Pod Bearing Trees
( Originally Published 1927 )
Whenever we see blossoms of the sweet-pea type on a tree or pods of the same type as the pea's swinging from the twigs, we may be sure that we are looking at a member of the pod-bearing family, leguminosae, to which herbaceous and woody plants both belong. The family is one of the largest and most important in the plant kingdom, and its representatives are distributed to the uttermost parts of the earth. Four hundred and fifty genera contain the seven thousand species already described by botanists. Varieties without number belong to the cultivated members of the family, and new forms are being produced by horticulturists all the time. This great group of plants has fed the human race, directly and indirectly, since the First Man appeared on earth. Clovers, alfalfas, lentils, peas, beans yield foodstuffs rich in all the elements that build flesh and bone and nerve tissues. They take the place of meat in vegetarian dietaries.
Besides foods, the pod-bearers yield rubber, dyestuffs, balsams, oils, medicinal substances, and valuable timber. A long list of ornamental plants, beautiful in foliage and flowers, occurs among them, chiefly of shrub and tree form.
Last, but not least, among their merits stands the fact that leguminous plants are the only ones that actually en-rich the soil they grow in, whereas the rest of the plant creation feed upon the soil, and so rob it of its plant food and leave it poorer than before.
Pod-bearers have the power to take the nitrogen out of the air, and store it in their roots and stems. The decay of these parts restores to the soil the particular plant food that is most commonly lacking and most costly to replace. Farmers know that after wheat and corn have robbed the soil of nitrogen, a crop of clover or cow peas, plowed under when green and luxuriant, is the best restorer of fertility. It enriches by adding valuable chemical elements, and also improves the texture of the soil, increasing its moisture-holding properties, which commercial fertilizers do not.
Seventeen genera of leguminous plants have tree representatives within the United States. These include about thirty species. Valuable timber trees are in this group. All but one, the yellow-wood, have compound leaves, of many leaflets, often fernlike in their delicacy of structure, and intricacy of pattern. With few exceptions the flowers are pretty and fragrant in showy clusters. The ripening pods of many species add a striking, decorative quality to the tree from midsummer on through the season. Thorns give distinction and usefulness to certain of these trees, making them available for ornamental hedges.
Three representatives of the genus robinia are among our native forest trees. They are known in early summer by their showy, pea-like blossoms in full clusters, and their compound leaves, that have the habit of drooping and folding shut their paired leaflets when night comes on, or when rain begins to fall. The pods are thin and small, splitting early, but hanging late on the twigs.
The Black Locust
Robinia Pseudacacia, Linn.
The black or yellow locust is a beautiful tree in its youth, with smooth dark rind and slender trunk, holding up a loose roundish head of dark green foliage. Each leaf is eight to fourteen inches long, of nine to nineteen leaflets, silvery when they unfold, and always paler beneath. In late May, the tree-top bursts into bloom that is often so profuse as to whiten the whole mass of the dainty foliage. The nectar-laden, white flowers have the characteristic "butterfly" form, the banner, wings, and keel of the type pease-blossom. The bees lead the insect host that swarms about them as long as a locust flower remains to offer sweets to the probing tongues. Cross-fertilization is the advantage the tree gains for all it gives. The crop of seeds is sure.
The angled twigs of the black locust break easily in windy weather. The rapid growth of the limbs spreads the narrow head, and its symmetry is soon destroyed, unless the tree grows in a sheltered situation. An old locust is usually an ugly, broken specimen, ragged-looking for three-fourths of the year. The twigs look dead, because their winter buds are buried out of sight! The bark is dull, deeply cut into irregular, interlacing furrows, roughened by scales and shreds on the ridges. In winter the pods chatter querulously, as the wind plays among the tree-tops.
