MEMBKANE- WINGED INSECTS. 271 



plants and trees, depositing therein their eggs. They 

 moisten these cuts also with an irritating fluid, which 

 causes the growth of the tumors called galls. When 

 the eggs are hatched, the larvaB live on the interior of 

 these tumors, just as the larvae of the Nut-weevil, 435, 

 live on the nuts in which they are hatched. It is re- 

 markable that the same tree should produce on its dif- 

 ferent parts galls of various forms and degrees of hard- 

 ness, according to the species by which the eggs are 

 deposited. The hardest gah 1 is the common gall-nut of 

 commerce, so much used in making ink, and in the proc- 

 ess of dying black. This is the product of an oak grow- 

 ing in the Levant. It has been found that the famous 

 " Apples of Sodom" are galls of a different consistence 

 on the same oak, occasioned by another species of Cy- 

 nips, or Gall-fly. While the oak apples, so familiar to 

 us, appear on the twigs of the oak, there are also differ- 



ent kinds of galls pro- 

 duced on the leaves, 

 the catkins or pendent 

 flowers, and even on 

 the root. Those on 

 the root are large and 

 woody, and eleven 

 hundred larvae have 

 been found in a single 

 one of them. While 

 the oak seems to be a 

 great favorite of the 

 Gall-flies, they infest 

 also some other trees 

 and shrubs. The gall 

 of the wild rose, Fig. 

 210, is very beautiful, 



negated in color, and 

 covered over with bristles. When cut open we find in 



