first close to the apex of the radicle, and if it could have re-
mained there all the time, the movement exhibited would have
Ouar. I, BRASSICA. 11
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 zine
plate. As far as we could
roughly seer by measure-
ments made with compasses
on other seeds, the tip alone,
for a length of only =, to
zig of an inch, is acted on
by geotropism. But the trac-
ing shows that the basal part
of the radicle continued to
circumnutate irregularly dur-
ing the whole time. The
actual extreme amount of
movement of the bead at the
end of the filament was nearly
Fig 1.
05 inch, but to what extent
the movement of the radicle
was magnified by the fila-
Brassca oleriacea: 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.
ment, which was nearly 3 inch
in length, it was impossible
to estimate.
Another seed was treated and observed in the same manner,
but the radicle in this case protruded ‘1 inch, and was not
Fig, 2.
an
Brassica oleracea: circumnutating and geotropic movement of radicle,
traced on horizontal glass during 46 hours.
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 9a.m. Jan. 31st to 7 a.m.
Feb. 2nd; but it continued to move during the whole of the
12 CIRCUMNUTATION OF SEEDLINGS. Cuar. I.
Qnd 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 curva-
ture. 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 move-
ments of the radicles of other plants, that they may be largely
trusted.
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 q; 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 cireumnutates as much as the pressure of the sur-
rounding 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
Cuap. L BRASSICA. 13
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 circum-
nutating, whilst it was straightening itself by growth along its
inner or concave surface. :
A somewhat different method of observation was next followed:
Fig. 3.
Brassica oleracea: cireumnutating movement of buried and arched hypo-
cotyl (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.
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 hypo-
cotyl, 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 st ows that the arched hypocoty] tends at this early
14 CIRCUMNUTATION OF SEEDLINGS. Cuar.-1
age to circumnutate irregularly. On the first day the greater
movenient (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. i5th of an inch, in 22m.5s. A
seedling Nolana prostrata travelled the same distance
in 10m. 38s. Seedling cabbages circumutated much
more quickly, for the tip of a cotyledon crossed
ydoth of an inch on the micrometer in 3 m. 20 s.; and
this rapid movement, accompanied by incessant oscil-
lations, 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.* He shows that
* ‘Bot. Zeitung,’ 1879, p. 649. burg,’ Jahrg. xvi. p. 16, as quoted
See also Winkler in ‘Verhandl. by Haberlandt, ‘ Schutzeinrichun-
des Bot. Vereins der P, Brunden- —_ gen der Keimpflanze,’ 1877, p. 52
Omar. II. CIRCUMNUTATION OF COTYLEDONS. 109
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 Gthago 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.
Cireumnutation of Cotyledons.— With all the dico-
tyledonous seedlings described in the last chapter, the
cotyledons were in constant movement, chiefly in a ver-
tical plane, and commonly once up and once down in
the course of the 24 hours. But there were many excep-
tions to such simplicity of movement; thus the cotyle-
dons of Ipomeea cerulea moved 13 times either upwards
or downwards in the course of 16h.18m. 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 Jacobeus
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 move-
ment to oscillations as complex as those of the
Ipomea 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 gene-
rally in nearly the same vertical plane, yet their
upward and downward courses never exactly coin-
110 CIRCUMNUTATION OF COTYLEDONS. Cuapr. IL
cided; so that ellipses, more or less narrow, were
described, and the cotyledons may safely be said to
have cireumnutated. 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 move-
ment 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 14h.15m. With Solanum lycopersicum the
cotyledons, after falling in the forenoon, zigzagged
from side to side between 12 and 4 pP.M., and then
commenced rising. The cotyledons of Lupinus luteus
are so thick (about ‘08 of an inch) and fleshy,* that
they seemed little likely to move, and were there-
fore 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 circum-
nutated ; and the figures described approached more
nearly to irregular circles than to irregular ovals or
ellipses, The sheath-like cotyledons of the Gra-
minez circumnutate, that is, move to all sides, as
plainly as do the hypocotyls or epicotyls of any dico-
tyledonous plants. Lastly, the very young fronds of
a Fern and of a Selaginella circumnutated.
In a large majority of the cases which were care-
fully 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
* The cotyledons, though bright &c , 1877, p. 95), on the gradationa
green, resemble to a certain ex- in the Leguminosw between sub-
tent hypogean ones; see the in- aérial and subterranean cotvle-
teresting discussion by Haber- dons,
jandt (‘Die Schutzcinrichtungen,’
Canp. II. CIRCUMNUTATION OF COTYLEDONS. 111
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
auother. 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 dico-
tyledonous 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
112 PULVINI OF COTYLEDONS. Cuap. II.
eotyledons 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 sink-
ing only a few degrees at night, although no doubt
such occur. We have now accounted for 64 genera
out of the 158, 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 re-
corded, 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, Trifo-
lium 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,
Cuap. II. PULVINI OF COTYLEDONS. 113
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 Mz-
mosa pudica, apparently the
whole of the short sub-
petioles of the leaflets have
been converted into pulvini.
With pulvinated leaves (ie.
those provided with a pul-
vinus) their periodical move-
ments depend, according to
Pfeffer,* on the cells of the
pulvinus alternately expand-
ing more quickly on one side
than on the other; whereas
the similar movements of
leaves not provided with pul-
vini, depend on their growth sich se 2 longitudinal section
7 . pulvinus on the summ‘t
being alternately more rapid of the petiole of a cotyledon,
on one side than on the drawn with the camera lucida,
magnified 75 times: p, p, pe-
other.t As long as a leaf _ tiole; f,fibro-vascular bundle;
provided with a pulvinus is Lai of bladeval
young and continues to grow,
its movement depends on both these causes combined ;t
and if the view now held by many botanists be sound,
namely, that growth is always preceded by the expan-
sion of the growing cells, then the difference between
the movements induced by the aid of pulvini and
* ‘Die Periodische Bewegun- + Batalin, ‘Flora, Oct. 1st, 1873
gen der Blattorgane,’ 1875. } Pfetter, ibid. p. 5.
{14 PULVINI OF COTYLEDONS. Guar. IL
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.
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? days,
ard 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 coty-
ledons 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 pro-
duced true leaves. With some species of Cassia, on
the other hand, it was obvious without any measure-
ment 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 m
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 exclu-
sively 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 com:
Onap. II. PULVINI OF COLYLEDONS. 115
paring the diagrams given in the last chapter. ‘Thus
the movements of the cotyledons of Brassica oleracea
and of Ipomea cerulea, 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
Jacobeus 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 Crucifere, Cucurbitacee,
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 ver-
tically up; on the 13th the first true leaf was formed, and was
embraced at night by the cotyledons; on April 9th, after an in-
terval of 35 days, six leaves were developed, and yet the coty-
ledons rose almost vertically at night. The cotyledons of
another seedling, which when first observed had already pro- .
duced a leaf, stood vertically at night and continued to do so for
Jl 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 4 3°
116 PULVINI OF COTYLEDONS. Cuap. IL
above it. Aftcr 24 days from the first observation (begun after
a true leaf had been developed) the cotyledons ceased to rise at
night.
Oaalis (Biophytum) sensitiva.—The cotyledons of several seed-
lings, 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.
Oxulis corniculuta.—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 hori-
zontal 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 ulbidu.—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 coty-
ledons 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 Jacobeus.—The cotyledons of some seedlings having
well-developed leaves rose to an angle of about 45° at night;
and even after 8 or 4 whorls of leaves had been formed, the co-
tyledons rose at night considerably above their diurnal hori-
zontal position.
Cassiz mimosoides.—The cotyledons of this Indian specics,
14 days after their first expansion, and when a leaf had beon
formed, stood during the day horizontal, and at night vertical.
Cassia sp ? (a large S. Brazilian tree raised from seeds sent us
fod
Cuap. II. PULVINI OF COTYLEDONS. 117
by F. Miiller)—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.
Cassiu neglectu (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 cotyle-
dons 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 * 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 down-
ward movements. In this respect cotyledons offer an
unusally good opportunity for comparing the structure
of the two halves; for the cotyledons of Owalis Valdi-
viana 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 speci-
men of O. Valdiviana. The cotyledons of both species
(8} 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 OU. Valdiviana it was the lower surface
which was wrinkled, and its cotyledons rise at night.
Trifolium is a natural genus, and the leaves of all
* Pfeffir, ‘Die Pu:iod. Bewegungen,’ 1875, p. 157.
118 PULVINI OF COTYLEDONS. Cuap. IL
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 7. resupi-
natum exhibit not a trace of.a pulvinus, nor of any
nocturnal movement. This was ascertained by mea-
suring 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 coty-
ledon, as is the usual rule with most plants. Ozalis cor-
niculata (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. trop«oloides, 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 abor-
tion. No such case has hitherto, we believe, been
deseribed. It is coloured green from its cells con-
taining 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. Fr-m these several reasons
and from our having partially traced the develop-
ment of the pulvinus from an early age, the caso
seems worth describing in some detail.
Onap. II, PULVINI OF COTYLEDONS. 119
When the cotyledons of 0. 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
Fig. 64,
A B.
Oxalis corniculata: A and B the almost rudimentary pulvini of the coty-
ledons of two rather old seedlings, viewed as transparent objects.
Magnified 50 times.
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 contain-
ing 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 j arts of the
9
120 PULVINI OF COTYLEDONS. Cuap. TL,
same pulvinus and in different individuals. In the accompany-
ing figures, A and B (Fig. 64), we have views of the epidermis *
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 0. rosea (see former
Fig. 63), or of O. Vuldiviana. With the seedlings, falsely called
0. tropeoloides, 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.
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.f
Average length of cells of pulvinus toe we we C07
Length of longest cell below the pulvinus .. .. .. 13
Length of longest cell above the pulvinus .. .. .. 20
Seedling 5 d cys old, cotyledon 3-1 mm. in length, with the pulvinus
quite distinct.
Average length of cells of pulvinus a ae 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 Be Gas Se ee 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 Gat feay a RS aS 7
Length of longest cell below the pulvinus .. .. .. 30
Length of longest cell above the pulvinus .. ..).. aU
* Longitudinal sections show pulvinus.
that the forms of the epidermic + Each division equalled +008
sella may be taken as a fairrepre- mm.
sentation of those constituting the
Ouar. IL. PULVINI OF COTYLEDONS 121
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 con-
siderably, 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 toa higher inclination than whilst young, yet they have
to pass through a larger angle (in one instance amounting to
68°) 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. corni-
culata 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 Jacobeus.—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 noc-
turnal 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
122 PULVINI OF COTYLEDONS. Crap. IL
the day. With older seedlings, having cotyledons 4 mm, in
length, which rise considerably at night, there is a well-deve-
loped pulvinus close to the bladc, colourless, and rather nar-
rower 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 24 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 upper-
most part of the petiole, continuing for only a short time to
increase in length, then being arrested in their growth, accom-
panied 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 Jacobus the cells at first increase a little in
length; in Ozalis corniculata they decrease a little,
owing to seli-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
Cuav. II. DISTURBED PERIODIC MOVEMENTS. 1238
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 subse-
quent contraction of their walls, we can perhaps under-
stand 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 de-
pendent on their action may be long-continued withou
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 seed-
ling 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.
124 DISTURBED PERIODIC MOVEMENTS. Cuar. IL.
For instance, the cotyledons of Beta vulgaris, Solanum lycoper-
sicum, Cerinthe major, and Lupinus luteus, when placed in dark-
hess, 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 Uxalis 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 Jacobceeus were not affected by 4h. 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 40h. Other seedlings were
placed in the dark after their cotyledons had opened in the
morning and these did not begin to close until about 4h. had
elapsed. The cotyledons of Owalis rosea sank vertically down-
wards after being left for 1h. 20m. 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 8. 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 1h. 13 m.
they began toopen. The cotyledons of young seedlings of another
Brazilian species and of C. neglecta, treated in the same manner,
behaved similarly, éxcepting 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 2h. to dull sunshine, and the cotyledons
Onap. IL SENSITIVENESS OF COTYLEDONS. 125
remained horizontal; it was then brought back to the table, and
after 50m. 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 83°. These two
pots with seedlings of the same age stood close together, and
were exposed to exactly the same amount of light, yet the coty-
ledons 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 seed-
lings, 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 dark-
ness; yet the cotyledons were partially open in the morning
and remained open in the dark for about 6h. The cotyledons
in another pot, similarly treated on another occasion, were open
at 7 am. and remained open in the dark for 4h. 30m, 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 coty-
ledons 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
8m., 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 9m.; 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 hori-
zontal again in less than half an hour. The pulvinus is the most
sensitive part, for on slightly pricking three cotyledons with e
326 COTYLEDONS SENSITIVE Cuap. IL
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 coty-
ledons 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 8. Brazil) rose 81° in the course of 26 m. after the pulvini
and the blades had both been rubbed during 1m. 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 8S. Brazil, did not move when their
blades were rubbed on six occasions with a pointed stick for
80s. or for 1m.; 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 60°. Several cotyledons of
C. neglecta (likewise from 8. Brazil) rose in from 5 m. to 15 m. to
various angles between 16° and 34°, after being rubbed during
lm. with a twig. Their sensitiveness is retained to a somewhat
advanced age, for the cotyledons of a little plant of C. eglecta,
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 2m. or
were lightly pinched: one rose 34°; a second only 6°; a third
18°; and a fourth 17°. A cotyledon of C. florida similarly
treated rose 9°; one of C. corymbosa rose 73°, 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.
ncdosa, 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 Leguminose from Cassia. Both cotyledons of an oldish
seedling, with the first true leaf partially unfolded, were rubbed
for 1m. with a fine twig, and in 5m. each rose 32°; thoy
Ouap. IL. TO CONTACT. 127
remained in this position for 15m., but when looked at again
40m. after the rubbing, each had fallen 14°. Both cotyledons of
another and younger seedling were lightly rubbed in the same
manner for 1m., 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. Lfundii, an African water plant, are thick
and fleshy ; they ure 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 1m. or 2m.; 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
gases perhaps the pulvinus was accidentally pricked, for on
pricking the pulvinus of another cotyledon it rosea little. It
thus appears that the cotyledons of Mimosa are less sensitive
than those of the previously mentioned plants.*
Osalis sensitivu.—The blades and pulvini of two cotyledons,
standing horizontally, were rubbed or rather tickled for 30s.
with a fine split bristle, and in 10m. 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 hori-
zontal. On hitting a pot rapidly with a stick for 1m., the coty-
ledons of two seedlings were considerably raised in the course
of llm. 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 obser-
vations were made before we were aware at what an extraordi-
narily 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 secms to exist some relation between
* The sole notice which we p. 865), “les cotyledons du M
have met with on the scnsitive- _pudica tendent 4 se raprochcr par
ne.s of cotyledons, relates to Mi- Jeurs faces supéricures lorsqu’on
mosa; for Aug. P. De Candolle _ les irrite.”
says (‘Phys. Vég.,’ 1832, tom. ii.
128 SENSITIVENESS OF COTYLEDONS. Cxar IL
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 con-
nected ; but this is not necessarily the case, for the
cotyledons of Oxalis sensitiva did not rise when kept
on one occasion for 14 h., and on a second occasion
for nearly 4h., in a dark closet. Some other coty-
ledons, as those of Githago segetum, are much affectea
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 de-
scribed 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 de-
pendent position. But the relation between the sen-
sitiveness 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.
Quay, IIL. SENSITIVENESS OF RADICLES. 129
CHAPTER IIL.
SENSITIVENESS OF THE APEX OF THE RApDICLE TO CONTACT AXD 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—Tro-
pxolum— Gossypium—Cucurbita— Raphanus—Aisculus, 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
yadicles 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 point-
ing 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
130 SENSITIVENESS OF RADICLES. Cuar. IL
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 flat-
tened transversely: after an interval of 2 h. 30 m.
the flattening became oblique; and after an addi-
tional 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 direc-
tion 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 de-
scended 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
‘8 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. Never-
theless, 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
Cuar. IIL. SENSITIVENESS OF RADICLES. 131
their curvature; and Sachs has shown* 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 rectan-
gular form; but this view leaves wholly unexplained
the curvature of the upper part, extending for a length
of 8-10 mm.
We were therefore led to suspect that the apex
was sensitive to contact, and that an effect was trans-
mitted 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 experi-
inents which were tried, as the result proved remark-
able. The fact of the apex of a radicle being sensitive
to contact has never been observed, though, as we shall
* © Arbeiten Bot. Inst. Wiirzburg,’ Heft iii. 1873, p. 398.
132 SENSITIVENESS OF THE APEX Cuap. IIL
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 direc-
tion, such as the stamens of Berberis, the lobes of
Dionea, &c.; and many organs, such as tendrils, whe-
ther 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 gyth of an inch (i.e. about 14 mm.),
or oblong bits of nearly the same size, were found to
Cuap. III. OF THE RADICLE OF THE BEAN. 133
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 cir-
cumstances, 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
134 SENSITIVENESS OF THE APEX — Cuap. III,
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 perpendi-
cularly downwards, often bend somewhat, even as much
Fig. 65.
A. B. Cc.
~
Vicia faba: A, radicle beginning to bend from the attached little square
of card; B, bent ata rectangle; C, bent into a circle or loop, with the
tip beginning to bend downwards through the action of geotropism.
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
Cuar. II. OF THE RADICLE OF THE BEAN. 135
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, &c., 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 down-
ward 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 ger-
minating 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.
In the first 12 trials, little squares or oblongs of sanded card,
1:8 mm. in length, and 15 or only 0°9 mm. in breadth (ie. ‘071
ot 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 be-
hind: after 9 h. deflected in the plane in which the bean ig
flattened, 50° from the perpendicular and from the card, and in
opposition to Sachs’ curvature: no change next morning, 23h.
from the time of attachment.
(2.) Radicle 55 mm. in length, card fixed behind: after 9h.
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.
10
136 SENSITIVENESS OF THE APEX Caap. IiL
(3.) Radicle 11 mm. in length, card fixed behind: after 9h.
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 23h. the extreme tip was slightly bent to-
wards the card; the general curvature of the radicle remaining
the same.
(4.) Radicle 9 mm. long, card fixed behind and a little
laterally: after 9h. 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 ¥3 h. no
change.
(5.) Radicle 8 mm. long, card affixed almost laterally: after
9h. 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 perpen-
dicular: after 23 h. no change.
(6.) Radicle 9 mm, long, card affixed in front: after 9h. de-
flected 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
spontancously, as far as we have seen, as much as 40° in the
course of 9h. After 23h. no change.
(7.) Radicle 7 mm. long, card affixed to the back: after 9h.
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 22h. 30 m. this part of the radicle
had become straight.
(8.) Radicle 12 mm. long, card affixed almost laterally: after
9h. 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 22h. 30m. the extreme tip had become
slightly curved towards the card.
(9.) Card fixed laterally: after 11h. 30m. no effect, the
radicle being still almost vertical.
(10.) Card fixed almost laterally: after 11h. 30m. deflected
90° from the vertical and from the card, in a plane inter-
mediate between that of the bean itself and one at right
Cuar. III. OF THE RADICLE OF THE BEAN. 137
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 11h. 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 11h. no
effect, but after 24h. 40m. 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.
(18.) A radicle of considerable length had a small square of
card fixed with shellac to its apex laterally: after only 7h. 15m.
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 9h. 15 m. deflected through 90° from the
perpendicular and from the card. After 24h. 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 8h. no effect;
after 23h. 3m. from time of affixing, radicle much curved from
the square.
(19.) Square of card affixed with shellac: after 24h. no effect,
but the radicle had not grown well and seemed sickly.
(20.) Square of card affixed with shellac: after 24h. no effect.
(21, 22.) Squares of card affixed with shellac: after 24h.
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
‘138 SENSITIVENESS OF THE APEX Cuap. TL
9h. very slightly curved from the card; after 24h. tip curved
towards card. Refixed new square laterally, atter 9h. distinctly
curved from the card, and after 24 h. curved at right angles frcm
the perpendicular and from the card.
(24.) A rather large oblong piece of card fixed with shellac to
apex: after 24h. 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 9h. deflection from the perpendicular considerable; after
24h. deflection reduced. Refixed a fresh square with shellac:
after 24h. 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 9h. the deflection from the perpendicular
and from the card amounted to nearly a right angle; after 24h.
deflection much reduced ; after an additional 24 h. radicle almost
straight.
(27.) Square of card fixed with shellac to apex of young
radicle: after 9h. deflection from the card and from the perpen-
dicular a right angle; next morning quite straight. Refixed
a square laterally with shellac; after 9h. a little deflection,
which after 24h. 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 14h. 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 9h. the radicle was deflected nearly 45° from the perpen-
dicular and from the card. After 36 additional hours angle of
deflection reduced to about 30°.
(30.) A very small piece, less than 5th of an inch square, of
thin tin-foil fixed with shellac to the apex of a young radicle;
after 24h. no effect. Tin-foil removed, and a small square of
sanded card fixed with shellac; after 9h. deflection at nearly
right angles from the perpendicular and from the card. Next
Cuar. III. OF THE RADICLE OF THE BEAN. 1389
morning deflection reduced to about 40° from the perpen-
dicular.
(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 9h. radicle greatly deflected from the card.
After two additional days the deflection had decreased and was
only 35° from the perpendicular.
(32.) Smal] 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 15h. deflected at
nearly 90° from the perpendicular and from the card.
(34.) Small oblong of sanded card gummed to apex: after
15h. 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 24h. from’ time of attachment greatly deflected
obliquely and partly in opposition to Sachs’ curvature.
(36.) Small piece of card, rather less than 35th 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 deflec-
tion, which after 24 h. from time of fixing increased to nearly
90°. After an additional day terminal portion was curled into
a Joop, 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 cciled into a ring.
140 SENSITIVENESS OF THE APEX Cuapr. IIT.
(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 consider-
ably 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.
(48.) 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 attach-
ment 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 squarer
Cuar. III. OF THE RADICLE OF THE BEAN. 141
of common card were affixed with thick gum-water to
the tips of the radicles of seven beans, as a pre-
liminary 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. 10m. 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 sensitive-
ness, 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 toa
temperature of between 69° and 72° F.; some, how-
ever, were placed in the hot-house where the tempera-
ture 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. There-
fore 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 mis-
take in the first six experiments. But before finally
relinquishing the subject, we resolved to make one
142 SENSITIVENESS OF TRE APEX Cuapr. IIT.
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
50° and 60° F. The result was that in every one of
these cases (included in the above-described experi-
ments) the radicle was deflected in the course of a few
hours from the attached object. All the above re-
corded successful trials, and some others presently to
be given, were made in a sitting-room at the tempera-
tures just specified. It therefore appears that a tem-
perature 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
Cuar. III OF THE RADICLE OF THE BEAN. 143
sume 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 pro-
perly 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 atten-
tion that when the attached objects failed to act, there
was no bending of any kind, excepting Sachs’ curva-
ture. The force of our evidence would have been
greatly weakened if occasionally, though rarely, the
radicles had become curved in any direction inde-
pendently of the attached objects. In the foregoing
numbered paragraphs, however, it may be observed
that the extreme tip sometimes becomes, after a con-
siderable interval of time, abruptly curved towards the
bit of card; but this is a totally distinct phenomenon,
as will presently be explained.
Summary of the Results of the foregoing Experiments
on the Radicles of Vicia faba.—Altogether little squares
(about 4th 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 frag-
144 SENSITIVENESS OF THE APEX Cuar. IIL,
ments of very thin glass, &c., 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, &c., 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 conse-
quently 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 tempe-
rature, 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 11h. 30m. 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. Itis 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. 10m. from the time
Cnar. III. OF THE RADICLE OF THE BEAN. 145
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, &c., 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 espe-
cially 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 in48 h. Weat first attributed the straighten-
ing 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* 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
eases. 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,
* ‘Arbeiten Bot. Instit., Wiirzburg,’ Heft iii. p. 456.
146 SENSITIVENESS OF THE APEX Cuap., UL
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 8mm. This occurred chiefly when the first
enrvature 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.
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
Onar. I. OF THE RADICLE OF THE BEAN. 147
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
yooth of a grain; so that a weight of rather less
than 54th of a grain (0°32 mgs.) 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 sth of an inch. These after being
touched with thick gum-water, were placed on the tip
of eleven radicles. Three of them were affected; one
being defiected in 8 h. 15 m. to an angle of about 90°
from the perpendicular; a second to the same amount
when looked at after 9h.; but after 24h. 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
148 SENSITIVENESS OF THE APEX Cuap. ITI.
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 syth 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 ;
Cuar. TI. OF THE RADICLE OF THE BEAN. 149
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 discri-
minating between thin card and very thin paper, and
is deflected from the side pressed by the more re-
sisting 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 pro-
duced. 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 curva.
150 SENSITIVENESS OF THE APEX Cuap. 1h
ture 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 im the jars,
and tiey were exposed to a temperature 14°-16° C.
(57°-61? F.). The observations were made ft dif-
ferent t,nes. Three were examined 12 h. after’ being
sliced, and were all slightlr; enzsadi trom the cut
surface; and the curvature ,{ncreased considerzoly after
an additional 12h. Eight were examined afer 19 h.:
four after 22 h. 30 m.; ancl 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 i. 830 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 injurcd
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
Cuar. III. OF THE RADICLE OF THE BEAN. 151
to bend over towards the injured side.* Buti the
following experiments we endeavoured, generally with
success, to irritate the tips on one side, without ladly
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 24 h. 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 addi-
tional interval of 27 h. (ie. in 48 h. after the appli-
cation 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 cf
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.
The power of an Irritant on the apex of the Radicle
* Ciesielski found this tobe the pended over water, with a thick
case (‘ Untersuchungen iiber die layer of grease, which is very
Abwartskriimmung der Wurzcl,’ injurious or even fatal to grow-
1871, p. 28) after burving with ing parts; for after 48 lours
heated platinum one side of a __ five of these radicles were curved
radicle. So did wo when we towards the greased side, twa
painted longitudinally half of the remaining straight.
whole length of 7 radicles, sus-
11
152 SENSITIVENESS OF THE APEX Cuap. IIL.
of the Bean, compared with that of Gieotropism—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 irri-
tation from the attached object. Radicles were there-
fore 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 simul-
taneously 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 5h.! 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, 13 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
Cnar. 1. OF THE RADICLE OF THE BEAN. 1538
with their flat surfaces parallel to the cork-lid, so that
Sachs’ curvature would not tend to make the hori-
zoutally 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, geo-
tropism 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 horizon-
tally. 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 sti-
mulus. 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 geo-
tropism 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 dependert radicle, and the apex begins to
154 SENSITIVENESS OF THE RADICLE. Cuar. IIL
curve upwards, this movement will be opposed by geo-
tropism 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 geo-
tropism 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* 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 verti-
cally 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
* *Arbciten Pot. Inst. Wiirzburg,’ Heft iv. 1874, p. 605-617.
Czar, III. SENSITIVENESS OF THE RADICLE. 155
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 curva-
ture 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 touch-
ing object. It is possible that some secondary radicles
are more sensitive than others ; for Sachs has proved *
the interesting fact that each individual secondary
tadicle possesses its own peculiar constitution.
Sensitiveness to contact of the Primary Radicle, a little
above the apex, in the Bean (Vicia faba) and Pea (Pisum
sativwm).—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 { 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. Haber-
landt remarks,} 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 =;th
* « Arbeiten Bot. Instit., Wiirz- t ‘Die Schutzeinrichtungen der
burg,’ Heft. iv. 1874, p. 620. Keimpflanze,’ 1877, p. 25.
¢ Ibid. Heft iii. 1873, p. 437.
156 SENSITIVENESS OF THE Guar. [IL
inch square, or rather less) were attached in the same
manner to one side of the radicle at a distance of 3 or
4mm. above the apex. In our first trial on 15 radicles
no effect was produced. Ina second trial on the same
number, three became abruptly curved (but only one
strongly) towards the card within 24h, 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.
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 4mm. from the apex was momen-
tarily touched with dry caustic, it was only faintly
discoloured, and no permanent injury was caused. This
was shown by several radicles thus treated straighten-
ing 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.* We experimented on a variety (York-
* Sacha, ‘ Arbeiten Bot, Institut., Wirzburg,’ Heft iii. p. 438.
Cuar. III. UPPER PART OF THE RADICLE. 157
shire 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.
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
158 SENSITIVENESS OF THE APEX Cuar. II
analogous cases will be immediately described. The
fact is here mentioned because it was a striking spec-
tacle, 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 or
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 sym-
metrical curvature; so that here some influence is
transmitted from the apex for this distance along the
radicle.
Pisum sativum (var. Yorkshire Hero) : Sensttiveness 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 8h. 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.
Jn one the terminal portion of the radicle was bent at
right angles (A, Fig. 66) after 24 h.; 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
Cuap. III. OF THE RADICLE OF THE PEA. 159
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
Fig. 66.
ae
As B.
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.
interval of 5h. 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 tempera-
ture 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 unaccount-
ably small; but all the radicles which were at all bent,
were bent away from the cards.
We now tried the effects of widely different tempera-
tures on the sensitiveness of these radicles with squares
160 SENSITIVENESS OF THE APEX Cuap. ITI,
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,
bunt 10 out of the 18 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 24h., 4 were conspicuously curved from the
cards, 2 slightly, and 7 not at all; so that this tem-
perature 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 pro-
jected almost horizontally. The two remaining ra-
dicles were not affected.
With radicles of the bean, when eatended 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 18 radicles of the pea; the squares being
attached with shellac, and the temperature between
58°~60° F. The result was somewhat different; for.
Ouar. IIL OF THE RADICLE OF THE PEA. 161
these radicles are either less strongly acted on by
geotropism, or, what is more probable, are more sen-
sitive 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 23h. three of them pointed vertically down-
wards, and the fourth at an angle of 45° beneath the
horizon. These four radicles therefore did not seem
Fig. 67.
A. B.
Pisum satioum: 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.
to have been at all affected by the attached squares,
Four others were not acted on by geotropism within
the first 6 or 8h., 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
162 SENSITIVENESS OF THE APEX Onap. LL.
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 30h.
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.
Similar experiments were not always quite so suc-
cessful as in the above cases. Thus 6 radicles, horizon-
tally 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 com-
parison or controls, 3 became slightly and 3 almost
rectangularly geotropic within the 7h. 30m.; 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 (ig. 67).
An analogous trial was now made, but instead of
attaching squares of card to the lower sides of the
Cuar. TI. OF THE RADICLE OF PHASEOLUS. 163
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 cau-
terised, 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. 45 m. 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. LBesides 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 remain-
ing 14 were not affected. Considering the unfavour-
able 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
Gt SENSITIVENESS OF THE APEX Cuap. WL
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 con-
siderable 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 24h. 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 -!;th 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 12
radicles became curved from the blackened side, the
CHar. UI. OF THE RADICLE OF PHASEOLUS. 165
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 vaustic, and
after 15 h. 30 m. was found curved from the perpen-
dicular 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
166 SENSITIVENESS OF THE APEX = Cnar. ITY
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 differ-
ence 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 analo-
gous cases with Drosera, for a strong solution of car-
bonate 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 induces such
bending. Similar results were observed with Dionxa
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 beiug
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 witb
Cuar.11 OF THE RADICLE OF TROPAOLUM. 167
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 23h. 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.
Tropxolum 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
15h. or 16h. to about 90°. In one instance a loor
12
168 SENSITIVENESS OF THE APEX = Cusp. IIL
was nearly completed in 16h. There can, therefore,
be no doubt that the apex is hig] ly 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 sus-
pended in damp air. Of 388 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 tempera-
ture 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 tem-
perature 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
Cusp. II. OF THE RADICLE OF CUCURBITA. 169
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 ex-
hibited 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 of amm. 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 Ra-
dicle—The tips proved ill-fitted for the attachment of
cards, as they are extremely fine and flexible. More-
over, 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
170 SENSITIVENESS OF THE APEX Cuap. IL
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 4} mm. in length, or
even less. In 4 h. 3J 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 alens. Of 10 control specimens tried in the same
jars at the same time, not one was in the least curved.
In 8h. 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 in-
creased immensely in length ; in 5 of them the curva-
ture was nearly the same, in 2 it had increased, and
in 8 it had decreased. The contrast presented by the
10 controls, after both the 8 h. 40 m. and the 24h.
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 conditiona
Cusp. I. OF THE RADICLE OF RAPHANUS. 171
they grow better and more naturally than in damp
air; and their tips were slightly cauterised on the
lower side, brown marks about } mm. in length
being thus caused. Uncauterised specimens similarly
placed became much bent downwards through geo-
tropism in the course of 5 or 6 hours. After 8 h.
only 3 of the cauterised ones were bowed downwards,
and this ina slight degree; 4 remained horizontal ;
and 3 were curved upwards in opposition to geo-
tropism 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 irre-
gularly, 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
scemed 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°
172 SENSITLVENESS OF THE APEX = Cuar. III
and a third very slightly from the perpendicular and
from the cauterised side.
Aisculus hippocastanum : Sensitiveness of the apex of
the Radiele—-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 sc
uniformly and symmetrically curved, that its appear-
ance 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.
AG'40'a.m.27t*
Coty'edon umbilicus: circumnutation of stolon, traced from 11.15 a.m
Aug. 25th to 11 a.m. 27th. Plant illuminated from above. Th
terminal internode was +25 inch in length, the penultimate 2°25, ana
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.
the terminal portion soon began to bend downwards and con-
tinued 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
Cnar. 1V. CIRCUMNUTATION OF STOLONS. 221
of the penultimate internode; and its chief seat was at the
distance of 14 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 10.85 p.m. On the fullowing day (26th) it was ob-
Fig. 90,
ou! ames
1°30!
855 >
2 85am
6°40'a.m.20®
520’, re
1'a.me~ 6°40'um.27
Cotyledon umbilicus: circumnutation and downward movement of another
etolon, 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.
served 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 4m. on the 25th. Nor did it
sink down during the 28th, but continued to circumnutate about
the same place.
Another stolon, which resembled the last in almost every
222 CIRCUMNUTATION OF STOLONS. Cuar. IY,
respect, was observed during the same two days, but only twa
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 con-
tinued to fall; in the evening and during the night it travelled
from some unknown cause in an oblique direction.
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
uided 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.
Cuai IV. CIRCUMNUTATION OF FLOWER-STEMS. 223
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 biiefly 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 cir-
cumnutate whilst growing.
Oxalis carnosa.— The peduncle which springs fromm the thick
and woody stem of this plant bears three or four sab-peduncles.
Fig. 91.
Oxalis carnosa : flower-stem, feebly illuminated from above. its cireumnuta
tion 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,
A filament with little triangles of paper was fixed within the
calyx of a flower which stood upright. Its movements were
observed for 48h.; 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
224 CIRCUMNUTATION OF FLOWER-STEMS Cuar. IV
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.
Tho peduncles of Oxalis acelosellu likewise bend downwards, and
afterwards, when the pods are nearly mature, upwards; and this
is effected by a circumnutating movement.
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 U. sensitiva undeigoes 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 coutinuous, but that the peduncle oscillated up and
down. We may therefore conclude that it cireumnutated. 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 noother genus,as far as we know, is the peduncle
furnished witha pulvinus. The peduncle of U. Ortegesit behaved
differently from that of VU. sensitiva, for it stood at a less angle
above the horizon in the middle of the day, than 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 bh. 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, aud after 10.30P.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
bave 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
Cuar. IV. CIRCUMNUTATION OF FLOWER-STEMS. 225
Trifolium repens cireumnutate in a complicated course during
several days. I may add that the gynophore of Arachis hypogea,
Fig. 92.
110'.20pm.24F
Y
t
Trifolium subterrancum: main flower-peduncle, illuminated from above,
circumnutation traced on horizontal glass, from 8.40 a.m. July 23rd
to 10.30 p.m. 24th.
which looks exactly like a peduncle, circeumnutates whilst growing
vertically downwards, in order to bury the young pod in the
ground.
