ORIGIN AND SIGNIFICANCE OF CORN BELT MAIZE 139 



pothesis that one could inbreed this vigorous crop, identify the inferior 

 strains in it, and then set up an elite cross-pollinated germ plasm. This hy- 

 pothesis was clearly and definitely stated by East and Jones {Inbreeding and 

 Outbreeding, 1919, pp. 216-17). 



Experiments with maize show that undesirable qualities are brought to light by self- 

 fertilization which either eliminate themselves or can be rejected by selection. The final re- 

 sult is a number of distinct types which are constant and uniform and able to persist in- 

 definitely. They have gone through a process of purification such that only those individu- 

 als which possess much of the best that was in the variety at the beginning can survive. The 

 characters which they (pure lines) have, can now be estimated more nearly at their true 

 worth. By crossing, the best qualities which have been distributed to the several inbred 

 strains can be gathered together again and a new variety recreated. After the most desirable 

 combinations are isolated, their recombination into a new and better variety, which could 

 be maintained by seed propagation, would be a comparatively easy undertaking. 



Though other corn breeders and corn geneticists may not have committed 

 themselves so definitely in print, such a notion was once almost universal 

 among hybrid corn experts. Modified versions of it still influence breeding 

 programs and are even incorporated in elementary courses in maize breeding. 



The facts reported above would lead us to believe that heterosis, having 

 resulted from the mingling of two widely different germ plasms, will probably 

 have many genes associated with characters which in their relatively homo- 

 zygous state are far from the Corn Belt ideal of what a corn plant should look 

 like. It is highly probable that much of the so-called "junk" revealed by in- 

 breeding was extreme segregants from this wide cross, and that it was closely 

 associated with the genes which gave open-pollinated dents their dispersed 

 vigor. It is significant that some very valuable inbreds (L317 is a typical ex- 

 ample) have many undesirable features. For this reason, many such inbreds 

 are automatically eliminated even before reaching the testing stage. 



If one accepts the fact that Corn Belt dents resulted from the compara- 

 tively recent mingling of two extremely different races of maize, then on the 

 simplest and most orthodox genetic hypotheses, the greatest heterosis could 

 be expected to result from crosses between inbreds resembling the Southern 

 Dents and inbreds resembling the Northern Flints. If heterosis (as its name 

 implies) is due to heterozygous genes or segments, then with Corn Belt corn 

 on the whole we would expect to find the greatest number of differing genes 

 when we reassembled two inbreds — one resembling the Northern Flint, the 

 other resembling the original Southern Dent. 



Theory (Anderson, 1939a), experiment (Anderson, 1939b; Brown, 1949), 

 and the results of practical breeding show that linkage systems as differenti- 

 ated as these break up very slowly. On the whole, the genes which went in 

 together with the Northern Flints still tend to stay together as we have 

 demonstrated above. This would suggest that in selecting inbreds, far from 

 trying to eliminate all of the supposed "junk," we might well attempt to 

 breed for inbreds which, though they have good agronomic characters like 

 stiffness of the stalk, nevertheless resemble Northern Flints. On the other 

 hand, we should breed also for those which resemble Southern Dents as close- 



