IO 
BRITISH GALLS 
II. COMPOUND OR BUD GALLS 
Several adjacent plant organs are involved in the 
production of these galls, which chiefly arise from buds. 
“ They are extraordinarily varied in their characters, some 
being merely abbreviated axes clothed with scale-like leaves ; 
in others only the base of the shoot is involved, and above 
the gall it continues its growth quite normally; whilst in 
others, again, the axial portion of the structure is much 
swollen, and the leaves hardly represented at all ” (Kerner). 
It is difficult to arrange them in groups, but three fairly 
well marked may be distinguished. 
i. Bud-like Galls 
Several or all the parts of a shoot are involved, its axis 
is deformed and thickened, and elongation is suppressed. 
(a) Modified Foliage Buds 
i. Apparently leafless, the leaves transformed into tuber¬ 
cles and knobs. This section includes the various bud galls 
of the Oak— e.g., the Oak-apple caused by Biorrhiza pallida 
(Plate IV.) and swellings on Poplar branches caused by the 
beetle Saperda populnca (Plate VI.). 
ii. Galls covered with scale-like bracts, or more or less 
fully developed green foliage leaves. 
A familiar representative of this section is the Artichoke 
gall caused by the hymenopteron Andricus fecundator in Oak 
buds, figured in Chapter II. 
(b) Metamorphosed Flower Buds 
In these the corolla does not open ; the calyx becomes 
enlarged and often fleshy, the gall resembling a bud or 
bulbil. The gall caused by the dipteron Contarinia loti in the 
flower buds of the Bird’s-foot Trefoil is a typical example. 
See Fig. i, p. 15. 
