Sept. 1. 1920 Fixed Intermediate, Hordeum intermedium haxtoni 583 



one heterozygous group are included with the homozygous 2 -rowed as 

 phenotypes. The F2 plants in group 6, however, unquestionably are 

 heterozygous for intermedmm X 2-rowed, a single main factor difference 

 separating the intermedium and 2-rowed forms. 



Group 7 may be considered as composed of plants homozygous for 

 2-rowed, since with the exception of the two plants noted there was no 

 fertility exhibited in the progeny. 



The seven groups just discussed consist of Fj plants assembled in groups 

 because of their evident similarity of genetic constitution. In other 

 words, these groups are genetic classes in contradistinction to the pheno- 

 typic classes of the F3 generation. In Table II the data on these groups 

 are summarized. The second column of this table gives the genetic 

 constitution of each group. Except for the subdivisions ot group i, 

 this classification was verified in the F3 generation. In the third column 

 a hypothetical formula is suggested for each group. These formulas are 

 based on a 2 -factor difference between the 6-rowed and the 2-rowed 

 forms. The Manchuria 6-rowed parent is supposed to possess both fac- 

 tors, while in the 2-rowed Svanhals parent both supposedly are lacking. 



Table II-^ — Summary of Fn plants of the cross between Manchuria and Svanhals 



This hypothesis accounts for the results very well. The 2-rowed 

 segregates of group 7 are homozygous in the absence of both factors. 

 The fixed intermediates or H. intermedium forms of group 5 are homo- 

 zygous for the presence of one factor and for the absence of the other. 

 The heterozygous groups, 2, 3, 4, and 6, are all heterozygous for one or 

 both factors. Groups 2, 4, and 6, which are heterozygous for only one 

 factor, give F3 progeny of limited distribution. Group 3, which is 

 heterozygous for both factors, gives all classes in the F3 generation.- 