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,
1} inch' in length, was carefully observed during a whole day,
and it made 43 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.* According to Sachs f¢ the flower-stems, whilst growing,
* ‘The Movements and Habits 1875 p. 68.
of Climbing Plants,’ 2nd edit., ¢ ‘ Text-Book of Botany,’ 1875,
226 CIRCUMNUTATION OF LEAVES. Caap. IV.
of many plants, for instance, those of Brassica napus, revolve or
circumnutate; those of Allium porrwm bend from side to side,
and, if this movement had been traced on a horizontal glass,
no doubt ellipses would have been formed. Fritz Miiller has
described * the spontaneous revolving movements of the flower-
stems of an Alisma, which he compares with those of a climbing
plant.
We made no observations on the movements of the different
parts of flowers. Morren, however, has observed ¢ in the
stamens of Sparmannia and Cereus a “ fren-issement spontané,”
which, it may be suspected, is a circumnutating movement.
The circumnutation of the gynostemium of Stylidium, as de-
scribed by Gad,t is highly remarkable, and apparently aids in
the fertilisation of the flowers. The gynostemium, whilst spon-
taneously 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.
We have now seen that the flower-stems of plants
belonging to such widely different families as the
Crucifere, Oxalide, Leguminose, Primulacesw, Scro-
phularinee, Alismacee, and Liliacez, 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, &c., have ob-
p. 766. Linneus and Treviranus
(according to Pfeffer, ‘Die Pe-
riodischen Bewegungen,’ &c., p.
162) state that the flower-stalks
of many plants ovcupy different
positions by night and day, and
we shall s e in the chapter on
the Sle-p of Plants that th’s im-
plies cireumnutation.
* ‘Jenaische Zeitsch.,” B. v.
p. 133.
+ “N. Mem. de l’Acad R. de
Bruxelles,’ tom. xiv. 1841, p. 3.
t ‘Sitzungbericht des bot. Ve-
reins der P. Brandenburg,’ xxi
p. 84.
Cu..v IV. DICOTYLEDUNS. 227
served, 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 1t night. From considerations hereafter to be
given, plants of this nature are here excluded, and
will be treated of separately. As we wished to ascer-
tain whether all young and growing leaves cireumnu-
tated, we thought that it would be sufficient if we
observed between 30 and 40 genera, widely distributed
throughout the vegetable series, selecting some un-
usual 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 ob-
served 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 Fig. 93.
vertical glass (when not stated (es,
to the contrary) in the manner x
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 ar-
rangement of the species, with Surracenia purpurea: cireum-
the number of the Family ap- nutation of young pitcher,
a traced from 8 A.M. July 3rd
pended, is the same as in the to 10.15a.m. 4th. Temp.
case of stems. 17°-18° C, Apex of pitcher
20 inches from glass, so
movement greatly mag-
(1.) Sarracenia purpurea (Sarra- nified. iia .
cenes, Fam. 11).—A young leaf, or
pitcher, 83 inches in height, with the bladder swollen, but with
the hood not as yet open, had a filament fixed transversely
228 CIRCUMNUTATION OF LEAVES. Cuap.: IV.
across its apex ; it was observed for 48 h., and during the whole
of this time it cireumnutated in a nearly similar manner, but
to a very small extent.
The tracing given (Fig. 93) relates
only to the movements during the first 26 h.
Fig. 94+
Glaucten luteum: circumnuta-
tion 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 53 inches
from the glass.
(2.) Glauctum luteum (Papave-
races, Fam. 12).—A youns; plant,
bearing only 8 leaves, hal a fila-
ment attached to the youngest leaf
but one, which was 3 inches in
length, including the petiole. The
circumnutating movement was
traced during 47h. On both days
the leaf descended from before 7 a.m.
until about 11 am., 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.
(8.) Crambe maritima (Crucifere,
Fam. 14).—A leaf 93 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
sosmall in extent. The apex, how-
ever, certainly changed its course at
least 6 times in the course of 14h.
A more vigorous young plant, bear-
ing 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
65 inches in length. The leaf stood up almost vertically, but the tip
Cuap. IY. DICOTYLEDONS. 229
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 con- .
woe : ee Fig. 95.
tinually circumnutating ; ; =
but the proper periodicity 640%m.264 m
of its movements was dis- \
turbed by its being only Sams SX
dimly illuminated from eer:
above through a dduble { “y 10220'p.m.2af
skylight. We infer that \
this was the case, because H
two leaves on plants grow- '
ing out of doors, had their H
angles above the horizon y
measured in the middle \
of the day and at 9 to i
about 10 p.m. on succes-
sive 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 y
they fell to their former i
position. Now it may be 6°50 a.m 244
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 Crombe maritima: circumnutation of leaf,
preceding night; and this disturbed by being insufficiently illumi-
may bo attributed to the ttl from sore, toad trom 750 4
leaf adjusting itself tothe — 154 inches from the vertical glass, so that
dim light, coming exclu- the tracing was much magnified, but is
sively from above. here reduced to one-fourth of original scale.
(4.) Brassica oleracea (Cruciferee).—Hofmeister and Batalin *
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
\
7250'a.m.23°2 \
\
\
* ¢ Flora,’ 1873, p. 437
230 CIRCUMNUTATION OF LEAVES. Cuar. IV
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
Jeaf fell during the whole morning, and rose in the evening and
during the early part of the night. The ascending and descend-
ing lines did not coincide, so that an irregular ellipse was formed
each 24h. 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.
In order to ascertain the effect of darkness, a filament was
fixed to a leaf 54 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 aninch. 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 pm., 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,* 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 con-
siderably at night.
(3.) Dianthus caryophyllus (Caryophyllee, Fam. 26).— The
* ‘Trans. Bot. Soc. Edinburgh,’ see Darwin, ‘ Animals and Plants
vol. xiii. p. 32, With respect to under Domestication,’ 2nd edit
the origin of the Swedish turnip, vol. i. p. 344.
Caar. IV. DICOTYLEDONS. 231
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 am. on the following
morning it stood only a little above the horizon. In Fig. 96
Fig. 96
ie mah
H
i
H
/
i
i]
6°50! a.m 16%
0°30 p.m 15%
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% inches from the vertical glass, so tracing not
greatly magnified. The leaf was 53 incheslong. Temp. 153°-17}° C.
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,
tcgether with some loops, pursued during the next 2} days.
As th: leaf continued to move all the time to the left, it is
evident that the zigzag line represents many circumnutations.
(6.) Camellia Japonica (Camelliacese, Fam. 82).—A youngish
leaf, which together with its petiole was 23 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
16
232 CIRCUMNUTATION OF LEAVES. Cuar. IV
petiole very short,
Fig. 97.
\\
Camellia Japonica: cir-
cumnuutation of leaf,
traced from 6.40
A.M. June 14th to
6.50 am. 15th.
Apex of leaf 12
inches from the ver-
tical glass, so figure
considerably mag-
nified. Temp. 16°
163° C,
much movement could not be expected
Nevertheless, the apex changed its course
completely seven times in the course of
113 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 cireumnutated 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.
In the chapter on the Sleep of Plants
we shall see that the leaves in several Malvaceous genera sink
6°50'a.m.t6th Be
6°.30'p.m.164
Fig. 98.
9°. 30’ a.m.t4th
10°. 25’pmish
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
93 inches from the vertical glass, so figure moderately magnified.
Temp. 15°-16}° C.
at night; and as they often do not then occupy a vertical
position, especially if they have not been well illuminated during
Cuap. IV. DICOTYLEDONS. 233
the day, it is doubtful whether some of these cases onght not
to have been included in the present chapter.
(7.) Pelargonium zonale (Geraniaceew, Fam. 47).— A young
leaf, 1; 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 discolur (Ampelidex, Fam. 67).—A leaf, not nearly
full-grown, the third from the apex of Fig. 99.
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 con-
spicuous.
(9.) Vicia faba (Leguminose, 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 ter-
minal leaflets, and its movements were
traced during 513 h. The filament fell ae"
all morning (July 2nd) till 3 p.m., and Cissus discolor « cire
; coler : circumnu-
then rose greatly till 10.35 p.m.; but tation of leaf, traced
the rise this day was so great, com- from 10.35 am. May
pared with that which subsequently ee pe
a ¢ pex of leaf 82 inches
occurred, that it was probably due in from the vertical glass,
part to the plant being illuminated 7
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 8rd) the leaf again fell in the morning, then circumnu-
tated 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.
234 CIRCUMNUTATION OF LEAVES. Cnap. IV
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°
Fig. 100.
648’ a.n.3 72,
6° 45'a.m.
410° 15'a.m 4%
72 15'p.m. 2d
Vécia fabs; circumnoutation of leaf, traced from 7.15 p.m. July 2nd te
10.15 a.m. 4th. Apex of the two terminal leaflets 73 inches from the
vertical glass. Figure here reduced to two-thirds of original scale.
Temp. 17°-18° C.
between 12.20 p.m. and 10.45 p.m., and to have fallen 23° 30
between the latter hour and 10.20 a.m. on the following morning.
The main petiole was now secured to a stick close to the base
Cuar. IV. DICOTYLEDONS. 235
of the two terminal leaflets, which were 1°4 inch in length; and
the movements of one of them were traced during 48h. (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.n.
on the second day represents 5 very small ellipses, with their
Fig. 101.
10°30 ame
£0°40'a.m. 4!
Vicia faba: circumnutation of one of the two terminal leaflets, the maia
petiole having been secured, traced from 10.40 a.m. July 4th to 10.30 a.m
6th. Apex of leaflet 63 inches from the vertical glass, Tracing here
reduced to one-half of original scale. Temp, 16°-18° C.
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.
236
CIRCUMNUTATION OF LMAVES.
Cuar. IV
(10.) Acacia retinoides (Leguminose).—The movement of a
young phyllode, 23 inches in length, and inclined at a consider-
able angle above the horizon, was traced
during 45 h. 30 m.; but in the figure here
given (Fig.102), its cireumnutation is shown
during only 21h. 30m. During part of
this time (viz., 14 h. 30m.) the phyllode
Fig 102,
described a figure re-
Cm presenting 5 or 6
small ellipses. The
actual amount of
movement in a ver-
tical direction was °3
inch. The phyllode
rose considerably be-
tween 1.30 p.m. and
4pm., but there was
no evidence on either
day of a regular pe-
riodic movement.
(11.) Lupinus spe-
ciosus (Leguminose).
—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 123 h. the leaf moved eight times
up and seven times down; so that it
described 7} ellipses in this time, and
this is an extraordinary rate of movement.
The summit of the petiole was then secured
Acacia retino‘des : cir-
cumnutation of a
young _ phyllode,
traced from 10.45
aM. July 18th to
8.15 am. 19th.
Apex of phyllode 9
inches from the
vertical glass; temp.
165°-172° C.
Fig. 103,
Lupinus speciosus: cir-
cumnatation of leaf
traced on vertical
glass, from 10.15 a.M.
to 5.45 P.M.3 ie.,
during 6 h. 30 m.
to a stick, and the separate leaflets were found to be continually
zircumnutating.
Cnap. IV. DICOTYLEDONS. 237
(12.) Echeveria stolonifera (Crassulacee, Fam. 84).—The older
leaves of this plant are so thick and fleshy, and the young onea
so short and broad, that it seemed
very improbable that any circum-
nutation could be detected. A fila-
ment 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 8 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 ai
occasionally there was distinct cir- /
cumnutation, though on a very smal] Lcheveria stolonifera: circum
scale nutation of leaf, traced
> from 8.20 a.m. June 25th
(13.) Bryophyllum (vel Calunchee) to 8.45 a.m. 28th. Apex
calycinum (Crassulacese).— Duval- of leaf 124 inches from the
Jouve (‘Bull. Soc. Bot. de France, 8/85, 0 ise bs aa
Feb. 14th, 1868) measured the dis- 930 94)9G
tance between the tips of the upper
pair of !eaves 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 :—
Fig. 104.
8 aM. 2 P.M. 7 PM.
Nov. 16 . - 15mm . . . 25mm... (?)
gp 1D we ow we 4B 55 . . . 60, » » » 48mm.
Dec. 2 22) yy et AB we, 58 BB
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 (Droseracex, Fam. 85).—The move-
ments of a young leaf, having a long petiole but with its tentacles
(or gland-bearing hairs) as yet unfolded, were traced during
47h.15m. The figure (Fig. 105) shows that it cireumnutated
largely, chiefly in a vertical direction, making two ellipses each
238 Cuar. IV.
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 observ-
ing 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.
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
CIRCUMNUTATION OF LEAVES.
Fig. 105,
At 25p m7)
\,10°40'pm8
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.
little in a slightly zigzag line.
On the following morning, at
7 am., 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 in-
duced 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 3p.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 leat
nap. IV. DICOTYLEDONS. 239
circumnutates on a small scale, at least whilst absorbing car-
bonate 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 re-
moved and with an eye-piece micrometer, of which each
division equalled 53, 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 <4, of an inch in
20 m., or y35 of inch in 1 h. 40 m.; but as it likewise moved
from side to side to an extent of above 54, of inch, the move-
ment 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 yJ55 Of an inch. During the next 72 h. it was looked at
repeatedly, and during this whole time it moved only another
too 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 there-
fore 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 appa-
rently 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.) Dioncea muscipula (Droseraceze).—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
240
CIRCUMNUTATION OF LEAVES.
Cuar, IV
petiole was only 1:2 inch in length, had a filament fixed exter-
nally along the midrib of the still closed lobes, which projected
at right angles to the petiole, In the evening this leaf com-
Fig. 106.
Donea muscipuia: cir-
cumnutation of a
young and expanding
leaf, traced on a hori-
zontal glass in dark-
ness, from noon Sept.
24th to 10 a.m. 25th.
Apex of leaf 133
inches from the glass,
so tracing consider-
ably magnified.
pleted an ellipse in the course of 2h. On
the following day (Sept. 25th) its move-
ments 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 cireumnu-
tated,
A rather old, horizontally extended
leaf, with a filament attached along the
under side of the midrib, was next
observed during 7h. 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
14h. 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 circum-
nutate 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 circumnu-
tation.
Another full-grown leaf had a filament
attached externally along one side of the
midrib and parallel to it, so that tlie fila-
ment would move if the lobes closed. It
_ Should be first stated that, although a touch on one of the sensi-
tive 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 onght to have been observed for a
Onap. IV. DICOTYLEDONS 241
longer period ; although, as we have seen, a young leaf com-
pleted a fairly large ellipse in 2h. A drop of an infusion of
raw meat was then placed or 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. 30m. 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 follow-
ing 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 am. the lobes were completely
shut. The course pursued, as may be seen in the figure, was
Fig. 107.
48pm 10°45’ pm.254
; Spm. Ys vamos?
Cb. 25%
Diona.1 musciwda : 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 8} inches from the
vertical glass. Figure here reduced to two-thirds of original scale.
strongly zigzag, and this indicates that the closing of the lobcs
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
cireumnutate. 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.
It is sometimes stated in botanical works that the lobes close
or sleep at night; but this is an error. To test the statement,
vary 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
242 CIRCUMNUTATION OF LEAVES. Cuap. IV.
seem to be continually opening and shutting to a very small
extent. A neurly 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 54, of an inch. The apex of
the paper-triangle was now seen to be in constant slight move-
ment; for in 4h. it crossed nine divisions, or ;85 of an inch,
and after ten additional hours it moved back and had crossed
x$o in an opposite direction. The plant was kept in rather
too cool a place, and on the following day it moved rather less,
namely, 535 in 3 h., and ;2, 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. ;3, 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 Dionwa 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 (;4, 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
Cuap. IV. DICOTYLEDONS. 243
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 +2,5 or rsa, and in
one instance of +5 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 conspi-
cuous 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 ina room. The apex oscillated forwards
and backwards in the same manner as before; but the jerks for-
ward were less in extent, viz. about ~3,5 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 thuscaused. After 10 m., however, vigorous
oscillations commenced, perhaps owing to the plant having been
warmed and thus stimulated. Thecandle was then removed and
before long the oscillations ceased ; nevertheless, when looked at
again after an interval of 1h. 30m., 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 7255 or only 55 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 +25 of
an inch stil] continued. On the following day a little infusion
244 CIRCUMNUTATION OF LEAVES. Cuar IV
of raw meat was placed on the leaf, which caused the lobes tc
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 +5, 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 2} 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 fora
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.) Lucalyptus resinifera (Myrtacer, 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 as-
sumed 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 fre-
Fucaljptus resinifera : circumnu- 3
tation of a leaf, traced, A, from quently; and two tracings were
6.40 aM. tol p.m. June 8th; made (see A and B, Fig. 108), as
oe eee ae poe a single one would have been too
from the horizontal! ies 8 complicated. The apex changed
figures considerably magnified, its course 13 times in the course
of 16h., chiefly up and down, but
with some lateral movement. The actual amount of movement
in any one direction was small.
(17.) Daklia (garden var.) (Composite, Fam. 122).—A fine young
Fig. 108.
Duar, IV. DICOTYLEDONS. 245
leaf 5% inches in length, produced by a young plant 2 feet high,
growing vigorously in a large pot, was directed at an angie ot
about 45° beneath the horizon. On June 18th the leaf descended
from 10 a.m. till 1135 a.m. (see Fig. 109); it then ascended
greatly till 6 p.m., this ascent being probably due to the light
Fig. 109.
P40 amt1I™
10 25° ‘pmis®
120 cre
**8° 10m,
20%
0 ofm.18%
os an.
ft
Dahha: circumnutation of leaf, traced from 10 A M. June 18th to 8.10 a.n,
20th, but with a break of Lh. 40 m. on the morning of the 19th, as,
owing to the glass filament pointing too much to one side, the pot had
to ke 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 43 in a horizontal line.
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
246 CIRCUMNUTATION OF LEAVES. Cuap. IV.
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.
(18.) Mutisia clematis (Composite).—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 * 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.
(19.) Cyclumen Persicwum (Primulacee, 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 after-
wards, 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.
* «Tho Movements and Habits of Climbing Plants,’ 1875, p. 118
Onapr. IV. DICOTYLEDONS. 247
Q0.) Allamanda Schottii (Aprcynex, Fam. 144).—The young
leaves of this shrub are elongated, with the blade bowed so much
Fig. 110.
9 6 45 amo
ao sdamss
6°40’ a.m, 54
\
\
Tpms
C5 pm 4h
Cyclamen Persicum : circumnutation of leaf, traced from 6.45 A.M. June 2n¢
to 6.40 a.m. 5th, Apex of leaf 7 inches from the vertical glass.
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. 43 inches in length, stood at 2.50 p.m op
17
248
CIRCUMNUTATION OF LEAVES.
Cuar. IV
Dee, 5th at an angle of 13° beneath the horizon, but by 9.30 p.m.
Fig. 111.
(
(Petunia violacea: downward move-
ment 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.
wenerally 173° C.
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° be-
neath the horizon, and 9.30 p.m.
34° above it, so had risen 394°.
The chief cause of the rising
movement lies in the straighten-
ing 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 expo-
sure to a strong light is appa-
rently requisite for the periodi-
cal change of curvature in the
blade, and for the slight rising
of the petiole.
(21.) Wigandia (Hydroleacee,
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.
Onap. Iv. DICOTYLEDONS. 249
(22.) Petunia violacea (Solanew, Fam. 157)—A very young
leaf, only 3 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 hori-
zontal. The strongly marked zigzag line in the figure on p. 248
(Fig. 111), shows that this was effected by modified circum-
nutation ; 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 Fig. 112,
more horizontal as it grew older. The
angles which two older leaves formed
together, were measured in the even-
ing and about noon on 3 successive
days, and each night the angle de-
creased a little, though irregularly.
(23.) Acanthus mollis (Acanthacer,
Fam. 168).—The younger of two
leaves, 2' inches in length, petiole
included, produced by a seedling
plant, was observed during 47 h.
Early on each of the three morn-
ings, the apex of the leaf fell; and
it continued to fall till 3 p.m, on /
the two afternoons when observed. re
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 epi-
nastic growth more and more hori-
zontal; 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
Acanthus mollis : circumnuta-
tion 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°-16}° C.
.vose every night; and the rise between noon and 10.15 p.M.,
when measured on one occasion, was 10°.
This rise was chiefly
250 CIRCUMNUTATION OF LEAVES. Cnar. IV.
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 circumuutate periodically, falling in the
morning and rising in the afternoon and night.
(24.) Cannabis sativa (Cannabinee, 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.* 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 8am. May 29th, and at
10.30 p.m. were considerably declined. On a subsequent day two
leaves stood at 2P.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.
(25.) Pinus pinaster (Conifer, 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 cireumnu-
tating. Thesame little plant, when grown to & height of 5 itches,
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 am. Aug. Ist On
August Ist it cireumnutated about the same small spac, 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
* We were led to observe this Ficra, 1879, p. 66. We regret that
plant by Dr. Carl Kraus’ paper, we cannot fully understand parts
‘ Beitrigze zur Kentnissder Bewe- _ of this paper.
gungen Wacksender Laubblitter,’ i
Cua. IV. DICOTYLEDONS. 251
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
UW’45' a.m, 318*
Fig. 113.
A. B.
6°40 cm.
6°40'amse (ono
Pinus pinaster: circumnutation of young leaf, traced from 11.45 a.m,
July 31st to 8.20 am. Aug. 4th. At 7 A.M. Aug. 2nd the pot waa
moved an inch to one side, so that the tracing consists of two figures.
Apex of leaf 143 inches from the vertical glass, so movements much
magnified,
growth, and at the close of our observations the leaf was not
nearly so horizontal as it would ultimately become.
Pinus austriaca.—Two Icaves, 3 inches in length, but not
202 CIRCUMNUTATION OF LEAVES. Cuap. IV.
quate fully grown, produced by a lateral shoot, on a young tree
3 feet in height, were observed during 29h. (July 31st), in the
same manner as the leaves of the previous species. Both these
Fig. 114.
——
Oycas pectinata: circum-
nutation of one of the
terminal leaflets, traced
from 8.30 a.M. June
22nd to 8 aM. June
24th. Apex of leaflet
7% inches from the ver-
tical glass, so tracing
not greatly magnified,
and here reduced to
one-third of original
scale; temp. 19°-21°C,
leaves certainly circumnutated, making
within the above period two, or twe and
a half, small, irregular ellipses.
(26.) Cycas pectinatu (Cycadese, Fam
224).— A young leaf, 114 inches in
length, of which the leaflets had only
recently become uncurled, was observed
during 47h. 30m. The main petiole
was secured to a stick at the base of the
two terminal leaflets. To one of the
latter, 33 inches in length, a filament
was fixed; the leaflet was much bowed
downward, but as the terminai 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 640 am. 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.
CIRCUMNUTATION OF LEAVES:
MonocorTyLepons.
(27.) Canna Warscewiczit (Cannacee,
Fam. 2).—The movements of a young
leaf, 8 inches in length and 38: in
breadth, produced by a vigorous young
plant, were observed during 45 h,
50m., 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 unti)
about 5p.m., and ascended during the rest of the evening and
Cuap. IV. MONOCOTYLEDONS. 253
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.
A. B.
Canna Warscewiczti: cireumnutation of leaf, traced (A) from 11.30 a.m
June 10th to 6.40 a.st, 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 (Iridew, 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
fivetimes. 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.
(29.) Crinum Capense (Amaryllidee,
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
Fig. 116.
Tris pseudo-acorus ; circume
nutation 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 mag-
nified. Temp. 15°-16° C.
only 1:4 broad at the base. Whilst quite young they stand up
almost vertically to the height of about a fvot; afterwards
254 CIRCUMNUTATION OF LEAVES. Cuaar. IV.
their tips begin to bend over, and subsequenily hang vertically
down, and thus continue to grow. A rather young leaf was
selected, of which the dependent tapering point was as yet only
55 inches in length, the upright basal part being 20 inches high,
though this part would ultimately become shorter by being
more bent over. enter by the windows being opened at the same time that
the blinds were pulled up, so that in spite of the sun shining
on the plant the temperature was not raised.
The effect of an increase of temperature in diffused light 1a
* In all the diagrams 1 mm.in ment. In Figs.-133 and 134 the
the horizontaldirection represents temperature is represented (along
oue minute of time. Each mm. tle ordinates) in the scale of 1
in the vertical direction repre- mm. to each 0°1°C. In Fig
sents one degree of angular move- 135 cach mm. equals 02° B,
Cuar. VII. SLEEP OF LEAVES. 333
shown in Fig. 135. The temperature began to rise at 11.35
A.M. (in consequence of the fire being lighted), but by 12.42 a
marked fall had occurred. It may be seen in the diagram that
when the temperatuie was highest there were rapid oscillations
Fig. 134,
=
a
fo)
ro)
cu
Averrhoa bilimbi: aneular movements of leaflet during a change from
bright illumination to shade; temperature (broken line) remaining
nearly the same.
of small amplitude, the mean position of the leaflet being at the
time nearer the vertical. When the temperature began to fall,
the oscillations became slower and larger, and the mean position
of the leaf again approached the horizontal. The rate of oscil-
lation was sometimes quicker than is represented in the above
diagram. Thus, when the temperature was between 31° and
‘oanqeroduiy Jo aduvyo ayy swoys
aUI] Taxorq ayy, ‘ewes oy} Suyuremer 4ySty t amnqeseduray Jo esueyo ve SULINP yayee] yo quoWaAcUL IE[NZUE : squypg DOYL.aAP
Cuap. VIL.
Z
jo)
—
foal
=
=)
Zz
—
lm)
=)
o
=]
_
oO
=)
iS]
a
&
—
=)
fo)
=
Cuar. Vil. SLEEP OF LEAVES. 335
32° C., 14 oscillations of a few degrees occurred in 19m. On
the other hand, an oscillation may be much slower ; thus a leaflet
was observed (temperature 25° C.) to
rise during 40 m. before it fell and
completed its oscillation.
Porlieria hygrometrica (Zygophyllex)
—The leaves of this plant (Chilian
form) are from 1 to 1} inches in length,
and bear as many as 16 or 17 small
leaflets on each side, which do not
stand opposite one another. They are
articulated to the petiole, and the
petiole to the branch by a pulvinus.
We must premise that apparently two
forms are confounded under the same
name: the leaves on a bush from Chili,
which was sent to us from Kew, bore
many leaflets, whilst those on plants
in the Botanic Garden at Wirzburg
bore only 8 or 9 pairs; and the whole
character of the bushes appeared some-
what different. We shall also see that
they differ in a remarkable physio-
logical peculiarity. On the Chilian
plant the petioles of the younger leaves
on upright branches, stood horizontally
during the day, and at night sank
down vertically so as to depend parallel
and close to the branch beneath. The
petioles of rather older leaves did not
become at night vertically depressed,
but only highly inclined. In one
instance we found a branch which had
grown perpendicularly downwards,
and the petioles on it moved in the same
direction relatively to the branch as
just stated, and therefore moved up-
wards. On horizontal branches the
younger petioles likewise move at night
in the same direction as before, that is,
Fig. 136.
Policria hygrometrica : cir:
cumnutation and nycti-
tropic movements of pe-
tiole of leaf, traced from
9.35 am. July 7th to
about midnight on the
8th. Apex of leaf 73
inches from the vertical
glass. Temp. 193°-205°C,
towards the branch, and are consequently then extended hori-
zontally; but it is remarkable that the older petioles on the
336 Cuap. VIL
MODIFIED CIRCUMNUTATION.
same branch, though moving a little in the same direction, also
bend downwards; they thus occupy a somewhat different posi-
tion, relatively to the centre of the earth and to the branch, from
that of the petioles on the upright branches. With respect to
the leaflets, they move at night towards the apex of the petiole
until their midribs stand nearly parallel to it; and they then
lie neatly imbricated one over the other. Thus half of the upper
surface of each leaflet is in close contact with half of the lower
surface of the one next in advance; and all the leaflets, except-
ing the basal ones, have the whole of their upper surfaces and
half of their lower surfaces well protected. ‘Those on the oppo-
site sides of the same petiole do not come into close contact
at night, as occurs with the leaflets of so many Leguminose,
but are separated by an open furrow; nor could they exactly
coincide, as they stand alternately with respect to one another.
The circumnutation of the petiole of a leaf ¢ of an inch in
length, on an upright branch, was observed during 46 h.,
and is shown in the preceding diagram (Fig. 186). On the
first morning, the leaf fell a little and then rose until 1 p.m,
and this was probably due to its being now illuminated through
a skylight from above; it then circumnutated on a very small
scale round the same spot until about 4 p.m., when the great
evening fall commenced. During the latter part of the night or
very early on the next morning the leaf rose again. On the
second day it fell during the morning till 1 p.m., and this no
doubt is its normal habit. From 1 to 4 p.m. it rose in a zigzag
line, and soon afterwards the great evening fall commenced. It
thus completed a double oscillation during the 24h.
The specific name given to this plant by Ruiz and Pavon, indi-
cates that in its native arid home it is affected in some manner
by the dryness or dampness of the atmosphere.* In the Botanic
Garden at Wirzburg, there was a plant in a pot out of doors
which was daily watered, and another in the open ground which
was never watered. After some hot and dry weather there was
a great difference in the state of the leaflets on these two plants;
those on the unwatered plant in the open ground remaining half,
* «Systema Veg. Flore Peru-
vianw et Chilensis,’ tom. i. p. 95,
1798. We cannvt understand the
wccount given by the authors of
the behaviow: of this plant in its
native home There is much
about its power of foretell:ing
changes in the weather; and it
appeurs asif the brightness of the
sky largely determined the open-
ing and closing of the leaticts.
Cuap. VIL. SLEEP OF LEAVES. 337
or even quite, closed during the day. But twigs cut from thie
bush, with their ends standing in water, or wholly immersed in
it, or kept in damp air under a bell-glass, opened their leaves
though exposed to a blazing sun; whilst those on the plant
in the ground remained closed. The leaves on this same plant,
after some heavy rain, remained open for two days; they then
became half closed during two days, and after an additional
day were quite closed. This plant was now copiously watered,
and on the following morning the leaflets were fully ex-
panded. The other plant growing in a pot, after having been
exposed to heavy rain, was placed before a window in the Labo-
ratory, with its leaflets open, and they remained so during the
daytime for 48 h.; but after an additional day were half closed.
The plant was then watered, and the leaflets on the two following
days remained open. On the third day they were again half
closed, but on being again watered remained open during the
two next days. From these several facts we may conclude that
the plant svon feels the want of water; and that as soon as this
occurs, it partially or quite closes its leaflets, which in their
then imbricated eondition expose a small surface to evaporation.
It is therefore probable that this sleep-like movement, which
occurs only when the ground is dry, is an adaptation against
the loss of moisture.
A bush about 4 feet in height, a native of Chili, which was
thickly covered with leaves, behaved very differently, for during
the day it never closed its leaflets. On July 6th the earth ix
the small pot in which it grew appeared extremely dry, and
it was given a very little water. After 21 and 22 days (on
the 27th and 28th), during the whole of which time the plant
did not receive a drop of water, the leaves began to droop, but
they showed no signs of closing during the day. It appeared
almost incredible that any plant, except a fleshy one, could
have kept alive in soil so dry, which resembled the dust on
aread. On the 29th, when the bush was shaken, some leaves
fell off, and the remaining ones were unable to sleep at night.
Jt was therefore moderately watered, as well as syringed, late in
theevening. On the next morning (80th) the bush looked as fresh
as ever, and at night the leaves went to sleep. It may be added
that a small branch while growing on the bush was enclosed,
by means of a curtain of bladder, during 13 days in a large
bottle half full of quicklime, so that the air within must have been
intensely dry ; yet the leaves on this branch did not suffer in the
338 MODIFIED CIRCUMNUTATION. Cnar. VI
least, and did not close at all during the hottest days. Another
trial was made with the same bush on August 2nd and 6th (the soi!
appearing at this latter date extremely dry), for it was exposed
out of doors during the whole day to the wind, but the jleaflets
showed no signs of closing. The Chilian form therefore differs
widely from the one at Wirzburg, in not closing its leaflets
when suffering from the want of water; and it can live for a
surprisingly long time without water.
Tropeolum majus (?) (cultivated var.) (Tropeoles).—Several
plants in pots stood in the greenhouse, and the blades of
the leaves which faced the front-lights were during the day
highly inclined and at night vertical; whilst the leaves on
the back of the pots, though of course illuminated through
the roof, did not become vertical at night. We thought, at first,
that this difference in their positions was in some manner
due to heliotropism, for the leaves are highly heliotropic. The
true explanation, however, is that unless they are well illu-
minated during at least a part of the day they do not sleep at
night; and a little difference in the degree of illumination deter-
mines whether or not they shall become vertical at night. We
have observed no other so well-marked a case as this, of the
influence of previous illumination on nyctitropic movements.
The leaves present also another peculiarity in their habit of
rising or awaking in the morning, being more strongly fixed or
inherited than that of sinking or sleeping at night. The move-
ments are caused by the bending of an upper part of the petiole,
between 4 and 1 inch in length; but the part close to the blade,
for about + of an inch in length, does not bend and always
remains at right angles to the blade. The bending portion does
not present any external or internal difference in structure
from the rest of the petiole. We will now give the experiments
on which the above conclusions are founded.
A large pot with several plants was brought on the morning
of Sept. 3rd out of the greenhouse and placed before a north-east
window, in the same position as before with respect to the light,
as far as that was possible, On the front of the plants, 24 leaves
were marked with thread, some of which had their blades hori-
zontal, but the greater number were inclined at about 45°,
heneath the horizon; at night all these, without exception,
becume vertical. Early on the following morning (4th) they
reassumed their former positions, and at night again became
vertical. On the 5th the shutters were opened at 6.15 a.m.. and
Cuap. VII. SLEEP OF LEAVES. 339
by 8.18 a.m., after the leaves had been illuminated for 2 h. 3 m.,
and had acquired their diurnal position, they were placed in a
dark cupboard. They were looked at twice during the day and
thrice in the evening, the last time at 10 30 p.m., and not one had
become vertical. At 8 a.m. on the following morning (6th) they
still retained the same diurnal position, and were now replaced
before the north-east window. At night all the leaves which
had faced the light had their petioles curved and their blades
vertical; whereas none of the leaves on the back of the plants,
although they had been moderately illuminated by the diffused
light of the room, were vertical. ‘They were now at night placed
in the same dark cupboard; at 9 a.m. on the next morning (7th)
all those which had been asleep had reassumed their diurnal
position. The pot was then placed for 3h. in the sunshine, so
as to stimulate the plants; at noon they were placed before the
same north-east window, and at night the leaves slept in the
usual manner and awoke on the following morning. At noon on
this day (8th) the plants, after having been left before the north-
east window for 5 h. 45 m. and thus illuminated (though not
brightly, as the sky was cloudy during the whole time), were
replaced in the dark cupboard, and at 3 p.m. the position of the
leaves was very little, if at all, altered, so that they are not
quickly affected by darkness; but by 10.15 p.m. all the leaves
which had faced the north-east sky during the 5h. 45m. of
illumination stood vertical, whereas those on the back of the
lant retained their diurnal position. On the following morning
(9th) the leaves awoke as on the two former occasions in the dark,
and they were kept in the dark during the whole day; at night
avery few of them became vertical, and this was the one in-
stance in which we observed any inherited tendency or habit in
this plant to sleep at the proper time. That it was real sleep
was shown by these same leaves reassuming their diurnal posi-
tion on the following morning (10th) whilst still kept in the
dark.
The pot was then (9.45 a.m. 10th) replaced, after having been
kept for 86 h. in darkness, before the north-east window; and at
night the blades of all the leaves (excepting a few on the back of
the plants) became conspicuously vertical.
