There are many species of Acer, most of which are tall trees; and they are chiefly distinguished from each other by the shape of the leaves and of the samaras, or keys, the wings of which, in some species, are near together, as shown at d in fig. 123, and in others widely apart, as in the common hedge Maple (A. campestris), and in the Norway Maples, as shown at a in fig. 125. This figure represents the flowers of the Norway Maple (Acer platanoides), which are in what botanists call a corymb, and stand erect, instead of drooping like those of the sycamore. The leaves are deeply five-lobed, and the lobes are so coarsely toothed, that the teeth have almost the appearance of lobules. The buds of this plant in winter are large and red, and when they open in spring, the bracts (b) curl back over the scales (c). The leaves become of a clear yellowish red in autumn, and the whole plant is very ornamental. When a leaf of this tree is broken off, a milky sap issues from the broken petiole or leaf-stalk, which is of an acrid nature; differing in this respect, materially from the sap of the trunk, which is very sweet. Sugar indeed may be made from the sap of the trunk of almost all the Maples; but particularly in America, from that of the Sugar Maple (Acer saccharinum). The flowers of the red American Maple (Acer rubrum) are red, and as from their colour, and their appearing a fortnight before the leaves, they are very conspicuous, I have given a magnified representation of them in fig. 126, that my readers may have an opportunity of examining the male and female flowers from a living tree. In fig. 126, a a are male flowers, having no stigmas; and b b are female ones, having no stamens.
Fig. 125.—Flowers and Samara of the Norway Maple.
Fig. 126.—Flowers of the Red Maple (Acer rubrum).
The leaves of Acer rubrum become red in autumn. The Tatarian Maple differs from the other species in having entire leaves, and the samaras are red when young; but all the other kinds of Acer common in British gardens bear a strong family likeness to each other. The Ash-leaved Maple is now made into a separate genus, and is called Negundo fraxinifolia. This tree is easily distinguished from the Maples by its compound leaves, which resemble those of the Ash, and its long pea-green shoots, which have very few buds. The male and female flowers of the Negundo are on different trees, and they are so small as to be seldom seen, though the racemes of samaras or keys which succeed the flowers are very conspicuous. The Negundo is a native of America, and its leaves turn yellow in autumn.
ORDER XLV.—HIPPOCASTANEÆ, OR ÆSCULACEÆ. THE HORSE-CHESTNUT TRIBE.