The antheridia are filled with a mass of mucilage containing a multitude of cells, in each of which there is a spiral filament furnished with cilia, as in [fig. 49]. As soon as the filaments are mature, the cells open; the mobile filaments, or spermatozoids, are free, and come out through a pore in the antheridia, in multitudes like pollen out of an anther.
While the antheridia are in process of formation, the female buds expand and exhibit flask-shaped archegonia, similar to that in [fig. 45], seated in a rosette of leaves. When this archegonium is fertilized by the spermatozoids, its internal germ cell is developed by cell division into a conical body elevated upon a stalk; and this at length tears across the walls of the flask-shaped archegonium by a circular fissure, carrying the higher part upwards as a calyptra or hood ([fig. 47] c) upon its summit, and leaving the lower part to form a kind of collar round the base of the stalk.
Fig. 48. Polytrichum commune:—group of antheridia mixed with hairs and sterile filaments (paraphyses), the central one discharging its contents.
Fig. 49. Polytrichum commune:—B, cellular contents of an antheridium previously to the development of the spermatozoids; C, the same, showing the first appearance of the spermatozoids; D, the same, mature and discharging the spermatozoids.
The urn-shaped organ or sporangium has a double wall, and in its centre a fusiform or deeply winged columella. Between these two there is a tissue of a most delicate texture, divided into spherical cells, each of which usually produces four unripe spores, which get an exterior coat when fertilised, and then it is that the stalk lengthens, and the flask-shaped archegonium is torn across.
The urns are closed by a lid or operculum of a flat, convex, or pointed form, which falls off when the spores are ripe to give them egress. The mouth of the urn in most of the mosses is surrounded by a deciduous annulus of two or three rows of elastic cells, which are supposed to aid in scattering the spores, for the mosses have no elaters. Although the separation of the lid may at once expose the spores, they may be covered with a membrane entire or toothed at the circumference, or there may be one or two rows of teeth surrounding the mouth of the urn like a fringe; these teeth form the peristome, and their number is always a multiple of 4, varying from 4 to 64 (see [fig. 47] p). Sometimes they are divided half way down, sometimes they are prolonged into straight twisted hairs. The teeth arise from the thickening of the walls of two contiguous cells; when there are two rows of teeth, the outer row frequently arises from the layer of cells which line the outer wall of the urn, the inner row from the outermost layer of the spore sac; sometimes, when the peristome is double, three strata of cells are requisite to form the teeth. The urns of the Encalypta vulgaris are represented at [fig. 47] B; one is covered with the hood or calyptra, while from the other the lid has fallen off, showing the mouth of the urn with its toothed peristome.
When a spore begins to grow, its outer coat is ruptured, its innermost coats protrude and form a projecting extremity, which becomes developed into a confervoid pro-embryo, analogous to the mycelium of fungi, but is distinguished by the chlorophyll contained in its cells. Many spores may concur or not in its formation; but the pro-embryo of each spore is capable of transforming one or more of the cells seated upon its various ramifications immediately into buds, which grow up into leafy stems, as the Funaria hygrometrica, so that here we have the peculiar condition of one spore giving rise to the development of a number of plants.[[68]] In process of growth each of these plants would produce antheridia and archegonia, and, by the process described, a full-grown Funaria hygrometrica with its urns and hoods, as represented in [fig. 47] A, would be the result.
If the moss be annual or biennial it dies after bearing fruit; if perennial, two or more successive crops of archegonia are formed. The mode of fructification, therefore, resembles that of flowering plants, with this difference, that the fructification of the latter produces a young plant from each embryonic cell, while in mosses the fructification of one embryonic cell produces a sporangium or urn containing spores, that is, a multitude of reproductive bodies, which have no trace of cotyledons or axis.[[69]]