The black locust is found from Pennsylvania to Iowa, and south from Georgia to Oklahoma. The lumber is coarse-grained, heavy, hard, and exceptionally durable in contact with the soil or water. This makes it especially adaptable for fence posts and boat bottoms. Crystals, called raphides, in the wood cells, take the edges off tools used in working locust lumber. Yet it is sought by manufacturers of mill cogs and wheel hubs, and railroad companies plant the trees for ties.
The locust-borer has ruined plantations of this tree of late years, and trees in the woods have become infested except in mountainous regions not yet reached by the pest. Trees become distorted with warty excrescences and the lumber is riddled with burrows made by the larvae. Until the entomologist finds a remedy in some natural parasite of the locust-borer, the outlook for locust culture seems dark enough. No insecticide can reach an enemy that hides in the trunk of the tree it destroys.
The Clammy Locust
R. viscosa, Vent.
The clammy locust has beautifully shaded pink flowers in clusters, each blossom accented by the dark red, shiny calyx, and the glandular exudation of wax, that covers all new growth. A favorite ornamental locust, this little tree has been widely distributed in this and other temperate countries of the globe. Its leaves are delicately feathery, with the dew-like gum brightening them, as it does also the hairy, curling pods that flush as they ripen. In winter the twigs are ruddy. The trees grow wild on the mountains of the Carolinas and nowhere else.
The Honey Locust
Gleditsia triacanthos, Linn.
The honey locust is a tall handsome flat-topped tree, with stiff horizontal, often drooping branches, ending in slim brown polished twigs, with three-branched thorns, stout and very sharp, set a little distance above the leaf scar of the previous season. Occasionally a thornless tree occurs.
Inconspicuous greenish flowers, regular, bell-shaped, appear in elongated clusters, the fertile and sterile clusters distinct, but on the same tree. The leaves are almost full-grown when the blossoms appear. Their feathery, fern-like aspect is the tree's greatest charm in early June. When the pods replace the flowers they attract attention and admiration as their velvety surfaces change from pale green to rose and they curve, as they lengthen, into all sorts of graceful and fantastic forms. The sweet, gummy pulp of the honey locust pods is considered edible by boys, who brave the thorns to get them. As the autumn approaches, the pulp turns bitter, and dries around the shiny black seeds. The purple pods cling and rattle in the wind long after the yellow leaves have fallen. One by one, they are torn off, their S-curves tempting every vagrant breeze to give them a lift. On the crusty surface of snowbanks and icy ponds, they are whirled along, and finally lodge, to rot and liberate the seeds. It takes much soaking to pre-pare the adamantine seeds for sprouting. The planter scalds his seed to hasten the process. Nature soaks, freezes, and thaws them, and thus the range of the honey locust is extended.
In the wild, this tree is found from Ontario to Nebraska, and south to Alabama and Texas. It chooses rich bottom lands, but is found also on dry gravelly slopes of the Alleghany Mountains. Trunks six feet in diameter are still in existence, preserved from the early forests of the Wabash Basin in Indiana. They tower nearly one hundred and fifty feet above the ground, and their branches are a formidable array of thorns (see illustration, page 198), that have grown into proportions unmatched in trees of slender build and fewer years. Such a veteran honey locust is one of the most picturesque figures in a winter landscape.
Honey locust wood is hard, coarse-grained, heavy, and durable in contact with water and soil. It is made into wheel-hubs, fence-posts, and fuel. In all temperate countries this species has been used as a shade and ornamental tree and as a hedge plant.
The Kentucky Coffee Tree
Gymnocladus dioicus, K. Koch
The Kentucky coffee tree is the one clumsy, coarse member of a family that abounds in graceful, dainty species. Its head is small and unsymmetrical, above a trunk that often rises free from limbs for fifty feet above ground. The branches are stiff and large, bare until late spring, when the buds expand and the shoots are thrown out. The leaves are twice compound, often a yard in Iength and half as wide; the leaflets, six to fourteen on each of the five to nine divisions of the main rib. No other locust can boast a leaf numbering more than one hundred leaflets, each averaging two inches in length. When the tree turns to gold in autumn, it is a sight to draw all eyes.
