The Effect of Electric Discharges on the Rate of Growth of Plants

Abstract

In the present paper the authors describe the results of experiments on the effect of electric discharges upon the rate of growth of certain plants. The currents applied are of three kinds, viz. high-tension A. C., high-tension D. C. and high tension high-frequency current. The experiments were carried out, since 1921, in the Botanical Garden of the Tokyo Imperial University.
Field experiments on the electro-culture have hitherto given no consistent results, some workers reporting a considerable increase in crop production, while others stating no such effect. The authors conducted their experiments in a green house so as to keep culture conditions uniform for both the electrified and control plants. The electric current of very low intensity was induced in the plants by applying high voltage to a thin wire net-work suspended at a distance of 15-30cm above the plant. The determination of the result was done by estimating the dry weight of plants, grown as fully as possible under the conditions of experiments.
Preliminary tests with high-tension A. C. Several kinds of plants were treated with high-tension A. C. of 50 cycles and at 21, 000 volts. The electrified plants have shown mostly an accelerated growth. For instance, the two series of experiments with buckwheat showed the average increase of yield amounting to 9.8% and 8.0% respectively for the electrified.
High-frequency current experiments. High frequency voltage was produced by a set of three quenched spark-gaps in series. The fundamental frequency of the wave was about 130, 000 cycles and the E. M. F. measured with needle point, spark-gaps was about 13, 000 volts (crest value-spark distance being 1.5 -1.6cm.) The results obtained were not uniform, but in a recent experiment the electrified buckwheat gave the yield 12.6% greater than the control.
High-tension D. C. experiments. High-tension D. C. was obtained by rectifying 50-cycle A. C. by means of a kenotron. The aerial net work was kept as (-) pole while the plants (+) pole and the voltage was held unchanged in some cases, but in others controlled within 10, 000 and 15, 000 volts (effective, measured at A. C. side, ) so as to keep the current passing through the plant nearly same. The first few experiments did not show much differences in the growth between the electrified and control plants. But the effect upon tobacco plants was rather conspicuous, as may be seen from the picture shown below, the increase in dry weight being 21.70 of the control.
Experiments with the coleoptile of oat. Besides the culture experiments above mentioned, the authors have made more minute observations on the change of the growth rates of coleoptile of oats under the influence of electric discharges. The temperature of the dark chamber in a thermostat was kept constant within a range of 0.01°C. A charged point of platinum wire was fixed at a distance of 30mm just above the plant. The rate of growth was measured every 5 minutes with a horizontal microscope which was illuminated by weak red light only while taking the reading. The results of experiments are shown in curves 1-32. From these it may be concluded:
1. The control test shows that the normal growth rata of coleoptile is quite uniform. (See Curve 1.)
2. The three kinds of electric currents show the effect of almost the same nature, viz. "immediately after the discharge the growth rate diminishes, but after about 15 minutes tends to increase and attains a maximum in about 1/2-3/4 hour, often reverting to the original rate after 1-2 hours." The phenomena observed may be appropriately termed "the electro-growth reaction."
3. It seems that a certain voltage at a certain distance between the poles gives the maximal growth effect.
4. The observed change in growth rates is due solely to the electricity applied, although the authors are not yet certain whether it is caused only by weak electric current passing through the plant or by some ionic actions.