BEGINNINGS OF THE HETEROSIS CONCEPT 



25 



eral morphological characteristics. They had been derived from seven sepa- 

 rate self-pollinations of sibs in a family which I had reason to think was 

 genetically homogeneous. This could not fail to make a great imj)ression. 

 Had these several pure-bred self-fertilized strains come from different 

 breeders and from more or less disconnected experiments, as did the selfed 



TABLE 2.2 



GRAIN-ROW COUNTS AND YIELDS OF EAR CORN IN CULTURES OF 



WHITE DENT MAIZE GROWN AT THE STATION FOR 



EXPERIMENTAL EVOLUTION IN 1906 



lines available to Dr. East, the observation that they showed themselves to 

 be genetically distinguishable biotypes would have given no cause for the 

 special conclusions I drew from them. It would have been strange, indeed, 

 if strains thus derived from heterogeneous sources had not been genetically 

 different, one from another. 



Comparison of the results for 1907, presented in Table 2.3, with those for 

 1906 in Table 2.2, shows a heavy accentuation of grain-row classes 8 and 10 

 and a marked decrease in classes 18 to 20, inclusive. There was also a sig- 

 nificant increase in all higher classes, with further extension of the range from 

 a maximum of 32 to about 40. The increase in the frequencies of the low 



