List of the Insect Fauna of the County. 105
before the removal of pressure, as in the case of plant-
cuttings, the growth of trees, &c. Gall-growth may be
similarly affected by the removal of pressure through the
puncture made by certain gall-producers, and in obvious
other ways.
Sir James Paget has recently followed up Dr. Hollis's
suggestions in enunciating the importance of the comparative
pathology of oak-galls, in the remarkable address before
quoted. I cannot forbear giving his valuable remarks relative
to gall pathology in extenso, with the hope that some of our
members may be led to take up this interesting study, which
so closely affects both animal and vegetable physiologists.
These were his words :—
"Of all morbid processes in plants, none, I think, are so
suggestive as are those produced by parasites, whether vege-
table or animal. The whole subject would be far too large
to speak of, even if I were familiar with it; it is, indeed, a
subject of the gravest national importance; but, keeping to
the design with which I started, and which was only that of
pointing out where useful pathological knowledge may be
gained, I will speak of only some of the changes which are
produced by insects. The most remarkable of these are the
galls; and, among the many hundreds of them that have
been described, I may assume that you know some in their
natural mode of growth—such as the common oak-apple,
with which some celebrate the restoration of our monarchy;
and the bedeguar of the wild rose ; the bright crimson oak-
spangle, the currant-gall, or the artichoke-gall, or the gall of
pharmacy. But, besides the hundreds of different true galls,
there are still more hundreds of changes of structure in
leaves and stems and roots, all produced by the irritant
secretions of insects, and all such as may justly be ascribed
to processes of inflammation. In some, as in the 'curl' of
the leaves of the whitethorn, you find thickenings of leaves
which are lifted, rolled, or curled into chambers, which serve
for defence of the Aphides or other insects ; in some, the
thickened and distorted clusters of leaves, in buds or on
twigs, roll up and are mutually fastened, so as to form the
walls of similar defensive lodgings; in some cases, leaves
become swollen as with a kind of oedema; in some, their
layers separate as if with blistering; or leaves, or stems, or
fruits, or clusters of flowers, buds, or roots, produce variously
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