THE GENERA OF MOSSES. 
115 
conical form, and of a somewhat different texture and 
colour, which, by age, often shrinks to the appearance of a 
mere lid to its orifice. Sometimes it is more rigid (as in 
Splachnum, Tayloria^ and Gymnostomum Donianum)^ and 
is then not unfrequently called an exserted columella. It 
also, in some instances, adheres closely to the summit of the 
interior of the operculum (as in Gymnostomum Hiemii, 
and Hypnum dendroides), which it raises or depresses, ac- 
cording to the degree of dryness or humidity to which it is 
exposed. It is this part which we conceive to be the stigma 
of Palisot de Beauvois, but which we propose to desig- 
nate by the more appropriate name of Opercular Mem- 
brane. 
We have not been able to trace this conical membrane 
in the Polytricha, unless what Mr Brown * mentions as 
the pulpy continuation of the columella within the oper- 
culum be considered as such : but, as he afterwards t re- 
marks, the uniform texture, and exact form of the tympa- 
num or epiphragma, closing the mouth of the theca, remain 
to be accounted for. To us this epiphragma appears to be 
very different from, but to supply the place of, the opercular 
membrane ; it adheres, when young, to the summit of the 
columella, and entirely closes the stoma ; then passing to the 
base of each tooth, is reflected so as to line it to the very apex, 
thus forming a real membranaceous inner peristome ; and, — 
a structure easily seen, if the epiphragma, of probably any 
species of the genus, be carefully removed, and placed un- 
der the microscope, — the margin will be found to be beauti- 
fully split into segments, or cilise, equal in number to the 
teeth. This we cannot but consider, as we have already 
* Linn. Trans, vol. x. p. 318. f Ibid. vol. xii. p. 567. 
