20 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 



Iii the Hanna X Zeocriton cross there are a number of homozygotes 

 of a density intermediate between the densities of the parents. The 

 homozygotes of this cross appear to fall in groups. Three near the 

 dense parent have internode lengths ranging from 2.06 to 2.30 mm. 

 Three near the lax parent have internode lengths ranging from 4.15 

 to 4.30 mm. Four moderately dense intermediates have internode 

 lengths varying from 2.88 to 3.19 mm., and two lax intermediates 

 have internode lengths of 3.41 and 3.69 mm. This grouping is arbi- 

 trary, as the difference between the two intermediate groups is little 

 more than between individuals of either intermediate group. Some 

 homozygous intermediates from this cross have densities approxi- 

 mately the same as those of parents used in other crosses studied. 



SUMMARY OF RESULTS. 



The observational accuracy is such that differences in density 

 greater than 0.2 mm. are significant when the measurements are 

 taken in the middle part of the spike. 



Except in the Hanna and Steigum varieties the seasonal fluctua- 

 tions in the means of the parents were not more than 0.2 mm. The 

 seasonal variations in the means of the 2-rowed were greater than in 

 the 6-rowed varieties. 



The density of the F x generation does not have an unvarying relation 

 to the density of the parents. In the Svanhals X Manchuria cross 

 density is dominant in the F x generation. In the Pyramidatum X Jet 

 cross it was intermediate. 



The two F x generations grown were no more variable than the 

 parental sorts and all crosses gave segregation in F 2 . Although the 

 number of F 2 plants grown averaged no greater than that of the 

 parental forms, the frequency ranges extended from the modal class 

 of one parent to the modal class of the other and often beyond these 

 classes. 



The F 3 generation contained progeny groups which were no more 

 variable for length of rachis internode than pure lines of the parents. 

 Rather extensive studies of a number of F 4 generations gave further 

 evidence of purity of several of these F 3 lines. 



The Manchuria X Svanhals and Pyramidum X Jet crosses gave 

 forms homozygous for densities similar to those of the parents but 

 none homozygous for intermediate densities. Crosses between Hanna 

 and Reid Triumph and between Hanna and Zeocriton gave types 

 homozygous for densities intermediate between the densities of the 

 parents, as well as near those of their parents. The latter cross pro- 

 duced homozygous forms similar to Reid Triumph, Hanna, and their 

 homozygous intermediates, as well as forms like the Zeocriton parent. 

 The range of means of these homozygous forms was almost continu- 

 ous, although there was an indication of two centers of intermediate 



