2o2 



THE AMERICAN X A TUB ALLS T [Vol. XL V 



also reported on sixteen hybrid combinations all but 

 two of which gave increased yields in the Fj. From the 

 work of all these men, especially from my own compari- 

 sons between F 1 and F 2 hybrids, it has become obvious 

 that the secret of the highest success in corn breeding 

 from an economic point of view lies in finding those 

 strains which will produce the largest yield and then 

 utilizing the first-generation hybrids each year. 



The point which most interests us on the present occa- 

 sion is not, however, the economic importance of using 

 first generation crosses, but the evidence which appears 

 to me clearly indicate that a normally cross-bred plant 

 like Indian corn harmonizes in its fundamental nature 

 with such normally self -fertilized material as beans, 

 wheat and other grains, and such clonal varieties as pota- 

 toes, Paramecium, etc., that the egg-cells and sperm-cells 

 of even the most complex hybrids present a limited num- 

 ber of different types which can be assorted into homo- 

 zygous combinations, and that, therefore, the progressive 

 change resulting from continued selection may be simply 

 explained as the gradual segregation of homozygous 

 types or of the most efficient heterozygous combinations. 



The fact that yield and perhaps many other qualities 

 attain their highest development in the ease of complex 

 hybrids naturally leads to the unconscious selection of 

 heterozygous plants for the next year's cultures, and the 

 continual breaking up of these complex hybrids in sub- 

 sequent generations gives a result which closely resem- 

 bles fluctuating variation, but which is fundamentally 

 different from it. The genuineness of the gains made by 

 selection in corn might naturally lead to the conclusion 

 that fluctuations are inherited were it not for the abun- 

 dant evidence now available showing that a considerable 

 portion of the variation presented is not fluctuational, 

 but is due to the presence of a mixture of different types 

 which any selection partially segregates. 



