Abstract
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Physical and Natural History Society, March 2.—M. Casimir de Candolle gave the result of his researches on the movements of the leaves of Dionaa mwcipula, undertaken for the purpose of ascertaining if the anatomical constitution of these leaves furnished a sufficient explanation of these movements. His investigation has confirmed this hypothesis and has proved to him that the movements referred to, as well as those of the sensitive, for instance, are the result of the turgescence of the tissues and not of electric currents or other causes. The leaf of Dionsea is composed of two essential parts; one part petiolary, and at the extremity of that a limb or circular leaf, whose two halves are movable around the central nerve. Each of these two valves carries three hairs, which it is sufficient to touch very gently, with a human hair for example, to cause the valves to close. Having investigated the internal structure of these valves, M. de Candolle has found that they are composed of two different kinds of tissues. The upper layer is composed of parenchymatous cells, relatively young and yet turgescent; the inferior layer of cells much older, which are no longer turgescent. At a given moment, and in consequence of the shock communicated to the upper layer, the water which it contained is expelled, a contraction is produced, and the leaf closes. All the arrangements of the leaf and especially that of the secondary nerves, which are perpendicular to the great nerve, contribute to bring about this maximum movement. The gradual development of these leaves is in favour of this theory; the valves of all the young leaves are at first rolled up and they are stretched out at the moment of complete expansion. The leaf does not close if one simply touches the leaf; it is necessary to touch one of the hairs. Their anatomical structure was then examined and M. de Candolle found that they are composed of very elongated cells, forming a rigid cone, which rests on an articulation formed by two great cells, round which it turns very easily. The least shock communicated to this long arm of the lever, is transmitted with great readiness to the internal layers of the leaf, and develops the phenomenon of turgescence, which is not produced when simply the epidermis of the leaf is touched. These hairs are not true hairs, but excrescences in intimate relation with the interior parenchyma; hence their energetic action in the internal portions of the leaf.
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Societies and Academies . Nature 14, 344 (1876). https://doi.org/10.1038/014344a0
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DOI: https://doi.org/10.1038/014344a0