Remarks.—This tree cannot be distinguished from the sugar maple by its form, but at short range can be separated from it by its richer green foliage and by the drooping habit of the lower lobes of the leaves. It is commonly separated from the sugar maple by the darker color and by the narrower and shallower furrows of the bark, but these characters will not always separate the two species. Hence, when buying black maple trees from a nurseryman you may receive the sugar maple. Those who distinguish the two species agree that the black maple is the more desirable tree for shade tree planting. The black and sugar maple are the two most desirable trees for shade tree planting in Indiana. They are long lived, have a very desirable form, beautiful foliage, a long leaf period, and are quite free from disease and insect injury.
ACER NIGRUM. F. A. Michaux. Black Maple. (× 1/2.)
5. Acer sáccharum Marshall. Sugar Maple. Sugar Tree. Hard Maple. Rock Maple. [Plate 115.] Usually large, tall trees. The bark of small trees is smooth or rough, becoming fissured on old trees, tight or on very old trees sometimes the ridges loosen on one edge and turn outward. The leaves are extremely variable on different trees, and frequently show a wide variation on the same tree, as to form and in the presence or absence of hairs on the petioles and on the under surface of the leaves. In our area all of the forms which have the majority of the leaves longer than wide or about as wide as long, may be considered as falling within the type. The average sized leaves are 6-12 cm. long, 3-5 lobed, more or less cordate at the base, generally with a broad sinus, sometimes truncate or slightly wedge-shape, sinuses generally wide-angled and rounded at the base, sometimes acute, hairy beneath when young, becoming smooth at maturity except for a few hairs along the veins or in the main axils of the veins, or sometimes remaining more or less pubescent over the whole under surface, more or less glaucous beneath; flowers appear in April or May, on hairy pedicels 3-7 cm. long, the staminate and pistillate in clusters on the same or different trees; fruit ripening in autumn, samaras glabrous and usually 2-4 cm. long.
Distribution.—Newfoundland to Georgia, west to Manitoba and south to Texas. A frequent to a very common tree in all parts of Indiana. It is confined to rich uplands, or along streams in well drained alluvial soil. Throughout our area it is constantly associated with the beech. It is absent in the "flats" of the southeastern part of the State, and on the crest of the ridges of the "knob" area of Indiana, but it is a frequent or common tree on the lower slopes of the spurs of the "knobs."
Remarks.—The under surface of the leaves of the sugar maple in the northern part of its range are green, while those of the southern part of its range are quite glaucous beneath. To distinguish these two intergrading forms the southern form has been called Acer saccharum var. glaucum Sargent[61]. All of the trees seen in Indiana have leaves more or less glaucous beneath. This character, however, is not always evident in dried specimens. The writer prefers not to apply the varietal name to the forms of our area. The sugar maple always has been and will continue to be one of the most important trees of the State. In its mass distribution in Indiana it ranks not less than third. In the quality and uses of its wood it is equalled or exceeded only by the oak, ash and hickory. When compared with white oak it is a little lighter but thirty per cent stronger and fifty-three per cent stiffer. The greatest amount of the annual cut of maple is worked into flooring which is shipped to all parts of the world. It is much used in the manufacture of furniture and ranks third in use for veneer and hard wood distillation, and as a fuel wood is excelled only by hickory. Since pioneer times, the sap of this tree has been made into sirup and sugar and their manufacture now forms a valuable industry. On an average it takes 3 to 4 gallons of sap to make a pound of sugar, and an average sized tree will annually yield about 3 to 4 pounds of sugar.