The root hairs, fastening the plant to the ground, are rows of cells with brown walls and oblique partitions. They often merge insensibly into the green filaments (protonema) already noticed. These latter have usually colorless walls, and more numerous chloroplasts, looking very much like a delicate specimen of _Cladophora_ or some similar alga. If a sufficient number of these filaments is examined, some of them will probably show young moss plants growing from them (Fig. 63, _A_, _k_), and with a little patience the leafy plant can be traced back to a little bud originating as a branch of the filament. Its diameter is at first scarcely greater than that of the filament, but a series of walls, close together, are formed, so placed as to cut off a pyramidal cell at the top, forming the apical cell of the young moss plant. This apical cell has the form of a three-sided pyramid with the base upward. From it are developed three series of cells, cut off in succession from the three sides, and from these cells are derived all the tissues of the plant which soon becomes of sufficient size to be easily recognizable. The protonemal filaments may be made to grow from almost any part of the plant by keeping it moist, but grow most abundantly from the base of the stem. The sexual organs are much like those of the liverworts and are borne at the apex of the stems. The antheridia (Figs. 59, 60) are club-shaped bodies with a short stalk. The upper part consists of a single layer of large chlorophyll-bearing cells, enclosing a mass of very small, nearly cubical, colorless, sperm cells each of which contains an excessively small spermatozoid. The young antheridium has an apical cell giving rise to two series of segments (Fig. 60, _A_), which in the earlier stages are very plainly marked. When ripe the chlorophyll in the outer cells changes color, becoming red, and if a few such antheridia from a plant that has been kept rather dry for a day or two, are teased out in a drop of water, they will quickly open at the apex, the whole mass of sperm cells being discharged at once. Among the antheridia are borne peculiar hairs (Fig. 59, _p_) tipped by a large globular cell. [Illustration: FIG. 61.--_A_, _B_, young; _C_, nearly ripe archegonium of _Funaria_, optical section, × 150. _D_, upper part of the neck of _C_, seen from without, showing how it is twisted. _E_, base of a ripe archegonium. _F_, open apex of the same, × 150. _o_, egg cell. _b_, ventral canal cell.] Owing to their small size the spermatozoids are difficult to see satisfactorily and other mosses (_e.g._ peat mosses, Figure 64, the hairy cap moss, Figure 65, _I_), are preferable where obtainable. The spermatozoids of a peat moss are shown in Figure 60, _D_. Like all of the bryophytes they have but two cilia.