XXI. Monoecia. Stamens and pistils in separate flowers, but on the same plant.
The orders of this class are, like those of the last, distinguished by the number of the stamens, or by some other charac ter of the foregoing classes. The most genuine examples of it are such as have a different structure in the two kinds of flowers, besides the essential difference with respect to stamens and pistils, as the oak, chesnut, teazle.
XXII. Dioecia. Stamens and pistils like Xxii. Dioecia. Stamens and pistils like the former in separate flowers, but on two separate plants.
The orders of this class are character ised like those of the preceding. The willow, hop, hemp, &c. belong to it.
XXIII. Polygamia. Stamens and pistils Xxiii. Polygamia. Stamens and pistils separate in some flowers, united in others, either on one, two, or three distinct plants. Dr. Smith has first suggested that no plants should be admitted into this class, without a difference in the accessory parts of their flowers, over and above what concerns the stamens and the pistils. Without such a rule, the class would be overwhelmed with the trees of tropical countries.
The orders are, Monoecia, when the se veral kinds of flowers grow on one plant, as Atriplex: Dioecia, when they are situ ated on two separate ones ; and Trioecia, when they occupy three several individu als of the same species.
XXIV. Crl,ptogamia. Stamens and pisXxiv. Crl,ptogamia. Stamens and pis- tils either not well ascertained, or not to be numbered with certainty.
1. Fakes, ferns, whose flowers:are al most entirely unknown. The seed-ves sels commonly grow on the back of the leaf, thence denominated a frond, and are either naked or covered with a mem brane. In some few they form spikes or clusters of capsules.
2. Musci, mosses, a peculiar family of plants, possessing great elegance, though diminutive in size ; extremely tenacious of life, growing in the hottest as well as the coldest climates; flourishing most in the damp wintry months. Their her bage consists of pellucid leaves, some times accompanied with a stem : their capsule is of one cell and of one valve, closed with a vertical lid ; seeds nume rous and small ; the capsule is covered with a calyptra or membranous veil, the summit of which is the stigma, a circum stance absolutely peculiar to this family ; the stamens are mostly in a separate flow er, and numerous. The late Dr. Hedwig
of Leipsic is celebrated for his discove ries relating to mosses. He has distin guished their genera by the peristomium or fringe, which in most cases surrounds the mouth of the capsule. This fringe is either single or double. In the former case it consists of either four, eight, six teen, thirty-two, or sixty-four teeth. The inner peristomium when present is more membranous, plaited, and jagged. The principles of Iledwig have been adopted, with a few requisite limitations, by the most able writers in this branch of botany.
3. Hepaticc, liverworts. The herbage of these plants is most generally a frond, or leaf, bearing the fructification ; but they differ most essentially from the last order in the want of a lid to the capsule, which is formed quite on a different prin ciple from that of mosses, and very vari ous in the several genera. Jungerman nia and Marchantia are examples of this order.
4. Algx, flags. The herbage of these is also frondose, being sometimes a pow dery crust, sometimes leathery or gela tinous ; the seeds are embedded in frond, or in some appropriate receptacle ; the stamens are scarcely known. The vast family of Lichen occurs here, the most hardy of vegetables, clothing ex posed rocks, trunks of trees, and barren heaths, in the most cold and inhospitable climates. On one of them the rein-deer depends for sustenance in the winter. Others are useful in dyeing and even me dicine. The numerous and various tribe of sea-weeds, Fucus, Conferva, and Ulva, are classed here.
5. Fuligi, mushrooms. These are fleshy in substance, of quick growth, and gene rally of short duration. They are divided into Angiocarpi, which bear seeds inter nally ; and Gymnocarpi, whose seeds are imbedded in an exposed membranous or gan. Many of these are eatable, some poisonous. Linnaus bad a great preju dice against the use of any of them as food.