CHAPTER III 

 GALLS 



The study of galls and gall-producers is a fascinating one, and may be 

 pursued at all seasons of the year. The British galls number nearly 300, 

 and occur on all parts of plants. They are in most cases the result of 

 insect agency, but some are due to the presence of nematoid worms within 

 the tissues of the plants, and yet others are the result of attacks by fungi. 

 No plants are more susceptible to galls than are the various species of Oak, 

 and of the many kinds of oak-galls which have been described the greater 

 number are produced by gall-wasps, insects belonging to the Cynipidae, a 

 family of the Hymenoptera. A wonderful feature connected with the life- 

 history of these gall-producers is the phenomenon of alternating generations, 

 in which we have an insect producing an offspring, which at no time re- 

 sembles its parent, but which, on the other hand, itself brings forth a 

 progeny, which returns in its form and nature to the parent insect, so that 

 the latter does not meet with its resemblance in its own brood, but in 

 another generation. The two generations produce galls of very different 

 character. One generation consists of females only, the other includes both 

 males and females. We will now call attention to a few of the more 

 common and interesting oak-galls, and give examples of this strange re- 

 lationship. 



The Cherry Gall (Dryophanta scutellaris) is found on the under-surface 

 of the leaf, attached to the midrib and its offshoots. As its name implies, 

 it resembles a cherry in size, form, and colour, having a diameter of about 

 f in., and being yellow, yellowish-green, pale-green or rose-coloured. It is 

 found from July to October, and the imago emerges during the autumn and 

 winter. It is the largest and most brightly coloured of the leaf-galls. The 



alternate sexual generation is found in the next species. 



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