346 GEORGE E. NICHOLS 



the initial and medial stages are but stages of development. 



. . A formation, in short, is the final stage of vegetational 

 development in a climatic unit. It is the cHmax community 

 of a succession which termnnates in the highest life-form pos- 

 sible in the chmate concerned. . . . It is delimited chiefly 

 by development, but this can be traced and analysed only by 

 means of physiognomy, florist ic and habitat." 



It will be seen from the foregoing quotation that Clements 

 regards as the climatic formation what from the writer's point 

 of view would be termed the regional climax association-com- 

 plex (or association-type). It is the opinion of the writer that 

 the climax association-complex should not be so regarded, but 

 that the entire edaphic formation-complex of the region, or, as 

 before stated, the vegetation of the region in its entirety, should 

 be considered as constituting a unit from the standpoint of 

 regional physiographic ecology. It seems more logical to re- 

 gard the climax communities of the region, like other ecologically 

 parallel series of communities, as belonging to a common as- 

 sociation-type. As the most mesophytic type of vegetation 

 attainable under the existing clim.atic conditions, the climax 

 association-type may be looked upon as the climatic indicator, 

 but not as the climatic formation. To sum up, the vegetation 

 of any region having an essentially uniform climate throughout, 

 taken in its entirety, constitutes a climatic formation, the gen- 

 eral ecological aspect of which is determined by that of the 

 climax association-type of the region. 



The advisability of using the terms: edaphic formation and cli- 

 matic formation. In a review of Clements' ''Plant Successions," 

 Tansley (22, p. 203) objects that if the concept of formation is 

 restricted to a climax stage determined by chmate, then ''it 

 leaves out of account the estabhshment of permanent communi- 

 ties of distinct life-form owing to edaphic conditions or to con- 

 ditions determined by biotic reaction on the soil. It was to 

 cover cases of this kind that Schimper introduced the term 

 edaphic formation, and if its use be not allowed it is difficult to see 

 how we are to classify such communities." Schimper (19, p. 

 161) says that "two ecological groups of formations should be 



