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NATURE-STUDY REVIEW [12:5— May, 1916 



II. Root, Stem, Leaf, and Flower Galls. 



i. Root galls: those situated upon or within the roots. 



2. Stem galls: those situated upon or within the main stem, 

 the branches or the suckers. 



3. Leaf galls: those situated upon or within or enclosed by 

 the blade, the petiole, the stipules, the bract, or the scales. 



4. Flower galls: those situated upon or within or enclosed 

 by the calyx, the corolla, the catkin or the subsequent fruit 

 or seed. 



III. Unilarval, Multilarval, and Multinymphal galls. 



1. Unilarval galls: those possessing but one larva. 



2. Multilarval galls : those possessing more than one larva. 



3. Multinymphal galls : those in which the young insects are 

 nymphs, such as the plant lice. 



Fig. 10. Willow Apple Gal! 



Rounded and fleshy, somewhat resembling a miniature apple. 

 Yellowish green, usually with a rosy cheek. Measures about 

 one-half inch in diameter. On leaves of bush willow. (After 

 Beutenmuller). 



IV. Galls Produced by Mouth Parts or by Oviposition. 



1. Galls produced by mouth parts. 



2. Galls produced by oviposition (the egg-laying apparatus). 

 The method of classification that .seems to be most in vogue 



at the present time is number II above. Galls may also be 

 classified according to the agent causing them, — a subject 

 that will be discussed later. 



The Structure of Insect Galls 



The structure of insect galls varies to a great degree. The sim- 

 plest galls have thin walls upon which the larvas feed until a mere 

 shell is left. When they have reached their full growth the larvae 



