NOTICES OF BOOKS. 191 
taken as a ground for comparison; to show wherein it differs from 
that of adjacent countries ; to determine the amount and the causes 
of these differences ; among these causes, to demonstrate the slight 
importance of the chemical influence of the subjacent rocks and the 
great importance of their mechanical influence,— such is the object 
that I propose to myself. In other words, and to put the question 
more precisely, I have, in the first place, sought to show that, in the 
country to which my study refers, there exist evident relations between 
the dispersion of the species and the subjacent rocks, so that the 
former appears constantly as the expression of a certain condition of 
the latter. Afterwards, without pretending that there is no chemical 
influence of the subjacent rocks upon the physiological phenomena of 
vegetation, I have endeavoured to establish that the grand facts of dis- 
tribution are not the results of such chemical influence, but those of 
the mechanical condition of the detritus of the same rocks." — (Intro- 
duction, pp. 3, 4.) 
" This work is divided into four parts. The last is essentially 
subsidiary, and forms a collection of data leading to the other three. 
It contains an enumeration of the vascular plants of the country, with 
their stations, their soils, their altitudes, their general area, and their 
Jurassic habitats more particularly. It offers a picture (tableau) or 
the flora of the Jura as complete as possible. The first part contains - : 
an investigation of the circumstances which determine the station. 
The conditions of climate and of soil are there treated in detail, and 
more especially that of the subjacent rocks: the different districts of 
the country are there classed under this double point of view. The - 
second part includes a comparative examination of the vegetation 
and the flora in these different districts. The Jura serves for a 
basis and datum of comparison in this examination, which brings 
out the vegetable distinctions between this chain of mountains, 
the surrounding plains, the Vosges, the Schwarzwald, the Albe, the 
Kaiserstuhl, &e. The third is devoted to seeking the share of in- 
fluence of the subjacent rocks in these differences, and conduces to 
establish the small importance of their chemical nature, and, on the 
other hand, the great importance of their mechanical properties. It 
is endeavoured afterwards to indicate some characters of the contrasted 
floras, and to establish a classification in this respect. Finally, are 
passed in review the principal facts relative to the distribution of the 
