Page:Researches on Irritability of Plants.djvu/57

34 mode of excitation. In subsequent chapters we shall also study in detail the various characteristics of response and its time-relations.

The ideal method of stimulating a plant is one in which the intensity might be maintained uniform or varied in a definite and known manner.

If the stimulus exceeds a certain critical value, the tissue is injured with concomitant diminution or abolition of excitability.

One practical method of quantitative stimulation is by electro-thermic stimulus, where the plant-tissue is subjected to a sudden and definite thermal variation.

The plant may also be excited by the action of a constant current.

Another method of excitation is by the discharge of a condenser.

And lastly, excitation may be induced in the plant by a single induction-shock or by a series. As in the skeletal muscle of animals, so in the pulvinus of Mimosa, the break-shock is more effective than the make-shock.