Galvanotropism of Roots.

Abstract

Every one interested in plant irritability has always considered the galvanotropic response of roots as remarkable.

From previous work it could be deducted that for high densities of current or long exposures, anodic curvature (Elfving's curvature) is obtained.

For low densities of current or short exposure, cathodic curvature (genuine galvanotropic response) is obtained.

The opinions differ in many respects regarding the origin ascribed to this last curvature. Brunchorst believes an injury is produced by H₂O₂; Rischawi considers the phenomenon similar to the electrosmosis of water in du Bois-Reymond's experiments with albumin. Ewart and Bayliss attribute this fact to chemiotropic stimulation. Gassner finds it a traumatic response to unilateral injury.

But in practically all this work the technic is too crude. For instance, the formation or diffusion of products of electrolysis is scarcely considered; often electrodes and roots dip in the same liquid. Often, too, the density of current is not given.

For these reasons the experiments were repeated and the technic elaborated keeping in mind the following points: (1), reduction of polarisation products (non-polarizable electrodes); (2), prevention of diffusion of electrolysis products by agar blocks; (3), variable densities of current by use of troughs with definite geometrical shapes and sizes.

The electrodes used were zinc—zinc sulphate electrodes. The densities of current varied between 0.058 MA/cm² and 1 MA/cm², the potential difference from 0.5 volt to 115 volts; the time of exposure from 15 minutes to 360 minutes. The plants used were Vicia faba and Phaseolus vulgaris. The seedings, grown in sawdust at 20° C., were employed when the roots had 4 to 6 cm. in length, the part dipping in the liquid ranging from 8 to 10 mm.