Page:Popular Science Monthly Volume 17.djvu/682

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M. L. GRANDEAU, Professor in the School of Forestry, of France, was the first to point out definitely the influence of atmospheric electricity on the nutrition of vegetation.

His labors are described in the "Annales de Chimie et de Physique," for February, 1879, and he there gives the results of experiments carried out in 1876-’78.

These experiments are little known, but are of the highest importance to agriculture. As they bear upon similar experiments under-taken by the writer, a résumé is merited. M. Grandeau was led, from the common observation that the underwood in a dense forest disappears, to consider the influence of trees on the vegetation beneath them. Studying the causes generally assigned in explanation of this natural phenomenon, such as diminution of light, and the influence of the green light reflected by the trees, these appeared to him insufficient, and he concluded that the loss of electricity, due to the trees acting as an electrical screen, was the cause of the retarded growth—a theory that his experiments, as well as those of M. Mascart, ultimately confirmed.

The experiments consisted in placing plants under similar conditions of soil, light, and water, but covering one plant with a cage of iron-wire netting of very large mesh, the netting acting as a faradic cage, or somewhat as a lightning-conductor; the wires of the netting were one fiftieth of an inch in diameter, and the mesh six inches by four. Illustrative of the effect of this arrangement, the case may be cited of two tobacco-plants, otherwise under similar conditions:

Without Cage. Under Cage
Total height 1·05 metre 0·69 metre
Number of leaves 14 10
Weight of fresh leaves 107 grammes 70 grammes

Chemical analysis showed defective nutrition in the plant placed under the cage, and withdrawn from electric influence. These experiments were greatly extended, and trials were made as to the relation of electrical effect and nitrification of the soil, and the assimilation of the ammonia of the atmosphere by plants. ,The results are summed up by M. Grandeau as follows:

"That trees withdraw, for their own profit, electricity from the atmosphere, and insulate, as completely as a metallic cage, the plants they cover. Insulation produced by a high tree can extend to the extreme limits of its foliage. A plant withdrawn from the influence