4 BULLETIN 869, II. S. DEPARTMENT OF AGKICULTURE. 
was not used in any of the crosses, but is included because of an 
inherited variation found in it. The form used is lax and differs 
from nutans in having only rudiments of lateral florets. 
RELIABILITY OF EXPERIMENTAL METHODS. 
In this investigation the feasibility and accuracy of density deter- 
minations were tested in many ways. The length of internode was 
computed from the measurement of 10 internodes in the middle of 
the spike. All measurements were taken in millimeters. 
To test the observational accuracy, the populations from wnich the 
density of three parents was determined were remeasured after a lapse 
of three weeks. The difference in the measurements of Manchuria 
was 0.02±0. 01 mm.; of Zeocriton, 0.04±0.01 mm.; and of Hanna, 
0.12 ±0.02 mm. Differences as small as 0.2 mm. in means of varie- 
ties, therefore, can not be demonstrated by the method used. As 
seasonal fluctuations in the means often are as great as this, the 
method of taking the data is sufficiently accurate. 
The internode measurement was taken in the middle of the spike, 
not only because of the greater convenience, but because experiments 
indicated that the internodes in this zone are less variable than in 
other parts of the spike. Measurements were taken in different parts 
of the spike on approximately 100 plants of each of the Zeocriton, 
Pyramidatum, Manchuria, and Hanna parents. Where the spikes 
were long enough, six different sections were measured, i. e., nodes 
1-11, 3-13, 5-15, 7-17, 11-21, and the last 10 internodes toward the 
tip. In Pyramidatum the measurements for nodes 7-18 and 11-22 
could not be made. The means for these measurements, in milli- 
meters, were as follows: Zeocriton, 1.37, 1.47, 1.66, 1.81, 1.95, and 
2.15; Pyramidatum, 1.98, 2.12, 2.17, and 2.15; Manchuria, 2.88, 
3.13, 3.35, 3.42, 3.36, and 3.38; Hanna, 3.90, 4.17, 4.40, 4.47, 4.35, 
and 3.90. 
The Zeocriton is the only variety in which there is a progressive 
increase in internode length from the base to the tip. If the factor 
or factors determining this progressive increase segregate in a normal 
way, the progeny of a cross between this type and one in which this 
peculiarity is absent or less pronounced, as in Pyramidatum, might 
contain types easily misinterpreted. The mean of a pure recessive 
for a main density factor might easily differ by 0.2 to 0.4 mm. from 
the parent, due to the gain or loss of this marked progressive increase 
of internode length found in Zeocriton. 
Contrary to results previously reported by Harlan (9), no change 
in internode length due to the presence of sterile nodes was observed. 
