On leaf, beneath, stoutly conical, varying in size from 1½ mm. to
4 mm. high. Tip erect or often bent to one side. Smooth, green to
purplish-red and finally a brown when old. Attached to smaller veins by
short pedicel, hidden from view, however, by the rounded base of the
gall. Walls medium in thickness, possessing the rather soft texture of
charcoal when dry; brown in color.
This form is often found in enormous numbers on certain trees, bringing
about early disintegration of the affected leaves. The lower leaves are
more heavily infested due to the fact that the insects are apt to reach
these first in their flight from the ground in the spring.
Osten Sacken, Lowe’s Monogr. Dip. N. Am. Pt. 1, p. 192. 1862.
Beutenmuller, Am. Mus. Nat. Hist. Guide Leaflet No. 16, p. 28,
Fig. 59.
Reprint from Am. Mus. Jour. Vol. 4, 1904.