ECOLOGICAL SUCCESSION. 333 



plasm theory. This is, however, to be regarded as a renewal of 

 interest turned aside at first by conflict with the church and later 

 by the absorption of attention by the lines of work noted above, 

 for the recognition of .succession by Buffon preceded Darwin's 

 "Origin of Speices" by one hundred and eighteen years (Cowles, 

 'il) and occasional subsequent but early observations have 

 strengthened the total evidence for this phenomenon. It is only 

 a few years since we were regarding the environment as an un- 

 understandable hodge-podge. Now we must recognize that 

 environments are characterized by the most orderly of phenomena, 

 some of which w r ere noted by early observers, and have often 

 been verified and actually experimentally demonstrated during 

 the last twenty years, by the plant ecologists. With this better 

 understanding of the environments and the better knowledge 

 of animal physiology, the relations of animals to environments 

 considered physiologically appear particularly definite. Our 

 knowledge is sufficient to enable one to indicate certain proba- 

 bilities in this connection, which are based upon established 

 principles. 



In connection with the introduction of some of the principles 

 of ecological classification and the logical necessities of such an 

 attempt, the reader must not lose sight of the fact that there 

 are, in practice, two points of view for investigation. One is that 

 of evolution. The other that of physiology. One may make a 

 physiological explanation of the behavior or structure of an 

 organism and in no way explain its evolution, or on the other 

 hand, he may contribute to the knowledge of the evolution of an 

 organism without contributing to the knowledge of its physiology. 

 This distinction is becoming less sharp with each year's progress 

 in investigation, due merely to the adoption of physiological 

 methods in the study of evolution and morphology. Again the 

 reader must bear in mind the fact that regardless of widespread 

 ideas to the contrary, ecology or ethology belongs primarily to the 

 physiological point of view, and is therefore outside of the range 

 of criticism from the point of view of evolution or the current germ 

 plasm doctrine. Its frequent confusion with various branches of 

 evolutionary speculation, such as mimicry, structural adaptation, 



