Walnut (Juglans), a botanical genus of about ten species (nat. ord. Juglandaceae), natives of the temperate regions of the northern hemisphere, extending into Mexico, the West Indies and tropical South America. They are all trees, usually of large size, with alternate stalked, unequally pinnate leaves, and abounding in an aromatic resinous juice. The scars left by the fallen leaves are unusually large and prominent. The buds are not unlike those of the ash; and it frequently happens that in the axils of the leaves, instead of one, several buds may be formed. The utility of this is seen in seasons when the shoot produced from the first bud is killed by frost; then one of the supplementary buds starts into growth, and thus replaces the injured shoot. The flowers are unisexual and monoecious, the numerous males borne in thick catkins proceeding from the side of last year's shoot. The female flowers are solitary or few in number, and borne on Short terminal spikes of the present season's growth. In the male flower the receptacle is "concrescent" or inseparate from the bract in whose axil it originates. The receptacle is, in consequence, extended more or less horizontally so that the flowers appear to be placed on the upper surface of horizontally spreading stalks. The perianth consists of five or six oblong greenish lobes, within which is found a tuft, consisting of a large number of stamens, each of which has a very short filament and an oblong two-lobed anther bursting longitudinally, and surmounted by an oblong lobe, which is the projecting end of the connective. There is usually no trace of ovary in the male flowers, though by exception one may occasionally be formed.
The female flower consists of a cup-like receptacle, inseparate from the ovary, and bearing at its upper part a bract and two bracteoles. From the margin springs a perianth of four short lobes. The one-celled ovary is immersed within the receptacular tube, and is surmounted by a short style with two short ribbon-like stigmatic branches. The solitary ovule springs erect from the base of the ovarian cavity. The fruit is a kind of drupe, the fleshy husk of which is the dilated receptacular tube, while the two-valved stone represents the two carpels. The solitary seed has no perisperm or albumen, but has two large and curiously crumpled cotyledons concealing the plumule, the leaves of which, even at this early stage, show traces of pinnae.
The species best known is J. regia, the common walnut, a native of the mountains of Greece, of Armenia, of Afghanistan and the north-west Himalayas. Traces of the former existence of this or of a very closely allied species are found in the PostTertiary deposits of Provence and elsewhere, proving the former much wider extension of the species. At the present day the tree is largely cultivated in most temperate countries for the sake of its timber or for its edible nuts. The timber is specially valued for furniture and cabinet work and for gunstocks, the beauty of its markings rendering it desirable for the first-named purpose, while its strength and elasticity fit it for the second. The leaves and husk of the fruit are resinous and astringent, and are sometimes used medicinally as well as for dyeing purposes. A Spiritus Nucis Juglandis is given as an antispasmodic. It doubtless owes its properties to the alcohol which it contains. Sugar is also prepared from the sap in a similar manner to that obtained from the maple. The young fruits are used for pickling. When ripe the seeds are much esteemed as a delicacy, while in France much oil of fine quality is extracted from them by pressure. There are several varieties in cultivation, varying in the degree of hardihood, time of ripening, thickness of shell, size and other particulars. In the climate of Great Britain a late variety is preferable, as securing the young shoots against injury from frost, to which otherwise they are very subject. The kernel of the large-fruited variety is of very indifferent quality, but its large shells are made use of by the French as trinket cases.
The walnut is mentioned in the earliest British botanical writings, and is supposed to have been introduced by the Romans. It grows well, and ripens its fruit in the southern and midland counties of England; but large trees may be seen as far north as Ross-shire in sheltered places. The tree succeeds in deep, sandy or calcareous loams, and in stiff loams resting on a gravelly bottom. It requires free exposure to air and light. It is propagated by seeds, and occasionally by budding, grafting or inarching for the perpetuation of special varieties. Seedlings should be protected from frost during the first winter. The trees form their heads naturally, and therefore little pruning is required, it being merely necessary to cut off straggling growths, and to prevent the branches from interlacing. The best time for performing this is in the autumn, just after the fall of the leaf. Plants raised from the seed seldom become productive till they are twenty years old. The fruit is produced at the extremities of the shoots of the preceding year; and therefore, in gathering the crop, care should be taken not to injure the young wood. In some parts of England the trees are thrashed with rods or poles to obtain the nuts, but this is not a commendable mode of collecting them.
Among the American species J. nigra, the black walnut, is especially noteworthy as a very handsome tree, whose timber is of great value for furniture purposes, but which is now becoming scarce. In Britain it forms a magnificent tree. The white walnut or butternut, J. cinerea, is a smaller tree, though it sometimes reaches 100 ft. in height; its inner bark yields an extractive, juglandin, given as an hepatic stimulant and cathartic in doses of 2-5 grains.
Closely allied to the walnuts, and sometimes confounded with them, are the hickories.
