EXTENSION OF COEN CULTURE BY HYBRIDS. 31 



Experiments similar to those conducted by Sliull may have a 

 special bearing in this connection. The reduction in vigor which 

 accompanies the inbreeding to which his strains are subjected would 

 have an effect similar to growing the plants under adverse conditions 

 and would tend to eliminate all but the strongest individuals. This 

 would, in fact, constitute an effective form of selection, and with 

 such strains thrown into the vigorous condition of first-generation 

 hybrids a maximum performance might be expected. 



While the best results may in general be expected from crossing 

 two varieties both of which are productive, crossing with a low- 

 yielding variety may operate to increase the yield above that of a 

 much higher yielding variety with which it is crossed. The Chinese 

 variety mentioned on page 23 is a small variety producing only 0..39 

 pound per plant in the experiments reported. Yet in four of the 

 five cases where this variety was crossed with higher yielding varieties 

 the yield of the hybrid exceeded that of the variety with wliich it was 

 crossed. The average yield of the five varieties with which the 

 Chinese corn was crossed was 0.764 pound per plant, nearly double 

 that of the Chinese, yet the average yield of the five hybrids was 1 .004 

 pounds per plant, an increase over the highest yielding parent of 

 nearly 33 per cent. If the increased vigor of hybrids is in any way 

 associated with the distinctness of the parent types, the remarkable 

 behavior of this series of crosses may perhaps be understood. This 

 Chinese variety is one of the most divergent types and must have 

 been isolated from all ordinary types of corn for a very long time. 

 Evidence was presented in a former publication " that the introduc- 

 tion of corn in China was probably pre-Columbian. In these and 

 other crosses where low-yielding varieties producing more than one 

 ear to the plant operated to increase the yield of larger-eared types, 

 the greater yields appeared to have been brought about by an 

 increase in the number of ears with only a slight reduction in their 

 size. 



EXTENSION OF CORN CULTURE BY FIRST-GENERATION HYBRIDS. 



In addition to increased vield in corn-growing regions the vigor of 

 first-generation hybrids may also allow of an extension of corn grow- 

 ing beyond the present area of production. 



Even a slight increase in the drought resistance of corn would 

 make possible the extension of corn culture into large regions where 

 the growing of this crop is now too precarious to justify the effort. 

 The subject is of such importance as to warrant the investigation of 

 every possibility. 



«A New Type of Indian Corn from China, Bulletin l(jl, Bureau uf Plant Industry, 

 U. S. Dept. of Agriculture, 1909, pp. 20-24. 

 191 



