1922] WATERMAN—PLANT COMMUNITIES 5 
NicHots (6) recognized this and returned to SCHIMPER’s dis- 
tinction between climatic and edaphic formations. His unit next 
above the association was the edaphic, later called the physiographic 
formation, which he defined as the association-complex occupying a 
physiographic unit area, while the climatic formation was a complex 
of physiographic formations forming the vegetation, taken in its 
entirety, of any region in which the essential climatic relations are 
similar or uniform throughout. This TANSLEy criticized, because 
“nothing like a sharp line can be drawn between one climatic region 
and another, so that it becomes impossible to delimit ae goes 
tions in NicHots’ sense.” TANSLEY accepts CLEMENTS’ “‘associes”’ 
for all stages which have not reached a relatively stable (climax) 
condition, and defines the association as a mature quasi-organism 
which is relatively fixed and stable. He then defines the formation 
as including ‘‘all the vegetation which is naturally grouped around 
the association, determined by the particular collection of environ- 
mental factors which ‘make up the ecological conception of the 
habitat.”” NuicHots has not published as yet any further statement 
on the formation, but in his paper at the Toronto meeting he seems 
to adhere to his division of formations as physiographic and climatic. 
As a result of a study of literature on formations, as well as 
actual conditions in the field, especially in connection with the 
preparation of the present paper, the writer has reached the follow- 
ing conclusions, on which the definitions of the terms involved will 
be based 
1. That there is a distinct advantage in omitting from the defini- 
tion of the formation all reference to the habitat, as was done in the 
case of the association. 
2. That it is inadvisable to connect the idea of the formation 
with a climax association, because the determination of climax is 
one of the purposes of a genetical study, and it is clearly undesirable 
to define a term which should be usable from the beginning of a study 
in such a way that it cannot properly be used until the study has 
been completed. In such a case it would be necessary to secure an 
additional term for the community in the process of development. 
This is cumbersome and unsatisfactory, as is illustrated in 
CLEMENTS’ use of ‘“‘associes” and “association,” which does not 
