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Life Movements In Plants

Jagadis Chandra Bose

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LIFE MOVEMENTS IN PLANTS

LIFE MOVEMENTS IN PLANTS

BY SIR JAGADIS CHUNDER BOSE, Kt., M.A., D.Sc., C.S.I., C.I.E., PROFESSOR EMERITUS, PRESIDENCY COLLEGE, DIRECTOR, BOSE RESEARCH INSTITUTE. WITH 92 ILLUSTRATIONS B.R. Publishing Corp. Delhi Cataloging in Publication Data-DK Bose, Jagadish Chandra, 1858–1937. Life movements in plants. Reprint. 1. Plants—Irritability and movements. 2. Growth (Plants). 3. Plants—Development. 4. Botany. I. Title. First Published 1918 Reprinted 1985 Published in India by B.R. PUBLISHING CORPORATION 461, VIVEKANAND NA

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I.—THE PROBLEM OF MOVEMENT IN PLANTS

I.—THE PROBLEM OF MOVEMENT IN PLANTS

By Prof. Sir J. C. Bose . The phenomenon of movement in plants under the action of external stimuli presents innumerable difficulties and complications. The responding organs are very different: they may be the pulvini of the ‘sensitive’ or those of the less excitable leguminous plants; the petioles of leaves, which often act as pulvinoids; and organs of plants in a state of active growth. Taking first the case of the pulvinus of Mimosa , we find that it responds to mechanical stimulation, to co

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II.—THE “PRAYING” PALM TREE

II.—THE “PRAYING” PALM TREE

By Sir J. Bose , Assisted by Narendra Nath Neogi , M.Sc. Perhaps no phenomenon is so remarkable and shrouded with greater mystery as the performances of a particular Date Palm near Faridpur in Bengal. In the evening, while the temple bells ring calling upon people to prayer, this tree bows down as if to prostrate itself. It erects its head again in the morning, and this process is repeated every day of the year. This extraordinary phenomenon has been regarded as miraculous, and pilgrims have bee

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III.—ACTION OF STIMULUS ON VEGETABLE TISSUES

III.—ACTION OF STIMULUS ON VEGETABLE TISSUES

By Sir J. C. Bose, Assisted by Narendra Nath Sen Gupta . The leaf of Mimosa pudica undergoes a rapid fall when subjected to any kind of shock. This plant has, therefore, been regarded as “sensitive,” in contradistinction to ordinary plants which remain apparently immobile under external stimulus. I shall, however, show in course of this Paper that there is no justification in regarding ordinary plants as insensitive. Let us first take any radial organ of a plant and subject it to an electric sh

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IV.—DIURNAL VARIATION OF MOTO-EXCITABILITY IN MIMOSA

IV.—DIURNAL VARIATION OF MOTO-EXCITABILITY IN MIMOSA

BY Sir J. C. Bose. Several phenomena of daily periodicity are known, but the relations between the recurrent external changes and the resulting periodic variations are more or less obscure. As an example of this may be cited the periodic variation of growth. Here the daily periodicity exhibited by a plant is not only different in varying seasons, but it also differs in diverse species of plants. The complexity of the problem is very great, for not only are the direct effects of the changing envi

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V.—RESPONSE OF PETIOLE-PULVINUS PREPARATION OF MIMOSA PUDICA

V.—RESPONSE OF PETIOLE-PULVINUS PREPARATION OF MIMOSA PUDICA

By Sir J. C. Bose , Assisted by Surendra Chandra Das , M.A. The most suitable plant for researches on irritability of plants is Mimosa pudica , which can be obtained in all parts of the world. An impression unfortunately prevails that the excitatory reaction of the plant can be obtained only in summer and under favourable circumstances; this has militated against its extensive use in physiological experiments, but the misgiving is without any foundation; for I found no difficulty in demonstrat

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VI.—ON CONDUCTION OF EXCITATION IN PLANTS

