28 BREEDING CROP PLANTS 



The general nature of the results in this field may be illustrated 

 by a cross between barley varieties which differ in the average 

 length of mternodes of the rachis (see Table I). 



In this cross between Hanna and Zeocriton, lax and dense 

 varieties respectively, the F 2 ranged from above the modal class 

 of Hanna to the modal class of Zeocriton even though only 141 

 individuals were studied. The calculated coefficient of varia- 

 bility for the F 2 was three or four times greater than for the 

 parental varieties. Several small F 3 families were grown from 

 Fz plants representing different densities. By examining the 

 table one will note that some F 3 lines bred comparatively true, 



FIG. 8. Average spikes of the Zeocriton (left), Hanna (right) and four homo- 

 zygous lines. Mean densities are as follows: Zeocriton, 1.9 mm.; Hanna X 

 Zeocriton, 448-1, 2.3 mm.; 448-5, 2.9 mm.; 448-11-3, 3.7 mm.; 448-16, 4.3 mm.; 

 Hanna, 4.6 mm. 



the ranges for density being no greater than for the parental 

 lines and the coefficients of variability also being low. Other 

 7' ! 3 lines were as variable as the F 2 generation while still others 

 were more variable than the parents but less variable than the F 2 . 

 Several F s lines, which appeared homozygous, were tested in 

 F 4 and some of these on the basis of the more extensive test again, 

 gave evidence of homozygosity. The general nature of the 

 results is illustrated in Fig. 9. These results show that homo- 

 zygous lines for density may be obtained in F 3 and F 4 , and that 

 in this cross homozygous lines were obtained which approached 

 the densities of the parents as well as homozygous lines with 



