MIMOSA, the SENSITIVE PLANT, in botany, a genus of the polygamia monoclea class. The calix of the hermaphrodite consists of five teeth, and the corolla of five segments; it has five or more stamens, one pistillum, and the fruit is a pod; the calix, corolla, and stamens of the male are the same with those of the female. There are 43 species, all natives of the Indies.—The mimosa is called the sensitive plant from its remarkable property of shrinking its leaves and branches upon being touched by the hand or any thing else. This motion it performs by means of three distinct articulations, viz. of a single leaf with its pedicle, of the pedicle to its branch, and of the branch to the trunk or main stem: the primary motion of all which is the closing of the two halves of the leaf on its rib; then the rib or pedicle itself closes; and if the motion wherewith the plant is moved be very strong, the very branches have the sensation propagated to them, and apply themselves to the main stem, as the simple leaves did before to their ribs, and these ribs to their branches; so that the whole plant, in this state, forms itself, from a very complexly branched figure, into a sort of straight cylindrical one.
Many attempts have been made to account for the motion of this plant upon mechanical principles; but all these attempts have hitherto proved unsatisfactory.