VI.—ON CONDUCTION OF EXCITATION IN PLANTS

By Sir J. C. Bose . The plant Mimosa offers the best material for investigation on conduction of excitation. With regard to this question the prevailing opinion had been that in plants like Mimosa , there is merely a transmission of hydro-mechanical disturbance and no transmission of true excitation comparable with the animal nerve. I have, however, been able to show that the transmission in the plant is not a mechanical phenomenon, but a propagation of excitatory protoplasmic change. Thi

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VII.—ON ELECTRIC CONTROL OF EXCITATORY IMPULSE

VII.—ON ELECTRIC CONTROL OF EXCITATORY IMPULSE

By Sir J. C. Bose. I have in my previous works [L] described investigations on the conduction of excitation in Mimosa pudica . It was there shown that the various characteristics of the propagation of excitation in the conducting tissue of the plant are in every way similar to those in the animal nerve. Hence it appeared probable that any newly found phenomenon in the one case was likely to lead to discovery of a similar phenomenon in the other. As the transmission of excitation is a pheno

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VIII.—EFFECT OF INDIRECT STIMULUS ON PULVINATED ORGANS

VIII.—EFFECT OF INDIRECT STIMULUS ON PULVINATED ORGANS

By Sir J. C. Bose, Assisted by Guruprasanna Das , L.M.S. The leaf of Mimosa pudica undergoes an almost instantaneous fall when the stimulus is applied directly on the pulvinus which is the responding organ. The latent period, i.e. , the interval between the application of stimulus and the resulting response is about 0.1 second. Indirect stimulus, i.e. , application of stimulus at a distance from the pulvinus, also causes a fall of the leaf; but a longer interval will elapse between the incidence

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IX.—MODIFYING INFLUENCE OF TONIC CONDITION ON RESPONSE

IX.—MODIFYING INFLUENCE OF TONIC CONDITION ON RESPONSE

By Sir J. C. Bose Assisted by Guruprasanna Das. In experiments with different pulvinated organs, great difference is noticed as regards their excitability. If electric shock of increasing intensity from a secondary coil be passed through the pulvini of Mimosa , Neptunia , and Erythrina arranged in series, it would be found that Mimosa would be the first to respond; a nearer approach of the secondary coil to the primary would be necessary for Neptunia to show sign of excitation. Erythrina woul

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X.—THE HIGH MAGNIFICATION CRESCOGRAPH FOR RESEARCHES ON GROWTH[S]

X.—THE HIGH MAGNIFICATION CRESCOGRAPH FOR RESEARCHES ON GROWTH[S]

By Sir J. C. Bose, Assisted by Guruprasanna Das, L.M.S. In discussing the difficulties connected with investigations relating to longitudinal growth and its variations, special stress must be laid on the importance of maintaining external conditions absolutely constant. This constancy can only be maintained in practice for a short time. Lengthy periods of observation, moreover, introduce the uncertainty of complication arising from spontaneous variation of growth. The possibility of accurate

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XI.—EFFECT OF TEMPERATURE ON GROWTH

XI.—EFFECT OF TEMPERATURE ON GROWTH

By Sir J. C. Bose, Assisted by Surendra Chunder Dass , M.A. Accurate determination of the effect of temperature on growth presents many serious difficulties on account of numerous complicating factors. In nature, the upper part of the plant is exposed to the temperature of the air, while the root underground is at a very different temperature. Growth, we shall find, is modified to a certain extent by the ascent of sap. (See p. 189 , Expt. 70 .) The activity of this latter process is determined b

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XII.—THE EFFECT OF CHEMICAL AGENTS ON GROWTH

XII.—THE EFFECT OF CHEMICAL AGENTS ON GROWTH

By Sir J. C. Bose , Assisted by Guruprasanna Das . Chemical agents are found to exert characteristic actions on growth. The method of investigation sketched here opens out an extended field of investigation. The effect of a chemical substance, I find, to be modified by (1) the strength of the solution, (2) the duration of application, and (3) the condition of the tissue. A poisonous substance in minute doses is often found to exert a stimulating action. Too long continued action of a

