66 Mr. Menzizs’s Arrangement of the 
trichum commune, page 229, the author makes the following obfer- 
vation : | 
“ Polytrichum hoc calyptré gaudet duplici: .extertore pilofa, interiore 
multo minore, membranaced, albidd, levi; exteriore obteéta.” 
I do not find that Leers made any practical application. of this | 
difcovery, or traced it in any other fpecies: but Mr. Curtis, a va- 
luable member of this Society,|, who made the fame difcovery the 
year following, purfued it further, and finding the double calyptra 
conftant in other fpecies as well as the Polytrichum commune, he ap- 
plied it, with his ufual perfpicuity and difcernment, as a diftinguifh- 
ing character of the genus, in one of the numbers of his Fiera 
Londinenfis, publifhed in the year 1778; and I am confident that 
a more beautiful or a more obvious one could not be felected, hav~ 
ing found it conftant and invariable in every {pecies here deferibed, 
except the Polytrichum magellanicum, which has only a fingle {mooth 
calyptras but thenit fo ftrongly poffeffes the peculiar habits, and 
every other charateriftic of the genus, that I think it cannot pof- 
fibly be feparated. I have therefdre drawn up the following general 
charaéter, which, with the above exception, will be found appli-. 
cable to every individual of this natural family. 
PLO UL TeR Te) BOM. 
‘Natural Charaéter. 
THE plants of this genus, whether fingle or branched, grow 
moftly ere€t from the ground, and have an unpliant ftiffnefs or ri- 
gidity of appearance that peculiarly diftinguifhes them from moft 
others of this natural order. 
3 The 
