577. The Royal or Common Walnut-tree is a native of Persia and the northern parts of China. It is found in most parts of Europe as far as 55° north latitude. The walnut-tree was formerly much cultivated in Britain for its wood, which was highly prized before the introduction of mahogany, and to which it is still preferred by many people of taste, who consider its colour to be superior to the red brown of mahogany. In many parts of the continent of Europe this wood is still extensively used for articles of domestic furniture, and both there and in England for the stocks of guns and other fire-arms. The tree thrives best when planted in a dry, deep, and strong loamy soil, rather light than heavy. It will not succeed on heavy or cold-bottomed land. It grows rapidly until it has attained a considerable size. In favourable soils and sites in this country it frequently attains a height of 60 feet, with a stem of 30 or 36 inches in diameter; but it has been known to reach a height of 80 feet, with a stem of 3 1/2 or 4 feet in diameter.

When the tree is young, its timber is soft and white, and inferior to that of most other young trees; but after it has attained the age of about fifty years it becomes hard and solid, and the colour becomes darker as it advances in age. After sixty years is probably the best time for cutting it down; the wood is then in the best condition for the cabinetmaker or gun-stock manufacturer.

Trees that are intended to be cultivated for the sake of their timber should not be transplanted, as it injures the taproot, and causes the tree to become branchy.

Walnut, on account of its scarcity, is seldom used for the purposes of building; indeed, it is of too flexible a nature for beams, though it appears to have been used by the ancients for that purpose. Pliny observes that it has the good property of giving warning by cracking before it breaks; hence when the baths of Antendros failed, the bathers were alarmed in time to save themselves.

The wood of the walnut-tree is durable and not liable to be destroyed by worms. The heart-wood is of a greyish brown, with blackish-brown pores, often much veined, with darker shades of the same colour; the sap-wood is greyish white. The colours are much brightened, and the veins rendered more distinct by oiling. Its texture is not so uniform as that of mahogany, the pores being somewhat more thickly set on one side of the annual ring. It has no large rays nor flowered appearance. It has a slightly bitter taste when green, and a perceptible odour. It does not work so easily as mahogany, but may in general be brought to a smoother surface. It shrinks very little.

The cohesive force of a square inch of walnut varies from 5360 to 8130 lbs.; its modulus of elasticity for a square inch is 837,000 lbs. in a green state; the weight of a cubic foot varies from 40 to 48 lbs. in adry state.

These properties were ascertained from a green specimen; the strength and stiffness would be greater in a dry state.

578. The Hickory or White Walnut (J. alba) is very common in most parts of North America. It is a large tree, rising to a great height, perfectly straight, and of nearly uniform thickness for a considerable part of its length. The trunk sometimes exceeds 3 feet in diameter. One part of the wood is more porous than that of the common walnut, but the other is more compact. The wood of young trees is extremely tough and flexible, making excellent handspikes, shafts and poles of wheel-carriages, and fishing-rods.

579. The Black Virginia Walnut (J. nigra) is also found in America, from Pennsylvania to Florida. The tree is large, and the wood is heavier, stronger, and more durable than that of the European walnut. It is of a fine grain, beautifully veined, and is susceptible of a high polish. It is well adapted for naval purposes, as it is said not to be liable to the attack of sea-worms in warm latitudes. The heart-wood, when properly seasoned, is strong and tough, and not liable to twist or warp.

The black walnut is extensively used in America for various purposes, where it is highly esteemed as the most valuable of the walnut-tree species.