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CHAPTER XIII.

 

INSECT GALLS OF THE VICINITY
OF TORONTO.

By
A. COSENS, M.A., Ph.D.

TilE term "gall" is applied to any enlargement of plant cells, tissues, or organs induced by the stimulus of a parasitic organism as a regular incident in the life history of the parasite.

Galls are divided into two classes according to the agent that produces the stimulus, namely Phytocecidia, those owing their origin to parasitic plants, and Zoocecidia, those produced by animal parasites.

From the Bryophytes to the Spermatophytes nearly all plants are subject to gall formations of the latter class. These are incited by mites (Acarina) and by insects in several different orders as follows :

Hemiptera (Families Aphididae, Psyllidae), Diptera (Families Cecidomyidae, Trypetidae), Coleoptera (Families Buprestidae, Cerambycidae, Curculionidae). Lepidoptera (Families Gelechiidae, Sesiidae, Tineidae), Hymenoptera (Families Cynipidae, Tenthredinidae).

The type of gall produced by the orders Acarina and Hemiptera is simple in structure, consisting usually of a more or less pronounced folding in the

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