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ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 47 



Fig. 38. — Oak galls of three types stimulated by small wasps belonging 

 to the family Cynipidae: A, gouty oak gall; B, wool sower gall; C, oak apple 

 gall. The abnormal growth of plant tissue is stimulated in some mysterious 

 fashion by these insects in the early part of the growing season. Each gall 

 contains one or more larval cells. The wasp larvae eventually transform 

 to the winged form and abandon the galls. 



