CHAPTER I 



CLIMATE 



Used in a wide sense, the term vegetation may be applied 

 to the general appearance of an aggregate of plants as 

 it is viewed ia 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 cMmate. 



CLIMATIC FACTORS. 



These may all, on analysis, be expressed in terms of 

 two factors of the environment : 



I. Heat. 

 II. Humidity. 



I. Heat. 



The only heat received by the earth which has any 

 effect upon climate is that which is derived from the sun. 