At 6.45 a.m. (11th) after the plants had been illuminated on the
same side as before during only 25m., the pot was turned round,
so that the leaves which had faced the light now faced the
interior of the room, and not one of these went to sleep at night;
340 MODIFIED CIRCUMNUTATION. Cap. VIL.
whilst some, but not many, of those which had formerly stood
facing the back of the room and which had never before been
well illuminated or gone to sleep, now assumed a vertical posi-
tion at night. On the next day (12th) the plant was turned
round into its original position, so that the same leaves faced
the light as formerly, and these now went to sleep in the usual
manner. We will only add that with some young seedlings
kept in the greenhouse, the blades of the first pair of true leaves
(the cotyledons being hypogean) stood during the day almost
horizontally and at night almost vertically.
A few observations were subsequently made on the circum-
nutation of threc leaves, whilst facing a north-east window; but
the tracings are not given, as the leaves moved somewhat
towards the light. It was, however, manifest that they rose
and fell more than once during the daytime, the ascending and
descending lines being in parts extremely zigzag. ‘The nocturnal
fall commenced about 7 p.m., and the leaves had risen consider-
ably by 6.45 a.m. on the following morning.
Leguminose.—This Family includes many more genera with
sleeping species than all the other families put together. The
number of the tribes to which each genus belongs, according to
Bentham and Hooker’s arrangement, has been added.
Crotolaria (sp. ?) (Tribe 2).—This plant is monophyllous, and
we are informed by Mr. T. Thiselton Dyer that the teaves rise
up vertically at night and press against the s‘em.
Lupinus (Tribe 2)—The palmate or digitate leaves of the
species in this large genus sleep in three different manners.
One of the simplest, is that all the lcaflets become steeply in-
clined downwards at night, having been during the day ex-
tended horizontally. This is shown in the accompanying
figures (Fig. 187), of a leaf of L. pilosus, as seen during the
day from vertically above, and of another leaf asleep with the
leaflets inclined downwards. As in this position they are
crowded together, and as they do not become folded like those
in the genus Oxalis, they cannot occupy a vertically dependent
position ; but they are often inclined at an angle of 50° bencath
the horizon. In this species, whilst the leaflets are sinking,
the petioles rise up, in two instances when the angles were
measured to the extent of 23°. The leaflets of L. sub-carnosus and
arboreus, which were horizontal during the day, sank down at
night in nearly the same manner ; the former to an angle of 38°,
and the latter of 36°, beneath the horizon: but their peticles
Cuap. VI. SLEEP OF LEAVES. 341
did not move in any plainly perceptible degree. It is, however,
quite possible, as we shall presently see, that if a large number
of plants of the three foregoing and of the following species
Fig. 137.
A.
Tupinus pilosus: A, leaf seen from vertically above in daytime; B, leaf
asleep, seen laterally at night.
were to be observed at all seasons, some of the leaves would be
‘found to sleep in a different manner.
In the two following species the leaflets, instead of moving
downwards, rise at night. With LZ. Hartwegii some stood at
noon at a mean angle of 36° above the horizon, and at night
at 51°, thus forming together a hollow cone with moderately
steep sides. The petiole of one leaf rose 14° and of a second
11° at night. With ZL. luteus a leaflet rose from 47° at noon to
65° above the horizon at night, and another on a distinct leat
rose from 45° to 69°. The petioles, however, sink at night to
a small extent, viz., in three instances by 2°, 6°, and 9° 30’.
Owing to this movement of the petioles, the outer and longer
leaflets have to bend up a little more than the shorter and inner
ones, in order that all should stand symmetrically at night.
We shall presently see that some leaves on the same individual
plants of L. luteus sleep in a very different manner.
We now come to a remarkable position of the leaves
when asleep, which is common to several species of Lupines.
On the same leaf the shorter leaflets, which generally face the
centre of the plant, sink at night, whilst the longer ones
on the opposite side rise; the intermediate and lateral ones
merely twisting on their own axes. But there is some variability
with respect to which leaflets rise or fall. As might have been
expected from such diverse and complicated movements, the
342 MODIFIED CIRCUMNUTATION. Cuar. VI’.
base of each leaflet is developed (at least in the case of L. luteus)
into a pulvinus. The result is that all the leaflets on the
game leaf stand at night more or less highly inclined, or even
quite vertically, forming in this latter case a vertical star. This
occurs with the leaves of a species purchased under the name vf
Fig. 138
c
Tuginus pubescens: A, leaf viewed laterally duri: g the day; B, same leaf
at night; C, another leaf with the leaflet forming a vertical star at
night. Figures reduced.
1. pub scens ; and in the accompanying figures we see at A (Fig.
138) the leaves in their diurnal position; and at B the same
plant at night with the two upper leaves having their leaflets
almost vertical. At C another leaf, viewed laterally, is shown
with the leaflets quite vertical. It is chiefly or exclusively the
youngest leaves which form at night vertical stars. But there
Cuar. VIL SLEEP OF LEAVES. 343
1s much variability in the position of the leaves at night on the
same plant; some remaining with their leaflets almost horizontal,
others forming more or less highly inclined or vertical stars, and
some with ali their leatlets sloping downwards, as in our first
class of cases. It is also a remarkable fact, that although all the
plants produced from the same lot of seeds were identical im
appearance, yet some individuals at night had the leaflets of all
their leaves arranged so as to form more or less highly inclined
stars; others had them all sloping downwards and never forming
a star; and others, again, retained them either in a horizontai
position or raised them a little.
We have as yet referred only to the different positions of tne
leaflets of L. pubescens at night; but the petioles likewise differ
in their movements. That of a young leaf which formed a
highly inclined star at night, stood at noon at 42° above the
horizon, and during the night at 72°,so had risen 30°. The
petiole of another leaf, the leaflets of which occupied 1 similar
position at night, rose only 6°. On the other hand, the petiole
of a leaf with all its leaflets sloping down at night, fell at this
time 4°. The petioles of two rather older leaves were subse-
quently observed ; both of which stood during the day at exactly
the same angle, viz., 50° above the horizon, and one of these rose
7°—8°, and the other fell 3°—4° at night.
We meet with cases like that of L. pubescens with some other
species. On a single plant of /. mutabilis some leaves, which
stood horizontally during the day, formed highly inclined stars
at night, and the petiole of one rose 7°. Other leaves which
likewise stood horizontally during the day, had at night all their
leaflets sloping downwards at 46° beneath the horizon, but
their petioles had hardly moved. Again, L. luteus offered a still
more remarkable case, for on two leaves, the leaflets which stood
at noon at about 45° above the horizon, rose at night to 65° and
69°, so that they formed a hollow cone with steep sides. Four
leaves on the same plant, which had their leaflets horizontal at
noon, formed vertical stars at night; and three other leaves
equally horizontal at noon, had all their leaflets sloping down-
wards at night. So that tle leaves on this one plant assumed
at night three different positions. Though we cannot account
for this fact, we can see that such a stock might readily give
birth to species having widely different nyctitropic habits.
Little more need be said about the sleep of the species of Lu-
pinus; several, namely, L. polyphyllus, nanus, Menziesti, speciosus,
23
B44 MODIFIED CIRUUMNUTATION. Cuap. VIE.
and «lbifrons, though observed out of doors and in the green-
house, did not change the position of their leaves sufficiently at
night to be said to sleep. From observations made on two
sleeping species, it appears that, as with Topavium majus, the
leaves must be well illuminated during the day in order to sleep
at night. For several plants, kept all day in a sitting-room
with north-east windows, did not sleep at night; but when the
pots were placed on the following day out of doors, and were
bronght in at night, they slept in the usual manner. The trial
was repeated on the following day and night with the same
result.
Some observations were made on the circumnutation of the
leaves of L. luteus and arb.reus, It will suffice to say that the
leaflets of the latter exhibited a double oscillation in the course
of 24h.; for they fell from the early morning until 1015 a.m.,
then rose and zigzagged greatly till 4 p.m., after which hour the
great nocturnal fall commenced. By 8 a.m. on the following
morning the leaflets had risen to their proper height. We have
seen in the fourth chapter, that the leaves of Lupinus sprciosus,
which do not sleep, circumnutate to an extraordinary extent,
making many ellipses in the course of the day.
Cytisus (Fribe 2), Trigonella and Medicago (Tribe 3).—Only
Fig, 139.
Medicago marina A. leaves during the day; B, Icaves asleep at night.
a few observations were made on these three genera. The
petioles on a young p'ant, about a foot in height, of Cytisus
fragrans rose at night, on one occasion 23° and on another 33°.
The three leaflets’ als) hend upwards, and at the same time
Onav. VIL SLEEP OF LEAVES. 345
approach each other, so that the base of the central leaflet
overlaps the bases of the two lateral leaflets. They bend
up so much that they press against the stem; and on looking
down on one of these young plants from vertically above, the
lower surfaces of the leaflets are visible; and thus their upper
surfaces, in accordance with the general rule, are best protected
from radiation. Whilst the leaves on these young plants were
thus behaving, those on an old bush in full flower did not sleep
at night.
Trigonelia Cretica resembles a Melilotus in its sleep, which will
be immediately described. According to M. Royer,* the leaves
of Medicago maculata rise up at night, and “se renversent un
peu de maniére 4 presenter obliquement au ciel leur face in-
ferieure.” A drawing is here given (Fig. 189) of the leaves
of M. marina awake and asleep; and this would almost serve
for Cytisus fragrans in the same two states.
Melilotus (Tribe 3).—The species in this genus sleep in a
remarkable manner. The three leaflets of each leaf twist through
an angle of 90°, so that their blades stand vertically at night
with one lateral edge presented to the zenith (Fig. 140). We
shall best understand the other and more complicated move-
ments, if we imagine ourselves always to hold the leaf with the
tip of the terminal leaflet pointed to the north. The leaflets in
becoming vertical at night could of course twist so that their
upper surfaces should face to either side; but the two lateral
leaflets always twist so that this surface tends to face the north,
but as they move at the same time towards the terminal leaflet,
the upper surface of the one faces about N.N.W., and that cf
the other N.N.E. The terminal leaflet behaves differently, for
it twists to either side, the upper surface facing sometimes east
and sometimes west, but rather more commonly west than east.
The terminal leaflet also moves in another and more remarkable
manner, for whilst its blade is twisting and becoming vertical,
the whole leaflet bends to one side, and invariably 1o the side
towards which the upper surface is directed; so that if this.
surface faces the west the whole leaflet bends to the west, until
it comes into contact with the upper and vertical surface of
the western lateral leaflet. Thus the upper surface of the
terminal and of one of the two lateral leaflets is well protected.
The fact of the terminal leaflet twisting indifferently to either
* - Annales des Sc. Nat. Bot.’ (5th series), ix. 1868, p. 368.
346 MODIFIED CIRCUMNUTATION. : Cuap. VIL
side and afterwards Lending to the same side, seemed to us so
remarkable, that we endeavoured to discover the cause. We
imagined that at the commencement of the movement it might
be determined by one of the two halves of the leaflet being
a little heavier than the other. Therefore bits of wood were
gummed on one side of several leaflets, but this produced no
effect; and they continued to twist in the same direction as
Fig. 140.
Cc.
Melilotus officinalis: A, leaf during the daytime. B, another leaf asleep.
C, a leaf asleep as viewed from vertically above; but in this case the
terminal leaflet did not happen to be in such close contact with the
lateral one, as is usual.
they had previously done. In order to discover whether the
same leaflet twisted permanently in the same direction, black
threads were tied to 20 leaves, the terminal leaflets of which
twisted so that their upper surfaces faced west, and 14 white
threads to leaflets which twisted to the east. These were ob-
served occasionally during 14 days, and they all continued, with
a single exception, to twist and bend in the same direction; for
Cuap. VIL. SLEEP OF LEAVES. 347
oue leaflet, which had originally faced east, was observed after
9 days to face west. The seat of both the twisting and bending
movement is in the pulvinus of the sub-petioles.
We believe that the leaflets, especially the two lateral ones,
in performing the above described complicated movements
generally bend a little downwards; but we are not sure of this,
for, as far as the main petiole is concerned, its nocturnal move-
ment is largely determined by the position which the leaf
happens to occupy during the day. Thus one main petiole was
observed to rise at night 59°, whilst three others rose only 7°
and 9°. The petioles and sub-petioles are continually circum-
nutating during the whole 24 h., as we shall presently see.
The leaves of the following 15 species, M. officinalis, suaveolens,
parviflora, alba, infesta, dentutu, gracilis, sulcata, elegans, ccerulea,
petitpierreana, macrorrhiza, Italica, secundiflora, and Taurica,
sleep in nearly the same manner as just described; but the
bending to one side of the terminal leaflet is apt to fail unless
the plants are growing vigorously. With Jf. petitpierreana and
secundiflora the terminal leaflet was rarely seen to bend to one
side. In young plants of M. Italica it bent in the usual manner,
but with old plants in full flower, growing in the same pot and
observed at the same hour, viz., 8.30 p.m., none of the terminal
leaficts on several scores of leaves had bent to one side, though
they stood vertically ; nor nad the two lateral leaflets, though
standing vertically, moved towards the terminal one. At
1030 p.m., and again one hour after midnight, the terminal
leaflets had become very slightly bent to one side, and the
lateral leaflets had moved a very little towards the terminal one,
so that the position of the leaflets even at this late hour was far
from the ordinary one. Again, with M. Taurica the terminal
leaflets were never seen to bend towards either of the two lateral
leaflets, though these, whilst becoming vertical, had bent towards
the terminal one. The sub-petiole of the terminal leaflet in
this species is of unusual length, and if the leaflet had bent to
one side, its upper surface could have come into contact only
with the apex of either lateral leaflet; and this, perhaps, is the
meaning of the loss of the lateral movement.
The cotyledons do notsleep at night. The first leaf consists of
a single orlicular kaflet, which twists at night so that the blade
stands vertically. It is a remarkable fact that with /. Taurica,
and in a somewhat less degree with M. macrorrhiza and petit-
pierrcana, all the many small and young leaves produced during
348 MODIFIED CIRCUMNUTATION. Crap. VIL
the early spring from shoots on some cut-down plants in the
greenhouse, slept in a totally different manner from the normal
one; for the three leaflets, instead of twisting on their own axes
so as to present their lateral edges to the zenith, turned upwards
and stood vertically with their apices pointing to the zenith.
They thus assumed nearly the same position as in the allied
genus Trifolium; and on the same principle that embryological
characters reveal the lines of descent in the animal kingdom, so
the movements of the small leaves in the above three species of
Melilotus, perhaps indicate that this genus is descended from
a form which was closely allied to and slept like a Trifolium.
Moreover, there is one species, MM. messanensis, the leaves of
which, on full-grown plants between 2 and 8 feet in height,
sleep like the foregoing small leaves and like those of a Trifolium.
We were so much surprised at this lattcr case that, until the
flowers and fruit were examined, we thought that the seeds of
some Trifolium had been sown by mistake instead of those of a
Melilotus. It appears therefore probable that M. messanensis
has either retained or recovered a primordial habit.
The circumnutation of a leaf of M. officinalis was traced,
the stem being left free; and the apex of the terminal leaflet
described three laterally extended ellipses, between 8 a.m. and
4p.m.; after the latter hour the nocturnal twisting movement
commenced. It was afterwards ascertained that the above
movement was compounded of the circumnutation of the stem
on a sinall scale, of the main petiole which moved most, and of
the sub-petiole of the terminal leaflet. The main petiole of a
leaf having been secured to a stick, close to the base of the sub-
petiole of the terminal leaflet, the latter described two small
ellipses between 10.30 4am.,and2pm. At 7.15 p.m, after this
same leaflet (as well as another) had twisted themselves into
their vertical nocturnal position, they began to rise slowly, and
continued to do so until 10.35 p.m., after which hour they were
no longer observed.
As M. messunensis sleeps in an anomalous manner, unlike that
of any other species in the genus, the circumnutation of a
terminal leaflet, with the stem secured, was traced during two
days. On each morning the leaflet fell, until about noon, and
then began to rise very slowly; but on the first day the rising
movement was interrupted between 1 and 3 p.m. by the formation
of a laterally extended ellipse, and on the second day, at the
game time, by two smaller ellipses. The rising movement then
Cuar. VIL. SLEEP OF LEAVES. 3419
recommenced, and became rapid late in the evening, when
the leaflet was beginning to go to sleep. The awaking or
sinking movement had already commenced by 6.45 a.m on both
mornings.
Trifolium (Tribe 3).—The nyctitropic movements of 11
species were observed, and were found to be closely similar. If
we select a leaf of 7. repens having an upright petiole, and with
the three leaflets expanded horizontally, the two lateral leaflets
will be seen in the evening to twist and approach each other,
until their upper surfaces come into contact. At the same time
they bend downwards in a plane at right angles to that of their
former position, until their midribs form an angle of about 45°
with the upper part of the petiole. ‘[his peculiar change of
position requires a considerable amount of torsion in the pul-
vinus. The terminal leaflet merely rises up without any twist-
Fig. 141.
Trifolium repens: A, leaf during the day; B, leaf asleep at night.
ing, and bends over until it rests on and forms a roof over the
edges of the now vertical and united lateral leaflets. Thus the
terminal leaflet always passes through an angle of at least 90°,
generally of 130° or 140°, and not rarely—as was often observed
with J. subterraneum—of 180°. In this latter casc the terminal
leaflet stands at night horizontally (as in Fig. 141), with its
lower surface fully exposed tothe zenith. Besides the difference
in the angles, at which the terminal leaflets stand at night in
the individuals of the same species, the degree to which the
lateral leaflets approach each other often likewise differs.
We have seen that the cotyledons of some species and not of
others rise up vertically at night. The first true leaf is generally
unifoliate and orbicular; it always rises, and either stands verti-
cally at night or more commonly bends a little over so as to expose
the lower surface obliqnely to the zenith, in the same manner
as does the terminal leaflet of the mature leaf. But it does not
twist itself like the corresponding first simple leaf of Melilotus.
350 MODIFLED CIRCUMNUTATION, Cuar. VIL
With 7. Punnonicum the first true leaf was generally unifoliate,
but sometimes trifoliate, or again partially lobed and in an
intermediate condition.
Circumnutation—Sachs described in 1863* the spontaneous
up and down movements of the leaflets of 7. ‘ncarnatum, when
kept in darkness. Pfeffer made many observations on the
similar movements in 7. pratense.t He states that the terminal
leaflet of this species, observed at different times, passed through
angles of from 30° to 120° in the course of from 13 to4h. We
observed the movements of ZY. subterraneum, resupinatum, and
repens.
Trifolium subterranerm.—A petiole was secured close to the
base of the three leaflets, and the movement of the terminal
loaflet was traced during 263 h., as shown in the figure on the
next page.
Between 6.45 am.and 6 p.m. the apex moved 8 times up
and 3 times down, completing 3 ellipses in 11 h.15 m. The
ascending and descending lines stand nearer to one anothcr
than is usual with most plants, yet there was some lateral
motion. At 6 p.m. the great nocturnal rise commenced, and
on the next morning the sinking of the leaflet was continned
until 8.80 a.m., after which hour it circumnutated in the manner
just described. In the figure the great nocturnal rise and
the morning fall are greatly abbreviated, from the want of
space, and are merely represented by a short curved line. The
leaflet stood horizontally when at a point a little beneath the
middle of the diagram; so that during the daytime it oscillated
almost equally above and beneath a horizontal position. At
8.30 a.m. it stood 48° beneath the horizon, and by 11.80 a.m. it
had risen 50° above the horizon; so that it passed through 98°
in 8h. By the aid of the tracing we ascertained that the
distance travelled in the 3 h. by the apex of this leaflet was
1:03 inch. If we look at the figure, and prolong upwards in
our mind’s eye the short curved broken line, whieh repre-
sents the nocturnal course, we see that the latter movement is
merely an exaggeration or pro'ongation of one of the diurnal
ellipses. ‘The same leaflet had been observed on the previous
day, and the course then pursued was almost identically the
same as that here described.
* ¢ Flora,’ 183, p. 497.
+ ‘Die Period, Bewegungen, 1875, pp. 35, 52.
Cuar. VIL SLEEP OF LEAVES,
Trifolium respinatum.—A plant left entirely frec
before a north-east win-
dow, in such a position
that a terminal leaflet
projected at right angles
to the source of the light,
the sky being uniformly
clouled all day. The
movements of this leaflet
were traced during two
days, and on both were
closely similar. Those
executed on the second
day are shown in Fig.
143. The obliquity of
the several_lines is due
partly to the manner in
which the leaflet was
viewed, and partly to its
having moved a little to-
wards the light. From
7.50 a.m. to 8.40 a.m, the
leaflet fell, that is, the
awakening movement was
continued. It then rose
and moved a little late-
rally towards the light.
At 12.30 it retrograded,
and at 2.30 resumed its
original course, having
thus completed a small
ellipse during the middle
of the day. In the even-
ing it rose rapidly, and
by 8 a.m. on the following
morning had returned to
exactly the same spot as
on the previous morning.
The line representing the
nocturnal course ought
to be extended much
higher up, and is here
abbreviated into a short,
351
was placed
("68 inch in length), traced (rom
glass, and movement, as here shown,
Plant illuminated from above; temp. 16°~17° C,
0 9.15 AM. 5th. Apex of leaf 3 inches from the vertical
circumnutation and nyctitropic movement of terminal leaflet
reduced to one-half of original scale.
Trifolium subterraneum :
6.45 am. July 4th t
magnified 52 times,
352 MODIFIED CIRCUMNUTATION. Cuar. VIL
curved, broken line. The terminal leaflet, therefore, of this
species described during the daytime only a single additional
ellipse, instead of two ad-
Fig. 143. ditional ones, as in the
case of TZ. subterranewm.
But we should remember
that it was shown in the
fourth chapter that the
; stem circumnutates, as no
y doubt does the main petiole
* and the sub-petioles; sa
that the movement repre-
sented in fig. 143 is a com-
pounded one. We tried
to observe the movements
of a leaf kept during the
day in darkness, but it
Trifolium resupinatum: circumnutation began to go to pe P after
and nyctitropic movements of the ter- 2h. 15 m., and this was
minal leaflet during 24 hours, well pronounced after 4 h.
80 m.
Trifolium repens—A stem was secured close to the base of
a moderately old leaf, and the movement of the terminal leaflet
was observed during two days. This case is interesting solely
from the simplicity of the movements, in contrast with those of
the two preceding species. On the first day the leaflet fell
between 8 a.m. and 3 p.m., and on the second between 7 a.m.
and1lpm. Qn both days the descending course was somewhat
zigzag, and this evidently represents the circumnutating move-
ment of the two previous species during the middle of the day.
After 1 p.m., Oct. Ist (Fig. 144), the leaflet began to rise, but
the movement was slow on both days, both before and after
this hour, until4 p.m. The rapid evening and nocturnal rise
then commenced. Thus in this species the course during 24h.
consists of a single great ellipse; in 7. resupinatum of two
ellipses, one of which includes the nocturnal movement and is
much elongated; and in T. subterranenm of three ellipses, of
which the nocturnal one is likewise of great length.
Securigera coronilla (Tribe 4).—The leaflets, which stand
opposite one another and are numerous, 1ise up at night,.come
into close contact, and bend backwards at a moderate angle
towards the base of the petiole.
Cuar VIL.
SLEEP OF LEAVES.
353
Lotus (Tribe 4).—The nyctitropic movements of 10 species
in this genus were observed, and found to be the same, The
main petiole rises a little at night, and
the three leaflets rise till they become
vertical, and at the same time approach
each other. This was conspicuous with
L, Jacobeus, in which the leaflets are
almost linear. In most of the species
the leaflets rise so much as to press
against the stem, and not rarely they
become inclined a little inwards with
their lower surfaces exposed obliquely
to the zenith. This was clearly the
case with L. major, as its petioles are
unusually long, and the leaflets are thus
enabled to bend further inwards. The
young leaves on the summits of the
stems close up at night so much, as
often to resemble large buds. The
stipule-like leaflets, which are often of
large size, rise up like the other leaflets,
and press against the stem (Fig. 145).
All the leaficts of L. Gebelii, and pro-
bably of the other species, are provided
at their bases with distinct pulvini, of
a yellowish colour, and formed of very
small cells. The circumnutation of a
terminal leaflet of L. periyrinus (with
the stem secured) was traced during
two days, but the movement was so
simple that it is not worth while to
give the diagram. The leaflet fell
slowly from the early morning till
about 1 p.m. It then rose gradually
at first, but rapidly late in the evening.
Fig. 144,
\
)
,
oe,
Y
ae
.
Trifolium repens : circum
nutation and nyctitropic
movements of a nearly
full-grown terminal
leaflet, traced on a ver-
tical glass from 7 A.M.
Sept. 30th to 8 a.m. Oct.
Ist. Nocturnal course,
represented by turved
broken line, much ab-
breviated.
It occasionally stood still for about 20 m. during the day, and
sometimes zigzagged a little.
The movement of one of the
basal, stipule-like leaflets was likewise traced in the same
manner and at the same time, and its course was closely similar
to that of the terminal leaflet.
In Tribe 5 of Bentham and Hooker, the sleep-movementa
of species in 12 genera have been observed by ourselves and
854 MODIFIED CIRCUMNUTATION. Cuar VII
others, but only in Robinia with any care. Psoralea acaulis
raises its three leaflets at night; whilst Amorpha fruticosu,*
Dalea alopccuroid:s, and Indigofera tinctoria depress them.
Duchartre ¢ states that Tephrosia caribeea is the sole example
of “ folioles couchées le long du petiole et vers la base;” but a
Fig. 145.
A. B.
Lotus “C: eticus : A, stem with leaves awake during the day; B, with leaves
asleep at night. SS, stipule-like leaflets.
similar movement occurs, a8 we have already seen, and shall
again see in other cases. Wistaria Sinensis, according te
Royer,t ‘“abaisse les folioles qui par une disposition bizarre
sont inclinées dans la méme feuille, les supérieures vers le
* Ducharte, ‘léments de t ‘Ann. des Sciences, Nats,
Botanique,’ 1867, p. 849. Bot.’ (Sth series), ix. 1868.
+ Ibid., p. 347.
Cuap. VILL. SLEEP OF LEAVES. 395
sommet, les inférieures vers la base du petiole commun;” but
the leaflets on a young plant observed by us in the green-
house merely sank vertically downwards at night. The leaficts
are raised in Spherophysa salsola, Colutea arborea, and a ——
Cassia pubescens: A, wpper part of plant during the day ; B, same p aut
at night. Figures reduced from photographs.
movements of this species, compared with those of the former
species, consists in the leaflets not rotating nearly so much;
872 MODIFIED CIRCUMNUTATION. Cuap. VIL
therefore their lower surfaces face but little outwards at night.
The petioles, which during the day are inclined only a little
above the horizon, rise at night in a remarkable manner, and
stand nearly or quite vertically. This, together with the
dependent position of the leaflets, makes the whole plant won-
derfully compact at night. In the two foregoing figures, copied
from photographs, the same plant is represented awake and
asleep (Fig. 155), and we see how different is its appearance.
Cassia mimosvides—At night the numerous leaflets on each
leaf rotate on their axes, and their tips move towards the apex
of the leaf; they thus become imbricated with their lower
surfaces directed upwards, and with their midribs almost
parallel to the petiole. Consequently, this species differs from
all the others seen by us, with the exception of the following
one, in the leaflets not sinking down at night. A petiole, the
movement of which was measured, rose 8° at night.
Cassia Barclayana.—The leaflets of this Australian species are
numerous, very narrow, aud almost linear. At night they rise up
alittle, and also move towards the apex of the leaf. For instance,
two opposite leaflets which diverged from one another during
the day at an angle of 104°, diverged at night only 72°; so that
each had risen 16° above its diurnal position. The petiole of a
young leaf rose at night 34°, and that of an older leaf 19°,
Owing to the slight movement of the leaflets and the consider-
able movement of the petiole, the bush presents a different
appearance at night to what it does by day; yet the leaves can
hardly be said to sleep.
The circumnutating movements of the leaves of C. floribunda,
cealliantha, and pubescens were observed, each during three or four
days; they were essentially alike, those of the last-named species
being the simplest. The petiole of C. floribunda was secured to
a stick at the base of the two terminal leaflets, and a filament
was fixed along the midrib of one of them. Its movements were
traced from 1P.m. on August 13th to 8.30 am. 17th; but thoss
during the last 2 h. are alone given in Fig. 156. From 8 a.m. on
each day (by which hour the leaf had assumed its diurnal posi-
tion) to 2 or 8 P.M., it either zigzagged or circumnutated over
nearly the same small space; at between 2 and 3 p.m. the great
evening fall commenced. The lines representing this fall and
the early morning rise are oblique, owing to the peculiar manner
in which the leaflets sleep, as already described. After the
leaflet was asleep at 6 P.m., and whilst the glass filament hung
Cuar. VIL SLEEP OF LEAVES. 373
perpen ticularly down, the movement of its apex was traced
until 10.30 p.m.; and during this whole time it swaycd from
side to side, completing more than one ellipse.
Bauhinia (Tribe 15).— Fig. 156
The nyctitropic movements
of four species were alike,
and were highly peculiar.
A plant raised from seed
sent us from South Brazil i
by Fritz Miiller, was more ;
especially observed. The
leaves are large and deeply
nvtched at their ends. At
night the two halves rise
up and close completely /
together, like the opposite ;
leaflets of many Legumi-
nose. With very young
plants the petioles rise con- i
siderably at the same time;
one, which was inclined at
noon 45° above the hori- i
zon, at night stood at 75°; /
it thus rose 30°; another i Ww
rose 34°. Whilst the two F
halves of the leaf are closing, i
the midrib at first sinks
vertically downwards and
afterwards bends _ back-
wards, so as to pass close A
sO
Apex of leaflet 53 inches from the
e 33 inches long, Temp. 16°-174°C. Figure reduced to one-half
cireunmutation and nyctitropic movement of a terminal leaflet (1% inch in length)
traced from 8.30 a.M. to same hour on following morning.
Main petiol
xc
along one side of its own i =
upwardly inclined petiole; f a ed
the midrib being thus di- Py fees
rected towards the stemor / yf SS 8
axisof the plant. Theangle / Bese
which the midrib formed ;, SEES
with the horizon was mea- # &
sured in one case at dif-
ferent hours: at noon it stood horizontally; late in the even-
ing it depended vertically; then rose to the opposite side, and
at 10.15 p.m. stood at only 27° beneath the horizon, being
dirccted towards the stem. It had thus travelled through 153°
374 MODIFIED CIRCUMNUTATION. Cuar. VIL.
Owing to this movement—to the leaves being folded—and to
the petioles rising, the whole plant is as much more compact at
night than during the day, as a fastigiate Lombardy poplar is
compared with any other species of poplar. It is remarkable
that when our plants had grown a little older, viz., to a height
of 2 or 8 feet, the petioles did not rise at night, and the midribs
of the folded leaves were no longer bent back along one side of
the petiole. We have noticed in some other genera that the
petioles of very young plants rise much more at night than do
those of older plants.
Tamarindus Indica (Tribe 16).—The leaflets approach or
roeet each other at night, and are all directed towards the apex
of the leaf. They thus become imbricated with their midribs
parallel to the petiole. The movement is closely similar to
that of Hematoxylon (see former Fig. 153), but more striking
from the greater number of the leaflets.
Adenanthera, Prosopis, and Neptunia (Tribe 20),—With Ade-
nanthera pavonia the leaflets turn edgeways and sink at night.
In Prosopis they turn upwards. With Neptunia oleracea the
leaflets on the opposite sides of the same pinna come into
contact at night and are directed forwards. The pinne them-
selves move downwards, and at the same time backwards or
towards the stem of the plant. The main petiole rises.
Mimosa pudica (Tribe 20).—This plant has been the subject of
innumerable observations; but there are some points in rela-
tion to our subject which have not been sufficiently attended
to. At night, as is well known, the opposite leaflets come into
contact and point towards the apex of the leaf; they thus be-
come neatly imbricated with their upper surfaces protected. The
four pinne also approach each other closely, and the whole leaf
is thus rendered very compact. The main petiole sinks down-
wards during the day till late in the evening, and rises until
very early inthe morning. The stem is continually circumnu-
tating at a rapid rate, though not to a wide extent. Some very
young plants, kept in darkness, were observed during two days,
and although subjected to a rather low temperature of 57°-—59° F.,
the stem of one described four small ellipses in the course ot
12h. We shall immediately see that the main petiole is like-
wise continually circumnutating, as is each separate pinna and
each separate leaflet. Therefore, if the movement of the apex
of any one leaflet were to be traced, the course described would
be compounded of the movements of four separate parts.
Cuap. VIL SLEEP OF LEAVES. 375
A filament had been fixed on the previous eveiing, longi-
tudinally to the main petiole of a nearly full-grown, highly-
sensitive leaf (four inches in length), the stem having been
secured to a stick at its base; and a tracing was made ona
vertical glass in the hot-house under a high temperature. In
the figure given (Fig. 157), the
first dot was made at 8.80 a.m.
August 2nd, and the last at 7
P.m.on the 3rd. During 12 h.on
the first day the petiole moved
thrice downwards and twice
upwards. Within the same
length of time on the second
day, it moved five times duwn-
wards and four times upwards.
As the ascending and descend-
ing lines do not coincide, the
petiole manifestly circumnu-
tates; the great evening fall
and nocturnal rise being an
exaggeration of one of the cir-
cumnutations. It should, how-
ever, be observed that the pe-
tiole fell much lower down in
the evenings than could be
seen on the vertical glass or is
represented in the diagram.
After 7 p.m. on the 38rd (when
the last dot in Fig. 157 was
made) the pot was carried into
a bed-room, and the petiole was
found at 12.50 a.m. (i.e. after
midnight) standing almost up- i
right, and much more highly 6pm. andi pmard
inclined than it was at 10.40 ; ;
p.m. When observed again at sialic pudica aera pe ar]
4 a.m. it had begun to fall,and —{ioje, traced during 34 h. 30 mo
continued falling till 6.15 a.m.,
after which hour it zigzagged and again circumnutated. Similar
observations were made on another petiole, with nearly the
same result.
On two other occasions the movement of the main petiole
25
Fig. 157,
376 MODIFIED CIRCUMNUTATION. Cuar. VII
was observed every two or three minutes, the plants being kept
at a rather high temperature, viz., on the first occasion at
77°—81° F., and the filament then described 23 ellipses in 69 m.
On the second occasion, when the temperature was 81°—86° F.,
it made rather more than 8 ellipses in 67 m. Therefore,
Fig. 157, though now sufficiently complex, would have been in-
comparably more so, if dots had been made on the glass every
2 or 3 minutes, instead of every hour or half-hour. Although
the main petiole is continually and rapidly describing small
ellipses during the day, yet after the great nocturnal rising
movement has commenced, if dots are made every 2 or 3
minutes, as was done for an hour between 9.30 and 10.30 pm.
(temp. 84° F.), and the dots are then joined, an almost abso-
lutely straight line is the result.
To show that the movement of the petiole is in all proba-
bility due to the varying turgescence of the pulvinus, and not
to growth (in accordance with the conclusions of Pfeffer), a very
old leaf, with some of its leaflets yellowish and hardly at all
sensitive, was selected for observation, and the plant was kept
at the highly favourable temp. of 80° F. The petiole fell from
8 am. till 10.15 a.m., it then rose a little in a somewhat zigzag
line, often remaining stationary, till 5 p.m, when the great
evening fall commenced, which was continued till at least
10 p.m. By 7 a.m. on the following morning it had risen to the
same level as on the previous morning, and then descended in
a zigzag line. But from 10.30 a.m. till 4.15 p.m. it remained
almost motionless, all power of movement being now lost. The
petiole, therefore, of this very old leaf, which must have long
ceased growing, moved periodically ; but instead of circum-
nutating several times during the day, it moved ouly twice
down and twice up in the course of 24h., with the ascending
and descending lines not coincident.
