Life Movements in Plants

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-—Re¬ sponse of pulvinus of Mimosa to variation of turgor— Different modes of stimulation . . . . . 31 Apparatus for ' study of variation of excitability— U niform periodic stimulation—The Response Recorder—Effects of • external condition on excitability—Effects of light and darkness—Effect of excessive turgor—Influence bffem- pel&ture—Diurnal variation of excitability—Effect of physiological inertia ..... . 43

Effect of wound or section in modification of normal excitability—The change of excitability after imme^ion in water—Quantitative determination of the rate of decay of excitability in an isolated preparation—Effect of amplit^tion of uppe* half of the pulvinus—Effect of. removal of the lo\yer half—Influence of weight of leaf on rapidity of responsive fall—The action of chemical .agents—Effect of “fatigue” on response— 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 cf stimulus on $ub-tonic tissues' and tissues, in optimum condition —Canalisation of conducting path by stimulus —Effect of injury on conductivity . ... 97

Mettod of conductivity-balance—Control of transmitted excitation in Amrrhoa hilimli by electric current— 1 Up- - bill ’ transmission—Transmission ‘ downhill ’—Electric con- trol of nervous impulse in animal—Directive action of current on conduction of excitation—Effects of direction of current oh velocity of transmission in Mimosa —De¬ termination of variation of conductivity by method of, Minimal Stimulus and Response—Influence of direction of current on conduction of exeitatiou in animal nerve ' ’

—Variation of velocity of transmission —After-effects u oi Heterodroinous and Homodromous currents — Laws of .variation of. nervous conduction under electric current . 107 Conduction of excitation—Dual . character of the trans¬ mitted impulse—Effect / of distance of . application of ■ stimulus—Periods of transmission of positive and 0 nega- ■ rive impulses—Effects of Direct &d Indirect stimulus ■. 135 * Theory of assimilation and dissimilation—Unmasking* of positive effect— Modification of response under artificial depression of tonic condition — Positive response In sub- ■ tonic specimen ..«***. 1^

C. Effect of physiological depression on diurnal move- merit of Arenga sac-char if era * * • . * 29. Diurnal variation of excitability of a summer specimen 70 39. Effect of constant current,:;in removal of' fatigue . 92 42, ..Effect.,of .injury ia depressing conductivity in. nonrial 55. Positive, diphasic, and' negative responses of extremely Kysoar, and of effects of cold and warmth on stationary and moving plates .... $•??«#* $ 7 # Curve showing the relation between growth and tem¬ perature .

73. Effect of continuous electric stimulation on growth 14. Immediate and after-effects of friction, and of wound 82. Effect of elettric stimulus on sub-tonic specimen of wheat seedling 86. Effect of light in diminution of amplitude and reductimi of diastolic limit of pulsation of Desmodium &1> Antagonistic effect of warmth 'in reduction of . *■ . systolic■.■■■ limit . . , ■ . . . . “88* • -Gaai&casfcile response of a growing bud of Crinum .■ THf 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 9 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 2uay be similar or dissimilar. An identical agent, again, ma?? 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 front it. Some plants close their leaflets on the approach of darkness, in the So-called position of 4 sleep * apparently similar ‘ sleep ’ movement is induced in others by the action of the midday snn.

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 re¬ action in growing organa. Thus in a tendril, one-sided con¬ traction causes a shortening of the concave side and a sudden increase of growth on the convex. No explana¬ tion of this dill'erenCe 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 fight 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 th*j ’ 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 in¬ dividuality of the plant that determines the choice of iis 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 deter¬ mined by the point of application, direct stimulus produc¬ ing one effect, and indirect the diametrically opposite. The normal reaction is again modified by the tonic con¬ dition 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 pf these diverse factors.

For a comprehensive study of the phenomenon of plant movement, it is therefore necessary to investigate ia 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 investiga¬ tion has to include the effects exhibited not merely by the .pulvinated hut al£o by growing organs. As a result of such a comprehensive study, it may perhaps be possible to discover some fundamental reaction operative in bring¬ ing about, the responsive movement in all plant organs.

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 edn<- stancy of external conditions, during the period of experi¬ ment ; 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 5 however, come into' play after a certain lapse of time. They may be eliminated by reduction of the period of experiment.

In order fo 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 dia* appear, if we succeeded in carrying out in detail invo»tigtt* tions of effects of vthe different individual factors in opef^c lion. 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 in* vestigations by which the pioblem found its solution.

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 nas 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, Phmnix 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 J to the vertical. In consequence of the diurnal move¬ ment, the trunk throughout its entire length is erected in the morning, and depressed in the afternoon. The high¬ est point of the trunk thus moves up and down through one metre; the 4 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 Fig. 1. Thj Faridpur ‘Praying’ Palm; the upper photograph shows position in the morning; the lower, position in the afternoon. The two fixed stakes are one metre in height. In front is seen erect trunk of a different Palm. distance of about five metres. To the popular imagination the tree appears like a living giant, more than t\vicjr~tiie- height of a human being, which leans forward in the evening from its towering height and ben is its neck till the crown of leaves press against the ground in an apparent attitude of devotion (Fig. 3). 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.

