6 BULLETIN 734, U. S. DEPARTMENT OF AGRICULTURE. 
migrating through the soil, attack the wheat seedlings, penetrating 
between the leaf sheaths, causing them to become wrinkled, distorted, 
and swollen. The larve so adjust their zone of infection that almost 
all remain near the young growing portion of the plant. In this 
way, as the plant grows they are elevated toward the flowering parts. 
When the plant blossoms, the larve, which up to 
this time appear not to have taken nourishment, 
enter the flowering parts, from which they ob- 
tain food. Here they develop sexuality, pair, lay 
eggs, and die. These eggs hatch and produce 
larve. When the wheat plant matures these 
larvee become coiled and dried up, forming the 
inner yellowish-white portion of the black gall 
as is shown in figure 5. The nematodes have great 
tenacity of life, and in many respects are analo- 
gous to the well-known 7 7richinae of pork. They 
bear a temperature of 125° F. and are also very 
resistant to frost and low temperature. 
Heads infected with the nematode disease re- 
semble heads infected with the stinking smut of 
wheat. They are usually thicker and shorter than 
normal heads, the glumes of the spikelet are 
spread somewhat, and in place of the normal seed, 
dark galls, incapable of germination and full of 
larvee, are to be found. 
Information gathered from those whose crops 
of grain have been infected with this disease is to 
the effect that it is easily recognized in the field 
on account of the darker green appearance of the 
heads and their somewhat longer maturing period. 
The plants are smaller, having a blighted and 
blackened appearance. Sometimes only one side 
of the spike is affected, while the other side is 
normal. There may also be some sound grains in 
the infected spikelet, and in some instances the 
head may not be infected at all, the only apparent 
infection being the formation of tumor-like or 
abcess-like elevations on the leaves of the plant. 
Figure 6 shows the similarity between wheat 
heads infected with the nematode disease and with the stinking-smut 
disease of wheat in comparison with an unaffected wheat head. 
Soil conditions seem to have an important bearing on the disease. 
Spots in fields which become water-logged, or parts of the field where 
trash has accumulated, show the greatest percentage of infected 
plants. : ee 
* 150 
iq. 4.—The nematode Tylenchus tritici. 
