Page:An introduction to physiological and systematical botany (1st edition).djvu/239

 Rh it, especially the compound radiated ones, as the Daisy, Sun-flower, Marigold, &c. In their forms Nature seems to have delighted to imitate the radiant luminary to which they are apparently dedicated, and in the absence of whose beams many of them do not expand their blossoms at all. The stately Annual Sun-flower, Helianthus annuus, displays this phænomenon more conspicuously on account of its size, but many of the tribe have greater sensibility to light. Its stem is compressed in some degree, to facilitate the movement of the flower, which, after following the sun all day, returns after sun-set to the east, by its natural elasticity, to meet his beams in the morning. Dr. Hales thought the heat of the sun, by contracting the stem on one side, occasioned the flower to incline that way; but if so, it would scarcely return completely at night. There can be no doubt, from the observation of other similar flowers, that the impression is made on their radiated florets, which act as wings, and seem contrived chiefly for that purpose, being frequently destitute of any other use. A great number of leaves