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INSECT GALLS

 

is originated by the act of ovipositing. In the case of the Cynipid galls, however, it has been clearly demonstrated that gall production does not commence until the larvae begin to feed.

The following is a list of some of the commoner species of Zoocecidia found in this locality:

 

Order ACARINA.

A large number of the galls in this group are still unclassified, but the type characters are well marked. The different species constitute a clear phylogenetic series from the simple erineum to the well-developed pouch gall. The distinction between the different members of Phis series is largely a difference in degree rather than in kind, and seems to be explainable on the assumption of a gradually increasing intensity of stimulus from the lowest to the highest member of the series. A simple erineum type is that found on the underside of the leaves of Fagus grandi f olia, Ehrh., while Eriophyes abnormis, a pouch gall on the leaves of Tilia americana, L., stands at the other end of the series. As an average between these extremes may be placed such a form as the " dimple " gall on the leaves of Quercus macrocarpa, Michx.

 

Order HEMIPTERA.

These galls are characterized by a folding and wrinkling of the leaf when they occur on that organ, and in this particular resemble the types of the pre-ceding section.

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