Oct.is.i9u First-Ge-neraiian Maize Hybrids 91 



parents are for the most part those more closely associated with vigor — 

 ■viz, height, number of suckers, and length of leaf. The differences 

 between the two hybrids are such that without exception Ph96 stands 

 closer to the \'oorhee5 Red variety and Phgy closer to the Egyptian 

 variety. It is probably a coincidence that in both hybrids the resem- 

 blance is to the female parent. 



COXCLUSIOXS 



So large a proportion of first-generation maize hybrids have been 

 found to give increased \"ields and the increase is frequently of such 

 magnitude that the utilization of this factor of productiveness becomes a 

 practical question. It is therefore highly desirable to understand the 

 reasons why some crosses give favorable results and others give little or 

 no increase over the jield of the p>arents. A necessary step in this 

 direction is to develop a reliable method of measuring the effect of 

 crossing, apart from other factors that influence }-ield. 



The development of satisfactorv- methods of compearing the yield of 

 first -generation hybrids with that of their parents has been retarded by 

 (i) a failure to fuUy appreciate the importance of individual diversity 

 in hybrids, (2) the abnormal beha\-ior of seh'-pollinated maize plants, 

 and (3) the diMculty of securing for comp>arison hybrids and j>arents 

 with identical ancestry. It is believed that the method here described 

 avoids these difiaculties and affords more accurate means of comparing 

 first -generation maize hybrids mth their parents. 



The method is illustrated by an exp>eriment in crossing two varieties of 

 sweet com in which it was found that the progeny from one hybrid ear 

 yielded nearly double that of the other hybrid ear involved in the experi- 

 ment. To have taken either ear alone would have led to entirely erro- 

 neous conclusions regarding the increase secured as a result of crossing. 

 The increase in \ield due to crossing as measured by the method here 

 proposed was 31 per cent. 