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XIII.—EFFECT OF VARIATION OF TURGOR AND OF TENSION ON GROWTH

XIII.—EFFECT OF VARIATION OF TURGOR AND OF TENSION ON GROWTH

By Sir J. C. Bose. The movements of leaves of sensitive plants are caused by variation of turgor in the pulvinus induced by stimulus. The down movement or negative response of Mimosa is caused by a diminution or negative variation of turgor, while the erection or positive response is brought about by an increase, or positive variation of turgor. We shall now investigate the change induced in a growing organ in the rate of growth by variation of turgor. Turgor may be increased by enhancing the ra

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XIV.—EFFECT OF ELECTRIC STIMULUS ON GROWTH

XIV.—EFFECT OF ELECTRIC STIMULUS ON GROWTH

By Sir J. C. Bose, Assisted by Guruprasanna Das. In plant physiology, the word ‘stimulus’ is often used in a very indefinite manner. This is probably due to the different meanings which have been attached to the word. An agent is said to stimulate growth, when it induces an acceleration. But the normal effect of stimulus is to cause a retardation of growth. It is probably on account of lack of precision in the use of the term that we often find it stated, that a stimulus sometimes accelerates

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XV.—EFFECT OF MECHANICAL STIMULUS ON GROWTH

XV.—EFFECT OF MECHANICAL STIMULUS ON GROWTH

By Sir J. C. Bose. Amongst the various stimuli which induce excitation in Mimosa may be mentioned the irritation caused by rough contact, by prick, or wound. Friction causes moderate stimulation, from which the excited pulvinus recovers within a short time. But a prick or a cut induces a far more intense and persistent excitation; the recovery becomes protracted, and the wounded pulvinus remains contracted for a long period. I shall now describe the effect of mechanical irritation on growth. For

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XVI.—ACTION OF LIGHT ON GROWTH

XVI.—ACTION OF LIGHT ON GROWTH

By Sir J. C. Bose , Assisted by Guruprasanna Das . The next subject of inquiry is the normal effect of light on growth. I speak of the normal effect because, under certain definite conditions, to be described in a later Paper, the response undergoes a reversal. The Crescograph is so extremely sensitive that it records the effect of even the slightest variation of light. Thus, as I have already mentioned, the opening of the blinds of a moderately-lighted room induces, within a short time, a marke

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XVII.—EFFECT OF INDIRECT STIMULUS ON GROWTH

XVII.—EFFECT OF INDIRECT STIMULUS ON GROWTH

By Sir J. C. Bose , Assisted by Guruprasanna Das. It has been shown that the direct application of stimulus gives rise in different organs to contraction, diminution of turgor, fall of motile leaf, electro-motive change of galvanometric negativity, and retardation of the rate of growth. I shall now inquire whether Indirect stimulus, that is to say, application of stimulus at some distance from the responding organ, gives rise to an effect different from that of direct application. I have alrea

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XVIII.—RESPONSE OF GROWING ORGANS IN STATE OF SUB-TONICITY

XVIII.—RESPONSE OF GROWING ORGANS IN STATE OF SUB-TONICITY

By Sir J. C. Bose. The normal response of a growing organ to Direct stimulus is negative , that is to say, a retardation of the rate of growth. This is the case under forms of stimuli as diverse as those of mechanical and electric shocks, and of the stimulus of light. After my investigations on the normal retarding effect of light on growth, I was considerably surprised to find the responses occasionally becoming positive , an acceleration instead of retardation of growth. I shall first g

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XIX.—RESUMPTION OF AUTONOMOUS PULSATION AND OF GROWTH UNDER STIMULUS

