20 



Journal of Agricultural Research 



Vol. XIX. No. I 



A most striking example of coherence is the negative correlation of 

 secondary branches with all three of the nodes above group. The 

 other coherences are v.ith male branches, branch silking first, and days 

 to pollen. The only clear evidence of disherence 

 is with male secondaries and length of internode 

 on third. 



1 



FiG. 12. — Secondary index: fre- 

 quency distribution of plants 

 in F". Class value, 20 per 

 cent. One plant at 340. 



SECONDARY INDEX 



This character, which is the number of secondary 

 branches expressed as a percentage of the total 

 branches, distinguishes more sharply between maize 

 and teosinte than does the direct measurement 

 of either primary or secondary branches. Second- 

 ary tassel branches are relatively as well as abso- 

 lutely much more numerous in teosinte than in 

 maize. In teosinte they equal or exceed the 

 number of primary branches, while in maize the 

 number of secondaries equals the number of the 

 primaries only in some of the large tropical varieties. 



In the F2 hybrid plants the mean was 70, with a 

 very skew distribution (fig. 12) but with no evi- 

 dence of more than one mode. 



The correlations are similar to those with the 

 direct measurements of tassel branches, except the additional coherences 

 with number of alicoles and rows in central spike. 



TASSEL BRANCHES ON TIirRD 



In teosinte the modal number of tassel branches on the third branch 

 from the top is two. When teosinte is grown under 

 rather unfavorable conditions where the number of 

 branches is reduced, there Is evidence of a bimoda] 

 distribution, in that plants with two branches or none 

 are more numerous than plants with a single branch. 

 In maize the number is zero, since all branches 

 from the upper nodes of maize are normally un- 

 branched. 



In the F2 hybrid plants the mean was 6.1. The 

 distribution (fig. 13) was skew, with slight indication 

 of two modes. 



Although closely correlated with the tassel 

 characters of the main stalk, this character 

 shows no significant correlations outside the 

 group except with number of nodes on third. 

 This is in the direction of a disherence; but the relation is doubtless 

 physiological, since both characters would be similarly affected by 

 changes in general vigor. 



Fig. 13.— Tassel braucheson 

 third: frequency distrib- 

 ution of plantsinFi.CIass 

 value, two branches. 



