16 BULLETIN 842, U. S. DEPARTMENT OF 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 larvae 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 larva? 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 larva? penetrate and produce the most con- 

 spicuous signs of the disease. Either before or just after differen- 

 tiation of the terminal flower buds larva? 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 larvse 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 larvse go into dormancy as the galls mature. 



ADULTS. 



As soon as the larva? 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. 



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 

 larva?, is also subject to great variations within the same individual. 

 Young females may not measure more than 168 \i, 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- 



