86 Jotirnal of Agricultural Research voi. in, No. i 



may be as serious as that incurred by the use of old seed. If the condi- 

 tions of growth where the pure seed is produced are more favorable 

 than those under which the hybrid seed is produced, natural selection 

 will be less rigorous. There is also the possibility of direct effect of en- 

 vironment on the yielding power of the seed and the possibility of new- 

 place effect. 



A further disturbing factor lies in the differences between the indi- 

 vidual plants that produce the hybrid seed and those producing the pure 

 seed which is to represent the parental varieties. When seed from a 

 large number of plants is used, these differences tend to counterbalance 

 each other and give an average of value for practical purposes, but in- 

 formation which might extend our knowledge regarding the nature and 

 causes of the increase may be completely obscured by this method of 

 averaging. 



Some of these difficulties can be avoided if the hybrid seed is obtained 

 by hand pollination. By this means seed of both parent varieties of the 

 same age as the hybrid seed and grown under similar conditions can be 

 secured. Inaccuracies due to diversity among individual plants will, 

 however, be increased, since the number of plants involved will necessa- 

 rily be smaller, and, as before, differences in the behavior of individual 

 crosses which might throw Ught on the nature of the increases will be 

 masked if conclusions are based upon averages. To avoid this last diffi- 

 culty, the individual hybrid ears may be kept separate and an ear-to-row 

 method of making comparisons with the parents may be applied. 



Differences in the breeding value of individuals are now appreciated in 

 the breeding of pure strains and have led to the adoption of the method of 

 separating the offspring of individuals into progeny rows. The results 

 here reported show a diversity among the hybrid ears that result from 

 crossing different plants of the same parent varieties that is even greater 

 than that usually found between pure seed ears of a single variety, and 

 the evidence indicates that individual diversity in hybrids will be found 

 as important as in pure varieties. 



In comparing an individual maize hybrid with its parents account must 

 be taken of the fact that to behave normally maize must be cross-polli- 

 nated, and to secure cross-pollinated seed of the parent varieties two 

 plants of each variety must be used, but only one plant of each variety 

 can be represented in an individual hybrid ear. To avoid in some 

 measure these sources of inaccuracy the method followed in the experi- 

 ments here described is suggested. 



DESCRIPTION OF METHOD 



To compare the behavior of two varieties, which may be called A and B, 

 with that of a hybrid between them, two plants were selected in each 

 variety, Ai and A2 in the one variety and Bi and B2 in the other variety. 

 The following hand pollinations were made: A1XA2, A2XB1, B1XB2, 

 and B2 X Ai . The result is two hybrid ears and one cross-pollinated ear of 

 each variety. It is believed that the mean yield produced by seed from 

 the two hybrid ears compared with the mean yield produced by seed from 

 the two pure seed ears gives a fair measure of the effects of hybridization. 

 By making two hybrids involving all the plants used in producing the 

 pure seed ears individual differences that affect the yielding power of the 

 pure seed ears are similarly represented in the hybrids. Thus, in both the 



