Mr. R. Spruce on the Musci and Hepaticce of the Pyrenees. 91 



luxuriant on limestones of which the surface rapidly decomposes ; 

 hence the older limestones, which in the Pyrenees are often trans- 

 formed into marble, are never in that state prolific in mosses. Of 

 those species which absolutely refuse to vegetate on limestone (and 

 they are not very numerous), some are found on a great variety 

 of rocks ; but probably when carefully examined these rocks would 

 be found to contain some one element, essential to all the species 

 making choice of them. Silex, for example, seems necessary to 

 certain Grimmice ; and there are a few mosses rarely found except 

 on rocks containing a large proportion of iron. It is scarcely 

 necessary to mention that many mosses are never found on rocks 

 at all, but by exception, some preferring the bark of living trees 

 [cortical) and others decayed trunks or logs [lignal). 



Distribution of Musci and Hepatica in the Pyrenees, according 

 to latitude and longitude. — The distribution of plants on any given 

 portion of the eartVs surface requires to be estimated both hori- 

 zontally and vertically, and if the surface to be considered extend 

 through several degrees of latitude, the two modes will require 

 to be exhibited both separately and in combination. It is ob- 

 vious that a comparison of the vegetation of any portion of the 

 earth with that of any other portion, or of the whole, must 

 always be incomplete, until the whole of the earth's surface shall 

 have been examined. Hence the following account of the dis- 

 tribution of Musci and Hepaticae in the Pyrenees can only be re- 

 garded as approximatively correct. I enumerate 390 Musci and 

 91 Hepaticse in the Pyrenees. Taking the whole number of 

 Musci known in the world to be 2400 (which is rather over than 

 under the limit), and of Hepaticse to be 1200, this would show 

 the Pyrenees to possess nearly one-sixth of the entire family of 

 Musci and but one-thirteenth of the Hepaticse, or twice as great 

 a proportion of the former as of the latter. But this proportion 

 is very nearly what we should arrive at in comparing the Musci 

 and Hepaticse of Europe with those of the rest of the world, so 

 much more numerous are Hepaticse in the southern than in the 

 northern hemisphere. 



The species which attain absolutely their northern limit in the 

 Pyrenees seem to be only the four following : — 



Hypnum aureum. Tortula caespitosa. 



Bryum platyloma. Soulhbya tophacea. 



Those which attain their southern limit are apparently much 

 more numerous ; but when the mountains of Spain come to be 

 fully explored, the list will probably be somewhat lessened ; and 

 I ought to acknowledge that, possessing no complete list of the 

 Cryptogamia of Italy, I may have assigned the Pyrenees as the 

 southern limit for a few species which in reality extend farther 