For an investigation in elucidation of this phenomenon it was necessary :— the tree day and night, and determine the time of its maximum erection and fall. ?>. To discover the cause of the periodic movement of the tree. between the diurnal movement of the tree, and the diurnal variation of moto-excitability in Mimosa pud tea, I shall now describe the principle and construction of my recording apparatus (Fig. 2) seen attached to a horizon¬ tally growing stem of Mimosa pudica. When used to trace

the movement of the palm tree, a reducing device is employ¬ ed to keep the record within the plate. A lever, R 1 , records the movement of the attached tree or plant on a moving plate of smoked glass. The plate is not in contact with the Fig. 2. Apparatus for automatic record of movement of trees and plants; T, differential metallic thermometer; R, recording lever for temperature; R 1 , for "recording plant movemeEt; C, clock-work for oscillation of recording plate. The same deck-work moves plate laterally in 24 -hours.

tip of the recording lever, but separated from it by a dis¬ tance of about 3 mm. A special oscillating device, actuated by clock-work, C, makes the plate move forwards and back- awards. The forward movement brings about a momentary contact of the recording tip with the smoked plate inscrib¬ ing a dot. These single dots are made at intervals of 15 minutes; at the expiration of the hour, however, contact is made three times in rapid succession, printing a thick dot. It is thus easy to determine the movement of the tree at all times of the .day and night. A second lever,. R, placed above, gives on the same plate, thermographic record of the diurnal variation of temperature. For this I use a differ¬ ential thermometer, T, made of a compound strip of brass and steel. Curvature is induced by the differential expansion of the two pieces of metal. The up or down movement of the free end of the compound strip is farther magnified by the recording lever. This arrangement was extremely sensitive and gave accurate record of variation of tempera¬ ture. . By the forward . movement of the oscillating plate two dots are made at the same time,—one for‘the tem¬ perature and the other for the corresponding movement of the tree. As. the two recorders do not move vertically up or down, but describe a circle, the dots vertically one abo^e the other may not correspond as regards time. Any possi¬ bility of error in calculation is obviated by the fact that the thick dots in both the records are made every hour, and the subsequent thin dots at intervals of 15 minutes.

A difficulty arose at the beginning in obtaining sanction of the proprietor to attach the -recorder to the tree. He m was apprehensive that its miraculous power might disappear by profane contact with foreign-looking instruments. His misgivings w^ere removed on the assurance that the instru¬ ment was made in my laboratory in India, and that it would be attached to the tree by one of my assistants, who was the son.of a priest. From results of observation it is found that the tree moves through its entire length; the fall of„ the highest

Fig. 3. Bvcord of diurnal movement of the ‘Praying’ Palm (Pk'vnix dacty- Ufera). Thermographic curve for 24 hours commencing at 9 m the evening is given in tb'* upper record; the corresponding diurnal curve of movement of the tree is given in the lower. Successive dots at intervals of 15 minutes: thick dots at intervals of an hour. passive, but an active force is exerted ; the force nt^ep ax y io counteract this movement is equivalent to the w 47 kilograms : in other words, the force is sufficient to lift a man off the ground. But far greater force would be re¬ quired to restrain the change of curvature of the neck of

Before entering into the investigation of the cause of periodic movement I shall give a general account of its characteristics. A casual observation would lead one to conclude that the tree lifted itself at sunrise and prostrated at sunset. But continuous record obtained with my recorder attached to the upper part of the trunk shows that the tree was' never at rest, but in a state of continuous-' movement, which underwent periodic reversals (iig. '«$)• The tree attained its maximum erection at 7 in the morning, after which there is a rapid movement of fall. The down movement reached' its maximum at 3-15 P,M., after which it was reversed and the tree erected itself to it© greatest height at 7 next morning. This diurnal periodicity was maintained day after day. ;

The next question which I . wished to investigate, was whether *he movement of the particular Farklpur tree ;was a unique phenomenon-. It appeared more likely that similar movement would, under careful observation, be detected in all trees. The particular palm free was growing at a con* siderable inclination to the vertical; the nyovcmeflt of the tree and its leaves became easily noticeable, since the ground afforded a fixed and striking object of reference. In a tree growing more or less erect, the moventent, if any,

would escape, notice, since such movements would be exe¬ cuted with only the empty space as the background. Experiment 1 .—Believing the phenomenon to be uni¬ versal I experimented with a different Date Palm .that was growing at my research station at Sijbaria on the Fig. 4. Record of the Sijbaria Palm from noon for 24 at intervals of 15 minutes. angfes, situated at a distance of about 200 miles from Fandpur. lhe surrounding conditions were very different. The tree was much younger; it was 2 metres'in height and me med 20 to the verbal. The curve obtained wffh this tree (Fig. 4) w<,s vary similar to that of the Faridpur Palm t ough the extent to the movement was much reduced.’ The tree attained the highest erect position at 7-15 am. and

