I76 GEORGE E. NICHOLS Vol. IV, No. 2 



this order should be strictly adhered to or that the three criteria of classifica- 

 tion should receive equal emphasis. For one thing, in actual field work we 

 are seldom able to study our material in that orderly sequence which is possible 

 in a laboratory: the exigencies of time and space prevent. The point to be 

 emphasized here is simply this, that in the field these three points of view 

 should be kept clearly in mind; let the order of their application take what 

 form it will. For another thing, the relative emphasis which shall be placed 

 on these different points of view will be determined in part by the bias of 

 the observer, in part by the nature of the facts. This is particularly true 

 when it comes to the process of organizing the data obtained from field work 

 and the actual construction of a comprehensive classification : one or another 

 point of view must be adopted as the primary basis of subdivision. Generally 

 speaking, in attempting to bring out the larger subdivisions of the vegetation 

 of any region in their relation to environment, I am inclined to give precedence 

 to the geographically determined^ vegetation-units (i.e., the climatic and physi- 

 ographic formations) ; but where these are not clearly defined it would seem 

 better to subordinate them to those determined by successional relations (i.e., 

 the successional series), or by physiognomy and ecological structure (i.e., the 

 association-types) . 



Where an area to be surveyed comprises more than one climatic region, 

 the first step in classification should naturally be to clearly differentiate the 

 climatic formations, since different climatic formations are best considered 

 separately. As the outstanding criterion of the climatic formation, it is the 

 climatic climax association-type, primarily, with reference to which such dif- 

 ferentiation is made. When it comes to the study of the vegetation within a 

 particular climatic region, with a view to the detailed classification of the 

 various plant communities which collectively go to make up the climatic for- 

 mation, a general familiarity with the character of the climate climax and 

 also with the larger features of the vegetation as a whole is a logical pre- 

 requisite. Without such familiarity it seems self-evident that lack of per- 

 spective may obscure the essential relationships which it is the chief object of 

 classification to make clear. 



In practical field studies two general methods of attack are open, which 

 might be characterized, respectively, as ( i ) working from the top downward 

 and (2) working from the bottom upward. By the first method we start 

 with the larger features of the vegetation and by a process of analysis work 

 out the lesser in their relation to the larger. By the second we start with the 

 lesser features and by a process of synthesis aim to achieve the same result. 

 Of the two, the first is perhaps the better adapted to give one a broad per- 

 spective and a proper sense of proportion ; it is the method which one would 

 be inclined to follow in making a preliminary survey of any region or a survey 

 designed to bring out only the major features of the vegetation. The second 

 method is one which is naturally employed, in conjunction with the first, in 



