112 Adams, Ecological Succession of Birch. [\nrii 



observations. The constructive imagination is liable to be de- 

 veloped in this type. This includes many extremely valuable and 

 useful students on account of their tendency to condense, sift and 

 formulate great masses of isolated facts. They are students of 

 ideas and relations rather than collectors of "facts." 



Each class, especially the well-marked types and extremes, often 

 finds it difficult or impossible to understand the point of view of the 

 other class. This frequently leads to misunderstandings and often 

 to mutual contempt. Cope and Marsh clearly illustrate these 

 two types of minds among our American naturalists. 



By this time some may wonder why this subject has been intro- 

 duced. It has been with a definite purpose, because frequently 

 these opposed points of view cause delays in the development of 

 many subjects. Thus a forewarning to students of bird ecology 

 may produce good results if the individual student makes a conscious 

 effort to counterbalance such deficiencies as go with his particular 

 type of mind. In the past, details have tended to produce confusion 

 through the neglect of general ideas. It is rarely that a word of 

 warning on this subject is out of place, because the balanced 

 "golden mean" investigator is never too abundant. The quotations 

 at the head of this article have an immediate bearing upon the 

 subject at this point. 



Not only is habitat preference, the association of avian species, 

 their succession, and the laws expressing these relations of much 

 interest, but they are of much importance scientifically as well as 

 in a practical way. It is therefore desirable that naturalists realize 

 the necessity of understanding the "rules of the game" if the true 

 relations of birds are to be studied to the best advantage. No ade- 

 quate substitute has yet been devised to replace a grasp of general - 

 principles. 



Throughout this paper emphasis is placed on the definifeness of 

 the dominant major environmental influences and complexes 

 because the irregular features have apparently received undue 

 emphasis and have retarded the recognition of certain important 

 definite relations. 



