INHERITANCE IN THE BAELEY SPIKE. V 
INHERITANCE OF LENGTH OF INTERNODES IN CROSSES BETWEEN 
PURE LINES. 
Each cross studied has been considered as a separate family. 
For convenience, the data from each such family will be discussed 
separately. In considering crosses, statements will be made as to 
the number of homozygous and heterozygous forms. Such state- 
ments can be only relative. Using the variability of the pure lines 
as a standard, it is assumed that progeny lines of low variability are 
homozygous, while those of high variability are heterozygous. There 
is no reasonable doubt of the classification of the extremes, but there 
is a borderland where the most varying homozygotes may be in doubt. 
FAMILY MANCHURIA (360) X SVANHALS (458). 
The actual F x generation of the cross between Manchuria and 
Svanhals, which was the basis of later generations discussed in this 
bulletin, was grown in 1915. A considerable number of crosses 
between these same pure lines of Manchuria and Svanhals were made 
in 1917 in the greenhouse at Washington, D. 0. The data for the F t 
reported in Table II (sec. A) are from this greenhouse seed. On the 
basis of the coefficient of variability, this F x generation proved 
no more variable than the parents. 
In 1917 the mean average density in millimeters of the Svanhals 
parent was 2.53 ±0.01 mm.; of the Manchuria, 3.34 ±0.01 mm.; and 
of the Fj, 2.70 ±0.01 mm. There is almost a complete dominance of 
the dense over the lax form. 
An F 2 generation was grown both in 1916 and in 1918. The means 
for these two F 2 generations were 2.94 ±0.01 and 2.96 ±0.02 mm., 
respectively. The variation as determined by the frequency distri- 
bution and the coefficient of variability was much greater in F 2 than 
in Fj_ or in the parental forms, the coefficient of variability of the F x 
generation being 6.30 ±0.30 mm. and of the F 2 generations of 1916 
and 1918, 10.20±0.27 and 11.82 ±0.48 mm., respectively. 
Thirty-two F 3 lines, representing all F 2 types of density, were 
grown. Thirteen of these F 2 plants appeared to give homozygous 
progeny in the F 3 generation. The writers recognize that too few 
plants were grown in F 3 to determine with certainty which forms 
were homozygous. Eight of these 13 lines were continued in F 4 , and 
five of these appeared to be homozygous. These results show that a 
considerable number of the F 2 plants selected bred true in F 3 , although 
no conclusion as to the actual percentage can be made. 
The five types which proved to be homozygous in F 4 gave mean 
densities as follows: 378-1, mean 2.57 ±0.01 mm.; 378-11, mean 
2.64 ±0.01 mm.; 378-14, mean 3.37 ±0.02 mm.; 378-23, mean 2.55 ± 
0.01 mm.; 378-31, mean 2.58 ±0.01 mm. Selection 378-88 gave the 
highest coefficient of any third-generation line. Two heads were 
selected which bred true in F 4 for densities near the Manchuria parent. 
182694°— 20— Bull. 869 2 
