488 



THE AMERICAN NATURALIST [Vol. XLIII 



Such a claim could have been made only for a static 

 system, since a genetic conception of the problem neces- 

 sarily involves the indefinite postponement of the ap- 

 proach toward a final solution. 



The appearance of the classics of Warming and 

 Schimper served to impress all with the inherent com- 

 plexity of the problem. We are no longer deeply con- 

 cerned with the discussion as to whether temperature 

 or moisture is the more important geographic factor. 

 Neither do we hope to erect a stable system of geographic 

 divisions upon either of these bases. When we recall 

 that for North America alone not less than sixty different 

 proposals of geographic zones and regions have been pub- 

 lished during the last century, the futility of the point 

 of view which disregards all but one or two climatic fac- 

 tors and emphasizes boundary lines, must be apparent. 

 But we shall be still more impressed with the inadequacy 

 of these proposals if we attempt to relate the actual dis- 

 tribution of plants or plant formations to these "regions." 



Eecently there has been a rapid increase of local ecolog- 

 ical studies in which the successional processes of vegeta- 

 tion have been emphasized. These studies have appre- 

 hended to a greater or less extent the dynamics of the 

 habitat and the plant formation. The separation of the 

 local vegetation into stages has assumed the dominance 

 in each, of a distinct complex of environmental factors. 

 The occurrence of distinct boundaries has neither been 

 assumed nor insisted upon. 



Local studies, however, can not lead to general concep- 

 tions of vegetation unless compared and united into larger 

 units. This brings us to the fact that the larger units 

 generally recognized are transcontinental zones and re- 

 gions. But zones and regions are static entities. They 

 are developed upon assumptions wholly different from 

 those upon which the local studies have been founded. 

 Usually in zonal classification temperature is recognized 

 as all-important and rainfall an unfortunate disturber of 

 symmetry. Not a few are based upon phenological as- 



