which a history with plates is given in the sixth volume of the Linnæan Society's Transactions, I found the drupa and all its contents apparently perfect, except that there was only a minute cavity where the embryo shuld have been, in consequence of the want of another tree with stamens, which was not to be found perhaps nearer than Japan. Gardeners formerly attempted to assist Nature by stripping off the barren flowers of Melons and Cucumbers, which, having no germen, they found could not come to fruit, and were therefore, as they supposed, an unnecessary encumbrance to the constitution of the parent plant. But finding they thus obtained no fruit at all, they soon learned the wiser practice of admitting air as often as possible to the flowering plants, for the purpose of blowing the pollen from one blossom to the other, and even to gather the barren kind and place it over that destined to bear fruit.
The œconomy of various aquatic plants throws great light upon the subject before us. Different species of Potamogeton, Engl. Bot. t. 168, 297, 376, &c., Ruppia maritima, t. 136, and others, float entirely under wa-
