472 



Saw-flies, Gall-flies, Ichneumons, 



common bullet gall, H . globulus, of the small twigs, i to 

 eter, has the kernel surrounded by a hard woody substance. 



inch in diam- 



FIG. 664. An oak-apple, or fibrous gall of the California live-oak; in upper figure the 

 gall shown in position on the oak-twig; in lower, a gall cut open to show the inside. 

 (Upper figure slightly reduced; lower figure natural size.) 



In California the white or valley oaks bear very commonly conspicuous 

 large white spherical to kidney-shaped galls (Fig. 665) which are attached 

 to the branches, and often occur in such abundance as to make the injured 

 tree look like some new kind of fruit-tree in heavy bearing. This gall is 

 caused by the gall-fly Andricus calijornicus, one of the largest of the Cyni- 

 pidae, and the gall itself attains a larger size than any other known to me. 

 It begins as an elongate swelling underneath the bark of the fresh twigs, 

 but soon breaks through as a shining, smooth excrescence rapidly increasing 

 in size. A single gall is inhabited by from six to a dozen larvae. A curious 

 oak-leaf gall is the jumping seed-gall (Fig. 666), a small and shot-like gall which 



