[Illustration: O. arbòreum.] =Oxydéndrum arbòreum=, DC. (SORREL-TREE. SOURWOOD.) Leaves in size and shape much like those of Peach trees. Flowers small, urn-shaped. Small-sized tree, 15 to 50 ft. high; wild in rich woods, Pennsylvania and southward, mainly in the mountains. Rare in cultivation, but very beautiful, especially in autumn, when its leaves are brilliantly colored, and the panicles of fruit still remain on the trees. It is perfectly hardy both at the Arnold Arboretum, Boston, and the Missouri Botanical Garden, St. Louis. GENUS =51. KÁLMIA.= Evergreen shrubs with alternate, entire, thick, smooth leaves. Flowers large, beautiful, cup-shaped, in showy clusters. Fruit a small, 5-celled, many-seeded capsule. [Illustration: K. latifòlia.] =Kálmia latifòlia=, L. (MOUNTAIN-LAUREL. CALICO-BUSH.) The only species which grows at all tree-like has ovate-lanceolate or elliptical, smooth, petioled leaves, tapering at both ends and green on both sides. Flowers in terminal corymbs, clammy-pubescent, white to pink. June. Pod depressed, glandular. Shrub or small tree, 4 to 25 ft. high, with reddish twigs; wild in rocky hills and damp soils through out; occasionally planted. Wood very hard and close-grained. GENUS =52. RHODODÉNDRON.= Shrubs or low trees with usually alternate, entire leaves and showy flowers in umbel-like clusters from large, scaly-bracted, terminal buds. Fruit a dry 5-celled pod with many seeds. [Illustration: R. máximum.] =Rhododéndron máximum=, L. (GREAT LAUREL.) Leaves thick, 4 to 10 in. long, elliptical-oblong or lance-oblong, acute, narrowed toward the base, very smooth, with somewhat revolute margins. Flowers large (1 in.), with an irregular bell-shaped corolla and sticky stems, in large clusters, white or slightly pinkish with yellowish dots. July. Evergreen shrub or tree, 6 to 20 ft. high, throughout the region, especially in damp swamps in the Alleghany Mountains; occasionally cultivated. GENUS =53. CLÈTHRA.= Shrubs or trees with alternate, simple, deciduous, exstipulate, serrate leaves. Flowers (July and August) conspicuous, white, in elongated terminal racemes which are covered with a whitish powder. Fruit 3-celled pods with many seeds, covered by the calyx. * Leaves thin, large, 3 to 7 in. long, pale beneath 1. * Leaves thickish, smaller, green both sides 2. [Illustration: C. acuminàta.] 1. =Clèthra acuminàta=, Michx. (ACUMINATE-LEAVED CLETHRA. SWEET PEPPER-BUSH.) Leaves 3 to 7 in. long, oval to oblong, pointed, thin, abruptly acute at base, finely serrate, on slender petioles, smooth above and glaucous below. Racemes drooping, of sweet-scented flowers, with the bracts longer than the flowers. Filaments and pod hairy. A small tree or shrub, 10 to 20 ft. high, in the Alleghanies, Virginia, and south. Not often in cultivation, but well worthy of it. [Illustration: C. alnifòlia.]