CHAPTER II 



THE EFFECT OF CLIMATE UPON VEGETATION— TYPES 

 OF VEGETATION 



The two most important factors in the plant's environ- 

 ment axe climate and soU. In the preceding chapter 

 we considered one of these— climate — and we showed 

 that the type of climate anjrwhere prevailing may be 

 expressed in terms of two external agencies, variously 

 combined — heat and moisture. 



Types of climate operate over wide areas, and if it is 

 true that the character of the vegetation varies with the 

 climate, it should be possible, in some rough way at least, 

 to distinguish broad types of vegetation, just as it is 

 possible to distinguish broad types of cUmate. Let 

 us see how this may be done. 



If one were able to survey the vegetation of a coimtry 

 as a whole, viewing it from a distance, so as to see its 

 broad outlines without being disturbed by details, what 

 are the types which would stand out most conspicuously ? 

 It would not require great powers of observation to give 

 an answer. One person might say woodland, grassland, 

 desert. To these another might add marshes, and 

 another heath. 



These are types of vegetation regarded as aspects of 

 scenery, but how far is it possible to associate them with 

 definite conditions of cUmate ? A marsh is wet, wood- 

 lands are generally damp, and grasslands dry ; heath 

 is very dry, and deserts are almost rainless. But there 

 are two types of grassland — one, meadow-land, which 

 is wet ; and the other, pasture or prairie, which is dry. 

 The term " woodland " is still more vague, since it includes 

 several types easily distinguishable from each other. 

 For example, there are evergreen woods and deciduous 



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