The effect of a direct electric current of very low intensity on the rate of growth of the coleoptile of barley

Abstract

Although many workers have studied the effect of electric currents on the irritable responses of plants there have been only a few scattered observations of the effect of such currents on the rate of growth. A number of the older workers investigated the effect on roots of passing electric currents through the soil, but the direct action of the current on the root was not differentiated from the electrolytic action on the soil solution. Later workers appear to have established a response by curvation to weak currents, the so-called galvanotropism of roots. It has, of course, been known that large currents will bring about the death of cells—no doubt in the main by electrolysis—and that somewhat smaller currents would quickly stop the growth of a stem. Lemström in 1885 and Gassner in 1907 each made isolated observations of the effect on seedlings of cereals of a discharge from metallic points fixedm above the plants, the points being charged by means of an influence machine. Both report an increase in growth as a result of such treatment, but observations on voltage, strength of current, rate of growth, and the variation between plant and plant are alike wanting. Bose has a number of scattered observations, based on single plants, showing that a “tetanising” current lasting a few seconds may increase or decrease temporarily the rate of growth, and that a seedling will exhibit minute changes in the rate of growth when subjected to so-called “wireless” stimulation, which was in reality response to stimulation by a high-frequency current through a wire attached to the plant. These experiments lasted only for a few seconds or at most a few minutes and no measurements of current are given. Exact knowledge of the direct effect of electric currents on the rate of growth of actively developing organs was thus practically wanting. Since there was this gap in our knowledge, and the authors had been engaged on studying the effect of a high-tension electric discharge on the dry weight and grain production of plants, it was determined to make a careful study of the growth-reactions of plants to electric currents which continue over a considerable period. In such a study, carefully controlled conditions and accurately measured currents must be employed, and full consideration must also be paid to the variation in the response of individual plants. Accordingly, experiments were begun in 1918 on the coleoptile (sheathed plumule or young stem) of the seedling of barley ( Hordeum vulgare ). In all the experiments no electrodes in contact with the plant were used, but the ionization current from a highly charged point placed at a little distance above the plant was employed. The progress of the work has been delayed owing to the fact that the observations could only be made during half the year, and also owing to the great variability in the rate of growth of individual plants, so that for a trustworthy mean result numerous observations were required.