106 The Galls of Essex; a Contribution to a
shaped and variously constructed growths of cellular paren-
chymatous tissue and cork, and, more sparingly, of woody
tissue or of cells whose thick walls become as hard as wood.
Besides, some of the monstrous growths of parts of plants,
and some of the viviparous variations, and of the undue
metamorphoses of leaves, are to be referred to the influence
of parasites.
''It may seem bold to speak of so many hundreds of widely
various morbid processes as having any essential character
in common, or as fit to be included under one name; yet I
think we may regard the whole of these as being such as, in
our pathology, we should call inflammatory hypertrophies
or hyperplasiae. They all show a rapid increase of lowly
organised structures, by derivation from, and in continuity
with, those pre-existing. There is, as in the products of our
inflammations, a general likeness among these new structures,
whatever be the part of the plant from which they are
derived, and all bear, a general likeness to the structures
formed after injuries of actively growing parts. In the
morbid growths formed by these new structures, the deflection
from the natural shape and construction of the part, in con-
tinuity with which they have grown, is often not complete ;
they often retain marks of characteristic normal forms, and
sometimes acquire marks of natural variation from the
species. Moreover, all these morbid growths have their
origin in what may justly be called 'irritation' of the part
on which they grow; and in all of them, I think, we may
note signs of degeneracy from natural conditions, either in
the absence of stomata or similar structures, or in the
presence of the red, or yellow, or other colours commonly
noticed in decay.
"Here, I believe, are reasons enough for regarding all these
galls and gall-like products of disease, generated in plants by
insects, as analogous with a large group of the products of
inflammation which we study in our own pathology; and
the analogy is not the less because neither group can be
circumscribed with any exact definition.
"I will not be tempted to speak long, but I beg you to
think long, of the marvellous facts of natural adjustment
which we have here, in this intense example of the 'sic vos,
non vobis.' Here are the bare facts. Each species of these
parasitic insects can compel some part of a plant into such
disease as shall supply good food, or well-built and well-
placed lodging, or both, for itself or for its eggs and larvae, or
even for part of the life of its complete offspring. Each