Complexity of the problem—Effects of different forms of stimuli—​Diverse responses under identical stimulus—​Modi­fi­ca­tion of response determined by intensity and point of application of stimulus, and tonic condition of organ—​Response of pulvinated and growing organs—​Necessity for shortening the period of experiment1

II.—THE “PRAYING” PALM TREE.

Description of phenomenon—The Recording apparatus—​Record of diurnal movement of the tree—​Universality of tree movement—​Cause of periodic movement—​Periodic movement of trees, and diurnal variation of moto-ex­cit­abil­ity in Mimosa pudica—​Relative effects of light and temperature—​Physiological character of the movement—Transpiration and diurnal movement—​Diurnal movement in inverted position—​Effect of variation of temperature on geotropic curvature—​Reversal of natural rhythm by artificial variation of temperature5

III.—ACTION OF STIMULUS ON VEGETABLE TISSUES.

Different types of Response Recorders—Response of a radial organ—​​Response of an anisotropic organ—Response of pulvinus of Mimosa pudica—​Tabular statement of apex time and period of recovery in different plants—​Response of pulvinus of Mimosa to variation of turgor—​Different modes of stimulation31

IV.—THE DIURNAL VARIATION OF EXCITABILITY IN MIMOSA.

Apparatus for study of variation of ex­cit­abil­ity—Uniform periodic stimulation—​The Response Recorder—Effects of external condition on ex­cit­abil­ity—​Effects of light and darkness—​Effect of excessive turgor—​Influence of temperature—​Diurnal variation of ex­cit­abil­ity—​Effect of physio­logic­al inertia43

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

Effect of wound or section in modi­fi­ca­tion of normal ex­cit­abil­ity—​The change of ex­cit­abil­ity after immersion in water—​Quantitative determination of the rate of decay of ex­cit­abil­ity in an isolated preparation—​Effect of amputation of upper half of the pulvinus—​Effect of removal of the lower half—​Influence of weight of leaf on rapidity of responsive fall—​The action of chemical agents—​Effect of “fatigue” on response—The action of light and darkness on ex­cit­abil­ity73

VI.—CONDUCTION OF EXCITATION IN PLANTS.

Hydro-dynamic versus physio­logic­al theory of conduction of excitation—​Arrest of conductivity by physio­logic­al blocks—​Convection and conduction of excitation—​Effect of temperature on velocity—​Effect of season—​Effect of age—​Effect of dessication of conduct­ing tissue—Influence of tonic condition on conduction—​Effect of intensity of stimulus on velocity of trans­mission—​Effect of stimulus on sub-tonic tissues and tissues in optimum condition—​Canalisation of conduct­ing path by stimulus—​Effect of injury on conductivity97

VII.—ELECTRIC CONTROL OF EXCITATORY IMPULSE.

Method of conductivity-balance—Control of transmitted excitation in Averrhoa bilimbi by electric current—​‘Uphill’ trans­mission—​Transmission ‘downhill’—Electric control of nervous impulse in animal—Directive action of current on conduction of excitation—Effects of direction of current on velocity of trans­mission in Mimosa—Determination of variation of conductivity by method of Minimal Stimulus and Response—Influence of direction of current on conduction of excitation in animal nerve—Variation of velocity of trans­mission—After-effects on Heterodromous and Homodromous currents—Laws of variation of nervous conduction under electric current107

VIII.—EFFECT OF INDIRECT STIMULUS ON PULVINATED ORGANS.

Conduction of excitation—Dual character of the transmitted impulse—​Effect of distance of application of stimulus—Periods of trans­mission of positive and negative impulses—Effects of Direct and Indirect stimulus135

IX.—MODIFYING INFLUENCE OF TONIC CONDITION ON RESPONSE.

Theory of assimilation and dissimilation—Unmasking of positive effect—​Modi­fi­ca­tion of response under artificial depression of tonic condition—Positive response in sub-tonic specimen141

PART II.

GROWTH AND ITS RESPONSIVE VARIATIONS.

X.—THE HIGH MAGNIFICATION CRESCOGRAPH FOR RESEARCHES ON GROWTH.

