THE GENERA OF MOSSES. 135 
in the process of time, they will not be found to inhabit. 
In general, where they do occur, extensive peat or turf 
bogs, as in Britain, Germany, and Sweden, are found to 
be almost entirely formed by them. 
Hist. Dillenius *, who first, in a system of Musco- 
logy, constituted this genus, defined it, " Musci genus 
capsulas uniformes proferentis, quae capsulae ab ahis diffe- 
runt, quod nudag sint, seu calyptra destitutse," &c. LiN- 
N^us, however, finding a calyptra in many of those de- 
scribed, removed several of them to the Hypna^ and to a 
new genus of his own formation, PJiascum^ — " Anthera 
operculata ore ciliata, calyptra caduca minuta," wherein it 
may be seen he had altered the nomenclature of Dille- 
Nius. He still, however, kept up, with very little varia- 
tion, the former definition of Sphagnum — " Anthera oper- 
culata; ore laevi, calyptra nulla," retaining under it Sphag- 
num alpinum and S. arhoreum. In the true Sphagna^ the 
erroneous definition is accounted for by the remarkably 
fugacious and delicate nature of the calyptra. That it 
really possesses one, is now placed beyond a doubt ; but it 
generally falls oflT at the time the theca emerges from the 
perichaetial leaves ; and it is even difficult before that pe- 
riod to remove those leaves without also detaching it. 
The two other plants comprised in this genus by Lin- 
N^us, S. alpinum and arhoreum^ have been generally re- 
ferred, in later times, the one to Dicranum, the other to 
Neckera ; but in neither is the calyptra of so fugacious a 
nature, as to apologise for such a mistake even among the 
* DiLLENius, though this generic name had been previously applied to 
plante, was the first to restrict it to the Musci. 
