GALLS 181 



a simple gall, such as in the rolled leaves of Geranium 

 sanguineum, or of the Bedstraws. But in most cases such a 

 distortion of the parts is attended with shortening and 

 other changes in the axis, altering very greatly the whole 

 aspect of the shoot. Other bud-galls are buds that have 

 remained abortive, or have swollen a little, the leaf-members 

 becoming like widened leaf-scales. Others are more changed 

 in aspect, forming large masses of tissue, in which it is 

 difficult to recognise the ordinary parts of the plant. Some 

 of the compound galls are the w r ork of several gall- makers in 

 co-operation ; others are produced by a single gall-maker 

 for the protection and nourishment of several larvee, each of 

 which occupies its own chamber. Occasionally gall-makers 

 that habitually form compound galls may also produce 

 simple galls or vice versa ; and among the dimorphous gall- 

 flies the one gall may be a compound, the other a simple, 

 form. 



Compound Galls may be divided into nearly the same 

 groups as Simple. The Hair-galls and Roll-galls, however, 

 are less numerous, and may in fact be regarded as mere 

 assemblages of simple galls of these types, in which the 

 growth of the branch itself is interfered with and its 

 appearance changed. Compound Mantle- galls are often 

 formed by the fusion of the edges of members usually free. 

 Closed Bud-galls are formed by gall-makers of various groups, 

 e.g. Gall-apples on Oaks. 



Bud-galls differ in aspect according as they result from leaf- 

 buds or from flower-buds. If a leaf-shoot is stunted, as the effect 

 of the attack, the leaves are apt to be much increased in num- 

 ber and to be short and broad, overlapping at the edges. Thus 

 a cone-like body is formed, as by a gall-midge on the Yew 

 and by another on Bedstraw, if the leaves are closely placed 

 one on the other ; or a rosette, as is often seen on Sallows 

 and Hawthorn, if the short broad leaves spread apart. When 

 the bases of the leaves become fleshy, and unite for a time, a 

 body very like the fruit of some Conifer may result, as so 

 commonly occurs on spruce twigs owing to the attack of the 

 spruce Aphis. 



Flower-bud galls resemble usually swollen buds that 

 never open. Often they are conspicuously coloured. The 



