Page:Life Movements in Plants.djvu/64

(Fig. 10). Stronger shocks induce greater contraction

Fig. 10. Response of a straight tendril of Passiflora to electric shock. Successive dots at intervals of 5 seconds. The vertical lines below are at intervals of a minute. In this and in all following records (unless stated to the contrary) up-curve represents contraction, and down-curve expansion or recovery.

with prolongation of the period of recovery. The specimen was afterwards killed by application of poisonous solution of potassium cyanide; this brought about a permanent abolition of response. The experiment just described may be taken as typical of response of radial organs.

In a radial organ contraction takes place equally in all directions; it therefore shortens in length, there being no movement in a lateral plane. But, if any agency renders one side less excitable than its opposite, diffuse stimulation will then induce greater contraction on the more excitable side which will therefore become concave.

RESPONSE OF AN ANISOTROPIC ORGAN.

Excessive stimulation is found to reduce the excitability of an organ. Under unilateral mechanical stimulation a