Bryales

In _Sphagnum_, _Andreaea_ and some genera of the Bryales the protonema or some of its branches have the form of flat plates or masses of cells.

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With the possible exception of _Archidium_, the sporogonium is throughout the Bryales constructed on one plan.

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In all other Bryales there is a definite columella extending from the base to the apex of the capsule, the archesporium is derived from the outermost layer of cells of the endothecium, and an air space is formed between the spore-sac and the wall.

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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.

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The former subdivision of the Bryales into Musci Cleistocarpi and Musci

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This isolated example thus appears to approach the Bryales in its mode of dehiscence.

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Bryales depend mainly on the construction of the peristome.

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On account of the absence of a columella _Archidium_ is sometimes placed in a distinct group, but since its peculiarities have possibly arisen by reduction it seems at present best retained among the Bryales.

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