PART IV : ECOLOGY. 



314. Definition. — Physiology, in its broadest sense, may 

 be divided into physiology proper and ecology. Ecology is 

 that portion of botanical science which treats of the relations 

 of the plant to the forces and beings of the world about it, 

 as distinguished from physiology proper, which treats of the 

 relations of the plant as a whole to the chemical and physical 

 forces within it. The forces without the plant necessarily 

 limit and modify the action of the forces within it ; conse- 

 quently it is quite impossible to draw a sharp distinction be- 

 tween those subjects which belong to ecology and those which 

 belong to physiology proper. Parts II and IV, therefore, will 

 be found to overlap in many places. Several of the subjects 

 already treated under physiology belong in part to the present 

 section. For example, the movements of plants are due not 

 to internal causes alone, but to internal causes as modified by 

 external conditions. In this part only a bare outline of the 

 adaptations of plants in form and habit to their physical sur- 

 roundings and to other living beings can be given. 



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