INHERITANCE IN THE BARLEY SPIKE. 5 
EFFECTS OF ENVIRONMENT AND VARYING SOURCES OF SEED ON 
DENSITY. 
Wide differences of condition, such as obtain in California as com- 
pared with. Minnesota, are sufficient to modify the expression of 
density. As will be seen by referring to Table I, the annual fluctua- 
tions of density measurements in a pure variety are not sufficient in 
Minnesota to introduce any large error in the conclusions, especially 
when it is considered that progeny are compared only with parents 
"of the same year's growth. 
In 1918 there was an opportunity to test the effect of Yigor of plant 
on density. One section of the nursery produced Manchuria plants 
which averaged 110 centimeters in height, while the same strain in 
another part of the nursery averaged only 82 centimeters. A similar 
difference was apparent in Svanhals. The internode lengths of the 
Manchuria plants were 3.36 ±0.01 and 3.33 ±0.01 mm., respectively, 
and of Svanhals, 2.56 ±0.01 and 2.65 ±0.01 mm., respectively, both 
being within the limits of observational accuracy. 
Sometimes the F x generation of a cross was grown in the Washing- 
ton greenhouse and the seed from it was still rather immature when 
sown in Minnesota. Plants of Manchuria from greenhouse seed gave 
a mean internode length of 3.22 ±0.02 mm., as compared with 
3.34 ±0.02 mm. in plants from field-grown seed. In Svanhals, the 
difference was less, 2.49 ±0.02 as compared with 2.52 ±0.01 mm. 
Neither variation is large enough to have any particular significance 
in this study. 
PURITY OF PARENTAL FORMS. 
The variation which may be expected in a pure line within a single 
season and from season to season is shown in Table I. The 6-rowed 
varieties gave about the same mean average length of internode in 
all three seasons. With the 2-rowed varieties there was more seasonal 
fluctuation in average density. All varieties of this group gave a 
higher mean length of internode in 1918 than in 1917. In Steigum 
the seasonal difference reached its maximum of 0.51 ±0.03 mm., 
and in Hanna the seasonal variation also was large. Individuals 
of different densities in the different varieties were selected as 
parents. The only possibility of inherited variation within the same 
variety occurred in deficiens. The progeny of plant 333-5-1 is sig- 
nificantly lower in mean density. Only two or three deficiens types 
have been grown in the nursery, and the progeny showed no evidence 
of hybridization. As the chance of mixture or accidental crossing 
is small, it might be interpreted that we had chanced to select a spike 
in which a sudden change in the factors for density had taken place. 
