Part 53

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 clusters, 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-platanus, 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 coarsely and sparsely toothed or notched; bark not longitudinally white-striped; large trees.

e. Twigs coarse; 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.

dd. Leaves finely and abundantly toothed; bark longitudinally white-striped; a bushy tree or shrub.

aa. Leaves compound; twigs usually with whitish bloom. A. negundo, p. 193.

+WINTER KEY TO THE SPECIES OF ACER+

a. Terminal buds usually under 1/4 inch in length.

b. Buds white-woolly; twigs usually with a whitish bloom; opposite leaf-scars meeting; fruit often persistent on the tree until spring. A. negundo, p. 193.

bb. Buds not white-woolly; twigs without whitish bloom; opposite leaf-scars not meeting; fruit not persistent on the tree in winter.

c. Buds reddish or greenish; twigs bright red.

d. Twigs strictly glabrous; buds glabrous; spherical flower buds clustered on the sides of the shoot; pith pink; large trees.

e. Twigs rank-smelling when broken; tip of outer bud-scales often apiculate; tips of branches curving upwards; bark separating into long, thin flakes loose at the ends. A. saccharinum, p. 185.

ee. Twigs not rank-smelling when broken; tip of outer bud-scales rounded; tips of branches not conspicuously curving upwards; bark rough-ridged, but seldom forming loose flakes. A. rubrum, p. 187.

dd. Twigs appressed-hairy, at least near the tip; buds somewhat tomentose; spherical flower buds absent; pith brown; shrub or bushy tree. A. spicatum, p. 179.

cc. Buds brownish; twigs brownish or grayish.