XIX.—RESUMPTION OF AUTONOMOUS PULSATION AND OF GROWTH UNDER STIMULUS

By Sir J. C. Bose. The autonomous activity of growth is ultimately derived from energy supplied by the environment. The internal activity may fall below par with consequent diminution or even arrest of growth; this condition of the tissue I have designated as sub-tonic. The inert plant can only be stirred up to a state of activity by stimulus from outside; and we saw that under the action of stimulus the rate of growth of a sub-tonic tissue was enhanced. As the general question of depression of

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XX.—ACTION OF LIGHT AND WARMTH ON AUTONOMOUS ACTIVITY

XX.—ACTION OF LIGHT AND WARMTH ON AUTONOMOUS ACTIVITY

By Sir J. C. Bose. In the preceding Paper I have shown the essential similarity of effect of stimulus on autonomous activity of the Desmodium leaflet, and of the growing organ. It was shown how stimulus revived the pulsatory activity of Desmodium leaflet in a state of standstill, in the same way as it renewed the arrested growth-activity. The investigation of this subject was rendered possible by the successful device of my Oscillating Recorder. A very light glass fibre was used for the cons

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XXI.—A COMPARISON OF RESPONSES IN GROWING AND NON-GROWING ORGANS

XXI.—A COMPARISON OF RESPONSES IN GROWING AND NON-GROWING ORGANS

By Sir J. C. Bose, Assisted by Guruprasanna Das. I have in the preceding series of Papers demonstrated the effects of various forms of stimuli on growth. I have also given accounts of numerous reactions which are extraordinarily similar, in growing and non-growing organs. In fact certain characteristic reactions observed in motile pulvinus of Mimosa and other ‘sensitive’ plants led to the discovery of the corresponding phenomena in growing organs. For fully realising the essential similarity

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WORKS BY THE SAME AUTHOR.

WORKS BY THE SAME AUTHOR.

RESPONSE IN THE LIVING AND NON-LIVING. With 117 Illustrations, 8vo. 10 s. 6 d. 1902 PLANT RESPONSE: AS A MEANS OF PHYSIOLOGICAL INVESTIGATION. With 278 Illustrations, 8vo. 21 s. 1906 COMPARATIVE ELECTRO-PHYSIOLOGY. A PHYSICO-PHYSIOLOGICAL STUDY. With 406 Illustrations, 8vo. 15 s. 1907 RESEARCHES ON IRRITABILITY OF PLANTS. With 190 Illustrations, 8vo. 10 s. 6 d. net 1913 LIFE MOVEMENTS IN PLANTS, VOL. I. With 92 Illustrations, 8vo. 10 s. 6 d. 1918 Longmans, Green &amp; Co. London, New York, B

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PREFACE TO VOLUME II.

PREFACE TO VOLUME II.

I have in the present volume dealt with the intricate phenomena of different tropisms. The movements in plants under the stimuli of the environment—the twining of tendrils, the effect of temperature, the action of light inducing movements sometimes towards and at other times away from the stimulus, the diametrically opposite responses of the shoot and the root to the same stimulus of gravity, the day and night positions of organs of plants—these, and many others present such diversities that it

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XXII.—THE BALANCED CRESCOGRAPH

XXII.—THE BALANCED CRESCOGRAPH

We shall in the succeeding series of papers deal with the subject of tropism in general. Different plant organs undergo curvature or bending, sometimes towards and at other times away from the stimulus which induces it. The problem is very intricate; the possibility of its solution will depend greatly on the accurate determination of the immediate and after-effects of various stimuli on the responding organ. The curvature induced in the growing organ is brought about by variation, often extremel

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XXIII.—ON TROPIC MOVEMENTS

XXIII.—ON TROPIC MOVEMENTS

The diverse movements induced by external stimuli in different organs of plants are extremely varied and complicated. The forces in operation are manifold—the influence of changing temperature, the stimulus of contact, of electric current, of gravity, and of light visible and invisible. They act on organs which exhibit all degrees of physiological differentiation, from the radial to the dorsiventral. An identical stimulus may sometimes induce one effect, and at other times, the precisely opposit

