The oaks are readily distinguished by their peculiar fruit, an acorn or nut, enclosed at the base in a woody cup. The female flower contains a single ovary, three-celled at first, but becoming one-celled and one-seeded by abortion. The male flowers are in small clusters on the usually slender and pendent stalk, forming an interrupted catkin. The alternate leaves are more or less deeply lobed or cut in many species, but in some of the deciduous and many of the evergreen kinds are nearly or quite entire on the margin.
The well-known Q. Robur, one of the most valued of the oaks, and the most celebrated in history and myth, may be taken as a type of oaks with sinuated leaves. Though known in England, where it is the only indigenous species, as the British oak, it is a native of most of the milder parts of Europe and of the Caucasus mountains in Asia. In Great Britain and in most of its Continental habitats two varieties exist, now usually regarded as distinct species : one, Q. pedunculata, has the acorns, generally two or more together, on long stalks, and the leaves nearly sessile; while in the other, Q. sessiliflora, the fruit is without or with a very short peduncle, and the leaves are furnished with well-developed peti oles. The British oak is one of the large trees of the genus, though old specimens are often more remarkable for the great size of the trunk and main boughs than for very lofty growth. The spreading branches have a tendency to assume a tortuous form, causing a zigzag development ; to this peculiarity the picturesque aspect of ancient oaks is largely due. When standing in dense woods the trees are rather straight and formal in early growth, and the gnarled character traditionally assigned to the oak applies chiefly to its advanced age. The fruit is shed the first autumn.
Vast oak forests still covered the greater part of England and central Europe in the earlier historic period. Many of the ancient oaks that remain in England may date from Saxon times ; the growth of trees after the trunk has become hollow is extremely slow, and the age of such venerable giants is only a matter of vague surmise. The celebrated Newland oak in Gloucestershire, known for centuries as "the great oak," was 47-4 ft. in girth at 5 ft. from the ground. The wood of the British oak, when grown in perfec tion, is one of the most valuable produced in temperate climates.
The heart-wood varies in colour from dark brown to pale yellow ish-brown; hard, close-grained, and little liable to split accidentally. The oak of Britain was formerly in great demand for the construc tion of merchant shipping. The finely-grained heart-wood is sought by the cabinetmaker for the manufacture of furniture, as are also the gnarled and knotted portions of slowly-grown trees, which are sawn mto veneers. Oak was formerly largely used by wood-carvers and was thus applied at a very early date; the shrine of Edward the Confessor, still existing in the abbey at Westminster, sound after the lapse of Boo years, is of dark-col oured oak-wood.
The cultivation of this oak in Europe forms one of the most important branches of forestry. Its growth is slow, though it varies greatly in different trees; when grown for large timber oak can rarely be profitably felled till the first century of its growth is completed. The British oak is often grown as an ornamental tree in the eastern United States, where, however, it is usually short-lived. In the southern parts of Australia and in New Zealand it seems to flourish as well as in its native home. An important product of oak woods is the bark, formerly the chief tanning material of Europe. The acorns of the oak possess a considerable economic importance as food for swine. In the Saxon period the "mast" seems to have been regarded as the most valuable produce of an oak wood.
Of the European timber oaks, the next in importance to the British oak is Q. Cerris, the Turkey oak of the nurserymen. This oak abounds all over the Turkish peninsula, on the Taurus ranges, and in many parts of southern Europe; it was introduced into England about 1735, and is now common in parks and plantations.
The evergreen oak of southern Europe is Q. Ilex, usually a small tree, frequently of rather shrub-like appearance, with abundant glossy dark-green leaves, more or less prickly at the margin. The ilex, also known as the "holm oak" from its resemblance to the holly, abounds in all the Mediterranean countries. The stem sometimes grows 90 ft. in height, but it does not often reach a great size. In its native lands it attains a vast age ; Pliny attributes to several trees then growing in Rome a greater antiquity than the city itself.