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BULLETIN 925, IT. S. DEPAETMEXT OF AGEICULTURE. 



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en 



Fig. 3. — Frequency distribution for the length of 

 the third branch in an F 2 of Tom Thumb pop 

 corn X Florida teosinte. 



character affected is the length of the ear stalk, which shows a reduc- 

 tion in internode length similar to that of the main culm. "While 

 this may be considered simply as the general extension of the 

 brachytic tendency to all the lateral branches, as indicated also by 

 the condition of the suckers, it must be remembered that the brachytic 

 nature of the ear stalk on plants of normal stature is not ordinarily 

 reflected in the main culm. 



This further shortening of the ear stalk on brachytic plants indi- 

 cates that the brachytic stalks of normal ears are the result of a 



genetic change separate from 

 that which caused brachytic 

 internodes on the main culm. 

 Support for this latter con- 

 tention is derived from a hy- 

 brid between Florida teosinte 

 and Tom Thumb pop corn 

 (3). If the ear stalk is an 

 example of brachysm similar to that of the main stalk, the second 

 generation of the hybrid between teosinte and maize should give the 

 same evidence of segregation of this character as is found with the 

 internodes of the main culm when plants with brachytic culms are 

 crossed with those of normal stature. 



With the second-generation plants, the third branch from the top 

 on the main culm is assumed to be homologous with the ear stalk of 

 normal maize, since it is borne at approximately the same node as 

 the ear of maize. The frequency distribution for the length of this. 

 branch on second-generation plants of the Tom Thumb X Florida 

 hybrid is shown in figure 3. 



It is apparent that there is no bimodality in the distribution of 

 branch lengths, and it must be concluded that the brachysm of the 

 ear stalk of normal maize does not behave as a simple Mendelian 

 character in crosses with teosinte. 



Slight evidence for the discontinuous nature of the brachysm of 

 ear stalks is to be found in the second generation of a cross between 

 Boone County "White and the brachytic strain. The frequency dis- 

 tributions for the length of the ear stalk on brachytic plants directly 

 descended from the original variation and on the first and second 

 generation plants of the brachytic-Boone cross are shown in figure 

 4. While the brachytic plants had shorter ear stalks than normal 

 plants, the frequency distribution for this character on the normal 

 segregates of the second generation of the hybrid suggests a bimodal- 

 ity that is most easily explained by assuming an independent inheri- 

 tance of the ear-stalk character. Too much confidence must not be 

 placed in results of this sort, as it is obvious that at least one other 

 factor besides length of internode is involved in the length of the 



