Hayes and Garber - Cucurbit Breeding

268 BREEDING CROP PLANTS
condition of most fruit material.
A commercial variety may be
extremely valuable and yet be heterozygous for many characters.
On the other hand, the commercial variety may be homozygous
for a large part of its characters. It seems reasonable to conclude
that the more nearly homozygous the parental variety,
other things being equal, the greater value it would have as a
parent.
The ability of impressing its characteristics upon the larger
part of its offspring has been called prepotency by animal breeders.
Such prepotency is genetically explained by the supposition that
the prepotent parent is homozygous for certain dominant factors
for the characters under observation. Hedrick and Wellington
(1912) showed that some crosses between apple varieties produced
a considerable percentage of individuals with small fruits.
Thus the cross between Rails and Northern Spy gave great
variability in size of apples, while the cross between Sutton and
Northern Spy gave progeny in which no trees were obtained
which produced small fruit. One of the great difficulties is that
it takes several years to learn the varieties which when crossed
will give certain desired combination.
Another difficulty which must be considered is that many
varieties of fruits are self-sterile. This is of utmost importance
in commercial fruit production for it is necessary to interplant
such a variety with some variety which produces an abundance of
pollen which is capable of fertilizing the variety in question and
TABLE LXXI.
INCREASE IN WEIGHT OF SEED AND FRUIT DUE TO CROSS-
POLLINATION
Pollination