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



2.84 ±0.02 mm.; 406-19, mean 3.29 ±0.01 mm.; 406-22, mean 

 4.37 ±0.01 mm. 



Aside from these, individual heads grown in F 4 which appear to 

 give homozygous progeny as a result of the single season's test are 

 as follows: 406-4-3, mean 3.72 ±0.03 mm.; 406-9-1, mean 4.30 ±0.04 

 mm.; 406-18-5, mean 3.40 ±0.02 mm.; 406-18-9, mean 2.66 ±0.02 

 mm. 



The means for these four F 4 families are somewhat unreliable 

 because of the small number of individuals grown. All coefficients 

 of variability, however, are very small. 



These results show that homozygous intermediates may be pro- 

 duced, as well as homozygous types, which give about the same aver- 

 age density as the parental forms. No analysis of average differ- 

 ences as small as 0.2 to 0.3 mm. has been attempted. The fact that 

 environmental or other seasonal characters may modify the expres- 

 sion of a character nullifies such close analysis. 



FAMILY "HANNA (460) X ZEOCRITON (1039). 



The Hanna used in the cross with Zeocriton is the same pure line 

 that was used in the cross with Reid Triumph. Zeocriton is a very 

 dense 2-rowed form. This cross is between the most dense and the 

 most lax form used in this study. 



The F 2 generation shown in Table II (sec. E) ranged from above 

 the modal class of Hanna to the modal class of Zeocriton, even though 

 only 141 individuals were studied. It has a correspondingly high 

 coefficient of variability. 



An examination of the coefficients obtained in later generations 

 show that some are as large as those obtained in the F 2 line. Others 

 are intermediate, being significantly larger than any obtained in the 

 pure forms, while still others are as small as those obtained for the 

 pure parental lines. This would indicate that the mode of inheritance 

 was more complex than in the cross between Pyramidatum X Jet 

 previously mentioned. 



Selection 448-9, which was almost as variable in the F 3 as in the 

 F 2 generation, was selected for further experiment, the progeny of 

 30 plants being measured in the F 4 generation. Data from 7 of the 

 30 progeny lines are presented, as the remaining 23 all appeared to 

 be segregating. Results of density studies in F 4 lines 448-9-7, 

 448-9-14, 448-9-16, and 448-9-29 are given, as these indicate the 

 segregation obtained in the unpresented lines. No F 4 line of greater 

 coefficient of variability than 448-9-7 was obtained, and none with a 

 wider frequency range than 448-9-16. Three lines appear to be 

 homozygous, as determined by the frequency distribution and coeffi- 

 cient of variabilitv. These are shown in Table III. 



