136 STRUCTURE AND UNITS OF VEGETATION. 



"A plant formation, then, comprises the progressive associations which 

 cuhninate in one or more stable or chief associations, and the retrogressive 

 associations which result from the decay of the chief associations, as long as 

 these changes occur in the same habitat. . . . The above examples of 

 succession are given in order to show the importance of regarding the forma- 

 tion from the point of view of its developmental activities. . . . Every 

 formation has at least one chief association; it may have more; and they may 

 be regarded as equivalent to one another in their vegetational rank. They are 

 more distinct and more fixed than progressive or retrogressive associations. 

 They are usually, but not invariably, closed associations. They always 

 represent the highest limit that can be attained in the particular formation 

 in which they occur, a limit determined by the general fife conditions of the 

 formation." 



Tansley (1911 : 12) has adopted the same view: 



"Thus each of the types of vegetation, woodland, scrub, and grassland, 

 within a given formation, is a plant association, and so is each definite phase in 

 the primary development of a formation. The highest type of association 

 within a formation (often woodland), to which development tends, is called 

 the chief association of the formation. In the absence of disturbing factors, 

 such as the interference of man, land-slips, and so on, the chief associations 

 will ultimately occupy the natural formation area to the exclusion of the other 

 associations, which may collectively be termed subordinate assodations." 



Cowles (1910) has also recognized the essential difiference between develop- 

 mental and final communities, in using the term "cUmatic formation," which 

 Moss (1910 : 38) points out is equivalent to his chief association. Moss regards 

 Cowles's term as unfortunate, because it is used in a very different sense from 

 the same term of Schimper. This is hardly the case, for while Schimper's 

 term covers more than one kind of unit, the recognition of climatic and 

 edaphic formations seems clearly to have taken some accoimt at least of devel- 

 opment. {Cf. Skottsberg (1910 : 5) and Vestal (1914 : 383).) 



In spite of differences in their views of the formation, the nine authors just 

 quoted, Hult, Klinge, Drude, Warming, Schimper, Clements, Moss, Cowles, 

 and Tansley, have all distinguished more or less clearly between climax and 

 developmental associations. Such a distinction naturally does not end with 

 associations, but extends throughout the units. Hence it is here proposed to 

 recognize and define a series of developmental units in the life-history of the 

 chmax formation, which is essentially analogous with association, consociation, 

 society, and clan. In fact, a failure to do this causes us to ignore practically 

 all the developmental study of the past 20 years, and to make the develop- 

 mental analysis of vegetation difficult and confusing, if not impossible. 



Associes. — ^The associes is the developmental equivalent of the association. 

 It corresponds to the initial and intermediate formations of Clements (1902, 

 1904) and to the subordinate associations of Moss (1910) and Tansley (1911). 

 It is composed of two or more consocies, i. e., developmental consociations, 

 just as the association consists of two or more consociations. Like the asso- 

 ciation, it is based upon life-form, floristic composition, and habitat, but differs 

 from it in as much as all of these are undergoing constant or recurrent develop- 

 mental changes. In so far as each sere is concerned, the associes is transient, 

 though it may persist for many years, and the association is permanent. 

 Obviously, a medial or final associes may become an association when the 



