Page:Researches on Irritability of Plants.djvu/46



the case of contractile animal muscle, various stimuli give rise to excitation, and it is a very remarkable fact that the same stimuli exercise a similar excitatory influence on the pulvinus of Mimosa. Classifying these stimuli, we find that they are:—


 * 1. Mechanical.—A blow will excite animal muscle and cause mechanical response. A similar effect is induced by a mechanical blow in the pulvinus of Mimosa. A prick or cut also will cause contraction in either.


 * 2. Chemical.—Various chemical agents are found to induce excitation in both animal and vegetal contractile tissues. Thus dilute hydrochloric acid or ammonia causes excitation of both muscle and pulvinus.


 * 3. Thermal.—The application of a hot wire will induce responsive contraction in both cases.


 * 4. Electrical.—The muscle may be excited by an induction-shock. The pulvinus of Mimosa is also excited by such shocks. Other modes of electrical stimulation, such as that of condenser-discharge and that of the application of a constant electrical current, are found effective in causing excitation of animal tissues. It will be seen in the

Rh