Method of high mag­ni­fi­ca­tion—Automatic record of the rate of growth—​Determination of the absolute rate of growth—​Stationary method of record—​Moving plate method—​Precaution against physical disturbance—​Determination of latent period and time-relations of response—​Advantages of the Crescograph—​Magnetic amplification—​The Demonstration Crescograph151

XI.—EFFECT OF TEMPERATURE ON GROWTH.

Method of discontinuous observation—Method of continuous observation—​Determination of the cardinal points of growth—​The Thermocrescent curve—​Relation between temperature and growth173

XXII.—EFFECT OF CHEMICAL AGENTS ON GROWTH.

Effect of stimulants—Effect of anæsthetics—​Action of different gases—​Action of poisons183

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

Response to positive variation of turgor—​Method of irrigation—​Effect of artificial increase of internal hydrostatic pressure—​Response to negative variation of turgor—Method of plasmolysis—​Effect of alternative variations of turgor on growth—​Response of motile and growing organs to variation of turgor—​Effect of external tension188

XIV.—EFFECT OF ELECTRICAL STIMULUS ON GROWTH.

Effect of intensity—Effect of continuous stimulation—​Continuity between ‘incipient’ and actual contraction—​Immediate effect and after-effect195

XV.—EFFECT OF MECHANICAL STIMULUS ON GROWTH.

Effect of mechanical irritation—Effect of wound200

XVI.—ACTION OF LIGHT ON GROWING ORGANS.

Method of experiment—Normal effect of light—​Determination of the latent period—​Effect of intensity of light—​Effect of continuous light—​Effects of different rays of the spectrum205

XVII.—EFFECT OF INDIRECT STIMULUS ON GROWTH.

Mechanical and electrical response to Indirect Stimulus—​Variation of growth under Indirect Stimulus—​Effects of Direct and Indirect Stimulus213

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

Theory of assimilation and dissimilation—​Unmasking of positive effect—​Modi­fi­ca­tion of response under artificial depression of tonic condition—​Positive response in sub-tonic specimen—​Abnormal ac­cel­er­ation of growth under stimulus—​Continuity between abnormal and normal responses—​Positive response to sub-minimal stimulus219

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

Resumption of pulsatory activity of Desmodium leaflet at standstill—​Renewal of growth under stimulus—​General laws of effects of Direct and Indirect Stimulus227

XX.—ACTION OF LIGHT AND WARMTH ON AUTONOMOUS ACTIVITY.

The Oscillating Recorder—Record of pulsation of Desmodium gyrans—​Effect of diffuse light in diminution of amplitude and reduction of diastolic limit of pulsation—Antagonistic action of warmth in reduction of systolic limit233

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

Contractile response of growing and non-growing organs—Time-relations of mechanical response of pulvinated and growing organs—​Similar modi­fi­ca­tion of response under condition of sub-tonicity—​Opposite effects of Direct and Indirect stimulus—Exhibition of negative electric response under Direct, and positive electric response under Indirect stimulus—​Similar modi­fi­ca­tion of autonomous activity in Desmodium gyrans and in growing organs under parallel conditions—​Similar excitatory effects of various stimuli on pulvinated and growing organs—​Similar discriminative excitatory effects of various rays in excitation of motile and growing organs—​Action of white light—​Action of red and yellow lights—​Action of blue light—​Action of ultra-violet rays—​Action of infra-red rays—​Diverse modes of response to stimulus—​Mechanical response—​Electromotive response—​Response by variation of electric resistance239

ILLUSTRATIONS.

PART I.
RESPONSE OF PLANT ORGANS.

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 constant electric current, to induction shock, to the action of chemical agents, to light, and to warmth as differentiated from thermal radiation. The reactions induced by these agents may be similar or dissimilar. An identical agent, again, may give rise to movements which are not merely different, but sometimes even of diametrically opposite characters. Certain organs, for example, direct themselves towards light, others away from it. Some plants close their leaflets on the approach of darkness, in the so-called position of ‘sleep’; apparently similar ‘sleep’ movement is induced in others by the action of the midday sun.

