Jagadish Chandra Bose

“ All these different forms of stimulus induce an excitatory contraction, a diminution of turgor, and a negative mechanical response or fall of a motile leaf.
SUMMARY.
A radial organ responds to stimulus by contraction in length; as all its flanks are equally excitable there is no lateral movement under diffuse stimulus.
Physiological anisotrophy is induced in an organ, originally radial and isotropic, by the unequal action of the environment on its different sides. Diffuse stimulus induces a greater contraction of the more excitable side. ”

“ 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. ”

“ 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 ”

“ Subjection to sudden darkness thus acts as a stimulus inducing a marked but transient fall of excitability. Under the continuous action of darkness, however, the excitability is at first restored and then undergoes a persistent depression. ”

“ 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. ”

“ Still more marked is the effect of temperature. Lowering of temperature depresses and finally abolishes the moto-excitability: rise of temperature enhances it up to an optimum temperature, but beyond this point the excitability undergoes depression. The change in excitability induced by the variation of external condition is not immediate; the induced effect, generally speaking, lags behind the inducing cause. ”

“ For the purpose of this investigation I enclosed the plant in a glass chamber, raising the temperature to the desired degree by means of electric heating. Responses to identical stimuli were then taken at different temperatures. It was found that the effect of heightened temperature, up to an optimum, was to enhance the amplitude of response. ”

“ 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. ”

“ From the responses of organs rendered anisotropic by the differential action of the environment we pass to others which show certain amount of anatomical and physiological differentiation between their upper and lower sides. ”

“ In the Oscillating Recorder the recording plate itself moves to and fro, making intermittent contact with the writer about once in a minute. The recording smoked glass plate is allowed to fall at a definite rate by the unwinding of a clock wheel. By an electromagnetic arrangement the holder of the smoked glass plate is made to oscillate to and fro, causing periodic contact with the writer. ”

“ 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. ”

“ These experiments show that owing to physiological inertia, the variations of excitability in the plant often lag considerably behind the external changes which induce them.
Effect of high temperature: Experiment 18.—It has been shown that the moto-excitability is enhanced by rising temperature; there is, however, an optimum temperature above which the excitability undergoes a depression. ”

“ 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 ”

“ Moderate depression followed by quick restoration.
very well be done by application of a stream of cooled water, because, as we have seen, absorption of water by the pulvinus is attended by a loss of excitability: diluted glycerine has, however, no such drawback. ”

“ Thus with a given specimen it was found that while at 22°C. the amplitude of response was 2.5 mm., it became 22 mm. at 27°C., and 52 mm. at 32°C. The excitability is enhanced under rising, and depressed under falling temperature. The moto-excitability of Mimosa is practically abolished at the minimum temperature of about 19°C.
Effect of lowering of temperature: Experiment 17.—A simple way of exhibiting the effect of lowering of temperature is by artificial cooling of the pulvinus. This cannot
Fig. ”