The spores arise from a single layer of cells near the outside of the inner mass of cells (_G_, _sp._). These cells (_H_, _sp._) are filled with glistening, granular protoplasm; have a large and distinct nucleus, and no chlorophyll. They finally become entirely separated and each one gives rise to four spores which closely resemble those of the liverworts but are smaller. Near the base of the capsule, on the outside, are formed breathing pores (Fig. 58, _F_) quite similar to those of the higher plants. If the spores are kept in water for a few days they will germinate, bursting the outer brown coat, and the contents protruding through the opening surrounded by the colorless inner spore membrane. The protuberance grows rapidly in length and soon becomes separated from the body of the spore by a wall, and lengthening, more and more, gives rise to a green filament like those we found attached to the base of the full-grown plant, and like those giving rise to buds that develop into leafy plants. CLASSIFICATION OF THE MOSSES. The mosses may be divided into four orders: I. The peat mosses (_Sphagnaceæ_); II. _Andreæaceæ_; III. _Phascaceæ_; IV. The common mosses (_Bryaceæ_). [Illustration: FIG. 64.--_A_, a peat moss (_Sphagnum_), × ½. _B_, a sporogonium of the same, × 3. _C_, a portion of a leaf, × 150. The narrow, chlorophyll-bearing cells form meshes, enclosing the large, colorless empty cells, whose walls are marked with thickened bars, and contain round openings (_o_).] The peat mosses (Fig. 64) are large pale-green mosses, growing often in enormous masses, forming the foundation of peat-bogs. They are of a peculiar spongy texture, very light when dry, and capable of absorbing a great amount of water. They branch (Fig. 64, _A_), the branches being closely crowded at the top, where the stems continue to grow, dying away below. [Illustration: FIG. 65.--Forms of mosses. _A_, plant of _Phascum_, × 3. _B_, fruiting plant of _Atrichum_, × 2. _C_, young capsule of hairy-cap moss (_Polytrichum_), covered by the large, hairy calyptra. _D_, capsules of _Bartramia_: i, with; ii, without the calyptra. _E_, upper part of a male plant of _Atrichum_, showing the flower, × 2. _F_, a male plant of _Mnium_, × 4. _G_, pine-tree moss (_Clemacium_), × 1. _H_, _Hypnum_, × 1. _I_, ripe capsules of hairy-cap moss: i, with; ii, without calyptra.] The sexual organs are rarely met with, but should be looked for late in autumn or early spring. The antheridial branches are often bright-colored, red or yellow, so as to be very conspicuous. The capsules, which are not often found, are larger than in most of the common mosses, and quite destitute of a stalk, the apparent stalk being a prolongation of the axis of the plant in the top of which the base of the sporogonium is imbedded. The capsule is nearly globular, opening by a lid at the top (Fig. 64, _B_).