CORN BREEDING 33 
HYBRIDIZATION 
Many of our present agronomic varieties of corn originated as 
intentional or accidental hybrids. Thus, Reid originated from a 
mixture (with consequent crossing) of Gordon Hopkins corn and -an 
early-maturing yellow variety grown generally in Tazewell County, 
111. The Gordon Hopkins corn, seed of which was brought from 
Brown County, Ohio, failed to mature well in Illinois in 1846. The 
immature seed from this crop produced a poor stand when planted 
in 1847, and the missing hills were replanted with local corn. Seed 
from the mixed crop of 1847 was the foundation stock from which 
Reid was developed by careful selection. Many other varieties 
originated similarly. 
This is typical of the usual function of hybridization in plant 
breeding. Indeed, plant breeding consists essentially in hybridizing 
to create new combinations from which to obtain the best by selec- 
tion. Because of the fact that corn is cross-fertilized so largely, 
even the most carefully selected varieties are only mixtures of 
hybrids within which there already is an abundance of variation. 
Hybridization as a basis for obtaining new combinations conse- 
quently has not played an important part in recent corn improve- 
ment. The present discussion will be limited, therefore, to the utili- 
zation of F x crosses between varieties of corn as a means of obtaining 
larger yields. 
As early as 1876, Beal (5) of the Michigan Agricultural Experi- 
ment Station called attention to the larger yields frequently obtained 
in the first generation after crossing two varieties of corn and 
suggested that such F x generation crosses or hybrids might be used 
to obtain increased corn yields generally. * 
Many crosses between varieties of corn have been compared with 
their parents. The yields of 244 crosses between standard varieties 
of corn, previously summarized (62), may well be taken as an ex- 
ample of what is to be expected in such comparisons. Of the 244 
crosses, 201 yielded more than the average of the parents and 43 
yielded less than this average. This is striking evidence of the 
tendency of hybrid vigor to increase yields. It does not mean that 
all of the 201 were really advantageous crosses, however. Such a 
cross must yield more than the best local varieties to be worth grow- 
ing commercially. Of the 244 crosses referred to, 86 (about one- 
third) yielded over 5 per cent more than the better parent. There 
is no way of telling exactly how many of them were better than the 
best local varieties, but possibly less than 25, or about 1 out of 
every 10. 
MAINTAINING HYBEID SEED 
As hybrid vigor is limited to the first generation, it is necessary 
to produce the hybrid seed each year (or a supply for two years 
every alternate year). A plan has been suggested for doing this 
conveniently while at the same time maintaining pure seed stocks 
of the parent varieties (9). As this is applicable equally well in 
producing seed of crosses between selfed lines, it will be given in 
some detail. 
