Page:Life Movements in Plants.djvu/164

134 Feeble heterodromous current enhances conductivity, homodromous current, on the other hand, depresses it.

Ineffectively transmitted excitation becomes effectively transmitted under heterodromous current. Effectively transmitted excitation, on the other hand, becomes ineffectively transmitted under the action of homodromous current.

The after-effect of a current is a transient conductivity change, the sign of which is opposite to that induced during the passage of current. The after-effect of a heterodromous current is, thus, a transient depression, that of homodromous current, a transient enhancement of conductivity.

The characteristic variations of conductivity induced in animal nerve by the direction and intensity of current are in every way similar to those induced in the conducting tissue of the plant.

These various effects are demonstrated by the employment of not one, but various kinds of testing stimulus, such as the excitation caused (1) by a single break-induction shock or (2) by a series of equi-alternating tetanising shocks or (3) by chemical stimulation.