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In Sphagnum, as in Anthoceros, the archesporium is derived from the amphithecium; in all other mosses it is the outermost layer of the endothecium.

In the young condition the wall of the capsule, which consists of two layers of cells, encloses a mass of similar cells developed from the archesporium.

The archesporium arises by the next divisions in the outer layer of cells, and thus extends over the summit of the columella.

In some species, although the columella and archesporium arise in the usual way, both give rise to mingled spores and elaters, and no sterile columella is developed.

The development of the sporogonium proceeds as in the Bryales, but the dome-shaped archesporium extends over the summit of the columella and an air-space is wanting.