Hypnum.-} D I P L O P E R I S T O M I. 151 



or a Grimmia. We are aware how difficult it is to frame 

 characters in a few words, which may separate plants so closely 

 allied ; and we should not be disposed to disagree much with 

 those who, after a due investigation of the peculiarities of each 

 species, might choose to consider them varieties arising from 

 the difference of soil and climate ; the one being found on the 

 trunks of decaying trees in Jamaica, the other in Ireland, in a 

 wood, close by a spring, which has been ascertained to have a 

 higher temperature than any neighbouring spring, and in a spot 

 warmer, perhaps, than any other in Britain. 



There is still another plant which we cannot pass over un- 

 noticed, since in the form of the leaves, and its two nerves, and 

 mitriform calyptra, (making it a Hookeria^) there is the most 

 perfect conformity. We mean the Leskea depressa of Swartz 

 and Hedwig; and also a native of Jamaica. But this is a 

 smaller plant ; its surculi, though depressed, have not the leaves 

 so decidedly bifarious, nor are these latter nearly so strongly re- 

 ticulated ; their margin is not thickened, nor at all serrated ; and 

 the lid of the capsule is shorter. 



XXXIII. HYPNUM. 



GEN. CHAR. Fruitstalks lateral; Peristome double; the ex- 

 terior of 16 teeth ; the interior of a membrane cut into 

 16 equal segments, with filiform processes frequently 

 placed between them ; Calyptra dimidiate. (TAB. III.) 



In so extensive a genus as the present we would gladly follow 

 many of the most eminent Muscologists in keeping Leskea apart 

 from it, were not the character of that genus so difficult to be 

 discovered, and the individuals which compose it so closely allied 

 in other respects to the rest of the Hypna. The character is, as 

 is well known, founded upon the absence of the filiform processes 

 between the segments of the inner peristome. These, indeed, 

 vary in number ; and some of the real Hypna of authors, such as 

 H. lutescens, have very short processes, which make them exactly 

 intermediate between Hypnum and Leskea. 



K 4 



