Hayes and Garber - Cucurbit Breeding

CLASSIFICATION AND INHERITANCE OF SMALL GRAINS 99
In classifying the cultivated varieties of barleys, the density
of the spike, its shape, and the appearance of the awns as well
as the color of the seed, have been used. Smooth-awned varieties
are being produced and it is only a question of time before
nearly all awned varieties will be represented by both the rough
and smooth-awned forms.
Species Crosses. Two general results have been obtained
from crossing two- and six-rowed varieties. The most frequent
result is an intermediate condition in FI in which the lateral florets
are awned, but produce little or no fruitfulness. In F 2 a 1 : 2 : 1
ratio of six-rowed, intermediate, and two-rowed forms is obtained.
Six-rowed and two-rowed forms breed true to these respective
characters in later generations. Results of this nature can easily
be explained on a single main factor difference (Biffen, 19076;
Gaines, 1917).
The intermedium barleys have generally been considered to
be of hybrid origin. A cooperative study carried on at the Minnesota
Experiment Statioa has shown the probable origin of some
intermedium forms (Harlan and Hayes 1920). In a cross between
Manchuria, a six-rowed barley, and Svanhals, a two-rowed
variety, the F\ was slightly fruitful and produced intermediate
developed awns on the lateral florets. In F 2 a wide range of forms
was obtained. The genetic nature of the F 2 plants was determined
by growing seed of each in F 3 . From the F 3 results it
was possible to classify F% plants as follows :
1. Those that bred true for the six-rowed character.
2. Those that segregated, giving six-rowed, awned intermediate forms
with very high fruitfulness of the lateral florets and intermedium, forms in
a 1:2:1 ratio.
3. Intermedium forms that bred true, giving few or no awns on lateral
florets and producing approximately 50 per cent, of barren lateral florets.
4. Those that gave all forms as in F-z.
5. Those that produced intermediates and tw r o-rowed types.
6. Those that produced six-rowed, awned intermediates with little or no
fruitfulness in the lateral florets and two-rowed forms in a 1:2:1 ratio.
7. Those that bred true for the two-rowed condition.
Results were accurately explained by considering the Manchuria
parent to contain two factors, one for six-rowed and one for
intermedium, which was hypostatic to the six-rowed factor. It