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Acacia Trees

Few exotic trees have been so much discussed, or have undergone such vicissitudes of popularity and neglect as has the species commonly known as the Acacia tree (Robinia pseud-Acacia, L.).

Acacia Tree Origins

Golden Acacia Tree

Originally a native of North America, its seed is said to have been first introduced into Europe either, in 1601, by Jean Robin, herbalist to Henri IV., whose "Histoire des Plantes" was published in 1620, or by his son Vespasian, who grew it in the Jardin des Plantes in 1635. Parkinson, in his "Theatrum Botanicum" (1640), speaks of it as grown "to an exceeding height" by the elder Tradescant at Lambeth, he having possibly received it direct from Virginia, through his son. This tree was still standing when Sir William Watson examined the remains of Tradescant's garden in 1749. Evelyn, in his "Sylva" (1664), says of it: "By reason of its brittle nature, it does not well resist . . . our high winds; and the roots, which insinuate and run like liquorice under ground, are apt to emaciate the soil, and, therefore, haply not so commendable in our gardens as they would be agreeable for variety of walks and shade. They thrive well in His Majesty's new plantation in St. James's Park." These particular trees were, however, felled before the year 1712. John Ray, the contemporary of Evelyn, mentions the species as growing in Bishop Compton's garden at Fulham; whilst by 1731, as recorded by Philip Miller in his "Gardener's Dictionary," it had become common, and was known as ripening seed in this country.

Acacia Tree Uses

It had long been valued as a timber tree in the United States, and in Virginia and New England was used for treenails in shipbuilding, being hard, strong, inelastic, and durable. Much attention was directed to it in Europe for this and other purposes in 1762, in 1786, and at subsequent dates. It was described as suitable for axletrees, cogs, or wedges, as being a good fuel, and even as capable of cultivation as green forage for cattle; and in 1791 a Mr. Ebenezer Jessup proposed in the Gentleman's Magazine that ten thousand acres in the New Forest and Forest of Dean should be planted with this tree for the purposes of the navy, stating that he knew posts made of its wood to last from 80 to 100 years.

William Cobbett, while farming on Long Island, between 1817 and 1819, was struck with its utility, and on his return to England brought home some of its seed, which, from 1823, he cultivated on an enormous scale at Kensington and Barnes. He wrote of the tree in terms of the most extravagant eulogy, styling it the "tree of trees," and prophesying that it was destined to speedily replace most of the hard-wood trees in cultivation. Ignoring the fact that the Robinia was already well known in England under the name "Acacia," not only to botanists but also to nurserymen, he popularized the American name "Locust," and obtained so large a sale for it, though at a price more than six times its ordinary market value, that he not only imported the seed by tons, but even bought up plants raised from English seed to sell again at fancy prices.

Confused in the 17th century with the Acacias of Egypt and Arabia, which it resembles mainly in foliage and fruit, and by the American colonists with the Carobbean, Locust, or St. John's-bread, of South Europe (Ceratonia siliqua), whence its French name, "Carouge des Americans," this tree was named by Linnaeus after its introducer, and in reference to this confusion, Robinia pseud-Acacia, the Robinia, or False Acacia.

Acacia Tree Family

All three trees belong to the great family Leguminosae, the Pea and Bean tribe; but the pea-shaped blossoms of the Robinia, which are generally white, as distinguished from the small, many-stamened, yellow, bottle-brushlike flowers of the true Acacia, have given to the former the popular names of White Acacia, or "Acacia blanc."

Robinia is allied to the Restharrows (Oncnis), and to the Brooms and Laburnums (Cytisus), belonging with them to the section Loteae of the sub-order Papilionaceae. The members of this sub-order take their name from the supposed resemblance of their pea-like blossoms to a butterfly, and are further characterized by having ten stamens in each flower. In the section Lotea the pod-like fruit or "legume," which gives its name to the whole order, is not divided up into joints; and the seed is occupied by an embryo, or young plant, the primary rootlet, or "radicle," of which rests against the edges of its two leaves, or "cotyledons," whilst these cotyledons are themselves flat, and in the process of sprouting or germination rise above ground as the two first foliage-leaves of the plant. In this last respect the seed resembles that of a bean more than that of a pea, in which the cotyledons, remaining within the seed, act merely as storehouses of reserve nutriment, and the next pair of leaves produced are the first to rise above ground.

The genus Robinia is distinguished by its pods being flat and being furnished with a projecting flange externally along that margin to which the seeds are attached internally--the margin termed "ventral"--and also by its leaves being made up of several pairs of leaflets with an odd terminal one. The distinctive characteristics of the species known as the False Acacia are its scented flowers, generally white, and hanging in a loose raceme or cluster, like that of the Laburnum, the egg-shaped leaflets, and the pair of prickles at the base of each leaf representing the "stipules." These appendages are very variable in different plants, being often absent altogether or but small and fugacious, represented by large leaf-like structures as in the Pea, or performing the entire function of the leaves, as in some Vetches.

