382 THE CANADIAN' ENTOMOLOGIST 



larger in the gall originating from that tissue. This is exemplified 

 in the gaWs produced by Eiirosta solidaginis Fhch, Aulacidea nabali 

 Brodie and numerous other species. 



But glands also occur in certain galls on parts of the host that 

 are normally glandless. Thus they are plentiful in the gall pro- 

 duced by Neolasioptera perfoJiata ¥e\t on Eupatorium perfoUatum 

 L, but are not found in the same location in the normal, but are, 

 however, present at the base of the stem. In E. nrticcefolium 

 Reichard they likewise occur in the transitional region between 

 stem and root, while in E. piirpureum L they are present in the 

 roots, petioles and flowering axes, as well as in the cortex and pith 

 of the stem. In the case of gland production, it is clear that not 

 only have active characteristics of the protoplasm in that direction 

 been stimulated to an activity greater than the normal maximum, 

 but nearly dormant properties have cometimics been aroused into 

 action. 



The trichomes exemplify the principle in a very similar manner 

 to the glands. When the gall produces types different from the 

 normal, these are invariably found on the reproductive axes of the 

 host. The unicellular acicular hairs of Eriophyes querci Garman 

 are totally unlike the stellate hairs of the leaf, but their exact 

 counterparts are found on the reproductive axes of the host Querciis 

 macrocarpa Miciix. The much convoluted type of hair present in 

 the Acarina dimple gall on the leaves of Acer negundo L. are found 

 plentifully distributed over the reproductive axes, although the 

 normal leaf hairs are straight. The trichome-producing activity 

 of the protoplasm has thus been stimulated by the foreign organ- 

 ism to a degree reached in the normal only at the time of reproduc- 

 tion. 



The production ofaeriferous tissue in certain Salicaceous galls 

 also substantiate the principle in a very striking manner. These 

 galls contain examples of a typical aeriferous tissue, comparable, 

 indeed, to that found in such aquatics as Nympha^a, Potamogeton 

 or Saururus; while in the corresponding parts of the host it does 

 not occur. Indeed, this statement may be extended to include all 

 the species of the host genus. A cross section of the gall originated 

 on Salix cordata Miihl. by Rhabdophaga triticoides Walsh shows 

 this tissue surrounding each larval eel'. It is present in the abnormal 



