26 



Journal of Agricultural Research 



Vol. xrx, No. 1 



<ito 



SO 





tx 



A 



silking. Witli a view to obtaining an expression of the tendency to pro- 

 duce secondary branches independent of the length of the primary 

 branch, the number of nodes silking on the third branch was expressed 

 as a percentage of the total number of nodes on the branch. 



In teosinte the percentage is normally 100/ in 

 maize o. In Fg hybrid plants the range was from 

 o to 100. The modal number was 100, with the 

 numbers diminishing with fair regularity to o 

 (fig. 22). The mean was 78. 



With the exception of the negative correlation 

 with position of best spike, all the coherences are 

 obviously physiological. On the other hand, the 

 disherent correlation with height would appear to 

 be genetic. 



PROPHYLLARY GROUP 

 PROPHYLLARY SPIELS 



Prophyllary branches are rare in maize and have 

 never been observed in Tom Thumb. In varieties 

 where prophyllary branches do occur they are 

 simple. In teosinte, prophyllary branches are 

 always well-developed ; 



so 



FiG. 22. — Nodes silking in- 

 dex: frequency distribution 

 of plants in Fj. Class value, 

 10 per cent. 





and in Florida teosinte, 



the average number of 



spikes is 6.3, wdth a 



range from 3 to 11. 



The disposition of the 



spikes in teosinte is 



shown in Table I. This 

 character is therefore one that is sharply con- 

 trasted in the parents. Two of the F^ plants 

 in which this character was recorded each 

 produced a single prophyllary spike. 



In the second generation, 23 of the plants 

 either had no prophyllary branch or it was not 

 sufficiently developed to bear a spike. In 23 

 plants the branch consisted of an unbranched 

 spike. The remaining 68 plants had from 2 to 

 14 spikes. The mean number for all plants 

 was 3.1, the distribution (fig. 23) being skew but with no evidence 

 of more than one mode. The three significant correlations are all 

 coherent, but all may be physiological. 



• This follows from the fact that although there is no branch produced in the axil of the uppermost leaf 

 there is a fruiting branch borne in the axil of the prophyllmn. 





iDl 



d 



Fig. 23.— Prophyllary spikes: fre- 

 quency distribution of plants in 

 F2. Class value, one spike. 



