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1911 Encyclopedia Britannica
(0. Eng., ac), a word found, variously modified, in all Germanic languages, and applied to plants of the genus Quercus, natural order Fagaceae (Cupuliferae of de Candolle), including some of the most important timber trees of the north temperate zone. All the species are arborescent or shrubby, varying in size from the most stately of forest trees to the dwarfish bush. Monoecious, and bearing their male flowers in catkins, they are readily distinguished from the rest of the catkin-bearing trees by their peculiar fruit, an acorn or nut, enclosed at the base in a woody cup, formed by the consolidation of numerous involucral bracts developed beneath the fertile flower, simultaneously with a cup-like expansion of the thalamus, to which the bracteal scales are more or less adherent. The ovary, three-celled at first, but becoming one-celled and one-seeded by abortion, is surmounted by an inconspicuous perianth with six small teeth. The male flowers are in small clusters on the usually slender and pendent stalk, forming an interrupted catkin; the stamens vary in number, usually six to twelve. The alternate leaves are more or less deeply sinuated 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 oaks are widely distributed over the temperate parts of Europe, Asia, North Africa and North America. In the western hemisphere they range along the Mexican highlands and the Andes far into the tropics, while in the Old World the genus, well represented in the Himalayas and the hills of China, exists likewise in the peninsula of Malacca, in the Indian Archipelago and Malaya to the Philippine Islands and Borneo. On the a, Diagram of male flower.
b, Diagram of female flower.
c, Female flowers of Q. pedunculata, slightly enlarged.
mountains of Europe and North America they grow only at moderate elevations, and none approach the arctic circle. The multitude of species and the many intermediate forms render their exact limitation difficult, but those presenting sufficiently marked characters to justify specific rank probably approach 300 in number.
The well-known Q. Robur, one of the most valued of the genus, and the most celebrated in history and myth, may be taken as a type of the 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, extending from the shores of the Atlantic to the Ural; its most northern limit is attained in Norway, where it is found wild up to lat. 63Â°, and near the Lindesnaes forms woods of some extent, the trees occasionally acquiring a considerable size. In western Russia it flourishes in lat. 60Â°, but on the slope of the Ural the 56th parallel is about its utmost range. Its northern limit nearly coincides with that of successful wheat cultivation. Southwards it extends to Sardinia, Sicily and the Morea. In Asia it is found on the Caucasus, but does not pass the Ural ridge into Siberia. In Britain and in most of its Continental habitats two varieties exist, regarded by many 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 petioles. But, d' 4 a From Kotschy, Die Eicher Europas, Vienna, 1862, Plate XXXII. Fio. i. - Flowers of Oak (Quercus). c d, Male flowers of Q. sessiliflora, much enlarged.
e, Female flowers of Q. sessiliflora, after fertilization, enlarged.
though the extreme forms of these varieties are very dissimilar, innumerable modifications are found between them; hence it is more convenient to regard them as at most sub-species of Q. Robur. The British oak is one of the largest 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, owing to the central shoots becoming abortive, and the growth thus being continued laterally, causing a zigzag development, more exaggerated in old trees and those standing in From Kotschy, op. cit. Plate XXV11.
FIG. 2. - Q. pedunculata; half natural size.
exposed situations; 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, especially the sessile-fruited kinds, and the gnarled character traditionally assigned to the oak applies chiefly to its advanced age. The broad deeply-sinuated leaves with blunt rounded lobes are of a peculiar yellowish colour when the buds unfold in May, but assume a more decided green towards midsummer, and eventually become rather dark in tint; they do not change to their brown autumnal hue until late in October, and on brushwood and saplings the withered foliage is often retained until the spring. The catkins appear soon after the young leaves, usually in England towards the end of May; the acorns, oblong in form, are in shallow cups with short, scarcely projecting scales; the fruit is shed the first autumn, often before the foliage changes.
Vast oak forests still covered the greater part of England and central Europe in the earlier historic period; and, though they have been gradually cleared in the progress of cultivation, oak is yet the prevailing tree in most of the woods of France, Germany and southern Russia, while in England the coppices and the few fragments of natural forest yet left are mainly composed of this species. The pedunculated variety is most abundant in the southern and midland counties, the sessilefruited kinds in the northern parts and in Wales, especially in upland districts; the straighter growth and abundant acorns of this sub-species have led to its extensive introduction into plantations. The name of "durmast" oak, originally given to a dark-fruited variety of Q. sessiliflora in the New Forest, has been adopted by foresters as a general term for this kind of oak; it seems to be the most prevalent form in Germany and in the south of Europe. Many of the ancient oaks that remain in England may date from Saxon times, and some perhaps from an earlier period; the growth of trees after the trunk has become hollow is extremely slow, and the age of such venerable giants only matter of vague surmise. The celebrated Newland oak in Gloucestershire, known for centuries as "the great oak," was by the latest measurement 472 ft. in girth at 5 ft. from the ground. The Cowthorpe oak, standing (a ruin) near Wetherby in Yorkshire, at the same height measures 382 ft., and seems to have been of no smaller dimensions when described by Evelyn two centuries ago; like most of the giant oaks of Britain, it is of the pedunculate variety.
