Fig. 149.—Cryptogamous Plants.
The Mosses have fibrous roots, and slender wiry stems, densely covered with leaves, which are very small, and laid over each other like scales (see a in fig. 149). The theca (g) is urn-shaped, and it is produced singly; in most cases, on a long, slender, wiry stem, called a seta, which signifies a bristle, but sometimes without any stalk. It always springs from a tuft of leaves, differing both in size and shape from ordinary leaves, which form what is sometimes called the perichætium. Among these may occasionally be seen a few stalks, resembling the Lichen called Cup-moss, which terminates in a kind of cup, and thickened at the base. The cups and upper parts soon die away, and the thicker part left among the leaves swells, and in time rises on a stalk of its own, carrying away one of the leaves with it on its head. This is the theca, and the leaf it carried away, and which resembles an extinguisher, is called the calyptra, and it remains on till the sporules are nearly ripe. When the calyptra falls, the theca is found to be covered with a little lid called the operculum; which also falls off in time, and shows the mouth or stoma of the theca. This mouth is sometimes naked, and sometimes covered with a kind of film; but generally it is surrounded by a row of long, slender, hair-like teeth called the peristome or fringe. When there are two rows of these hair-like teeth, the inner ones, which are finer than the others, are called the cilia; and the number of both the cilia and the teeth is always some number that can be divided by four. In the cavity of the theca is a central axis called the columella, and around that are found the sporules, kept together by the lining of the theca, which forms a kind of open bag. This is the usual construction of all the numerous genera of mosses; but in some kinds, as for example in the Hair-moss (Polytrichium), in addition to the theca, a number of granules are found among the leaves, which are said to be capable of producing young plants.
ORDER CCXVII.—HEPATICÆ.
These plants greatly resemble Mosses in their appearance, but they differ in their construction. The theca has no lid, but bursts into valves; and it generally contains not only sporules, but tubes formed of curiously twisted threads, called elaters. Jungermannia and Marchantia have a calyptra, which the other genera are without; and in Jungermannia the theca has a sort of sheath, which is sometimes called the calyx. There are also stalked granules called anthers, and warts which form on the leaves, and break up into a kind of sporules.
SUB-CLASS II.—APHYLLEÆ.
ORDER CCXVIII.—LICHENES.
Though these plants are said to have no leaves, they consist almost entirely of a kind