Quoting:The galls of Pemphigus rhois Fitch (Fig. 113) are large, bladdery and evidently the pocketing of a single leaflet of the host plant, Rhus glabra or R. typhina. My specimens of these galls were fully mature, and I was therefore unable to follow the line of development. The leaf structure was modified into the characteristic Aphididae gall structure. Fibro-vascular bundles were numerous and near the inner surface of the gall. Opposite each bundle was a large cavity filled with some substance which I was unable to determine.