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The sleep of plants has been frequently the subject of inquiry and admiration.

"Vigiliæ Plantarum.—Botanists, under this term, comprehend the precise time of the day in which the flowers of different plants open, expand, and shut.  As all plants do not flower in the same season, or month; in like manner, those which flower the same day in the same place, do not open and shut precisely at the same hour.   Some open in the morning, as the lipped flowers, and compound flowers with flat spreading petals; others at noon, as the mallows; and a third set in the evening, or after sun-set, as some Geraniums and Opuntias.  The hour of shutting is equally determined.  Of those which open in the morning,