THE GENEEA OF MOSSES. 
77 
even adhering, to the summit of the operculum, well deser= 
ving the name, therefore, of elongated columella. Dr 
Hooker says, " the extremity of the sac is lengthened out 
into a columella f ' a minute dissection, however, very dis- 
tinctly shews the columella to be continued from the base, 
and the sporular sac to be attached to it at the mouth of 
the theca. The columella, into which, according to Dr 
Hooker, the sporular sac is lengthened out, is our oper- 
cular membrane ; between which, and the summit of the 
columella strictly so called, the line of separation is very 
evident. 
The peristome of this moss is worthy of much attention. 
It consists of a beautiful white, plicate, and slightly twisted 
cone. This Hedwig considered to be formed entirely of 
cilise^ connected together into a membrane furnished with 
sixteen sulcae, or furrows. " I have myself seen,*" says Dr 
Hooker, " what appeared to be distinct ciliae, but whether 
they were really so, or only the plicae of the membrane, I 
could not satisfy myself neither have we been able to 
trace any thing satisfactory beyond a mere ridge, formed 
by the duplication of the membrane. 
Almost all authors describe the peristome of Diphyscium 
as double, mistaking the crenate margin of the theca for 
an outer one ; but this appearance is, indeed, w idely dif- 
ferent from any thing like teeth. Weber and Mohr ob- 
serve, " Peristomium exterius vix ullum. Marginem oris 
crenulatum pro tali sumsit Hedw. Ehrh. denegavit.'' 
Thus censuring He dwig, but adopting his opinion. Bri- 
DEL and others represent the plicse of the membrane as al- 
ternating with the crenulse of the margin ; in some cases 
we have clearly perceived this, but, as it depends upon the 
margin being cleft into a definite number of segments, it is 
rather uncertain w^hether it uniformly occurs. 
