354 Transactions of the Canadian Institute [vol. ix 



Associated with these isolated masses of vessels, often occurs a small 

 amount of bast that appears normal. When the detached cambium is 

 curved, wood is almost invariably produced on the inside of the curve and 

 bast on the outside, giving rise in some cases to almost perfect concentric 

 bundles. 



The club-shaped cells of the nutritive zone do not follow the general 

 rule and radiate out from the larval cell, but are oriented with their long 

 axes at right angles to the cambium. The nuclei of the cells in this zone 

 are abnormally large and often present good examples of amitosis (Text 

 Fig. 6). 



The normal cortex passes over the gall with little alteration during 

 the early stages of development, but later a cork cambium is differenti- 

 ated that throws off the cortex and covers the gall with its characteristic 

 corky layer. 



Neuroterus majalis Bassett. 

 Host Quercus alba L. 



A polythalamous gall originating in the mesophyll of the leaf and 

 divided into two nearly equal parts by the blade. The galls are found 

 usually in contact with the side of the midrib and extending out to the 

 margin of the leaf. 



This gall is characterized by a fiat, irregular shape and a finely granu- 

 lar epidermis. It is translucent and of a light green colour until the pro- 

 ducers emerge when it becomes light brown and opaque. 



The apertures of exit of the mature insects seem to occur invariably 

 on the upper surface of the gall. 



Dimensions: — Diameter parallel to leaf blade 12-24 nim.; diameter 

 at right angles to leaf blade 7-9 mm. 



Only the mature gall was examined. At this stage the nutritive 

 zone consists merely of a narrow line of collapsed tissue (Fig. 67). From 

 two to three rows of cells constitute a protective layer. The tangential 

 walls of these sclerified cells are unequally thickened, the heavier deposit 

 being on the wall nearer the larval chamber. The parenchyma zone 

 consists of large thin-walled cells, the majority of which are empty and 

 devoid of nuclei. A small-celled epidermis continuous with that on the 

 normal leaf passes over the gall. 



Summary. 



All the galls in this group have three tissue zones developed and 

 only very seldom is the fourth absent. The three always present are the 

 epidermal, the parenchyma or tannin and the nutritive. The paren- 

 chyma zone, as shown by Cook^^ is subject to a great amount of varia- 

 tion. The fourth, not always present, is the protective or sclerenchyma 

 zone. 



