Page:Life Movements in Plants.djvu/136

106 the stamen of Berberis. The conduction of excitation consists, on the other hand, of propagation of excitatory protoplasmic change. The tranmission [sic] in the petiole of Mimosa is a phenomenon of conduction.

This conduction takes place along vascular elements. The conductivity is very much greater in the longitudinal than in the transverse direction.

Rise of temperature enhances, and fall of temperature lowers, the rate of conduction. Excitation is transmitted in both directions; the centrifugal velocity is greater than the centripetal.

Dessication [sic] of conducting tissue by glycerine enhances the conducting power. Local application of cold depresses or arrests the conduction. Application of poison permanently abolishes the power of conduction.

Conductivity is modified by the effect of season, being higher in summer than in winter.

The power of conduction is also modified by age. In young specimens the conducting power is low, the conductivity is at its maximum in fully grown organs; but a decline of conductivity sets in with age.

The tonic condition of a tissue has an influence on conductivity. In an optimum condition, the velocity is the same for feeble or strong stimulus. Excessive stimulation induces a temporary depression of the conducting power.

The effects are different in a sub-tonic tissue: velocity of transmission increases with intensity of stimulus; after-effect of stimulus is to initiate or enhance the conducting power. The conducting path is canalised by stimulus.