430 THE AMERICAN NATURALIST [Vol. XL VIII 



the assemblage of plants and the assemblage of animals 

 are intimate and regular of occurrence ; so much so that 

 (1) the two are coextensive, (2) the two constitute to- 

 gether a community which may be called a biotic asso- 

 ciation, (3) neither plant nor animal assemblage usually 

 occurs independently of the other, (4) the geographic 

 distribution of many of the plant and animal species 

 which make up the assemblages are in general corre- 

 spondence, (5) the species composition of the association, 

 over its range, varies no more widely, relatively speak- 

 ing, than would an assemblage of plants alone. Perhaps 

 the single view-point of the botanist, on one hand, and 

 the zoologist, on the other, has tended to a neglect of the 

 dual character of the one problem. Probably most botan- 

 ists and zoologists agree that relations of animals and 

 plants within a habitat are most intimate, and there is 

 a tacit assumption that all the organisms in one place 

 constitute the true system of interrelations, but botanists 

 have spoken of plant communities, and zoologists of 

 animal communities. There are numerous disharmonies 

 and variations in agreement of plant and animal assem- 

 blages, but these must not be allowed to obscure general 

 facts of correspondence. 



It is recognized that plants and animals of an area of 

 essentially homogeneous physical conditions are inter- 

 dependent, the animals as a group being wholly depend- 

 ent upon the plants for food, and many of the plants 

 being directly dependent upon animals, as in the matter 

 of pollination. All are directly or indirectly affected by 

 animals in some way. It is also recognized that the 

 plants are a good index to conditions for animal life, the 

 plant assemblage affecting animals locally in modifica- 

 tion of the physical environment, and more directly in 

 providing food, shelter, etc. (.4: 601). It is further ac- 

 cepted that plants and animals respond to general en- 

 vironmental conditions in similar manner (Craig, 1908). 

 Thus considered, the character of the plant population of 

 an area is an index to general character, or ecological 



