AND BUXBAUMIA. 337 



destitute of them, or having them much less developed and 

 strictly confined to the nerve. 



In the form and position of the male flowers there is 

 probably an absolute uniformity in the whole of this group : 

 but the only peculiarities consist in the perigonial leaf or 

 bractea being formed chiefly of the sheathing part of the 

 stem-leaf ; and in the new shoot proceeding from the centre 

 of the star-like cluster. In P. undulatum, however, the 

 former character is by no means obvious, and the latter is 

 not perhaps constant ; and both are only presumed to exist 

 in Lyellia. 



The double calyptra of Polytrichum, long considered as 

 the essential character of the genus, equally exists in [ss? 

 Dawsonia. But this outer or spurious calyptra, formed of 

 densely matted hairs originating from the vaginula and the 

 apex of the inner cucullate calyptra, is wanting in several 

 species of Polytrichum, in some of which, and in Lyellia, 

 the true calyptra is furnished with a few hairs only, either 

 scattered over the whole of its surface, or confined to its 

 apex; while in others, as in Polylrichum undulatum, it is 

 nearly, and in P. magellanicum and Iceviyatum, entirely 

 smooth. 



Respecting the teeth of the peristomium of Polytrichum, 

 I have very little to add, except that in P. magellanicum 

 they appear to be eighty in number, whicli is a higher 

 multiple of sixteen than has hitherto been noticed in this 

 genus, and the greatest number that has yet been found in a 

 single series in the order. 



On the nature of the transverse membrane or tympanum 

 of Polytrichum, I have formerly made some remarks in 

 treating of Bawsonia, and have there considered it as the 

 remains of the pulpy continuation of the columella, originally 

 occupying the cavity of the operculum. But its uniform 

 texture, as well as its exactly circular form and equal margin 

 remain to be accounted for ; unless this regularity may be 

 supposed to depend on the circular, and apparently cor- 

 responding, aperture of the inner membrane. 



Most authors have described the tympanum of Poly- 

 trichum as minutely perforated. These pores I have never 



22 



