104 BREEDING CROP PLANTS 



crosses has been made at the Minnesota Station in cooperation 

 with the Office of Cereal Investigations (Hayes and Harlan, 

 1920). In a cross between Manchuria and Svanhals, the FI 

 proved nearly as dense as the Svanhals parent. Fz and F 3 

 results showed these parents to differ by one main density 

 factor. 



Pyramidatum, a dense, six-rowed form, was crossed with 

 Jet, a lax two-rowed form. The average length of internode of 

 Pyramidatum was 2.11 mm., of Jet 3.92 mm., of theFi, 2.86 mm. 

 of F 2 , 3.01 mm. All forms were grown the same year. The 

 Fz generation gave a continuous range of variability which 

 reached beyond the modal classes of the parents. Forms bred 

 true in F 3 to densities which were not widely different from those 

 of the parents but no homozygous intermediates were obtained. 

 Apparently these parental types differ by a single main density 

 factor. There are other minor factors which influence the 

 expression of density. One such minor factor difference is 

 known. Some barleys have a slight progressive increase in inter- 

 node length from the base to the tip of the spike, in others all 

 internodes have nearly the same average length. 



Different results were obtained in a cross between Hanna, a 

 lax, two-rowed variety, and Zeocriton, a very dense variety. 

 The FZ gave somewhat similar segregation as in preceding 

 crosses, but the ^3 lines showed intermediates as well as extremes 

 breeding true. Certain Fs families were as variable as Fz, 

 others were more variable than the parents, and still others were 

 homozygous. Four possible modes of density were found in 

 which homozygous segregates were obtained, the very dense 

 with means from 2.1 to 2.3, the dense with means ranging from 

 2.8 to 3.2, the lax with means ranging from 3.4 to 3.7, and the 

 very lax with means ranging from 4.2 to 4.3. If a large number 

 of types could have been tested, it seems very reasonable to con- 

 clude that. homozygous forms with an almost continuous range in 

 average length of internode from the very dense to the very lax 

 could have been obtained. Several main density factors are 

 here involved together with minor factors. 



The Barley Awn in Relation to Yield. 1 The long rough 

 awn of barley makes the crop very disagreeable to handle. 

 Hooded varieties have been frequently tried out but have not 

 been extensively grown because they do not yield as well as 



1 See HARLAN and ANTHONY (1920). 



