Part 5

i. Leaves thick, abruptly pointed, very lustrous above, not clustered at the ends of the branches. NYSSA, p. 209.

ii. Leaves thin, long-pointed, not lustrous above, clustered at the ends of the branches. CORNUS, p. 202.

dd. Margin of leaves serrate, toothed or lobed.

e. Margin of leaves serrate to toothed.

f. Branches armed with stiff, sharp thorns. CRATAEGUS, p. 151.

ff. Branches not armed.

g. Base of leaves decidedly oblique.

h. Leaf-blades about as long as they are broad, heart-shaped. TILIA, p. 201.

hh. Leaf-blades 1-1/2 - 2 times as long as they are broad, oval to ovate.

i. Leaves thin, coarsely but singly serrate; fruit a globular drupe, ripe in autumn. CELTIS, p. 131.

ii; Leaves thick, coarsely and doubly serrate; fruit a samara, ripe in spring. ULMUS, p. 122.

gg. Base of leaves essentially symmetrical.

h. Teeth coarse, 2-5 per inch of margin.

i. Leaves very glabrous both sides; fruit a prickly bur.

j. Leaves 3-5 inches long, very lustrous beneath; bark close, smooth, steel-gray. FAGUS, p. 93.

jj. Leaves 6-8 inches long, not lustrous beneath; bark fissured, brownish. CASTANEA, p. 95.

ii. Leaves pubescent or white-tomentose, at least beneath; fruit not a prickly bur.

j. Leaves 2-4 inches long, broadly ovate to suborbicular; fruit a very small capsule, falling in spring. POPULUS, p. 44.

jj. Leaves 4-7 inches long, oblong-lanceolate to obovate; fruit an acorn, falling in autumn. QUERCUS, p. 96.

hh. Teeth fine, 6-many per inch of margin.

i. Leaf-petioles laterally compressed; leaves tremulous. POPULUS, p. 44.

ii. Leaf-petioles terete; leaves not tremulous.

j. Leaf-blades at least 3 times as long as they are broad.

k. Twigs brittle; fruit a very small capsule, falling in spring. SALIX, p. 34.

kk. Twigs tough; fruit a fleshy drupe, falling in late summer or autumn. PRUNUS, p. 152.

jj. Leaf-blades not more than twice as long as they are broad.

k. Leaf-blades about twice as long as they are broad.

l. Margin of leaves singly serrate; fruit fleshy.