236 OAK. 



The "Marble Galls," figured (p. 235), seldom cause much 

 injury, but they occasionally occur in such large numbers 

 that they appear to be the most hurtful of the forty-two or 

 more kinds of Galls which are to be found on Oaks in Great 

 Britain. 



Oak Galls infest all parts of the tree ; some kinds occur on 

 leaves, some affect the formation of the buds, others occur on 

 the bark, root, and catkins, one kind is to be found in the 

 twigs, and one in the acorn ; but with the exception of the 

 Marble Gall and the " Common Spangle " Galls {Neiiroterus 

 lenticularis) , which sometimes so completely load the back of 

 the leaves as to cause premature withering, it does not appear 

 that any kinds are often materially hurtful. 



The females of these Gall Flies (which belong to the order 

 Hymenoptera) are provided with a peculiar apparatus for egg- 

 laying, by means of which they are able to insert one or 

 more eggs with a small quantity of fluid into the part chosen 

 for attack, and thus set up an irritation in the living tissues 

 which causes the diseased growth, resulting in the shape of 

 galls. 



In the case of Cynips kollari the egg is laid in the young 

 bud when forming in the axil of the leaf, and the consequence 

 is the globular growth of cellular tissue which we find (before 

 the Marble Gall is mature), with the grub lying in the 

 middle ; towards autumn this changes to a pupa, similar to 

 that figured (p. 235), and generally the Gall Fly comes out 

 shortly after, but sometimes not until the following year, or 

 possibly even later. It is furnished with four transparent wings 

 of the expanse marked by the line beneath the figure (p. 235), 

 the body and abdomen are of a rusty or ochreous brown, 

 and the base of the abdomen pitchy. Up to the year 1881 

 females only had been observed of this species, and I am not 

 aware of any discovery of the male having been recorded 

 since. 



This gall of the C. kollari was noticed in such great 

 numbers in the south-west of England, about the year 1854, 

 as to give rise to an impression that it had then first appeared 

 in this country ; and, from its being especially observed in 

 Devonshire, the name of "Devonshire Gall " was bestowed 

 upon it. Further investigation, however, showed that its 

 presence had been noted previously, and that the appearance 

 was only remarkable for its great amount ; now it is widely 

 spread throughout the country, and is to be found as far 

 north as the hills of Bayndee, near Banfi", and Eedcastle, in 

 Eoss-shire. 



Prevention and Eemedies. — This gall is chiefiy to be found 



