INHERITANCE IN THE BARLEY SPIKE. 15 



The Svanhals parent gave a mean of 2.71 ±0.01 mm. and the 

 Manchuria one of 3.46 ±0.01 mm. in 1918. No sorts were obtained 

 which were homozygous for densities very different from those of 

 the parents. 



FAMILY MANCHURIA (360) X STEIGUM (17). 



The parental forms of the Manchuria and Steigum cross gave 

 nearly the same average density in 1916. In 1918 the Manchuria 

 parent gave about the same average density as in 1916, but the 

 Steigum averaged somewhat higher than in the previous year. The 

 coefficient of variability of the Manchuria parent in 1917 was 4.19 ± 

 0.15 mm.; of the Steigum parent, 4.90 ±0.17 mm.; and of the F 2 gen- 

 eration which was grown in 1916, 7.69 ±0.21 mm. The data are 

 reported in Table II (sec. B). 



As Table II shows, some forms bred true in F 3 and in F 4 , while 

 others were as variable as the F 2 generation. Selection 368-22 in 

 the F 3 and F 4 generations gave means of 3.21 ±0.02 and 3.29 ±-0.01 

 mm., respectively. When compared with the parental forms, it 

 seems that we have here a lower density line than either parent. As 

 the number of individuals is small in many F 3 lines, it does not seem 

 profitable to analyze more closely the results obtained. 



FAMILY PYRAMIDATUM (476) X JET (454). 



Table II (sec. C) shows that the parental forms of the cross between 

 Pyramidatum and Jet are of very different densities. The Pyrami- 

 datum parent gave a mean density of 2.11 ±0.01 mm. in 1918; 

 the Jet, 3.92 ±0.01 mm.; while the F t generation averaged 2.86 ±0.01 

 mm. The F x generation is, therefore, slightly more dense than the 

 parental average, which is 3.01 mm. This is quite different from the 

 F l generation in the cross between Manchuria and Svanhals, in which 

 there was an almost complete dominance of the dense over the 

 lax form. 



The F 2 generations were grown both in 1916 and in 1918. The 

 means for these two F 2 generations were about the same as the 

 parental average, being 2.92 ±0.04 mm. and 3. 10 ±0.03 mm., respec- 

 tively. The highest coefficient of variability for the Jet parent is 

 6.93 ±0.39 mm., while the highest coefficient for Pyramidatum is 

 6.16 ± 0.21 mm. The coefficients of variability for the two F 2 genera- 

 tions are 16.44 ±0.87 mm. and 18.38 ±0.81 mm., respectively, while 

 the frequencies of the F 2 generations range from above the modal 

 class of the lax parent to the modal class of the dense parent. It is 

 of interest to note that with a total of 87 F x plants, none were of the 

 same frequency range as that of the parents, all being of intermediate 

 density. Of the 22 F 2 plants continued in F 3 , ten would have been 

 included within the limits of this F x population. Of these ten, eight 

 gave about as variable a progeny as the F 2 generation, while two 



