1912] Morphology and Biology of Insect Galls 299 



Order Acarina. 



The following species are described in this section : — 

 Order Acarina. 



Fam. Eriophyidae. 



Eriophyes Sp. {Fagus grandifolia Ehrh.) 



Eriophyes guerci. {Quercus macrocarpa Michx.) 



Eriophyes Sp. {Acer negundo L.) 



Eriophyes Sp. {Populus grandidentata Michx.) 



Eriophyes Sp. {Populus tremuloides Michx.) 



Eriophyes Sp. {Prunus nigra Ait.) 



Eriophyes abnormis. {Tilia americana L.) 



Eriophyes serotinae Beut. {Prunus serotina Ehrh.) 



The numbers referred to are from "A Catalogue of the Phytoptid 

 Galls of North America," by George H. Chadwick, 23rd Report of the 

 State Entomologist, New York State Museum, 1907. 



Eriophyes Sp. 



Chadwick's No. 65 



Host Fagus grandifolia Ehrh. 



This gall occurs on the under side of the leaves of the host plant. 

 It is an erineum, white and frost-like at first, turning to a brown colour 

 at a later stage. 



The anatomical structure of the interior of the leaf remains per- 

 fectly normal, the effect of the stimulation being confined to the epider- 

 mis. This produces a large number of unicellular, capitate hairs, re- 

 sembling miniature mushrooms, the resemblance to which is the more 

 striking since the stalks of the hairs are bulbous at the base, as shown 

 in Fig. 3. The hairs on the normal leaf are long, acicular and unicellular. 

 As this gall is produced with no increase in the number of cells in the leaf, 

 anatomically it stands as a simple type of "hypertrophy", the remaining 

 forms all exhibit the more advanced phenomenon of cell proliferation. 

 Eriophyes querci (Garman). 

 Chadwick's No. 112 

 Host Quercus macrocarpa Michx. 



In this gall, which is of the "dimple" type, the depression is on the 

 under and the elevation on the upper side of the leaf. The hollow is 

 filled with a dense mass of brown pubescence. In rare cases the elevation 

 is on the under side of the leaf, when the pubescence then covers it. 



The leaf blade in this case has become of nearly twice the normal 

 thickness. This has resulted from cell division which has occurred in 

 the tissues of both the palisade and the spongy parenchyma, producing 

 a compact mass of undifferentiated cells, entirely without intervening air 

 spaces. This tissue is shown in Fig. 6. 



