Robinia PseÙdo-AcÀcia LinnÆus. Locust. Black Locust. Plate 109. Medium sized trees with deeply furrowed bark; twigs at first green and hairy, becoming at the end of the season glabrous and a light brown, the stipules developing in about a year into a pair of woody spines about 2 cm. long; leaves pinnate, 1.5-3 dm. long; leaflets 7-17 on short stalks, ovate to oblong, 2-6 cm. long, rounded at base, rounded or pointed and with a small indenture at apex, margin entire, pubescent on both sides at first, becoming at maturity glabrous above and remaining more or less pubescent below, especially on the midrib; flowers in loose racemes, white, expanding in May or June; fruit a flat and slightly curved pod about 5-10 cm. long, glabrous; seeds usually 4-8 in each pod, about 4 mm. long and 2.5 mm. wide; wood heavy, very hard, close-grained, takes a good polish, very durable in contact with the soil.

Distribution.—Appalachian Mountains from Pennsylvania south to northern Georgia, and in Arkansas. In Indiana it is found as an escape in all parts and was doubtless native along the Ohio River, at least in the southeastern part of the State. Thomas[59] says: "We had gazed at the majestic beech of this country (near Rising Sun) three feet in diameter; we had seen the honey locust, the black walnut, a buckeye of equal magnitude; and then we saw with surprise, the black locust almost a rival in stature." Drake[60] says: "The flowering locust is abundant in Kentucky. Along the Ohio River it is rarely found more than 30 miles north of the river."

Remarks.—This tree is generally known as the locust tree, but is sometimes called the yellow locust.

Locust wood is somewhat lighter than white oak, but it is 34 percent stiffer and 45 per cent stronger. These remarkable qualities added to its durability in contact with the ground make it one of the most desirable trees for forest planting. The wood has been used principally for posts, ties, tree nails, etc. The locust when grown close together usually grows to 8-12 inches in diameter. There are, however, specimens that have grown in the open that are almost three feet in diameter. The pioneers used it extensively for ornamental planting, and it has escaped from such planting in all parts of the State. It propagates easily by root shoots which is the principal mode of spreading, except where the seed fall on exposed soil.

Plate 109

The locust has of recent years been extensively planted for post timber. It is very easily propagated from seedlings and grows rapidly. It is adapted to all kinds of soil, except a wet one. It prefers a well drained soil and seems to grow as fast in a loose clay soil as in a black loam. When used for forest planting the spacing should be from 5×5 feet to 8×8 feet. The spacing should be governed by the quality of the soil, and the amount of pruning that can be done. The locust has the habit of having the terminal to end in a fork and having one or more very large side branches. The best management requires that the very large side branches be removed as soon as they are noted, and one part of the terminal forks be cut off.

The locust until recently gave great promise of being an important tree for planting sterile, washed and eroded slopes, on which it usually thrives and in many cases grows thriftily. However, reports from all parts of the State show that locust groves wherever planted are being killed by the locust body borer. The locust has also been attacked by the twig borer, bag worm and the leaf miner. At present there are no known economic means of controlling these destructive pests, and until they can be controlled, the planting of locust for commercial purposes will not prove profitable.