1912] Morphology and Biology of Insect Galls 301 



Eriophyes Sp. 



Chadwick's No. 88. 



Chadwick considers this form, first described by Jarvis,^^ the same 



as his No. 87. But the latter is characterized by a depression on the 



under side of the leaf, the former by an elevation, so that the two are 



constantly distinct. 



Host Populus tremuloides Michx. 

 A dimple gall with the elevation on the under surface of the leaf. 

 The elevation is a lighter green than the surrounding normal leaf and 

 the folds that occupy the concavity are greenish-yellow or reddish in 

 colour. 



In dealing with the anatomical structure it is to be noted that the 

 spongy parenchyma has in this case remained normal. The folds are 

 produced in the same manner as in the preceding species, except that in 

 this form it is the upper epidermis that undergoes the folding process. 

 The nature of this folding can be seen in Fig. i. 



Eriophyes Sp. 

 Chadwick's No. 93. 

 Host Prunus nigra Ait. 

 A very much elongated pouch gall, greenish or whitish in colour, 

 found on the upper side of the leaf with the opening on the under side. 

 All the characteristics of the normal mesophyll have been com- 

 pletely altered in the affected part of the leaf. Its cells, which, with the 

 epidermis, constitute the wall of the gall, are larger than the normal and 

 are elongated parallel to the long axis of the outgrowth. The upper 

 epidermis which forms the epidermis of the gall has not been affected, 

 but the cells of the lower epidermis which line the gall cavity have become 

 much enlarged and in addition have produced a large number of closely 

 set trichomes which project into the gall cavity. The nature of these is 

 shown in the upper part of Fig. 5. These structures are often from 2 to 

 3 cells in length. Around the opening of the gall a circle of closely set 

 acicular hairs occurs. The hairs on the outside of the gall and on the 

 normal leaf are also of the acicular type. The vascular strands are much 

 larger than those of the normal leaf but appear to be simply the stimulated 

 normal veins. 



Eriophyes ahnormis (Garman). 



Chadwick's No. 144 



Host Tilia americana L. 



A very much lobed pouch-gall, usually on the upper side of the leaf, 



found rarely on the under side. The opening which is on the opposite 



side of the leaf to the pouch is surrounded by a dense growth of acicular 



trichomes. 



