CHAPTER I 
CLIMATE 
UseEp in a wide sense, the term vegetation may be applied 
to the general appearance of an aggregate of plants as 
it is viewed in a natural scene. Thus conceived, the 
vegetation forms a constituent feature of the landscape. 
Most of us have derived from pictures some idea of the 
great differences that exist in the vegetation in different 
parts of the world, and it is not difficult to associate 
these differences with the climate. Thus the prairies 
are great plains covered with grass, but the prairie is 
a dry region upon which trees cannot grow. A large 
part of Mexico is a semi-desert, the stony soil of which 
is sparsely studded with queer-looking fleshy plants, 
called cacti. The plains of the Amazon and the Congo 
are covered with great tropical forests, in which the 
vegetation is most luxuriantly developed, but these 
regions are very hot and among the rainiest in the world. 
From these and similar examples, it is easy to infer that 
a close relation exists between the vegetation of a district 
and the climate. We will consider how close this relation 
is, after we have examined the various external factors 
which influence and determine climate. 
CLIMATIC FACTORS. 
_ These may all, on analysis, be expressed in terms of 
two factors of the environment : 
I. Heat. 
Il. Humidity. 
I. Heat. 
The only heat received by the earth which has any 
effect upon climate is that which is derived from the sun. 
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