CHAPTER IV 
THE SELECTING POWER OF ENEMIES 
Ir is impossible to conceive of an environ- 
ment, without also calling to mind that which 
is invested. A biological environment is the 
sum of many factors which, added together, 
permit of life. A study of these factors 
shows that they are not homogeneous, but 
that each of them is made up of a continuous 
series of diversities. Many obviously have 
this constitution, such as temperature, alti- 
tude above sea-level, the relation of the differ- 
ent points on a tree-trunk to the points of the 
compass. Others seem to form a discontin- 
uity, but in these cases steps are probably not 
absent, only crowded together. 
Just as environment cannot be conceived 
alone, so living matter cannot: the two are 
inextricably mingled. The structure of living 
matter is bound to its function: and function 
is action on environment. Without environ- 
ment, living matter could not be recognised. 
The Environment of a Umt of LInving 
42 
