26b. Stem or branches not th.o.r.n.y --27.
27a. Leaflets entire 7a, in =LEGUMINOSAE=, p. 58.
27b. Leaflets entire except for a few large glandular teeth near their base =SIMARUBACEAE=, p. 65.
27c. Leaflets serrate their entire length --28.
28a. Upper leaflets less than 25 mm. wide 4b, in =ROSACEAE=, p. 51.
28b. Upper leaflets more than 25 mm. wide =JUGLANDACEAE=, p. 21.
29a. Leaves opposite --30.
29b. Leaves alternate --32.
30a. Leaves entire =CORNACEAE=, p. 83.
30b. Leaves toothed or lobed, not entire --31.
31a. Leaves lobed 1b, in =ACERACEAE=, p. 70.
31b. Leaves merely toothed 27b, in =CAPRIFOLIACEAE=, p. 111.
32a. Leaves entire --33.
32b. Leaves toothed --36.
32c. Leaves lobed --47.
33a. Leaves heart-shape 3a, in =LEGUMINOSAE=, p. 58.
33b. Leaves not heart-shape --34.
34a. Twigs and foliage spicy-aromatic 1b, in =LAURACEAE=, p. 41.
34b. Twigs and foliage not aromatic --35.
35a. Pith 5-angled; fruit an acorn 3a, in =f.a.gACEAE=, p. 22.
35b. Pith not 5-angled; fruit a berry 1a, in =CORNACEAE=, p. 83.
36a. Leaves oblique at base, i. e., one side of the leaf larger than the other --37.
36b. Leaves symmetrical, not oblique at base --38.
37a. Leaves heart-shape, about as broad as long =TILIACEAE=, p. 72.
37b. Leaves oval or ovate, much longer than wide 1a, in =URTICACEAE=, p. 23.
38a. Stems th.o.r.n.y 41b, in =ROSACEAE=, p. 54.
38b. Stems not th.o.r.n.y --39.
39a. Leaves finely toothed, with 3-many teeth per centimeter of margin --40.
39b. Leaves coa.r.s.ely toothed, with 1-2 teeth per centimeter of margin --46.
40a. Petioles laterally compressed 2a, in =SALICACEAE=, p. 19.
40b. Petioles not compressed --41.
41a. Leaves, or many of them, crowded on short spur-like branches --42.
41b. Leaves scattered, not on short spur-like branches --43.
42a. Bark of the trunks separating in thin papery or leathery sheets =BETULACEAE=, p. 21.
42b. Bark of the trunk not papery or leathery 24b, in =ROSACEAE=, p. 53.
43a. Lateral leaf-veins straight and parallel, and terminating in the teeth =BETULACEAE=, p. 21.
43b. Lateral veins more or less curved, and not ending in the teeth --44.
44a. Leaves palmately veined, about as broad as long; juice somewhat milky 2b, in =URTICACEAE=, p. 23.
44b. Leaves pinnately veined; juice not milky --45.
45a. Willows, with slender leaves and brittle twigs 8a, in =SALICACEAE=, p. 19.
45b. Trees with lanceolate, ovate, or oblong leaves and tough twigs 30, in =ROSACEAE=, p. 54.
45c. Cottonwoods, with broad, heart-shape or rounded leaves 1a, in =SALICACEAE=, p. 19.
46a. Petioles laterally compressed 2a, in =SALICACEAE=, p. 19.
46b. Petioles not compressed; lateral veins straight and parallel, running directly to the teeth =f.a.gACEAE=, p. 22.
47a. Stem th.o.r.n.y 41b, in =ROSACEAE=, p. 54.
47b. Stem not th.o.r.n.y --48.
48a. Leaves palmately veined --49.
48b. Leaves pinnately veined --51.
49a. Lobes of the leaf entire 1b, in =LAURACEAE=, p. 41.
49b. Lobes of the leaf serrate --50.