84 BRITISH OAK GALLS. 



The scales completely conceal, and effectually shelter, 

 the inner pip during its formation. 



This pip, which is the true gall, constitutes the 

 nourishment for the larva, and within the tissues it eats 

 a cavity, forming the larval chamber. In shape it may 

 be pyriform, an elongated oval, or like a grape-pip. 

 The smaller or lower end is truncated or flattened, and 

 placed in direct contact with, and afl&xed to, the axis 

 of the bud. The distal end is deeply depressed, 

 within which is situated a very small yellowish cone 

 having a glossy vertex. At first the colour is pale 

 green or greenish-yellow, which, hoAvever, soon 

 becomes dark green, and later reddish-brown. Early 

 in its formation it is soft and sapp}^ the cell walls thick, 

 and easily opened w^ith a finger-nail, later it hardens 

 greatly. When nearing maturity numerous (40-50) 

 longfitudinal striations, which extend from base to sum- 

 mit, may be seen on its surface. The average dimen- 

 sions are 8 mm. high and 12 mm. at greatest girth. 

 The interior is oval, whitish in colour, the larva occupy- 

 ing the entire space. 



Until it attains its full growth the gall remains 

 firmly fixed, but about the second week in August the 

 axis of the bud contracts ; the base of the scales thus 

 being brought close together press against the lower 

 part of the pip, causing it to separate from the axis 

 and finally to l)e pushed upwards until it falls out. 

 In Plate XX two strol)iles can be seen wliere the galls 

 have reached a position in which a movement of the 

 branch will cause them to fall. They were in this 

 condition when found by the author. 



During the early formation of the leaf-scales the 

 shape of the mass is more or less globular. Three 

 types of this form can l)e seen at ^7, e in Plate XXI. 

 It then emerges into the form of an ellipse or an oval, 

 r*, c/, the central scales soon afterwards pushing theii' 

 way through the distal apex and forlning a cone or 

 strobile, when the appearance {}j) is like that of a 

 miniature artichoke, hence one of its popular names. 



