Absorption of Water by the Leaves of Plants


THE experiments of Boussiugault, referred to in NATURE, vol. xviii. p. 672, find a fitting sequel in those of the Rev. G. Henslow, detailed in a paper read before the Linnean Society on November 7. Although gardeners universally maintain that growing plants have the power of absorbing water through their leaves, both in the liquid and the gaseous form, in addition to the power of suction through the roots, yet the contrary theory has been in favour during recent years among vegetable physiologists. The first recorded experiments of any value on the subject were about the year 1727, by Hales,1 as described in his “Statical Essays;”the conclusion to which he came being that “it is very probable that rain and dew are imbibed by vegetables, especially in dry seasons.”This result was confirmed by Bonnet in 1753. A century later, however, in 1857, Duchartre, experimenting on the absorptive power of plants, came, after considerable wavering, to the conclusion that rain and dew are not absorbed by the leaves of plants. This opinion lias been, with but little exception, held by all physiologists during the last twenty years, notably by De Candolle and Sachs; the explanation offered of the fact that withered plants revive when placed in moist air or when the leaves are moistened, being that transpiration is thus stopped, or is more than counterbalanced by the root-absorption. In his “Text-book of Botany”(English edition, p. 613), Sachs says:—“When land-plants wither on a hot day, and revive again in the evening, this is the result of diminished transpiration with the decrease of temperature and increase of the moisture in the air in the evening, the activity of the roots continuing; not of any absorption of aqueous vapour or dew through the leaves. Rain again revives withered plants, not by penetrating the leaves, but by moi-tening them, and thus hindering further transpiration, and conveying water to the roots, which they then conduct to the leaves.”McNab has, however, proved that leaves do transpire, even in a moist atmosphere, provided thev are exposed to the action of light.

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