36 



PEOPAGATION OF PLANTS. 



In the true Oak Apple (figure 7), the cell-matter im- 

 mediately surrounding the larvffi in the center of the 

 gall becomes very hard aud woody, while the space be- 

 tween this center kernel and tlie rind of the gall is filled 

 with a grayish, light, spongy matter. In what is called 

 the "Bastard Oak-Apple, " produced by the Cynips 

 inanis on the Bed Oak, the centi-al kernel or cell is not 

 hard and woody, and the rind is connected with the 

 center by slender radiating filaments, as shown in figure 

 8. Another species of Cynips produces a yery distinct 

 gall on the acorn of both the Black and Red Oak indis- 

 criminately. Different species of insects not only pro- 

 duce difEerent kinds of galls on the Oak, but upon vari- 

 ous other kinds of trees 

 and shrubs, and even upon 

 many herbaceous plants. 

 The Pine-cone Gall of the 

 Willow is a familiar object 

 in every swamp where the 

 Heart-leaved Willow (Salix 

 cordata), is found, and is 

 the result of the depositing 

 of eggs of a minute species 

 of gall-gnat. As soon as the 

 eggs are deposited in the 

 young twig of the Willow, 

 the cell-matter proceeds to 

 form a cone-like structure, 

 something entirely differ- 

 ent and entirely foreign to 

 the natural functions of the plant, and this movement 

 continues until the gall is complete, the outer part being 

 covered with regularly formed scales, the whole resem- 

 bling a small pine cone. There may be thousands of these 

 galls in the same field or swamp, but all will be found 

 nearly of one size, and built up on the same general plan. 



Fig. 8.— BASTABD OAK APFLE. 



