22 BULLETIN 925, U. S. DEPARTMENT OF AGRICULTURE. 



generation, since they would result from self-pollinating plants ex- 

 hibiting the variation. 



If the hypothesis is correct that both the Boone and the brachytic 

 parents were heterozygous for the variation, three classes of progeny 

 should be obtained from self-pollinated F x plants, one class produc- 

 ing nothing but normal-eared plants, one with 25 per cent of the 

 plants with staminate-spiked ears, and one with all the plants having 

 ears with staminate spikes. The ratio in which these progenies 

 should appear would be the familiar 1:2:1. 



As in the other hypothesis, the F 2 progenies which would have all 

 the plants exhibiting the variation would be recognized in the F 15 

 since they would show the variation in that generation. Since only 

 three self-pollinated progenies have been grown thus far, it is not 

 possible to test crucially the two hypotheses. The F x progenies 

 which furnished seed for the second generation were grown in the 

 greenhouse. The ears produced by these plants gave no indication 

 of staminate spikes, and it was only in the larger planting in the 

 field that the variation appeared in the first-generation plants. 



The three second-generation Boone-brachytic progenies were fairly 

 consistent with respect to the percentage of plants that produced 

 the variation, all three closely approximating 25 per cent with 

 staminate tips. The variation obviously is detrimental, since the 

 ears affected are reduced in length. Although the staminate spike 

 is not developed entirely at the expense of the pistillate portion, the 

 evidence from the Boone-brachytic hybrid indicates that the length 

 of the ear is reduced about one-half the length of the staminate spike. 



It is of practical interest, therefore, to determine whether this un- 

 desirable variation is associated with stature. In this respect the 

 three Boone-brachytic progenies differ somewhat. All three prog- 

 enies show that the gene, or at least one of the genes for staminate 

 spikes, is located in the same chromosome with the gene for stature. 

 In the present hybrid, staminate spikes are associated with normal 

 stature, so that the improvement in yield of the brachytic variation 

 is not threatened in these cases. It must not be overlooked, however, 

 that by suitable crosses these correlations could be reversed, thereby 

 increasing the percentage of brachytic plants with the undesirable 

 staminate spike variation. 



The three progenies exhibit varying degrees of closeness of the rela- 

 tionship of stature to staminate spikes on the ear, with an average cor- 

 relation of 0.37±0.112. Such a correlation coefficient indicates a 

 rather loose linkage, but it is apparent that in some progenies this 

 relationship might be very much closer. That such cases may be ex- 

 pected is shown by the F 2 of the brachytic-Hopi hybrid where the 

 brachytic plants appeared in combination with the staminate spike 



