dd. Thorns unbranched on twigs, situated at the nodes; lateral

buds not superposed, not covered by bark; fruit a small pome. CRATAEGUS, p. 151.

bb. Twigs, branches or trunks unarmed.

c. Leaf-scars mainly crowded on short, stout, lateral shoots.

d. Bundle-scar 1; fruit a cone, usually present. LARIX, p. 17.

dd. Bundle-scars 2; fruit a globose drupe falling in autumn. GINKGO, p. 3.

cc. Leaf-scars distributed along the lateral branches.

d. Leaf-scars (or some of them) 3 at a node, i. e., whorled. CATALPA, p. 223.

dd. Leaf-scars 1-2 at a node, i.e., not whorled.

e. Leaf-scars 2 at a node, i.e., opposite.

f. Terminal buds 1/2 - 1-1/2 inches long, resin-coated; twigs very stout. AESCULUS, p. 195.

ff. Terminal buds rarely exceeding 1/2 inch in length, not resin-coated; twigs not conspicuously stout.

g. Leaf buds with 1 pair of scales visible.

h. Buds scurfy-pubescent. VIBURNUM, p. 229.

hh. Buds glabrous. CORNUS, p. 203.

gg. Leaf buds with 2 or more pairs of scales visible.

h. Bundle-scars usually 3, distinct, separated. ACER, p. 174.

hh. Bundle-scars many, minute, more or less confluent in a U-shaped line. FRAXINUS, p. 211.

ee. Leaf-scars 1 at a node, i.e., alternate.

f. Bundle-scars 1-3.

g. Bundle-scar only 1, or appearing as 1.

h. Twigs bright green, spicy-aromatic; bundle-scar appearing as a horizontal line; terminal bud present; pith homogeneous. SASSAFRAS, p. 139.

hh. Twigs brownish, not spicy-aromatic; bundle-scar appearing as a large dot; terminal bud absent; pith chambered. CELTIS, p. 131.

gg. Bundle-scars 3 or in 3 compound, but distinct groups.

h. Terminal bud present.

i. Stipule-scars present.

j. First scale of lateral bud directly in front, i.e., exactly above the center of the leaf-scar; twigs brittle; pith somewhat star-shaped in cross-section. POPULUS, p. 45.

jj. First scale of lateral bud not directly in front, i. e., to one side of the center of the leaf-scar; twigs not brittle; pith circular in cross-section. PRUNUS, p. 153.

ii. Stipule-scars absent.

j. Buds bright to dark red, the terminal 1/8 - 1/4 inch long.

k. Branches contorted, bearing many short, spur-like branchlets; fruit an apple an inch or more in diameter, light green. PYRUS, p. 143.

kk. Branches not contorted, not bearing short, spur-like branchlets; fruit berry-like, 1/2 inch long, blue-black. NYSSA, p. 209.

jj. Buds brownish to gray, the terminal exceeding 1/4 inch in length.

k. Buds narrow-conical, sharp-pointed; leaf-scars small, narrowly crescent-shaped; twigs about 1/16 inch thick; pith homogeneous; fruit berry-like, not present. AMELANCHIER, p. 149.

kk. Buds broadly conical to ovoid, blunt-pointed; leaf-scars conspicuous, broadly heart-shaped; twigs about 1/4 inch thick; pith chambered; fruit a nut, often present. JUGLANS, p. 61.

hh. Terminal bud absent (sometimes present on short shoots of _Betula_).

i. Stipule-scars present.

j. Bud-scale only 1 visible; twigs brittle. SALIX; p. 34.

jj. Bud-scales 2 or more; twigs not brittle.

k. Bark smooth, close, warty or peeling into papery layers, but not flaky nor rough-ridged.

l. Tip of bud appressed; fruit berry-like. CELTIS, p. 131.

ll. Tip of bud not appressed; fruit not berry-like.