18 
BULLETIN" 137, U. S. DEPARTMENT OP AGRICULTURE. 
i 
k °22 23 24 2S 26 27 23 29 30 3/ 32 33 
Fig. 10. — Curve showing the density (num- 
' ber of internodes in 1 decimeter) of 100 
spikes of Manchuria barley from a field 
near Excelsior, Minn. 
The use of this formula, while it makes the statement of density 
more definite, disturbs the natural curve of the measurements to 
some extent. In all densities below 31 the tendency is to condense 
the grouping; above that fig- 
ure the opposite is true. The 
worst effect — that of bunching 
the figures when two-length 
measurements fall upon the 
same density — was avoided by 
the use of fractions. None of 
the curves have been smoothed, 
however, and it will be noticed 
that those of the greater den- 
sities, especially, are slightly 
rough. This roughness is more mathematical than real, but it 
seemed more desirable to present the figures as they were than to 
make them still more artificial by smoothing them. 
In a pedigreed strain the curve 
of density is normally sharp, with 
a single summit. If the seeding 
is not pure, or if the heads from 
two plats become mixed, the curve 
is- flattened and is characterized 
by more than one summit. Al- 
though included for another rea- 
son, the normal curve of a pedi- 
greed barley is well illustrated in 
figure 12. When this is compared 
with the curve of the field sample 
of Manchuria shown in figure 10, 
the significance of density is read- 
ily appreciated, especially when it 
is remembered that the Manchuria 
is what is known as a variety and 
contains no types that merge into 
such other 6-rowed varieties as 
Bay Brewing or Odessa. 
That density of selections is an 
accurate and comparable note in a 
nursery where the object is to 
obtain like conditions for all selections is shown in figure 11. The 
Sandrel was included twice in the 1913 planting. The beds were 
separated by such a distance as to represent the extremes of soil 
variation in the nursery. The difference in density is very slight. 
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1 t 
1 ' 
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/ / 
\v 
/ / 
1 \ 
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V \ 
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--. 
«. ^ 
40 
! 
to 
23 24 25 26 27 28 29 SO 3/ 
Fig. 11. — Curves showing the density of 
100 spikes from two plats of Sandrel 
(No. 35) barley planted in different 
parts of the 1913 nursery at St. Paul, 
Minn. 
