THE GENERA OF MOSSES. 
1^1 
the apophysis, columella, and opercular membrane, as well 
as the interval between the lining and the theca, is always 
filled up with a pulpy matter. This is beautifully illustrat- 
ed in Buxbaumia^ and is what Mr Brown and Mr Tur- 
ner have observed in Polytrichum *. This, however, 
which is quite different from the sporular granular sub- 
stance, rapidly dries up in some mosses ; producing, among 
other appearances, the curious effect which the apophysis 
has, in the mature capsules of Splachnum ruhrum and ^S*. 
luteum. In most instances, however, it is more durable in 
the apophysis, and is also sometimes permanent in the co- 
lumella, as in Polytrichurriy and has then been improperly 
compared to the placention of seeds in phaenogamous or co- 
tyledonous plants. 
Although we have noticed the distinction between the 
columella and the opercular membrane, to which it is fre- 
quently so united as to appear a single body, — and con- 
sider the former in the hght of a modified continuation of 
the lining of the theca, we shall, to avoid confusion, still 
continue to call it a columella, and to use the terms of ab- 
sent^ elongated, or eocserted, according as it appears in the 
mature theca to have subsided, or, taken in conjunction 
with its opercular membrane, to have remained of undi- 
minished length. 
The stoma or mouth of the theca is either naked, as in 
Gymnostomum and Hedwlgia; or, generally, furnished 
with a series of ciliae, called teeth {denies) ; which may be 
either in a single series, as in Splachnum, Grimmia, and 
Dicranum ; or in a compound or double series, as in 
HooJceria, Hypnum, and Bryum. In all mosses which 
possess a peristomium, it arises from the surface of the 
* Brown in Linn. Trans, vol. x. p. 318. 
