THE GENUS DAWSONIA. 351 



but did not adhere : by degrees the pulp dries up, and in 

 the ripe capsule leaves only the membrane or tympanum of 

 an inorganic appearance, and firmly cohering with the teeth 

 by the inner side of their apices. It does not therefore pu 

 properly belong to the operculum, though in some cases it 

 may adhere to it, as does the analogous process of the colu- 

 mella in Dawsonia and in several other mosses. 



The affinity of Dawsonia to Buxbaimiia is certainly 

 less strict than to Poli/frichmn, and rests chiefly on the 

 similarity of the figure of the capsule, and in the central 

 process of the columella, which is still more evident in 

 Buxhaimiia, where it forms part of the Linnean generic 

 character, though unaccountably overlooked by Schmidel 

 in his masterly dissertation ; but, if I mistake not, 

 actually represented by him [in fig. 14, b -^J, and con- 

 founded with the peristomium, which in this case, I sup- 

 pose, had adhered to the operculum, as I have repeatedly 

 found it to do, and thus escaped his notice. Hedwig con- 

 siders the plaited membrane which constitutes the peristo- 

 mium of Buxhawmia, as derived from the inner membrane 

 of the capsule, and quotes the figure just mentioned of 

 Schmidel in proof of this origin. In both species, however, 

 I find it arising from the exterior membrane, though con- 

 siderably, within its margin, which in Buxhaumia apliylla 

 is said by Hedwig to be divided into teeth, — an appearance 

 I could not observe in the few ripe capsules I have dissected. 

 In other respects, the two species seem essentially to agree, 

 and therefore ought not to be separated, as Ehrhart and 

 some late writers have done. The generic character com- 

 prehending both, I would propose to alter in the following 

 manner. 



BUXBAUMIA. 



Capsula obhqua, hmc convexior, vel gibba. 



Peristomium intra marginem, quandoque dentatum, mem- 

 branse exterioris ortura, tubulosum, pUcatum, apice aper- 

 tum . 



1 Sclimidel, Disseiiaiiones Botmiici Jr. 



