Sensitive Plant. a name commonly given to certain species of Mimosa (see MIMOSÆ), on account of the peculiar phenomena of irritability (q.v.) which their leaves exhibit in their collapse when touched or shaken. Numerous species of Mimosa possess this property, and, indeed, most of the species in a greater or less degree; but those in which it is most conspicuous are humble herbaceous or half-shrubby plants. They have leaves beautifully divided, again and again pinnate, with a great number of small leaflets, of which the pairs close upwards when touched. On repeated or rougher touching the leaflets of the neighbouring pinnæ also close together, and all the pinnæ sink down, and at last the leaf-stalk itself slinks down, and the whole leaf hangs as if withered. If the stem is shaken all the leaves exhibit the same phenomena. After a short time the leaf-stalk rises, and the leaflets expand again. On account of this curious and interesting property some of the sensitive plants are frequently cultivated in our hothouses. They are generally treated as annuals, although capable of longer life. M. sensitiva, one of the best-known species on the continent of Europe, is a native of Brazil, with prickly stems and leaf-stalks, and small heads of rose-coloured flowers. M. pudica is the species most commonly cultivated in British hothouses; it is a branching annual growing from 1 to 2 feet high. M. casta, M. pudibunda, M. palpitans, and
M. viva are also among the most sensitive species. See the section on the movement of plants at PLANTS; also Dr G. Haberlandt, Das reizende Gewebesystem der Sinnpflanze (Leip. 1890).