MIMOSA. The Mimoseae (so named from their mimicry of animal movements) form one of the three suborders of Leguminosae, and are characterized by their (usually small) regular flowers and valvate corolla. Their 28 genera and 1100 species are arranged by Bâillon in four series, of which the acacias (see Acacia) and the true mimosas are the most important. They are distributed throughout almost all tropical and subtropical regions, the acacias preponderating in Australia and the true mimosas in America. The former are of considerable importance as sources of timber, gum, and tannin, but the latter are of much less economic value, though a few, like the talh (J∕. ferruginea) of Arabia and Central Africa, are important trees. Most are herbs or undershrubs, but some South-American species are tall woody climbers. They are often prickly. The roots of some Brazilian species are poisonous, and that of Μ. pudica, I.., has irritating properties. Μ. sensitiva has been used in America in the treatment of fistula, <fcc., probably as an astringent. The mimosas, however, owe their interest and their extensive cultivation, partly to the beauty of their usually bipinnate foliage, but still more to the remarkable development in some species of the sleep movements manifested to some extent by most of the pinnate Leguminosae, as well as many other (especially seedling) plants. In the so-called “sensitive plants” these movements not only take place under the influence of light and darkness, but can be easily excited by mechanical and other stimuli. When stimulated, say at the axis of one of the secondary petioles, the leaflets move upwards on each side until they meet, the movement being propagated centripetally. It may then be communicated to the leaflets of the other secondary ...