Page:Collected Physical Papers.djvu/412

392 Wireless waves and growth.—The results obtained by the Balanced Crescograph prove that electric waves used in signalling through space are effective in modifying the rate of growth. The perceptive range of the plant is far greater than ours; it not only perceives but also responds to different rays of the vast ethereal spectrum.

Opposite reactions under feeble and strong stimulation.—This appears to be a universal phenomenon, characteristic of response of both inorganic and living substances under diverse modes of stimulation. This is seen in the responses of inorganic matter to electric radiation. In the positive class, e.g. Osmium in which the response to moderate stimulation is by a diminution of resistance, a subminimal stimulus induces a response by an increase of resistance (p. 137). Similar opposite responses under moderate and feeble stimulation are also exhibited by negative class of substance represented by Arsenic (p. 137). The electromotive response of metallic wires under mechanical stimulation also exhibits this characteristic (p. 204). A short-lived negative twitch is often observed preceding the normal response designated as positive. This is due to the fact that it takes a short time before the responding substance can absorb the whole amount of incident stimulus, the first moiety absorbed being sub-minimal (p. 181). This characteristic effect is exhibited not only by electromagnetic receivers (p. 189) but also by photo-electric cells responding to light (p. 190) and by strain cells under mechanical stimulation (p. 204).

In plants also similar reactions are observed. This is seen in the opposite effects of feeble and strong intensity of electric waves in enhancement and retardation of growth respectively (p. 355).