In Mimosa, the responsive movement is brought about by a sudden diminution of turgor in the pulvinus. But very little is definitely known about the responsive reaction in growing organs. Thus in a tendril, one-sided contraction causes a shortening of the concave side and a sudden increase of growth on the convex. No explanation of this difference has hitherto been forthcoming. Under the action of light of different intensities a growing organ may approach the source of light, or place itself at right angles or move away from it. Again under the identical stimulus of gravity, the root moves downwards, and the shoot upwards. The sign of response in different organs thus changes, apparently without any reason. It is thus seen, that there is hardly any responsive movement that has been observed of which an example directly to the contrary may not be found. For this reason it has appeared hopeless to unify these very diverse phenomena, and there has been a tendency towards a belief that it was not any definite physio­logic­al reaction, but the individuality of the plant that determines the choice of its movement.

The complexities which baffle us may, however, arise from the combination of factors whose individual reactions are unknown to us. I shall show, for example, how the movement of a pulvinus under a given stimulus is determined by the point of application, direct stimulus producing one effect, and indirect the diametrically opposite. The normal reaction is again modified by the tonic condition of the plant. There is again the likelihood of the presence of other modifying factors. It is clear how very different the results would become by the permutation and combination of these diverse factors.

For a comprehensive study of the phenomenon of plant movement, it is therefore necessary to investigate in detail the effect of a given stimulus under definite changes of the environmental condition. With regard to a given stimulus we have to determine the effects of intensity, of duration, and of the point of application. The in­ves­ti­ga­tion has to include the effects exhibited not merely by the pulvinated but also by growing organs. As a result of such a comprehensive study, it may perhaps be possible to discover some fundamental reaction operative in bringing about the responsive movement in all plant organs.

I shall in the course of the following series of Papers, describe the different apparatus by which the movement of pulvinated organ and its time-relations are automatically recorded. In a growing organ the induced movement under stimulus is brought about by the change in its rate of growth. That the change is solely due to the particular stimulus can only be assured by strict maintenance of constancy of external conditions, during the period of experiment; this constancy can, in practice, be secured only for a short time. The necessity for shortening the period of experiment also arises from a different consideration; for numerous and varied are the stimulating and mechanical interactions between neighbouring organs. These effects, however, come into play after a certain lapse of time. They may be eliminated by reduction of the period of experiment.

In order to shorten the period of experiment for the study of growth movements, the rate of growth has to be very highly magnified, so as to determine the absolute rate and its variations in the course of a minute or so. I shall in a subsequent Paper give full account of an apparatus I have been able to devise, by which it is possible to record automatically the rate of growth magnified many thousand times.

I stated that anomalies of plant movements would disappear, if we succeeded in carrying out in detail in­ves­ti­ga­tions of effects of the different individual factors in operation. In illustration of this I shall, in the first Paper of the series, give an account of the mysterious movement of the ‘Praying’ Palm of Faridpur, and describe the in­ves­ti­ga­tions by which the problem found its solution.

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 been attracted in large numbers. It is alleged that offerings made to the tree have been the means of effecting marvellous cures. It is not necessary to pronounce any opinion on the subject; these cures may be taken as effective as other faith-cures now prevalent in the West.

This particular Date Palm, Phœnix dactylifera, is a full-grown rigid tree, its trunk being 5 metres in length and 25 cm. in diameter. It must have been displaced by storm from the vertical and is now at an inclination of about 60° to the vertical. In consequence of the diurnal movement, the trunk throughout its entire length is erected in the morning, and depressed in the afternoon. The highest point of the trunk thus moves up and down through one metre; the ‘neck,’ above the trunk, is concave to the sky in the morning; in the afternoon the curvature disappears, or is even slightly reversed. The large leaves which point high up against the sky in the morning are thus swung round in the afternoon through a vertical distance of about five metres. To the popular imagination the tree appears like a living giant, more than twice the height of a human being, which leans forward in the evening from its towering height and bends its neck till the crown of leaves press against the ground in an apparent attitude of devotion (Fig. 1). Two vertical stakes, each one metre high, give a general idea of the size of the tree and movements of the different parts of the trunk.