Hayes and Garber - Cucurbit Breeding

104 BREEDING CROP PLANTS
crosses has been made at the Minnesota Station in cooperation
with the Office of Cereal Investigations (Hayes and Harlan,
1920). In a cross between Manchuria and Svanhals, the FI
proved nearly as dense as the Svanhals parent. Fz and F' 3
results showed these parents to differ by one main density
factor.
Pyramidatum, a dense, six-rowed form, was crossed with
Jet, a lax two-rowed form. The average length of internode of
Pyramidatum was 2.11 mm., of Jet 3.92 mm., of theFi, 2.86 mm.
of F 2 ,
3.01 mm. All forms were grown the same year. The
Fz generation gave a continuous range of variability which
reached beyond the modal classes of the parents. Forms bred
true in F 3 to densities which were not widely different from those
of the parents but no homozygous intermediates were obtained.
Apparently these parental types differ by a single main density
factor. There are other minor factors which influence the
expression of density. One such minor factor difference is
known. Some barleys have a slight progressive increase in internode
length from the base to the tip of the spike, in others all
internodes have nearly the same average length.
Different results were obtained in a cross between Hanna, a
lax, two-rowed variety, and Zeocriton, a very dense variety.
The F z gave somewhat similar segregation as in preceding
crosses, but the F* lines showed intermediates as well as extremes
breeding true. Certain F s families were as variable as F 2 ,
others were more variable than the parents, and still others were
homozygous. Four possible modes of density were found in
which homozygous segregates were obtained, the very dense
with means from 2.1 to 2.3, the dense with means ranging from
2.8 to 3.2, the lax with means ranging from 3.4 to 3.7, and the
very lax with means ranging from 4.2 to 4.3. If a large number
of types could have been tested, it seems very reasonable to conclude
that homozygous forms with an almost continuous range in
average length of internode from the very dense to the very lax
could have been obtained. Several main density factors are
here involved together with minor factors.
The Barley Awn in Relation to Yield. 1 The long rough
awn of barley makes the crop very disagreeable to handle.
Hooded varieties have been frequently tried out but have not
been extensively grown because they do not yield as well as
1
See HARLAN and ANTHONY (1920).