478 MUTATION AND PLANT BREEDING 



ily means. The bars represent s G among F 5 progenies, given as geno- 

 typic coefficients of variability. 



Similar results are presented for crosses A and D in Figure 4. 

 Particular attention may be directed toward the comparisons of 

 the treatments in cross A. In cross A, PI and P2 are high-yielding, 



9 Cross B Cross C 



7c 



30 J 



20 J J 



10 . 



-10 . 

 -20 _ 

 -30 



HS 



J 



JJ 



J 



Cross mean 



J J j , J 



V J L 



J H 



PI P2 PIX P2X F FX PI P2 PIX P2X F FX 



Legend 



J 



J AMONG F. PLANT PKOG. 

 G 3 



Fj FAM x (F 6 generation) 



Figure 3. — F 3 variation in yield of P, PX, F, and FX among F 5 plant 

 progenies (in F 6 generation) of high and low F 2 families (selected in F,J 

 from two crosses (B and C). The variation is shown as in Figure 1. 



X-ray-induced mutants from the same pure line. Each of these 

 parental lines was selected because of its superiority in yield to 

 the pure breeding mother line from which it was derived. The 

 mother line received a dose of 18.5 Kr X-rays in 1949. The two 

 mutants and their hybrid received an additional 15 Kr in the X 3 

 generation to create what could be called the X 5 Xi and the 

 X 5 FiX x generations. The results shown in Figure 4 indicate not 

 only a substantial genotypic variance in PIX, P2X, and F 2 X but also 

 in the F 2 . 



The differences between the means of the high and low selec- 

 tions attained significance in 1960 in only 3 of the 11 comparisions 