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XXIV.—TROPIC CURVATURE WITH LONGITUDINAL TRANSMISSION OF EFFECT OF STIMULUS

XXIV.—TROPIC CURVATURE WITH LONGITUDINAL TRANSMISSION OF EFFECT OF STIMULUS

I have in previous chapters explained that the direct application of stimulus gives rise in different organs to contraction, diminution of turgor, fall of motile leaf, electro-motive change of galvanometric negativity, and retardation of the rate of growth. I have also shown that indirect stimulation ( i.e. application of stimulus at some distance from the responding organ) gives rise to a positive or erectile response of the responding leaf or leaflet (indicative of an increase of turgor), ofte

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XXV.—TROPIC CURVATURE WITH TRANSVERSE TRANSMISSION OF EFFECT OF STIMULUS

XXV.—TROPIC CURVATURE WITH TRANSVERSE TRANSMISSION OF EFFECT OF STIMULUS

We have next to consider a very large class of phenomena arising out of the direct stimulation of one side and its transversely transmitted effect on the opposite side. The unilateral stimuli to which the plant is naturally exposed are those of contact, of light, of thermal radiation, and of gravity. There is besides the stimulation by electric current. I shall presently show that these tropic curvatures are determined by the definite effects of direct and indirect stimulations. Under unilateral

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XXVI.—MECHANOTROPISM: TWINING OF TENDRILS

XXVI.—MECHANOTROPISM: TWINING OF TENDRILS

In response to the stimulus of contact a tendril twines round its support. Certain tendrils are uniformly sensitive on all sides; but in other cases, as in the tendril of Passiflora , the sensitiveness is greater on the under side. A curvature is induced when this side is rubbed with a splinter of wood, the stimulated under side becoming concave. This movement may be distinguished as a movement of curling . There is, as I shall presently show, a response where the under side becomes convex, and

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XXVII.—ON GALVANOTROPISM

XXVII.—ON GALVANOTROPISM

Before describing the effect of unilateral application of an electrical current in inducing tropic curvature, I shall give an account of the polar effect of anode and cathode on the pulvinated and growing organs. In my previous work [6] on the action of electrical current on sensitive pulvini I have shown that:— (1) at the 'make' of a current of moderate intensity a contraction takes place at the cathode; the anode induces no such contractile effect; (2) at the 'make' of a stronger current both

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XXVIII.—ON THERMONASTIC PHENOMENA

XXVIII.—ON THERMONASTIC PHENOMENA

In describing thermonastic curvatures Pfeffer says that "a special power of thermonastic response has been developed by various flowers, in which low temperatures produce closing movements, and high temperatures, opening ones. The flowers of Crocus vernus and Crocus luteus are specially responsive, as also those of Tulipa Gesneriana for these flowers perceptibly respond to a change of temperature of half a degree centigrade." [7] We have hitherto studied the response of various organs to stimulu

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XXIX.—ON PHOTOTROPISM

XXIX.—ON PHOTOTROPISM

In different organs of plants the stimulus of light induces movements of an extremely varied character. Radial organs exhibit tropic movements in which the position of equilibrium is definitely related to the direction of incident stimulus. Nastic movements under the action of light are, on the other hand, regarded as curvatures of the organ which show "no relation to the stimulus but is determined by the activity of the plant itself". [9] There are thus two classes of response to light which se

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XXX.—DIA-PHOTOTROPISM AND NEGATIVE PHOTOTROPISM

XXX.—DIA-PHOTOTROPISM AND NEGATIVE PHOTOTROPISM

I have explained how under the action of unilateral light the positive curvature attains a maximum. There are, however, cases where under the continued action of strong light the tropic movement undergoes a reversal. Thus to quote Jost: "Each organism may be found in one of the three different conditions determined by the light intensity, viz. (1) a condition of positive heliotropism, (2) a condition of indifference, (3) a condition of negative heliotropism" [12] . No explanation has however bee

