CHAPTER XIV 

 PLANT ASSOCIATIONS 



148. General statement. In the preceding chapters 

 plants have been studied as individuals that have certain 

 structures and that live and work in certain conditions. 

 There is another aspect of plants that must be considered, 

 when one regards them as " clothing " the earth. This is 

 the broadest view of plants, and it requires a great deal of 

 training to appreciate it fully. The purpose of the present 

 chapter, therefore, is not to discuss this subject, but to give 

 the elementary student, with some knowledge of plants as 

 individuals, a glimpse of it. The two aspects of plants re- 

 ferred to may be illustrated by the two methods of studying 

 people : they may be studied as individuals engaged in various 

 kinds of work, or they may be studied as groups associated 

 in villages and cities. It is true that the earth is covered 

 by individual plants, but it is also true that these plants are 

 associated together in various ways, forming what may be 

 called plant communities. It is this community life of plants 

 that is to be considered in the present chapter. 



149. Plant associations. It is a fact of common obser- 

 vation that plants are not scattered indiscriminately over the 

 surface of the earth, regardless of one another and of the 

 conditions for growth. It is recognized, for example, that 

 there are forests, prairies, plains, and swamps, each one of 

 which represents an association of plants that characterizes 

 it. Into each association certain plants are admitted, and 

 from each association many plants are excluded. That is, 



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