Mr. R. Spruce on the Musci and Hepatice 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. Si/ex, for example, seems necessary to 
certain Grimmie ; 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 (/ignal). 
Distribution of Musci and Hepatice in the Pyrenees, according 
to latitude and longitude.—The distribution of plants on any given 
portion of the earth’s 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 Hepatacee in the Pyrenees can only be re- 
garded as approximatively correct. I enumerate 390 Musci and 
91 Hepatice im 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 Hepatic 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 Hepaticz, or twice as great 
a proportion of the former as of the latter. But this proportion 
is very nearly what we should arrive at m- comparing the Musci 
and Hepatice of Europe with those of the rest of the world, so 
much more numerous are Hepatic in the southern than in the 
northern hemisphere. 
The species which attain absolutely their northern limit in the 
Pyrenees seem tobe only the four following :— 
Hypnum aureum. Tortula czespitosa. 
Bryum platyloma. Southbya 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 
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