lxx Journal of Proceedings.
especially. These he thought partook of a vegetative or fungoid, para-
sitical nature, and were clearly distinct in their origin and development
from true galls produced by insects.
Mr. Letchford called attention to the very remarkable chemical sub-
stances found in abundance in the tissues of many galls. These
substances appeared to exist in the sap of the trees, but became concen-
trated in the galls, and seemed to be a necessary concomitant of their
growth.
Mr. Henry Walker gave some details as to the morphological structure
of galls, and alluded to the appearance of the Devonshire or "Marble-
gall" (Cynips Kollari), near London, within living memory. Many years
ago the late Frederick Smith put a large quantity of these galls into
Highgate Wood, and he thought it was possible that the rapid spread of
the marble-gall might have had some connection with that circumstance.
Mr. Walker also called attention to the bearing of the very remarkable
observations of Dr. Adler as to the existence of di-morphism in galls
upon the current theories of evolution.
Mr. Meldola stated that there had always appeared to him one difficulty
in connection with the mechanical theory of galls which he would be glad
to see explained. He did not wish his remarks to be considered in
any way critical, but he could not help feeling that there, was an objection
which Mr. Fitch would perhaps throw some light upon. In accordance
with what he would call the purely mechanical theory of galls these
growths were caused by the presence of the egg of the insect laid in the
leaf-tissue or other part of the plant, and acting as a local irritant. He
could easily understand how on this view differently formed galls might
result from the irritating action of eggs laid in different parts of the
plant, but he could not see how on this theory it was possible to account
for the fact that on the leaves of the same plant a large number of insects
could each give rise to a differently formed gall. It had been proved that
the egg continued to grow for some time within the gall, but this did not
appear to him sufficient to explain the fact mentioned. A different form
of egg, and a different rate of growth for each species, was assumed,
but this was so far only an assumption ; experimental and observational
proofs were required in order to demonstrate conclusively that there
existed a connection between the form and rate of growth of the egg
and the form of the gall. As to the points raised by Mr. Walker,
Mr. Meldola said that he had lately been working at them, and hoped
to address some remarks upon the subject to the Club at the Annual
Meeting.
In reply, Mr. Fitch stated, with reference to Dr. Pearce's remarks,
that Sir James Paget, in making his comparisons, had expressly noted
the great contrasts between the pathology of animals and plants.
From his own point of view also it was by no means intended to
institute a comparison between the special viruses which we know are
capable of being artificially introduced into the human body, or with