378 Transactions of the Canadian Institute. [vol. ix 



EXPLANATION OF PLATES. 

 Plate I. 



Fig. I. Eriophyes Sp. (Populus tremuloides Michx.). Section showing 

 the folding of the upper epidermis of the leaf . X50. 



Fig. 2. Eriophyes Sp. {Populus grandidentata Michx.). Section showing 

 the nature of the folding produced on the lower surface of the 

 leaf. X60. 



Fig. 3. Eriophyes Sp. {Fagus grandifolia Ehrh.). Section through a 

 number of capitate trichomes. The almost normal character of 

 the leaf is shown. X50. 



Fig. 4. Eriophyes Sp. {Acer negundo L.). Section through the gall, 

 showing a large number of convoluted trichomes. X35. 



Fig. 5. Eriophyes Sp. {Prunus nigra Ait.). Longitudinal section in 

 which is shown the elongation of the cells in the direction of the 

 long axis of the gall. The peculiar nature of the trichomes is 

 also shown. X30. 



Fig. 6. Eriophyes querci Garman {Quercus macrocarpa Michx.). Section 

 in which the long acicular trichomes are shown, as also the thick- 

 ening of the leaf blade. X30. 



Fig. 7. Unclassified gall on the leaf of Populus balsamifera L. The 

 uniform nature of the abnormal cells is apparent. The gall 

 cavity is occupied by the mycelium of a fungus. Xio. 



Fig. 8. Transverse section of band of sclerenchyma from the preceding 

 gall, showing the pores that traverse the tissue. X 120. 



Plate II. 



Fig. 9. Aphid corrugations on the leaf of Betula tenia L. produced by 

 the fourth generation of Hamamelistes spinosus Shimer. The 

 formation of the larval chambers by the closing of the folds is 

 shown. X22. 



Fig. ID. Hamamelistes spinosus Shimer on the leaf of Hamamelis vir- 

 giniana L. Transverse section that passes through a spine, 

 cross sections of two bundles are shown. X 35. 



Fig. II. Chermes abietis Choi, on the stem of Pi-cea abies (L) Karst. 

 Longitudinal section, showing two larval chambers with their 

 apertures of exit. A number of resin ducts are cut near the 

 margin of the section. X30. 



Fig. 12. Hormaphis hamamelidis Fitch on the leaf of Hamamelis vir- 

 giniana L. Longitudinal section passing through the apertur* 

 of exit. Xio. 



