100 THE AMERICAN NATURALIST [Vol. LI 



3. When distinct reaction systems are involved,^ as in 

 species crosses, the phenomena must be viewed in the 

 light of a contrast between systems rather than between 

 specific factor differences, and the results obtained will 

 depend upon the degree of mutual compatibility displayed 

 between the specific elements of the two systems. 



4. Sterility in such cases depends upon non-specific in- 

 compatibility displayed between the elements of the sys- 

 tems involved, and the degree of this sterility depends 

 upon the degree of such incompatibility rather than upon 

 a certain number of factors concerned in the expression of 

 such behavior. 



5. The consequences of the application of such a con- 

 ception to the complex type of behavior in (Enothera are 

 pointed out, and the suggestion is specifically made that 

 the type of behavior exhibited by Lamarckiana and its 

 segregants in hybridization may be referred to such com- 

 plex system interactions. 



LITEEATURE CITED 



