414 



G. F. SPRAGUE 



Comparisons between the two systems of breeding may be made in a num- 

 ber of ways. Selection during inbreeding is normally practiced within and 

 among families. If only the two families having the highest oil percentage 

 were retained and these compared with the mean of the second cycle popula- 

 tion, the differences are very slight but in favor of the selfing series. If these 



S2 S3 S4 S5 



Gana fO'Hona of I nbnaedinq 



Fig. 26.4 — A comparison of mean oil percentages in the corn kernel from the recipro- 

 cal backcrossed Illinois High Oil X wxOs420 during five generations of inbreeding and 



selection. 



two lines are compared with the extreme deviate of the recurrent series the 

 lines are lower in oil by nearly three per cent. If the comparison is made 

 between the mean of the S5 lines and the mean of the second cycle population 

 the lines are again lower, the contrast being 7.5 and 10.5 per cent of oil 

 respectively. 



Any comparison involving these two series must also take into account 

 the time at which the comparisons were made. In the selfing series, genetic 



