22 



BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 



Jot 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 x 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 JHannaX 

 Zeocriton crosses is very striking. Each showed wide segregation 



so 



JO 



40 



30 



X 20 



I 



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1 

 1 



i 



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1 

 < 

 1 



\ 

 \ 































r 

 f 

 1 



1 

 \ 



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1 

 1 





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'/=/ 







^S\ 





9 











/.& /.ff 2.0 2.2 2.4 2.& 2.3 3.0 3.2 3.4 3.& 3.3 4.0 4.2 4.4 4.& 4.3 



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 F 3 

 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 obtained. 





