Mar. 22, 1924 
Nematode Disease Caused by Tylenchus tritici 
937 
HEAD SYMPTOMS 
The diseased heads generally differ from the healthy heads in size and 
shape, and sometimes in color. They also remain green longer than 
healthy ones. A healthy wheat head between two diseased heads is 
shown in Plate 3, C and D. Occasionally, however, we find diseased 
heads which compare favorably in size with uninfected ones. Especially 
is this true when they contain but few galls. The glumes of the diseased 
ears stand out more nearly horizontally, especially when immature, owing 
to the greater diameter of the galls as compared with that of the kernels. 
This makes the heads resemble somewhat those infected with bunt. In 
rye this is not so much the case, for the galls in this cereal usually are 
smaller than the rye kernels, and, unless a head is badly diseased, it may 
closely resemble a healthy one (PI. 3, E and F). 
The infected culms, as a rule, are shorter than the healthy ones. Appl 
(r) gives an average difference between the two of about 10 cm. A 
similar shortening was observed in the infected wheat and rye in the 
experimental plats at the Arlington Experiment Farm. Measurements 
of several hundred healthy and diseased culms of wheat showed an aver¬ 
age difference of 12 cm. Data on the weight of the straw and grain 
from normal and diseased rye plants showed that the reduction in the 
yield of straw and grain from infected plants was considerable (Table V). 
If one head in a stool is infected it does not necessarily follow that the 
others in that stool also are diseased. Just as we may have galls and 
normal kernels in the same head, so also there may be both diseased 
and healthy heads in the same plants. This fact was established by 
sowing heavily inoculated kernels several inches apart so that the plants 
would stool profusely. The plants were examined carefully at maturity 
and the individual heads threshed. The data obtained are presented 
n Table X. 
Table X .—Number of healthy and infected heads in individual stools of wheat grown 
on inoculated soil at the Arlington Experiment Farm, Rosslyn, Va., in IQ 20 
Number of culms in the stool. 
Infected 
heads. 
Healthy 
heads. 
Shat¬ 
tered ® 
and 
sterile 
heads. 
6 . 
5 
1 
0 
3 
1 
0 
2 
2 
0 
8 
0 
4 
1 
3 
0 
4 
9 
2 
4 
3 
2 
3 
3 
0 
6 
z 
2 
1 
7 
8 
s 
2 
1 
6 
2 
S 
a Shattered heads include those partly or wholly threshed by birds or by handling before final data 
were obtained. 
NUMBER AND ARRANGEMENT OF GALES IN SPIKELETS 
In healthy wheat and rye a spikelet usually produces tsfro or three 
kernels, one in each developed floret. But in wheat affected with the 
nematode disease a floret often produces two to four galls, formed from 
