490 Annals Entomological Society of America [Vol. VI, 



and become winged sexupara, of which ten to twelve may be 

 found in a single gall with the parent. These winged sexupara 

 begin to emerge in the vicinity of Fort Collins about the first 

 week of August and continue to emerge till the last of September 

 and soon give brith to the sexual forms. 



The apterous females {fundatrigenia or virgogenia), occur 

 in leaf galls, at least from about July 17th to September 20th, 

 a portion of their young also staying in the galls with them 

 and becoming sexupara, and a portion migrating as soon 

 as born to form new galls, as late as September 1st. If this 

 interpretation is correct, the alate fundatrigenia in this species 

 seems only to distribute the species from one tree to another, 

 but we have no observations that fully confirms this hypothesis. 

 The Galls. (Figures 1, 9, and 10.) 



Throughout the summer the galls are started upon the very 

 tenderest young leaves only, by first instar lice which locate 

 on the ventral surface of the leaves. There may be from one 

 to a large number of these galls on the leaves, the entire surface 

 of the leaf being included in gall development very often when 

 • the lice are abundant. The galls are paler green than the re- 

 maing portions of the leaves; are long oval in general form; 

 commonly 6 to 8 mm. in length, but may be as long as 10 mm., 

 and always upon the upper or dorsal surface of the leaf. 



While it is common to find these galls abundant upon the 

 narrow leaved cottonwood, Populus an gtisti folia, in Colorado, 

 we have never taken one of these galls on any of the several 

 varities of broadleaved cotton wooods which are more common. 

 It is entirely possible, therefore, that the specimens recorded 

 in this paper from other states may belong to a distinct species. 

 The galls sent from California by Professor E. Bethel, George , 

 P. Weldon, and A. C. Maxson; from Maine by Doctor Edith 

 M. Patch; from Michigan by Professor R. L. Pettit, and those 

 taken by the writer at Portland, Oregon, were all from broad 

 leaved cottonwoods. On the broad leaved cottonwoods, the 

 galls are usually placed near the leaf margin so that the long 

 diameter of the gall is parallel with the leaf margin.* 



*Since writing the above paper Mr. George M. List has collected additional 

 material of this species for me at Manitou, on October 18th. Some of the galls 

 taken on this date still contain the virgogenia and alate sexupara as described 

 above and many sexual males and females. Probably it is only the belated sex- 

 upara that deposit their sexual young in the galls. This completes the roimd 

 of development on the cottonwood except for the egg stage, which doubtless 

 ■occurs on this tree, also. 



