* Mimosa. l. 321. The sensitive plant. Of the class Polygamy, one house. Naturalists have not explained the immediate cause of the collapsing of the sensitive plant; the leaves meet and close in the night during the sleep of the plant, or when exposed to much cold in the day-time, in the same manner as when they are affected by external violence, fold∣ing their upper surfaces together, and in part over each other like seales or tiles; so as to expose as little of the upper surface as may be to the air; but do not indeed collapse quite so far, since I have found, when touched in the night during their sleep, they fall still further; especially when touched on the foot-stalks between the stems and the leaflets, which seems to be their most sensitive or irritable part. Now as their situation after being exposed to external violence resembles their sleep, but with a greater degree of col∣lapse, may it not be owing to a numbness or paralysis consequent to too violent irri∣tation, like the saintings of animals from pain or fatigue? I kept a sensitive plant in a dark room till some hour after day-break; its leaves and leas-stalks were collapsed as in its most prosound sleep, and on exposing it to the light, above twenty minutes passed before the plant was thoroughly awake and had quite expanded itself. During the night the upper or smoother surfaces of the leaves are appressed together; this would seem to shew that the office of this surface of the leaf was to expose the fluids of the plant to the light as well as to the air. See note on Helianthus. Many flowers close up their petals during the night. See note on vegetable respiration in Part I.
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