374 THE CANADIAN ENTOMOLOGIST 



normal development and, in some instances, at least, we have the 

 conspicuous and rather characteristic rosette galls such as those of 

 species of Rhopalomyia upon Salidago and of Rhabdophaga upon 

 willow. 



The growing point of a plant stem, whether it forms a leaf, bud 

 or a flower, affords such ideal conditions for nourishment, that it 

 is not surprising that certain genera should be restricted in large 

 measure to such favourable habitus. This is particularly well 

 marked in Asphondylia and certain of its allies, which not only 

 confine themselves largely to bud galls, but have become so special- 

 ized that they are particularly adapted to the production of such 

 deformities. 



Leaf galls. The leaf gall, like the bud gall, usually begins as 

 a development upon expanding or tender tissues. The simplest 

 type is probably a marginal leaf roll, and this differs from certain 

 of the bud gaUs simply by the fact that in the roll only a portion 

 of the leaf is involved, while in the bud gall all of the several leaves 

 may be distorted or have iheir development arrested. Vein folds 

 are produced simply by the larvae congregating or restricting their 

 operations to this portion of the leaf rather than to the margin. 

 They vary greatly in character and may be limited to the midvein 

 or to the lateral veins, may be comparatively simple and compcr.ed 

 of greatly hypertrophied tissue or ornamented with a conspicuous 

 white pile or other development such as is found in that of Cecido- 

 myia niveipila O.S. These leaf rolls and vein folds are usually pro- 

 duced by a number or small colony of larvae. 



Blister leaf galls and the more highly developed globular or 

 conical galls are generally produced by single larvae hatching from 

 eggs deposited in or upon the buds before the leaves have unfolded. 

 The peculiar blister galls on Solidago and Aster are multilccular, 

 are easily recognized by the typical discoloration and thickening 

 of the leaf, and are produced almost without exception by the genus 

 Asteromyia. These galls represent a slightly more advanced con- 

 dition than obtains in certain species which live between the upper 

 and lower epidermis and either produce only a slight discoloration 

 as in certain species of the genus Cincticornia, or else excavate a 

 fairly well defined mine, such as that of Lasioptera excavata in 

 Crataegus. The globular or lobulate galls of Cincticornia glohosa 



