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. [Illustration: FIG. 150—USNEA FLORIDA. (_Old Trees._)] [Illustration: FIG. 151.—RAMALINA FASTIGIATA. (_Rocks and Trees._)] [Illustration: FIG. 152.—CORNICULARIA HETEROMALLA.—(_Old Trees._)] Though these plants are said to have no leaves, they consist almost entirely of a kind of leafy stem, called a frond or thallus, the branches of which are called podetia (see _a_ in _figs._ 150, 151, and 152). The spores or sporules are produced in what are called shields (_b_ in _figs._ 149, 150, and 151), which are generally embedded in the thallus, and which, when they are cup-shaped (as in _fig._ 150), are called scyphæ, and when flat (as in _fig._ 151), apothecia. The sporules, which are very numerous, are inclosed in receptacles of various forms, which are embedded in the shields. Some of the commonest lichens are _Usnea florida_ (_fig._ 150), and _Ramalina fastigiata_ (_fig._ 151), both of which are found on old oaks, and are generally called grey moss; and _Cornicularia heteromalla_ (_fig._ 152) is a brown mossy-looking lichen, often found on the bark. Other more interesting lichens are—the Iceland-moss (_Cetraria islandica_), the Reindeer-moss (_Cenomyce_, or _Cladonia rangiferina_), the Cup-moss (_Cenomyce pyxidata_), and the Orchil (_Rocella tinctoria_). ORDER CCXIX.—FUNGI.