Page:Life Movements in Plants.djvu/163

Rh laws, which are equally applicable to the conducting issuetissue [sic] of the plant and the nerve of the animal:—

1. The passage of a current induces a variation of conductivity, the effect depending on the direction and intensity of current.

2. Under feeble intensity, heterodromous current enhances, and homodromous current depresses, the conduction of excitation.

3. The after-effect of a feeble current is a transient conductivity variation, the sign of which is opposite that induced during the continuation of current.

The variation of conductivity induced by the directive action of current has been investigated by two different methods:—

The great difficulty arising from leakage of the exciting induction current into the polarising circuit was successfully overcome by the interposition of a choking coil.

The following summarises the effects of direction and intensity of an electric current, on transmission of excitation through the conducting tissue of the plant.

The velocity of transmission is enhanced against the direction of a feeble current, and retarded in the direction of the current.