350 Transactions of the Canadian Institute [vol. ix 



normal epidermis of the leaf passes over the surface of the gall without 

 modification. On the upper surface of the leaf a protective layer of about 

 five cells in depth separates the normal part of the leaf from the gall 

 tissue. On the under surface a corresponding protective layer occurs at 

 a distance of three rows of cells below the epidermis. The cells of this 

 protective zone have uniformly thickened sclerenchymatous walls. The 

 general structure of the gall is shown in Fig. 63. Inside this layer a 

 cambial tissue is dififerentiated, from which the cells of the nutritive zone 

 are produced directly. The nutritive cells are rectangular in outline and 

 arranged in radial lines, presenting very much the same appearance as 

 the cambium from which they have originated. 



Rhodites hicolor Harr. 

 „ ■ (Rosa blanda Ait. 

 \Rosa Carolina L. 



A monothalamous, spherical, hollow gall with a wall i to 2 mm. in 

 thickness. 



They originate singly or several close together from the upper sur- 

 face of the leaf. 



The gall bears numerous stiff prickles that average about the same 

 length as the diamecer of the gall. Colour green with red tints, turning 

 brown at maturity. 



Dimensions: — Average diameter 11.5 mm. 



The anatomical structure of this gall presents very little differenti- 

 ation of tissue. The parenchyma zone consists of large irregularly shaped 

 cells. This tissue passes into the nutritive layer with little change in the 

 shape or size of the cells. The protective zone is entirely absent. 



Rhodites ignolus OS. 

 Host Rosa blanda Ait. 



A polythalamous or occasionally monothalamous gall attached to 

 the under side of the leaves by a small extent of surface. These galls 

 are generally found clustered together and often deform the entire leaf. 



Dimensions: — ^Average longer diameter 11 mm.; average shorter 

 diameter 3-5 mm. 



While somewhat variable, the shape approximates usually to an 

 irregular oblate-spheroid. At the apex of the gall is a shallow depression 

 containing a small scale-like patch of tissue. The epidermis is glaucous 

 and light brown in colour. 



The anatomical structure of this species presents the rare feature of 

 two protective layers. These are each of about five cells in thickness in 

 the full-grown gall. One of them is found in the usual position separating 

 the parenchyma and the nutritive zones. The other is situated in the 



