2-4 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 



tions may be associated with the same variability which manifests 

 itself in seasonal fluctuations. They may be due to the differences 

 in the progressive density from the base to the tip of the rachis, which 

 is more marked in some than in other varieties. Other explanations 

 might be suggested, but in the absence of definite proof it seems 

 unwise to attempt a more detailed analysis of the results. 



CONCLUSIONS. 



Despite the handicaps of the investigations, a number of points are 

 established. 



(1) Internode length hi the barley rachis is a very stable character, 

 which is much less affected by environmental conditions than many 

 size characters. 



(2) Segregation occurs in the F 2 generation of crosses, and forms 

 homozygous for density apj^ear in this generation, their purity being 

 demonstrated in the F 3 generation. 



(3) In some crosses new lines with densities differing much from 

 those of their parents can not be secured, while in others lines with 

 very different densities may be isolated. 



(4) The inheritance of internode lengths may be interpreted on the 

 factor hypothesis. Some of the crosses studied appeared to differ 

 by a single main factor of density, while hi others two or three main 

 factors are necessary to explain the genetic results. Minor factors 

 were evident whose number or nature was not established and through 

 whose action the means of homozygous forms of intermediate 

 densities in some crosses ma}' become more or less continuous between 

 the means of the parents. 



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