SELECTION 327 
in F, hybrids in terms of dominance and linkage (p. 231, 2). The fact 
that different genotypes give diverse results when crossed is of immense 
practical significance. 
The Ear-to-row Method.—This has been the method of commercial 
corn improvement for many years and it is well illustrated by the Illinois 
corn breeding experiments, which have been going on continuously for 
over 20 years. The original purpose of the experiments was to produce 
new strains which would be more valuable as a source of feed for livestock. 
It was found that there was considerable variation in the relative amounts 
of protein and carbohydrates in the grains of different ears. Accordingly 
selection was begun with the object of increasing the protein and reducing 
the starch content of the grains; also of decreasing protein and increasing 
starch. As oil was worth three times as much as starch per unit of weight, 
selection for higher oil content was also begun. A low oil strain was 
started for comparison and such corn was soon found to be desirable for 
the production of pork and beef of high quality. 
The work was begun by Hopkins who picked out 163 ears of a local 
strain known as Burr’s White, made a chemical analysis of a few grains 
from each ear, and on that basis sorted them into four classes, viz., high 
and low protein and high and low oil. The strains were grown in isolated 
plots from the beginning. After 9 years of selection it was found to be 
necessary to prevent inbreeding. Accordingly in the tenth and succeed- 
ing years about 24 ears were selected for each plot and one row was 
planted from each ear, then the even numbered rows were detasseled. 
Subsequent selections were made from the detasseled rows, the first 
consideration always being high yield. Usually 20 ears were taken from 
each of the six higher yielding rows, or 120 ears for each plot. These 
were tested by chemical analyses and the most extreme variants in the 
desired directions were selected for the next planting. 
The results in general have been more regular in the high and low oil 
series than in the high and low protein strains. In the latter there seems 
to have been no very decided effect of selection after the first 10 years. 
Similarly there has been no continuous advance in the low oil strain since 
the seventeenth year of selection, but in the high strain the per cent. of oil 
has continued to increase slightly. The progressive effects of selection in 
the four series are graphically illustrated in Figs. 133 and 134. That the 
striking results depicted in these graphs were not caused by environ- 
mental conditions was proved by planting mixed plots with two grains of 
“high” and two of “low” corn in each hill so arranged that the resulting 
plants could be identified. This test, according to L. H. Smith, was made 
for three successive years, and subsequent analyses showed that under 
these conditions the different strains maintained their distinguishing 
chemical characters. 
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