538. Of the Oak there are upwards of sixty distinct species known to botanists, chiefly natives of Europe and America, several of which produce valuable timber. Five kinds of oak are enumerated by Vitiuvius, viz. the "esculus," the "cerrus," the "quercus," the "suber' and the "robur," the timber of each being distinguished by its peculiar properties; * but it would be difficult to identify some of the kinds mentioned by him with the species described by modern writers on botany.

Vitruvius shows, however, by his observations that the peculiarities of the different kinds were attended to, and they must have also been well understood by the Gothic builders in this country, for in the roofs and beams of most of their buildings we find a very superior kind of oak which closely resembles and is often mistaken for chestnut (see Art. 560). This kind was sometimes called the "Irish Oak." Evelyn commends the Irish oak "for resisting the worm,"* but to what species of oak he alludes it is difficult to say.

* Lib. ii., cap. ix.

At the present time the oak grown in Sussex is esteemed the best which England affords, though of late years the good "heart of oak" timber, from which it obtained its character, is becoming scarce. According to Marshall the superiority of the Sussex oak is chiefly to be attributed to the nature of the soil,† and perhaps also in some degree to good management, for proper attention and skill in the cultivation of trees make a considerable difference in the value of the timber.

English oak is spoken of in general by practical men as though there were but one species, and no difference in the quality of the wood except that produced by soil and situation; but to botanists two distinct species have long been known,‡ viz. the Quercus pedunculata,§ and the Quercus sessiliflora. Some however have considered these as mere varieties of one species, viz. the Quercus robur.*

* 'Silva,' Hunter's edit., vol. it, p. 222.

† ' Rural Economy of the Southern Counties,' vol. ii., p. 109.

‡See Ray's 'Synopsis Methodica Stirpium Britannicarum,' p. 440.

§ This tree, according to Sir J. E. Smith, 'Flora Brit.,' vol. iii., 1026, was called by Linnaeus and the older botanists the Quercus robur, which he has followed. It also appears to be the robur of Vitruvius, for he states that the robur is less liable to warp than the quercus (book ii., chap, iii.), which is precisely the case with the two English oaks, as the wood of the "robur" of Smith is much less liable to warp than that of the sessiliflora. Again, the description given by Vitruvius of the wood of the quercus in book ii., chap, ix., agrees in everything with the properties of that of the sessile-fruited oak; and as he describes the wood only, it is by it alone that the species is to be known. Perault (in his notes on Vitruvius) and Evelyn (in his 'Silva') apply the name robur to the sessile-fruited oak; but had these writers known that the wood of the sessile-fruited oak is more flexible than that of the other kind, they would not have done so.

539. Common British Oak (Q. pedunculata) is a native of nearly all parts of Europe, from Sweden to the Mediterranean. It is said to be found in the north of Africa and a part of Asia. It is that which is most frequently met with in the woods and hedges of the south of England and in the forests of France; but in Germany the Q. sessiliflora is more common.†

The leaves of this species are irregularly sinuated, with short or scarcely any footstalks (petioles); the acorns have long stalks. In favourable situations this species attains an immense size. A fine healthy tree growing in the grounds of Earl Cowper, at Panshanger, Herts, in 1820, measured nearly 18 feet in circumference, at 5 feet from the ground; and the whole height of the tree exceeded 75 feet. The wood of this species has often a reddish tinge; the larger medullary rays are always very numerous, producing a large flowery appearance. The grain is tolerably straight and fine, and it is generally free from knots, sometimes closely resembling foreign wainscot. It splits freely, and makes good laths for plasterers and slaters; and it is decidedly the best kind of oak for joists, rafters, and any other purpose where a stiff and straight-grained wood is desirable.

540. The Sessile-fruited Oak (Q. sessiliflora) is dispersed over the same range of countries as the common British oak, but seems to predominate in the forests of Germany, where it is 6aid to grow to valuable timber on a greater variety of soils than the latter. The Q. sessiliflora appears to have been first noticed as a distinct species in this country by Mr. Bobart, in Bagley Wood, and near Newbury, in

* Rhind's ' Hist, of the Vegetable Kingdom.' † Brown's ' Forester,' 4th edit. p. 177.

Berkshire, and called by him, "Bay Oak."* It has been observed by Miller near Dulwich, in Surrey, and it appears to be the common oak of the neighbourhood of Durham, and perhaps generally of the north of England.

There are also some very fine trees in the Earl of Mansfield's grounds at Kenwood, † where the author had an opportunity of comparing the trees of the two species, but could not observe any difference in their growth or general form, except that the sessile-fruited oak had a more graceful appearance, which renders it superior as an ornamental tree. In Bagot Park, Staffordshire, is a very large one, which goes by the name of the Squitchbank Oak, being upwards of 43 feet in circumference at the base, and 61 feet high. At Hazelgrove, in Somersetshire, is a fine oak 80 feet in height, and 30 feet in circumference at 4 feet from the ground.

The leaves of the sessile-fruited oak have, rather long footstalks, often nearly an inch in length, and they are more regularly and less deeply sinuated than those of the common or peduncled oak. The acorns sit close to the branches, having very short or scarcely any stalks. The wood is of a darker and more uniform colour, the grain less varied, the larger medullary rays not so abundant as that of the common oak; it is heavier, harder, and more elastic. The smoothness and gloss of the grain makes it resemble the wood of the chestnut. It is very liable to warp and become shaky in seasoning, also tough and difficult to split, which renders it unsuitable for laths. This is most probably the reason why oak laths are so seldom used in the north of England.