A REMARKABLE GALL ON THE OSIER.
73
Convolvulus-stem encircling an osier-stem actually covered a
spiral line of galls. Here, again, however, it is not surprising
that I should have failed; for it may very well be that
the galls do not swell and become apparent until some time
after the deposition of the ova. As a matter of fact, the Con-
volvulus-stems, though they remain encircling the osier-stems
well into (and I believe, right through) the winter, generally
slip down the osier-stem several inches after withering, so no
longer cover the spiral lines of galls.
Assuming this explanation of the spiral lines to be correct,
it is not difficult to identify the species of twining plant concerned.
Three species of twining plant (and three only) grew in the osier-
ground in question, namely:—(1) the Hop (Humulus lupulus),
(2) the Large Convolvulus (Calystegia sepium) and (3) the Common
Bindweed (Convolvulus arvensis). All of these grew there
commonly, especially the two first-named, the site being too
low and wet to suit the last named. Now, the Hop twines
dextrally ; so cannot be the plant concerned. Then, the
Common Bindweed, beside being scarce there, seldom climbs
to the height above the ground at which the galls are commonly
found ; so is not likely to be the plant concerned. It is, there-
fore, a fair conclusion that the Larger Convolvulus is that plant.
As a fact, a large number of the osier-stems are found to be
encircled by it ; it is a sinistral climber ; and it climbs regularly
to the height indicated.
But, while we can thus identify the twining-plant concerned,
it is otherwise with the creature which produces this very
remarkable gall, and this still remains unidentified. I trust
that this record may have the effect of causing it to be detected
elsewhere and properly identified.
EXPLANATION OF THE PLATES.
Plate 5, fig. 1. Gall on Osier-stem, as seen in spring.
Plate 5, fig. 2. Do. do. do. do.
Plate 5, fig. 3. Do. do. as seen in late summer (showing one
scar of exit).
Plate 5, fig. 4. Do. do. as seen in autumn (showing two
scars of exit).
Plate 5, fig. 5. Do. do. as seen in autumn (showing one scar
of exit).
Plate 6, figs. 6 & 7. Do. do. showing "claw-marks" and scars
of exit (enlarged).