Page:Life Movements in Plants.djvu/275

records of the responsive reactions of various lights on growing organs. I shall now give records of the effect of various lights on the pulvinus of Mimosa pudica. The amplitude and time relations of the curves of response will give a more precise idea of the quantitative effects of various lights in inducing excitation.

Action of white light: Experiment 95.—The source of light was an arc lamp; a pencil of parallel light is made to pass through a trough of alum solution. This process of excluding thermal rays is adopted for the visible rays of the spectrum. Colour filters were also used for obtaining red, yellow and blue lights. The pencil of light is thrown upwards by an inclined mirror on the lower half of the pulvinus. The response is taken by an Oscillating recorder, giving successive dots at intervals of 10 seconds, the magnification employed being 100 times. The pulvinus being subjected to light for 10 seconds gave response by a fall of the leaf (Fig. 89). The response to light
Fig. 89.—Effect of white light on the pulvinus of Mimosa. Successive dots in this and in the following records are at intervals of 10″. (Magnification 100 times). is thus found to be essentially similar to that induced by electric stimulus, the only difference being in the relative sluggishness of the reply. Electric shock passes instantaneously through the mass of the pulvinus, stirring up