181 



COMMON LOCUST. 



Robinia Pseudo-Acacia, Linnaeus. 



GENUS DESCRIPTION This genus comprises 7 species of tiees and shrubs native only to 

 North America but some are planted extensively in Europe. Three of the 7 species reach tree- 

 sissc while the others remain shrubs. The generic name is in commemoration of the French 

 botanist Jean Robin and his son Yespasien. 



FORM A medium-sized tree usually 30-45 ft. high with a diameter of 1-1J ft. but may reach 

 a height of 75 ft. with a diameter of 2-2J feet. Forest grown specimens are often straight, clean, 

 nml free fiom branches for 3 of height of tree. Open grown specimens usually branch low. 

 Crown usually uarrow, oblong, ani open. 



BARK On both young and old trunks rough, reddish-brown, deeply furrowed, with high 

 rather rounded ridges which do not peel off in scales; sometimes 1-1 \ inches in thickness. See 

 Fig. 83. 



TWIGS Rather stout, brittle, more or less zigzag, round to angular in cross-section, sometimes 

 ridged, greenish to reddish-brown; often bearing two spines at a node, covered with a few pale 

 lenticels, pith white and often angular. 



BUDS Alternate; terminal one absent; small, 3-4 superposed, imbedded in twig under leaf- 

 scar in a rusty somewhat hairy cavity. Their position is hardly visible in winter but becomes 

 evident in spring when growth starts. 



LEAVES Alternate, compound, 8-14 inches long; petioles slender, grooved on top, and swollen 

 at the base. Leaflets odd in number and stalked, ovate to oblong, 7-9 In number, 1-2 inches long, 

 usually rounded at apex and base, entire on margin. 



LEAF-SCARS Alternate, more than 2-ranked, rather large and conspicuous, Irregular in out- 

 line, covering the buds; often located between two prickles which are developed and hardened 

 stipules; contain 3 bundle-scars. 



FLOWERS Appear about May after the leaves or occasionally before the leaves, resembling 

 the blossom of a pea. Perfect, cream-white, about an inch r cross, fragrant, borne on slender 

 stalks about I of an inch long, arranged in loose drooping racemes 4-5 inches long. 



FRUIT A small, dark brown, and thin pod, 2-4 inches long and J of an Inch wide; usually con- 

 taining from 4-8 small dark brown mottled seeds. The pods often persist far Into winter. 



WOOD Ring-porous; rays quite distinct especially on radial section; heavy, very hard and 

 strong, very durable in contact with the soil, yellowish -brown to cherry-red or reddish-brown with 

 thin greenish or yellowish sapwood. Weighs about 46 Ibs. per cubic foot. Used extensively In 

 former time for ship building, and at present for posts, in turnery, for tree nails, insulator pins 

 and fuel. 



DISTINGUISHING CHARACTERISTICS The Common Locust, also known as the Black 

 Locust, Yellow Locust, White Locust, Locust, and Acacia, may be distinguished by Its droop- 

 ing racemes of white Irregular flowers, its odd-pinnate compound leaves, its twigs with two short 

 spines at a node, its 2-4 inches long leathery fruit pod and its deeply furrowed reddish- brown 

 bark. The leaf-scars located between the two spines when present and covering 3-4 rusty downy 

 superposed buds are also charactertistic. The characteristic coloration of the foliage of this 

 tree when attacked by the Locust Leaf Miner ami the characteristic swelling of the branches 

 when attacked by the Locust Borer aid in recognizing it. The presence of the fruiting 

 body of the Locust Rot (Femes rimosus) so common in southern Pennsylvania, is a sure means 

 of identifying the tree. 



RANGE Mountains of Pennsylvania, south to Georgia, westward to Iowa and Kansas. 

 Naturalized over an extensive area in America and widely planted in Europe. 



DISTRIBUTION IN PENNSYLVANIA Originally it was found only in the central and south- 

 ern portions of the Allegheny Mountains in this State. At present it is found all over the 

 State as an ornamental tree or in fence rows and in many places it has escaped into the forest 

 and abandoned fields. 



HABITAT Grows vigorously on moist fertile soil, especially on rich bottomlands and along 

 mountain streams. Also grows on rather rocky and sterile mountain slopes. Frequent on 

 abandoned charcoal hearths and mud-dams found near ore mines. 



IMPORTANCE OF THE SPECIES The real importance of this tree Is somewhat In doubt. 

 It produces excellent wood and grows rapidly in some localities, especially where It Is free 

 from enemies. Two insects, known as Locust Borer and Locust Leaf Miner, and a fungus known 

 as the Locust Rot (Fomes rimosus), are doing enormous damage to this tree locally. In 

 regions where these enemies are wanting and where suitable soil and climate are at band it may 

 be advisable to plant this tree especially when posts, poles, or ties are desired. It baa very 

 attractive flowers which may appear before, with, or after the leaves. 



