Fig. 327.—Betula verrucosa: a cone-scale; b fruit.
Fig. 328.—Diagrams of dichasia in the ♂-(A) and ♀-(B) catkins of Birch.
Order 2. Corylaceæ (Hazel-nuts). Monœcious. The ♂-catkins are long and cylindrical; the ♂-flowers are placed singly in the axil of the subtending-leaf (cover-scale); they are naked and formed of a number of divided stamens, which are partly united with the cover-scale, 4 in the Hazel, apparently 8 (Figs. [330] A, [329] B, C), more on the Hornbeam. The ♀-flowers have a very small, superior perianth; in the axil of each cover-scale a 2-flowered dichasium (Fig. [329] D) is present, of which the central flower (* in Fig. [330] B) is suppressed. The gynœceum is bicarpellary as in the Birches; the ovary is bilocular, with two long styles (Fig. [329] D-F); the loculi have 1 (-2) ovules (Fig. [330] B). Each single ♀-flower and fruit is surrounded by a leaf-like covering, the cupule (husk), which is formed of three floral-leaves (namely, the bract of a lateral flower, and its own bracteoles; thus in Fig. [330] B, α, α′, β’ form the cupule for the left-hand flower, and β, α1, β1, the cupule for the right-hand).
Corylus (Hazel-nut, Fig. [329]). The long, cylindrical ♂-catkins pass the winter naked, 2–3 together, on short branches. The very small ♀-catkins are enclosed in buds, in which they pass the winter; these buds are situated in the axils of the fallen foliage-leaves, and it is only by their larger size that they may be distinguished from the ordinary foliage-buds. In spring the ♀-catkins are easily recognised by their red, projecting stigmas (Fig. [329] A). The cupule—the “husk”—is tubular, fringed, and envelopes the nut. The leaves are alternate and unsymmetrical, the external side being larger than the internal; this is connected with the vernation, the blade being conduplicate in the bud; the stipules are deciduous. The bud-scales are formed of stipules, the most internal having a leaf-blade attached to them which is suppressed in the external ones. The cotyledons remain underground on germination.
Fig. 329.—Corylus avellana: A branch at the time of flowering with ♂-and ♀-catkins; B ♂-flower with subtending-leaf (bract) and two bracteoles; C the same without the anthers; D view of interior of ♀-dichasium shortly after fertilisation; E young fruit with cupule; F similar one with the cupule opened; G mature ♀-fruits; H nut.
Carpinus (C. betulus, Hornbeam). The ♂-and ♀-catkins do not appear till the leaves are shooting. The ♀-catkin in this instance is also long and cylindrical. The cupule in C. betulus is 3-lobed, and to a slight extent only embraces the base of the ribbed nut (Fig. [331]); each lobe corresponds to a floral-leaf. Whilst the carpels are placed medianly in Corylus, in Carpinus, on the other hand, they are situated transversely, as in the case of the Betulaceæ. The lamina of the leaf is not conduplicate in the bud, but flat, and folded only along the lateral veins, which are also indicated in the form of the fully-developed leaf; otherwise the vegetative characters are essentially the same as in the Hazel. The cotyledons are aerial.—Ostrya resembles the Hornbeam, but the cupule completely envelopes the nut, as a sac open at the apex (Eur., N. Am., Japan).
N. Am., Asia, and Europe; 25 species.—Fossil forms in the Oligocene. Wind-pollinated. Uses. As timber (Carpinus betulus) and firewood. The fruits of C. avellana (ordinary Hazel-nut), C. tubulosa (Lambert’s nut) and C. colurna (Turkish Filbert) are edible.
