304 Transactions of the Canadian Institute [vol. ix 



Dimensions: — Length along line of attachment to midrib, 10-12 mm. ; 

 Width, 4-5 mm. 



In the part of the leaf blade that forms the gall all resemblance to 

 the normal mesophyll has disappeared. A compact mass of tissue has 

 taken its place, the cells of which are much larger than normal meso- 

 phyll cells. Towards the interior of the gall the cells become smaller" 

 and richer in protoplasmic contents. The upper epidermis forming the 

 interior of the gall remains practically normal, except that it produces 

 longer and more abundant trichomes than when unstimulated. These 

 trichomes are usually three cells in length. A cross section of this gall 

 shows two small groups of cells with porous laminated sclerenchymatous 

 walls, one of which is situated near the midrib and the other exactly op- 

 posite on the other side of the gall opening. Thus each side of the gall 

 aperture is bordered by a band of sclerified cells, as shown in the trans- 

 verse section of Fig. 8. 



Hormaphis hamamelidis Fitch. 

 Host Hamamelis virginiana L. 



The gall formed by this species is found on the upper side of the leaf 

 of the host, but the larvae escape from an opening on the under side. 

 The mature gall is conoidal in shape with the apex usually slightly bent 

 over. General structure is illustrated in Fig. 12. A circular ring of 

 tissue covered with pubescence surrounds the gall opening which is shown 

 in Fig. 12. 



Dimensions: — ^Average length of gall 10.5 mm.; diameter at base 

 4 mm. 



The gall is composed of small cells placed close together, forming a 

 compact and very uniform tissue. The cells are arranged with their 

 longer diameters pointing in the direction of the gall apex. In a longi- 

 tudinal section the vascular strands are seen to pass up each side at a 

 depth of about three cells from the gall cavity. The beaks of the larvae, 

 often found imbedded in the wall of the gall, were inserted far enough to 

 almost reach these vascular strands. The hairs that surround the gall 

 aperture are acicular and unicellular. 



Hamamelistes spinosus Shimer. 

 Host Hamamelis virginiana L. 



The galls in this species are modified flower buds. These are some- 

 what elliptical in outline with gradually tapering stalks. They are 

 covered with spines, which are usually curved. The opening is situated 

 at the union of the stalk and the gall proper. This opening is funnel- 

 shaped and is surrounded by a circular ring of tissue as in the preceding 

 species on the same host. The pubescence is absent in this case. 



