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.