Fig. 34.
Polytrichum commune. A large hair-moss.
t, t, Threads of green cells forming the protonema out of which moss-buds spring. mb, Buds of moss-stems. a, Minute green flower in which the antherozoids are formed (enlarged in Fig. 35). p, p1, p2, p3, Minute green flower in which the ovules are formed, and urn-plant springing out of it (enlarged in Fig. 35). us, Urn stems. c, Cap. u, Urn after cap has fallen off, still protected by its lid.
All this comes from the simple nature of the plants, each cell doing its own work. Nor are the mosses in any difficulty as to soil, for as the matted threads decay they form a rich manure, and the dying moss-stems themselves, being so fragile, turn back very readily into food. This is why mosses can spread over the poorest soil where even tough grasses cannot live, and clothe walls and roofs with a rich green.
Fig. 35.
Fructification of a moss.
A, Male moss-flower stripped of its outer leaves, showing jointed filaments and oval sacs os and antherozoid cells zc swarming out of a sac. zc´, Antherozoid cell enlarged. z, Free antherozoid. P, Female flower with bottle-shaped sacs bs. bs-c, Bottle-shaped sac, with cap being pushed up. u, Urn of Funaria hygrometrica, with small cap. u´, Urn, from which the cap has fallen, showing the teeth t which keep in the spores.