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XXXI.—THE RELATION BETWEEN THE QUANTITY OF LIGHT AND THE INDUCED PHOTOTROPIC CURVATURE

XXXI.—THE RELATION BETWEEN THE QUANTITY OF LIGHT AND THE INDUCED PHOTOTROPIC CURVATURE

I shall in this chapter describe experiments in support of the important proposition that the intensity of phototropic action is dependent on the quantity of incident light . The proportionality of the tropic effect to the quantity of light will be found to hold good for the median range of stimulation; the deviation from this proportionality at the two ends of the range of stimulation—the sub-minimal and supramaximal—is, as we shall find, capable of explanation, and will be fully dealt with in

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XXXII.—THE PHOTOTROPIC CURVE AND ITS CHARACTERISTICS

XXXII.—THE PHOTOTROPIC CURVE AND ITS CHARACTERISTICS

When a plant organ is subjected to the continued action of unilateral stimulus of light, it exhibits increasing tropic curvature, which in certain cases reaches a limit; in other instances a reversal takes place, seen in neutralisation, or in the conversion of the positive into negative curvature. I shall in this chapter enter into a detailed study of the phototropic curve, and determine its characteristics. As the vague terminology at present in use has been the source of much confusion, it is

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XXXIII.—THE TRANSMITTED EFFECT OF PHOTIC STIMULATION

XXXIII.—THE TRANSMITTED EFFECT OF PHOTIC STIMULATION

Plant organs exhibit, as we have already seen, a heliotropic curvature under direct stimulation. Still more interesting is the transmitted effect of light giving rise to a curvature. Thus if the tip of the seedling of wheat be exposed to light, the excitation is transmitted lower down into the region which acts as the responding organ. Growth is very active in this particular zone, and the change of growth, induced by the transmitted effect of stimulus, brings about a curvature by which the tip

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XXXIV.—ON PHOTONASTIC CURVATURES

XXXIV.—ON PHOTONASTIC CURVATURES

Phototropic response, positive or negative, is determined by the directive action of light. But photonastic reaction is supposed to belong to a different class of phenomenon, where the movement is independent of the directive action of light. I shall, however, be able to establish a continuity between the tropic response of a radial and the nastic movement of a dorsiventral organ. The intermediate link is supplied by organs originally radial, but subsequently rendered anisotropic by the unilater

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XXXV.—EFFECT OF TEMPERATURE ON PHOTOTROPIC CURVATURE

XXXV.—EFFECT OF TEMPERATURE ON PHOTOTROPIC CURVATURE

I shall in this chapter deal with certain anomalies in phototropic curvature, brought about by variation of temperature and by seasonal change; certain organs again are apparently erratic in their phototropic response. Sachs observed a positive phototropic curvature in the stems of Tropæolum majus in autumn; but this was reversed into negative in summer; similarly in the hypocotyl of Ivy, the positive curvature in autumn is converted into negative curvature in summer. Certain organs are apparent

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XXXVI.—ON PHOTOTROPIC TORSION

XXXVI.—ON PHOTOTROPIC TORSION

In addition to positive or negative curvatures light induces a responsive torsion. With regard to this Jost says:— "The mechanics of the torsions have not as yet been fully explained. It has long been believed that these torsions were occasioned only by the action of a series of external factors, such as light, gravity, weight of the organ which individually led to curvatures, but in combination induced torsions; but later investigations have shown that torsions might appear when light only was

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XXXVII.—RADIO-THERMOTROPISM

XXXVII.—RADIO-THERMOTROPISM

We have studied the tropic curvature induced by different rays of light. We saw that while the more refrangible rays of the spectrum were most effective, the less refrangible rays were ineffective. Below the red, there are the thermal rays about whose tropic effect very little is definitely known. The intricacies of the problem are very great owing to the difficulty of discriminating the effect of temperature from that of radiation; to this must be ascribed the contradictory results that have be

