Chap. XVII The Influence of Electricity on Vegetables
With regard to this part of our subject there has been considerable controversy between philosophers, some of them asserting that electricity is unfavourable, and others that it is advantageous to vegetation. It was asserted by the Abbè Bertholon, in his book entitled Electricitè des meteores, that plants situated near a metallic conductor increased considerably in consequence of their situation. And, on the other hand, Giardini says that plants growing near such conductors are generally unhealthy, and produce very little fruit, but upon removing the conductor the plants become luxuriant and fruitful.
The Abbè Bertholon in endeavouring to establish his opinion, constructed what he called an electro vegetometer by means of which the electricity of the atmosphere may be collected in abundance. “This apparatus (says he) having been raised with care in the midst of a garden, the happiest effects were perceived, viz. different plants, herbs and fruits, in greater forwardness than usual, more multiplied and of better quality.” These facts are analogous to an observation that I have often made, viz. that plants grow best, and are more vigorous near thunder rods, where their situation favours their developement. They likewise serve to explain why vegetation is so vigorous in lofty forests, and where the trees raise their heads far from the surface of the earth, so that they seek as it were the electric fluid at a far greater height than plants less elevated: while the sharp extremity of their leaves, boughs and branches serve as so may points granted them, by the munificent hand of nature, to draw down from the atmosphere that electric fluid which is so powerful an agent in forwarding vegetation, and in promoting the different functions of plants.—Such are the theory and experiments of the Abbè, but Doctor Ingenhaus, in two letters to Mr. Molitor, published in the journal de physique for 1786–88 has shewn the fallacy of the theory, by exposing the insufficiency of the experiments upon which it was established.
We shall translate a few passages from the Doctor’s letter, which will shew us his opinion and the result of his experiments.
I have frequently made experiments of this kind by exposing plants to a weak degree of electricity, and at other times to a considerable quantity, without ever being able to observe that plants under its influence prospered more than those which were not electrified at all. It even appeared to me more than once, that those which had been electrified were a little less thrifty than those which were not electrified.
In another place he says, Not being content with these experiments, I have made others infinitely more conclusive, by strewing seeds of mustard and cresses, over the largest plates of delf that I could procure, covering them with brown paper, and sprinkling them continually with a sufficiency of water. Each of these plates was covered with more than a thousand seeds; I kept them electrified night and day, according to the method which Mr. Schewankhard directed, in a letter quoted by Mr. Elermann, but which I shall not repeat in this place, lest I should swell this memoir: the vegetation of these little shrubberies was always more or less precarious, in proportion to the greater or less quantity of light that they received; the electricity really contributing nothing to advance the growth: thus the controversy stands, we leave the reader to form his own opinion.
That some plants are more affected than others by electricity is an unquestionable fact. It is however not true as some have affirmed, that the contractions of the mimosa or sensitive plant, are attributable to this cause. The plant is equally affected when touched either by a conductor or an electric.