70
THE ESSEX NATURALIST.
the stems were galled. In reality, however, there were a good
many, as the osier-ground was fairly large ; but most of the
galled stems, if not all, were to be found in one particular part
of it. Most of the osier-stems which bore galls were less than
an inch in diameter, but a few were larger. The galls on the
stems were, as a rule, from four to seven feet above the ground.
I observed that, in many cases, a majority of the galls were
on one side of the stem only. It might be supposed, not un-
naturally, that this was due, in some way, to the influence of sun-
light or aspect ; but the feature was not observable in all cases,
and I believe that no significance attaches to it.
In regard to the individual galls; each appears externally
as a sort of raised wrinkled scar, or pustule-like swelling, on
the bark, 1-2 mm. in height and about 5 mm. in diameter.
A very remarkable feature is seen in the fact that the galls
are not scattered haphazard over the bark, but are arranged,
with remarkable regularity, in lines or rows running spirally up
and round the stems, each gall being equi-distant from its neigh-
bour, with intervals of 7-8 mm, between (see figs. 1-5). These
spiral lines are, however, discontinuous and of very varying
lengths. Sometimes one sees a single gall only—apparently
the first of a row which was never continued. More often, one
finds rows of three, four or five galls ; while rows of six, seven
or eight are common ; and rows of nine or ten are not very
rare. The latter number, however, constitutes the maximum,
so far as I have observed. A line consisting of this number is
about 6-8 cm. in length ; and, as the osier-stems average 2-3
cm. in diameter, a row of this length is sufficient almost to
encircle the stem. I have seen no line of galls long enough
to encircle a stem more than once ; and most lines are far too
short even half to encircle a stem. The lines of galls, as they
encircle the stems spirally, rise at an angle of about 450—some
a little more ; others a little less. That is to say, a line
sufficiently long to encircle a stem once rises about 3-4 cm.
in so doing. On some stems, the lines are very confused, often
stopping short and apparently recommencing again a little
higher up. Occasionally, too, parallel lines are so close to-
gether and confused as to appear almost superimposed.
Another very noticeable feature was that all the spiral
lines rose and encircled the stem in the same direction. The
coil of the spiral is always sinistral ; that is to say, the spiral