582 Journal of Agricultural Research voLxix.no. n 



GENETIC GROUPS INDICATED BY THE PROGENY CLASSES 



The F2 plants in Table I are arranged in groups according to the segre- 

 gation shown in the F3 generation. 



Group I consists of plants which gave only 6-rowed progeny in the 

 F3 generation. Since the parents were 6-rowed, the plants in this group 

 are unquestionably homozygous for this character. 



Group 2 consists of plants which gave 6-rowed and intermedium but 

 no 2 -rowed forms. The Fj plants evidently correspond to those in the 

 high -fertility column of the Fg classification The classification of the 

 high-fertility grOup is readily made and is highly accurate. Since this 

 group gave 6-rowed, high-fertility, and intermedium segregates in ap- 

 proximately a I to 2 to I ratio, it is safe to assume that the high- 

 fertility plants are heterozygous for 6-rowed X intermedium which dififer 

 by a single factor. 



Group 3 gave all three homozygous classes and all heterozygous 

 classes as well. From this it is obvious that this group is comparable 

 to the F2 generation and is heterozygous for the same factor differences 

 as separate the original 6-rowed X 2-rowed forms. 



Group 4 gave 6-rowed, low-fertility awned, and 2-rowed forms in 

 approximately a i to 2 to i ratio. Since this low-fertility awned corre- 

 sponded in appearance to the Fj parents, it would seem that this group 

 also was heterozygous for 6-rowed X 2-rowed, which in this instance, 

 however, represents a single factor difference. It gave no intermedium 

 forms, nor did it give the high-fertility awned or the low-fertility awnless 

 forms. In other words, the intermedium character in both its homozygous 

 and its heterozygous aspects was absent. The fact that this group as 

 well as group 3 is heterozygous for 6-rowed X 2-rowed, even though 

 more factors are involved in one case than the other, can be reconciled 

 only on the basis that there are two types either of the 6-rowed or of 

 the 2-rowed forms, only one of which carries the possibilities of pro- 

 ducing intermedium forms. 



Group 5 consists entirely of Fj plants which gave only intermedium 

 forms in the F3 generation. In other words, out of 87 Fj plants there 

 were 7 homozygous for the the type which has been noticed so rarely in 

 barley studies and whose very occurrence has been questioned so fre- 

 quently. That the Fg plants showed no higher fertility was doubtless 

 due to their being grown in the greenhouse. Those plants of the F, 

 generation falling in the low-fertility class merely show the variation 

 which exists. They do not cast any doubt on the genetic character of 

 the F2 parents, because there were no 2-rowed segregates from any of 

 the seven F2 plants. 



Group 6 gives homozygous intermediates, low-fertility awnless, and 

 no-fertility awnless. The numbers in the classes are not significant in 

 this case, for some sterile spikes of intermedium and the larger part of 



