Art. LII.—The Effect of Current Electricity on Plant-growth: Further Experiments.
Communicated by the Secretary.
[Read before the Hawke's Bay Philosophical Institute, 9th October, 1893.]
In the “Transactions of the New Zealand Institute” for the year 1892 other previous experiments are detailed at some length.* The results which I obtained then were favourable to the growth of plants being accelerated by feeble and by comparatively powerful currents of electricity. For poles or plates to conduct the current through soil, silver and copper had been used. In one case more silver than the amount contained in a threepenny piece was incorporated in three-quarters of a cubic inch of soil. Plates of a substance not decomposable were substituted in two experiments, and, in a third, small quantities of guano were made to take the place of plates.
Experiment A.—Continuing with the same kind of plant as previously, two pieces of carbon were inserted in the ground ¾in. apart. Wires connected them with the poles of a Daniell cell of the common type, which gives a pressure of one volt. This current was sufficient to overcome the resistance of the soil between the carbons, and circulate round two seeds placed there. Moistened litmus paper proved the existence of not a small current, and, on reversal of the paper, change of colour was produced at the opposite end. The plants were subjected to the conditions of a hothouse, and the current was reversed every twelve hours. In five days from the time of sprouting one electrified shoot was 1in. higher than either of two ordinary plants which came up at the same time; the other electrified plant, appearing later, gained ½in. Comparing this result with that of experiment 5 given in my last paper, we are led to conclude that the silver dissolved in the earth in the course of the experiment retarded the growth.
Experiment B.—Again, small pieces of carbon were used with a one-cell current, but they were put in the earth after the plants appeared above the ground, and subjected to the ordinary conditions under which plants grow. At the end of two weeks these electrified plants were leading by ½in.
Experiment C.—This time thirteen small cells, each giving
[Footnote] * Trans. N.Z. Inst., vol. xxv., p. 479.
about half the current of a Daniel, were brought into play in the following manner: I filled two glass tubes of 1in. length with guano, and at one end of each tube fitted a section of carbon with wire attached. The sections of carbon and 1in. of each wire were then covered with guttapercha. This prevented any current passing through the earth, except by way of the guano in the tubes.
Two mustard-plants nearly 1in. above the surface of the ground were brought between the open ends of tubes, and the current turned on. During the period of three weeks the current was passed through the circuit intermittently, and always in the same direction. At the end of that time the gain over plants, equal in size at the commencement, was 2in., with size in proportion.
With seeds soaked in water, which were placed within a strong magnetic field, little or no effect was apparent. With zinc and carbon and zinc-cum-copper couples placed at distances of 1 and 2 yards, with rows of peas between, distinctly beneficial results have been observed.