CORN" BREEDING 55 
trial in hybrid combination. This takes time and decreases the like- 
lihood of obtaining the best possible combinations. There also is 
little evidence as to the relative value of single crosses, double crosses, 
and synthetic varieties for commercial utilization and practically 
none as to the possibility of obtaining lines that are themselves high 
yielding. Much remains for the future. In the meantime the utili- 
zation of the facts already learned will permit an increase in the acre 
yield of corn on many farms just as soon as high-yielding crosses 
between selfed lines that are adapted to the various sections of the 
country can be found and as soon as practical methods for producing 
and distributing seed of such crosses annually can be developed. 
DISCUSSION 
So-called varieties of corn really are complex mixtures of hybrids. 
They can be modified easily and quickly up to a certain point by 
mass selection. If mass selection is effective at all beyond this point, 
progress is so slow that the results can not be demonstrated from 
year to year. Nearly all of the present varieties of corn have been 
adapted by mass selection to the widely different conditions under 
which they are grown. The productiveness of many of them can be 
further increased by careful selection of seed from normal, vigorous, 
productive plants of a type adapted to the specific environment. 
The same means may be relied upon to maintain the productiveness 
of varieties which already have reached the approximate limits of 
improvement by mass selection. This kind of breeding is a proper 
function of the farmer who grows his own seed corn or who may 
specialize in seed corn for sale. It also is the only kind of corn 
breeding which most farmers are justified in undertaking. 
Ear-to-row selection was suggested as a marked improvement over 
mass selection on the basis of theoretical considerations. The sound- 
ness of the underlying theory, in so far as it is sound, has been shown 
repeatedly by the larger yields obtained from the immediate prog- 
enies of higher yielding parent ears. Ear-to-row selection failed as 
a means of increasing commercial production chiefly because mass 
selection was more nearly its equal in efficiency than had been thought 
to be the case. Ear-to-row selection was concerned only with hybrids, 
the methods followed being planned carefully to maintain a high 
degree of hybridity. As a consequence, the productiveness of the best 
progenies was only that of hybrid mixtures averaging better than the 
mixture which constituted the variety as a whole. Maximum yields 
were prevented by the poorer components of these mixtures. Fur- 
thermore, nothing was fixed. Even the larger yield frequently ob- 
tained from the immediate progeny of a more productive parent ear 
was lost during the segregation and recombination that took place 
while the seed was being multiplied for commercial utilization. It is 
barely possible that special cases will exist in which the use of 
ear-to-row selection may be justified. In view of the labor and ex- 
pense involved and its negligible advantages over mass selection, how- 
ever, ear-to-row selection can not be recommended as a general 
method. 
Many ¥ 1 crosses between varieties of corn have yielded more than 
the average of their parents and some have yielded more than the 
better parent. The only varietal crosses that are of value commer- 
