16 BULLETIN 842, U. S. DEPARTMENT OE AGRICULTURE. 
stages of development, including sexually mature females almost 
ready to lay eggs. This, however, is an unusually large number to 
find in a leaf gall. 
Ordinarily a wrinkling and rolling of leaves on infected seedlings 
is not accompanied by the production of leaf galls, and one may 
search in vain to find larva? within these wrinkled leaves. In just 
what manner the parasite induces this wrinkling without remaining 
in the leaf is not known. It may possibly be the result of the ex- 
traction of food substances in the form of plant juices from the 
leaves by the larvae when the leaves are young and inclosed in the 
outer leaf sheaths. 
While the leaves are sometimes invaded, it usually is the embryonic 
flowers into which the larvae penetrate and produce the most con- 
spicuous signs of the disease. Either before or just after differen- 
tiation of the terminal flower buds larvae pierce the outer layers of 
cells, reaching the inner tissues in numbers usually larger than 2 
and seldom more than 25. There they stimulate cell growth and 
gall production. "Within each gall a cavity is formed, and in this 
the larvae develop into sexually mature individuals, males and fe- 
males, in about equal numbers. These then copulate, and before the 
galls are mature the females lay thousands of eggs. The latter then 
hatch, and the new larvae go into dormancy as the galls mature. 
ADULTS. 
As soon as the larvae have entered the host tissues they rapidly 
develop within the cavity of the growing gall into sexually mature 
females and males which, as shown at equal magnification in figures 
5 and 6, are markedly different morphologically. They are of suffi- 
cient size to be plainly visible to the naked eye. 
FEMALES. 
Mature females vary considerably in length. The writer has 
found them in young green flower galls only 3.42 millimeters long, 
while Marcinowski's greatest measurement of length is 5.23 milli- 
meters. Doubtless even wider variations than these occur. The 
average length seems to be about 4 millimeters. Their greatest 
width, though larger in proportion to their length than that of the 
larvae, is also subject to great variations within the same individual. 
Young females may not measure more than 168 [jl, while old females 
when well filled with eggs are much wider. 
In general, the sexually differentiated females still remain spindle 
shaped, tapering gradually from the middle toward each end, but 
being somewhat thicker and fuller anteriorly (fig. 5). The head 
end terminates bluntly, while the tail end is distinctly pointed. Mor- 
