BULLETIN 137, U. S. DEPARTMENT OF AGRICULTURE. 



Fig. 10. — Curve showing the density (num- 

 ber of internodcs 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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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. 



