CHAPTEE IV 



THE SELECTING POWER OF ENEMIES 



IT 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 Unit of Living 