It has ulready been stated that the pinne move independently
of the main petiole. The petiole of a leaf was fixed to a cork
support, close to the point whence the four pinne diverge, with
a short fing filament cemented longitudinally to one of the twc
terminal pinuse, and a graduated semicircle was placed close
beneath it. By looking vertically down, its angular or lateral
movements could be measured with accuracy. Between noon
and 4.15 pu. the pinna changed its position to one side by only
7°; but not continuously in the same direction, as it moved
four times to one side, and three times to the opposite side,
Cuar. VIL. SLEEP OF LEAVES. 377
in one instance to the extent of 16°. This pinna, therefoie,
circumnutated. Later in the evening the four pinne approach
each other, and the one which was observed moved inwards
59° between noon and 6.45 p.m. Ten observations were made
in the course of 2h. 20m. (at average intervals of 14 m.),
between 4.25 and 6.45 p.m.; and there was now, when the leat
was going to sleep, no swaying from side to side, but a steady
inward movement. Here therefore there is in the evening the
same conversion of a circumnutating into a steady movement
iu one direction, as in the case of the main petiole.
It has also been stated that each separate leaflet circum-
nutates. A pinna was cemented with shellac on the summit of
a little-stick driven firmly into the ground, immediately beneath
a pair of leaflets, to the midribs of both of which excessively
fine glass filaments were attached. This treatment did not
injure the leaflets, for they went to sleep in the usual manner,
and long retained their sensitiveness. The movements of one
of them were traced during 49 h., as shown in Fig. 158. On the
first day the leaflet sank down till 11.30 a.m., and then rose
till late in the evening in a zigzag line, indicating circum-
nutation. On the second day, when more accustomed to its
new state, it oscillated twice up and twice down during the
24h. This plant was subjected to a rather low temperatura,
viz., 62°-—64° F.; had it been kept warmer, no doubt the move-
ments of the leaflet would have been much more rapid and
complicated. It may be scen in the diagram that the ascending
and descending lines do not coincide; but the large amount of
lateral movement in the evening is the result of the leaflets
bending towards the apex of the leaf when going to sleep.
Another leaflet was casually observed, and found to be con-
tinually circumnutating during the same length of time.
The circumnutation of the leaves is not destroyed by their
being subjected to moderately long continued darkness; but the
proper periodicity of their movements is lost. Some very young
seedlings were kept during two days in the dark (temp. 57°—59°
F.), except when the circumnutation of their stems was occa-
sionally observed; and on the evening of the second day the
leaflets did not fully and properly go to sleep. The pot was
then placed for three days in a dark cupboard, under nearly the
same temperature, and at the close of this period the leaflets
showed no signs of sleeping, and were only slightly sensitive to
a touch. On the following day the stem was cemented to a
378 MODIFIED CIRCUMNUTATION. Cuar. VIL
stick, and the movements of two leaves were traced on a vertical
glass during 72h. The plants were still kept in the dark, ex-
cepting that at each observation, which lasted 3 or 4 minutes,
Fig. 158,
10° 0'a nish
M30.
Mimosa pudica: circumnutation and nyctitropic movement of a leaflet
(with pinna secured), traced on a vertical glass, from 8 a.m. Sept. 14th
to 9 a.M. 16th.
they were illuminated by two candles. On the third day the
leaflets still exhibited a vestige of sensitiveness when forcibly
pressed, but in the evening they showed no signs of sleep.
Nevertheless, their petioles continued to cireumnutate distinctly,
Caap. VII. SLEEP OF LEAVES. 379
although the proper order of their movements in relation to the
day and night was wholly lost. Thus, one leaf descended during
the first two nights (i.e. between 10 p.m. and 7 A.m. next morn-
ing) instead of ascending, and on the third night it moved
chiefly in a lateral direction. The second leaf behaved in an
equally abnormal manner, moving laterally during the first
night, descending greatly during the second, and ascending to
an unusual height during the third night.
With plants kept at a high temperature and exposed to the
light, the most rapid circumnutating movement of the apex
of a leaf which was observed, amounted to 325 of an inch in
one second; and this would have equalled 3 of an inch in a
minute, had not the leaf occasionally stood still. The actual
distance travelled by the apex (as ascertained by a measure
placed close to the leaf) was on one occasion nearly 3 of an inch
in a vertical direction in 15 m.; and on another occasion & of an
inch in 60 m.; but there was also some lateral movement.
Mimosa albida.*—The leaves of this plant, one of which is here
figured (Fig. 159) reduced to 2 of the natural size, present some
Fig. 159.
Mimosa albida : leaf seen from vertioally above.
interesting peculiarities. It consists of a long petiole bearing
only two pinne (here represented as rather more divergent
than is usual), each with two pairs of leaflets. But the inner
* Mr. Thistleton Dyer informs Linn. Soc.,’ vol. xxx. p. 390) to
us that this Peruvian plant(which be “the species or variety which
was sent to us from Kew) is con- most commonly represents the
sidered by Mr. Bentham (Trans. _sensitiva of our gardens.”
380 MODIFIED CIRCUMNUTATION. Cuar, VIL
basal leaflets are greatly reduced in size, owing probably to the
want of space for their full development, so that they may be
considered as almost rudimentary. They vary somewhat in
size, and both occasionally disappear, or only one. Neverthe-
less, they are not in the least rudimentary in function, for they
are sensitive, extremely heliotropic, cireumnutate at nearly the
same rate as the fully developed leaflets, and assume when
asleep exactly the same position. With M. pudica the inner
leaflets at the base and between the pinne are likewise much
shortened and obliquely truncated; this fact was well seen in
some seedlings of M. pudica, in which the third leaf above the
cotyledons bore only two pinne, each with only 3 or 4 pairs of
leaflets, of which the inner basal one was less than half as long
as its fellow; so that the whole leaf resembled pretty closely
that of MW. albida. In this latter species the main petiole termi-
nates in a little point, and on each side of this there is a pair
of minute, flattened, lancct-shaped projections, hairy on their
margins, which drop off and disappear soon after the leaf is
fully developed. There can hardly be a doubt that these little
projections are the last and fugacious representatives of an
additional pair of leaflets to each pinna; for the outer one is
twice as broad as the inner one, and a little longer, viz. ~4, of an
inch, whilst the inner one is only $58 long. Now if the basal
pair of leaflets of the existing leaves were to become rudimen-
tary, we should expect that the rudiments would still exhibit
some trace of their present great inequality of size. The con-
clusion that the pinne of the parent-form of M. albida possessed
at least three pairs of leaflets, instead of, as at present, only two,
is supported by the structure of the first true leaf; for this
consists of a simple petiole, often bearing three pairs of leaflets.
This latter fact, as well as the presence of the rudiments, both
lead to the conclusion that M. albida is descended from a form
the leaves of which bore more than two pairs of leaflets. The
second leaf above the cotyledons resembles in all respects the
leaves on fully developed plants.
When the leaves go to sleep, each leaflet twists half round,
so as to present its edge to the zenith, and comes into close
contact with its fellow. The pinne also approach each other
closely, so that the four terminal leaflets come together. The
large basal leaflets (with the little rudimentary ones in contact
with them) move inwards and forwards, so as to embrace the
outside of the united terminal leaflets, and thus all eight leaflets
Cuar. VIL. SLEEP OF LEAVES. 881
(the rudimentary ones included) form together a single vertical
packet. The two pinne at the same time that they approach
each other sink downwards, and thus instead of extending hori-
zontally in the same line with the main petiole, as during the
day, they depend at night at about 45°, or even at a greater
angle, beneath the horizon. The movement of the main petiole
seems to be variable; we have seen it in the evening 27° lower
than during the day; but sometimes in nearly the same position.
Nevertheless, a sinking movement in the evening and a rising
one during the night is probably the normal course, for this
was well-marked in the petiole of the first-formed true leaf.
The circumnutation of the main petiole of a young leaf was
traced during 2? days, and was considerable in extent, but less
complex than that of Mf, pudica. The movement was much
more lateral than is usual with circumnutating leaves, and this
was the sole peculiarity which it presented. The apex of
one of the terminal leaflets was seen under the microscope to
travel 2, of an inch in 3 minutes.
Mimosu marginata.—The opposite leaflets riso up and approach
each other at night, but do not come into close contact, except in
the case of very young leaflets on vigorous shoots. Full-grown
leaflets circumnutate during the day slowly and on a small scale,
Schrankia uncinata (Tribe 20).—A leaf consists of two or three
pairs of pinne, each bearing many small leaflets. These, when
the plant isasleep, are directed forwards and become imbricated.
The angle between the two terminal pinne was diminished at
night, in one case by 15°; and they sank almost vertically down-
wards. The hinder pairs of pinne likewise sivk downwards,
but do not converge, that is, move towards the apex of the leaf.
The main petiole does not become depressed, at least during the
evening. In this latter respect, as well as in the sinking of the
pinne, there is a marked difference between the nyctitropic
movements of the present plant and of Mimosa pudica. It
should, however, be added that our specimen was not in a very
vigorous condition. The pinne of Schrankia aculeata alse sink
at night.
Acacia Farnesiana (Tribe 22).—The different appearance pre-
sented by a bush of this plant when asleep and awake is won-
derful. The same leaf in the two states is shown in the following
figure (Fig. 160). The leaflets move towards the apex of the
pinna and become imbricated, and the pinne then look like bits
of dangling string. The following remarks and measurements
B82 MODIFIED CIRCUMNUTATION. Cuar. VIL
do not fully apply to the small leaf here figured. The pinne
move forwards and at the same time sink downwards, whilst
the main petiole rises considerably. With respect to the degree
of movement: the two terminal pinnee of one specimen formed
together an angle of 100° during the day, and at night of only
38°, so each had moved 31° forwards. The penultimate pinne
during the day formed together an angle of 180°, that is, they
stood in a straight line opposite one another, and at night each
had moved 65° forwards. The basal pair of pinne were directed
Fig. 160.
&
(
iS
ONE
NAINA
ZS
Diy Ag MT Gi,
Wy) Le Gee
A. B.
Acacia Farnesiana, A, leaf during the day; B, the same leaf at night.
during the day, each about 21° backwards, and at night 38°
forwards, so each had moved 59° forwards. But the pinne at
the same time sink greatly, and sometimes hang almost perpen-
dicularly downwards. The main petiole, on the other hand,
rises much: by 8.80 p.m. one stood 34° higher than at noon,
and by 6.40 a.m. on the following morning it was still higher
by 10°; shortly after this hour the diurnal sinking move-
ment commenced. The course of a nearly full-grown leaf was
traced during 14 h ; it was strongly zigzag, and apparently
Cua. VIL, SLEEP OF LEAVES. 383
represented five ellipses, with their longer axes differently
directed.
Albizzia lophantha (Tribe 23).—-The leaflets at night come into
contact with one another, dnd are directed towards the apex of
the pinna. The pinne approach one another, but remain in the
same plane as during the day; and in this respect they differ
much from those of the above Schrankia and Acacia. The main
vetiole rises but little. The first-formed leaf above the coty-
ledons bore 11 leaflets on each side, and these slept like those
on the subsequently formed leaves; but the petiole of this first
leaf was curved downwards during the day and at night
straightened itself, so that the chord of its arc then stood 16°
higher than in the day-time.
Melaleuca ericceefolia (Myrtacee).—According to Bouché (‘ Bot.
Zeit., 1874, p. 359) the leaves sleep at night, in nearly the same
manner as those of certain species of Pimelia.
G@nothera mollissima (Onagrariee).—According to Linnzus
(‘Somnus Plantarum’), the leaves rise up vertically at night.
Passiflora gracilis (Passiflorace).—The young leaves sleep by
their blades hanging vertically downwards, and the whole length
of the petiole then becomes somewhat curved downwards.
Externally no trace of a pulvinus can be seen. The petiole of
the uppermost leaf on a young shoot stood at 10.45 a.m. at 383°
above the horizon; and at 10.30 p.u., when the blade was verti-
cally dependent, at only 15°, so the petiole had fallen 18°. That
of the next older leaf fell only 7°. From some unknown cause
the leaves do not always sleep properly. The stem of a plant,
which had stood for some time before a north-east window, was
secured to a stick at the base of a young leaf, the blade of
which was inclined at 40° below the horizon. From its position
the leaf had to be viewed obliquely, consequently the vertically
ascending and descending movements appeared when traced
oblique. On the first day (Oct. 12th) the leaf descended in a
zigzag line until late in the evening; and by 8.15 a.m. on the
18th had risen to nearly the same level as on the previous
morning. A new tracing was now begun (Fig. 161). The
leaf continued to rise until 8.50 a.m., then moved a little to the
right, and afterwards descended. Between 11 a.m. and 5 p.m. it
circumnutated, and after the latter hour the great nocturnal
fall commenced. At 7.15 p.m. it depended vertically. The
dotted line ought to have been prolonged much lower down in
the figure. By 6.50 a.m. on the following morning (14th) ihe
38t MODIFIED CIRCUMNUTATION. Cuap. VII.
leaf had risen greatly, and continued to rise till 7.50 a.m., after
which hour it redescended. It should be observed that the lines
traced on this second morning would have coincided with and
confused those previously traced, had not the pot been slided
a very little to the left. In the evening (14th) a mark was
placed behind the filament attached to the apex of the leaf, and
its movement was carefully traced from 5 p.m. to 10.15 Pu.
Fig. 161,
Passiflora gracilis: circumnutation and nyctitropic movement of leaf
traced on vertical glass, from 8.20 A.M. Oct. 18th to 10 a.m. 14th
Figure reduced to two-thirds of original scale. :
Between 5 and 7.15 p.m. the leaf descended in a straight line,
and at the latter hour it appeared vertically dependent. But
between 7.15 and 10.15 p.m. the line consisted of a succession
of steps, the cause of which we could not understand; it was,
however, manifest that the movement was no longer a simple
descending one.
Siegesbeckia orientalis (Composite).—Some seedlings were
raised in the middle of winter and kept in the hot-house; they
flowered, but did not grow well, and their leaves never showed
any signs of sleep. The leaves on other seedlings raised in May
were horizontal at noon (June 22nd), and depended at a consi:
Cuap. VIL. SLEEP OF LEAVES. 3885
derable angle beneath the horizon at 10 p.m. In the case of four
youngish leaves, which were from 2 to 2} inches in length,
these angles were found to be 50°, 56°, 60°, and 65°. At the
end of August, when the plants had grown to a height of 10 to 11
inches, the younger leaves were so much curved downwards at
night that they might truly be said to be asleep. This is one
Fig. 162.
Nicotiana glauca: shoots with leaves expanded during the day, and asleep:
at night. Figures copied from photographs, and reduced.
of the species which must be well illuminated during the day
in order to sleep, for on two occasions when plants were kept
all day in a room with north-east windows, the leaves did not
sleep at night. The same cause probably accounts for the
leaves on our seedlings raised in the dead of the winter not
sleeping. Professor Pfeffer informs us that the leaves of
another species (S. Jorullensis ?) hang vertically down at night.
386
MODIFIED CIRCUMNUTATION.
Cuar. VIL
Tj} omea cerulea and purpurea (Convolvulacee). —The lcaves on
very young plants, a foot or two in height, are depressed at night
ww tLpmio™
3 pin 10"
S10'am1g®
hi,
Nicotiana tabacum : circumnutation and nyc-
titropic mov
ement of a leaf (5j inches in
lagth), traced on a vertical glass, from
é pm. July 1
of leaf 4 inches from glass.
Figure reduced to one-half
18}° ©.
Oth to 8.10 a.m. 13th. Apex
Temp. 174$°-
original scale.
to between 68° and 80°
beneath the horizon;
and some hang quite
vertically downwards.
On the following morn-
ing they again rise into
a horizontal position.
The petioles become
at night downwardly
curved, either through *
their entire length or in
the upper part alone;
and this apparently
causes the depression
of the blade. It seemg
necessary that the
leaves should be well
illuminated during the
day in order to sleep,
for those which stood
on the back of a plant
before a north-east
window did not sleep.
Nicotiana tabacum
(var. Virginian) and
glauca (Solanese).—The
young leaves of both
these species sleep by
bendinh vertically up-
wards. Figures of two
shoots of N. glauca
awake and asleep (Fig.
162), are given on p
885 : one of the shoots,
from which the photo-
graphs were taken, was
accidentally bent to one
side.
At the base of the petiole of N. tabacum, on the outside, there
is a mass of cells, which are rather smaller than elsewhere, and
Oxav. VII. SLEEP OF LEAVES. 387
have their longer axes differently directed from the cells of the
parenchyma, and may therefore be considered as forming a sort
of pulvinus. A young plant of N. tabacum was selected, and
the circumnutation of the fifth leaf above the cotyledons was
observed during three days. On the first morning (July 10th)
the leaf fell from 9 to 10 a.m., which is its normal course, but
rose during the remainder of the day; and this no doubt was
due to its being illuminated exclusively from above; for properly
the evening rise does not commence until 8 or 4 p.m. In the
figure as given on p. 386 (Fig. 163) the first dot was made at
3 p.m.; and the tracing was continued for the following 65 h.
When the leaf pointed to the dot next above that marked 3 p.m.
it stood horizontally. The tracing is remarkable only from its
simplicity and the straightness of the lines. The leaf each day
described a single great ellipse; for it should be observed that
the ascending and descending lines do not coincide. On the
evening of the 11th the leaf did not descend quite so low as
usual, and it now zigzagged alittle. The diurnal sinking move-
ment had already commenced each morning by 7 4.m. The broken
lines at the top of the figure, representing the nocturnal vertical
position of the leaf, ought to be prolonged much higher up.
Mirabilis longiflora and jalapa (Nyctaginez).—The first pair
of leaves above the cotyledons, produced by seedlings of both
these species, were considerably divergent during the day, and
at night stood up vertically in close contact with one another.
The two upper leaves on an older seedling were almost horizontal
by day, and at night stood up vertically, but were not in close
contact, owing to the resistance offered by the central bud.
Polygonum aviculare (Polygonez).—Professor Batalin informs
us that the young leaves rise up vertically at night. This is
likewise the case, according to Linnzus, with several species
of Amaranthus (Amaranthacez); and we observed asleep move-
ment of this kind in one member of the genus. Again, with
Chenopodium album (Chenopodiez), the upper young leaves ot
some seedlings, about 4 inches in height, were horizontal or
sub-horizontal during the day, and at 10 p.m. on March 7th
were quite, or almost quite, vertical. Other seedlings raised in
the greenhouse during the winter (Jan. 28th) were observed day
and night, and no difference could be perceived in the position
of their leaves. According to Bouché (‘ Bot. Zeitung,’ 1874,
p. 359) the leaves of Pimelia linoides and spectabilis (Thymelex)
sleep at night.
388 MODIFIED CIRCUMNUTATION. Cuap, VIL
Euphorbia jacqguinieflora (Buphorbiacee).— Mr. Lynch
called our attention to the fact that the young leaves of this
plant sleep by depending vertically. The third leaf from the
summit (March 1]th) was inclined during the day 30° beneath
the horizon, and at night hung vertically down, as did some of
the still younger leaves. It rose up to its former level on the
following morning. The fourth and fifth leaves from the summit
stood horizontally during the day, and sank down at night only
38°. The sixth leaf did not sensibly alter its position. The
sinking movement is due to the downward curvature of the
petiole, no part of which exhibits any structure like that of
a pulvinus. Early on the morning of June 7th a filament was
fixed longitudinally to a young leaf (the third from the summit,
and 28 inches in length), and its movements were traced on
a vertical glass during 72 h., the plant being illuminated from
above through a skylight. Each day the leaf fell in a nearly
straight line from 7 a.m. to 5 p.m., after which hour it was so
much inclined downwards that the movement could no longer
be traced; and during the latter part of each night, or early in
the morning, the leaf rose. It therefore circumnutated in a
very simple manner, making a single large ellipse every 24 h.,
for the ascending and descending lines did not coincide. On
each successive morning it stood at a less height than on the
previous one, and this was probably due, partly to the increasing
age of the leaf, and partly to the illumination being insufficient ;
for although the leaves are very slightly heliotropic, yet, accord-
ing to Mr. Lynch’s and our own observations, their inclination
during the day is determined by the intensity of the light. On
the third day, by which time the extent of the descending
movement had much decreased, the line traced was plainly
much more zigzag than on any previous day, and it appeared
as if some of its powers of movement were thus expended. At
10 p.m. on June 7th, when the leaf depended vertically, its move-
ments were observed by a mark being placed behind it, and the
end of the attached filament was seen to oscillate slowly and
slightly from side to side, as well as upwards and downwards.
Phyllanthus Niruri (Euphorbiaces).— The leaflets of this
plant sleep, as described by Pfeffer,* in a remarkable manner,
apparently like those of Cassia, for they sink downwards at
night and twist round, so that their lower surfaces are turned
* ¢Die Period, Beweg.,’ p. 159,
*
Guar. VIL SLEEP OF LEAVES 389
outwards. They are furnished, as might have been expectod
from this complex kind of movement, with a pulvinus.
GYMNOSPERMS.
Pinus Nordmanniana (Coniferee).—M. Chatin states* that the
leaves, which are horizontal during the day, rise up at night, so
as to assume a position almost perpendicular to the branch froma
which they arise; we presume that he here refers to a horizontal
branch. He adds: “En méme temps, ce mouvement d’érection
est accompagné d’un mouvement de torsion imprimé & la partie
basilaire de la feuille, et ponvant souvent parcourir un arc de
90 degrés.” As the lower surfaces of the leaves are white,
whilst the upper are dark green, the tree presents a widely
different appearance by day and night. The leaves on a small
tree in a pot did not exhibit with us any nyctitropic move-
ments. We have seen in a former chapter that the leaves of
Pinus pinaster and Austriuca are continually circumnutating.
MoNocoTYLEDoNs.
Thalia dealbata (Cannacess).—The leaves of this plant sleep
by turning vertically upwards; they are furnished with a well-
developed pulvinus. It is the only instance known to us of
a very large leaf sleeping. The blade of a young leaf, which
was as yet only 13} inches in length and 63 in breadth, formed
at noon an angle with its tall petiole of 121°, and at night stood
vertically in a line with it, and so had risen 59°. The actual
distance travelled by the apex (as measured by an orthogonic
tracing) of another large leaf, between 7.30 a.m. and 10P.m., was
10} inches. The circumnutation of two young and dwarfed
leaves, arising amongst the taller leaves at the base of the plant,
was traced on a vertical glass during two days. On the first day
the apex of one, and on the second day the apex of the other leaf,
described between 6.40 a.m. and 4 pm. two ellipses, the longer
axes of which were extended in very different directions from the
lines representing the great diurnal sinking and nocturnal rising
movement.
Maranta arundinacea (Cannaceze).—The blades of the leaves,
which are furnished with a pulvinus, stand horizontally during
* «Comptes Rendus,’ Jan. 1876, p. 171.
390 MODIFIED CIRCUMNUTATION. Cuar. VII
the day or between 10° and 20° above the horizon, and at night
vertically upwards. They therefore rise between 70° and 90° at
night. The plant was placed at noon in the dark in the hot-
house, and on the following day the movements of the leaves
were traced. Between 8.40 and 10.30 a.m. they rose, and then
fell greatly till 1.37 p.m. But by 3p.m. they had again risen a
little, and continued to rise during the rest of the afternoon and
night; on the following morning they stood at the same level as
on the previous day. Darkness, therefore, during a day and a
half does not interfere with the periodicity of their movements.
On a warm but stormy evening, the plant whilst being brought
into the house, had its leaves violently shaken, and at night not
one went to sleep. On the next morning the plant was taken
back to the hot-house, and again at night the leaves did not
sleep; but on the ensuing night they rose in the usual manner
between 70° and 80°. This fact is analogous with what we
have observed with climbing plants, namely, that much agitation
checks for a time their power of circumnutation ; but the effect
in this instance was much more strongly marked and prolonged.
Colocasia antiquorum (Caladium esculentum, Hort.) (Aroides),
—The leaves of this plant sleep by their blades sinking in the
evening, so as to stand highly inclined, or even quite vertically
with their tips pointing to the ground. They are not provided
with a pulvinus. The blade of one stood at noon 1° beneath the
horizon; at4.20 p.m., 20°; at 6p.m., 48°; at 7.20 p.m.,69°; and at
8.30 P.m., 68°; so it had now begun torise; at 10.15 p.m. it stood
at 65°, and on the following early morning at 11° beneath the
horizon. The circumnutation of another young leaf (with its
petiole only 35 inches, and the blade 4 inches in length), was
traced on a vertical glass during 48 h.; it was dimly illuminated
through a skylight, and this seemed to disturb the proper perio-
dicity of its movements. Nevertheless, the leaf fell greatly
during both afternoons, till either 7.10 pm. or 9 p.m., when it
rose a little and moved laterally. By an early hour on both
mornings, it had assumed its diurnal position. The well-marked
lateral movement for a short time in the early part of the night,
was the only interesting fact which it presented, as this caused
the ascending and descending lines not to coincide, in accord-
ance with the general rule with circumnutating organs. The
movements of the leaves of this plant are thus of the most
simple kind; and the tracing is not worth giving. We have
seen that in another genus of the Aroidez, namely, Pistia, the
Cnar. VIL. SLEEP OF LEAVES. 391
leaves rise so much at night that they may almost be said te
sleep. '
Strephium floribundwm* (Graminee) — The oval leaves are
provided with a pulvinus, and are extended horizontally or
declinéd a little beneath the horizun during the day. Those
on tho upright culms simply rise up vertically at night, so
thet their tips are directed towards the zenith. (Fig. 164)
Fig. 164.
Strephium floribundum: culms with leaves during the day, and when aslzep
atnight. Figures reduced.
Horizontally extended leaves arising from much inclined or
almost horizontal culms, move at night so that their tips
point towards the apex of the culm, with one lateral marzin
directed towards the zenith; and in order to assume this
position the leaves have to twist on their own axes through au
angle of nearly 90°. Thus the surface of the blade always stands
vertically, whatever may be the position of the midrib or of the
leaf as a whole.
The circumnutation of a young leaf (2°3 inches in length) was
traced during 48 h. (Fig. 165). The movement was remarkably
simple; the leaf descended from before 6.40 a.m. until 2 or
2.50 p.m, and then rose so as to stand vertically at about 6 P.m.,
descending again late in the night or in the very early morning.
* A. Brongniart first observed a Soc. Bot. de France,’ tom. vii
that the leaves of this plant and 1860, p. 470.
of Marsilea sleep: see ‘ Bull. de
26
892 MODIFIED CIRCUMNUTATION. Cuar. VIL
Om the second day the descending line zigzagged slightly. As
Fig. 165.
r
Strephium floribundum : cireamnu-
’ tation and nyctitropic movement
of a leaf, traced from 9 a.m. June
26th to 8.45 a.m. 27th ; filament
fixed along the midrib. Apex of
leaf 8} inches from the vertical
giass; plant illuminated from
above. Temp. 23}°-243° C.
usual, the ascending and de-
scending lines did not coincide.
On another occasion, when the
temperature was a little higher,
viz., 22° 263° C., a leaf was
observed 17 times between 8.50
Am. and 12.16 p.m.; it changed
its course by as much as a
rectangle six times in this in-
terval of 8 h. 26 m., and de-
scribed two irregular triangles
and a half. The leaf, therefore,
on this occasion circumnutated
rapidly and in a complex
manner.
ACOTYLEDONS.
Marsilea quad. ifoliuta (Mar-
sileacez). —The shape of a leaf,
expanded horizontally during
the day, is shown at A (Fig. 166).
Each leaflet is provided with
a well-developed pulvinus.
When the leaves sleep, the two
terminal leaflets rise up, twist
half round and come into con-
tact with one another (B), and
are afterwards embraced by the
two lower leaflets (C); so that
the four leaflets with. their lower
surfaces turned outwards form
a vertical packet. The curva-
ture of the summit of the petiole
of the leaf figured asleep, is
merely accidental. The plant
was brought into a room, where
the temperature was only a little
above 60° F., and the movement
of one of the leaflets (the petiole
having been secured) was traced
Cuar VI SLEEP OF LEAVES. 393
during 24h. (Fig. 167). The leaf fell from the early morning
till 1.50 p.m., and then rose till 6 p.u., when it was asleep. A
A. B Cc,
arsilea quadrifolia'a: A, leaf during the day, seen from vertically above
B, leaf beginning to go to sleep, seen laterally; C, the same asleep.
Figures reduced to one-half of natural scale.
vertically dependent glass filament was now fixed to one of the
terminal and inner leaflets; and part of the tracing in Fig. 167,
after 6 P.M., shows that it continued to sink, making one zigzag,
until 10.40 p.m. At 6.45 a.m. on the following morning, the leaf
was awaking, and the filament pointed above the vertical glass,
Fig. 167.
G’p.m.
8°45am7®
L50'pm.
Marsilea juadrifoliatu ; circumnutation and nyctitropic movement of leaflet
traced on vertical glass, during nearly 24 h. Figure reduced to two-
thirds of original scale. Plant kept at rather too low a temperature.
but by 8.25 am. it occupied the position shown in the figure.
The diagram differs greatly in appearance from most of those
previously given; and this is due to the leaflet twisting and
moving laterally as it approaches and comes into conta:t with
394 MODIFIED CIRCUMNUTATION. Cuap. VII
its fellow. The movement of another leaflet, when asleep,
was traced between 6 p.m. and 10.85 p.m., and it clearly cir-
cumnutated, for it continued for two hours to sink, then rose,
and then sank still lower than it was at 6 p.m. It may be
seen in the preceding figure (167) that the leaflet, when the
plant was subjected to a rather low temperature in the house
descended and ascended during the middle of the day in a
somewhat zigzag line; but when kept in the hot-house from
9am. to3 p.m. at ahigh but varying temperature (viz., between
72° and 83° F.) a leaflet (with the petiole secured) circumnutated
rapidly, for it made three large vertical ellipses in the course of
the six hours. According to Brongniart, Marstlea pubescens sleeps
like the present species. These plants are the sole cryptogamic
ones known to sleep.
Summary and Concluding Remarks on the Nyctitropic
or Sleep-movements of Leaves.—That these movements
are in some manner of high importance to the plants
which exhibit them, few will dispute who have ob-
served how complex they sometimes are. Thus with
Cassia, the leaflets which are horizontal during the
day not only bend at night vertically downwards with
the terminal pair directed considerably backwards, but
they also rotate on their own axes, so that their lower
surfaces are turned outwards. The terminal leaflet
of Melilotus likewise rotates, by which movement one
of its lateral edges is directed upwards, and at the
same time it moves either to the left or to the right,
until its upper surface comes into contact with that ot
the lateral leaflet on the same side, which has like-
wise rotated on its own axis. With Arachis, all four
leaflets form together during the night a single
vertical packet; and to effect this the two anterior
leaflets have to move upwards and the two posterior
ones forwards, besides all twisting on their own axes.
In the genus Sida the leaves of some species move at
night througk an angle of 90° upwards, and of others
Crap. VII. SUMMARY ON SLEEP OF LEAVES. 395
through the same angle downwards. We have seen a
similar difference in the nyctitropic movements of the
cotyledons in the genus Oxalis. In Lupinus, again,
the leaflets move either upwards or downwards; and
in some species, for instance DL. luteus, those on one
side of the star-shaped leaf move up, and those on the
opposite side move down ; the intermediate ones rota-
{ing on their axes ; and by these varied movements, the
whole leaf forms at night a vertical star instead of a
horizontal one, as during the day. Some leaves and
leaflets, besides moving either upwards or downwards,
become more or less folded at night, as in Bauhinia
and in some species of Oxalis. The positions, indeed,
which leaves occupy when asleep are almost infinitely
diversified ; they may point either vertically upwards
or downwards, or, in the case of leaflets, towards the
apex or towards the base of the leaf, or in any inter-
mediate position. They often rotate at least as much
as 90° on their own axes. The leaves which arise
from upright and from horizontal or much inclined
branches on the same plant, move in some few cases
in a different manner, as with Porlieria and Strephium.
The whole appearance of many plants is wonderfully
changed at night, as may be seen with Oxalis, and
still more plainly with Mimosa. A bush of Acacia
Farnesiana appears at night as if covered with little
dangling bits of string instead of leaves. Excluding
a few genera not seen by ourselves, about which we
are in doubt, and excluding a few others the leaflets of
which rotate at night, and do not rise or sink much,
there are 37 genera in which the leaves or leaflets rise,
often moving at the same time towards the apex or
towards the base of the leaf, and 32 genera in which
they sink at night.
The nyctitropic movements of leaves, leaflets, and
B06 MODIFIED CIRCUMNUTATION. Cnar. VII
petioles are effected in two different ways ; firstly, by
alternately increased growth on their opposite sides,
preceled by increased turgescence of the cells; and
secondly by means of a pulvinus or aggregate of small
cells, generally destitute of chlorophyll, which become
alternately more turgescent on nearly opposite sides;
and this turgescence is not followed by growth except
during the early age of the plant. A pulvinus seems
to be formed (as formerly shown) by a group of cells
ceasing to grow at a very early age, and therefore does
not differ essentially from the surrounding tissues.
The cotyledons of some species of Trifolium are pro-
vided with a pulvinus, and others are destitute of one,
and so it is with the leaves in the genus Sida. We
see also in this same genus gradations in the state of
the development of the pulvinus; and in Nicotiana
we have what may probably be considered as the
commencing development of one. The nature of the
movement is closely similar, whether a pulvinus is
absent or present, as is evident from many of the
diagrams given in this chapter. It deserves notice
that when a pulvinus is present, the ascending and
descending lines hardly ever coincide, so that ellipses
are habitually described by the leaves thus provided,
whether they are young or so old as to have quite
ceased growing. This fact of ellipses being described,
shows that the alternately increased turgescence of
the cells does not occur on exactly opposite sides of the
pulvinus, any more than the increased growth which
causes the movements of leaves not furnished with
pulvini. When a pulvinus is present, the nyctitropic
movements are continued for a very much longer
period than when such do not exist. This has been
amply proved in the case of cotyledons, and Pfeffer
has given observations to the same effect with respect
Cuar. VII SUMMARY ON SLEEP OF LEAVES. 397
to leaves. We have seen that a leaf of Mimosa
pudica continued to move in the ordinary manner,
though somewhat more simply, until it withered and
died. It may be added that some leaflets of Trifolium
pratense were pinned open during 10 days, and on the
first evening after being released they rose up and
slept in the usual manner. Besides the long con-
tinuance of the movements when effected by the aid
of a pulvinus (and this appears to be the final cause
of its development), a twisting movement at night, as
Pfeffer has remarked, is almost confined to leaves thus
provided.
It is a very general rule that the first true leaf,
though it may differ somewhat in shape from the
leaves on the mature plant, yet sleeps like them ; and
this occurs quite independently of the fact whether or
not the cotyledons themselves sleep, or whether they
sleep in the same manner. But with Phaseolus Row-
burghii the first unifoliate leaves rise at night almost
sufficiently to be said to sleep, whilst the leaflets of
the secondary trifoliate leaves sink vertically at night.
On young plants of Sida rhombefolia, only a few
inches in height, the leaves did not sleep, though on
rather older plants they rose up vertically at night.
On the other hand, the leaves on very young plants of
Cytisus fragrans slept in a conspicuous manner, whilst
on old and vigorous bushes kept in the greenhouse,
the leaves did not exhibit any plain nyctitropic move-
ment. In the genus Lotus the basal stipule-like
leaflets rise up vertically at night, and are provided
with pulvini.
As already remarked, when leaves or leaflets change
their position greatly at night and by complicated
movements, it can hardly be doubted that these must
be in some manner beneficial to the plant. If so, we
398 MODIFIED CIRCUMNUTATION Oxap. VIE
must extend the same conclusion to a large number of
sleeping plants; for the most complicated and the
simplest nyctitropic movements are connected together
by the finest gradations. But owing to the causes spe-
cified in the beginning of this chapter, it is impossible
in some few cases to determine whether or not certain
movements should be called nyctitropic. Generally,
the position which the leaves occupy at night indi-
cates with sufficient clearness, that the benefit thus
derived, is the protection of their upper surfaces from
radiation into the open sky, and in many cases the
mutual protection of all the parts from cold by their
being brought into close approximation. It should be
remembered that it was proved in the last chapter, that
leaves compelled to remain extended horizontally at
night, suffered much more from radiation than those
which were allowed to assume their normal vertical
position.
