473 
BOOK V. 
GEOGRAPHY. 
Under this head is to be considered the manner in which 
plants are affected by climate or station, and the conditions 
under which particular forms of vegetation are confined to 
certain zones of temperature ; as the palms to the tropics, 
the true pines to extra-tropical regions. 
This is one of the most curious and difficult subjects with 
which we can occupy ourselves. It embraces a consideration 
of the constitution of the atmosphere, and geological structure 
of all parts of the globe ; and of the specific effects of par- 
ticular conditions of climate and soil upon vegetation : all 
points of extreme importance, concerning which existing 
data are rarely sufficient to enable us to arrive at satis- 
factory conclusions. It involves the discussion of the plan 
upon which the world was originally clothed with verdure ; 
and, as Humboldt most truly observes, it is closely connected 
with " the physical condition of the world in general. Upon 
the predominance of certain families of plants in particular 
districts depend the character of the country, and the whole 
face of Nature. Abundance of grasses forming vast savannahs, 
or of palms, or coniferae, have produced most important effects 
upon the social state of the people, the nature of their manners, 
and the degree of developement of the arts of industry." 
If we examine the surface of the globe, we shall find its 
vegetation varying according to its inequalities and its differ- 
ences of soil ; we shall see that the plants of the valleys are 
not those of the mountain, nor those of the marsh like the 
vegetables of the river or of dry grounds ; it will also be seen 
that the vegetation of all valleys, all mountains, marshes, or 
