SPECIES HYBRIDIZATION 



243 



the admixture be relatively slight, the inharmonious elements may not 

 greatly affect the workings of the reaction system, and there would result 

 individuals showing practically the entire set of characters of one or the 

 other parent, and such individuals would be fully fertile. A slightly 

 greater proportion of inharmonious elements in the reaction system would 

 result in such profound disturbances in its functioning as to produce the 

 abnormal individuals of various kinds which make up so large a propor- 

 tion of the progeny from such parentage. When the proportions of 

 inharmonious elements in the gametes becomes still greater, they fail to 

 function at all. It is upon the formation of such non-functional gametes 

 or the attempt to produce them, that the partial sterility of the hybrid 

 depends, and since in this particular case these form by far the greater 

 proportion of gametes, the hybrid is very nearly completely sterile. 



The relations may be illustrated by Table XXXVIII which represents 



TABLE XXXVIII. RECOMBINATION SERIES IN GAMETES OF FI OF N. tabacum X N. 



sylvestris 