The fact of the leaves of several plants not sleeping
unless they have been well illuminated during the
day, made us for a time doubt whether the pro-
tection of their upper surfaces from radiation was in
all cases the final cause of their well-pronounced
nyctitropic movements. But we have no reason to
suppose that the illumination from the open sky,
during even the most clouded day, is insufficient for
this purpose; and we should bear in mind that leaves
which are shaded from being seated low down on the
plant, and which sometimes do not sleep, are likewise
protected at night from full radiation. Nevertheless,
we do not wish to deny that there may exist cases in
which leaves change their position considerably at
night, without their deriving any benefit from such
movements.
Although with sleeping plants the blades almost
Cuav. VII. SUMMARY ON SLEEP OF LEAVES. 399
always assume at night a vertical, or nearly vertical
pusition, it is a point of complete indifference whether
the apex, or the base, or one of the lateral edges, is
directed to the zenith. It is a rule of wide generality,
than whenever there is any difference in the degree of
exposure to radiation between the upper and the lower
surfaces of leaves and leaflets, it is the upper which is
the least exposed, as may be seen in Lotus, Cytisus,
Trifolium, and other genera. In several species of
Lupinus the leaflets do not, and apparently from
their structure cannot, place themselves vertically at
night, and consequently their upper surfaces, though
highly inclined, are more exposed than the lower; and
here we have an exception to our rule. But in other
species of this genus the leaflets succeed in placing
themselves vertically; this, however, is effected by a
very unusual movement, namely, by the leaflets on
the opposite sides of the same leaf moving in opposite
directions.
It is again a very common rule that when leaflets
come into close contact with one another, they do so
by their upper surfaces, which are thus best protected.
In some cases this may be the direct result of their
rising vertically; but it is obviously for the pro-
tection of the upper surfaces that the leaflets of
Cassia rotate in so wonderful a manner whilst sinking
downwards; and that the terminal leaflet of Melilotus
rotates and moves to one side until it meets the lateral
leaflet on the same side. When opposite leaves or
leaflets sink vertically down without any twisting,
their lower surfaces approach each other and some-
times come into contact; but this is the direct and
inevitable result of their position. With many species
of Oxalis the lower surfaces of the adjoining leaflets
are pressed together, and are thus better protected
400 MODIFIED CIRCUMNUTATION, Cuar. VIL
than the upper surfaces; but this depends merely ou
each leaflet becoming folded at night so as to be able
to sink vertically downwards. ‘The torsion or rotation
of leaves and leaflets, which occurs in so many cases,
apparently always serves to bring their upper surfaces
into close approximation with one another, or with
other parts of the plant, for their mutual protection.
We see this best in such cases as those of Arachis,
Mimosa albida, and Marsilea, in which all the leaflets
form together at night a single vertical packet. If
with Mimosa pudica the opposite leaflets had merely
moved upwards, their upper surfaces would have come
into contact and been well protected; but as it is,
they all successively move towards the apex of the
leaf; and thus not only their upper surfaces are pro-
tected, but the successive pairs become imbricated and
mutually protect one another as well as the petioles.
This imbrication of the leaflets of sleeping plants is a
common phenomenon.
The nyctitropic movement of the blade is gene-
rally effected by the curvature of the uppermost part
of the petiole, which has often been modified into a
pulvinus; or the whole petiole, when short, may be
thus modified. But the blade itself sometimes curves
or moves, of which fact Bauhinia offers a striking
instance, as the two halves rise up and come inte
close contact at night. Or the blade and the upper
part of the petiole may both move. Moreover, the
petiole as a whole commonly either rises or sinks at
night. This movement is sometimes large: thus the
petioles of Cassia pubescens stand only a little above
the horizon during the day, and at night rise up
almost, or quite, perpendicularly. The petioles of the
younger leaves of Desmodium gyrans also rise up ver-
tically at night. On the other hand, with Amphi-
Cuap. VII. SUMMARY ON SLEEP OF LEAVES. 401
carpea, the petioles of some leaves sank down as
much as 57° at night; with Arachis they sank 39°,
and then stood at right angles to the stem. Gene-
rally, when the rising or sinking of several petioles on
the same plant was measured, the amount differed
greatly. This is largely determined by the age of the
leaf: for instance, the petiole of a moderately old leaf
of Desmodium gyrans rose only 46°, whilst the young
ones rose up vertically; that of a young leaf of Cassia
floribunda rose 41°, whilst that of an older leaf rose
only 12°. It is a more singular fact that the age of
the plant sometimes influences greatly the amount of
movement; thus with some young seedlings of a Bau-
hinia the petioles rose at night 30° and 34°, whereas
those on these same plants, when grown to a height
of 2 or 3 feet, hardly moved at all. The position of
the leaves on the plant as determined by the light,
seems also to influence the amount of movement
of the petiole; for no other cause was apparent
why the petioles of some leaves of Melilotus officinalis
rose as much as 59°, and others only 7° and 9° at
night.
In the case of many plants, the petioles move at
night in one direction and the leaflets in a directly
opposite one. Thus, in three genera of Phaseolee the
leaflets moved vertically downwards at night, and the
petioles rose in two of them, whilst in the third they
sank. Species in the same genus often differ widely
in the movements of their petioles. Even on the same
plant of Lupinus pubescens some of the petioles rose 30°,
others only 6°, and others sank 4° at night. ‘The
leaflets of Cassia Barclayana moved so little at night
that they could not be said to sleep, yet the petioles
of some young leaves rose as much as 34°. These
several facts ay parently indicate that the movements
402 MODIFIED CIRCUMNUTATION. Cuar. VIL
of the petioles are not performed for any special pur-
pose; though a conclusion of this kind is generally
rash. When the leaflets sink vertically down at night
and the petioles rise, as often occurs, it is certain that
the upward movement of the latter does not aid the
l-aflets in placing themselves in their proper posi-
tion at night, -for they have to move through a
greater angular space than would otherwise have been
necessary.
Notwithstanding what has just been said, it may be
strongly suspected that in some cases the rising of
the petioles, when considerable, does beneficially serve
the plant by greatly reducing the surface exposed to
radiation at night. If the reader will compare the
two drawings (Fig. 155, p. 371) of Cassia pubescens,
copied from photographs, he will see that the dia-
meter of the plant at night is about one-third of
what it is by day, and therefore the surface exposed
to radiation is nearly nine times less, A similar
conclusion may be deduced from the drawings (Fig.
149, p. 858) of a branch awake and asleep of Des-
modium gyrans. So it was in a very striking manner
with young plants of Bauhinia, and with Ozals
Ortegesit,
We are led to an analogous conclusion with respect
to the movements of the secondary petioles of certain
pinnate leaves. The pinne of Mimosa pudica con-
verge at night; and thus the imbricated and closed
leaflets on each separate pinna are all brought close
together into a single bundle, and mutually protect
one another, with a somewhat smaller surface exposed
to radiation. With Albizziu lophantha the pinne close
together in the same manner. Although the pinne
of Acacia Farnesiana do not converge much, they
sink downwards. Those of Nepiunia oleracea likewise
Cuap. VII. SUMMARY ON SLEEP OF LEAVES. 403
move downwards, as well as backwards, towards the
base of the leaf, whilst the main petiole rises. With
Schrankia, again, the pinne are depressed at night.
Now in these three latter cases, though the pinne
do not mutually protect one another at night, yet
after. having sunk down they expose, as does a
dependent sleeping leaf, much less surface to the
zenith and to radiation than if they had remained
horizontal.
Any one who had never observed continuously a
sleeping plant, would naturally suppose that the leaves
moved only in the evening when going to sleep, and
in the morning when awaking; but he would be quite
mistaken, for we have found no exception to the rule
that leaves which sleep continue to move during the
whole twenty-four hours; they move, however, more
quickly when going to sleep and when awaking than
at other times. That they are not stationary during
the day is shown by all the diagrams given, and by
the many more which were traced. It is troublesome
to observe the movements of leaves in the middle of
the night, but this was done in a few cases; and
tracings were made during the early part of the night
of the movements, in the case of Oxalis, Amphicarpma,
two species of Erythrina, a Cassia, Passiflora, Euphorbia
and Marsilea; and the leaves after they had gone to
sleep, were found to be in constant movement. When,
however, opposite leaflets come into close contact with
one another or with the stem at night, they are, as we
believe, mechanically prevented from moving, but this
point was not sufficiently investigated.
When the movements of sleeping leaves are traced
during twenty-four hours, the ascending and descend-
ing lines do not coincide, except occasionally and by
accident for a short space; so that with many plants a
404 MODIFIED CIRCUMNUTATION. Caar. VIL.
single large ellipse is described during each twenty-four
hours. Such ellipses are generally narrow and ver-
tically directed, for the amount of lateral movement is
small. That there is some lateral movement is shown
by the ascending and descending lines not coinciding,
and occasionally, as with Desmodium gyrans and Thalia
dealbata, it was strongly marked. In the case of Meli-
lotus the ellipses described by the terminal leafiet
during the day are laterally extended, instead of ver-
tically, as is usual; and this fact evidently stands in
relation with the terminal leaflet moving laterally
when it goes to sleep. With the majority of sleeping
plants the leaves oscillate more than once up and
down in the twenty-four horrs; so that frequently two
ellipses, one of moderate size, and one of very large size
which includes the nocturnal movement, are described
within the twenty-four hours. For instance, a leaf
which stands vertically up during the night will sink
in the morning, then rise considerably, again sink in
the afternoon, and in the evening reascend and assume
its vertical nocturnal position. It will thus describe,
in the course of the twenty-four hours, two ellipses of
unequal sizes. Other plants describe within the same
time, three, four, or five ellipses. Occasionally the
longer axes of the several ellipses extend in different
directions, of which Acacia Farnesiana offered a good
instance. ‘The following cases will give an idea of the
rate of movement: Oxalis acetosella completed two
ellipses at the rate of 1 h. 25 m. for each; Marsilea
quadrifoliata, at the rate of 2h.; Trifolium subterraneum,
one in 3 h. 80 m.; and Arachis hypogea, in 4 h. 50 m.
But the number of ellipses described within a given
time depends largely on the state of the plant and
ou the conditions to which it is exposed. It often hap-
pens that a single ellipse may be described during one
Cuar. VII. SUMMARY ON SLEEP OF LEAVES. 405
day, and two on the next. Erythrina corallodendron
made four ellipses on the first day of observation
and only a single one on the third, apparently owing
to having been kept not sufficiently illuminated and
perhaps not warm enough. But there seems likewise
to be an innate tendency in different species of the
same genus to make a different number of ellipses in
the twenty-four hours: the leaflets of Trifolium repens
made only one; those of T. resupinatum two, and those
of T. subterraneum three in this time. Again, the
leaflets of Oxulis Plumiertt made a single ellipse; those
of O. bupleurifolia, two; those of O. Valdiviana, two or
three; and those of O. acetosella, at least five in the
twenty-four hours.
The line followed by the apex of a leaf or leaflet,
whilst describing one or more ellipses during the day,
is often zigzag, either throughout its whole course or
only during the morning or evening: Robinia offered
an instance of zigzagging confined to the morning,
and a similar movement in the evening is shown in
the diagram (Fig. 126) given under Sida. The amount
of the zigzag movement depends largely on the plant
being placed under highly favourable conditions. But
even under such favourable conditions, if the dots which
mark the position of the apex are made at consider-
able intervals of time, and the dots are then joined,
the course pursued will still appear comparatively
simple, although the number of the ellipses will be
increased; but if dots are made every two or three
minutes and these are joined, the result often is that
all the lines are strongly zigzag, many small loops,
triangles, and other figures being also formed. This
fact is shown in two parts of the diagram (Fig. 150)
of the movements of Desmodium gyrans. Strephiwm
floribundum, observed under a high temperature,
406 MODIFIED CIRCUMNUTATION. Cuav VIL
made several little triangles at the rate of 43 m.
for each. Mimosa pudica, similarly observed, de-
scribed three little een in 67 m.; and the apex
of a leaflet crossed 53,5 of an inch in a second, or
0:12 inch in a mifematé, The leaflets of kyerrlioa
made a countless number of little oscillations when
the temperature was high and the sun shining. The
zigzag movement may in all cases be considered as
an attempt to form small loops, which are drawn out
by a prevailing movement in some one direction. The
rapid gyrations of the little lateral leaflets of Des-
modium belong to the same class of movements,
somewhat exaggerated in rapidity and amplitude.
The jerking movements, with a small advance and
still smaller retreat, apparently not exactly in the
same line, of the hypocotyl of the cabbage and of
the leaves of Dionza, as seen under the microscope,
all probably come under this same head. We may
suspect that we here see the energy which is freed
during the incessant chemical changes in progress in
the tissues, converted into motion. Finally, it should
be noted that leaflets and probably some leaves, whilst
describing their ellipses, often rotate slightly on their
axes; so that the plane of the leaf is directed first to
one and then to another side. This was plainly seen
to be the case with the large terminal leaflets of Des-
modium, Erythrina and Amphicarpeea, and is probably
common to all leaflets provided with a pulvinus.
With ~espect to the periodicity of the movements of
sleeping leaves, Pfeffer* has so clearly shown that
this depends on the daily alternations of light and
darkness, that nothing farther need be said on this
* ‘Die Periodischen Bewegungen der Blattorgane,’ 1875, p. 80, et
passim.
Caap. VII SUMMARY ON SLEEP OF LEAVES. 407
head. But we may recall the behaviour of Mimosa
in the North, where the sun does not set, and the
complete inversion of the daily movements by artificial
light and darkness. It has also been shown by us,
that although leaves subjected to darkness for a mode-
rately long time continue to circumnutate, yet the
periodicity of their movements is soon greatly dis-
turbed, or quite annulled. The presence of light or
its absence cannot be supposed to be the direct cause:
of the movements, for these are wonderfully diversified
even with the leaflets of the same leaf, although all
have of course been similarly exposed. The move-
ments depend on innate causes, and are of an adaptive
nature. The alternations of light and darkness
merely give notice to the leaves that the period has.
arrived for them to move in a certain manner. We:
may infer from the fact of several plants (Tropeolum,
Lupinus, &c.) not sleeping unless they have been well.
iJuminated during the day, that it is not the actual
decrease of light in the evening, but the contrast
between the amount at this hour and during the early
part of the day, which excites the leaves to modify
their ordinary mode of circumnutation.
As the leaves of most plants assume their proper:
diurnal position in the morning, although light be:
excluded, and as the leaves of some plants continue to:
move in the normal manner in darkness during at
least a whole day, we may conclude that the periodi-
city of their movements is to a certain extent in-
herited.* The strength of such inheritance differs
* Pfeffer denies such inherit- ‘‘Nachwirkung,” or the after-
ance; he attributes (‘ Die Period.
Bewegungen,’ pp. 30-56) the
periodicity when prolonged for
a day or two in darkness, to
27
effects of light and darkness.
But we are unable to follow his
train of reasoning. ‘There doea
not seem to be any more reason fox
408 MODIFIED CIRCUMNUTATION. Cuar. VII
much in different species, and seems never to be rigid ;
for plants have been introduced from all parts of the
world into our gardens and greenhouses; and if their
movements had been at all strictly fixed in relation to
the alternations of day and night, they would have
slept in this country at very different hours, which
is not the case. Moreover, it has been observed that
sleeping plants in their native homes change their
times of sleep with the changing seasons. *
We may now turn to the systematic list (p. 320).
This contains the names of all the sleeping plants
known to us, though the list undoubtedly is very
imperfect. It may be premised that, as a general
rule, all the species in the same genus sleep in
nearly the same manner. But there are some ex-
ceptions; in several large genera including many
sleeping species (for instance, Oxalis), some do not
sleep. One species of Melilotus sleeps like a Tri-
folium, and therefore very differently from its con-
‘geners; so does one species of Cassia. In the genus
Sida, the leaves either rise or fall at night; and with
Lupinus they sleep in three different methods. Re-
turning to the list, the first point which strikes us, is
that there are many more genera amongst the Legu-
minose (and in almost every one of the Leguminous
tribes) than in all the other families put together;
and we are tempted to connect this fact with the great
attributing such mov ments to this
cause than, for instance, the in-
herited habit of winter and
summer wkcat to grow best at
different seasons; fir this habit
is lost after a few years, like the
‘movements of leav:s in darkness
-after a few days. No doubt some
effict must be produced on the
seeds hy the long-continucd culti-
vation of the pareut-plants under
difterent climates, but no one pro-
bably would call this the “ Nach-
wirkung ” of the climates,
= Pfeffer, ibid., p. 46.
Cuap VII. SUMMARY ON SLEEP OF LEAVES. 405
mobility of the stems and leaves in this family, as
shown by the large number of climbing species which
it contains. Next to the Leguminose come the Mal-
vacee, together with some closely allied families. But
by far the most important point in the list, is that we
meet with sleeping plants in 28 families, in all the
great divisions of the Phanerogamic series, and in one
Cryptogam. Now, although it is probable that with
the Leguminosz the tendency to sleep may have been
inherited from one or a few progenitors and possibly
so in the cohorts of the Malvales and Chenopodiales,
yet it is manifest that the tendency must have been
acquired by the several genera in the other families,
quite independently of one another. Hence the ques-
tion naturally arises, how has this been possible ?
and the answer, we cannot doubt, is that leaves owe
their nyctitropic movements to their habit of cir-
cumnutating,—a habit common to all plants, and
everywhere ready for any beneficial development or
modification.
It has been shown in the previous chapters that the
leaves and cotyledons of all plants are continually
moving up and down, generally to a slight but some-
times to a considerable extent, and that they describe
either one or several ellipses in the course of twenty-
four hours; they are also so far affected by the alter-
nations of day and night that they generally, or
at least often, move periodically to a small extent;
and here we have a basis for the development of the
greater nyctitropic movements. That the movements
of leaves and cotyledons which do not sleep come
within the class of circumnutating movements cannot
be doubted, for they are closely similar to those of
hypocotyls, epicotyls, the stems of mature plants, and
of various other organs. Now, if we take the simplest
410 MODIFIED CIRCUMNUTATION. Cuap. VIL
case of a sleeping leaf, we see that it makes a single
ellipse in the twenty-four hours, which resembles one
described by a non-sleeping leaf in every respect, except
that itis much larger. In both cases the course pursued
is often zigzag. As all non-sleeping leaves are inces-
santly circumnutating, we must conclude that a part
at least of the upward and downward movement of one
that sleeps, is due to ordinary circumnutation; and it
seems altogether gratuitous to rank the remainder of
the movement under a wholly different head. With
a multitude of climbing plants the ellipses which they
describe have been greatly increased for another pur-
pose, namely, catching hold of a support. With these
climbing plants, the various circumnutating organs have
been so far modified in relation to light that, differently
from all ordinary plants, they do not bend towards it.
With sleeping plants the rate and amplitude of the .
movements of the leaves have been so far modified in
relation to light, that they move in a certain direction
with the waning light of the evening and with the
increasing light of the morning more rapidly, and to
a greater extent, than at other hours
But the leaves and cotyledons of many non-sleeping
plants move in a much more complex manner than in
the cases just alluded to, for they describe two, three,
or more ellipses in the course of a day. Now, if a
plant of this kind were converted into one that slept,
one side of one of the several ellipses which each
leaf daily describes, would have to be greatly increased
in length in the evening, until the leaf stood ver-
tically, when it would go on circumnutating about the
same spot. On the following morning, the side of
another ellipse would have to be similarly increased
in length, so as to bring the leaf back again into its
diurnal position, when it would again circumnutate
Cuar. VII SUMMARY ON SLEEP OF LEAVES. 411
until the evening. If the reader will lock, for in-
stance, at the diagram (Fig. 142, p. 351), representing
the nyctitropic movements of the terminal leaflet of
Trifolium subterraneum, remembering that the curved
broken lines at the top ought to be prolonged much
higher up, he will see that the great rise in the evening
and the great fall in the morning together form a
large ellipse like one of those described during the
daytime, differing only in size. Or, he may look at
the diagram (Fig. 103, p. 236) of the 34 ellipses
described in the course of 6 h. 35 m. by a leaf of
Lupinus spectosus, which is one of the species in this
genus that does not sleep; and he will see that by
merely prolonging upwards the line which was already
rising late in the evening, and bringing it down
again next morning, the diagram would represent the
movements of a sleeping plant.
With those sleeping plants which describe several
ellipses in the daytime, and which travel in a strongly
zigzag line, often making in their course minute loops,
triangles, &c., if as soon as one of the ellipses begins
in the evening to be greatly increased in size, dots are
made every 2 or 3 minutes and these are joined, the
line then described is almost strictly rectilinear, in
strong contrast with the lines made during the day-
time. This was observed with Desmodium gyrans and
Mimosa pudica. With this latter plant, moreover, the
pinne converge in the evening by a steady move-
ment, whereas during the day they are continually
converging and diverging to a slight extent. In all
such cases it was scarcely possible to observe the
difference in the movement during the day and even-
ing, without being convinced that in the evening the
plant saves the expenditure of force by not moving
laterally, and that its whole energy is now expeaded
412 MODIFIED CIRCUMNUTATION, Cuap. VIL
in gaining quickly its proper nocturnal position by
a direet course. In several other cases, for instance,
when a leaf after describing during the day one or
more fairly regular ellipses, zigzags much in the
evening, it appears as if energy was being expended,
so that the great evening rise or fall might coin-
cide with the period of the day proper for this
movement.
The most complex of all the movements performed
by sleeping plants, is that when leaves or leaflets,
after describing in the daytime several vertically
directed ellipses, rotate greatly on their axes in the
evening, by which twisting movement they occupy
a wholly different position at night to what they do
during the day. For instance, the terminal leaflets
of Cassia not only move vertically downwards in the
evening, but twist round, so that their lower surfaces
face outwards. Such movements are wholly, or almost
wholly, confined to leaflets provided with a pulvinus.
But this torsion is not a new kind of movement
introduced solely for the purpose of sleep; for it
has been shown that some leaflets whilst describing
their ordinary ellipses during the daytime rotate
slightly, causing their blades to face first to one side
and then to another. Although we can see how the
slight periodical movements of leaves in a vertical
plane could be easily converted into the greater yet
simple nyctitropic movements, we do not at present
know by what graduated steps the more complex
movements, effected by the torsion of the pulvini,
have been acquired. A probable explanation could
be given in each case only after a close investigation
of the movements in all the allied forms.
From the facts and considerations now advanced we
may conclude that nyctitropism, or the sleep of leaves
Cuap. VIL MODIFIED CIRCUMNUTATION. 413
and cotyledons, is merely a modification of their ordi-
nary circumnutating movement, regulated in its period
and amplitude by the alternations of light and dark-
ness. The object gained is the protection of the upper
surfaces of the leaves from radiation at night, often
combined with the mutual protection of the several
parts by their close approximation. In such (ee >
lL
A. B. Cc.
Vicia faba. state of radicles which had been extended horizontally for
23h. 30 m.: A, B, C, tips touched with caustic; D, E, F, tips uncaute-
rised. Lengths of radicles reduced to one-half scale, but by an accident
the beans themselves not reduced in the same degree.
A, B,C (Fig 196), were still horizontal, whilst the three control
specimens had become within 8 h. slightly geotropic, and
strongly so (D, EB, F) in 23h. 30m. A dot had been made on
all six radicles at 10 mm. from their tips, when first placed
horizontally. After the 23 h. 30m. this terminal part, originally
10 mm. in length, had increased in the cauterised specimens to
a mean length of 17:3 mm., and to 15°7 mm. in the control
radicles, as shown in the figures by the unbroken transverse
line; the dotted line being at 10 mm. from the apex. The con-
trol or uncauierised radicles, therefore, had actually grown less
582 SENSITIVENESS TO GRAVITATION. Cuar. XL
than the cauterised; but this no doubt was accidental, fot
radicles of different ages grow at different rates, and the growth
of different individuals is likewise affected by unknown causes.
The state of the tips of these three radicles, which had been
cauterised for a rather longer time than usual, was as follows:
the blackened apex, or the part which had been actually touched
by the caustic, was succeeded by a yellowish zone, due probably
to the absorption of some of the caustic; in A, both zones
together were 1:1 mm. in length, and 1:4 mm. in diameter at the
base of the yellowish zone; in B, the length of both was only
0 7 mm., and the diameter 0’7 mm.; in C, the length was 0°8
mm., and the diameter 1:2 mm.
Three other radicles, the tips of which had been touched with
caustic during 2 or 8 seconds, remained (temp. 58°-59° F )
horizontal for 23h.; the control radicles having, of course,
become geotropic within this time. The terminal growing part,
10 mm. in length, of the cauterised radicles had increased in
this interval to a mean length of 24°5 mm., and of the controls
to a mean of 26mm. A section of one of the cauterised tips
showed that the blackened part was 0°5 mm. in length, of which
0:2mm. extended into the vegetative point; and a faint dis-
coloration could be detected even to 1°6mm. from the apex of
the root-cap.
In another lot of six radivles (temp. 55°-57° F.) the three
control specimens were plainly geotropic in 83 h.; and after 24 h.
the mean length of their terminal part had increased from
10 mm. to21mm. When the caustic was applied to the three
cauterised specimens, it was held quite motionless during
5 seconds, and the result was that the black marks were ex-
tremely minute. Therefore, caustic was again applied, after
83 h., during which time no geotropic action had occurred.
When the specimens were re-examined after an additional
interval of 153 h., one was horizontal and the other two showed,
to our surprise, a trace of geotropism which in one of them
soon afterwards became strongly marked; but in this latter
specimen the discoloured tip was only 2mm. in length. The
growing part of these three radicles increased in 21h. from
10 mm. to an average of 16°5 mm.
It would be superfluous to describe in detail the behaviour
of the 10 remaining cauterised radicles. The corresponding
control specimens all became geotropic in 8h. Of the cauterised,
6 were first looked at after 8h., and one alone showed a trace
Cuar. Xl. TRANSMITTED EFFECTS: VICL‘ 533
of geotropism ; 4 were first looked at after 14h., and one alone
of these was slightly geotropic. After 23-24h.,5 of the 10 were
still horizontal, 4 slightly, and 1 decidedly, geotropic. After
48h. some of them became strongly geotropic. The cauterised
radicles increased greatly in length, but the measurements are
not worth giving.
As five of the last-mentioned cauterised radicles had become in
24h. somewhat geotropic, these (together with three which were
still horizontal) had their positions reversed, so that their tips
were now a little upturned, and they were again touched with
caustic. After 24h. they showed no trace of geotropism; whereas
the eight corresponding control specimens, which had like-
wise been reversed, in which position the tips of several pointed
to the zenith, all became geotropic ; some having passed in the
24h. through an angle of 180°, others through about 135°, and
others through only 90°. The eight radicles, which had been
twice cauterised, were observed for an additional day (i.e. for 48 h.
after being reversed), and they still showed no signs of geotro-
pism. Nevertheless, they continued to grow rapidly; four were
measured 24h. after being reversed, and they had in this time
increased in length betweon 8 and 11 mm.; the other four were
measured 48 h. after being reversed, and these had increased by
20, 18, 23, and 28 mm.
In coming to a conclusion with respect to the effects of cauter-
ising the tips of these radicles, we should bear in mind,
firstly, that horizontally extended control radicles were always
acted on by geotropism, and became somewhat bowed down-
wards in 8 or 9h.; secondly, that the chief seat of the curvature
lies at a distance of from 8 to 6mm. from the tip; thirdly, that
the tip was discoloured by the caustic rarely for more than
1mm. in length; fourthly, that the greater number of the cau-
terised radicles, although subjected to the full influence of
geotropism during the whole time, remained horizontal for 24 h.,
and some for twice as long; and that those which did become
bowed were so only in a slight degree; fifthly, that the cau-
terised radicles continued to grow almost, and sometimes quite,
as well as the uninjured ones along the part which bends most,
And lastly, that a touch on the tip with caustic, if on one side,
far from preventing curvature, actually induces it. Bearing all
these facts in mind, we must infer that under normal conditions
the geotropic curvature of the root is due to an influence trans-
mitted from the apex to the adjoining part where the bending
ASPs SENSITIVENESS TO GRAVITATION. Cuap. XL
takes place; and that when the tip of the root is cauterised it is
unable to originate the stimulus necessary to produce geotropic
curvature.
As wu had observed that grease was highly injurious to some
plants, we determined to try its effects on radicles. When the
cotyledons of Phalaris and Avena were covered with grease
along one side, the growth of this side was quite stopped or
greatly checked, and as the opposite side continued to grow, the
cotyledons thus treated became bowed towards the greased side,
This same matter quickly killed the delicate hypocotyls and
young leaves of certain plants. The grease which we employed
was made by mixing lamp-black and olive oil to such a con-
sistence that it could be laid on in a thick layer. The tips of
five radicles of the bean were coated with it for a length of
3 mm., and to our surprise this part increased in length in 23 h.
to 7°1mm.; the thick layer of grease being curiously drawn
out. It thus could not have checked much, if at all, the growth
of the terminal part of the radicle. With respect to geotropism,
the tips of seven horizontally extended radicles were coated for
a length of 2 mm., and after 24h. no clear difference could be
perceived between their downward curvature and that of an
equal number of control specimens. The tips of 33 other radicles
were coated on different occasions for a length of 8 mm.; and
they were compared with the controls after 8h., 24h., and 48h.
On one occasion, after 24h., there was very little difference in
curvature between the greased and control specimens; but
generally the difference was unmistakable, those with greased
tips being considerably less curved downwards. The whole
growing part (the greased tips included) of six of these radicles
was measured and was found to have increased in 23h. from
10 mm. to a mean length of 17°7 mm.; whilst the corresponding
part of the controls had increased to 20°83 mm. It appears there-
fore, that although the tip itself, when greased, continues to
grow, yet the growth of the whole radicle is somewhat checked,
and that the geotropic curvature of the upper part, which was
free from grease, was in most cases considerably lessened.
Pisum sativum.—Five radicles, extended horizontally over
water, had their tips lightly touched two or three times with dry
caustic. These tips were measured in two cases, and found to
be blackened for a length of only half a millimeter. Five other
radicles were left as controls. The part which is most bowed
through geotropism lies at a distance of several millimeters from
Cuar. XI. TRANSMITTED EFFECTS: PHASEOLUS. 535
the apex. After 24 h., and again after 32 h. from the commence-
ment, four of the cauterised radicles were still horizontal, but
one was plainly geotropic, being inclined at 45° beneath tke-
horizon. The five controls were somewhat geotropic after 7 h.
20m., and after 24 h. were all strongly geotropic; being inclined.
at the following angles beneath the horizon, vz., 59°, 60°, 65°,
57°, and 48°. The length of the radicles was not measured in
cither set, but it was manifest that the cauterised radicles had.
grown greatly.
The following case proves that the action of the caustic by
itself does not prevent the curvature of the radicle. Ten radicles
were extended horizontally on and beneath a layer of damp
friable peat-earth; and before being extended their tips were
touched with dry caustic on the upper side. Ten other radicles
similarly placed were touched on the lower side; and this would
tend to make them bend from the cauterised side; and therefore,
as now placed, upwards, or in opposition to geotropism. Lastly,
ten uncauterised radicles were extended horizontally as controls.
After 24 h. all the latter were geotropic; and the ten with their
tips cauterised on the upper side were equally geotropic; and.
we believe that they became curved downwards before the con--
trols. The ten which had been cauterised on the lower side
presented a widely different appearance: No. 1, however, was.
perpendicularly geotropic, but this was no real exception, for on.
examination under the microscope, there was no vestige of
a coloured mark on the tip, and it was evident that by a mistake
it had not been touched with the caustic. No.2 was plainly
geotropic, being inclined at about 45° beneath the horizon; No.3.
was slightly, and No.4 only just perceptibly geotropic; Nos. 5
and 6 were strictly horizontal; and the four remaining ones were
bowed upwards, in opposition to geotropism. In these four
cases the radius of the upward curvatures (accoiding to Sachs’
cyclometer) was 5mm.,10mm., 30 mm.,and 70mm. ‘This cur-.
vature was distinct long betore the 24h. had elapsed, namely,
after 8h. 45m. from the time when the lower sides of the tips
were touched with the caustic.
Phaseolus multiflorus.—EHight radicles, serving as controls, were
extended horizontally, some in damp friable peat and some in
damp air. They ail became (temp. 20°-21° C.) plainly geo-
tropic in 8h. 30 m., for they then stood at an average angle of 63°
beneath the horizon. A rather greater length of the radicle is
bowed downwards by geotropism than in the case of Vicia fuba
85 ‘
536 SENSITIVENESS TO GRAVITATION. Cuar. XI.
that is to say, rather more than 6mm. as measured from the apex
of the root-cap. Nine other radicles were similarly extended,
three in damp peat and six in damp air, and dry caustic was
held trans erscly to their tips during 4 or 5 seconds. Three of
their tips were afterwards examined: in (1) a length of 0°68 mm.
was discoloured, of which the basal 0:186 mm. was yellow, the
apical part being black; in (2) the discoloration was 0°65 mm.
in Jength, of which the basal 0-04 mm. was yellow; in (3) the dis-
coloration was 0°6 mm. in length, of which the basal 0:13 mm.
was yellow. Therefore less than 1 mm. was affected by the caustic,
but this sufficed almost wholly to prevent geotropic action; for
after 24 h. one alone of the nine cauterised radicles became
slightly geotropic, being now inclined at 10° beneath the horizon ;
the eight others remained horizontal, though one was curved a
little laterally.
The terminal part (10 mm. in length) of the six cauterised
radicles in the damp air, had more than doubled in length in
the 24 h., for this part was now on an average 20°7 mm. long.
The increase in length within the same time was greater in
the control specimens, for the terminal part had grown on an
average from 10 mm. to 26°6 mm. But as the cauterised
‘adicles had more than doubled their length in the 24 h., it is
manifest that they had not been seriously injured by the
caustic. We may here add that when experimenting on the
effects of touching one side of the tip with caustic, too much
was applied at first, and the whole tip (but we believe not more
than 1 mm. in length) of six horizontally extended radicles was
killed, and these continued for two or three days to grow out
horizontally.
Many trials were made, by coating the tips of horizontally
extended radicles with the before described thick grease. The
geotropic curvature of 12 radicles, which were thus coated for
a length of 2 mm., was delayed during the first 8 or 9 h., but
after 24 h. was nearly as great as that of the control speci-
mens. The tips of nine radicles were coated for a length of 3 mm.,
and after 7 h. 10 m. these stood at an average angle of 80°
beneath the horizon, whilst the controls stood at an average of
54°. After 24 h. the two lots differed but little in their degree
of curvature. In some other trials, however, there was a fairly
well-marked difference after 24 h. between those with. greased
‘tips and the controls. The terminal part of eight control speci-
mens increased in 24 h. from 10 mm. to a mean length of
Cuar. XI. TRANSMITTED EFFECTS; CUCURBITA. 537
24°3 mm., whi!st the mean increase of those with greased tips
was 20°7 mm. The grease, therefore, slightly checked the
growth of the terminal part, but this part wes not much
injured; for several radicles which had been greased for a
length of 2 mm. continued to grow during seven days, and were
then only a little shorter than the controls. The appearance
presented by these radicles after the seven days was very
curious, for the black grease had been drawn out into the finest
longitudinal strie, with dots and reticulations, which covered
their surfaces for a length of from 26 to 44 mm., or of 1 to
1:7 inch. We may therefore conclude that grease on the tips
of the radicles of this Phaseolus somewhat delays and lessens
the geotropic curvature of the part which ought to bend
most.
