63 



consecutive summers, together with his extensive opportunities 

 of studying North American vegetation on a large scale for a 

 period of 15 months in 1913-1915, during which time he made 

 numerous journeys throughout the western half of the continent 

 from the Great Plains to the Pacific coast and from the Canadian 

 Rockies to the Mexican boundary, testing principles and processes 

 of vegetational development, eminently fit him to evaluate and 

 correlate the results of investigations in restricted areas. 



The very complete set of abstracts of publications dealing 

 with succession from the time of the earliest investigation (King, 

 1685) to the present (Chapter II); together with an historical 

 summary of the units of vegetation (Chapter VII), a concise 

 statement of the several views on the "Direction of Develop- 

 ment" (Chapter VIII), and the various systems of classification 

 (Chapter IX) in which the careful and full discussion of the 

 views of such authors as Cowles, Cajander, and Moss are given, 

 is a very valuable feature of the book, affording the student the 

 necessary perspective for an understanding of the present status 

 of the subject. 



The principle, stated in 1904,* that the plant formation is a 

 complex organism with a characteristic development and struc- 

 ture, is here elaborated and developed, forming the fundamental 

 thesis. The formation is put entirely upon a developmental 

 basis. "As an organism, the formation arises, grows, matures, 

 and dies. Its response to the habitat is shown in processes or 

 functions and in structures which are the record as well as the 

 result of these functions. Furthermore, each climax formation 

 is able to reproduce itself, repeating with essential fidelity the 

 stages of its development. The life-history of a formation is a 

 complex but definite process, comparable in its chief features 

 with the life of an individual plant. The climax formation is the 

 adult organism, the fully developed community, of which all 

 initial and medial stages are but stages of development. Succes- 

 sion is the process of the reproduction of a formation, and this 

 reproductive process can no more fail to terminate in the adult 

 form in vegetation that it can in the case of the individual plant." 



* Clements, F. E., Development and Structure of Vegetation, Rep. Bot. Surv. 

 Nebr. 7. 



