50 



S YMBIOSIS—DISJ UNCTI VE 



of symbiosis will be discussed in succeeding paragraphs. Obviously 

 our ability to properly place any given symbiotic phenomenon in 

 the above classification depends entirely upon our knowledge of the 

 relationship in question. In many cases our knowledge is still far 

 from adequate. 



34. Social Disjunctive Symbiosis.— This is the type of symbiosis 

 in which the organisms concerned are not in actual contact, at least 

 not all of the time, and in which there is no direct food relation. It 

 includes, therefore, all of the ordinary interrelations of the various 

 species of plants that are living together in any plant community, 

 such as a forest, a swamp, or a meadow (Fig. 20). Since synecology 





Fig. 20.— a forest community with numerous kinds of plants living together in 



social disjunctive symbiosis. 



is concerned almost entirely with these various kinds of plant com- 

 munities they will constitute the subject matter of several later 

 chapters and it will suffice here to point out only a few of the social 

 relations concerned. In a forest community, for example, the trees 

 have very important symbiotic relations with all other plants in the 

 forest. This comes about largely through the fact that the trees 

 control to a large extent such factors of the environment as light, 

 space relations, water supply, and to a certain extent available food 

 materials. Through this large measure of control of the environ- 

 ment they even determine what species of plants may live in the 

 forest. The social relations in such a community are in certain 

 respects comparable to those of a human community where man 

 controls the environment. There is usually a well-marked division 



