CURRANT GALLS.
Still more singular is the gall found in the catkins of the oak. The flies deposit their eggs in the stalk of the stamen-bearing flowers, which in consequence become adorned with what appear to be straggling bunches of currants or bird-cherries. Placed at short distances from each other on the thread-like stem, these excrescences so much resemble currants in size, shape, and mode of growth, that they have been named “currant galls.”
ARTICHOKE-GALL.
Among the species of gall to which our oaks are subject, there are some which grow at the end of the twig, as for instance, that called the artichoke-gall, which comes the nearest in appearance to the nut-gall of commerce, since it is, in common with that nut, an irregular development, not of the leaf or flower, but of the bud. The artichoke-gall might indeed be easily mistaken for the fruit of the tree, by any one unacquainted with the habit of the oak. It is a cone-like body, consisting of a number of leafy scales overlapping each other, but on being dissected it is found, like other galls, to contain insects in various stages of their growth, according to the season. In the same way, the nut-gall, being a disease of the bud, or extremity of the young shoots of the oak on which it grows, has the appearance common to some other kinds of fruit, and would seem to be the ordinary produce of the stalk, did we not find that acorns also grow on the same tree. The hard and brittle texture of the gall-nut also, so different from the substance of our own oak-galls, would be still more likely to deceive, and indeed has deceived a highly respectable writer, who declares from his observation of the dried galls of commerce, that the nut is the fruit of a tree, and not a mere excrescence.[[4]]
[4]. Aikin.
How it is that the different species of gall-fly should produce such varied results, and why one excrescence should be the oak-apple, another the spangle, a third the artichoke, and a fourth the nut, is indeed a mystery. But that these small insects do really produce the excrescences in question, is an ascertained fact, and a most important one in the commercial world.
Nut galls contain a large quantity of the vegetable principle called tannin, being the astringent property for which oak-bark is in so much repute. They also abound in an acid called from thence gallic acid, which is the important ingredient in black dyes, and in fixing and improving several other colours, as well as in the composition of ink.
BLISTERING BEETLE.