THE GENERA OF MOSSES. 113 
theca; mistaking the plicae, or folds, of the columella, 
found more or less in all the Polytrichoideay for actual dis- 
sepiments. It is also, except in the genera Andrcea, Phas- 
cum and Voitia, furnished with a deciduous lid or opercu- 
lum, and the sporulae are evacuated by the open apex ; at 
its base is sometimes a carnose body, termed an apophysis^ 
having externally the appearance of being a continuation 
of the theca, and Mable to be confounded with it; but 
within, is well marked by the total absence of sporulse, and 
by its containing a pulpy mass similar to that which at an 
early period fills up the cavity of the columella, and sur- 
rounds the sporular bag. The theca is generally support- 
ed by a fruit-stalk, called a seta {pedunculus^ or pedicel- 
lus, of some authors), which varies in length from almost 
a total absence to above three inches, and in structure re- 
sembles the theca. The only exception to this fact is 
found in the genera Andrtsa and Sphagnum ; the former 
is, with its small apophysis, sessile on an elongated recep- 
tacle ; and the latter also, entirely sessile on a highly 
curious receptacle, resembling a thin section of a cylinder 
placed transversely upon a peduncle of nearly the same 
nature as the receptacle itself, and altogether different 
from a true seta, although like to it in form. The base of 
the true or apparent seta, it is worthy of remark, is general- 
ly furnished with leaves of a different kind from those of 
the stem and branches ; they have received the name of 
Perichatial leaves, and at one time entirely surround the 
receptacle, seta, theca, and calyptra. The presence or ab- 
sence of these leaves, has been considered by some authors, 
as Pali SOT de Beauvois, as worthy to assist in the con- 
struction of genera: thus, Pogonahim would differ from 
Polijtrichum, CecalypJium from Dicranam, kc. to which 
we cannot assent ; for, on this principle, Andraa nivalis 
might even be separated from the others. Jt may, how- 
yoL. IV. H 
