Page:Life Movements in Plants.djvu/276

246 the active tissues to responsive contraction. The latent period is, therefore, as short as 0-1 second and the maxi- mum contraction is effected in about 3 seconds. In the case of the stimulus of light the shock-effect is rot so great ; excitation, moreover, has to pass slowly from the surface of the pulvinus inwards. Hence the latent period is twelve seconds, and the period of maximum contrac- tion is as long as 90 seconds. As the stimulation is moderate, the recovery is effected in 11 minutes, instead of 16 minutes, which is the usual period for Mimosa to recover from an electric shock. The important conclusion to be derived from this experiment is, that light is a mode of stimulation end that it induces a responsive contraction, similar to that caused by other forms of sti- muli. This contractile response under light is exhibited not merely by the motile pulvinus of 3Iimi)sa, but by other pulvini as well, such as those of Erythrina indica, and of the ordinary bean plant.

Action of red and yellow lights. — The pulvinus gave little or practically no response to these lights.

Action of blue light : E.qjeriment 96. — Light was applied for 10 seconds and the amp'itu le of response was similar to that induced by white light (Fig. 90).

Fig. 90. — Effect of blue light on pulvinus of Mimosa.