10 BULLETIN 842, U. S. DEPARTMENT OF AGKICULTURE. 
have grown together and usually show separate interior cavities, as 
well as deep external furrows, along the lines where the separate 
units have coalesced. The simple galls are by far the more common 
and usually occur singly in each flower, although as many as three 
separate galls have been found in a single flower. Sometimes a 
young gall may be seen developing in place of one stamen, while the 
other two stamens and the pistil still appear almost normal. It is 
rather rare, however, for a normal kernel and one or more galls to 
develop within the same flower. A young gall is not uncommonly 
found in place of each of the three stamens, and later these may 
produce a single trilobed compound gall. In such cases ovarial de- 
velopments are absent. More commonly, however, a single gall is 
initiated either in the ovary or the young staminate tissues, and it 
then usually causes atrophy or nondevelopment in the other repro- 
ductive parts of the flower. 
Only the reproductive organs or adjacent tissues of the flowers 
have been found affected, but every flower on a spike may be in- 
vaded. It is not uncommon, therefore, to find every flower of a 
mature spike containing nothing but galls. Heads of wheat well in- 
fected with larva? are often reduced in size, have their glumes stick- 
ing out at a greater angle from the rachilla than normal ones, and 
mature somewhat later than the uninfected spikes. Because of their 
thickness, the dark maturing galls are often not entirely covered by 
the glumes, so that they become exposed and thus serve as a con- 
spicuous symptom whereby infected spikes may be readily distin- 
guished in the field (PL III). 
CAUSE OF THE DISEASE. 
The cause of the nematode disease discussed in this paper may 
be readily seen with the unaided eye when the contents of a gall 
are placed in clear water. With the aid of a hand lens, the milky 
white fibrous mass thus liberated, as shown in Plate V, B, can be 
readily observed to consist of thousands of straight or curved 
threadlike elements, the larvae of the nematode Tylenchus tritici 
(Steinbuch) Bastian. If watched carefully they will be seen soon to 
begin active eellike movements. Occasionally among a white mass 
of larvae from a mature gall one may see with the naked eye the 
brown misshapen remains of adult males and females, and with the 
assistance of a microscope find a few eggs, the stage from which 
the larvae developed. In young galls, living adults of both sexes 
and an abundance of eggs and larvae may be found. 
EGGS. 
When viewed from the end the eggs seem to be almost perfectly 
circular in cross section, fe. lateral view, which is that most com- 
monly seen (fig. 2), they are elongate, granulated bodies, usually 
