C. E. Moss. 
32 
habitats and coincides with the alternation of the principal plant 
associations (“ Pflanzenbestande ”). On p. 286, Drude defined the 
conception of the “formation” which he held at that time as 
follows:—“Any independent principal association, which has found 
its natural termination in itself, which consists of similar or of 
biologically connected plant-forms, and which is confined to a locally 
determined substratum of similar conditions of maintenance 
(altitude, exposure, substratum, water supply) has the value of a 
vegetation formation,—it being assumed that no actual change of 
association would occur on the site of such a principal association 
without external changes : the association has “ reached its term ” 
[“ abgeschlossen ”] ” (cf. Warming, 1909 : 143). 
As a definition of a closed, ultimate, or chief association of a 
formation this statement of Drude’s is excellent; and there can be 
no doubt that Drude’s arrangement of the different forests of 
Germany into fourteen “ formations ” is a great advance on the 
merely physiognomical view; though, as his “ formation ” is 
essentially only a particular kind of association, it is not quite 
consistent with the views of those authors who regard the formation 
as related to the association as the genus is to the species. There 
may be associations which are also formations, just as certain 
genera only contain a single species ; but probably such formations 
are less frequent than monotypic genera. 
Schimper (1898, 1903: 160, et seq.) laid the proper emphasis 
on the fundamental relation between the habitat and the formation. 
He stated (p. 161) that “every formation is in its floristic and 
ecological character a product of climate and soil.” 
Pound and Clements (1898; 1900: 314) wished to preserve 
Drude’s concept of the formation ; but their subdivision of “ the 
river bluff formation ” into “ (1) the red oak hickory formation" and 
“(2) the burr oak elm formation ” (pp. 324-333 [italics mine]) does 
not tend to clearness of thought. 
Cowles (1899: 111) propounded a view which has become 
widely adopted when he compared the formation with the genus 
and the association (“society”) with the species. Cowles stated 
his view as follows:—“ One might refer to particular sedge swamp 
societies near Chicago, or to the sedge swamp formation as a whole : 
by this application, formation becomes a term of generic value, 
plant-society of specific value.” 
Ganong (1903 : 300, et.seq.) regarded the salt marsh associations 
with which he was dealing as subdivisions of a larger unit, the wild 