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XXXVIII.—RESPONSE OF PLANTS TO WIRELESS STIMULATION

XXXVIII.—RESPONSE OF PLANTS TO WIRELESS STIMULATION

A growing plant bends towards light, and this is true not only of the main stem but also of its branches and attached leaves and leaflets. Light affects growth, the effect being modified by the intensity of radiation. Strong stimulus of light causes a diminution of the rate of growth, but very feeble stimulus induces an acceleration. The tropic effect is very strong in the ultra-violet region of the spectrum with its extremely short wave length, but the effect declines practically to zero as we

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XXXIX.—GEOTROPISM

XXXIX.—GEOTROPISM

No phenomenon of tropic movement appears so inexplicable as that of geotropism. There are two diametrically opposite effects induced by the same stimulus of gravity, in the root a movement downwards, and in the shoot a movement upwards. The seeming impossibility of explaining effects so divergent by the fundamental reaction of stimulus, has led to the assumption that the irritability of stem and root are of opposite character. I shall, however, be able to show that this assumption is unnecessary

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XL.—GEO-ELECTRIC RESPONSE OF SHOOT

XL.—GEO-ELECTRIC RESPONSE OF SHOOT

The experiments that have been described in the preceding chapter show that the upper side of a horizontally laid shoot undergoes excitatory contraction, in consequence of which the organ bends upwards. The fundamental geotropic reaction is, therefore, not expansion, but contraction which results from all modes of stimulation. In confirmation of the above, I wished to discover and employ new means of detecting excitatory reaction under geotropic stimulus. In regard to this, I would refer to the

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XLI.—THE MECHANICAL AND ELECTRICAL RESPONSE OF ROOT TO VARIOUS STIMULI

XLI.—THE MECHANICAL AND ELECTRICAL RESPONSE OF ROOT TO VARIOUS STIMULI

In the last chapter we studied the electric response of the shoot to the stimulus of gravity, and found that the excitatory effect of that stimulus is similar to that of other forms of stimulation. Before taking up the subject of the geo-electric response of the root to gravitational stimulus, I shall describe the effects of other forms of stimuli on the mechanical and electrical response of the root. In connection with this subject, it should be borne in mind that the responsive curvature in th

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XLII.—GEO-ELECTRIC RESPONSE OF ROOT

XLII.—GEO-ELECTRIC RESPONSE OF ROOT

The effects of various stimuli, direct and indirect, on the response of the root have been described in the last chapter. These responsive reactions have been found to be in no way different from those of the shoot. But the shoot and the root exhibit under the stimulus of gravity, responsive movements which are diametrically opposite to each other. These opposite effects of an identical stimulus have been regarded as due to specific differences of irritability in the two organs, specially evolve

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XLIII.—LOCALISATION OF GEO-PERCEPTIVE LAYER BY MEANS OF THE ELECTRIC PROBE

XLIII.—LOCALISATION OF GEO-PERCEPTIVE LAYER BY MEANS OF THE ELECTRIC PROBE

The obscurities which surround the phenomenon of geotropism arise: (1) from the invisibility of the stimulating agent, (2) from want of definite knowledge as to whether the fundamental reaction is contractile or expansive, and (3) from the peculiar characteristic that the stimulus is only effective when the external force of gravity reacts internally through the mass of contents of the sensitive cells. The experiments that have been detailed in the foregoing chapters will have removed most of th

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XLIV.—ON GEOTROPIC TORSION

XLIV.—ON GEOTROPIC TORSION

I have explained that in a dorsiventral organ, lateral application of various stimuli induces a responsive torsion by which the less excitable side is made to face the stimulus (p. 403). I shall in this chapter show that the effect of stimulus of gravity is in every respect similar to other forms of stimulation. Fig. 179. —Diagram of arrangement for torsional response under geotropic stimulus. The less excitable upper half of pulvinus is, in the above figure, to the left and the torsional respon

