20 



BULLETIN 925, U. S. DEPARTMENT OF AGRICULTURE. 



strated in figure 8, which shows frequency distributions of the three 

 types of plants for the length of the longest internode. The longest 

 internode, disregarding the very uppermost, which is sometimes dim- 

 cult to differentiate from the rachis of the tassel, is found almost 

 always well below the ear, and hence below the area affected in the 

 adherent plants. 



If the adherent variation is considered as being due to a single 

 factor, completely coupled or linked with normal stature, then the 

 adherent plants should be 25 per cent of the total, while the observed 

 percentage is 19 + 1.85. While this deviation seems large, the nature 

 of the variation is such that many of the plants must be eliminated 

 in the seedling stage and doubtless escape notice. The percentage 

 of adherent plants necessitates the assumption that this variation is 

 recessive to the normal condition, and if the above hypothesis of 

 perfect linkage with normal stature is correct, self-pollinated ad- 

 ^ herent plants 



should produce 

 nothing but ad- 

 herent plants of 

 normal stature. 

 The F x of a bra- 

 chytic adherent 

 cross should be 

 normal with re- 

 spect to both characters, and in the second generation there should 

 be three classes of plants in the proportion of one normal in stature 

 and adherent, two normal in stature and nonadherent, and one 

 brachytic and nonadherent. The Boone plant which was crossed 

 with brachytic must have been heterozygous for adherence, or other- 

 wise it would have exhibited this character. Therefore, the prog- 

 enies of one-half of the F 1 plants should have 25 per cent of the 

 • plants adherent. As yet only three progenies have been grown and 

 two have exhibited the variation, but 30 additional hand-pollinated 

 ears remain to be tested. 



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Pig. 8. — Frequency distribution of the length of the longest in- 

 ternode on brachytic, adherent, and normal plants from the 

 second generation of brachytic X Boone. 



EARS ENDING IN STAMINATE SPIKES. 



The staminate spike variation was found not only in the Boone- 

 brachytic hybrid but also in some of the other brachytic-normal 

 hybrids. The ears in this variation terminate in single spikes bear- 

 ing several rows of paired staminate spikelets. The number of rows 

 of these staminate spikelets, in the cases where they can be deter- 

 mined with reasonable accuracy, is usually less than the number of 

 rows of seeds upon the ear. 



The character is extremely variable in expression, especially in the 

 second generation of the Boone-brachytic hybrid. In this hybrid, 



