Electrostatic Measurement of the Geoelectric Effect in Coleoptiles

Abstract

THE so-called geoelectric potential, which develops between the upper and lower side of a plant when it is placed in a horizontal position, has been investigated by many workers^1–5 using different types of fluid electrodes which were applied directly to both sides of the plant. The original explanation of the cause of this potential given by Brauner⁶ has lately proved to be unsatisfactory⁷ and a new theory was proposed⁸. To test this theory it was necessary to carry out electric measurements on plants during much longer periods of time than has been done earlier. This was possible by using electrodes some-what similar to those devised by Clark⁵. The results obtained by this method were difficult to reproduce and differed generally from those reported by earlier workers. During extensive measurements on Avena coleoptiles, Pisum, Helianthus and Zea mays, it was found that the results are often strongly influenced by the direct-contact electrodes. Therefore, it was thought necessary to measure these potentials without touching the plants at all, and to this end an entirely new measuring technique was developed.