72
THE ESSEX NATURALIST.
to one side, until it reaches the position in which we find the
cist. The passage through the wood to the cist was traceable
in all the autumn-gathered stems I examined, though not very
easily, as it seems to close somewhat quickly. Apparently,
the gall-insect, on reaching maturity, passes right through
the stem and emerges on the further side. On two of the stems
shown may be seen some large hollows (figs. 6 and 7), which I
regard as scars of exit.
I am greatly indebted to Miss A. Hibbert-Ware, F.L.S., who
has been kind enough to devote much time and care to an
attempt to discover in the tunnels some trace of the gall-producer
from which one might be able to identify the species. In this,
she has failed ; which was, perhaps, not remarkable, inasmuch
as the only material available for examination was ten years
old. "The cause of the gall" (she writes) is certainly a
miner, and the tunnels show (by frass) plenty of signs of
having had an occupant ; but there it begins and ends."
Finally, how are we to account for the very-remarkable
arrangement of the individual galls in spiral lines on the bark
of the osier-stem ? I suggest that the gall-producer is some
creature accustomed to shelter beneath the stem of some climbing
plant which twines round the stems of the osiers. This creature
apparently punctures the bark of the osier along the line of the
stem of the twining plant, inserting its ova into the wounds
thus caused, at intervals, in a line, one after the other, to the
number of not more than ten together. It then proceeds,
doubtless, to repeat the process on some other part of the bark.
It is hardly possible, I think, to explain, on any other
hypothesis, the various phenomena described above ; but there
is, I fear, little hope of demonstrating its truth by direct
observation—I mean by observing the gall-producer actually
in the act of depositing its ova. On Mr. Swanton's suggestion,
I visited the osier-ground several times during the spring,
summer, autumn and early winter of 1916, in the hope that
I might be able to detect some gall-producing creature sheltering
between the stem of the osier and the stem of the twining plant.
In this, however, I was entirely unsuccessful. It was, perhaps,
hardly to be expected that I should succeed ; for it may very
well be that the visits of the gall-producer for the purpose of
depositing its ova are short and transient, perhaps nocturnal.
I was not able even to observe a single case in which a twined