.V8 



Transactions of the Canadian Institute 



[vol. IX 



Dimensions: — Diameter along the leaf average 2.5 mm.; shorter 

 diameter, average 1.5 mm. 



The abnormal part of the leaf differs very markedly from the normal. 

 The cuticle is entirely absent from the upper surface of the leaf that 

 lines the interior of the gall. While the epidermis is uniformly thickened 

 the normal cells have much heavier outer walls. The normal meso- 

 phyll cells are circular to widely elliptical in outline (Fig. 28), but the 

 abnormal cells are very much elongated (Figs. 29, 30). Since the en- 

 dodermis is poorly developed the mesophyll is not clearly separated from 

 the pericycle. In this region the transfusion tissue is well represented, 

 but the non-pitted parenchyma is not so abundant as in the normal 

 (Fig. 31). The abnormal resin ducts are increased in size and have the 

 protective layer irregularly developed. 



In tabulated form is given a comparison of the anatomical structure 

 of a normal leaf with one infected by the gall producer Cecidomyia bal- 

 samicola Lintner and one from a witches' broom produced by Mcidium 

 elatinum on Ahies balsamea (L.) Mill. 



The data for the last named were obtained from Anderson. ^ 



Affected with Ceci- 

 domyia balsamicola 

 Lintner. 



Abnormally thick- 

 ened on the lower 

 surface (outside of 

 the gall), not de- 

 veloped on the 

 upper (inside). 



On the outside of 

 the gall the epider- 

 mal cells are ir- 

 regular and have 

 uniformly thicken- 

 ed walls; they are 

 not clearly lami- 

 nated but pore 

 canals are more 

 plentiful than in 

 the normal. The 

 inner epidermis is 

 not thickened. 



The same as the 

 preceding affected 

 by the fungus. 



Leaf Structure. 



Cuticle 



Epidermis 



Normal Leaves. 



Well developed on 

 both surfaces. 



The outer are 

 thicker than the in- 

 side walls. Both 

 are laminated and 

 perforated by pores. 



Affected with 

 Mcidium elatinum 



Present but less 

 developed. 



Epidermal cells 

 more irregular than 

 in normal ; less 

 thickened and sel- 

 dom laminated and 

 provided with pore 

 canals. 



Stomata 



Hypoderm 



More numerous on 

 the lower than on 

 the upper leaf sur- 

 face. 



Well developed at 

 the basal half of the 

 leaf. 



Like the normal 

 but fewer on each 

 surface. 



Hypodermal cells 

 fewer, but usually 

 larger, thicker 

 walled and more 

 irregular than in 

 normal leaves. 



Cells irregularly de- 

 veloped, invariably 

 curved and com- 

 pletely filled with 

 laminated scleren- 

 chyma. 



