PREVIOUS EXPERIMENTS WITH FIRST-GENERATION HYBRIDS. 17 i 



results. The omission of single members from the series would ' 



materially change the average. The lack of uniformity in the condi- i 

 tions is indicated by the great disparity between the yields of duplicate 



varieties in this experiment, which ranged as high as 15 bushels per i 



acre.'^ i 



EXPERIMENTS IN NEW YORK. 



After a further lapse of fifteen years, the subject was again ' 

 approached from a somewhat different direction by Dr. G. H. Shull 

 of the Carnegie Biological Laboratory at Cold Spring Harbor, N. Y. 

 In his first paper he suggests the possible use of first-generation ' 

 hybrids in the following statement: 



The problem of getting the seed corn that shall produce the record crop, or which ' 



shall have any specific desirable characteristic combined with the greatest vigor, may 

 possibly find a solution, at least in certain cases, similar to that reached by Mr. Q. I. 

 Simpson in the breeding of hogs by the combination of two strains which are only at 

 the highest quality in the first generation, thus making it necessary to go back each ' 



year to the original combination, instead of selecting from among the hybrid offspring 

 the stock for continued breeding. 6 



The following year Doctor Shull stated his views in greater detail 

 and reported on the result of crossing two closely related strains. <^ 

 Before these results can be properly appreciated it will be necessary \ 

 to briefly consider the problem from Slmll's standpoint. It is con- ' 



sidered that even the most nearly uniform varieties of corn consist of 

 numerous strains, ''elementary species" or ''biotypes," all more or 

 less mixed and hybridized. To this miscellaneous hybridizing I 



Doctor Shull attributes the vigor and fertility of a variety. The > 



method he suggests for the improvement of corn is to isolate the j 



different strains and by making predetermined combinations to 

 ascertain which mil be the most favorable for agricultural purposes. 

 It is fully recognized that isolating the pure strains or biotypes will 

 very greatly reduce their vigor and yield, but by making a combina- 

 tion of the proper strains it is believed that the degree of fertility of i 

 the cross will reach that of the most productive plants in the original i 

 mixed strain and that an increase of the total yield can be obtained i 

 in this way. : 



Two self-fertilized strains which were separated from a common 

 stock in 1904 and continuously self-fertilized since that time were i 



reciprocally crossed in 1907. In 1908 the yields of these reciprocal 

 crosses were compared with each other, with the self-fertilized parents, 



a Morrow, G. E., and Gardner, F. D., op. cit., p. 338. 



b Shull, G. H. The Composition of a Field of Corn. Report, American Breeders' 

 Association, vol. 4, 1908, p. 300. ' 



c Shull, G.H. A Pure Line Method in Corn Breeding. Report, American Breeders' i 



Association, vol. 5, 1909, p. 51. 

 191 



