150
The Galls of Essex; a Contribution to a
Populus nigra, L. Leaf-stalk. The petioles of the leaves
are swollen into pea-sized, hollow galls, which split when
mature, and liberate the aphidious tenants. Pemphigus
bursarius, Hartig.
Populus nigra, L. Leaf-stalk. The galls on the petioles
are twisted into a spiral form, and are not so thick and
discoloured as the above-mentioned species. Pemphigus
spirothecae, Koch.
Coniferae.
Abies communis, L. Bud. The "pine-apple" galls on our
common spruce are best known in their old woody condition,
as they remain on the tree for some time after the Aphides
have quitted them. When fresh the gall resembles a small
green cone, as it consists of a mass of short, fleshy, ovate,
imbricate leaves at the base of a young branch; these enclosed
cavities open when the gall is mature, and liberate the
Aphides in early summer. Adelges Abietis, Linne.
Taxus baccata, L. Terminal leaves. At the end of a branch
we often find a rosette of crowded and somewhat shortened
leaves. The gnat larva lives within the bases of the leaves,
and pupates therein in spring; the gall-gnats emerge from
the "artichoke" galls in June. Cecidomyia Taxi, Inchbald.
 Gramineae.
Triticum repens, L. Top shoot. In autumn or winter
we find the imbricate, closely-sheathed leaves of a top shoot
converted into a more or less cylindrical hard gall, which
tapers towards both ends, attaining a length of from one to
one and a half inch. In this country one of the parasitic
Eurytomidae (Chalcididae) has been given as the gall-maker,
which is undoubtedly a Dipteron, and is probably Lonchaea
parvicornis, Meigen.