V 
Aspects of Ecology. 251 
Meanwhile we are convinced that both species and formations have 
a real objective existence, though widespread doubt exists in both 
cases, especially among those who have not given attention to their 
actual study. The real differentiating factors in the two cases are 
probably of entirely different nature and in both cases we are far 
from having explored them to the bottom. Nevertheless we have 
full confidence that finality in these provinces will be reached in 
the course of future work. The work of Jordan, of De Vries, and of 
the Mendelians seems to furnish a beginning in the one province, while 
Dr. Clements’ researches constitute an important advance in the 
other. Meanwhile it is difficult to resist the conviction that the 
differences to which the skilled systematist and the skilled phyto¬ 
geographer attach importance are th<^ external expression of real 
breaks in the grouping of causal factors. That there is an 
enormous amount of careless and quite valueless species-making 
and formation-making is unfortunately true, but that we are on the 
paths of progress towards attainable goals seems to us certain. 
If these conclusions be valid, it follows that both species 
and formations have an objective existence, while all higher classi- 
ficatory units are of the nature of abstract groupings. The lower 
units into which the species and formation may be divided, on the 
other hand, are concrete, and have to be investigated. 
The primary divisions of a formation, which are usually known as 
associations, Dr. Clements prefers to call consocics. We doubt if 
his objection to the employment of the word “association” in this 
sense, based on an anticipated confusion between its abstract and 
concrete uses, is serious, and we prefer the older term. Dr. Clements 
attributes the development of “consocies” to “alternation” and 
from bis discussion of the latter, to which we have already referred, 
it would appear that “consocies” in his view are due to differences 
of habitat. But from his discussion of the formation it would 
seem that difference of habitat gives rise to different formations 
and to zonation within the formation, but presumably not to 
“ consocies,” which would have to be referred to we have called 
“historical accident.” “There is an inherent tendency to the 
segregation of facies, arising out of physical or historical reasons, 
or from a combination of both.The primary areas which thus 
arise have been called associations,” i.c., “consocies.” Does this 
mean that “consocies” may or may not be due to efficient difference 
of habitat ? This is a point of capital importance, and the analysis 
is by no means clear. 
