146 EDGAR ANDERSON AND WILLIAM L BROWN 



experiments show that the method is reliable, such a procedure should 

 expedite most corn breeding programs. 



Our method of scoring does not take into account the variation brought 

 about by the infusion of germ plasm other than that from Northern Flints 

 and Southern Dents. Perhaps this is one reason why we have not ob- 

 tained higher correlations between differences in inbred morphology and 

 yield. There are a few inbreds in the Corn Belt which appear to be affiliated 

 either with Caribbean flints or the Basketmaker complex. Scoring of such 

 inbreds on a scale designed for Northern Flints and Southern Dents un- 

 doubtedly leads to conflicting results. It is hoped that experiments now in 

 progress will aid in clarifying this situation. 



SIGNIFICANCE OF FLINT-DENT ANCESTRY 

 IN CORN BREEDING 



The Flint-Dent ancestry of Corn Belt maize bears upon many other breed- 

 ing problems besides those concerned with heterosis. Its widest usefulness is 

 in giving a frame of reference for observing and thinking about the manifold 

 and confusing variation of Corn Belt maize. When one becomes interested 

 in any particular character of the corn plant, he no longer needs to examine 

 large numbers of inbreds to understand its range of variation and its general 

 over-all direction. He merely needs to examine a few inbreds, and a Northern 

 Flint and a Southern Dent. A good part of the variation will then be seen to 

 fall into a relatively simple series from an extreme Northern Flint type to the 

 opposite Southern Dent extreme, with various intermediates and recombina- 

 tions in between. This is quite as true for physiological or biochemical char- 

 acters as for glumes, lemmas, or other morphological characters. One is then 

 ready to study further inbreds with a framework in his mind for sorting out 

 and remembering the variation which he finds. 



The actual breeding plot efficiency of this understanding will be clearer if 

 we cite a practical example. Now that corn is picked mechanically, the size, 

 shape, texture, and strength of shank are important. When maize was picked 

 by hand, the hand had a brain behind it. Variations in ear height, in the 

 stance of the ear, and in the strength and shape of the shank were of minor 

 significance. Now that machines do the work, it is of the utmost practical im- 

 portance to have the shank standardized to a type adapted to machine 

 harvesting. When this necessity was brought to our attention a few years 

 ago, there were few published facts relating to variation in the shank. Exam- 

 ination of a few inbreds showed that though this organ varied somewhat 

 within inbreds, it varied more from one line to another than almost any 

 other simple feature of the plant. We accordingly harvested typical shanks 

 from each of 164 inbreds being grown for observation in the breeding plots 

 of the Pioneer Hi-Bred Corn Company. We also examined a number of 

 Northern Flints, and had they been available, we would have studied the 



