88 Journal of Agricultural Research voi. m. No. i 



The mean of the two parents is S4.2±3.o per cent of the general yield. 

 The mean of the two hybrids is ii5-9±3-3 per cent. The mean yield of 

 the hybrids is thus 31.7 + 4.5 percent higher than the mean of the parents, 

 and this increase is ascribed to the effects of crossing. 



Table I. — Yield and height of the Egyptian and Voorhees Red varieties of sweet corn 

 and Izt'o hybrids between them 



[Detenninations expressed as average percentages of the mean of the four kinds.l 



Variety of com. 



Yield. 



Height. 



Egyptian 



Voorhees Red. 

 Hybrid Phg6. . 

 Hybrid Phg;.. 



Per cent, 



112. 8±4. 6 



55. 6±4. o 



89. o±5. I 



142. 8±4.3 



Per cent. 

 III-3±I.0 



84. o± . 9 

 100. o±i. 2 

 103. 6± I. I 



A striking feature of the results obtained is the difference between the 

 yield of the two hybrid ears, which amounts to 53.8 ±6.7 per cent. Had 

 the ear Ph96 alone been taken as representing a hybrid between these 

 varieties, the hybrid would have exceeded the average of the parents by 

 only 4.8 per cent, a difference upon which no reliance could be placed. 

 If, on the other hand, the ear Ph97 had been taken, the difference in favor 

 of the hybrid would have appeared as 58.6 per cent. 



The relative height of the four kinds was determined in the same 

 manner as the yield — that is, the height of each plant was compared 

 with the mean height of all the plants of the hill in which it grew, the 

 latter being taken as 100. The average heights expressed in this way 

 are given in column 2, Table I. 



The average height of the parents is 97.6 ±0.7 per cent of the general 

 mean. That of the hybrids is ioi.8±o.8 per cent. The difference is 

 4.2 ±1.1 per cent. There is, then, a distinct increase in the height of 

 plants as a result of crossing, but the increase is much less than the 

 increase in yield, and the difference between the two hybrids is nmch 

 less than was the case with the yield. 



It has usually been found that the increase that follows crossing affects 

 the vegetative characters even more than the reproductive. If height 

 be taken as an index of vegetative vigor, the reverse would seem to be 

 true in the present cross. 



Increased vegetative vigor may have resulted in an increase of the 

 branches rather than of the main stalk. To definitely settle this point, 

 it would have been necessary to weigh or measure all of the suckers. 

 This was not done, but the number of suckers was recorded for each of 

 the kinds, and the difference, though small, indicates that a part of the 

 increased vegetative vigor of the hybrids was expressed in the production 

 of suckers. A total of 18 suckers was produced in the two pure-seed 

 rows, while 35 were produced in the two hybrid rows. The association 

 between vegetative vigor and yield is further shown by the fact that the 

 hybrid Ph97 exceeded the hybrid Ph96 both in yield and in the produc- 

 tion of suckers. It should be borne in mind, however, that an increased 

 yield and an increased production of branches may not always be thus 

 associated. It is to be expected that under some conditions excessive 



