47 



Saw-flies, Gall-flies, Ichneumons, 



position, and the interesting response or reaction of the plant to the growth- 

 stimulating irritation of the gall-fly larva are subjects which have attracted 

 much attention and study, but concerning which much remains to be dis- 

 covered. In size and shape the galls present amazing variety ; some are irreg- 

 ular little swellings on the leaves, others are like small trumpets, others like 



rosettes or star-like with radiating 

 points; on the twigs some are spherical, 

 some elongate, and some large and 

 reniform. Figs. 657 to 665 show 

 something of 

 this variety. 

 In their interior 

 make-up they 

 also differ 

 much ; some 

 have a large 

 hollow central 

 space ; some 



FIG. 658. FIG. 659. 



FIG. 658. Galls on leaf of California white oak. (Natural 



size.) 

 FIG. 659. Trumpet-galls on leaves of California white oak. 



(Natural size.) 



are filled with open, spongy tissue, and some are 

 solid except for the cells and tunnels of the larvae. 

 In some but a single larva lives; in others are three 

 or four or a dozen. Externally some are smooth, 

 some roughened, some hairy. They occur on leaves, 

 branches, and roots in both oak and rose. Only FIG. 660. Galls on leaf 



a few Cynipid galls are known on other plants of California white oak. 



* . . e . (Natural size.) 



than these. In the face of the host of species of Cyni- 



pidae found in this country over 200 gall-making kinds are known, besides 

 a score of parasitic species and their small size and generally similar appear- 

 ance, we shall not undertake to describe any of the various species. Corn- 

 stock describes in his Manual several of the more common eastern galls, or 



