EFFECT OF ELECTRICITY ON PLANTS The relation that exists between electrical stimulation and plant growth has been a subject of much study. covering is great range of methods and conditions, and producing varied and conflicting results ; but the question has not yet had the care ful and systematic study necessary to the formu lation of rules for practical application. Much has been written on the subject, and the reader will find a few citations at the end of this article. It is here possible to give only a very general outline of the experimental methods that have been tried and the results.
Historical sketch of methods and results.
Investigations pertaining to the effects of elec tricity on plants have been made by various ex perimenters for 150 years or more. It might be supposed that electricity, which so universally manifests itself in nature, would under certain con ditions be capable of acting as a stimulus to plants. That the roots of plants are susceptible to the influence of galvanic currents (galvanotropism) has been shown by the experiments of Elfving, Bruncherst and others ; and Hegler has shown that the aerial hyphm of Phyannyees nitens are nega tively electrotropic ; that is, they bend away from Hertz waves. It has also been known for some time, through the experiments of Kunkel and others, that electric currents exist in the plant itself. The cause of these currents has been attrib uted to minute streams of water passing through the plant. The experiments of Haake have shown that differences in the electrical potential in the plant are chiefly caused by metabolism and res piration.
The influence of current electricity on plants has received the most attention. Attention was first called to the influence of electricity on growing plants about the middle of the eighteenth century. The experiments made by Dr. Mainbray, of Edin burgh, in 1746, were among the first. He electrified two myrtles for a period of one month, and reported that not only was their growth accelerated but that they put forth blossoms, which was not true of myrtles not electrified. About the same time, Nollet, a distinguished French physicist, who had heard of Mainbray's experiments, took up the sub j-ct. He had previously been occupied with the
phenornma connected with the behavior of fluids in c Lpiliary tubes, and Mainbray's experiments sug gested to him the possibility of the increased growth in plants being due to the increase in the flow of sap brought about by electrical stimulation. His first experiments were made on various fruits, which after being weighed were electrified and then weighed again, and the result showed that elec tricity considerably accelerated evaporation. In 1717, Nollet experimented with two wooden pots filled with earth, in which were planted mustard seeds. One was treated daily with an electrical machine, the other being kept as a check. He found as a result of electrifying that germination was considerably increased, and in the course of a week or more the electrified plants were nine inches high, while the non-electrified ones were only three inches high. Nollet repeated the experiment a number of times with various plants, always obtaining the same result. He found, however, that the electrified plants were, as a rule, weaker than the non-electrified. dallabert, in 1746, re peated Nollet's experiments on mustard and cress seeds, and obtained similar results. He also elec trified bulbs of hyacinths, jonquils and narcissus placed on cakes of resin in glasses filled with water, the resin being connected with wires leading to a frictional machine. He found, as had Nollet, that the electrified ones gave off more moisture than the non-electrified ones, and also that the electrified plants grew more rapidly. Their leaves were larger and their flowers opened sooner than the ones not electrified.
Experiments were made about the same time also on bulbs planted in boxes, with similar results. In 1747, Doze electrified several different kinds of shrubs, the growth of which was accelerated. Similar results were obtained by Menon, in 1748. In 1771, Sigaud de la Fond experimented with bulbs, and found that when they were electrified they grew faster and formed more healthy plants.