Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/750

Rh 692 OAK ference ; but the increase of the trunk is usually very much slower, and when grown for large timber oak can rarely be profitably felled till the first century of its growth is com pleted. The tree will continue to form wood for 150 or 200 years before showing any symptoms of decay. As firewood oak holds a high position, though in Germany it is considered inferior to beech for that purpose. It makes excellent charcoal, especially for metallurgic pro cesses ; the Sussex iron, formerly regarded as the best produced in Britain, was smelted with oak charcoal from the great woods of the adjacent Weald, until they became so thinned that the precious fuel was no longer obtainable. An important product of oak woods is the bark that from a remote period has been the chief tanning material of Europe. The most valuable kind is that obtained from young trees of twenty to thirty years growth, but the trunks and boughs of timber trees also furnish a large supply ; it is separated from the tree most easily when the sap is rising in the spring. It is then carefully dried by the free action of the air, and when dry built into long narrow stacks until needed for use. The value of oak bark depends upon the amount of tannin contained in it, which varies much, depending not only on the growth of the tree but on the care bestowed on the preparation of the bark itself, as it soon ferments and spoils by exposure to wet, while too much sun-heat is injurious. That obtained from the sessile -fruited oak is richer in tannic acid than that yielded by Q. pedunculata, and the bark of trees growing in the open is more valuable than the produce of the dense forest or coppice. The bark of young oak branches has been employed in medicine from the days of Dioscorides, and is occasionally used in modern practice, chiefly as an astringent : in decoction it is given as a gargle for throat affections depending on relaxation, and is administered in dysenteric haemorrhages and some forms of diarrhoea ; it was regarded by the practitioners of a former age as useful in consumption, a disease from which tanners are said to be nearly exempt. Poultices made of the crushed or pow dered bark have been used with advantage where astringent external applications are indicated ; as a tonic it has in modern medicine given place to other remedial agents. The astringent principle is a peculiar kind of tannic acid, called by chemists querci- tannic, which, yielding more stable compounds with gelatine than other forms, gives oak bark its high value to the tanner. According to Neubauer, the bark of young oaks contains from 7 to 10 per cent, of this principle ; in old trees the proportion is much less. The acorns of the oak possess a considerable economic importance as food for swine. In the Saxon period the &quot;mast&quot; seems to have been regarded as the most valuable produce of an oak wood ; nor was its use always confined to the support of the herds, for in time of dearth acorns were boiled and eaten by the poor as a substitute for bread both in England and France, as the sweeter produce of Q. Esculus is still employed in southern Europe. Large herds of swine in all the great oak woods of Germany depend for their autumn maintenance on acorns ; and in the remaining royal forests of England the inhabitants of the neighbouring villages yet claim their ancient right of &quot; pannage,&quot; turning their hogs into the woods in October and November. Some trees of the sessile-fruited oak bear sweet acorns in Britain, and several varieties were valued by the ancient Italians for their edible fruit. A peculiar kind of sugar called quercite exists in all acorns. A bitter principle to which the name of quercin has been applied by Gerber, its discoverer, has also been detected in the acorn of the common oak ; the nutritive portion seems chiefly a form of starch. A spirit has been distilled from acorns in process of germination, when the saccharine principle is most abundant. The British oak grows well in the northern and middle States of America ; and, from the superiority of the wood to that of Q. alba and its more abundant production of acorns, it will probably be much planted as the natural forests are destroyed. The young trees require protection from storms and late frosts even more than in England ; the red pine of the north-eastern States, Pinus resinosa, answers well as a nurse, but the pitch pine and other species may be employed. In the southern parts of Australia and in New Zealand the tree seems to flourish as well as in its native home. The oak in Europe is liable to injury from a great variety of insect enemies : the young wood is attacked by the larva? of the small stag-beetle and several other Coleojrtera, and those of the wood -leopard moth, goat moth, and other Lepidoptera feed upon it occasionally ; the foliage is de voured by innumerable larvse ; indeed, it has been stated that half the plant-eating insects of England prey more or less upon the oak, and in some seasons it is difficult to find a leaf perfectly free from their depredations. The young shoots are chosen by many species of Cynipidae and their allies as a receptacle for their eggs, giving rise to a variety of gall-like excrescences, from which few oak trees are quite free. Of the European timber trees of the genus, the next in importance to the British oak is Q. Ccrris, the Turkey oak of the nurserymen. This is a fine species, having when young straighter brandies than Q. Eobur, but in old age the boughs generally curve downwards, and the tree acquires a wide spreading head ; the bark is dark brown, becoming grey and furrowed in large trees ; the foliage varies much, but in the prevailing kinds the leaves are very deeply sinuated, with pointed, often irregular lobes, the footstalks short, and furnished at the base with long linear stipules that do not fall with the leaf, but remain attached to the bud till the following spring, giving a marked feature to the young shoots. The large sessile acorns are longer than those of Q. Eobur, and are dark- brown when ripe ; the hemispherical cups are covered with long, narrow, almost bristly scales, giving them a mossy aspect ; the fruit ripens the first autumn. The foliage in some of the numerous varieties is almost evergreen, and in Britain is retained long after the autumnal withering. This oak abounds all over the Turkish peninsula, and forms a large portion of the vast forests that clothe the slopes of the Taurus ranges and the south shores of the Black Sea ; it is likewise common in Italy and Sardinia, and occurs in the south of France and also in Hungary. It was introduced into England by Miller about 1735, and is now common in parks and plantations, where it seems to flourish in nearly all soils. The Turkey oak in southern England grows twice as fast as Q. Robur ; in the mild climate of Devonshire and Cornwall it has reached a height of 100 feet and a diameter of 4 feet in eighty years, which is about the limit of its profitable growth for timber. The wood is hard, heavy, and of fine grain, quite equal to the best British oak for indoor use, but of very variable durability where exposed to weather. The ships of Greece and Turkey are largely built of it, but it has not always proved satisfactory in English dockyards. The heart -wood is dark in colour, takes a fine polish, and from the prominence of the med ullary rays is valuable to the furniture maker ; it weighs from 40 to 50 ft&amp;gt; the cubic foot. The comparatively rapid growth of the tree is its great recommendation to the planter ; it is best raised from acorns sown on the spot, as they are very bitter and little liable to the attacks of vermin ; the tree sends down a long tap root, which should be curtailed by cutting or early transplanting, if the young trees are to be removed. It seems peculiarly adapted for the mild moist climate of Ireland. It succeeds in many parts of the United States, but is less hardy than the native species. It would appear well fitted for New Zealand planting. Acorns are pro duced on the Turkey oak in great abundance in some seasons, but in cold wet years do not always ripen in Britain ; notwithstanding their bitterness they are greedily eaten by swine. Some southern varieties of this tree bear acorns comparatively sweet, and they are sometimes eaten after being roasted, in which process the tannic acid is partly destroyed. Dalechamps says that some of the esculent acorns of southern Europe occasionally prove unwholesome, causing etfects resembling those of poisoning by Lolium tcmulentum. In North America, where the species of oak are very numerous, the most important member of the group is Q. alba, the white oak, abounding all over the eastern districts of the continent from Lake Winnipeg and the St Lawrence countries to the shores of the Mexican Gulf. In aspect it more nearly resembles Q. Robur than any other species, forming a thick trunk with spreading base and, when