526 S. O. MAST 



7. As to the nature of the chemical processes associated with 

 the responses no definite conchisions can be drawn; but if the 

 absorption is the same in the photosensitive tissues of all of the 

 organisms studied these processes differ in all species in which 

 the relation between wave-length and stimulation differs. It 

 can not, however, be concluded, even if this is true, that they 

 are the same in all of the species in which this relation is the 

 same, for the relation between chemical reactions and wave- 

 length is, in all probability, the same for certain substances that 

 differ. Further progress in this analysis depends largely upon 

 further work on the relation between photochemical reactions 

 and wave-length. 



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