Gossypium. herbaceum—tThe ralicles of this plant bend,
through the action of geotropism, for a length of about 6 mm.
Five radicles, placed horizontally in damp air, had their tips
touched with caustic, and the discoloration extended for a
length of from 2 tol mm. They showed, after 7 h. 45 m. and
again after 23 h., not a trace of geotropism; yet the terminal
portion, 9 mm. in length, had increased on an average to
15°9 mm. Six control radicles, after 7h. 45 m., were all plainly
geotropic, two of them being vertically dependent, and after
23 h. all were vertical, or nearly so.
Cucurbita ovifera.—A large number of trials proved almost
useless, from the three following causes: Firstly, the tips of
radicles which have grown somewhat old are only feebly geo-
tropic if kept in damp air; nor did we succeed well in our
experiments, until the germinating seeds were placed in peat
and kept at a rather high temperature. Secondly, the hypocotyls
of the seeds which were pinned to the lids of the jars gradually
became arched; and, as the cotyledons were fixed, the movement
of the hypocotyl affected the position of the radicle, and caused
confusion. Thirdly, the point of the radicle is so fine that it is
difficult not to cauterise it either too much or too little. But
we managed generally to overcome this latter difficulty, as the
following experiments show, which are given to prove that a
touch with caustic on one side of the tip does not prevent the
upper part of the radicle from bending, Ten radicles were laid
horizontally beneath and on damp friable peat, and their tips
were touched with caustic on the upper side. After 8h. all
were plainly geotropic, three of them rectangularly; after 19 h.
588 SENSITIVENESS TO GRAVITATION. Cuar. XI.
all were strongly geotropic, most of them pointing perpen-
dicularly downwards. Ten other radicles, similarly placed, had
their tips touched with caustic on the lower side; after 8 h.
three were slightly geotropic, but not nearly so much. so as the
least geotropic of the foregoing specimens; four remained hori-
zontal; and three were curved upwards in opposition to geo-
tropism. After 19 h. the three which were slightly geotropic
had become strongly so. Of the four horizontal radicles, one
alone showed a trace of geotropism; of the three up-curved
radicles, one retained this curvature, and the other two had
become horizontal.
The radicles of this plant, as already remarked, do not succeed
well in damp air, but the result of one trial may be briefly
given. Nine young radicles between ‘3 and ‘5 inch in length,
with their tips cauterised and blackened for a length never
exceeding 3 mm., together with eight control specimens, were
extended horizontally in damp air. After an interval of only
4h. 10 m. all the controls were slightly geotropic, whilst not
one of the cauterised specimens exhibited a trace of this action.
After 8 h. 35 m., there was the same difference between the
two sets, but rather more strongly marked. By this time both
sets had increased greatly in length. The controls, however,
never became much more curved downwards; and after 24h.
there was no great difference between the two sets in their
degree of curvature.
Eight young radicles of nearly equal length (average ‘36 inch)
were placed beneath and on peat-earth, and were exposed to a
temp. of 75°-76° F. Their tips had been touched transversely
with caustic, and five of them were blackened for a length of
about 0°5 mm., whilst the other three were only just visibly dis-
coloured. In the same box there were 15 control radicles, mostly
about ‘36 inch in length, but some rather longer and older, and
therefore less sensitive. After 5 h., the 15 control radicles were
all more or less geotropic: after 9 h., eight of them were bent
down beneath the horizon at various angles between 45° and 90°,
the remaining seven being only slightly geotropic: after 25 h. all
were rectangularly geotropic. The state of the eight cauterised
yadicles after the same intervals of time was as follows: after
5 h. one alone was slightly geotropic, and this was one with
the tip only a very little discoloured: after 9 h. the one just
mentioned was rectangularly geotropic, and two others were
slightly so, and these were the three which had been scarcely
Cuap. XI. TRANSMITTED EFFECTS: ZEA. 539
affected by the caustic; the other five were still strictly hori-
zontal. After 24h. 40 m. the three with only slightly discolourcd
tips were bent down rectangularly; the other five were not in
the least affected, but several of them had grown rather tor-
tuously, though still in a horizontal plane. The eight cauterised
radicles which had at first a mean length of ‘36 inch, after 9 h.
had increased to a mean length of ‘79 inch; and after 24 h.
40 m. to the extraordinary mean length of 2 inches. There
was no plain difference in length between the five well cau-
terised radicles which remained horizontal, and the three with
slightly cauterised tips which had become abruptly bent down.
A few of the coutrol radicles were measured after 25 h., and
they were on an average only a little longer than the cauterised,
viz., 2:19 inches. We thus see that killing the extreme tip of
the radicle of this plant for a length of about 0°5 mm., though it
stops the geotropic bending of the upper part, hardly interferes
with the growth of the whole radicle.
In the same box with the 15 control specimens, the rapid geo-
tropic bending and growth of which have just been described,
there were six radicles, about ‘6 inch in length, extended hori-
zontally, from which the tips had been cut off in a transverse
direction for a length of barely 1 mm. These radicles were
examined after 9 h. and again after 24 h. 40m., and they all
remained horizontal, They had not become nearly so tortuous
as those above described which had been cauterised. The
radicles with their tips cut off had grown in the 24 h. 40 m. as
much, judging by the eye, as the cauterised specimens.
Zea muys.—The tips of several radicles, extended horizontally
in damp air, were dried with blotting-paper and then touched
in the first trial during 2 or 3 seconds with dry caustic; but
this was too long a contact, for the tips were blackened for a
length of rather above 1 mm. They showed no signs of geo-
tropism after an interval of 9 h., and were then thrown away.
In a second trial the tips of three radicles were touched for a
shorter time, and were blackened for a length of from 0°5 to
0°75 mm.: they all remained horizontal for 4h., but after 8 h.
30 m. one of them, in which the blackened tip was only 0°5 mm.
in length, was inclined at 21° beneath the horizon. Six con-
trol radicles oll became slightly geotropic in 4 h., and strongly
so after 8h. 30 m., with the chief seat of curvature generally
between 6 or 7 mm. from the apex. In the cauterised specimens,
the terminal growing part, 10 mm. in length, increased during
040 SENSITIVENESS TO GRAVITATION. Cuar. XI.
the 8 h. 30 m. to a mean length of 13 mm.; and in the controle
to 143 mm.
In a third trial the tips of five radicles (exposed to a temp.
of 70°-71°) were touched with the caustic only once and very
slightly ; they were afterwards examined under the microscope,
and the part which was in any way discoloured was on an
average ‘76 mm, in length. After 4h. 10 m. none were bent;
after 5 h, 45 m., and again after 23 h. 30 m., they still remained
horizontal, excepting one which was now inclined 20° beneath
the horizon. The terminal part, 10 mm. in length, had in-
creased greatly in length during the 23 h. 30 m., viz., to an
average of 26 mm. Four control radicles became slightly geo-
tropic after the 4 h. 10 m., and plainly so after the 5 h, 45 m,
Their mean length after the 23 h. 80 m. had increased from
10 mm. to31_mm. Therefore a slight cauterisation of the tip
checks slightly the growth of the whole radicle, and manifestly
stops the bending of that part which ought to bend most under
the influence of geotropism and which still continues to
increase greatly in length.
Concluding Remarks.—Abundant evidence has now
been given, showing that with various plants the tip
of the radicle is alone sensitive to geotropism; and
that when thus excited, it causes the adjoining parts
to bend. The exact length of the sensitive part seems
to be somewhat variable, depending in part on the age
of the radicle; but the destruction of a length of from
less than 1 to 1:5 mm. (about th of an inch), in the
several species observed, generally sufficed to prevent
any part of the radicle from bending within 24 h., or
even for a longer period. The fact of the tip alone
being sensitive is so remarkable a fact, that we will
here give a brief summary of the foregoing experiments, -
The tips were cut off 29 horizontally extended radicles
of Vieta faba, and with a few exceptions they did not
become geotropic in 22 or 23 h., whilst unmutilated
radicles were always bowed downwards in 8 or 9h. It
should be borne in mind that the mere act of cutting
Cyar. XI. TRANSMITTED EFFECTS: CONCLUSION. 541
off the tip of a horizontally extended radicle does not
prevent the adjoining parts from bending, if the tip
has been previously exposed for an hour or two to the
influence of geotropism. The tip after amputation is
sometimes completely regenerated in three days; and
it is possible that it may be able to transmit an
impulse to the adjoining parts before its complete
regeneration. The tips of six radicles of Cucurbita
ovifera were amputated like those of Vicia faba; and
these radicles showed no signs of geotropism in 24h. ;
whereas the control specimens were slightly affected
in 5 h., and strongly in 9 h.
With plants belonging to six genera, the tips of the
radicles were touched transversely with dry caustic ;
and the injury thus caused rarely extended for a greater
length than 1 mm., and sometimes to a less distance, as
judged by even the faintest discoloration. We thought
that this would be a better method of destroying the
vegetative point than cutting it off; for we knew, from
many previous experiments and from some given in
the present chapter, that a touch with caustic on one
side of the apex, far from preventing the adjoining
part from bending, caused it to bend. In all the
following cases, radicles with uncauterised tips were
observed at the same time and under similar circum-
stances, and they became, in almost every instance,
plainly bowed downwards in one-half or one-third of
the time during which the cauterised specimens were
observed. With Vicia faba 19 radicles were cau-
terised; 12 remained horizontal during 23-24 h.;
6 became slightly and 1 strongly geotropic. Eight of
these radicles were afterwards reversed, and again
touched with caustic, and none of them became geo-
tropic in 24 h., whilst the reversed control specimens
became strongly bowed downwards within this time.
542 SENSITIVENESS TO GRAVITATION. Cuar. XI.
With Piswm sativum, five radicles had their tips touched
with caustic, and after 32 h. four were still horizontal.
The control specimens were slightly geotropic in
7h. 20 m., and strongly so in 24h. The tips of 9 other
radicles of this plant were touched only on the lower
side, and 6 of them remained horizontal for 24 h., or
were upturned in opposition to geotropism ; 2 were
slightly, and 1 plainly geotropic. With Phaseolus
multiflorus, 15 radicles were cauterised, and 8 re-
mained horizontal for 24h.; whereas all the controls
were plainly geotropic in 8h. 30m. Of 5 cauterised
radicles of Gossypium herbaceum, 4 remained horizontai
for 23 h. and 1 became slightly geotropic; 6 control
radicles were distinctly geotropic in 7h.45m. Five
radicles of Cucurbita ovifera remained horizontal in
peat-earth during 25 h., and 9 remained so in damp
air during 83 h.; whilst the controls became slightly
geotropic in 4 h.10m. The tips of 10 radicals of this
plant were touched on their lower sides, and 6 of
them remained horizontal or were upturned after 19 h.,
1 being slightly and 3 strongly geotropic.
Lastly, the tips of several radicles of Vicia, faba and
Phaseolus multiflorus were thickly coated with grease
fora length of 3 mm, This matter, which is highly
injurious to most plants, did not kill or stop the growth
of the tips, and only slightly lessened the rate of
growth of the whole radicle; but it generally delayed
a little the geotropic bending of the upper part.
The several foregoing cases would tell us nothing,
if the tip itself was the part which became most
bent; but we know that it is a part distant from the
tip by some millimeters which grows quickest, and
which, under the influence of geotropism, bends most.
We have no reason to suppose that this part is injured
by the death or injury of the tip; and it is certain
Cuap. XI. TRANSMITTED EFFECTS : CONCLUSION. 543
that after the tip has been destroyed this part goes on
growing at such a rate, that its length was often doubled
inaday. We havealso seen that the destruction of the
tip does not prevent the adjoining part from bending,
it this part has already received some influence from
the tip. As with horizontally extended radicles, of
which the tip has been cut off or destroyed, the part
which ought to bend most remains motionless for
many hours or days, although exposed at right angles
to the full influence of geotropism, we must conclude
that the tip alone is sensitive to this power, and trans-
mits some influence or stimulus to the adjoining parts,
causing them to bend. We have direct evidence of
such transmission ; for when a radicle was left extended
horizontally for an hour or an hour and a half, by
which time the supposed influence will have travelled
a little distance from the tip, and the tip was then
cut off, the radicle afterwards became bent, although
placed perpendicularly. The terminal portions of
several radicles thus treated continued for some time
to grow in the direction of their newly-acquired curva-
ture; for as they were destitute of tips, they were no
longer acted on by geotropism. But after three or
four days when new vegetative points were formed, the
radicles were again acted on by geotropism, and now
they curved themselves perpendicularly downwards.
To see anything of the above kind in the animal
kingdom, we should have to suppose that an animal
whilst lying down determined to rise up in some par-
ticular direction ; and that after its head had been cut
off, an impulse continued to travel very slowly along
the nerves to the proper muscles ; so that after several
hours the headless animal rose up in the predeter-
mined direction.
As the tip of the racicle has been found to be the
544 fENSITIVENESS TO GRAVITATION Cuap. XI
part which is sensitive to geotropism in the members of
such distinct families as the Leguminose, Malvaceae,
Cucurbitaceee and Graminew, we may infer that this
character is common to the roots of most seedling
plants. Whilst a root is penetrating the ground, the
tip must travel first; and we can see the advantage of
its being sensitive to geotropism, as it has to deter-
mine the course of the whole root. Whenever the tip
is deflected by any subterranean obstacle, it will also
be an advantage that a considerable length of the root
should be able to bend, more especially as the tip
itself grows slowly and bends but little, so that the
proper downward course may be soon recovered. But
it appears at first sight immaterial whether this were
effected by the whole growing part being sensitive to
geotropism, or by an influence transmitted exclusively
from the tip. We should, however, remember that it
is the tip which is sensitive to the contact of hard
objects, causing the radicle to bend away from them,
thus guiding it along the lines of least resistance in
the soil. It is again the tip which is alone sensitive,
at least in some cases, to moisture, causing the
radicle to bend towards its source. These two kinds
of sensitiveness conquer for a time the sensitiveness
to geotropism, which, however, ultimately prevails.
Therefore, the three kinds of sensitiveness must often
come into antagonism ; first one prevailing, and then
another; and it would be an advantage, perhaps a
necessity, for the interweighing and reconciling of
these three kinds of sensitiveness, that they should
be all localised in the same group of cells which have
to transmit the command to the adjoining parts of
the radicle, causing it to bend to or from the source of
irritation.
Finally, the fact of the tip alone being sensitive to
Car. XI. TRANSMITTED EFFECTS: CONCLUSION. 648
the attraction of gravity has an important bearing on
the theory of geotropism. Authors seem generally to
look at the bending of a radicle towards the centre of
the earth, as the direct result of gravitation, which is
believed to modify the growth of the upper or lower
surfaces, in such a manner as to induce curvature in
the proper direction. But we now know that it is the
tip alone which is acted on, and that this part trans-
mits some influence to the adjoining parts, causing
them to curve downwards. Gravity does not appear
to act in a more direct manner on a radicle, than it
does on any lowly organised animal, which moves
away when it feels some weight or pressure.
546 SUMMARY AND Cuap. XII,
CHAPTER XII
Sommary anp Conctupine Remarks,
Nature of the circumnutating movexent—History of a germinating
seed— The radicle first protrudes and cireumnutates—Its tip
highly sensilive—Emergence of the hypocotyl or of the epicutyl
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 vr organs—Modified
circumnutation—Epinasty and hyponasty—Movements of climbing
plants —Nyctitropic movements—Movements excited by light and
gravitation -— Loealised sensitiveness —Resemblance between the
movements of plants and animals—The tip of the radicle acts like
a brain.
Ir may be useful to the reader if we briefly sum up
the chief conclusions, which, as far as we can judge,
have been fairly well established by the observations
given in this volume. All the parts or organs in
every plant whilst they continue to grow, and some
parts which are provided with pulvini after they have
ceased to grow, are continually circumnutating. This
movement commences even before the young seedling
has broken through the ground. The nature of the
movement and its causes, as far as ascertained, have
been briefly described in the Introduction. Why
every part of a plant whilst it is growing, and in some
cases after growth has ceased, should have its cells
rendered more turgescent and its cell-walls more
extensile first on one side and then on another, thus
inducing circumnutation, is not known. It would
appear as if the changes in the cells required periods
of rest.
Cwap, XII. CONCLUDING REMARKS. 547
In some cases, as with the hypocotyls of Brassica,
the leaves of Dionza and the joints of the Gramine,
the circumnutating movement when viewed under the
microscope is seen to consist of innumerable small
oscillations. ‘The part under observation suddenly
jerks forwards for a length of 002 to ‘001 of an inch,
and then slowly retreats for a part of this distance;
after a few seconds it again jerks forwards, but with
many intermissions. The retreating movement appa-
rently is due to the elasticity of the resisting tissues.
How far this oscillatory movement is general we do
not know, as not many circumnutating plants were
observed by us under the microscope; but no such
movement could be detected in the case of Drosera
with a 2-inch object-glass which we used. The pheno-
menon is a remarkable one. The whole hypocotyl
of a cabbage or the whole leaf of a Dionea could not
jerk forwards unless a very large number of cells on
one side were simultaneously affected. Are we to sup-
pose that these cells steadily become more and more
turgescent on one side, until the part suddenly yields
and bends, inducing what may be called a micro-
scopically minute earthquake in the plant; or do the
cells on one side suddenly become turgescent in an
intermittent manner; each forward movement thus
caused being opposed by the elasticity of the tissues ?
Circumuutation is of paramount importance in the
life of every plant; for it is through its modification
that many highly beneficial or necessary movements
have been acquired. When light strikes one side
of a plant, or light changes into darkness, or when
gravitation acts on a displaced part, the plant is
enabled in some unknown manner to increase the
always varying turgescence of the cells on one side;
so that the ordinary circumnutating movement is
548 SUMMARY AND Cnap. XII
modified, and the part bends either to or from the
exciting cause; or it may occupy a new position, as
in the so-called sleep of leaves. The influence which
modifies circumnutation may be transmitted from one
part to another. Innate or constitutional changes,
independently of any external agency, often modify
the circumnutating movements at particular periods
of the life of the. plant. As circumnutation is uni-
versally present, we can understand how it is that
movements of the same kind have been developed in
the most distinct members of the vegetable series.
But it must not be supposed that all the movements
of plants arise from modified circumnutation ; for, as
we shall presently see, there is reason to believe that
this is not the case.
Having made these few preliminary remarks, we
will in imagination take a germinating seed, and con-
sider the part which the various movements play in
the life-history of the plant. The first change is the
protrusion of the radicle, which begins at once to
circumnutate. This movement is immediately modi-
fied by the attraction of gravity and rendered geo-
tropic. The radicle, therefore, supposing the seed to
be lying on the surface, quickly bends downwards, fol-
lowing a more or less spiral course, as was seen on the
smoked glass-plates. Sensitiveness to gravitation re-
sides in the tip; and it is the tip which transmits
some influence to the adjoining parts, causing them
to bend. As soon as the tip, protected by the root-
vap, reaches the ground, it penetrates the surface, if
this be soft or friable; and the act of penetration is
apparently aided by the rocking or circumnutating
movement of the whole end of the radicle. If the sur-
face is compact, and cannot easily be penetrated, then
Cuar. XII. CONCLUDING REMARKS. 549
the seed itself, unless it be a heavy one, is displaced
or lifted up by the continued growth and elongation
of the radicle. But in a state of nature seeds often
get covered with earth or other matter, or fall into
crevices, &c., and thus a point of resistance is afforded,
and the tip can more disily penetrate the ground.
But even with seeds lying loose on the surface there
is another. aid: a multitude of excessively fine hairs
are emitted from the upper part of the radicle, and
these attach themselves firmly to stones or other ob-
jects lying on the surface, and can do so even to glass;
and thus the upper part is held down whilst the tip
presses against and penetrates the ground. The
attachment of the root-hairs is effected by the lique-
faction of the outer surface of the cellulose walls, and
by the subsequent setting hard of the liquefied matter.
This curious process probably takes place, not for
the sake of the attachment of the radicles to superficial
objects, but in order that the hairs may be brought into
the closest contact with the particles in the soil, by
which means they can absorb the layer of water sur-
rounding them, together with any dissolved matter.
After the tip has penetrated the ground to a little
depth, the increasing thickness of the radicle, together
with the root-hairs, hold it securely in its place; and
now the force exerted by the longitudinal growth of
the radicle drives the tip deeper into the ground.
This force, combined with that due to transverse
growth, gives to the radicle the power of a wedge.
Even a growing root of moderate size, such as that
of a seedling bean, can displace a weight of some
pounds. It is not probable that the tip when buried
in compact earth can actually circumnutate and thus
aid its downward passage, but the circumnutating
movement wili facilitate the tip entering any lateral
,
550 SUMMARY AND Cuar, XII
or oblique fissure in the earth, or a burrow made by
an earth-worm or larva; and it is certain that roots
often run down the old burrows of worms. The tip,
however, in endeavouring to circumnutate, will con-
tinually press against the earth on all sides, and this
can hardly fail to be of the highest importance to the
plant ; for we have seen that when little bits of card-
like paper and of very thin paper were cemented on
opposite sides of the tip, the whole growing part of
the radicle was excited to bend away from the side
bearing the card or more resisting substance, towards
the side bearing the thin paper. We may therefore
feel almost sure that when the tip encounters a stone
or other obstacle in the ground, or even earth more
compact on one side than the other, the root will bend
away as much as it can from the obstacle or the more
resisting earth, and will thus follow with unerring
skill a line of least resistance.
The tip is more sensitive to prolonged contact with
an object than to gravitation when this acts obliquely
on the radicle, and sometimes even when it acts in the
most favourable direction at right angles to the radicle.
The tip was excited by an attached bead of shellac,
weighing less than doth of a grain (0°33 mg.) ; it is
therefore more sensitive than the most delicate ten-
dril, namely, that of Passiflora gracilis, which was barely
acted on by a bit of wire weighing =5th of a grain. But
this degree of sensitiveness is as nothing compared with
that of the glands of Drosera, for these are excited by
particles weighing only 7g4+qp of a grain. The sensi-
tiveness of the tip cannot be accounted for by its
being covered by a thinner layer of tissue than the
other parts, for it is protected by the relatively thick
root-cap. It is remarkable that although the radicle
bends away, when one side of the tip is slightly touched
Cnap. XIL CONCLUDING REMARKS. 551
with caustic, yet if the side be much cauterised the
injury is too great, and the power of transmitting somo
influence to the adjoining parts causing them to bend,
is lost. Other analogous cases are known to occur.
After a radicle has been deflected by some obstacle,
geotropism directs the tip again to grow perpendicu-
larly downwards; but geotropism is a feeble power,
and here, as Sachs has shown, another interesting
adaptive movement comes into play; for radicles at.
a distance of a few millimeters from the tip are
sensitive to prolonged contact in such a manner that
they bend towards the touching object, instead of from
it as occurs when an object touches one side of the
tip. Moreover, the curvature thus caused is abrupt;
the pressed part alone bending. Even slight pressure
suffices, such as a bit of card cemented to one side.
Therefore a radicle, as it passes over the edge of any
obstacle in the ground, will through the action of geo-
tropism press against it; and this pressure will cause
the radicle to endeavour to bend abruptly over the
edge. It will thus recover as quickly as possible its
normal downward course.
Radicles are also sensitive to air which contains
more moisture on one side than the other, and they
bend towards its source. It is therefore probable that
they are in like manner sensitive to dampness in the
soil. It was ascertained in several cases that this
gensitiveness resides in the tip, which transmits an
influence causing the adjoining upper part to bend
in opposition to geotropism towards the moist object.
We may therefore infer that roots will be deflected
from their downward course towards any source of
moisture in the soil.
Again, most or all radicles are slightly sensitive to
light, and, according to Wiesner, generally bend a little
35
DEQ SUMMARY AND Cuar. X11
from it. Whether this can be of any service to them
is very doubtful, but with seeds germinating on the
surface it will slightly aid geotropism in directing
the radicles to the ground.* We ascertained in one
instance that such sensitiveness resided in the tip, and
caused the adjoining parts to bend from the light.
The sub-aérial roots observed by Wiesner were all
apheliotropic, and this, no doubt, is of use in bringing
them into contact with trunks of trees or surfaces of
rock, as is their habit.
We thus see that with seedling plants the tip of thc
radicle is endowed with diverse kinds of sensitiveness ;
and that the tip directs the adjoining growing parts
to bend to or from the exciting cause, according to the
needs of the plant. The sides of the radicle are alsc
sensitive to contact, but in a widely different manner.
Gravitation, though a less powerful cause of move-
ment than the other above specified stimuli, is ever
present; so that it ultimately prevails and determines
the downward growth of the root.
The primary radicle emits secondary ones which
project sub-horizontally ; and these were observed in
one case to circumnutate. Their tips are also sensitive
to contact, and they are thus excited to bend away
from any touching object; so that they resemble in
these respects, as far as they were observed, the
primary radicles. If displaced they resume, as Sachs
has shown, their original sub-horizontal position; and
this apparently is due to diageotropism. The secondary
radicles emit tertiary ones, but these, in the case of
the bean, are not affected by gravitation ; consequently
they protrude in all directions. Thus the general
* Dr. Karl Richter, who has in Wien,’ 1879, p. 149), states that
especially attenled to this subject apheliotropism does not aid ra
“K. Akad. der Wissenschalten dicles in penetrating the ground,
Crar. XII CONCLUDING IEMARKS. 55@
arrangement of the three orders of roots is ex2ellently
adapted for searching the whole soil for nutriment.
Sachs has shown that if the tip of the primary
radicle is cut off (and the tip will occasionally be
gnawed off with seedlings in a state of nature) one of
the secondary radicles grows perpendicularly down-
wards, in a manner which is analogous to the upward
growth of a lateral shoot after the amputation of
the leading shoot. We have seen with radicles of the
bean that if the primary radicle is merely compressed
instead of being cut off, so that an excess of sap is
directed into the secondary radicles, their natural con-
dition is disturbed and they grow downwards. Other
analogous facts have been given. As anything which
disturbs the constitution is apt to lead to reversion,
that is, to the resumption of a former character, it
appears probable that when secondary radicles grow
downwards or lateral shoots upwards, they revert to
the primary manner of growth proper to radicles and
shoots.
With dicotyledonous seeds, after the protrusion of
the radicle, the hypocotyl breaks through the seed-
coats; but if the cotyledons aré hypogean, it is the
epicotyl which breaks forth. These organs are at first
invariably arched, with the upper part bent back
parallel to the lower; and they retain this form until
they have risen above the ground. In some cases,
however, it is the petioles of the cotyledons or of the
first true leaves which break through the seed-coats
as well as the ground, before any part of the stem
protrudes; and then the petioles are almost invariably
arched. We have met with only one exception, and that
only a partial one, namely, with the petioles of the twe
first leaves of Acanthus candelabrum. With Delphinium
nudicaule the petioles of the two cotyledons are com-
554 SUMMARY AND Cuar. XIL
pletely confluent, and they break through the ground
as an arch; afterwards the petioles of the successively
formed early leaves are arched, and they are thus
enabled to break through the base of the confluent
petioles of the cotyledons. In the case of Megarrhiza,
it is the plumule which breaks as an arch through the
tube formed by the confluence of the cotyledon-
petioles. With mature plants, the flower-stems and
the leaves of some few species, and the rachis of
. several ferns, as they emerge separately from the
ground, are likewise arched.
The fact of so many different organs in plants of
many kinds breaking through the ground under the
form of an arch, shows that this must be in some
manner highly important to them. According to
Haberlandt, the tender growing apex is thus saved
from abrasion, and this is probably the true explana-
tion. But as both legs of the arch grow, their power
of breaking through the ground will be much in-
creased as long as the tip remains within the seed-
coats and has a point of support. In the case of
monocotyledons the plumule or cotyledon is rarely
arched, as far as we have seen; but this is the case
with the leaf-like cotyledon of the onion; and the
crown of the arch is here strengthened by a special
protuberance. In the Graminee the summit of the
straight, sheath-lixe cotyledon is developed into a
hard sharp crest, which evidently serves for breaking
through the earth. With dicotyledons the arching of
the epicotyl or hypocotyl often appears as if it merely
resulted from the manner in which the parts are
packed within the seed; but it is doubtful whether
this is the whole of the truth in any case, and it cer-
tainly was not so in several cases, in which the arch-
ing was seen to commence after the parts had wholly
Caae, XII. CONCLUDING REMARKS. 555
escaped from the seed-coats. As the arching occurred
in whatever position the seeds were placed, it is no
doubt due to temporarily increased growth of the
nature of epinasty or hyponasty along one side of the
part.
As this habit of the hypocotyl to arch itself appears
to be universal, it is probably of very ancient origin.
It is therefore not surprising that it should be in-
herited, at least to some extent, by plants having
hypogean cotyledons, in which the hypocotyl is only
slightly developed and never protrudes above the
ground, and in which the arching is of course now
quite useless. This tendency explains, as we have
seen, the curvature of the hypocotyl (and the conse-
quent movement of the radicle) which was first
observed by Sachs, and which we have often had to
refer to as Sachs’ curvature.
The several foregoing arched organs are continually
circumnutating, or endeavouring to circumnutate, even
before they break through the ground. As soon as
any part of the arch protrudes from the seed-coats it
is acted upon by apogeotropism, and both the legs
bend upwards as quickly as the surrounding earth will
permit, until the arch stands vertically. By continued
growth it then forcibly breaks through the ground;
but as it is continually striving to circumnutate this
will aid its emergence in some slight degree, for we
know that a circumnutating hypocotyl can push away
damp sand on all sides. As soon as the faintest ray of
light reaches a seedling, heliotropism will guide it
through any crack in the soil, or through an entangled
mass of overlying vegetation; for apogeotropism by
itself can direct the seedling only blindly upwards.
Hence probably it is that sensitiveness to light resides
in the tip of the cotyledons of the Graminex, and in
§56 SUMMARY AND Cuar, XII
the upper part of the hypocotyls of at least some
plants.
As the arch grows upwards the cotyledons are
dragged out of the ground. The seed-coats are either
left behind buried, or are retained for a time still
enclosing the cotyledons. These are afterwards cast
off merely by the swelling of the cotyledons. But
with most of the Cucurbitaces there is a curious
special contrivance for bursting the seed-coats whilst
beneath the ground, namely, a peg at the base of the
hypocotyl, projecting at right angles, which holds down
the lower half of the seed-coats, whilst the growth
of the arched part of the hypocotyl lifts up the upper
half, and thus splits them in twain. A somewhat
analogous structure occurs in Mzmosa pudica and some
other plants. Before the cotyledons are fully ex-
panded and have diverged, the hypocotyl generally
straightens itself by increased growth along the con-
cave side, thus reversing the process which caused
the arching. Ultimately not a trace of the former
curvature is left, except in the case of the leaf-like
cotyledons of the onion.
The cotyledons can now assume the function of
leaves, and decompose carbonic acid; they also yield
up to other parts of the plant the nutriment which
they often contain. When they contain a large stock
of nutriment they generally remain buried beneath
the ground, owing to the small development of the
hypocotyl; and thus they have a better chance of
escaping destruction by animals. From unknown
causes, nutriment is sometimes stored in the hypocotyl
or in the radicle, and then one of the cotyledons or
both become rudimentary, of which several instances
have been given. It is probable that the extraordi-
nary manner of germination of Megarrhiza Californica,
Cuar. XIL CONCLUDING REMARKS. 557
Ipomea leptophylla and pandurata, ard of Quercus
virens, is connected with the burying of the tuber-like
roots, which at an early age are stocked with nutri-
ment; for in these plants it is the petioles of the
cotyledons which first protrude from the seeds, and
they are then merely tipped with a minute radicle and.
hypocotyl. These petioles bend down geotropically
like a root and penetrate the ground, so that the true
root, which afterwards becomes greatly enlarged, is
buried at some little depth beneath the surface. Gra-
dations of structure are always interesting, and Asa
Gray informs us that with Ipomea Jalappa, which
likewise forms huge tubers, the hypocotyl is still of
considerable length, and the petioles of the cotyledons
are only moderately elongated. But in addition to the
advantage gained by the concealment of the nutritious
matter stored within the tubers, the plumule, at least
in the case of Megarrhiza, is protected from the frosts
of winter by being buried.
With many dicotyledonous seedlings, as has lately
been described by De Vries, the contraction of the
parenchyma of the upper part of the radicle drags the
hypocotyl downwards into the earth; sometimes (it is
said) until even the cotyledons are buried. The hypo-
cotyl itself of some species contracts in a like manner.
It is believed that this burying process serves to
protect the seedlings against the frosts of winter.
Our imaginary seedling is now mature as a seedling,
for its hypocotyl is straight and its cotyledons are
fully expanded. In this state the upper part of the
hypocotyl and the cotyledons continue for some time
to circumnutate, generally to a wide extent relat. vely
to the size of the parts, and at a rapid rate. But
seedlings profit by this power of movement only when
it is modified, especially by the action of light and
058 SUMMARY AND Cuar. XII.
gravitation ; for they are thus enabled to move more
rapidly and to a greater extent than can most mature
plants. Seedlings are subjected to a severe struggle
for life, and it appears to be highly important to them
that they should adapt themselves as quickly and as
_perfectly as possible to their conditions. Hence also
it is that they are so extremely sensitive to light and
gravitation. The cotyledons of some few species are
sensitive to a touch; but it is probable that this is
only an indirect result of the foregoing kinds of sen-
sitiveness, for there is no reason to believe that they
profit by moving when touched.
Our seedling now throws up a stem bearing leaves,
and often branches, all of which whilst young are con-
tinually circumnutating. If we look, for instance, at a
great acacia tree, we may feel assured that every one of
the innumerable growing shoots is constantly describ-
ing small ellipses; as is each petiole, sub-petiole, and
leaflet. The latter, as well as ordinary leaves, gene-
rally move up and down in nearly the same vertical
plane, so that they describe very narrow ellipses.
The flower-peduncles are likewise continually circum-
nutating. If we could look beneath the ground, and
our eyes had the power of a microscope, we should see
the tip of each rootlet endeavouring to sweep small
ellipses or circles, as far as the pressure of the sur-
rounding earth permitted. All this astonishing amount
of movement has been going on year after year since
the time when, as a seedling, the tree first emerged
from the ground.
Stems are sometimes developed into long runners or
stolons. These circumnutate ina conspicuousmanner,and
are thus aided in passing between and over surrounding
obstacles. But whether the circumnutating movement
has been increased for this special purpose is doubtful
Cuar. XIL CONCLUDING REMARKS. 559
We have now to consider circumnutation in a
modified form, as the source of several great classes of
movement. The modification may be determined by
innate causes, or by external agencies. Under the first
head we see leaves which, when first unfolded, stand
in a vertical pcsition, and gradually bend downwards
as they grow older. We sce flower-peduncles bending
down after the flower has withered, and others rising
up; or again, stems with their tips at first bowed
downwards, so as to be hooked, afterwards straighten-
ing themselves; and many other such cases. These
changes of position, which are due to epinasty or
hyponasty, occur at certain periods of the life of the
plant, and are independent of any external agency.
They are effected not by a continuous upward or
downward movement, but by a succession of small
ellipses, or by zigzag lines,—that is, by a circum-
nutating movement which is preponderant in some
one direction.
Again, climbing plants whilst young circumnutate
in the ordinary manner, but as soon as the stem
has grown to a certain height, which is different for
different species, it elongates rapidly, and now the
amplitude of the circumnutating movement is im-
mensely increased, evidently to favour the stem catch-
ing hold of a support. The stem also circumnutates
rather more equally to all sides than in the case of
non-climbing plants. This is conspicuously the case
with those tendiils which consist of modified leaves,
as these sweep wide circles; whilst ordinary leaves
usually circumnutate nearly in the same vertical plane.
Flower-peduncles when converted into tendrils have
their circumnutating movement in like manner greatly
increased.
