CHAPTER III 

 THE TROPISMS 



"The understanding of complicated phenomena depends upon an 

 analysis by which they are resolved into their simple elementary 

 compounds." LOEB, Physiology of the Brain. 



"On s'est fait beaucoup d'idees fausses sur les tropismes; les 

 litterateurs, les philosophes; les savants meme, ont disserte sur eux 

 d'une facon tout a fait fantaisiste, les uns raillant, les autres louant 

 sans reserve, ce qu'ils n'avaient pas compris." GEORGES BOHN. 



THE TROPISMS IN GENERAL 



Certain stimuli exercise a directive effect upon the move- 

 ments of animals causing them to go toward or away from 

 the source of stimulation. Such movements are commonly 

 called tropisms. The flight of a moth toward the candle, 

 the gathering of male moths around a box containing a 

 female, the movements of protozoans away from regions of 

 unusual heat or cold may be taken as illustrations of such 

 directed movements. 



No attempt will be made to formulate an accurate defini- 

 tion of the word tropism because usage has not established 

 the meaning of the term with sufficient precision to render 

 this possible. There is considerable difference of opinion 

 in regard to the explanation of tropisms, and the kinds of 

 behavior to which the term should be applied. In what 

 follows phenomena will be described which have been com- 

 monly classed as tropisms however diverse they may be in 

 character and causation. 



The study of tropisms, which has attracted a large share 

 of attention in recent years, was given a great stimulus by 



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