The wood of the British oak, when grown in perfection, is. the most valuable produced in temperate climates. The heartwood varies in colour from dark brown to pale yellowishbrown; hard, close-grained, and little liable to split accidentally, it is, for a hard wood, easy to work. Under water it excels. most woods in durability, and none stand better alternate exposure to drought and moisture, while under cover it is nearly indestructible as long as dry-rot is prevented by free admission of air. Its weight varies from 48 to about 55lb the cubic foot, but in very hard slowly-grown trunks sometimes approaches 60 lb. The sap-wood is lighter and much more perishable, but is of value for many purposes of rural economy. The relative qualities of the two varieties have been the frequent subject of debate, the balance of practical testimony seeming to establish the superiority of Q. pedunculata as far as durability in water is concerned; but when grown under favourable circumstances the sessile oak is certainly equally lasting if kept dry. The wood of the durmast oak is commonly heavier and of a darker colour, hence the other is sometimes called by woodmen the white oak, and in France is known as the "chene blanc." The oak of Britain is still in demand for the construction of merchant shipping, though teak has become in some measure its substitute, and foreign oak of various quality and origin largely takes. its place. Its great abundance of curved trunks and boughs rendered the oak peculiarly valuable to the shipwright when the process of bending timber artificially was less understood; the curved pieces are still useful for knees. The younger oaks are employed by the carpenter, wheelwright, wagon-builder and for innumerable purposes by the country artisan. The most durable of fences are those formed of small oaks, split lengthwise by the wedge into thin boards. The finely-grained heart-wood is sought by the cabinetmaker for the manufacture From Kotschy, op. cit. Plate XXXII.
FIG. 3. - Q. sessiliflora; half natural size.
of furniture, and high prices are often given for the gnarled and knotted portions of slowly-grown trees, to be sawn into veneers. Oak was formerly largely used by wood-carvers, and is still in some demand for those artists, being harder and more durable than lime and other woods that yield more readily to the sculptor's tool. Oak 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-coloured oak-wood. The wood, of unknown age, found submerged in peat-bogs, and of a black hue, is largely used in decorative art under the name of "bog-oak." The oak grows most luxuriantly on deep strong clays, calcareous marl or stiff loam, but will flourish in nearly any deep well-drained soil, excepting peat or loose sand; in marshy or moist places the tree may grow well for a time, but the timber is rarely sound; on hard rocky ground and exposed hillsides. the growth is extremely slow and the trees small, but the wood is generally very hard and durable. The oak will not bear exposure to the full force of the sea gale, though in ravines and on sheltered slopes oak woods sometimes extend nearly to the shore. The cultivation of this tree in Europe forms one of the most important branches of the forester's art. It is frequently raised at once by sowing the acorns on the ground where the trees are required, the fruit being gathered in the autumn as soon as shed, and perfectly ripe seeds selected; but the risk of destruction by mice and other vermin is so great that transplanting from a nursery-bed is in most cases to be preferred.
The acorns should be sown in November on well-prepared ground, and covered to a depth of i a or 2 in.; the seeds germinate in the spring, and the seedlings are usually transplanted when one or two years old to nursery-beds, where they are allowed to grow from two to four years, till required for the plantation. Some authorities recommend the tap-roots to be cut in the second year, with the view of increasing the ball of fibre; but, if the trees are removed from the seed-bed sufficiently early, the root is best left to its natural development. The oak requires shelter in the early stages of growth; in England the Scotch pine is thought best for this purpose, though Norway spruce answers as well on suitable ground, and larch and other trees are sometimes substituted. The conifers are allowed to grow to a height of from 3 to 5 ft. before the young oaks are planted, and are gradually thinned out as the latter increase in size. The distance between the oaks depends upon the growth intended before thinning the young wood; usually they are placed from 8 to 12 ft. apart, and the superabundant trees cut out as they begin to interfere with each other. The lower branches often require removal, to ensure the formation of a tall straight trunk, and this operation should be performed before the superfluous shoots get too large, or the timber will be injured; but, as with all trees, unnecessary pruning should be avoided, as every branch removed lessens the vigour of growth. Where artificial copsewood is the object, hazel, hornbeam and other bushes may be planted between the oaks; but, when large timber is required, the trees are best without undergrowth.
