104 The Galls of Essex; a Contribution to a
growth of the normal organ affected by the gall the more
short-lived the abnormal formation. In other words, the
most quickly matured species of galls are always on the
short-lived organs of reproduction rather than on the slow-
growing organs of vegetation. For instance, in the oak,
compare the catkin galls with the root and stem galls—the
growth of Spathegaster baccarum galls with those of Aphilothrix
Sieboldi, for instance. In the galls of S. baccarum I have also
noticed that the growth is quicker in the catkin form than in
the leaf form; the spring bud galls (e.g., Spathegaster aprilinus,
Aphilothrix albopunctata, &c.) grow and mature much faster
than the autumn galls (Aphilothrix globuli, Andricus
gemma, &c).
In the galls of the Cynipidae we thus know that, soon after
the deposition of the egg, active animal growth commences ;
this immediately sets up irritation of the plant-tissues, and
according to the subtle specific character of the irritation and
the nature of the part of the plant acted upon, the particular
morbid or hypertrophied growth is produced and is main-
tained by an increased influx of nutritive material. This
growth, however, only continues during the active life of the
tenant; for as soon as the irritation ceases, apparently the
vegetal growth also stops. This is quite analogous to the
action of certain special irritants and the diagnoses of certain
inflammatory actions in causing oedematous swellings in
animal organisms, the different effects and nature of each
being well known; as with the multifarious forms of galls the
cause and effect are patent, but the subtle differences
occasioning such constant but diversified results are un-
traceable. In the animal kingdom, hypertrophy or thickening
of the cuticle is known to occur as the result of continued
pressure to any part; but a less pronounced form of hyper-
trophy of cuticle is seen in the various forms of warts, where
pressure is not an immediate agency in their production.
I believe no intelligible explanation of the cause of warts and
similar excrescences in the animal kingdom can be given; it
is so with the vegetable galls, but in this kingdom we well know
that the growth of the cambium tissue, &c, is accelerated