BOOKS AND CURRENT LITERATURE 49 



Clcnionts defines a plant formation as follows: "The unit of vege- 

 tation, the climax formation, is an organic entity. As an organism, 

 the formation arises, grows, matures, and dies. Its response to the 

 habitat is shown in processes or functions and in structures which are 

 th(> record as well as the result of these functions. Furthermore, 

 each climax formation is able to reproduce itself, repeating with essen- 

 tial fidelity the stages of its development. The life-history of a forma- 

 tion is a compk'X but definite process, comparable in its chief features 

 with the life-history of an individual plant. The climax formation is 

 the adult organism, the fully developed community, of which all initial 

 and medial stages are but stages of development. Succession is the 

 process of the reproduction of a formation, and this reproductive proc- 

 ess can no more fail to terminate in the adult form in vegetation than 

 it can in the case of the individual plant." 



He then proposed the following divisions of the plant formation— ^ 

 The association is the climax unit of the formation and is charactei'ized 

 usually by a mixture of two or more species. The same formation 

 may have several climax units or associations. The association is 

 made up of consociations which are the units of the association and 

 are characterized by a single dominant species. The society is a minor 

 group characterized by a subdominant species which may be promi- 

 nent within an area marked by the consociation or the association. 

 The society is a localized or recurrent dominant within a dominance. 

 These societies may be aspect societies or layer societies. The clan 

 is composed of secondary species and ranks below the society, although 

 it is not necessarily a subdivision of it. In this classification the for- 

 mation corresponds roughly to the subformation of the Swiss botanists, 

 while the formation of the English botanists conforms more nearly to 

 one of the developrnent units since it is limited to the types of vegeta- 

 tion which develop on any particular soil type. In the plant associa- 

 tion as defined by Clements three or more conditions can be recog- 

 nized: i. e., the association proper, where the dominant species are 

 mixed, and the areas where a single species is segregated and becomes 

 dominant. The difficulty in application hes in the fact that the unit 

 lecognized in the field, to which the term "association" has been 

 quite generally applied, will under this system become a consociation. 

 The older term "association" will be applied to the mixed area which 

 usually Hes between the consociations; as, for example, pure forests 

 of yellow pine represent a consociation, pure forests of Douglas fir a 

 consociation, and the mixed area between an association. The asso- 



