BEGINNINGS OF THE HETEROSIS CONCEPT 41 



planted in new plots of ground about one-fourth mile north of the original 

 Station grounds. 



The purpose of this replication was to determine the degree of consistency 

 of results secured in these new locations with those recorded for the cultures 

 grown in the different conditions of soil, drainage, exposure, lighting, etc., in 

 the East Garden. Summaries of these two sections of Table 2.7 show the cul- 

 tures grown in the new plot with average grain-row number 1.29 per cent 

 higher than in the same families grown in the East Garden. However, the 

 East Garden cultures produced a higher average yield of ear-corn by 4.70 

 per cent. 



Comparison between selfing and sibcrossing was made a subject of special 

 study in the inbred and Fi families in 1910. This was not continued in 1911 

 in the inbreds, but was given a further test in the derivation of the F2 families 

 from the Fi, and was carried forward to the derivation of F3 families from the 

 F2. These comparisons as they relate to Fi families are given in sections E 

 and F of Table 2.7. They show the F2 families derived from selfing their Fi 

 parents slightly superior to those Fo families produced from sibcrosses in 

 the Fi. This is indicated by an average grain-row number 3.1 per cent higher 

 and average yield 7.5 per cent higher in the Fo families from selfed Fi par- 

 ents, thus reversing the indications from the 1910 cultures. 



The comparison of selfing versus sibcrossing in the production of the F3 by 

 these two methods of breeding in F2 can be derived from section G for selfings 

 and section H for the sibcrosses. Summaries of these two sections show a 

 superiority from sibcrosses of 0.4 per cent in average grain-row number and 

 61.6 per cent in yield. A part of this discrepancy is clearly due to the inclu- 

 sion of families in the selfed group which had no direct counterpart in the 

 sibcrossed group. If we limit the comparison to the families which are repre- 

 sented in both groups, we can avoid this cause of distortion. We then find 

 the sibcrossed families superior to the selfed by 1.5 per cent in grain-row 

 number, and 48.6 per cent in yields. 



Comparative values between inbreds and crossbreds, as shown in sections 

 A and B of Table 2.7, and between crossbreds and Fi hybrids, are essentially 

 the same as in 1910. The ratios of inbreds, crossbreds, and Fi hybrids, with 

 respect to yields, is 0.29 to 1.00 to 1.22. Again the average grain-row number 

 is less in the Fi than in the crossbreds, and for the same reason. This particu- 

 lar group of Fi families came from parents with low average grain-row num- 

 bers, as compared with the broader parentage of the crossbreds. 



The relationship of F.-s to Fo can now be noted by comparing the results 

 in sections G and H of Table 2.7, with sections D, E, and F. There are sev- 

 eral ways in which such comparisons can be made. Perhaps as good a way 

 as any is simply to combine all of the F2's together, regardless of the con- 

 siderations which led these to be tabulated in three separate sections, and 

 compare the results with all the F3 families of sections G and H likewise 



