THE DEVELOPMENT AND STRUCTURE OF 

 VEGETATION.* 



Frederic E. Clements. 



Vegetation exhibits certain phenomena which are char- 

 acteristic manifestations of the forces which lie at its found- 

 ation. Sucn phenomena are peculiar to it, and are entirely- 

 distinct from those primary activities of the individual that 

 are termed functions. This conception will be clearer if we 

 consider vegetation as an entity, the changes and structures 

 of which are in accord with certain basal principles in much 

 the same fashion that the functions and structures of plants 

 correspond to definite laws. But the fundamental phe- 

 nomena of plants as individuals, and of plants united in a 

 complex termed vegetation are altogether different concepts. 

 Thus, functions are properties of individuals, and are funda- 

 mental for them alone. They are rhythmic or progressive 

 changes in the individual, and are characteristic of vege- 

 tation only in as much as it is a complex of such indi- 



*Read before the Botanical Society of America at the Denver 

 meeting, August 1901. 



Note. The principles here enunciated constitute at once the work- 

 ing basis and the conclusions of a special investigation into the phy- 

 logeny and structure of vegetation begun in 1897. These studies have 

 been pursued in the grassland and woodland formations of Nebraska, 

 and throughout the formations of the Rocky Mountains of Colorado. 

 Certain of these principles, association, invasion and zonation, have 

 long been recognized, but no systematic consideration of them has 

 been attempted heretofore. The principle of succession is more recent, 

 and is not so well developed, while alternation is herein defined and 

 analysed for the first time (Cfr. note. Rep. Bot. Surv. Nebr. 5:55 1901). 

 These principles were first formulated in their present relation early 

 in 1898 as working hypotheses, and have been subjected to constant 

 test in the field since that time. Their confirmation has been repeated 

 and conclusive, and they are now submitted as a definite and logical 

 basis for research in the development and structure of vegetation. 

 The present paper is intended to constitute the general portion of a 

 detailed report dealing with the physical factors of the prairie for- 

 mation in Nebraska, and with the structural expression of such factors. 

 The special portion will appear in a later report of the Survey, while 

 the application of the principles to mountain formations will be made 

 in a forthcoming volume upon the vegetation of the Rocky Mountains 

 of Colorado. 



