SELECTIONS 



329 



The futility of attempting to generalize regarding the effects of selec- 

 tions in plants must be obvious from what we now know about the com- 

 position of plant populations. With the application of Johannsen's 

 genotype conception in analyzing the composition of a field of maize the 

 problem of explaining the role of selection in the Illinois corn breeding 

 experiments was immediately simplified. This was perceived by Shull 

 who pointed out that the results of these experiments might be readily 

 explained on the ground that some hybrid combinations of genotypes 

 have greater capacity for the production of the desired qualities than 

 other combinations, and that the selection has gradually brought about 



FIG. 135. Result of selecting corn for high and low ears during 5 generations. The 

 white tape marks the position of the ears on the front row of plants in both plots. 



the segregation of those genotype combinations which had the highest 

 capacity for the production of the desired quality. 



Meanwhile Surface had made an illuminating analysis of the data 

 from the first 10 years of selection as reported by Smith. This treatment 

 is so valuable as to warrant its examination in some detail. At the time 

 the selections were made a careful record of the pedigree of each ear was 

 kept. These pedigrees are of course for the maternal side only since 

 self-pollination was not practised. From these data Surface prepared a 

 pedigree chart, for each of the four strains. The chart for the high- 

 protein strain is reproduced in Tables XL VIII and XLIX. As stated 

 above 24 ears containing the highest per cent, of protein were selected for 

 the 163 ears analyzed in 1896. These were given registry numbers from 

 101 to 124 inclusive as shown in column one of the two tables. For 

 convenience we may refer to these ears as the first generation of high- 



