Hayes and Garber - Cucurbit Breeding

FRUIT BREEDING 277
chromosome pairs. In heterozygous material, however, new
combinations of factors would be produced which might cause
changes in the external appearance of the organism. No cytological
basis for such cross-overs has been demonstrated.
Controlled Crosses. One of the earliest controlled experiments
in the breeding of fruits by crossing was started by Swingle,
in 1893, in Florida. This was an attempt to produce hardier
types by the use of wild citrus species. The hardy Chinese species,
Citrus trifoliata, was used as one of the parents. In 1897, 212
crosses were made between this species and orange varieties.
The three fruits that were produced gave thirteen hybrids, which
were so different from existing varieties of citrous fruits that
they were called "Citranges." Other crosses between citrous
species were made. One of the promising combinations was a
cross between the West India lime and the kumquat orange.
This orange is one of the hardiest of the evergreen citrous trees
while the lime is very tender. Further experiments are under
way and other promising wild relatives of the citrous fruits have
been obtained. Crosses of this nature are producing fruit varieties
which are successful in regions where citrous fruits could
not be grown formerly. The work shows .the necessity of a
thorough botanical knowledge of the wild relatives of the crop
which it is hoped to improve by breeding.
A somewhat similar method of work with the hope of producing
hardy apples for the Canadian Northwest was started by William
Saunders in Canada in 1888. The wild Siberian crab, Pyrus
baccata, which proved hardy on the prairies and withstood
temperatures of 50 below zero, was used as the female parent and
crossed with commercial apple varieties. Macoun (1915) states
that the fruit of Pyrus baccata averages J^ in. in diameter and is
quite astringent. The fruits obtained from some of the more
promising of the crosses were not so large as desired, although
some compared very favorably in size with ordinary crabs.
They were of good flavor and proved hardier than any varieties
of apples and crabs that had been tested up to that time. Several
are here listed.
Jewel, P. baccata X Yellow Transparent. Size 1.4 by 1.3 in.
Columbia, P. baccata X Broad Green.
Size 1.8 by 1.6 in.
Charles, P. baccata X Tetofsky. Size 1.6 by 1.5 in.
Recrosses between the best of these and apple varieties were