May, 1903.] Galls and Insects Producing Them. 4? 5. 



galls grow older the cells near the outer epidermis become elon- 

 gated as in the Phytoptus galls. 



In Pc))ipliigus iihiii/itsiis (Walsh) Oeslland (Fig. 49, a, b) on 

 U. Americana, we have the gall originating first as a fold in the 

 leaf which becomes developed into a conical structure. The struc- 

 ture of the gall shows that the characteristic structure of the leaf 

 is at first modified into a large number of small, irregular-shaped 

 cells (Fig. 49, b). The tendency for the cells near the outer 

 surface to elongate parallel to the surface begins with the further 

 development of the gall. In the very young galls the tannin is 

 in very small quantities, but increases as the gall grows older. 



In Colopha itlinicola Fitch (Fig. 50, a, b) we have a condition 

 almost identical with P. ulmi-fusus. The gall first appears as a 

 slight fold in the leaf and later develops into the characteristic 

 cockscomb gall. The cell structure is the same as in P. ulmi- 

 fusus. 



In Phylloxera carya-fallax Riley (Figs. 51, 52) on H. ovata, I 

 secured the 5'oungest galls possible to detect and identify. These 

 galls showed a slight projection from both surfaces of the leaf, 

 but at first the gall was not so conical as at a later period of its 

 development. However, the 5'oungest galls showed the charac- 

 teristic structure described in Part I of this series. The first 

 effect of the parasite attack appears to be the formation of a large 

 number of irregular cells. The arrangement of these cells is the 

 same in the young gall as in the more mature, but the fibro- vas- 

 cular bundles of the older specimens were not observed in the 

 young galls. 



I was not so successful in securing young specimens of P. 

 c.-globuli Walsh (Fig. 53), but, so far as I was able to observe, 

 the line of development coincided with P. c.-fallax. However, 

 the upper wall of the gall is at first very thin and grows in thick- 

 ness as the gall approaches maturity. 



Phylloxera eaiya-eaulis Fitch of Hickory ovata was studied very 

 careful!}- from a very complete series of specimens. The material, 

 especially the younger galls, did not cut well, and so was not 

 satisfactory for drawings. However, the development and struc- 

 ture were of the typical Phylloxera type corresponding very 

 closely with that just described for P. c.-fallax. The onl}- marked 

 peculiarity was the close association with fibro- vascular bundles, 

 the galls always occurring on very young green twigs, on mid-rib 

 or on prominent veins of the leaf. 



Pemphigus populi-transversus Riley (Figs. 55, a, b, and 56, a, b) 

 and P. p.-caulis Fitch (Figs. 57, a, b, c, and 58, a, b, c ) of the 

 Populus are galls growing on the petiole ; the former at some 

 point between the blade and stem, the latter at the base of the 

 leaf. In both cases the attack is made from the outside, the same 

 as in other Aphididae galls and in the Acarina galls. A careful 



