Walnut, the common name of large nutbearing forest trees of the genus juglans (from Lat. Joris glans, the nut of Jupiter), which with the hickories (carya) and a few others make up the walnut family (juglandacece), in which the trees have a colorless juice, a strongscented bark, compound leaves, the staminate flowers in catkins, the fertile in small clusters of two or more; the fruit a dry drupe, with a single four-lobed seed. In the walnut tree several accessory buds are formed, one above another, the uppermost far above the axil; the pith of the stems is in transverse plates; the odd-pinnate leaves have numerous leaflets; sterile flowers in long, simple, solitary lateral catkins, from the wood of the previous year, each with 12 to 40 stamens; fertile flowers in small clusters on a peduncle at the ends of the branches, each with a four-toothed calyx and four small petals, the ovary with two very short styles, and club-shaped, fringed stigmas; the outer portion of the drupe (epicarp) fleshy and fibrous, not splitting at maturity; the inner portion or nut (endocarp) irregularly furrowed, and in our species very rough, to which the husk clings at maturity.
The hickories are often incorrectly called walnuts. (See Hickory.) - Three species of walnut are indigenous to the United States. The black walnut (J. nigra) is found from New England to Florida, but is much less abundant east than west of the Alleghanies, where, especially in the valley of the Mississippi, it is one of the commonest trees; it is a large, quick-growing tree, and when in a forest has a clear trunk 30 to 50 ft. without a branch, but in open ground it branches low, and forms a wide-spreading head. A celebrated specimen stands on the grounds of W. C. Bryant at Roslyn, L. I., the seed of which is known to have been planted in 1713; at 3 ft. from the ground it measures 25 ft. in circumference. The leaflets are ovatelanceolate, somewhat heart-shaped or unequal at base, smooth above and minutely downy below; the fruit is spherical, the surface marked by rough dots, greenish yellow when ripe,, but soon turning black; the round, slightly flattened nut has a deeply corrugated, hard shell, with an oily kernel, which soon becomes rancid. The wood of the black walnut is hard, finegrained, and durable, and takes a fine finish. When first cut it is purplish brown, but with age it turns very dark, even almost black.
The husks of the fruit are used in dyeing, and an oil may be expressed from the kernels. On account of its rapid growth and the value of its timber, this is largely planted in the treeless portions of the western states; the nuts, gathered into heaps, are covered with straw and earth to keep out rain, and in spring are planted where the trees are to stand. The closely related J. cinerea is described under Butteenut. The only remaining species, the rock walnut (J. rupestris), is found in western Texas, New Mexico, and Arizona; it is a shrub, or sometimes a tree 30 ft. high, with numerous curved leaflets, and a globose fruit with a thin pulp, enclosing a nut about half an inch in diameter, with a remarkably thick shell, the kernel being only as large as a pea. - The European walnut (J. regia), also called in tins country English walnut, is a native of Asia, and probably of Greece. It grows abundantly throughout Europe, but in this country it rarely ripens its fruit. It forms a large tree; the leaflets are fewer than in our black walnut, oval, smooth, and with entire margins; the fruit is oval, the husk, unlike that of our species, thin and brittle, and readily breaking away from the smoothish, thin-shelled nut.
In Europe, where much attention is given to its cultivation, about a dozen named varieties are known, distinguished by the abundance, size, and shape of the fruit, the thinness of the shell, and quality of the kernel; these are propagated by grafting upon seedling stocks; one dwarf variety, called prceparturiens, produces fruit in three or four years from seed, a peculiarity that is continued by the seed; the double walnut, the noyer d bijoux of the French, is cultivated for its large nuts, the shells of which are converted into boxes to hold a pair of gloves, jewelry, etc. The sap of the tree (like that of our species) contains sugar, and has been used in some countries as a source of that product; it is sometimes concentrated and fermented to make walnut wine. The wood, especially from trees grown upon poor soil, is valued for cabinet work, though inferior in beauty to black walnut. The fruit when partly grown, and still so soft that a pin will pass readily through it, is used for pickling and to make walnut catsup; our butternut makes an excellent substitute. In Europe the nuts are esteemed only when fresh; those which are to be kept are mixed with layers of sand in jars, and buried.
In countries where the trees abound, large quantities of the nuts are pressed for their oil; for the finest the nuts are cracked, and the thin woody partitions carefully separated from the kernels, which are ground and pressed; this product is used for food, the same as olive oil.
Nut (1) and Seed (2, 3) of European Walnut.
Staminate and Pistillate Flowers.
Black Walnut (Juglana nigra) - Tree near Eoslyn, Long Island, N. Y.
European Walnut (Juglans regia).
A second pressing, after heating the residue, is used as a painter's oil, which is also obtained by heating the nuts at the first pressing if table oil is not required; the oil is used byartists and for the finer kinds of printers' ink, and is burned in lamps.