1. Monoecia. United flowers accompanied with barren or fertile, or both, all on one plant. Atriplex, Engl. Bot. t. 261, 232, &c., is an instance of this, having the barren flowers of 5 regular spreading segments, the united ones of 2 compressed valves, which, becoming greatly enlarged, protect the seed. In several species however the flowers are none of them united, each having only stamens or only pistils. Throughout the rest of the Order, as it stands in Linnæus and Schreber, I can find no genus that has the requisite character. Some of the grasses indeed have awns to one kind of flower only, but that part is too uncertain to establish a character upon; and this family is so natural in itself, and so liable to variations in the perfecting of its flowers or florets, that there can be no doubt of the propriety of classing its genera simply by the number of their stamens and styles, which are very constant.
2. Dioecia. The different flowers on two different plants. I can scarcely find a cer-