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XLV.—ON THERMO-GEOTROPISM

XLV.—ON THERMO-GEOTROPISM

I shall in this chapter investigate the effect of variation of temperature on geotropic response. We have to bear in mind in this connection, that for the exhibition of geotropic curvature two conditions are necessary: (1) the presence of a perceptive organ to undergo excitation under the stimulus of gravity, and (2) the motility of the organ. A motile organ, including both the pulvinated and growing, will exhibit no geotropic effect on account of the depression of the power of perception throug

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XLVI.—DIURNAL MOVEMENTS IN PLANTS

XLVI.—DIURNAL MOVEMENTS IN PLANTS

The subject has long been a perplexing one, and its literature is copious. After a good many years of experimental investigation, I have succeeded in analysing the main factors concerned in the many phenomena which have been described as Nyctitropism. The results of the researches are given in a sequence of five papers, which may be read separately, yet will be seen as so many chapters of what has been a single though varied investigation. The different chapters are: 1. Daily movements in relati

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XLVII.—DIURNAL MOVEMENT DUE TO ALTERNATION OF LIGHT AND DARKNESS

XLVII.—DIURNAL MOVEMENT DUE TO ALTERNATION OF LIGHT AND DARKNESS

The nyctitropic movements of the leaflet of Cassia alata and of the terminal leaflet of Desmodium gyrans furnish us with typical examples of the recurrent effects of light and darkness. The petiole of Cassia contains a number of paired leaflets each of which is about 5 cm. long and 2·5 cm. broad. The leaflets are extremely sensitive to light; at night each pair of leaflets fold themselves in a forward direction (see Fig. 150). With the appearance of light they open at first in a lateral directio

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XLVIII.—DIURNAL MOVEMENT DUE TO VARIATION OF TEMPERATURE AFFECTING GROWTH

XLVIII.—DIURNAL MOVEMENT DUE TO VARIATION OF TEMPERATURE AFFECTING GROWTH

It has been stated that there are two classes of diurnal movements caused by variation of temperature; one of these is due to differential growth induced on two sides of the organ, and the other is brought about by the induced variation of geotropic curvature. The former may be distinguished as Thermonastic , and the latter as Thermo-geotropic movement. Before laying down the criteria to distinguish the one class of phenomenon from the other, it would be advisable to refer to the somewhat arbitr

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XLIX.—DAILY MOVEMENT IN PLANTS DUE TO THERMO-GEOTROPISM

XLIX.—DAILY MOVEMENT IN PLANTS DUE TO THERMO-GEOTROPISM

Of the vast number of daily movements perhaps the largest proportion is due to thermo-geotropic reaction and its modifications. Thermo-geotropic movements have the following characteristics: 1. The organs are sensitive to the stimulus of gravity and the periodic movements are brought about by variation of geotropic curvature under change of temperature. 2. The movement is not confined to growing organs, but is also exhibited by organs which are fully grown and even by rigid trees. 3. The periodi

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L.—THE AFTER-EFFECT OF LIGHT

L.—THE AFTER-EFFECT OF LIGHT

We have considered two types of diurnal movement, one due to the predominant action of variation of light, and the other, to that of changing temperature. There are, however, other organs which are sensitive to variations both of light and of temperature. The effect of light is, generally speaking, antagonistic to that of rise of temperature; hence the resultant of the two becomes highly complex. Still greater complexity is introduced by the different factors of immediate and after-effect of lig

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LI.—THE DIURNAL MOVEMENT OF THE LEAF OF MIMOSA

LI.—THE DIURNAL MOVEMENT OF THE LEAF OF MIMOSA

In the standard curve of nyctitropic movement under thermo-geotropism described in a previous paper, the diurnal record consisted of an up-curve from thermal-noon to thermal-dawn, and a down-curve from the thermal-dawn to thermal-noon. The responding organ, which may be an inclined stem or a horizontally spread petiole, underwent an erection during the decline of temperature, and a fall with the rise of temperature. The diurnal record of the Mimosa leaf appears, however, to be totally different.

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