20 A Study of the Vegetation of 
The formation is the unit of vegetation. It is the climax com- 
munity of a natural area in which the essential climatic relations 
are similar or identical. It is an organic entity, covering a defi- 
nite area marked by a climatic climax. It consists of associations 
which are actual parts of the area with distinct spatial relations. 
The term association is restricted to those climax communities 
which are associated regionally to constitute the formation. As- 
sociations agree with their formations in physiognomy and devel- 
opment and are recognized chiefly by floristic differences. 
The consociation is the unit of the association. It is charac- 
terized by a single dominant. While the association is actually a 
grouping, the consociation is pure dominance. In the usual treat- 
ment, most consociations appear as associations. 
A society is a community characterized by one or more sub- 
dominants, that is by a species dominant over portions of an 
area already marked by the dominance of consociation or associa- 
tion. It is a localized or recurrent dominance within a dominance. 
The above units of vegetation are essentially climax. The fol- 
lowing are developmental. To ecologists who regard the forma- 
tion as an actual organism, it is essential to distinguish develop- 
mental and climax communities. 
The associes is the developmental equivalent of the association. 
It is composed of two or more consocies, 7. e., developmental 
consociations, just as the association consists of two or more con-. 
sociations. Like the association, 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 developmental 
changes. While the association is permanent, in so far as de- 
velopment is concerned, the associes is transient although it may 
persist for many years. 
A consocies is a developmental community marked by the strik- 
ing or complete dominance of one species belonging to the life- 
form typical of that stage of development. It differs from the 
consociation only in that it is a developmental or seral, while the 
latter is a climax community. 
A socies is a seral society characteristic of a developmental 
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