358 



GENETICS IN RELATION TO AGRICULTURE 



hill and to state the yield of each of the four plants as a percentage of the mean of 

 the hill in which it grew. The percentage standing of each kind in all the hills 

 was then averaged to secure the final expression of the relative behavior of the 

 four kinds. 



"This method of comparison is similar to the ingenious plan originated by 

 C. H. Kyle, for use in ear-to-row breeding. Kyle's method is to plant each of 

 the ears to be tested in a separate row and in each hill to plant one seed of a stand- 

 ard, or check, ear with which all ears are compared. Since comparative and not 

 absolute yields are desired in the study of hybrids and with only four kinds to 

 compare, the introduction of a check in the present experiment would have 

 increased the space occupied by the experiment without lessening the experi- 

 mental error." 



FIG. 149. Parents and Fi hybrid between two sub-species of Zea mays: Hall's Tyler 

 dent (left), Brewer's flint (right) and hybrid (center). The hybrid yielded 9 per cent, 

 more shelled corn than the dent and 20 per cent, more than the flint and proved the 

 most productive of all varieties and crosses in the 1913 test. (After Hayes, Conn. A. E. S.) 



Crossing Species, Sub-species, Varieties and Local Strains. Many 

 experiments have been made to test the increase in productivity of FI 

 hybrids between more or less closely related forms of maize. As it is 

 impossible to review them all, we give as an illustration Collins' summary 

 of the results. of 16 crosses made in 1908 between corns of diverse types 

 and from widely separated localities. The classification indicated by 

 Collins' descriptions are as follows : Zea mays indentata (starchy or dent 

 varieties) Maryland, Kansas dent, Brownsville, Chihuahua, Mexican 

 dent, Xupha (semi-starch); Zea mays amylacea (floury variety) 

 Tuscarora; Zea mays everta (pop) Cinquantino, Algerian, Tom Thumb; 

 Zea mays indurata (flint) Guatemala red, Salvador Black; Zea hirta 

 Bonafous Hairy Mexican, Huamamantla, Arribeno; Unclassified 

 Hopi, Chinese (waxy endosperm), Quezaltenango Black, Quarentano. 

 The yields of the 16 crosses and of their parents are given in Table 

 LII. 