The growth of the oak is slow, though it varies greatly in different trees; Loudon states that an oak, raised from the acorn in a garden at Sheffield Place, Sussex, became in seventy years 12 ft. in circumference; 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 completed. The tree will continue to form wood for i 50 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 processes; 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 sessilefruited 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, but is not used in modern practice. The astringent principle is a peculiar kind of tannic acid, called by chemists quercitannic, 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 Io % 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 "mast" 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 "pannage," 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 larvae of the small stag-beetle and several other Coleoptera, and those of the wood-leopard moth, goat moth and other Lepidoptera feed upon it occasionally; the foliage is devoured by innumerable larvae; 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. Cerris, the Turkey oak of the nurserymen. This is a fine species, having when young straighter branches than Q. Robur, 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. Robur, 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 Philip Miller about 1 735, 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 TOO ft. and a diameter of 4 ft. 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 medullary rays is valuable to the furniture maker; it weighs from 40 to 50 lb 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.
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 to the continent from Lake Winnipeg and the St Lawrence countries of 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 growing in glades or other open places, huge spreading boughs, less twisted and gnarled than those of the English oak, and covered with a whitish bark that gives a marked character to the tree. The leaves are large, often irregular in form, usually with a few deep lobes dilated at the end; they are of a bright light green on the upper surface, but whitish beneath; they turn to a violet tint in autumn. The egg-shaped acorns are placed singly or two together on short stalks; they are in most years sparing].y produced, but are occasionally borne in some abundance. On rich loams and the alluvial soils of river-valleys, when well drained, the tree attains a large size, often rivalling the giant oaks of Europe; trunks of 3 or 4 ft. in diameter are frequently found, and sometimes these dimensions are greatly ex ceeded. The wood is variable in quality and, though hard in texture, is less durable than the best oak of British growth; the heart-wood is of a light reddish brown varying to an olive tint; a Canadian specimen weighs 524 lb the cubic foot.
Q. obtusiloba, the post oak of the backwoodsman, a smaller tree with rough leaves and notched upper lobes, produces an abundance of acorns and good timber, said to be more durable than that of the white oak.
The pin oak, sometimes called the "burr-oak," Q. macrocarpa, is remarkable for its large acorns, the cups bordered on the edge by a fringe of long narrow scales; the leaves are very large, sometimes from Io in. to i ft. in length, with very deep lobes at the lower part, but dilated widely at the apex, and there notched. The tree is described by Prof. C. S. Sargent (Silva of North America) as one of the From Michaux, op. cit. Plate XXXV.
FIG. 5. - Q. rubra; one-fourth natural size.
most valuable timber trees of North America, its wood being superior in strength even to that of Q. alba, with which it is commercially confounded.
The over-cup oak, Q. lyrata, is a large tree, chiefly found on swampy land in the southern states; the lyrate leaves are dilated at the end; the globose acorns are nearly covered by the tuberculated cups.
In the woods of Oregon, from the Columbia river southwards, an oak is found bearing some resemblance to the British oak in foliage and in its thick trunk and widely-spreading boughs, but the bark is white as in Q. alba; it is Q. Garryana, the western oak of T. Nuttall. This tree acquires large dimensions, the trunk being often from 4 to 6 ft. in diameter; the wood is strong, hard and close grained; the acorns are produced in great quantity, and are used by the Indians as food.
The red oak, Q. rubra, has thin large leaves on long petioles, the lobes very long and acute, the points almost bristly; they are pink when they first expand in spring, but become of a bright glossy green when full-grown; in autumn they change to the deep purplered which gives the tree its name. Common throughout the northern and middle states and Canada, the red oak attains a large size only on good soils; the wood is of little value, being coarse and porous, but it is largely used for cask-staves; the bark is a valuable tanning material. A species nearly allied is the scarlet oak, Q. coccinea, often confounded with the red oak, but with larger leaves, with long lobes ending in several acute points; they change to a brilliant scarlet with the first October frosts, giving one of the most striking of the various glowing tints that render the American forests so beautiful in autumn. The trunk, though often of considerable size, yields but an indifferent wood, employed for similar purposes to that of Q. rubra; the bark is one of the best tanning materials of the country. Both these oaks grow well in British plantations, where their bright autumn foliage, though seldom so decided in tint as in their native woods, gives them a certain picturesque value.
Nearly akin to these are several other forms of little but botanical interest; not _ far removed is the black or dyer's oak, F rom Isotschy op. c i t. Plate XL. Q. tinctoria, a large and handsome species, with a trunk sometimes 4 ft. in FIG. 6. - Q. castaneaefolia, diameter, not uncommon in most forests one-third natural size. east of the Mississippi, especially in somewhat upland districts. The leaves are frequently irregular in outline, the lobes rather short and blunt, widening towards the end, but with setaceous points; the acorns are nearly globular. The wood is coarsely grained, as in all the red-oak group, but harder and more durable than that of Q. rubra, and is often employed for building and for flour-barrels and cask-staves. The bark, very dark externally, is an excellent tanning substance; the inner layers form the quercitron of commerce, used by dyers for communicating to fabrics various tints of yellow, and, with iron salts, yielding a series of brown and drab hues; the colouring property depends on a crystalline principle called quercitrin, of which it should contain about 8%. The cut-leaved oaks are represented in eastern Asia by several species, of which Q. mongolica is From Kotschy, op. cit. Plate XXXVIII.
