Deciduous trees. Twigs slender, zigzag, terete; pith small, round, continuous. Buds solitary or multiple, ovoid, obliquely sessile, the terminal lacking; scales about 6, 2-ranked. Leaf-scars alternate, 2-ranked, crescent-shaped or half-round bundle-traces 3, or multiplied; stipule-scars unequal.
Fig. 84. Ulmus alata.
Older twigs often corky-winged, or with irregular corky outgrowths
b. Twigs often corky-winged
b. Twigs often with irregular corky ridges
Fig. 79. Quercus marilandica.
Fig. 80. Quercus imbricaria.
Fig. 81. Ulmus rubra.
Fig. 82. Ulmus americana.
Fig. 83. Ulmus thomasi.
Twigs without corky outgrowths
b. Buds downy, dark-colored, nearly black;twigs rough, ashy-gray in color
b. Buds brown, glabrous or pale-pubescent; twigs smooth or sparingly pilose
1. U. rubra Muhl. Slippery Elm. Red Elm. (U. fulva Michx.). A tree 15-24 m. high, 3-7. 5 dm. thick, with tough reddish wood; bark rough, gray, the inner bark very mucilaginous (whence the name, slippery elm); twigs gray-buff, rough-hairy; buds downy with red hairs; flowers nearly sessile, in groups of several, beginning to appear in March. Moist soil, New England to North Dakota, south to Florida and Texas (Fig. 81 ).
2. U. americana L. American Elm. A handsome tree, 20-50 m. high, 6-18 dm. in diameter, usually with a spreading vase-shaped crown and somewhat drooping branchlets; bark gray, flaky, with alternating light and dark layers in cross section; twigs glabrous or sparingly pubescent; buds brown, glabrous or somewhat pubescent; flowers long-pedicelled, in groups of 3 or 4, beginning to appear in March. Mostly in bottomlands, Quebec to Saskatchewan, south to Florida and Texas (Fig. 82).
3. U. thomasi Sarg. Cork Elm. Rock Elm (U. racemosa Thomas). A tree attaining a height of 35 m. and a diameter of 12 dm. twigs glabrous or puberulent; bud-scales downy-ciliate; branches often with corky ridges. Rich woods, mostly on lime- . stone outcrops, New England to Minnesota and South Dakota, south to Tennessee and Kansas (Fig. 83 ).
4. U. alata Michx. Winged Elm. A small round-topped tree, up to 20 m. high; branches corky-winged; branchlets and buds nearly glabrous. Flowers in short racemes, appearing in March. Low woodlands, Florida to Texas, north to Virginia, Kentucky, and Missouri (Fig. 84).