482 BOTANICAL GAZETTE [DECEMBER 
this hybridity. Previous conclusions that F, hybrids between self-fertilized 
strains are on the average equal in yielding capacity, and in certain combina- 
tions much superior, to strains cross-bred in the normal manner, have been — 
confirmed; also that reciprocal crosses are essentially equal. In addition it 
is shown that the yield and quality of the crop are functions of the particular 
hybrid combination, the results being the same whenever the cross is repeated. 
The F, was found no more variable than the pure self-fertilized parental strains, 
but the F, was considerably more variable, the coefficients of variability in 
latter gives no coefficients, clearly demonstrates the segregation of different 
grades of such purely quantitative characters. East has also presented 
similar evidence of the segregation of a quantitative character (height of 
stalk) in the F,, but he makes no reference to the reviewer’s corresponding 
results published a year earlier. He gives no coefficient of variability for 
pure strains, but his coefficient for the F, was 8.68 per cent, while in the several 
F, families it ranged from 12.02 per cent to 15.75 per cent. 
eory that the increased vigor of cross-bred maize plants is due to a 
stimulation accompanying heterozygosis requires that crossing within the 
same biotype or within the same F, shall give no advantage over self-fertiliza- 
tion in the same biotype or in the same F,. The reviewer™ has reported on a 
number of such sib-crosses in comparison with corresponding self-fertiliza- 
tions, the advantage in favor of the crosses being so slight that they can be 
fdirly accounted for by the lack of complete genotypic purity in some of the 
self-fertilized families. Crosses between sibs in ten self-fertilized families had 
an average height of 20 dm. and gave an average yield per acre of 30. 17 bushels. 
as compared with a height of 19.28 dm. and a yield of 29.04 bushels in the 
offspring of self-fertilized parents. In the F, those families which sprang 
from sib-crosses in the F, had an average height of 23.30 dm. as compared 
with 23.55 dm. in families produced from self-fertilized parents, and the 
corresponding yields per acre were 47.46 and 41.77 bushels respectively. 
These results show that cross-fertilization is of no (or little) advantage except 
when it brings together unlike hereditary elements. The relations of F, 
and F, in regard to height of plants and yield per acre strikingly emphasize 
the economic importance of using hybridized seed corn. Ten F; families had 
an average height of 25 dm. and produced an average yield of 68.07 bushels, 
9 Emerson, R. A., The inheritance of sizes and shapes in plants. Amer. Nat. 
44:739-746. Igo. 
* East, E. M., The genotype hypothesis and hybridization. Amer. Nat. 45: 
160-174. figs. 6. 1911 
* SHULL, G. H., The genotypes of maize. Amer. Nat. 45:234-252. fig. I. 19tt- 
