140
The Galls of Essex; a Contribution to a
numbers on a leaf, but each gall
is single-celled. The galls are
mature and fall from the leaf in
autumn; the gall-flies emerge
therefrom in June. Biorhiza
renum, Hartig (Fig. 32) [aga-
mous form of Trigonaspis me-
gaptera] .
Quercus Robur, L. Leaf.
Early in the year some oak
leaves are occasionally noticed

to curl up and become consi-

Fig. 32. Biorhiza renum.
derably shortened; if examined
it will be noticed they have a
spherical, smooth, green, pea-
sized swelling at their base;
frequently the whole leaf is
galled, and two, three or more
galls are confluent. In section
this succulent gall exhibits a
moderately thin walled cavity,
which contains two thin, small,
brown, cocoon-like larva-cells,
separated by a very thin sep-
tum. Certain specimens of this
gall might be taken for a bud-

gall, but if closely examined the

Fig. 33. Andricus curvator.
midrib of the leaf is generally
noticeable. The galls are mature in spring or early
summer, and do not fall from the twig; the gall-flies
emerge therefrom in June or July. Andricus curvator,
Hartig. (Fig. 33.)
Quercus Robur, L. Leaf. The common cherry-gall of
the oak is a succulent, spherical, smooth, green or rosy
gall, of about the size of a cherry; it occurs on the
under side of the oak leaf, generally singly, but sometimes
three to five are found ou one leaf. It is single-celled
gathered before mature the gall shrivels considerably ;