Sensitive Plant

Sensitive Plant (Mimosa pudica), a branching Sonth American annual belonging to the suborder Mimoseae of the order Leguminosae, now naturalised in many tropical countries and common in our hot-houses. The leaves are bipinnate, with two or three pairs of pinnae, each with a large number of small pinnules. These are exceedingly sensitive to contact, assuming the nocturnal position immediately on being touched. [SLEEP IN PLANTS.] The seat of the movements is the parenchymatous swellings (pulvini) at the base of each leafiet, petiolule and petiole, and the movement is produced by an influx or efflux of water in the cells of one side of these structures. The conduction of the stimulus is effected by the continuity of the protoplasm through the cell-walls in the pulvini. The leaflets fold together down their midribs (conduplicate), each pinna then falls to an oblique downward direction, and then the main petiole fa11s similarly. Sudden variations in temperature or in intensity of light, electric and chemical stimuli, produce the same effects as contact.