The galls are produced from terminal buds on all parts of the tree, and each is made up of a number of transformed leaves and petioles, arranged in pairs opposite each other, in which the two leaves are opposite. They are sub-globular in outline and vary from less than one-half of an inch to nearly an inch in diameter. The outer basal portion of the gall is formed by an enormous enlargement of the bases of the petioles of two leaves which unite and form a receptacle like the cup of an acorn, holding the inner portions of the gall. In the central part of the gall the leaf blades may be entirely involved or their tips may be expanded.
Proceedings of the Iowa Academy of Sciences
©1890 Iowa Academy of Science, Inc.
Gillette, C. P.
"A New Cecidomid Infesting Box-Elder (Negundo aceroides),"
Proceedings of the Iowa Academy of Science, 1(Pt. 2), 108-109.
Available at: https://scholarworks.uni.edu/pias/vol1/iss2/44