Michigan Trees Part 37

[Ill.u.s.tration: +Locust. Black Locust+

1. Winter twig, 1.

2. Vertical section through lateral buds, enlarged.

3. Leaf, 1/2.

4. Raceme of flowers, 1/2.

5. Flower, with part of corolla removed, enlarged.

6. Fruit, 1/2.]

+LEGUMINOSAE+

+Locust. Black Locust+

_Robinia pseudo-acacia L._

HABIT.--A tree 50-75 feet high, with a trunk diameter of 2-3 feet; forming a narrow, oblong crown of irregular, more or less contorted branches.

LEAVES.--Alternate, compound, 8-14 inches long. Leaflets 7-21, short-petiolate, 1-2 inches long, about one-half as broad; ovate to oblong-oval; entire; very thin; dull dark green above, paler beneath, glabrous both sides. Petioles slender, p.u.b.escent.

FLOWERS.--May-June, after the leaves; perfect; showy and abundant; very fragrant; borne on slender pedicels in loose, drooping racemes 4-5 inches long; about 1 inch long; calyx short, bell-shaped, 5-lobed, hairy; corolla papilionaceous, white, 5-petaled; stamens 10.

FRUIT.--Late autumn, but persistent on the tree through the winter; a smooth, dark brown, flat pod 3-4 inches long, containing 4-8 small, flattish, brown seeds.

WINTER-BUDS.--Terminal bud absent; lateral buds minute, 3-4 superposed, partially sunken within the leaf-scar, rusty-hairy.

BARK.--Twigs smooth, green, more or less rough-dotted at first, becoming red-brown and armed with p.r.i.c.kles; dark red-brown and thick on old trunks, deeply furrowed into firm, sinuous ridges.

WOOD.--Heavy, very strong and hard, close-grained, very durable in contact with the soil, brown, with very thin, pale yellow sapwood.

NOTES.--Native to the Appalachian Mountains, but much planted in Michigan for ornamental and economic uses. Very rapid of growth in youth.

Short-lived. Seriously attacked by borers. Spreads by underground shoots.

[Ill.u.s.tration: +Ailanthus. Tree of Heaven+

1. Winter twig, 1.

2. Leaf, 1/8.

3. Leaflet, 1/2.

4. Staminate inflorescence, 1/4.

5. Staminate flower, enlarged.

6. Pistillate flower, enlarged.

7. Fruit, 1.]

+SIMARUBACEAE+

+Ailanthus. Tree of Heaven+

_Ailanthus glandulosa Desf._

HABIT.--A handsome, rapid-growing, short-lived tree, attaining a height of 50-70 feet and a trunk diameter of 2-4 feet, with a spreading, rather loose and open crown and a coa.r.s.e, blunt spray.

LEAVES.--Alternate, pinnately compound, 1-3 feet long. Leaflets 11-41 in number, 2-6 inches long and about one-third as broad; ovate-lanceolate; entire with the exception of two or more coa.r.s.e, glandular teeth at the base; glabrous, dark green above, paler beneath, turning a clear yellow in autumn or falling without change; ill-scented. Petioles smooth, terete, swollen at the base.

FLOWERS.--June, when the leaves are full grown; polygamo-dioecious; small, yellow-green, borne in upright panicles 6-12 inches or more in length; calyx 5-lobed; petals 5, greenish, hairy; stamens 10. Staminate flowers ill-scented, pistillate almost free from odor.

FRUIT.--October; 1-celled, 1-seeded samaras, spirally twisted, reddish or yellow-green, borne in crowded cl.u.s.ters.

WINTER-BUDS.--Terminal bud absent; lateral buds about 1/8 inch long, subglobose, brownish, downy.

BARK.--Twigs yellowish to red-brown, velvety-downy; thin, grayish and shallowly fissured on old trunks.

WOOD.--Soft, weak, of coa.r.s.e and open grain, pale yellow, satiny, with thick, lighter colored sapwood.

NOTES.--A native of China, but naturalized in the United States and planted frequently in southern Michigan as a foliage tree. Only the pistillate trees should be planted, as these are almost free from the objectionable odor of the staminate trees. The smoke and dust of our large cities have little effect on the foliage, and the trees are perfectly hardy in the southern part of the state.

+SUMMER KEY TO THE SPECIES OF ACER+

a. Leaves simple; twigs usually without whitish bloom.

b. Leaf-sinuses acute at the base.

c. Leaf-lobes long and narrow, the sides of the terminal lobe diverging; leaves silvery white beneath; twigs rank-smelling when broken. _A. saccharinum_, p. 185.

cc. Leaf-lobes short and broad, the sides of the terminal lobe converging; leaves not conspicuously white beneath; twigs not rank-smelling when broken.

d. Leaves 2-4 inches broad, thin, not pentagonally 5-lobed; wings of fruit 3/4-1 inch long.

e. Leaves distinctly white-downy beneath; twigs appressed-hairy, at least near the tip; fruit hanging in pendulous racemes, persistent on the tree until autumn; seed portion with pit-like depression on one side; usually a shrub or bushy tree. _A. spicatum_, p. 179.

ee. Leaves not distinctly white-downy beneath; twigs glabrous; fruit hanging in cl.u.s.ters, falling in early summer; seed portion without pit-like depression on one side; medium-sized tree. _A. rubrum_, p. 187.

dd. Leaves 4-7 inches broad, thick, pentagonally 5-lobed; wings of fruit 1-1/2 inches long. _A. pseudo-plata.n.u.s_, p. 191.

bb. Leaf-sinuses rounded at the base.

c. Lower sides of leaves and petioles distinctly downy, the lobes undulate or entire; leaves very thick, drooping at the sides. _A. saccharum nigrum_, p. 183.

cc. Lower sides of leaves and petioles essentially glabrous, the lobes serrate; leaves not thick, not drooping at the sides.

d. Leaves coa.r.s.ely and spa.r.s.ely toothed or notched; bark not longitudinally white-striped; large trees.

e. Twigs coa.r.s.e; petioles exuding a milky juice when cut; wings of fruit diverging by nearly 180; bark of the trunk closely fissured, not scaly. _A. platanoides_, p. 189.

ee. Twigs slender; petioles not exuding a milky juice when cut; wings of fruit diverging only slightly; bark of the trunk deeply furrowed, often cleaving in long, thick plates. _A.

saccharum_, p. 181.