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How the Spores Escape From the Spore-case

When the weather is damp, although the spores are ripe, the teeth of the Polytrichum mosses hold the membranous disk so that the spores cannot escape. When the weather is dry the teeth are so modified as to make a ring of holes between the teeth and the edge of the disk, through which the spores may pass.

There are mosses with their teeth triangular in shape. These have the bases of the triangles fastened at the rim and the points meeting at the centre. In some species the teeth simply arch up, remaining fastened at the points, and let the pores escape, while in other species they turn back like the ray flowers of a daisy.

Some species have at the base of the teeth a single or double row of short bead-like cells (annulus) which swell up at the proper time to push off the spore-case lid.

When the spores of the Hairy-cap are mature, the pedicel bends to bring the spore-case into a horizontal position, and the sides of the spore-case wrinkle up, and by so doing oust the spores.