124 
PROCEEDINGS OP THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
ample of these may be mentioned the “ Currant galls,” so 
common in the months of May and June throughout the 
whole country. These galls are very generally found on 
the leaves, projecting from the lower surface, but also 
visible above; but they very frequently occur on the male 
inflorescences, several usually being present on each of 
these. In this situation they look very like fruits, as each 
gall is usually much like a red currant in size, form, trans- 
luency, and colour; and it is to this fact that the popular 
name is due. Indeed I have been asked at times whether 
they were in reality not fruits, the larvse being taken for 
intruders. 
Dividing the galls on oaks that have yet been recorded 
from Scotland (including two or three found lately by 
myself, but not yet recorded), into groups according to the 
organ of the tree on which they are found, I shall briefly 
describe them, treating each form for the present as dis¬ 
tinct from every other. I shall afterwards return to the 
relations of the dimorphic species to one another. 
Root-galls. Of these there are few known from Scot¬ 
land. Mr Cameron has found the following in the neigh¬ 
bourhood of Glasgow:— 
Aphilothrix radicis Fab. the gall forming a rounded or 
irregularly pear-shaped body affixed to one of the roots. 
It may reach an inch or two in diameter, is at first pale 
and rather fleshy in texture, becoming brown and woody 
as it dries up, and on section is found to contain numerous 
oval cells, each enclosed in a thin hard wall, and each con¬ 
taining a single larva. These galls are formed in late sum¬ 
mer. The insects reared from them are bisexual. 
Biorhiza aptera Fab. produces galls on the roots also; 
these galls vary much in size, the individual galls being 
usually about the size of a pea, and rounded in form, but 
generally they are crowded in masses of considerable size, 
and may then be very irregular in form, and often more or 
less completely fused together; externally they are reddish 
in colour; their consistence and internal structure are much 
as in the former species. Both are difficult to find, and 
require continued and careful search; but they are pro¬ 
bably pretty widely diffused in Scotland. The galls of B. 
aptera are formed in late summer, the insects emerging 
in winter. They are wingless, and are all asexual. 
Bark-galls. Of this group, only two species found with 
us. Andricus nonduli is a very inconspicuous form, 
consisting merely of slight thickenings of the twigs 
of oaks. The bark is raised up here and there in small 
warts, or more generally, so many occur in the twig that 
for part of its length it becomes distinctly thickened and 
irregular in form. The presence of the galls is most readily 
detected after the insects have emerged by the existence of 
the small holes of exit. On making a section of a galled 
twig the galls are found to be situated in the bark. They 
are formed in early summer. The insects are asexual, 
and emerge from the galls in spring. 
Aphilothrix corticis L. forms galls imbedded in the 
bark of oaks. The callus formed over the stumps of felled 
trees or of lopped branches seems to be rather a favourite 
situation for the insects to select. While fresh the galls 
appear only as hemispherical or oval swellings, fleshy in 
texture, and covered with a reddish-yellow skin. The 
actual gall is situated below the level of the bark, is 
quite hidden, and has a compact special wall, the upper 
end of which separates away as a scale when the insect 
is ready to escape. The fleshy swelling also falls off, leav¬ 
ing free exit for the insects. The galls are formed in 
autumn, and the insects (asexual) emerge in spring. The 
old galls remain in the bark for a long time after the 
escape of the insects. Mr Cameron records them as rare 
at Kenmuir. 
Bud-galls. This group contains a considerable number 
of forms, all of which agree in the fact that they are formed 
by the alteration of the growing point of a bud, either 
latent, or attacked while in active growth. Many of them 
are very inconspicuous, and require to be closely sought 
for ere they can be found, as they often remain almost or 
altogether enclosed in the nearly unchanged bud-scales ; 
and when mature they fall to the ground, where they are 
so inconspicuous as to defy search. Others, on the con¬ 
trary, are among the most conspicuous of oak-galls, e.g., 
the “ Devonshire gall ” and the “ Artichoke gall,” already 
quoted. 
Trigonaspis megaptera Panz. produces galls in early 
summer in many parts of Scotland. These galls, at first 
sight, seem to be attached to the lower part of the trunk 
of the tree, apparently to the bark directly; but on careful 
examination each will be found to be in reality a bud-gall, 
though generally the bud is extremely ill-developed. The 
galls vary in size from about one-fourth to almost one-half 
inch in diameter; they are irregularly rounded, or may 
become polygonal from mutual pressure or from pressure 
on the bark of the tree. Frequently they are sunk in the 
moss so commonly met with on tree-trunks, from which they 
show as small pink bodies; but they may vary a good deal 
in colour. They are rather fleshy in texture ; and on sec¬ 
tion are found to have hardly any well-defined denser wall 
surrounding the central cavity. The insects usually 
emerge from them in the month of June. They are of 
both sexes, and a moderate amount of difference in 
appearances exists between the sexes. 
