Page:An introduction to physiological and systematical botany (1st edition).djvu/307

 Rh an essential part, the seeds being frequently naked, and guarded only by the calyx, as in the first order of the Linnæan class Didynamia, of which Lamium, ''Engl. Bot. t. 768, and Galeopsis, t. 667, are examples; also in the great class of compound flowers, Syngenesia, as well as in Rumex, t. 724, Polygonum, t.'' 989, the Umbelliferous tribe, numerous Grasses, &c.

The use of the Seed-vessel is to protect the seeds till ripe, and then in some way or other to promote their dispersion, either scattering them by its elastic power, or serving for the food of animals in whose dung the seeds vegetate, or promoting the same end by various other mens. The same organ which remains closed so long as it is juicy or moist, splits and flies asunder when dry, thus scattering the seeds in weather most favourable for their success. By an extraordinary provision of Nature, however, in some annual species of Mesembryanthemum, natives of sandy deserts in Africa, the seed-vessel opens only in rainy weather; otherwise the seeds might, in that country, lie long exposed