SYMMETRY RELATIONS 23 



organism as a whole as a mere symmetry machine, a 

 simplification which forms the foundation of the tropism 

 theory of animal conduct. 



It would, therefore, be a misconception to speak of 

 tropisms as of reflexes, since tropisms are reactions of 

 the organism as a whole, while reflexes are reactions of 

 isolated segments. Reflexes and tropisms agree, how- 

 ever, in one respect, inasmuch as both are obviously of 

 a purely physico-chemical character. 