We now come to our second group of circumnu-
560 SUMMARY AND Cuar. X1L
tating movements—those modified through external
agencies. The so-called sleep or nyctitropic move-
ments of leaves are determined by the daily alterna-
tions of light and darkness. It is not the darkness
which excites them to move, but the difference in the
amount of light which they receive during the day
and night; for with several species, if the leaves have
not been brightly illuminated during the day, they
do not sleep at night. They inherit, however, some
tendency to move at the proper periods, indepen-
dently of any change in the amount of light. The
movements are in some cases extraordinarily complex,
but as a full summary has been given in the chapter
devoted to this subject, we will here say but little on
this head. Leaves and cotyledons assume their noc-
turnal position by two means, by the aid of pulvini and
without such aid. In the former case the movement
continues as long as the leaf or cotyledon remains in
full health ; whilst in the latter case it continues only
whilst the part is growing. Cotyledons appear to
sleep in a larger proportional number of species than
do leaves. In some species, the leaves sleep and not
the cotyledons ; in others, the cotyledons and not the
leaves; or both may sleep, and yet assume widely
different positions at night.
Although the nyctitropic movements of leaves and
cotyledons are wonderfully diversified, and sometimes
differ much in the species of the same genus, yet the
blade is always placed in such a position at night, that
its upper surface is exposed as little as possible to full
radiation. We cannot doubt that this is the object
gained by these movements; and it has been proved
that leaves exposed to a clear sky, with their blades
compelled to remain horizontal, suffered much more
from the cold than others which were allowed to assume
Onar XII CONCLUDING REMARKS. 561
their proper vertical position. Some curious facts
have been given under this head, showing that hori-
zontally extended leaves suffered more at night, when
the air, which is not cooled by radiation, was prevented
from freely circulating beneath their lower surfaces ;
and so it was, when the leaves were allowed to go to
sleep on branches which had been rendered motionless.
In some species the petioles rise up greatly at night,
and the pinne close together. The whole plant is
thus rendered more compact, and a much smaller
surface is exposed to radiation.
That the various nyctitropic movements of leaves
result from modified circumnutation has, we think,
been clearly shown. In the simplest cases a leaf
describes a single large ellipse during the 24 h.; and
the movement is so arranged that the blade stands
vertically during the night, and reassumes its former
position on the following morning. The course pursued
differs from ordinary circumnutation only in its greater
amplitude, and in its greater rapidity late in the
evening and early on the following morning. Unless
this movement is admitted to be one of circumnu-
tation, such leaves do not circumnutate at all, and this
would be a monstrous anomaly. In other cases, leaves
and cotyledons describe several vertical ellipses during
the 24h.; andin the evening one of them is increased
greatly in amplitude until the blade stands vertically
either upwards or downwards. In this position it con-
tinues to circumnutate until the following moruing,
when it reassumes its former position. These move-
ments, when a pulvinus is present, are often compli-
cated by the rotation of the leaf or leaflet; and such
rotation on a small scale occurs during ordinary cir-
cumnutation. The many diagrams showing the move-
ments of sleeping and non-sleeping leaves aud coty-
562 SUMMARY AND Cuap. XII
ledons should be compared, and it will be seen that
they are essentially alike. Ordinary circumnutation
is converted into a nyctitropic movement, firstly by an
increase in its amplitude, but not to so great a degree
as in the case of climbing plants, and secondly by its
being rendered periodic in relation to the alterna-
tions of day and night. But there is frequently a
distinct trace of periodicity in the circumnutating
movements of non-sleeping leaves and cotyledons.
The fact that nyctitropic movements occur in species
distributed in many families throughout the whole
vascular series, is intelligible, if they result from the
modification of the universally present movement of
circumnutation ; otherwise the fact is inexplicable.
In the seventh chapter we have given the case of
a Porlieria, the leaflets of which remained closed all
day, as if asleep, when the plant was kept dry, appa-
rently for the sake of checking evaporation. Some-
thing of the same kind occurs with certain Graminee.
At the close of this same chapter, a few observations
were appended on what may be called the embryology
of leaves. The leaves produced by young shoots on
cut-down plants of Melilotus tawrica slept like those of
a Trifolium, whilst the leaves on the older branches
on the same plants slept in a very different manner,
proper to the genus; and from the reasons assigned
we are tempted to look at this case as one of reversion
to a former nyctitropic habit. So again with Desmo-
dium gyrans, the absence of small lateral leaflets on
very young plants, makes us suspect that the imme-
diate progenitor of this species did not possess lateral
leaflets, and that their appearance in an almost rudi-
mentary condition at a somewhat more advanced age
is the result of reversion to a trifoliate predecessor.
However this may be, the rapid circumnutating or
Cuapr. XIL. CONCLUDING REMARKS. 563
gyrating movements of the little lateral leaflets, seem
to be due proximately to the pulvinus, or organ of
movement, not having been reduced nearly so much
as the blade, during the successive modificatious
through which the species has passed.
We now come to the highly important class of
movements due to the action of a lateral light. When
stems, leaves, or other organs are placed, so that one
side is illuminated more brightly than the other, they
bend towards the light. This heliotropic movement.
manifestly results from the modification of ordinary
circumnutation ; and every gradation between the two
movements could be followed. When tke light was
dim, and only a very little brighter on one side than
on the other, the movement consisted of a succession
of ellipses, directed towards the light, each of which
approached nearer to its source than the previous one.
When the difference in the light on the two sides
was somewhat greater, the ellipses were drawn out
into a strongly-marked zigzag line, and when much
greater the course became rectilinear. We have
reason to believe that changes in the turgescence ot
the cells is the proximate cause of the movement
of circumnutation; and it appears that when a plant
is unequally illuminated on the two sides, the always
changing turgescence is augmented along one side,
and is weakened or quite arrested along the other
sides. Increased turgescence is commonly followed by
increased growth, so that a plant which has bent itself
towards the light during the day would be fixed in this
position were it not for apogeotropism acting during
the night. But parts provided with pulvini bend, as
Pfeffer has shown, towards the light ; and here growth
does not come into play any more than in the ordinary
cirenmuutating movements of pulvini.
564 SUMMARY AND Cuar. XIL
Heliotropism prevails widely throughout the vege-
table kingdom, but whenever, from the changed habits
of life of any plant, such movements become injurious
or useless, the tendency is easily eliminated, as we see
with climbing and insectivorous plants.
Apheliotropic movements are comparatively rare in
a well-marked degree, excepting with sub-aérial roots.
In the two cases investigated by us, the movement
certainly consisted of modified circumnutation.
The position which leaves and cotyledons occupy
during the day, namely, more or less transversely to
the direction of the light, is due, according to Frank,
to what we call diaheliotropism. As all leaves and
cotyledons are continually circumnutating, there can
hardly be a doubt that diaheliotropism results from
modified circumnutation. From the fact of leaves and
cotyledons frequently rising a little in the evening, it
appears as if diaheliotropism had to conquer during
the middle of the day a widely prevalent tendency to
apogeotropism.
Lastly, the leaflets and cotyledons of some plants
are known to be injured by too much light; and when
the sun shines brightly on them, they move upwards
or downwards, or twist laterally, so that they direct
their edges towards the light, and thus they escape
being injured. These paraheliotropic movements cer-
tainly consisted in one case of modified cirtumnuta-
tion; and so it probably is in all cases, for the leaves
of all the species described circumnutate in a con-
spicuous manner. This movement has hitherto been
observed only with leaflets provided with pulvini, in
which the increased turgescence on opposite sides is
not followed by growth ; and we can understand why
this should be so, as the movement is required only
for a temporary purpose. It would manifestly be dis-
Crap. XII. CONCLUDING REMARKS. 565
advantageous for the leaf to be fixed by growth in its
inclined position. For it has to assume its former
horizontal position, as soon as possible after the sun
has ceased shining too brightly on it.
The extreme sensitiveness of certain seedlings to
light, as shown in our ninth chapter, is highly remark-
able. The cotyledons of Phalaris became curved
towards a distant lamp, which emitted so little light,
that a pencil held vertically close to the plants, did
not cast any shadow which the eye could perceive
on a white card. These cotyledons, therefore, were
affected by a difference in he amount of light on their
two sides, which the eye could not distinguish. The
degree of their curvature within a given time towards
a lateral light did not correspond at all strictly with
the amount of light which they received; the light
not being at any time in excess. They continued for
nearly half an hour to bend towards a‘lateral light,
after it had been extinguished. They bend with
remarkable precision towards it, and this depends on
the illumination of one whole side, or on the obscura-
tion of the whole opposite side. The difference in the
amount of light which plants at any time receive in
comparison with what they have shortly before re-
ceived, seems in all cases to be the chief exciting cause
of those movements which are influenced by light.
Thus seedlings brought out of darkness bend towards
a dim lateral light, sooner than others which had pre-
viously been exposed to daylight. We have seen
several analogous cases with the nyctitropic move-
ments of leaves. A striking instance was observed in
the case of the periodic movements of the cotyledons
of a Cassia; in the morning a pot was placed in an
obscure part of a room, and all the cotyledons rose up
closed: another pot had stood in the sunlight, and
566 SUMMARY AND Cuar. X11
the cotyledons of course remained expanded; both
pots were now placed close together in the middle of
the room, and the cotyledons which had been exposed
to the sun, immediately began to close, while the
others opened; so that the cotyledons in the two pots
moved in exactly opposite directions whilst exposed
to the same degree of light.
We found that if seedlings, kept in a dark place,
were laterally illuminated by a small wax taper for
only two or three minutes at intervals of about three-
quarters of an hour, they all became bowed to the
point where the taper had been held. We felt much
surprised at this fact, and until we had read Wiesner’s
observations, we attributed it to the after-effects of
the light; but he has shown that the same degree
of curvature in a plant may be induced in the
course of an hour by several interrupted illumina-
tions lasting ‘altogether for 20 m., as by a continuous
illumination of 60 m. We believe that this case,
as well as our own, may be explained by the ex-
citement from light being due not so much to its
actual amount, as to the difference in amount from
that previously received; and in our case there were
repeated alternations from complete darkness to light.
In this, and in several of the above specified respects,
light seems to act on the tissues of plants, almost in
the same manner as it does on the nervous system
of animals.
There is a much more striking analogy of the same
kind, in the sensitiveness to light being localised in
the tips of the cotyledons of Phalaris and Avena, and
in the upper part of the hypocotyls of Brassica and
Beta; and in the transmission of some influence from
these upper to the lower parts, causing the latter to
bend towards the light. This influence is also trans-
Caar. XII. CONCLUDING REMARES. 567
mitted beneath the soil to a depth where no light
enters. It follows from this localisation, that the
lower parts of the cotyledons of Phalaris, &c., which
normally become more bent towards a lateral light
than the upper parts, may be brightly illuminated
during many hours, and will not bend in the least, if
all light be excluded from the tip. It is an interest-
ing experiment to place caps over the tips of the
cotyledons of Phalaris, and to allow a very little light
to enter through minute orifices on one side of the
caps, for the lower part of the cotyledons will then
bend to this side, and not to the side which has been
brightly illuminated during the whole time. In the
case of the radicles of Sinapis alba, sensitiveness to
light also resides in the tip, which, when laterally
illuminated, causes the adjoining part of the root to
bend apheliotropically.
Gravitation excites plants to bend away from the
centre of the earth, or towards it, or to place them-
selves in a transverse position with respect to it.
Although it is impossible to modify in any direct
manner the attraction of gravity, yet its influence
could be moderated indirectly, in the several ways
described in the tenth chapter; and under such
circumstances the same kind of evidence as that given
in the chapter on Heliotropism, showed in the plainest
manner that apogeotropic and geotropic, and probably
diageotropic movements, are all modified forms of
eircumnutation.
Different parts of the same plant and different
species are affected by gravitation in widely different
degrees and manners. Some plants and organs exhibit
hardly a trace of its action. Young seedlings which,
as we know, circumnutate rapidly, are eminently sensi-
tive; and we have seen the hypocotyl of Beta bending
37
568 SUMMARY AND Cuar. XT.
upwards through 109° in 3h. 8m. The after-effects
of apogeotropism last for above half an hour; and
horizontally-laid hypocotyls are sometiines thus car-
ried temporarily beyond an upright position. The
benefits derived from geotropism, apogeotropism, and
diageotropism, are generally so manifest that they
need not be specified. With the flower-peduncles of
Oxalis, epinasty causes them to bend down, so that
the ripening pods may be protected by the calyx
from the rain. Afterwards they are carried upwards
by apogeotropism in combination with hyponasty, and
are thus enabled to scatter their seeds over a wider
space. The capsules and flower-heads of some plants
are bowed downwards through geotropism, and they
then bury themselves in the earth for the protection
and slow maturation of the seeds. This burying
process is much facilitated by the rocking movement
due to circumnutation.
In the case of the radicles of several, probably of all
seedling plants, sensitiveness to gravitation is confined
to the tip, which transmits an influence to the adjoining
upper part, causing it to bend towards the centre of
the earth. That there is transmission of this kind was
proved in an interesting manner when horizontally
extended radicles of the bean were exposed to the
attraction of gravity for 1 or 14 h., and their tips were
then amputated. Within this time no trace of curva-
ture was exhibited, and the radicles were now placed
pointing vertically downwards; but an influence had
already been transmitted from the tip to the adjoining
part, for it soon became bent to one side, in the same
manner as would have occurred had the radicle
remained horizontal and been still acted on by geo-
tropism. Radicles thus treated continued to grow out
horizontally for two or three days, until a new tip was
Cuap. XII. CONCLUDING REMARKS. 569
reformed ; and this was then acted on by geotropism,
and the radicle became curved perpendicularly down.
wards,
It has now been shown that the following important
lasses of movement all arise from modified circum-
uutation, which is omnipresent whilst growth lasts,
and after growth has ceased, whenever pulvini are
present. These classes of movement consist of those
due to epinasty and hyponasty,—those proper to
climbing plants, commonly called revolving nutation,
—the nyctitropic or sleep movements of leaves and
cotyledons,—and the two immense classes of move-
ment excited by light and gravitation. When we
speak of modified circumnutation we mean that light,
or the alternations of light and darkness, gravitation,
slight pressure or other irritants, and certain innate
or constitutional states of the plant, do not directly
cause the movement; they merely lead to a tempo-
rary increase or diminution of those spontaneous
changes in the turgescence of the cells which are
already in progress. In what manner, light, gravita-
tion, &e., act on the cells is not known; and we
will here only remark that, if any stimulus affected
the cells in such a manner as to cause some slight
tendency in the affected part to bend in a beneficial
manner, this tendency might easily be increased
through the preservation of the more sensitive indi-
viduals, But if such bending were injurious, the
tendency would be eliminated unless it was over-
poweringly strong; for we know how commonly all
characters in al] organisms vary. Nor can we see any
reason to doubt, that after the complete elimination of
a tendency to bend in some one direction under a
certain stimulus, the power to bend in a directly
570 SUMMARY AND Cuap. XII
opposite direction might gradually be acquired through
natural selection.*
Although so many movements have arisen through
modified circumnutation, there are others which
appear to have had a quite independent origin; but
they do not form such large and important classes.
When a leaf of a Mimosa is touched it suddenly
assumes the same position as when asleep, but Briicke
has shown that this movement results from a different
state of turgescence in the cells from that which
occurs during sleep ; and as sleep-movements are cer-
tainly due to modified circumnutation, those from a
touch can hardly be thus due. The back of a leaf of
Drosera rotundifolia was cemented to the summit of
a stick driven into the ground, so that it could not
move in the least, and a tentacle was observed during
many hours under the microscope; but it exhibited
no circumnutating movement, yet after being mo-
mentarily touched with a bit of raw meat, its basal
part began to curve in 23 seconds. This curving
movement therefore could not have resulted from
modified circumnutation. But when a small object,
such as a fragment of a bristle, was placed on one side
of the tip of a radicle, which we know is continually
circumnutating, the induced curvature was so similar
to the movement caused by geotropism, that we can
hardly doubt that it is due to modified circumnu-
tation. A flower of a Mahonia was cemented to a
stick, and the stamens exhibited no signs of circum-
nutation under the microscope, yet when they were
lightly touched they suddenly moved towards the pistil.
Lastly, the curling of the extremity of a tendril when
* See the remarks in Frank’s 91, &c.), on natural selection in
Die wagerechte Richtung ven connection with geotropism, helio
Pflunzentheilen’ ‘1870, pp. 90, tropism, &e.
Crap. XII. CONCLUDING REMARKS. 571
touched seems to be independent of its revolving 01
circumnutating movement. This is best shown by the
part which is the most sensitive to contact, circum-
nutating much less than the lower parts, or apparently
not at all.*
Although in these cases we have no reason to
believe that the movement depends on modified cir-
cumnutation, as with the several classes of movement
described in this volume, yet the difference between
the two sets of cases may not be so great as it at
first appears. In the one set, an irritant causes an
increase or diminution in the turgescenve of the cells,
which are already in a state of change; whilst in the
other set, the irritant first starts a similar change in
their state of turgescence. Why a touch, slight
pressure or any other irritant, such as electricity, heat,
or the absorption of animal matter, should modify the
turgescence of the affected cells in such a manner as to
cause movement, we do not know. But a touch acts in
this manner so often, and on such widely distinct plants,
that the tendency seems to be a very general one; and
if beneficial, it might be increased to any extent. In
other cases, a touch produces a very different effect,
as with Nitella, in which the protoplasm may be seen
to recede from the walls of the cell; in Lactuca, in
which a milky fluid exudes; and in the tendrils of
certain Vitacee, Cucurbitacee, and Bignoniacez, in
which slight pressure causes a cellular outgrowth.
Finally, it is impossible not to be struck with the
resemblance between the foregoing movements of
plants and many of the actions performed uncon-
sciously by the lower animals.t With plants an
* For the evidence on this pp. 173, 174.
head, see the ‘Movements and + Sachs remarks to nearly the
Habits of Climbing Plants, 1875, same effict: “Dass sich dic le
-
572 SUMMARY AND Cuap. XII
astonishingly small stimulus suffices; and even with
allied plants one may be highly sensitive to the
slightest continued pressure, and another highly sensi-
tive toa slight momentary touch. The habit of moving
at certain periods is inherited both by plants and
animals; and several other points of similitude have
been specified. But the most striking resemblance is
the localisation of their sensitiveness, and the transmis-
sion of an influence from the excited part to another
which consequently moves. Yet plants do not of course
possess nerves or a central nervous system; and we
may infer that with animuls such structures serve only
for the more perfect transmission of impressions, and
for the more complete intercommunication of the
several parts.
We believe that there is no structure in plants more
wonderful, as far as its functions are concerned, than
the tip of the radicle. If the tip be lightly pressed
or burnt or cut, it transmits an influence to the upper
adjoining part, causing it to bend away from the
affected side; and, what is more surprising, the tip
ean distinguish between a slightly harder and softer
object, by which it is simultaneously pressed on oppo-
site sides. If, however, the radicle is pressed by a
similar object a little above the tip, the pressed part
does not transmit any influence to the more distant
parts, but bends abruptly towards the object. If the
tip perceives the air to be moister on one side than
on the other, it likewise transmits an influence to the
upper adjoining part, which bends towards the source
of moisture. When the tip is excited by light (though
bende Pflanzensulstanz derart lich, wie die verschiedenen Sinnes-
innexlich differenzirt, dass ecin- nerven des Thiere’ (‘ Arbiilen
zelne Theile mit spccifischen des Bot. Inst. in Wiirzburg, Bad,
Energien ausgeriistct sind, ahn- ii. 1879, p. 282).
Cuar. XII. CONCLUDING REMARKS. 573
in the case of radicles this was ascertained in only a
single instance) the adjoining part bends from the
light ; but when excited by gravitation the same part
bends towards the centre of gravity. In almost every
case we can clearly perceive the final purpose or advan-
tage of the several movements. Two, or perhaps more,
of the exciting causes often act simultaneously on the
tip, and one conquers the other, no doubt in accord-
ance with its importance for the life of the plant.
The course pursued by the radicle in penetrating the
ground must be determined by the tip; hence it
has acquired such diverse kinds of sensitiveness. It
is hardly an exaggeration to say that the tip of the
radicle thus endowed, and having the power of
directing the movements of the adjoining parts, acts
like the brain of one of the lower animals; the brain
being seated within the anterior end of the body,
receiving impressions from the sense-organs, and
directing the several movements,
INDEX.
ABIES,
A.
Abies communis, effect of killing or
injuring the leading shoot. 187
— pectinata, effect of killing or
injuring the leading shoot, 187
— _, affected by Heidium elatinum,
188
Abronia umbellata, its single, deve-
loped cotyledon, 78
——, rudimentary cotyledon, 95
—,, rupture of the seed coats, 105
Abutilon Darwinii, sleep of leaves
and not of cotyledons, 314
— , nocturnal movement of leaves,
823
Acacia Farnesiana, state of plant
when awake and asleep, 381, 382
——, appearance at night, 395
nyctitropic movements of
pinne, 402
——,, the axes of the ellipses, 404
lophantha, character of first
leaf, 415
— retinoides, circumnutation of
young phyllode, 236
Acanthosicyos horrida, nocturnal
movement of cotyledon 304
Acanthus candelabrum, inequality in
the two first leaves, 79
-—, petioles not arched, 553
—— latifolius, variability in first
leaves 79
e— mollis, seedling, manner of
breaking through the ground,
78, 79
—, circumnutation of young leaf,
249, 269
—— spinosus, 79
— movement of laves, 249
y
AMPHICARPGA.
Adenanthera pavonia, nyctitropie
movements of leaflets, 374
Zecidium elatinum, effect on the
lateral branches of the silver fir,
188
ZEsculus hiprocastanum, movementa
of radicle, 28, 29
——,, sensitiveness of apex of radicle,
172-174
Albizzia lophantha, nyetitropic move-
ments of leaflets, 383
, of pinne, 402
Allium cepa, conical protuberance
on arched cotyledon, 59
, circumnutation of basal half
of arched cotyledon, 60
—, mode of breaking through
ground, 87
——, straightening process, 101
—— porrum, movements of flower-
stems, 226
Alopecurus pratensis, joints affected
by apogeotropism, 503
Aloysia cttriodora, circumnutation
of stem, 210
Amaranthus, slec p of leaves 387
—- caudatus, noctural movement
of cotyledons, 307
Amorpha fruticosa, sleep of leaflets,
354
Ampelopsis trieuspidata, hyponastic
movement of hooked tips, 272-
275
Amphicarpea monoica, circumnuta-
tion and nyctitropic movements
of leaves, 265
——, effect of sunshine on leaflets,
445
—-, geotropic movements of
520
INDEX.
575
ANODA.
Anoda Wrightii, sleep of cotyledons,
302, 312
——, of leaves, 324
——,, downward movement of coty-
ledons, 444
Apheliotropism, or negative helio-
tropism, 5, 419, 432
Apios graveolens, heliotropic move-
ments of hypocotyl, 422-424
tuberosa, vertical sinking of
leaflets at night, 368
Apium graveolens, sleep of cotyle-
dons, 305
—, petroxelinum, sleep of cotylc-
dons, 30+
Apogeotropic movements effected by
jeints or pulvini, 502
Apogeotropism, 5, 494; retarded by
heliotropism, 501 ; concluding re-
marks on, 507
Arachis hypogea, circumnutation of
gynophure, 225
—, effects of rad’ation on leavis,
289, 29:3
——, movements of leaves, 357
——,, rate of movement, 404
, circumnutation of vertically
dependent young gynopliores, 519
, downward movement of the
same, 519
Arching of various organs, impor-
tance of, to secdling plants, 87,
88; emergence of hypocotyls or
epicotyls in the form of an, 553
Asparagus officinalis, circumnuta-
tion of plumules, 60-62.
, effect of lateral light, 484
Asplenium trichomanes, movement
in the fruiting fronds, 257, n.
Astragalus uliginosus, movement of
leaticts, 355
dvena sativa, movement of cotyle-
dons, 65, 66.
—-—, sensitiveness of tip of radicle
to moist air, 183
—-, heliotropic movement and cir-
cumnutation of cotyledon, 121,422
, Sensitiveness of cotyledon toa
lateral lizht, 477
——, young sheath-like cotyledons
strongly apogeotropic, 499”
BRASSICA.
Avena sativa, movements of oldish
cotyledons, 499, 500
Averrhoa bilimbi, leaf asleep, 330
—, angular movements when
going to sleep, 331-345
—-, leaflets exposed to bright
sunshine, 447
Azalea Indica, circumnutation of
stem, 208
B.
Bary, de, on the effect of the Auci-
dium on the silver fir, 188
Batalin, Prof, on the nyctitropic
movements of leaves, 283; on tlie
sleep of leaves of Sida napaa,
322; on Polygonum aviculare,
387; on the effect of sunshine on
leaflets of Oxalis acetosella, 447
Bauhinia, nyctitropic movements,
373
—,movementsof petioles of young
seedlings, 401
—, appearance of young plants
at night, 402
Beta vulgaris, circumnutation of
hypocotyl of seedlings, 52
—, movements of coty!edons, 52,
, effect of light, 124
, nocturnal movement of coty-
ledons, 307
» heliotropic movements of,
420
—, transmitted cffect of light on
hypucotyl, 482
——, apogeotiopic movement of
hypocotyl, 496
Bignonia capreolata, apheliotropic
movement of tendrils, 432, 450
Bouché on Melaleuca ericcefolia
383
Brassica napus, cireumnutation ot
fluwer-stem~, 226
Brass.ca oleracea, circumnutatior
of seedling, 10
—, of radicle, 11
—, geotropic movement of radicle,
11
INDEX.
BRASSICA,
Brassica oleracea, movement of
buried and arched hypocotyl, 13,
14, 15
——, conjoint circumnutation of
Fxpecaty! and cotyledons, 16, 17,
1
-——, of hypocotyl in darkness, 19
—, of a cotyledon with hypocotyl
secured to a stick, 19, 20
-——, rate of movemvnt, 20
—, ellipses described by hypo-
cotyls when erect, 105
—, movements of cotyledons, 115
——, —— of stem, 202
——, — of leaves at niyht, 229,
230
——., sleep of cotyledons, 301
—, cireumnutation of hypocotyl
of seedling plant, 425
——, heliotropic movement and
circumnutation of hypocotyls,
426
—, effect of lateral light on hypo-
cotyls, 479-482
—, apogeotropic movement of
hypocotyls, 500, 501
Brassica rapa, movements of leaves,
230
Brongniart, A., on the sleep of
Strephium floribundum, 391
Bruce, Dr., on the sleep of leaves in
Arerrhoa, 330
Bryophyllum (vel Calanchoe) calyei-
num, movement of leaves, 237
Cc.
Camellia Japonica, circumnutation
of leaf, 231, 232
Candolle, A. de, on Trapa natans,
95; on sensitiveness of coty-
ledons, 127
Canna Warscewiczii, circumnuta-
tion of plumules, 58, 59
—, of leaf, 252
Cannabis sativa,
leaves, 250
, nocturnal movements of coty-
ledons, 307
movements of
CASSIA,
Cannabis sativa, sinking of the young
leaves at night, 444
Cassia, nyctitropic movement of
leaves, 369
Cassia Barclayana, nocturnal move-
ment of leaves, 372
, slight movement of leaflets,40L
— calliantha, uninjured by ex-
posure at night, 289, n.
—, nyctitropic movement of
leaves, 371
—, circumnutating movement of
leaves, 372
—— corymbosa, cotyledons sensi-
tive to contact, 126
, nyctitropic movement of
lvaves, 369
floribunda, use of sleep move
ments, 289
——, effect of radiation on the
leaves at night, 294
—, circumnutating and nycti-
tropic movement of a terminal
leaflet, 372, 373
—-, movements of young and older
leaves, 400
—— florida, cotyledons sensitive to
contact, 126
——,, sleep of cotyledons, 308
—— glauca, cotyledons sensitive to
coutact, 126
——., sleep of cotyledons, 308
—— levigata, effect of radiation
on leaves, 289, n.
—— mimosoides, movement of coty-
ledons. 116
——,, sensitiveness of, 126
——, sleep of, 308
—,, nyctitropic
leaves, 372
——, effect of bright sunshine on
cotyledons, 446
—— neglecta, movements cf, 117
—, effect of light, 124
——., sensitiveness of cotyledong
movement of
—— nodosa, non-sensitive cotyle
dons, 126
——,, do not rise at nixht, 308
—— pubescens, non-sensitive coty
ledons, 126
INDEX
677
OASBIA,
Cassia pubescens, uninjured Sy ex-
posure at night, 293
——, sleep of cotyledons, 308
—-, nyctitropic movement of
leaves, 371
—, circumnutating movement
of leaves, 372
—, nyctitropic
petioles, 400
—, diameter of plant at night,
402
sp.(?) movement of cotyledons,
6
movement of
tora, circumnutation of coty-
ledons and. hypocotyls, 34, 35,
109, 308
—, effect of light, 124, 125
—, sensitiveness tv contact,
125 .
—, heliotropic movement and
circumnutation of hypocotyl,
431
—., hypocotyl of scedling slightly
heliotropic, 454
——, apogeotropic movement of old
hypocotyl, 497
——, movement of hypocotyl of
young seedling, 510
Caustic (nitrate of silver), effect of,
on radicle of bean, 150, 156; on
the common pea, 160.
Cells, table of the measurement
of, in the pulvini of Oxalis
corniculata, 120; changes in,
547
Centrosema. 305
Ceratophyllum demersum,
ments of stem, 211
Cereus Landbeckii, its rudimentary
cot) ledons, 97
speciossimus, circumnutation
of stem, 206, 207
Cerinthe major, circumuutation of
hypocotyl, 49
——,, of cotyledons, 49
——, ellipses described by hypo-
cotyls when erect, 107
— effect of darkness, 124
Chatin, M., on Pinus Nordman-
niana, 389
Chenopodium
move-
album, sleep of
ORINUM.
leaves, but not of cotyledons, 314,
19
Chenopodium album, movement of
leaves, 387
Chlorophyll injured by bright light,
446
Ciesielski, on the scnsitiveness of
the tip of the radicles, 4, 523
Circumuutation, meaning explained
1; modified, 263-279; and helio-
tropism, relation between, 435;
of paramount importance to every
plant, 547
Cissus discclor, circumnutation of
leaf, 233
Citrus aurantium, circur uutaticon
of epicoty], 28
——,, unequal cotyledons, 95
Clianthus Dumpieri, nocturnal
movement of leaves, 297
Cobeea scandens, cireumnutation of,
270
Cohn, on the water se-reted by
Lathrva squamaria, 86, n.; on
the movement of leaflets of Oxa-
lis, 447
Colutea arborea, nocturnal move-
ment of leaflets, 355
Conifere, circumnutation of, 211
Coronilla rosea, leaflets asleep, 355
Corylus avellana, cireumnutation of
young shoot, cmitted from the
epicotyl, 55, 56
—, arcl:ed epicotyl, 77
Cotyledon umbilicus, circumnuta-
tion of stolons, 219, 220
Cotyledons, rudimentary. 94-98;
circumnutation of, 109-112; noc-
turnal movements, 111, 112; pul-
vini or joints of, 112-122; dis-
turbed perivdic movements by
light, 123; sensitiveness of, to
contact, 125; nyctitropic move-
meuts of, 283, 297; list of edty-
ledons which rise or sink at
night, 300; concluding remarks
on their movemeuts, 311
Crambe maritima, circumnutation of
leaves, 228, 229
Crinum capense, shape af leaves,
253
572
INDEX.
CRINUM,
Crinum capense, circumnutation of,
254
Crotolaria (sp.?), sleep of leaves,
340
Cryptogams, circumnutation © of,
257-259
Cucumis dudaim, movement of coty-
ledons, 43, 44
— ,, sleep of cotyledons, 30£
Cucurbita aurantia, movement of
hypocotyl, 42
—, cotyledons vertical at night,
304
— ovifera, geotropic movement
of radicle, 38, 39
—, circumnutation of arched hypo-
eotyl, 39
—, of straight and vertical hypo-
cotyl, 40
——, movements of cotyledons, 41,
42, 115, 124
—, position of radicle, 89
—, rupture of the seed - coats,
102
——, cireumnutation of hypocotyl
when erect, 107, 108
—, sensitiveness of apex of ravli-
ele, 169-171
——, cotyledons vertical at night,
—, not affected by apogevtropism,
509
——, tips cauterised transversely,
‘
Curvature of the radicle, 193
Cycas pectinata, cireumnutation of
young lcaf, whilst emerging from
the ground, 58
——-, first leaf arched, 78
—, circumnutation of terminal
leaflets, 252
Cyclanen Persicum, movement of
ectzledon, 46
—, undeveloped cotyledons, 78,
96
-—, cireumnutation of peduncle,
225
——, —, of leaf, 246, 247
——, downward apheliotropic move-
ment of a flower peduncle, 433-
435
DESMODIUM.
Cyclamen Persicum, burying of th.
pods, 433
Cyperus alternifolius, circumnuti-
tion of stem, 212
—, movemcnt of stem, 509
Cytisus fragrans, circumnutation of
hypocotyl, 37
—, sleep of leaves, 344, 397
—, apogotropic movement of
stem, 494-49
D.
Dahlia, circumnutation of young
leaves, 244-246
Dalea alopecuroides, leaflets de-
pressed ai nigi.t, 354
Darkness, effect of, on the move-
ment of Icaves, 407
Darlingtonia Californica, its leaves
or pitchers aphefiotropic, 450), n.
Darwin, Charles, on Maurundia
semperflvrens, 225; on the Swedish
turnip, 230, n.; movements of
climbing plants, 266 271; the
heliotropic movement of the ten-
drils of Bignonia capreolata, 433;
revolution of climbing plints,
451; on the curling of a tendril,
570 :
—, Erasmus, on the peduncles of
Cyclamens, 433
—, Francis, on the radicle of
Sinapis alba, 486; on Hygrosco-
pic seeds, 489, n.
Datura — stramonium., nocturnal
movement of cotyledons, 298
Delpino, on cotyledons of Cheero-
phyllum and Corydalis, 96, x.
Delphinium nudicaule, mode of
breaking through the ground, 80
, continent petioles of two coty-
ledons, 553
Desmodium gyrans, movemcnt of
leaflets, 257, n.
, position of leaves at night.
5
—, sleep of leaves, not of coty
ledons, 314
1 ——. ceircumnutation and nyeti-
INDEX 579
DESMODIUM.
ype movement of leaves, 358—
Desmodium gyrans, movement of
lateral leaflets, 361
——. jerking of leaflets, 362
——,, nyctitropic movement of peti-
oles, 400, 401
——, diameter of plant at night,
402 e
—, lateral movement of leaves,
404
—, zigzag movement of apex of
leaf, 405
——, shape of lateral leaflet, 416
vespertilionis, 364, n.
Deutzia gracilis, circumnutation of
stem, 205
Diageotropism, 5; or transverse-
geotropism, 520
Diahcliotropism, 5; or Transversal-
Heliotropismus of Frank, 419;
influenced by epinasty, 439;
by weight and apogeotropism,
440
Dianthus caryophyllus, 230
, circumnutation of young leaf,
231, 209
Dicotyledons, circumnutation wide-
ly spread among, 68
Dionzcea, oscillatory movements of
leaves, 261, 271
Dionea museipula, c:rcumutation
of young expanding leaf, 239,
240
— , closure of the lobes and cir-
cumnutation of a full-grown leaf,
241
—, oscillations of 242-244
Diurnal sleep 419
Drosera Capens’s, structure of first-
formed leaves, 414
rolundifilia, movement of
young leat, 237, 238
—, of the tentacles, 239
-——, sensitiveness of tentacles,
261
shape of leaves, 414
—,, leaves not heliotropic, 450
——, leaves circumnutate largely,
454
——. sensitiveness of 570
EUCALYPTUS.
