346 Transactions of the Canadian Institute [vol. ix 



the larval chamber, but in the inner row the reverse is the case. On the 

 outside of the protective zone are about two layers of round, loosely con- 

 nected parenchyma cells (Fig. 51). The canal mentioned in the early 

 stage is still visible, penetrating the outer wall of the gall and that of the 

 larval chamber. A layer of collapsed tissue is now clearly defined around 

 the inside of the nutritive zone (Fig. 51). The inner layer of the paren- 

 chyma zone is also showing this same tendency to collapse. 



In the mature gall the nutritive zone is represented by only a narrow 



layer of shrunken tissue (Fig. 52), the individual cells of which cannot be 



distinguished. The inner layer of the parenchyma zone is now almost 



completely collapsed and the cell walls of the whole zone are wrinkled. 



Andricus imbricarice Ashmead. 



Host Quercus coccinea Muench. 



A globular gall issuing from the stem of the host plant. Several 

 galls are found near each other on the stem but they are never crowded. 



It is usually monothalamous, but occasionally dithalamous forms 

 are found, the larval cells are closely connected with the remainder of 

 the gall. When the gall drops off its point of attachment is marked by 

 a small, elliptical, depressed area surrounded by thin scales of tissue. 

 These scales represent tissue forced aside by the emergence of the young 

 gall. 



Dimensions: — Diameter 6-9 mm. 



This species has the four zones well differentiated. The most 

 striking features of the anatomical structures are the following : — 



The cells of the protective layer contain large crystal masses and 

 have their walls uniformly thickened. Radiating lines of cells pass out 

 from this protective zone (Fig. 48), through the parenchyma sheath and 

 end near the epidermis. These bands are composed of narrow, elongated 

 cells and are from i to 3 cells in width. These rows of cells contain a 

 great deal of starch and a substance that takes a very deep stain with 

 saffranin. Large cells of the parenchyma zone separate these bands of 

 cells from each other, as seen in Fig. 48. 



Andricus singularis Bassett. 

 Host Quercus rubra L. 



In the majority of cases this gall originates from the mesophyll of 

 the leaf blade but rarely it is found attached to the petiole. It is situated 

 near the margin of the blade of the leaf and projects about equally from 

 the upper and lower surface. 



It is a monothalamous gall closely resembling in external form 

 Dryophanta palustris O.S., but its outer wall is much firmer and it does 

 not wither so quickly after the producer emerges. The ellipsoidal, larval 

 chamber is suspended at the centre of the gall by radiating bands of 



