April I, 1920 



A Teosinte-Maize Hybrid 



15 



one is a function of the other. The other disherences may follow as 

 secondary relations due to this correlation with height. 



CIRCUMFERENCE INDEX 



In a population of 87, the circumference of the culm of Florida teosinte 

 averaged 61 mm. Under similar conditions the circumference of Tom 

 Thumb was approximately 35 mm. The mean of the F2 hybrid plants 

 was 56 mm. 



Since circumference is so closely associated with the general size of 

 the plant, the circumference measurement was recorded as a percentage 

 of the height of the plant, and the measure- 

 ment is termed a circumference index. 



While in direct m-easurement the culms of 

 teosinte are thicker than those of Tom Thumb, 

 teosinte is much more slender. In circum- 

 ference index a high value is therefore a 

 variation toward the maize parent. The 

 mean index of Florida teosinte was 2.7, that 

 of Tom Thumb about 6.0. The mean of the 

 hybrid plants was 4.5, with a normal dis- 

 tribution (fig. 5). 



Circumference shows one significant and 

 independent coherence, that with pollen to 

 silk, and a disherence with male secondaries. 



30 



I 



I 



NODES WITHOUT BRANCHES 



t\, Sj (*) V V<> '<^ k) Vi N n' ^ Si « 

 A>S/?C£A/r 



Fig. 5. — Circumference index: fre- 

 quency distribution of plants in 

 F2. Class value, s per cent. 



This character is the number of nodes be- 

 tween the lowest branch and the uppermost 

 sucker or the surface of the ground. In 

 teosinte, branches are normally developed in the axils of all leaves on the 

 main culm, except the uppermost. The tendency to suppress branches 

 at the nodes just above the ground appears, however, when the plants 

 are grown under unfavorable conditions. In a planting of Florida 

 teosinte at Chula Vista in 1918 the average number of nodes ^vithout 

 branches was 7.6. 



In maize there are always a number of nodes without branches between 

 the uppermost sucker and the lowest ear. In Tom Thumb where no 

 suckers are developed, the number can not be definitely determined, 

 since the surface of the ground can not be located with accuracy. But 

 since the average total number of leaves in Tom Thumb is 11 and there 

 is an average of 3 nodes above the single ear and about 5 nodes below the 

 surface of the ground, the medn number of nodes without branches is 

 about 3. 



