THE STUDY OF GALLS 



121 



FIGURE 230. A " Lodger " from a 

 marble gall. 



simply spherical, occur on the under- 

 sides of oak leaves. The artichoke 

 gall is derived from a bud and the 

 oak-apple also, though the insect 

 connected with the latter differs in 

 alternate generations, and one form 

 produces the root gall of the oak. 

 As an instance we might mention the 

 sheep's-wool gall formed on the young 

 male flowers of the oak (see figure 

 231). All sorts of problems will pre- 

 sent themselves to the students of 

 galls. Males of some of the insects 

 have never yet been found ; some 

 forms can only be distinguished by 

 the galls which are the result of 

 their exertions; and the questions of 

 " lodgers " and parasitic forms offer 

 a large field for investigation. Turn- 

 ing to other plants, the red "robin's 

 cushion " of the rose is familiar, and 

 there are galls on the sallow, black- 

 berry, and a host of other plants 

 which make up an interesting series. 

 The most satisfactory method of pre- 

 serving galls in order to make a 

 collection, is to dry the twigs which 

 bear them in sand or some other V 



material in accordance with the FIGURE 231. Sheep's-wool Galls 



on oak flowers. 



