Read Ebook: Life Movements in Plants Volume I by Bose Jagadis Chandra

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RESPONSE OF PLANT ORGANS.

PAGE

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 experiment 1

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 inertia 43

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 excitability 73

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 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 141

GROWTH AND ITS RESPONSIVE VARIATIONS.

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 Crescograph 151

Method of discontinuous observation--Method of continuous observation--Determination of the cardinal points of growth--The Thermocrescent curve--Relation between temperature and growth 173

Effect of stimulants--Effect of anaesthetics--Action of different gases--Action of poisons 183

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 tension 188

Effect of intensity--Effect of continuous stimulation--Continuity between 'incipient' and actual contraction--Immediate effect and after-effect 195

Effect of mechanical irritation--Effect of wound 200

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 spectrum 205

Mechanical and electrical response to Indirect Stimulus--Variation of growth under Indirect Stimulus--Effects of Direct and Indirect Stimulus 213

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 stimulus 219

FIGURE. PAGE.

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.

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.

SIR J. BOSE,

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.

For an investigation in elucidation of this phenomenon it was necessary:--

THE RECORDING APPARATUS.

A difficulty arose at the beginning in obtaining sanction of the proprietor to attach the recorder to the tree. He was apprehensive that its miraculous power might disappear by profane contact with foreign-looking instruments. His misgivings were removed on the assurance that the instrument 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 point of the trunk is one metre. The movement is not passive, but an active force is exerted; the force necessary to counteract this movement is equivalent to the weight of 47 kilograms: in other words, the force is sufficient to lift a man off the ground. But far greater force would be required to restrain the change of curvature of the neck of the hard and rigid tree.

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 . 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 its greatest height at 7 next morning. This diurnal periodicity was maintained day after day.

UNIVERSALITY OF TREE MOVEMENT.

The next question which I wished to investigate was whether the movement of the particular Faridpur tree was a unique phenomenon. It appeared more likely that similar movement would, under careful observation, be detected in all trees. The particular palm tree was growing at a considerable inclination to the vertical; the movement 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 movement, if any, would escape notice, since such movements would be executed with only the empty space as the background.

THE CAUSE OF PERIODIC MOVEMENT.

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 temperature begins to rise. It is therefore difficult to 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 complication arising from the other. Unfortunately screening the tree was impracticable. I shall presently describe other experiments 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 6-15 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 continuously 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 the up-movement reaching its highest point not at 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.

Bose--"Irritability of Plants," d. 60.

The records that have been given show that it is the diurnal variation of temperature, and not of light that is effective in inducing the periodic movement of the tree. Further experiments will be given in support of this conclusion.

RELATIVE EFFECTS OF LIGHT AND TEMPERATURE.

As regards the possibility of light exerting any marked influence on the movement of the Palm tree, I have shown from study of time-relations of the movement, that this could not be the case. Moreover, it is impossible for light to reach the living tissue through the thick layer of bark that surrounds the tree. That the effect of light is negligible will appear from the accounts of following experiments, where the possibility of the effect of changing intensity of light is excluded by maintaining the plant in constant darkness, or in constant light.

There are many practical advantages in working with a small specimen. It can easily be placed under glass cover or taken to a glass house, thus completely eliminating the troublesome disturbance caused by the wind.

PHYSIOLOGICAL CHARACTER OF THE MOVEMENT.

These experiments conclusively prove that the periodic movement of the leaf-stalk induced by variation of temperature is a physiological phenomenon, and from analogy we are justified in drawing the inference that the movement of the Faridpur tree is also physiological. The question, however, was finally settled by the unfortunate death of the tree which occurred the other day, nearly a year after I commenced my investigations. While presiding at my lecture on the subject, His Excellency Lord Ronaldshay, the Governor of Bengal, announced that a telegram had just reached him from his officer at Faridpur that "the palm tree was dead, and that its movements had ceased."

Since my investigation with the Faridpur 'Praying' Palm, I have received information regarding other Palms, which exhibit movements equally striking. One of the trees is growing by the side of a tank, the trunk of the tree being inclined towards it. The up-lifted leaves of this tree are swung round in the afternoon and dipped into the water of the tank.

Having found that the temperature is the modifying cause, the next point of inquiry relates to the discovery of the force, whose varying effects under changing temperature induces the periodic movement. I shall, in this connection, first discuss the various tentative theories that may be advanced in explanation of the movement.

TRANSPIRATION AND DIURNAL MOVEMENT.

It may be thought that the fall of the tree during rise of temperature may be due to passive yielding of the tree to its weight, there being increased transpiration and general loss of turgor at high temperature. I shall, however, show that the diurnal movement persists in the absence of transpiration.

In the diurnal movement of the 'Praying' Palm the concave curvature of the rigid neck in the morning, became flattened or slightly convex in the afternoon. The force necessary to cause this is enormously great, and could on no account result from the passive yielding to the weight of the upper part of the tree.

From the facts given above it will be seen that the diurnal movement is not brought about by variation in transpiration. I now turn to another phenomenon which appeared at first to have some connection with the movement of the tree. Kraus found that the tissue tensions of a shoot exhibit a daily periodicity. He, however, found that between 10?C. and 30?C., variation of temperature had no effect on the daily period. But as regards the diurnal movement of the tree, it is the temperature which is the principal factor. Kraus also found a daily variation of bulk in different plant-organs; this variation of bulk is connected with transpiration, for the removal of the transpiring leaves arrested this variation. But the periodic movement of the tree, as we have seen, is independent of transpiration.

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