1907-1908.] Galls, Gall-makers, and Cuckoo Flies. 39 



vascular tissue of the leaves. In the rudimentary condition 

 of the bud the undifferentiated microscopic cells of the meri- 

 stem are all alike ; nevertheless the insect invariably pierces 

 it at the exact points where the successive members of the 

 leaf-cycle subsequently arise, as determined by the laws of 

 phyllotaxis. 



One of the most abundant oak-galls appears in autumn in 

 the form of little yellow circular discs rather less than a three- 

 penny-piece, studded over with minute red hairs ; these are 

 the oak -spangles, and it is sometimes difficult to find on a 

 tree a single leaf which has not its under- surface plentifully 

 bespattered with them. They are produced by Neuroterus 

 baccarum, which is also responsible for the currant galls grow- 

 ing on the oak catkins. The exceedingly pretty silk-button 

 gall previously mentioned is also gregarious, and like the 

 spangle is only found on the under-side of the oak leaf. It 

 looks like a golden bead or minute ball of silk thread, and is 

 a very attractive object indeed. The maker of the silk-button 

 gall is Neuroterus numismatis. Spangle galls resembling 

 buttons, and almost as large as a shilling, have been obtained 

 from Sweden. Even more conspicuous is the marble gall 

 which appears in great numbers about the month of August 

 on the young branches of the oak ; at first it is somewhat 

 succulent and of a green or yellow colour, but when old it 

 becomes hard and brown, and as its name indicates, greatly re- 

 sembles a boy's marble. From being confined to Devon it was 

 at one time known as the Devonshire gall, but during the last 

 thirty years it has spread all over the land. On cutting it 

 in two we see a small central cavity containing a bluish -white 

 grub, the larva of the gall-fly Cynips Kollari. The gall-nuts 

 of commerce used in the manufacture of ink are very similar, 

 though the work of another species of Cynips. As sold by 

 the druggist, Aleppo galls are roundish nuts of a bluish-grey 

 colour, having the surface studded over with tubercles. Some 

 specimens show the little round hole by which the insect 

 escaped; others are completely closed, the occupant being 

 still inside. The cherry gall developed on the leaf, the arti- 

 choke gall, a deformed leaf-bud, resembling, as its name indi- 

 cates, a miniature artichoke ; a hard, woody, many-chambered 

 gall from one to three inches in length, growing on the roots 



