1 16 OUTLINES OF PLANT LIFE. 



relation of the plant as a whole to external forces and to 

 other living beings, both plants and animals. But it is con- 

 venient to separate the latter from physiology proper as 

 ecology. * (See Part IV. ) 



The study of physiology proper requires methods of controlling these 

 external forces, carefully planned and repeated experiments, and cau- 

 tious inferences. 



The study of ecology requires observation, in the field, of the physical 

 surroundings of plants, of their relation to their neighbors, and of their 

 adaptations to prevent injury by unfavorable physical conditions and the 

 attacks of other beings, and to take advantage of the favorable forces and 

 beneficent agents. 



146. Chemical and physical forces. — The functions of a 

 plant may be divided for the sake of convenience into nutri- 

 tion, respiration, growth, movement, and reproduction. 

 These are largely special modes of chemical and physical 

 action. Nutrition and respiration, for example, consist 

 chiefly of a series of chemical changes; while movement is 

 mainly a result of physical alterations in certain organs. 

 But the action of chemical and physical forces does not 

 suffice at present to explain all the activities of the living 

 plant. Moreover, the peculiar manifestation of these forces 

 which we call life occurs only in connection with the sub- 

 stance which we call protoplasm. 



147. The powers of protoplasm. — Although only a por- 

 tion of any plant is composed of living matter, it is to that 

 living matter only that we are to look for the seat of its 

 powers. 



The fundamental powers of protoplasm are four; it is 

 metabolic, irritable, contractile, and reproductive. 



148. Metabolism. — Protoplasm is metabolic, that is, it is 

 capable of initiating chemical changes in itself and in sub- 



* Spelled in lexicons, oecology, but best usage drops the o; sometimes 

 improperly called biology or plant biology. 



