A REMARKABLE GALL ON THE OSIER.
71
lines all rise to the left, if the observer takes the internal view
and imagines himself to be the stem or in the centre of the
coil (see figs. 1-5). The cause to which this curious spiral
arrangement of the galls is due will be considered hereafter.
Yet another remarkable feature, which I had overlooked
until Mr. Swanton called my attention to it, is that, immediately
to the left of each gall (again taking the internal view), and
at a distance of almost exactly 5 mm. from its centre, there is
generally a triangular notch-like mark on the bark, as though
its surface had been picked or scratched up by some very sharp
fine-pointed instrument operating horizontally from the left to
the right side (see figs. 6 and 7). These triangular notches have the
appearance of having been made by the claw of some creature ;
and, although such may not be their true nature, they may
be spoken of, for convenience, as "clawmarks."
That the pustule-like swellings on the bark which I have
spoken of as galls are really such admits of no doubt. If one
cuts down into the wood-tissue below each gall, one finds a spot
at which the wood is brown, dead and pithy. This spot lies
usually at a depth of 3-4 mm., and it contains an ill-defined
cavity or cist. On one visit to the osier-ground, on some
unnoted date in the autumn of 1916, I opened one of these
cists with my pocket knife and saw distinctly a small whitish
grub ; but, owing to the extreme confusion of war-time, the
stems I brought away for careful examination were mislaid.
I believe, however, that the stem shown as fig. 3 was the one in
question. At all events, it shows a cist at the bottom of the
notch cut in its side. Worse than all, the osier-ground itself
was soon after done away with completely, it being re-planted
with Cricket-bat Willows (Salix alba var. caerulea), a much more
profitable crop, so that no further specimens can be obtained
from it ; and I have never since been able to find any osier-
stems similarly galled in any other osier-ground I have searched,
either in Essex or elsewhere.
Returning to the individual galls : we may assume that they
indicate the points of entrance—the points at which the gall-
producing insect (if it be an insect) punctures the bark of the
osier with its ovipositor and inserts its ova. Doubtless, as
each ovum hatches, the grub eats its way inwards through
the solid wood. I observed that. it does not do this directly
towards the centre of the stem, but horizontally and rather