The Ailantus is a native of China, where it becomes a very large tree,
often attaining the height of seventy feet. It was imported into Great
Britain more than a century ago, for the benefit of the silk
manufacture. A species of silkworm, which was known to be hardy and
capable of forming its cocoons in the English climate, is attached to
this tree and feeds upon its leaves. “The _Bombyx cynthia_,” says
Mongredien, “thrives well in the open air (of England) in ordinary
seasons, and requires no care after being once placed on the tree. About
August it spins its cocoon on one of the leaflets, bending its edges
inwards, so as to form a partial envelope. As the tree is deciduous, the
leaf would drop and the cocoon with it, were it not that, by an
instinct, the insect, before spinning its cocoon, attaches by its
strongly adhesive threads the stalk of the leaf to the woody twig that
sustains it. Hence the leaves that bear the cocoons are the only ones
that do not drop, and there remain persistent through the whole of the
winter.”
This experiment with the Ailantus proved a failure; but the tree, being
very stately and ornamental, continued to be cultivated in
pleasure-grounds. It was introduced into the United States in the early
part of this century, and is now very common in almost all the States as
a wayside tree. It possesses a great deal of beauty, being surpassed by
very few trees in the size and graceful sweep of its large compound
leaves, that retain their brightness and their verdure after midsummer,
when our native trees have become dull and tarnished.
The leaves of the Ailantus are pinnate, containing from nine to eleven
leaflets, each of these being as large as the leaf of the beech-tree. It
has a great superficial resemblance to the velvet sumach, both in its
foliage and ramification, so that on first sight one might easily be
mistaken for the other; for its branches, though more elegant, have the
same peculiar twist that gives the spray of the sumach the appearance of
a stag’s horn. The flowers are greenish, inconspicuous, and in upright
panicles, resembling those of the poison sumach. They emit a very
disagreeable odor while the flowers are in perfection, impregnating the
air for a week or more.