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THE AMEBIC AN NATURALIST [Vol. XLIII 



to the eye that it is almost unnecessary. The figures 

 presented do not show the average increase to be ex- 

 pected by a cross. The manuring was heavy, the culti- 

 vation intensive, and the yields were beyond the ordi- 

 nary. But they do show that in practically every case 

 a combination of two high-bred varieties of seed corn is 

 more vigorous than either parent. 



The importance of this fact in commercial corn growing 

 is considerable, and is likely to increase in the future, 

 for the following reason. The corn breeding methods in 

 use vary as to detail, but their purpose is the same, 

 namely, to produce high-yielding strains. The older 

 idea was that continued selection of plus fluctuations 

 would invariably yield results. At present, there are 

 more adherents to the view that man can do more than 

 isolate from the mixture of types we call a commercial 

 variety the most perfect type that nature has produced 

 in this variety. It is all line breeding, and as it is 

 carried on on small plots, the tendency toward the pro- 

 duction of an inbred strain increases with the length of 

 time the work is prosecuted. Thus, unless new mutations 

 intervene, chance of improvement is limited to the latent 

 possibilities of the first breeding plot, 



Shull 7 has already suggested that either definite recom- 

 bination of previously isolated biotypes, or relaxation 

 of selection after partial isolation and rejection of the 

 less efficient biotypes, will be found to be the logical 

 procedure in corn breeding. 



The writer has become a convert to the first method 



Dr. Shull 7 as a timely coincidence, a copy of a paper that he had read at 

 the annual meeting of the American Breeders' Association, in January, 

 1909. In it he deals with a similar method of corn-breeding, namely, the 



recombination later. His method is more correct theoretically, but less 

 practical than that of the writer. From this paper I inferred that his 

 views must accord with the theory presented in this paper. Eeplies to my 

 inquiries show that our ideas are strictly in harmony, although Dr. Shull 

 had not treated the theoretical phase of the subject, having considered it 

 as beyond the scope of his paper. 