In some of the true Acacias they are also thorns, but are hollowed out so as to furnish lodgings for tribes of ants, which protect the shrub from other species of the same group of insects who would despoil it of its leaves; but the function of the solid prickles in the False Acacia is not so obvious--not, at least, when the tree is fully grown. From these prickles and its pod-like fruits this species derives its German name, "Schotendorn."

Growing the Acacia Tree

This tree can be raised either from seed, from cuttings, or by grafting; it will grow in any soil that is not too wet, and is a quick-growing but short-lived plant; but the quality of its timber undoubtedly varies according to the character of the soil in which it is grown. It may reach a height of seventy or eighty feet, with a diameter of two, three, or, in Kentucky, as much as four feet; and even in the neighborhood of London it has been known to reach forty feet within ten years, sometimes making shoots eight or ten feet long in a single season.

The wood of the best varieties, when well grown, is hard, strong, and durable, takes a good polish, and is prettily veined with brown. Besides its use in ship-building and for agricultural purposes, it is employed in America for the sills of doors and windows, for cabinet work, and in the making of toys. When quite dry it weighs forty-eight pounds per cubic foot, being, in fact, heavier, harder, stronger, tougher, more rigid, and more elastic than English Oak. Speaking absolutely, however, it is an inelastic wood, to which quality, coupled with its hardness, it owes its value for treenails. Acacia wood is somewhat twisted in its growth, and liable to crack, while the branches break off in a brittle, splintery manner. It must, moreover, be noted that the good qualities ascribed to this timber belong only to the variety known in America as the Red Locust.

The species has a latitudinal range from Canada to Carolina, and is very variable, especially when grown from seed, no less than sixteen varieties being described by Loudon. Some of these may be geographical races. Among them is one with yellow flowers, three destitute of prickles, and others with the leaves curled or with nearly erect or very pendulous branches; but the most important distinctions are those based on the color of the wood, which may be only the result of differences in soil and climate. Of these there are three varieties recognized in the United States: the Red Locust, with red heart-wood, the most beautiful and durable timber of the three; the Green Locust, with a greenish-yellow center, which is the commonest; and the White Locust, which is the least valuable. Is is stated that a post made of Red Locust will outlast two made of the White.

The bark remains smooth for ten or fifteen years, but then becomes longitudinally furrowed--in old trees to a considerable depth. The branches rise slightly when first springing from the nearly cylindrical main stem, but then spread out horizontally, giving off an abundance of secondary branches, which take a similar direction.

The leaves consist of from four to nine pairs of egg-shaped leaflets and a terminal one, in all eight, nine, or twelve inches long, the individual leaflets often exceeding an inch in length. Their late appearance and early fall is one of the chief drawbacks to the planting of the tree for ornamental purposes; but they have the countervailing advantage of being so smooth that the least shower cleans them of what little dirt can adhere to them, so that in the metropolis, or other large towns, they appear fresh and verdant in July and August, when most other foliage has become dull and soot-begrimed. The leaflets, like those of so many of the Leguminosa, close at night or in wet weather in what is termed "sleep," being then folded in a vertical plane, as when in the bud.

It is not to be supposed that much folk-lore should be associated with a tree of such recent introduction into Europe as the Acacia; but it is in connection with its clusters of pure white blossoms that this tree enters into the symbolism of the aborigines of its native land. The North-American Indian presents a blossoming branch of the Acacia to the lady of his choice as a declaration of his love. The botanist describes these blossoms as consisting of five sepals, five petals, ten stamens, and a single carpel. Of the five small green sepals, two at the back of the flower, i.e., nearest to the main stalk of the inflorescence, support the large, upright petal known as the "vexillum," or standard. At the sides are the smaller wings, and below are the remaining two petals, which in their partial union suggest the keel of a boat, and are, therefore, known technically by that name. This arrangement of the petals, which are elaborately molded over one another at their bases, and that of the ten stamens--the nine lower ones united into a tubular investment to the ovary, while the uppermost one is unattached--is, no doubt, connected, as is the honey and the perfume, with the visits of insects, to secure at least an occasional cross-pollination. In San Domingo an excellent liqueur is prepared from the blossoms. The flowers are succeeded by pods, about three inches long, each containing from five to six brownish black seeds, which ripen readily in this country.

Acacia Tree Enemies

The tree has but few enemies, though in America its timber sometimes suffers considerably from the ravages of a larva (Cossus robiniae) allied to our own goat-moth. Hares and rabbits devour the bark when young, and cattle are fond of the leaves, which they manage to eat, when within reach, in spite of the prickly stipules. The Acacia will not, however, serve as a cover for game, being intolerant either of shade or of the drip of other trees. Its moist, quick-growing sap-wood and succulent foliage, however, have caused the Acacia to be strongly recommended for the planting of railway embankments in forest areas, so as to intercept the sparks before they can spread to more inflammable timber-trees, such as the firs.

Though it becomes straggling from a habit of dying piecemeal when by no means an old tree, the airy lightness of its sprays of pure green foliage certainly renders the Acacia one of the most desirable of town trees.

Acacia Tree Pictures

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