The Common Alder (_Alnus glutinosa_), though so nearly allied to the Birch botanically, differs widely in its habits; as it always grows in low marshy situations, or near water, while the Birch prefers the summits of the loftiest hills. In the Alder, the male catkins are long and drooping, like those of the Birch; but they are generally produced in clusters of three or more together. The male flowers are furnished with three lobed bracts or scales, each containing three flowers, each flower having a calyx of four scales united at the base, and bearing four stamens. The female flowers are in close ovate catkins, produced in clusters of four or five together, instead of being cylindrical and solitary, as in the Birch; the scales of the catkins, though three-lobed, are only two-flowered, and the flowers have two long stigmas like those of the Birch. The ovary has two cells and two ovules, but it only produces one seed. The ripe fruit is a nut without wings, attached at the base to the scale of the cone-like catkin, the scales of the catkin becoming rigid, and opening, like those of the Scotch Pine, as the seed ripens. There are several species of Alder, some of which bear considerable resemblance to the American species of Birch; but they are easily distinguished by the female catkins of the Birch being always solitary, while those of the Alder are produced in clusters, and by the capsules of the Alder being without wings. CUPULIFERÆ—THE CUP-BEARING TREES. This order includes six genera of very important trees; all of which have their ripe fruit shrouded in a cup-like involucre, which they retain till ripe. The male and female flowers are on the same plant. THE GENUS QUERCUS. The fruit of all the species of Oak is an acorn, which is only partly covered by a scaly involucre called the cup. The shape of the acorn, and the height to which it is covered by the cup, differ in the different species; but the general character of both is always the same. [Illustration: FIG. 85.—THE OAK.] [Illustration: FIG. 86.—GERMINATION OF THE ACORN.]