474 
GEOGRAPHY. 
BOOK V. 
rivers, has a similar character in the same latitudes. The 
flora of the granitic mountains of Spain and Portugal is very 
different from that of the calcareous mountains of the same 
kingdoms; in Switzerland, Teucrium montanum always in- 
dicates a calcareous soil ; and the same may be said of certain 
Orchises, ustulata, and hircina, for instance, in our own coun- 
try. Hence it is inferred, that the differences in the character 
of vegetation, depend upon circumstances connected with 
the soil or atmosphere in which they grow. A great deal of 
ingenious discussion upon this matter will be found in De 
Candolle's article on botanical geography, published in the 
18th volume of the Dictionnaire des Sciences Naturelles. 
But as I do not observe much that can be called positive de- 
ductions from such facts as have been ascertained, I shall, 
without entering into speculations as to the causes why one 
description of plants grows in one situation, and others in 
another, confine myself to an exposition of the mere facts 
which appear to have been hitherto distinctly ascertained. 
It has been found convenient to divide the surface of the 
earth into different stations, when treating of botanical geo- 
graphy. In this part of the subject I shall adopt the arrange- 
ment and distinctions of De Candolle ; agreeing with him 
that they at least indicate the most remarkable differences of 
station, if they are not susceptible of any rigorous definition. 
He admits the following classes : — 
1. Maritime^ or saline plants; that is to say, those which, 
without being plunged in salt water, and floating on its sur- 
face, are nevertheless constrained to live in the vicinity of salt 
water, for the sake of absorbing what may be required for 
their nourishment. Among these it is requisite to distin- 
guish those which, like the Salicornia, grow in salt marshes, 
where they absorb saline principles, both by their leaves 
and roots, from those which, like Roccella fuciformis, exist 
upon rocks exposed to the sea air, and appear to absorb by 
their leaves alone ; and, finally, a third class, such as Eryn- 
gium campestre, which do not require salt water, but which 
live on the sea-coast, as well as elsewhere, because their 
constitution is so robust, that they are not affected by the 
action of salt. 