The flower spray is large, but the flowers are small, imperfect, salver-form, purplish green—the fertile ones forming thick, clumsy pods that dangle in clusters, and seem to weigh down the stiff branchlets. The fresh pulp used to be made into a decoction used in homeopathic practice. The ripe seeds were used in Revolutionary times as a substitute for coffee. How the pioneer ever crushed them is a puzzle to all who have tried to break one with a nut-cracker. In China the fresh pulp of the pods of a sister species is used as we use soap.
The wood is not hard, but in other respects it resembles other locust lumber. It is sometimes used in cabinet work, being a rich, reddish brown, with pale sapwood.
The range of the coffee tree extends from New York to Nebraska, and south through Pennsylvania, Tennessee and Oklahoma, with bottom lands as the tree's preference. Nowhere is this species common. Occasionally, it is planted as a street tree, in this country and abroad.
Cercis Canadensis, Linn.
The redbud covers its delicate angled, thornless branch-lets with a profusion of rosy-purple blossoms, typically pea-like, before the leaves appear. The unusual color, so abundant where little redbuds form thickets on the outskirts of a woodland, leads to a very general recognition of this tree among people who go into the April woods for early violets. It vies with the white banner of the shadbush, in doing honor to the spring. Later, the broad heart-shaped leaves cover and adorn the tree, concealing the dainty tapering pods that turn to purple as the polished leaf blades, unmarred by insect or wind, change from green to clear yellow before falling.
Tradition has given this charming little locust tree the name, "Judas-tree," from its European cousin, rumored to have been the one upon which the choice of Judas fell when he went out and hanged himself. It is an unearned stigma, better forgotten, for it does prejudice the planter against a tree that should be on every lawn, preferably showing its rosy flowers against a bank of evergreens.
Its natural range extends from New Jersey to Florida and west from Ontario to Nebraska and southward. The largest specimens reach fifty feet in height in Texas and Arkansas, in river bottom lands, and in the Southwest the tree is an abundant undergrowth—making a beautiful woodland picture in early spring.
Cladrastis lutea, K. Koch.
The yellow-wood was named by the wife of a pioneer, surely, for she soaked the chips and got from them a clear yellow dye, highly prized for the permanent color it gave to her homespun cotton and woolen cloth that must have gone colorless, but for dyestuffs discoverable in the woods.
The satiny grain of the wood, and its close hard texture, commended it to the woodsman, who used it for gun stocks. But the tree is too small to be important for the lumber it yields.
In winter the smooth pale bark of the "Virgilia," as the nurseryman calls it, reminds one of the rind of the beech. The broad rounded head, often borne on three or more spreading stems, is formed of drooping graceful branches, ending in brittle twigs. Summer clothes these twigs with a light airy covering of compound leaves, of seven to eleven broadly oval leaflets, on a stalk less than a foot in length. In autumn, the foliage turns yellow.
White flowers, pea-like, delicate, fragrant, in clusters a foot long, and so loose that the flowers seem to drip from the twig ends, drape the tree in white about the middle of June, when the young leaves show many tints of green to form a background for the blossoms.
This is the supreme moment of the year for one of the most charming of trees, in any park that cherishes one of these virgilias. In the wilds of eastern Tennessee, northern Alabama, and central Kentucky the species is found in scattered places. But the wild trees have scant food and they show it. The full beauty of the species is seen only in cultivation, as one sees it in the Arnold Arboretum, and in private gardens near Boston. Even the little pods, thin, satiny pointed, add a harmonious note of beauty, their silvery fawn color blending with the quiet Quaker drab worn by the tree all winter. Fortunately, this hardy beautiful park tree is easily raised from seeds and from root cuttings. It thrives on soil of many different kinds. It has no bad habits, no superior, and few equals among flowering trees.