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 of stimulus and the response; for it will take a definite time for the excitation to be conducted through the intervening tissue. I have already shown that this conduction of excitation in plant is analogous to the trans­mission of nervous impulse in animal.

The power of conduction varies widely in different plants. In the petiole of Mimosa pudica the velocity may be as high as 30 mm. per second. In the stem the velocity is considerably less, i.e., about 6 mm. per second in the longitudinal direction; but conduction across the stem is a very much slower process. In the petiole of Averrhoa the longitudinal velocity is of the order of 1 mm. per second.

DUAL CHARACTER OF THE TRANSMITTED IMPULSE.

The record of the transmitted effect of stimulus is found to exhibit a remarkable preliminary variation. This was detected by my delicate recorders, which gave magnifications from fifty to hundred times. I shall give a detailed account of a typical experiment carried out with Averrhoa carambola, which will bring out clearly the char­ac­ter­is­tic effects of Indirect Stimulus.

Fig. 52.—Effect of indirect Stimulus on leaflet of Averrhoa carambola. Stimulus was applied at the short vertical line. Successive dots at intervals of one second. Note the positive response preceding the negative.