22 
BULLETIN 869, U. S. DEPARTMENT OE AGRICULTURE. 
Jet cross. It was of intermediate density and no more variable than 
the parental forms. The second generation is shown in figure 1 as 
a multimodal curve with peaks at densities corresponding to those of 
the parents and the F t generation. The homozygous forms pro- 
duced closely approximated the densities of the parental varieties, as 
is illustrated by the curves. Although there is considerable varia- 
bility in the means of the more lax segregates, this is no greater than 
the seasonal variation of the means of several of the 2-rowed forms. 
The contrast between the Pyramidatum x Jet and the HannaX 
Zeocriton crosses is very striking. Each showed wide segregation 
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/.& /.& 2.0 2>.2 2.-& 2.& 2.3 3.0 3.2 3.*? 3.& 3.3 -Z.O <9.2 <&.*? *?.& <?.3 
Fig. 1.— Diagrams showing the densities of parental forms and Fi and F 2 generations of a cross between 
the Pyramidatum and Jet barleys (upper) and of four homozygous forms from this cross in the F3 
generation (lower). 
in the F 2 generation. Hanna X Zeocriton, however, produced a much 
smaller proportion of homozygous forms in F 3 and F 4 than the 
Pyramidatum- Jet cross. Homozygous intermediates as well as forms 
with the parental densities were produced in the F 3 generation. The 
heterozygous lines were of different types, some being as variable as 
the F 2 , while others were more variable than the pure forms, but less 
so than the F 2 generation. The means of the heterozygous forms 
were also of different values. The results are illustrated in figure 2. 
These graphs show the parental and F 2 types and four pure F 3 forms 
of unlike densities, as well as the heterozygous lines obtained. This 
cross has given nearly all sorts of densities, and by this one cross the 
different densities of the parental forms used in these experiments 
have been again ob tamed. 
