Fig. 91.—Male flower of the Hazel. that gradually the bud becomes a little branch, bearing the female flowers at its tip. Each flower has two long stigmas, and the ovary is enclosed in a closely-fitting calyx (c) toothed at the upper part, the whole being enveloped in a deeply cut involucre (d), which afterwards becomes the husk of the ripe nut. This in volucre is not closed, as in Fagus and Castanea, but it is open at top; the nut, as in all cupuliferæ, adhering to it, when young, by the hilum or scar visible at its base. There are about seven species of Corylus, of which the most remarkable is the Constantinople Nut (Corylus Colurna.) The Filbert is only a variety of Corylus Avellana.
THE GENUS CARPINUS.
Some botanists include this genus and that of Ostrya in the order Betulaceæ, instead of placing them in Cupuliferæ, as the nut of the Hornbeam is not surrounded by a cup or husk, but by a leaf-like involucre as shown in fig. 92,
Fig. 92.—Fruit of the Hornbeam. at a, b being the nut. Both the male and the female flowers are produced in long catkins, which have an exceedingly light and elegant appearance on the tree. The male flowers consist each of one bract, with twelve or more stamens attached to its base; and the female flowers have each two very long stigmas, and a ribbed calyx, which adheres to the ripe nut and assumes the appearance of a hard brown skin. The leaves are feather-nerved and persistent, like those of the Beech, frequently remaining on the tree, though in a withered state, till spring.
The nut appears ribbed when ripe, from the remains of the metamorphosed calyx, and it contains only one seed; though, as in the other allied genera, the ovary had two cells, with an ovule in each.
THE GENUS OSTRYA.
The Hop Hornbeam (Ostrya vulgaris) was included in the genus Carpinus by Linnæus; and indeed the general construction of the flowers is the same. The male catkins are, however, very much longer, and the female catkins much shorter, and closely resembling those of the Hop.
THE ORDER PLATANACEÆ.