Duchartre on Tephrosia caribea,
354; on the nyctitropic movemc nt
of the Cassia, 369
Doval-Jouve, on the movements of
Bryophyllum calycinum, 237; of
the narrow leaves of the Grami-
nce, 413
Dyer, Mr. Thiselton, on the leaves
of Crotolaria, 340 ; on Cassia flori-
bunda, 369, n., on the absorbent
hairs on the buried flower-heads
of Trifolium subterraneum, 517
E.
Echeveria stolonifera, circumnuta-
tion of leaf, 237
Echinocactus viridescens, its rudi-
mentary cotyledons, 97
Echinocystis lobata, movements of
tendrils, 266
—, apogeotropism of teudrile,
510
Elfving, F., on the rhizomes of
Sparganium ramosum, 189; on
the diageotropic movement in the
rhizomes of some plants, 521
Elymus arenareus, leaves closed
during the day, 413
Embryology of leaves, 414
Engelmann, Dr., on the Quercus
virens, 85
Epinasty, 5, 267
Epicotyl, or plumule, 5; manner
of breaking through the ground,
77; emerges from the ground
under the form of an arch, 553
Erythrina caffra, sleep of leaves,
367
corallodendron, movement of
terminal leafict, 367
erista-galli, effect of tem
perature on sleep of leaves,
318
tropic movement of
leaflets, 367
Eucalyptus resinifera, circumnutar
tion of leaves, 244
circumnutation and nyeti-
terminal
INDEX.
-
EUPHORBIA.
Euphorbia jacquinexflora, nycti-
tropic movement of leaves, 388
¥.
Flahault, M., on the rupture of
seed-coats, 102-104, 106
Flower-stems, circumrutation of,
223-226
Fragaria Rosacea, circumnutation
of stolon, 214-218
Frank, Dr, A. B., (he terms Helio-
tropism and Geotropism, first
used by him, 5,7.; radicles acted
on by geotropism, 70, n.; on the
stolons of Fragaria, 215; periodic
and nyctitropic movements of
leaves, 284; on the root-leaves
of plants kept in darkness, 443;
on pulvini, 485; on natural
selection in connection with
geotopten, heliotropism, &c.,
57!
—, on Transversal-Heliotropis-
mus, 419
Fuchsia, cireumnutation of stem,
205, 206
a.
Gazania_ ringens, circumnutation
of stem, 208
Genera containing sleeping plants,
820, 321
Geotropism, 5; effect of, on the
primary radicle, 196; the reverse
of apogeotropism, 512: effect on
the tips of radicles, 543
Geranium cinereum, 304
Endressit, 304
— Ibericum, nocturnal movement
of sotyledons, 298
— - Richardsoni, 304
-~ - rotundifolium, nocturnal move-
ment of cotyledon, 304, 312
——- subcaulescens, 304
Germinvating seed, history of a,
548 :
GYMNOSPERMSB.
Githago segetum, cireumnutation of
hypocotyl, 21, 108
——, burying of hypocotyl, 109
——, seedlings feebly illuminated,
124, 128
——,, sleep of cotyledon, 302
—, leaves, 321
Glaucium luteum, ciycumnutation
of young leaves, 228
Gleditschia, sleep of leaves. 368
Glycine hispida, vertical sinking of
leaflets, 366
Glycyrrhiza, leaflets depressed at
night, 355
Godlewskl, Emil, on the turge-
scence of the cells, 485
Gooseberry, effect of radiation, 284
Gossypium (var. Nankin cotton),
circumnutation of hypocotyl,
22
——, movement of cotyledon, 22, 23
——,, sleep of leaves, 324
—— arboreum (?), sleep of cotyle
dons, 303
Braziliense, nocturnal move-
ment of leaves, 32+
——, sleep of cotyledons, 303
—— herbaceum, sensitiveness of
apex of radicle, 168
——, radicles cauterised trans-
versely, 537
—— maritimum, nocturnal move-
ment of leaves, 324
Gravitation, movements excited by,
567
Gray, Asa, on Delphinium nudi-
caule, 80; on Megarrhiza Cali-
fornica, 81; on the movements in
the fruiting fron-ls of Asplenium
trichomanes, 257; on the Amphi-
carpea monoica, 520 ; on the
Ipomea Jalappa, 557
Grease, effect of, on radicles and
their tips, 182, 185
Gressner, Dr. H., on the cotyledons
of Cyclamen Persicum, 46, 77°
on hypocotyl of the same, 96
Gymnosperms, 389
INDEX.
581
HABEBLANDT.
H.
fiaberlandt, Dr., on the protube-
rance on the hypocotyl of Allium,
59; the importance of the arch
to seedling plants, 87; sub-
aerial and subterranean cotyle-
dons, 110, n.; the arched Lypo-
cotyl, 554
Hemat.aylon Campechianum, noc-
turnal movement of leaves, 368,
369
Hed: ra_ helix,
stem, 207
Hedysarum coronarium, nocturnal
movements of leaves, 356
Helianthemum prostratum, geotro-
pic movement of fluwer-heads,
518
Helianthus annuus, circumnutation
of hypocotyl, 45
—, arching of hypocotyl, 90
—, nocturnal movement of coty-
ledons, 305
Heliotropism, 5; uses of, 449; a
modified form of cireumnutution,
490
Helleborus niger, mode of breakiug
through the ground, 86
Hensen, Prof., on roots in worm-
burrows, 72
circumnutation of
Henslow, Rev. G., on the coty-
ledons of fhalaris Canariensis,
62
Hofmeister, on the curious move-
ment of Spirogyra, 3, 259, n.; of
the leaves of Pistia strativtes,
255; of cotyledons at night, 297 ;
of petals, 414
—— and Batalin on the movements
of the cabbage, 229
STooker, Sir J., on the effect of light
on the pitchers of Sarracenia,
450 ‘
Hypocotyl, 5; manner of breuk-
ing through the ground, 77;
emerges under the form of an
arch, 553
Hypocotyls and Epicotyls, circum-
TPOMA,
nutation and other movements
when arched.98; power of straight-
ening themselves, 100; rupture
of the seed-coats, 102-106; illus-
tration of, 106; circumnutation
when erect, 107; when in dark
108
Hyponasty, 6, 267
I.
Iberis umbellata, movemeut of stem,
202
Illumination, effect of, on the sleep
of leaves, 398
Imatophyllum vel Clivia (ap. ?),
movemeut of leaves, 255
Indigofera tinctoria, leaflets do-
pressed at night, 354
Inheritance in plants, 407, 491
Insectivorous and climbing plants
not heliotropic, 450; influence of
light on, 488
Ipomea bona nox, arching of hypo-
cotyl, 90
——, nocturnal position of coty-
ledons, 306, 312
cerulea vel Pharbitis nil,
circumnutation of seedliigs,
47
, movement of cotyledons, 47-
49, 109
——, nocturnal movements of coty-
ledons, 305 *
——,, sleep of leaves, 386
——, sensitiveness to light, 451
. the hypocotyledonous stems
heliotropic, 453
—, coccinea, position of coty-
ledons at night, 306, 312
— leptophylla, mode of breaking
through tle ground, 83, 8+
—, arching of the petioles of the
cotyledons, 90
—-, difference in sensitiveness to
gravitation in different parts,
509
—, extraordinary manner of gor
mination, 557
INDEX.
TPOMCEA.
Ipomea pandurata, manner of ger-
mination, 84, 557
—— purpurea (vel Pharbitis his-
pida), nocturnal movement of
cotyledons, 305, 312
— , sleep of leaves, 386
——, sensitiveness to light, 451
—, the hypocotyledonous stems
heliotropic, 453
Tris pseudo-acorus, circumnutation
of leaves, 253
Trmisch, on cotyledons of Ranun-
culus Ficaria, 96 |
Ivy, its stems heliotropic, 451
kK.
Kerner on the bending down of pe-
duncles, 414
Klinostat, the, an instrument de-
vised by Sachs to eliminate geo-
tropism, 93
Kraus, Dr. Carl, on the underground
slioots of Triticum repens, 189;
on Cannabis sativa, 250, 307,
el ; on the movements of leaves,
18
L.
Lactuea scariola, sleep of cotyle-
dons, 305
Lagenaria vulgaris, circumnutation
of seedlings, 42
2—, of cotyledons, 43
—, cotyledons vertical at night,
304
Lathrza squamaria, mode of
breaking through the ground,
85
—, quantity of water secreted,
85, 86, n.
Tathyrus nissolia, circumnuta-
tion of stem of young seedling,
——, ellipses described by, 107,
108
Leaves, circumnutation of, 226-
LOTUS.
262; dicotyledons, 226-252; mo
nocotyledons, 252-257 ; nyctitro-
pism of, 289; their temperature af-
fected by their position at night,
294; nyctitropic or sleep move-
ments, 315, 394; periodicity of
their movements inherited. 407;
embryology of, 414; s.-called
diurnal sleep, 445
Leguminosz, sleep of cotyledons,
308; sleeping species, 340
Le Maout and Decaisne, 67
Lepidium sativum, sleep of cotyle-
dons, 302
Light, movements excited by 418,
563; influence on most vegetable
tissues, 486; acts on plant as on
the nervous system of animals,
487
Lilium auratum, circumnutation of
stem, 212
,apogeotropie movement of
stem, 498, 499
Linneus, ‘Somnus Plantarum,’
280; on plants sleeping, 320;
on the leaves of Sida abutilon,
324; on Ginothera mollissima,
383
Linum Berendieri, nocturnal move-
ment of cotyledons, 298
—— usitatissimum, circumuutation
of stem, 203
Lolium perenne, joints affected by
apogeotropism, 502
Lonicera brachyroda, hooking of tho
tip, 272
, sens'tiveness to light, 453
Loomis, Mr., on the movements in
the fruiting fronds of Asplentum
trichomanes, 257
Lotus aristata, effect of radiaticn
on leaves, 292
—— Creticus, leaves awake ard
asleep, 354
— Gebelii, nocturnal movement
of cotyledons, 308
“so provided with pulvini,
—— Jacobzus, movements of coty
ledons, 35, 109
——, pulvini of, 115
INDEX.
583
LOTUS.
Lctus Jacobzus, movements at
night, 116, 121, 124 ;
, development of pulvini, 122
——, sleep of cotyledons, 308, 313
-—, nyctitropic movement of
leaves, 353
major, sleep of leaves, 352
—— perigrinus, movement of leaf-
lets, 353
Lunularea vulgar ts, cireumnutation
of fronds, 258
Lupinus, 340
albifrons, sleep of leaves, 344
— Hartwegii, sleep of leaves,
341
luteus, cireumnutation of coty-
ledons, 38, 110
, effect of darkness, 124
Lupinus, position of leaves when
asleep, 341
—, different positions of leaves at
night, 343
, varied movements of leaves
and leaflets, 395
Menziesii, sleep of leaves, 343
—— mutabilis, sleep of leaves,
343
nanus, sleep of leaves, 343
—— pilosus, sleep of leaves, 340,
1
— polyphyllus, sleep of leaves,
343
— pubescens, sleep of leaves by
day and night, 342
, position of: petioles at night,
343
-——, movements of petioles, 401
-— speciosus, circumnutation of
leaves, 236
Lynch, Mr. R., on Pachira aqua-
tica, 95, .; sleep movements of
Averrhoa, 330
XM.
Maranta arundinacea, nyctitropic
movement of leaves, 389-391
—, after much agitation do not
sleep, 319
38
MELILOTOS.
Marsilia quadrifoliata, effect of ra-
diation at night, 292
, circumnutation and nycti-
tropic movement of leaflets, 392-
304
» Yate of movement, 404
Martins, on radiation at night,
284, n.
Masters, Dr. Maxwell, on the lead-
ing shoots of the Coniferz, 211
Maurandia semperflorens, cireamnu-
tation of peduncle, 225
Medicago maculata, nocturnal posi-
tion of leaves, 345
marina, leaves awake and
asleep, 344 '
Meehan, Mr., on the effect of an
Aecidium on Portulaca oleracea,
189
Megarrhiza Californica, mode of
breaking through the ground,.
81
——, germination described by Asa.
Gray, 82
, singular manner of germina--
tion, 83, 556
Melaleuca ericcefolia, sleep of leaves,
383
Melilotus, sleep of leaves, 345
alba, sleep of leaves, 347
cerulea, sleep of leaves, 347
dentata, effect of radiation ai
night, 295
—— elegans, sleep of leaves, 347
gracilis, sleep of leaves, 347
infesta, sleep of leaves, 347
Italica, leaves exposed at:
night, 291
, Sleep of leaves, 347
—— macrorrhiza, leaves exposed at
night, 292
——,, sleep of leaves, 347
—— messanensis, sleep of leaves on
full-grown and young plants,
348, 416
officinalis, effect of exposure of
leaves at night, 290, 296
, nocturnal movement of leaves,
346, 347
——,, circumnutation of leaves, 348
, movement of petioles, 401
584
INDEX.
MELILOTUS.
Melilotus parviflora, sleep of caves,
347
— Petitpirrreauu, leaves exposed
at night, 291, 296
—-, sleep of leaves, 347
—- secundiflora, sleep of leaves,
347
—— swaveolens, leaves exposed at
night, 291
——, sleep of leaves, 347
——- sulcata, sleep of leaves, 347
— Taurica, leaves exposed at
night, 291
, sleep of leaves, 347, 415
‘Methods of observation, 6
Mimosa albida, cotyledons vertical
at night, 116
—, not sensitive to contact, 127
——., sleep of cotyledons, 308
, rudimentary leaflets, 364
—, nyctitropic movements of
leaves, 379, 380
—., circumnutation of the main
petiole of young leaf, 381
-——, torsion, or rotation of leaves
and leaflets, £00
-——, first true leaf, 416
, effect of bright sunshine on
basal leaflets, 445
marginata, nyctitropic move-
ments of leaflets, 381
pudica, movement of coty-
ledons, 105
—, rupture of the seed-coats,
105
—, circumnutation of cotyledons,
109 :
—, pulvini of, 113, 115
—, cotyledons vertical at night,
116
——, hardly sensitive to contact,
127
-—, effect of exposure at night,
293 ;
-—, nocturnal movement of leaves,
297
-—, sleep of cotyledons, 308
—, circumnutation and nycti-
tropic movement of main petiol2,
374-378
—, of leaflels, 378
NEPTUNIA.
Mimosa albida, cireumnutation and
nyctitropic movement of pinus,
402
—, number of ellipses describe2
in given time, 406
, effect of bright sunshine on
leaflets, 446
Mirabilis jalapa and longiflora,
nocturnal movements of cotyle-
dons, 307
—, nyctitropic movement of
leaves, 387
Mohl, on heliotropism in ten-
drils, stems, and twining plants,
451
Momentum-like movement, the ac-
cumulated effects of apogeo-
tropivm, 508
Monocotyledons, sleep of leaves,
389 -
Monotropa hypopitys, mode of
breaking through the ground, 86
Morren, on the movements of
stamens of Sparmannia and
Cereus, 226
Miiller, Fritz, on Cassia tora, 34;
on the circumnutation of Linum
usitatissimum, 203; movements
of the flower-stems of an Alisma,
226
Mutisia clematis,
leaves, 246
, leaves not heliotropic, 451
movement of
N.
Natural selection in connection
with geotropism, heliotropism,
&e., 570
Nephrodium molle, circumuutation
of very young frond, 66
, of older frond, 257
-—, slight movement of fronda
509
Neptunia oleracea, sensitiveness to
contact, 128
——,, nyctitropic movement of leaf:
lets, 374
——,, of pinnss, 402
INDEX.
585
NICOTIANA.
Nicotiana glauca, sleep of leaves,
385, 386
—, circumnutation of leaves,
386
Nobbe, on the rupture of the seed-
coats ina seedling of Martynia,
105
Nolana prostrata, movement of seed-
lings in the dark, 50
——., circumuutation of seedling,
108 3
Nyctitropic movement of leaves,
560
Nyctitropism, or sleep of leaves,
281; in connection with radia-
tion, 286; object gained by it,
413
0.
Observati: n, methods of, 6
Gnothera mollissima, sleep of leaves,
383
Opuntia basilaris, conjoint circum-
nutation of hypocotyl and coty-
ledon, 44
——, thickening of the hypocotyl,
96
——, circumnutation of hypccotyl
when erect, 107
——,, burying of, 109
Orange, seedling, circumnutation
of, 510
Orchis pyramidalis, complex move-
ment of pollinia, 489
Ozxalis acetosella, circumnutation of
flower-stem, 224
—, effects of exposure to radia-
tion at night, 287, 288, 296
, circumnutation and nycti-
tropiz movement in full-grown
leaf, 326
— , circumnutation of leaflet when
asleep, 327
——, rate of circumnutation of
leaflets, 404
-——, effect of sunshine on leaflets,
447
— , circumnutation of peduncle,
506
OXALIS,
Oxalis acetosella, seed-capsules, only
occasionally busied, 518
— _ articulatu, nocturnal muve
ments of cotyledons, 307
——_ (Biophytum) sensitiva, ra
pidity of movement of cotyledons
during the day, 26
—,, pulviuus of, 113
——, cotyledons vertical at night,
116, 118
bupleurifolia, circumnutation
of foliaceous petiole, 328
, nyctitropic movement of ter-
minal leaflet, 329
carnosa, circumuutation of
flower-stem, 223
, epinastic movements of flower-
stem, 504
——, effect of exposure at night,
288, 296
, movements of the flower-pe-
duncles due to upoyeotropism
and other forces, 503-506
corniculata (var. cuprea),
movements of cotyledons, 26
, Tising of cotyledons, 116
—, rudimentary pulviui of coty-
ledons, 119
——, development of pulvinus,
122
, effect of dull light, 124
——, experiments on leaves at night,
288
—— floribunda, pulvinus of coty-
ledons, 114
—-, nocturnal
307, 313
fragrans, sleep of leaves,
movement, 118,
— Ortegesii, circumnutation of
flower stems, 224
—, sleep of large leaves, 327
—., diameter, of plant at nigh‘,
402
— , large leaflets affected by bright
sunshine, 447
— Plumierii, sleep of leaves, 327
purpurea, exposure of leaflets
at night, 293
— rosea, ciicumnutation of coty
leduns, 23, 24
586
INDEX.
OXALIS,
Oxalis rosea, pulvinus of, 113
——, movement of cotyledons at
night. 117, 118, 307
, effect of dull light, 124
—, non-sensitive cotyleduns,
127
sensitiva, movement of coty-
ledons, 109, 127, 128
, circumnutation of flower-stem,
224
, nocturnal movement of coty-
ledons, 307, 312
—, sleep of leaves, 327
— tropeoloides, movement of co-
tyledons at night, 118, 120
—— Valdiviana, conjoint circum-
nutation of cotyledons and hypo-
cotyl, 25
——,, cotyledons rising vertically at
night, 114, 115, 117, 118
——,, non-sensitive cotyledons, 127
—,, nocturnal movement of coty-
ledon, 307, 312
— ,, sleep of leaves and not of co-
tyledons, 315
—, movements of leaves, 327
P.
Pachira aquatica, unequal cotyle-
dons, 95, n.
Pancratium littorale, movement of
leaves, 255
Paraheliotropism, or diurnal sleep
of leaves, 445
Passiflora gracilis, cireumnutation
and nyctitropic movement of
lraves, 383, 384
——, apogeotropic movement of
tendrils, 510
, sensitiveness of tendrils, 550
Pelargonium zonale, cirzumnutation
of stem, 203
——,and downward movement of
young leaf, 232, 233, 269
Petioles, the, rising of, beneficial to
plant at night, 402
Petunia violacea, downward move-
PHASEOLUS.
ment and cireumnutation of very
young leaf, 248, 249, 269.
Pfeffer, Prof., on the turgescence of
the cells, 2; on pulvini of leaves,
113, 117; sleep movements of
leaves, 280, 283, 284; nocturnal
rising of leaves of Malva, 324;
movements of leaflets in Desno-
dium gyrans, 358; on Phyllan-
thus Niruri, 388; influence of a
pulvinus on leaves, 396; periodic
movements of sleeping leaves,
407, 408; movements of petals,
414; effect of bright sunshine on
leaflets of Robinia, 445; effect of
light on parts provided with pul-
vini, 463
Phalaris Canariensis, movements of
old seedlings, 62
, circumnutation of cotyledons,
63, 64, 108
. heliotropic movement and cir-
cumnutation of cotyiedon towards
a dim lateral light, 427
——, sensitiveness of cotyledon to
light, 455
, effect of exclusion of light
from tips of cotyledons, 456
, manner of bending towards
light, 457
——. effects of painting with Indian
ink, 467
—, transmitted effects of light,
, lateral illumination of tip,
470
——,, apogeotropic movement of the
sheath-like cotyledons, 497
——., change from a straight up-
ward apogeotroyic course to cir-
cumnutation, 499
, apogeotropic movement of
cotyledons, 500
Phaseolus Hernandesii, nocturnal
movement of leaves and leaficts,
368
caracalla, 93
, nocturnal movement of leaves,
368
——,, effect of bright sunshine op
leaflets, 446
INDEX.
587
PHASEOLUS.
Phaseolus multiflorus, movenent of
radicles, 29
——, of young radicle, 72
—~——,, of liypocotyl, 91, 93
, 8eusitiveness of apex of radicle,
163-167
——, to moist air, 181
-—, cauterisation and grease on
the tips, 535
—, nocturnal movement of leaves,
368
——., nyctitropie movement of the
first unifoliate leaves, 397
— Roxburghii, effect of bright
sunshine on first leaves, 445
—., vulgaris, 93
——, sleep of leaves, 318
——, vertical sinking of leaflets at
night, 368
Phyllanthus Niruri, sleep of leaf-
lets, 388
— linoides, sleep of leaves,
387
Pilocereus Hvulletiit, rudimentary
cotyledons, 97
Pimelia spectabilis, sleep of leaves,
387
Pincers, wooden, through which
the radicle of a bean was allowed
to grow, 75
Pinus austriaca. circumnutation of
leaves, 251, 252
— Nordmanniana, nyctitropic
movement of leaves, 389
— pinaster, circumnutation of
hypocotyl, 56
—, movement of two opposite
cotyledons, 57
—, circumnutation of young leaf,
250, 251
—-, epinastic dowuward move-
ment of young leaf, 270
Fistia strativtes, movement of
loaves, 255
Pisum sativum, sensitiveness of
upex of radicle, 158
——, tips of radicles cauterised
transversely, 534
Plants, sensitiveness to light,
449; hygroscopic movements of,
489
QUERCUS.
Plants, climbing, circumnutation of,
261; movements of, 55)
» mature, circumnutation of.
201-214
Pliny on the sleep-movements af
plants, 280
Plumbago Capensis, civeumnutation
of stem, 208, 209
Poinciana Gilliesii, sleep of leaves,
368
Polygonum aviculare, leaves vertical
at night, 387
convolvulus, sinking of the
leaves at niglit, 318
Pontederia (sp.?), circumnutation
of leaves, 256
Porlieria hygrometrica, circum-
nutation an nyctitropie move-
ments of petiole of leaf, 335,
336
——, effect of watering, 336-338
——,, leaflets closed during the day,
413
Portulaca oleracea, efiect of Aici-
dium on, 189
Primula Sinensis, conjoint circum-
nutation of hypocotyl and coty-
ledon, 45, 46
Pringsheim on the injury to chloro-
phyll, 446
Prosopis, nyctitropic movements of.
leatiets, 374
Psoralea acaulis, nocturnal move-
ments of leaflets, 354
Pieris aquilina, rachis of, 86
Pulvini, or joints; of cotyledons,
112-122; influence of, on the
movements of cotyledons, 313;
effect cn nyctitropie movements,
396
Q.
Quercus (American sp.), cireumnu-~
tation of young stem, 53, 54
robur, movement of radicles,
54, 55
——, sensitiveness of apex of
radicle, 174-176
INDEX.
QUERCUS.
Quercus virens, manner of germina-
tion, 85, 557 .
R.
Radiation at night. effect of, on
laves, 284-286
Radicles, manner in which they
penctrate the ground. 69-77 ; cir-
cumnutation of, 69; experiments
with split sticks, 74; with
wooden pincers, 75 ; sensitiveness
of apex to contact and other irri-
tants, 129; of Vicia faba, 132-
158; various experiments, 135-
140; summary of results, 143-151;
power of an irritant on, com-
pared with geotropism, 151-154 ;
sensitiveness of tip to moist
air, 180; with greased tips,
185; effect of killing or injuring
the primary radicle, 187-191;
curvature of, 193; affected by
moisture, 198; tip alone sensitive
to geotropism, 549; protrusion
and circumnutation ina germina-
ting seed, 548; tip highly sen-
sitive, 550; the tip acts like the
brain of one of the lower animals,
573
-——, secondary, sensitiveness of
the tips in the bean, 154; become
vertically geotropic, 186-191
Ramey on the movements of the
cotyledons of Mimosa pudica,
and Clianthus Dampieri at night,
297
Ranunculus Ficaria, mode of
breaking through the grvund,
86, 90
—-—, single cotyledon, 96
, eftcet of lateral light, 484
Haphanus sativa, 8 nsitivencss of
apex of radicle, 171
, sleep of cotyledons, 301
Rattan, Mr., on the germination of
the seeds of Megarrhiza Califor-
nica, 82
Relation between circumnvtation
and heliotropism, 435
SACHS.
Reseda odorata, hypocotyl of seed.
ling slightly heliotropic, 454
Reversion, due to mutilation, 190
Rhipsalis cassytha, radimentery co-
tyledons, 97
Ricinus Borboniensis, circumnuta-
tion of arched hypocotyl, 53
Robinia, effect of bright sunshine
on its leaves, 445
— pseudo-acacia, leaflets vertical
at night, 355
Rodier, M., on the movements of
Ceratophyllum demersum, 211
Royer, Ch., on the sleep-movements
of plants, 281, ».; on the sleep of
leaves, 318 ; the leaves of Medi-
cago maculata, 345; on Wistaria
Sinensis, 354
Rubus idous (hybrid) circumnuta-
tion of stem, 205
——, apogeotropic movement of
stem, 498
Ruiz and Pavon, on Porlieria hy-
grometrica, 336 ;
Sacus on “ revolving nutation,” 1;
intimate connection between tur-
gescence and growth, 2,”.; coty-
ledon of the onion, 59; adapta-
tion of root-hairs, 69 ; the move-
ment of the radicle, 70, 72, 73;
movement in the hypocotyls of
the bean, &., 91; sensitiveness
of radieles, 131, 145, 198; sensi-
tiveness of the primary radicle
in the bean, 155; in the com-
mon pea, 156; effect of moist
air, 180; of killing or injuring
the primary radicle, 186, 187;
circumnutation of flower-steins,
225; epinasty, 268; movement
of leaflets of Trifolium incar-
natum, 350; action of light in
modifying the periodic move-
ments of leaves, 418; on geotro-
pism and heliotropism, 436, n.:
on Tropeolum majus, 458°
INDEX.
589
SARRACENIA,.
on the hypoentyls slightly helio-
tropic, and stems strongly aphe-
liotropic of the ivy, 453; he-
liotropism of radicles, 482; ex-
periments on tips of radicles
of bean, 523, 524; curvature of
the hypocotyl, 555 ; resemblance
between plants and animals,
571
Sarracenia purpurea, circumnuta-
tion of young pitcher, 227
Sazifraga sarmentosa, _ circum-
nutation of an inelined stolon,
218
Schrankia aculeata, nyctitropic
movement of the pinne, 381,
403
uncinata, nyctitropic move-
ments of leaflets, 381
Securigera coronillu, nocturnal
movements of leaflets, 352
Seed-capsules, burying of, 518
Seed-coats, rupture of, 102-106
Seedling plants, circumnutating
movements of, 10
Selaginella, circumnutation of, 258
Kraussié (?), cireumnutation of
young plant, 66
Sida napea, depression of leaves at
night, 322
—-, no pulvinus, 322
retusa, vertical rising of leaves,
322
rhombifolia, sleep of cotyledons,
308
— _, sleep of leaves, 314
, vertical rising of leaves, 322
— _, no pulvinus, 322
——, circumnutation and nycti-
tropic movements of leaf of young
plant, 322
——, nyctitropic
leaves, 397
Siegesbeckia orientalis, sleep of
leaves, 319, 384
Sinapis alba, lypocotyl bending to-
wards the light, 461
—-, transmitted effect of light on
radicles, 482, 483, 567
, growth of radicles in dark-
ness, 486
movement of
STAPELIA,
Sinapis ntyra, sleep of cotyledons,
301
Smilaz aspera, tendrils aphelio-
tropic, 451
Smithia Pfundii,
cotyledons, 127
, hyponastic movement of the
eurved summit of the stem, 274-
276
» cotyledons not sleeping at
night, 308
, vettical movement of leaves,
6
non ~ sensitive
—— sensitiva, sensitiveness of coty-
ledons to contact, 126
—, sleep of cotyledons, 3208
Sophora chrysophylla, leatlets rise at
night, J68
Solanum dulcamara, circumuuta-
ting stems, 266
—— lycopersicum, movement of
hypocotyl, 50
—,, of cotyledons, 50
——, effect of darkness, 124
——,, rising of cotyledons at night,
306
—, heliotropie movements of
hypocotyl, 421
—, effect ofan intermittent light,
457
, rapid heliotropism, 461
pulinacanthum, circumnu-
tation of arched hypocotyl, 51,
100
, of cotyledon, 51
, ellipses described by hypo-
cotyl when erect, 107
——, nocturnal movement of coty-
ledons, 306
Sparganium ramosum, rhizomes of,
Spherophysa salsola,
leaflets, 355
Spirogyra princeps, movements of,
rising of
2.
Stahl, Dr., on the effect of ei-
dium on shoot, 189; on the in-
fluence of light on swarm-spores,
488, n.
Stapelia sarpedon, circumnutation
of hypocotyl, 46, 47
590
INDEX.
STAPELIA.
Stapelia sarpedon, minute coty-
ledons, 97
Stellaria media, nocturnal move-
ment of leaves, 297
Stems, circumnutation of, 201-214
Stolons, or Runners, circumnuta-
tion of, 214-222, 558
Strasburger, on the effect of light
on spores of Hematoceus, 455, x. ;
the influence of light on the
swarm-spores, 488
Strawberry, stolons of the, circum-
nutate, but not affected by mode-
rate light, 454
Strephium floribundum, circumnu-
tation and nyctitropic movement
of leaves, 391, 392
T.
Tamarindus Indica, nyctitropic
movement of leaflets, 374
Transversal - heliotropismus (of
Frank) or diaheliotropism, 438
Trapa natans, unequal cotyledons, -
95, n.
Tecoma radicans, stems aphelio-
tropic, 451
Tephrosia caribea, 354
Terminology, 5
Thalia dealbata, sleep of leaves,
389
— ., lateral movement of leaves,
404
Trichosanthes anguina, action of the
peg on the radicle, 104
——,, nocturnal movement of coty-
ledons, 304
Trifolium, position of terminal leaf-
lets at night, 282
— globosum, with hairs protecting
the seed-bearing flowers, 517
glomeratum, movement of
cotyledons, 309
-— incarnatum,
cotyledons, 309
— Pannonicum, shape of firs’
true leaf, 350, £15
movemert of
TRITICUM.
Trifolium pratense, leaves esposed
at night, 293
repens, circumnutation cf
flower-stem, 225
——,, circumnutating and epinastic
movements of flower-stem, 276-
279
» ayctitropic movement of
leaves, 349
—, cireumnutation aud nycti-
tropic movements of terminal
leaflets, 352, 353
» Sleep movements, 349
— resupinatum, no pulvini to
cotyledons, 118
——,, circumnutation of stem, 204
—, effect of exposure at niyht,
295
—, cotyledons not rising at
night, 118, 309
, circumnutation and nycti-
tropic movements of terminal
leaflets, 351, 352
strictum, movements of coty-
ledons at night, 116, 118
—, nocturnal and diurnal move-
ments of cotyledons, 309-311,
313
—, movement of the left-nand
cotyledon, 316
subterraneum,
flower-heads, 71
—, of cotyledons at night, 116,
118, 309
—., circumnutation of flower-stem,
224, 225
, circumnutation and nycti-
tropic movements of leaves, 350
—,number of ellipses in 24
hours, 405
ee its flower Leads, 513,
movement of
——, downward movement of pe-
duncle, 515
. cireumnutating movement of
peduncle, 516
a Cretica, sleep of leaves,
4
Triticum repens, wndergroun}
a of, become apogvotropia,
INDEX.
591
TRITIOUM,
Triticum vulgare, sensitiveness of
tips of radicle to moist air, 184
Tropeolum majus (?), sensitiveness
of apex of radicle to contact, 167
——, circunmutation of stem, 204
—, influence of illumination on
nyctitropic movements, 338-340,
344
—, heliotropic movement and
circumnutation of epicotyl of a
young seedling, 428, 429
, of an old internode towards a
lateral light, 430
, stems of very young plants
highly heliotropic, of old plants
slightly apheliotropie, 453
— , effect of lateral light, 484
— minus (?), circumnutation of
buried and arched epicotyl, 27
U.
Ulex, or gorse, first-formed leaf of,
415
Uraria lagopus, vertical sinking of
leaflets at night, 365
Vaucher, on the burying of the
flower-heads of Trifolium sub-
terraneum, 513; on the protec-
tion of seeds, 517
Verbena melindres (?), cireumnuta-
tion of stem, 210
, apogeotropic movement of
stem, 495
Vv.
Vicia. faba, circumnutation of ra-
dicle, 29, 30
, of epicotyl, 31-33
——, curvature of hypocotyl, 92
, sensitiveness of apex of ra-
dicle, 132-134
——, of the tips of secondary ra-
dic es, 154
-——, of the primary radicle above
the apex, 155-158
, various experiments, 135-143
——, summary of results, 143-151
——,, power of an irritant on, com-
WILSON.
pared with that of geotropism,
151-154
Vicia faba, circumnutation of leaves,
233-235
——, circumnutat.on of terminal
leaflet, 235
——,, effect of apogeotropism, 444
—, effvct of amputating the tips
of radicles, 523
——, regeneration of tips, 526
—, short exposure to geotropic
action, 527 .
— , effects of amputating the tips
obliquely, 528
——,, of cauterising the tips, 529
——, of grease on the tips, 534
Vines, Mr., on cell growth, 3
Vries, De, on turgescence, 2; on
epinasty and hyponasty, 6, 267,
268; the protection of hypo-
cotyls during winter, 557 ; stolons
apheliotropic, 108; ihe nycti-
tropic movement of leaves, 283;
the position of leaves influeuced
by epinusty, their own weight and
apogeotropism, 440; apozeotro-
pism in petioles and midribs, 443;
the stolons of strawberries, 45+ ;
the joinis or pulvini of the Gra-
minex, 502
Ww.
Watering, effect of, on Porlieria
hygrometrica, 336-338
Wells, ‘Essay on Dew,’ 284, .
Wiesner, Prof., on the circumnuta-
tion of the hypocotyl, 99, 100;
on the hooked tip of climbing
stems, 272; observations on the
effect of bright sunshine un
chlorophyll in leaves, 446; the
effects of an intermittent light,
457; on aérial roots, 486; on
special adaptations, 490
Wigandia, movement of leaves, 248
Williamson, Prof, on leaves of
Drosera Capensis, 414
Wilson, Mr. A. §., on the move
nents of Swedish turnip leaves,
230, 298
592
INDEX.
WINELER.
Wiukler on the protection of seed-
lings, 108
Wistaria Sinensis, leaticts depressed
at night, 354
—, circumnutation with lateral
light, 452
Z.
Zea Mays, circumnutation of coty-
ledon, 64
ZUKAL.
Zea Mays, geotropic movement ci
radicles, 65
——, sensitiveness of apex of ra-
dicle to contact, 177-179
——, secondary radicles, 179
heliotropic movements of
seedling, 64,421 ~
—, tips of radicles cauterised,
539
Zukal, on the movements of Spiru-
lina, 259, n.
THE END.