friend, Francis Bauer, as well as from some observations of my own, I am disposed to believe that considerable diversities may exist in the placentation of mosses: that in some cases the seeds may be formed in a much greater portion of the columnula than in others: and it is even not improbable that in certain cases its whole substance may be converted into seeds; or, to speak more accurately, that it may produce seeds even to the centre, and that the cells in which they were probably formed may be re-absorbed. This I am inclined to think is the case in Phascum alternifolium of Dickson, in the ripe capsule of which there is hardly the vestige of a columnula; and I have observed the same structure in two new species of Anodontium of Bridel; which, if it equally exists in the only species of this genus hitherto described, would perhaps considerably strengthen its character. In these cases the inner membrane is also 316] evanescent; and such a structure, it may be remarked, equally militates against M. Beauvois' theory, whether we suppose the columella to have existed at an earlier stage, in the usual form, or not.
As to this organ being tubular, and discharging its contents by the top, it is neither consistent with what has been already observed, nor with the appearance of its remains in the ripe capsule: but, admitting for a moment its tubular nature, there are certain mosses in which no discharge could possibly take place in the way described; the column being elongated even to the apex of the operculum, to which it often continues to adhere, as in Buxbaumia, and in the first of the two new genera which I now proceed to describe.
DAWSONIA.
Peristomium penicillatum, ciliis numerosissimis capillaribus rectis æqualibus e capsulæ parietibus columellâque (!) ortis.
Capsula hinc plana, indè convexa.
Calyptra exterior e villis implexis, interior apice scabra.
Muscus hinc aretè affinis Polytricho, quocum foliis, floribus