FIG. 7. - Q. Ilex; half natural size.
widely spread over Dahuria, north China and the adjacent countries; one of the Chinese silkworms is said to feed on the leaves.
The chestnut oaks of America represent a section distinguished by the merely serrated leaves, with parallel veins running to the end of the serratures. Q. Prinus, a beautiful tree of large growth, and its subspecies castanea and montana, yield good timber. Q. Chinquapin or prinoides, a dwarf species, often only I ft. in height, forms dense miniature thickets on the barren uplands of Kansas and Missouri, and affords abundant sweet acorns; the tree is called by the hunters of the plains the "shin-oak." Q. castaneaefolia, represented in fig. 6, From Michaux, Histoire des clanes de l'Amerique. FIG. 4. - Q. alba; one-third natural size.
is a native of the woods of the Transcaucasian region of western Asia.
Evergreen oaks with entire leaves are represented in North America by Q. virginiana, also known as Q. virens, the live oak of the southern states; more or less abundant on the Atlantic coasts of the Carolinas and Florida, its true home is the country around the Mexican Gulf, where it rarely grows more than 50 or 60 m. inland. The oval leaves are dark-green above, and whitish with stellate hairs beneath, the margin entire and slightly recurved. The live oak is one of the most valuable timber trees of the genus, the wood being extremely durable, both exposed to air and under water; heavy and closegrained, it is perhaps the best of the American oaks for shipbuilding, and is invaluable for water-wheels and mill-work. The tree in England is scarcely hardy, though it will grow freely in some sheltered places.
The evergreen oak of southern Europe is Q. Ilex, usually a smaller tree, frequently of rather shrub-like appearance, with abundant glossy dark-green leaves, generally ovate in shape and more or less prickly at the margin, but sometimes with the edges entire; the under surface is hoary; the acorns are oblong on short stalks. The ilex, also known as the "holm oak" from its resemblance to the holly, abounds in all the Mediterranean countries, showing a partiality for the sea air. The stem sometimes grows 80 or 90 ft. in height, and old specimens are occasionally of large diameter; 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. The wood is very heavy and hard, weighing 70 lb the cubic foot; the colour is dark brown; it is used in Spain and Italy for furniture, and in the former country for firewood and charcoal. In Britain the evergreen oak is quite hardy in ordinary winters, and is useful to the ornamental planter from its capacity for resisting the sea gales; but it generally remains of small size. Q. Ballota, a closely allied species abundant in Morocco, bears large edible acorns, which form an article of trade with Spain; an oil, resembling that of the olive, is obtained from them by expression. Q. Ilex, var. Gramuntia, also furnishes a fruit which, after acquiring sweetness by keeping, is eaten by the Spaniards.
In America several oaks exist with narrow lanceolate leaves, from which characteristic they are known as "willow oaks." Q. Phellos, a rather large tree found on swampy land in the southern states, is the most important of this group; itstimberisof indifferent quality.
The cork oak, Q. Suber, the bark of which yields cork (q.v.), is a native of the west Mediterranean area. In Spain the wood is of some value, being hard and close-grained, and the inner bark is used for tanning. From its rugged silvery bark and dark-green foliage, it is a handsome tree, quite hardy in Cornwall and Devonshire, where it has grown to a large size.
The valonia of commerce, one of the richest of tanning materials, is the acorn of Q. Aegilops, a fine species indigenous to Greece and the coasts of the Levant, and sometimes called the "Oak of Bashan." The very large acorns are remarkable for their thick cups with long reflexed scales; the leaves are large, oblong, with deep serratures terminating in a bristle-like point. The cups are the most valuable portion of the valonia, abounding in tannic acid; immature acorns are sometimes exported under the name of "camatina." The allied Q. Vallonea of Asia Minor likewise yields valonia.
Some oaks are of indirect importance from products formed by their insect enemies. Of these the Aleppo gall (see Galls) is yielded by Q. infectoria, a native of Asia Minor and western Asia. Q. coccifera, a small bush growing in Spain and many countries around the Mediterranean, furnishes the kermes dye ([[Kermes). Q]]. persica, or according to some Q. mannifera, attacked by a kind of Coccus, yields a sweet exudation which the Kurds collect and use as manna, or as a substitute for honey or sugar in various confections (see Manna).
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Chisholm, Hugh, General Editor. Entry for 'Oak'. 1911 Encyclopedia Britanica. https://www.studylight.org/​encyclopedias/​eng/​bri/​o/oak.html. 1910.