1553. The third order, that of the _Tracheal mosses_, corresponds to the stem, or to the Gasteromycetes. A membranous trunk originates in water, which in certain places secretes the seeds in special vesicles or cysts--_Fucales_ or connate Confervæ. The fuci have at once the form of a stalk with root and leaves, because they correspond to these three organs of the axis. 1554. The fourth order, the _Floral mosses_, endeavours to obtain the _blossom_, and therefore elevates itself out of the water, but loses on that account the trunk-like character, and exhibits for the most part only membranous expansions, upon which seeds are secreted, which being usually of a beautiful colour, thus assume the appearance of corollæ--_Lichenales_. The lichens are fuci in dry situations. They correspond to the Pyrenomycetes or Sphæriaceæ. 1555. As the variegated colours appear in the blossom, so do they also in the lichens; but here they are for the first time chemically developed, distributed throughout the whole substance, and concealed. Most lichens yield colouring matters. 1556. As the stem is, in accordance with their signification, wanting to the lichens, they thus require a foreign trunk for their nutrition. They are therefore developed for the most part upon other plants, and principally upon the bark. 1557. Lastly, the fifth order, _Fruit-mosses_, originates through the development of a self-substantial _fruit_ upon a cauliform stem--the _Mosses_ proper. 1558. As these are the highest plants of this class, and those that directly precede the tracheal formation, so the bark already resolves itself into individual leaves, which are, however, still destitute of spiral vessels. 1559. What have been called the seeds or sporules are accumulated in a capsule-like fruit upon the summit of the stalk. This fruit corresponds to the pileated fungus, and therefore springs up in an opercular manner like the latter. 1560. But this capsule is only a spermoderm, which incloses albuminous granules that have no proper germ or seed-lobes; they are plants with seed-vessels or pyxidia, upon an open-leaved stalk. 1561. They divide likewise into sixteen families. (Vid. Tab. B.) _CLASS III._ _Trachea-plants--Ferns._ 1562. At first a fascicle only of spiral vessels can originate, which is necessarily surrounded by cellular tissue, and therefore lies in the middle of the plant. Such plants are the _Filices_ or ferns. 1563. As the spiral vessels are the antetype of the leaves, so does the trunk here obtain the form of the leaf, without itself producing true leaves. For, in the ferns, the fruits lie upon the back of the apparent leaf, which can only be the trunk. 1564. The fruits, being further removed from the fungi, no longer spring up in an opercular, but in a valvular, manner like the higher capsules. 1565. Green plants with imperfect spiral vessels and blossoms, and also with naked seeds devoid of true capsules, belong to the class of Ferns.