Plate XIX 



Fig. 1. Gall on Populus caused by Pemphigus oestlundi. (Cook, Eop. 

 I ml. Dept. Geol. and Nat. Ees.) 



Fig. 2. Poplar Loaf Gall-louse, Pemphigus populicaulis, and its gall: 

 a, incipient gall on under side of leaf ; b, gall from the 

 upper side of the leaf ; e, mature gall, showing aperture ; d 

 and e, incipient double galls ; /, wingless female ; g, winged 

 insect — / and g enlarged as indicated. (Riley, Amer. Ent.) 



Fig. 3. Poplar transverse gall and louse, Pemphigus popidi-transver- 

 sus: a, gall on Populus leaf; b, gall showing aperture; c, 

 winged female louse; d, antenna of winged female. En- 

 larged as indicated. (Riley.) 



