20 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTUKE. 
In 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 Fj 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, drosses 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 
