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Calyptra

The calyptra or veil is the dry remains of the outer wall of the archegonium in which first the egg-cell and then the embryo moss-plant were developed, for as the embryo within enlarges, the wall of the archegonium sooner or later ruptures near the base, and is carried up by the growing spore-case. This severed archegonium wall may be thin and smooth and often split up one side, or it may be as in the Hairy-caps rough with hairs, caused by the stretching and ultimate rupturing of the fibres which composed the tissue of the walls.