the lowest at 3-45 P.M. • Hence the movement of the Farid- pur Palm is not a solitary phenomenon. The recurrent daily movement of the tree must be due to some diurnal changes in the environment,—either the recurrent changes of light and darkness, or the diurnal changes of temperature. These changes synchronise to a certain extent; for, as the sun rises,, light appears and the tempera¬ ture begins to rise. It is therefore difficult lo discriminate the effect of light from that of temperature. The only satisfactory method of discrimination would have been in the erection of a large structure with screens to cut off light. The effect,, of fluctuation of temperature under constant darkness would have demonstrated the effect of one agent without complica¬ tion .arising from, the other* Unfortunately screening the tree • was impracticable. I shall presently describe other experi¬ ments where the action of light was completely excluded. ■

The curve of .movement of the tree, however, .affords us material for correct inference as regards the relative, effects' of light and temperature. The experiment was. commenced in March ; light appeared at about 5 A.M., the sunrise being at £-15 A.M, ; the sun set at 6-15 P.M., and it became dark by 7 P.M. The incident light would be the most intense at about noon ; after this it would ' decline continrously till night time. If the movement was due to light, its climax, either in up or down movement, would be reached at or about noon, and the opposite climax at midnight. But instead of this we find (Fig. 3) the up- movement reaching its highest point not., a*t noon, but at 7 in the morning; after this the* fall is rapid and continuous, and the lowest position was reached not in the evening but at 3-15 P.M. The fluctuation of light has, therefore, little to do with the movement of the* tree.

Turning next to the element of variation of temperature we are at once struck by the fact that the curve of move¬ ment of the tree is practically a replica of the thermo¬ graphic curve (Fig. 3). The fall of temperature is seen to induce a rise in the tree and vice versa . There is a lag in the turning points of the two curves ; thus while tempera¬ ture began to rise at 6 A.M., the tree did not begin to fall till 7 A.M. There is in this case a lag of an hour; but the latent period may, sometimes, be as long as three hours The delay is due to two reasons; it must take some time for the thick trunk of the tree to attain the temperature of the surrounding, and secondly, the physiological inertia will delay the reaction. As a result of other investigations, I find that the induced effect always lags behind the in¬ ducing cause. It is interesting in this connection to draw attention to the parallel phenomenon, which is described below, of lag in variation of sensibility of Mimosa in res¬ ponse to variation of temperature. In this case the lag was found tc be about three hours. Returning to the Palm, the tree continues to fall in the forenoon with'rising temperature* 'At about 2-30 p.m*. -the . temperature was at its maximum a£te- r . which it began to decline ; the movement of the tree was not reversed into erection till after 3-15 p.m., the lag being now 45 minutes nearly.

I may state here that the movement of the tree is not primarily affected by the periodicity of day and night, but by variation of temperature. In spring and in early sum¬ mer the rise of temperature during the early jmrt of the day -and the fall of the temperature from afternoon to next morning, are regular and continuous ; the corresponding movements of the tree *are also regular. Rut at other seasonsowing fo the sudden change of direction of the wind, the fluctuations of temperature -are irregular. Thus at night there may’ be a sudden rise, and in the earlier part of the day sudden fall of temperature. And the

record of movement of the tree is found to follow these fluctuations with astonishing fidelity, the rise of temperature being followed by a fall of' the tree ■ and vice versa* That the movement is determined by the temperature variation is exhibited in a striking manner in Fig. 4.. where, between 8 and 9 A.M., a common twitch will be noticed in the two curves. While trying to obtain some clue to the mysterious move-, meat of the tree, my attention was strongly attracted by certain striking similarities which the record of the move¬ ment of the tree showed to the curve of the diurnal variation of moto-excitability, of the pulvinus of Mimosa pudiea , an account of which will be found in a subse¬ quent:. Paper of the- series.*

The excitability of. the main pulvinus of■ Mimosa padica I find - does not remain constant during the 24 hours, but undergoes a striking periodic change. At certain hours of the day, the excitability is at its maximum; at .a different period it practically disappears. .The. period of insensibility is about 7 a.m*. which," strangely enough, is also the time when the palm tree attains its maximum height. At about 3 in the afternoon the excitability of Mimosa reaches its climax, and this is the time when the head of the palm tree bends down to its lowest position. For the determination of the periodic variation of excitability of Mimosa 1 devised a special apparatus by which an electric stimulus of constant intensity

* See also Bose—Diurnal Variation of Moto-Excitability in Jii worn—Annals cf Botany, VoL XXVII, No. CYIII, October, 1918. the same time. The amplitude of responsive fall o . ooder uniform stimulus *ave a measure ol excitability „ f era riot ion of rnoto-e suitability of Uimosa padica. The upper ZiZ the record of diu^l — -= - ,. r , , f Mimosa Comparison, of this figure ® ZZZ — of moto-exeitability of ^oso^Tbe excitability of Minima reached its maximum