PART IV: ECOLOGY. 



415. 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 rela- 

 tions of the plant to the forces and beings of the world about 

 it, as distinguished from physiology proper, which treats 

 of the relation 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 ; consequently it is quite impossible to draw a sharp dis- 

 tinction between 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 surroundings and to other living beings can 

 be given. 



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