194 



DAVENPORT ACADEMY OF SCIENCES. 



this form in fair abundance upon a single tree of Hicoria glabra 

 growing near a small stream in the vicinity of Arlington, Virginia, 

 and widely separated by hills and gullies from trees bearing the 

 genuine or typical gall. They contained (May i6th) besides the 

 other forms a considerable number of the winged migrants which 

 proved, after careful examination and comparison, to be absolutely 

 identical with those of Ph. c. -septum. The causes of this remark- 

 able and constant variation are not readily explained except by 

 the fact that the typical form has so far always been found upon 

 young trees with large and succulent leaves of Hicoria alba, while 

 those of perforans were upon trees of Hicoria glabra which had 

 already attained a height of over twenty feet and with the leaves 

 smaller and less succulent. As in the typical form, the gall is 

 mostly single though now and then two, three or even more 

 grow in close contact, generally close to the midrib, near its base, 

 or near the stronger, cross-ribs, and, instead of expanding horizont- 

 ally, they become narrow and considerably elongated above and 

 beneath, resembling a slender spur or nail forced through the leaf. 

 The length of the cones varies from 3-8™™- and the diameter at 

 base from 2-4™™- Both above and beneath, the cones usually 

 lean to one side, those above usually in the opposite direction 

 from those beneath, while cones growing near the edge of the leaf 

 curve outwardly and often to such a degree that both points almost 

 meet. Each cone splits into 6-8 slender bracts, fitting closely 

 together and lined inside with a white, woolly pubescense. 



At maturity the bracts of the upper cone separate to allow the 

 insects to escape, while those on the under side remain closed. 

 The inner structure of the galls is very similar to that of the typ- 

 ical form, though its walls are harder and thicker. Its color 

 above and beneath is of a paler green than the surrounding leaf, 

 incling toward the apex to purple or brown. The transverse 

 ribs between which these galls are stationed are, at the point of 

 junction, often considerably angulated, much thickened and of a 

 beautiful red or crimson color. 



Phylloxera cary^foli^ Fitch. 



Plate II., fig. 9; Plate IX., fig. 47. 



Phylloxera carywfoliw Fitch, Third Rep. Nox. and Ben. Ins. of 

 N. Y., p. 446. 



