CHAPTER XLVIL 



VEGETATION TYPES AND STRUCTURES. 



941. By vegetation type is meant the form and character of 

 vegetation elements under special conditions of environment. 

 We are concerned primarily with a study of the plant form as 

 related to environment, not with a study of floral elements or 

 plant relationships. Species which are not at all closely related 

 from a taxonomic standpoint may be of the same vegetation 

 type. 



942. The responsive type of vegetation. By this is meant the 

 reaction of vegetation to environment, the response of the plant 

 in adapting itself to its environment. Within certain limits 

 many plants will respond in a single season to a change of envi- 

 ronment and will assume a form of leaf and stem which fits them 

 to better endure the unfavorable conditions. This, however, 

 takes place where the change is not very great, or in case of cer- 

 tain plants which have a wide range of adaptability. Vegetation 

 types have been developed by gradual change through long 

 periods of time. Some of the striking vegetation types are those 

 of desert plants, those growing in sandy areas in moist climates, 

 or where the soil is very alkaline and interferes with absorption. 

 The types found in these situations are similar, since the plants 

 obtain water with difficulty from the soil, and so their aeral parts 

 in response to this take on a form which enables them to con- 

 serve water. There are several different classifications of vege- 

 tation types. Two of these, proposed by Warming and Schim- 



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