Mr. B«owN on Lydtia, LeploHomiiri,' afid^ ^uxhaimja, 567 



essential cliaracter of the genus, equally exists in Danisonia. 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 con- 

 fined to its apex ; while in others, as in Polytrichum imdulatum, it 

 is nearly, and in P. 7nageUa7iicum and Icevigatum, entirely smooth. 



Respecting the teeth of the peristomium oi Polytrichum,! have 

 very little to add, except that in P. niagellanicum they appear to 

 be eighty in number, which 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 

 T>awsonia, 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 ac- 

 counted for ; unless this regularity may be supposed to depend 

 on the circular, and apparently corresponding, aperture of the 

 inner membrane. 



Most authors have described the tympanum of Polytrichum as 

 minutely perforated. These pores I have never been able to de- 

 tect ; but I observe in many cases an appearance which may per- 

 haps account for the belief in their existence, namely, a minute 

 reticulation on the outer surface of the membrane, apparently 

 owing to the corresponding areolae of the inner surface of the oper- 

 culum, with which it was originally in contact. 



Polytrichum is remarkable for the various forms of its capsule. 

 Those species, indeed, in which it is quadrangular have been 



considered 



