The knots of large trees are sometimes of considerable site, I have portions of one of those of the Norfolk Island pine, (Auracaria excelsa,) which attained the enormous size of about four feet long, and four to six inches diameter. In substance it is thoroughly compact and solid, of a semi-transparent hazel-brown, and it may be cut almost as well as ivory, and with the same tools, either into screws, or with eccentric or drilled work, etc.; it is an exceedingly appropriate material for ornamental turning.*

It is by some supposed that the root of a tree is divided into about as many parts or subdivisions as there arc branches, and, that speaking generally, the roots spread around the trunk under ground, to about the same distance as the branches wave above; the little germs or knots from which they proceed being in the one case distributed throughout the length of the stem of the tree, and in the other crowded together in the shorter portion buried in the earth.

If this be true, we have a sufficient reason for the beautiful but gnarled character of the roots of trees when they arc cut up for the arts; many a block of the root of the walnut-tree, thus made up of small knots and curls, and that was first intended for the stock of a fowling-piece, has been cut into veneers and arranged in angular pieces to form the circular picture of a table, and few pictures of this natural kind will be found more beautiful. The roots of many trees also display very pretty markings; some are cut into veneers, and those of the olive-tree, and others, are much used on the Continent for making suuff-boxes.

The he tops of the pollard trees, such as the red oak, elm, ash, and other trees, owe their beauty to a similar crowding together of the little germs, whence have originated the numerous shoots which proeeeded from them after they had been lopped. The burrs or excescenes of the yew, and some other trees, appear to arise from a similar cause, apparently the unsuccessful attempts at the formation of branches from one individual spot, from this may arise those bosses or wens, which almost appear as the result of disease, and exhibit internally crowds of knots, with fibres surrounding them in the most fantastic shapes. Sometimes the burrs occur of immense size, so as to yield a large and thick slab of highly ornamental wood of most confused and irregular growth: such pieces are highly prized, and are cut into thin veneers to be used in cabinet-work.

* I am indebted to Maj. Brown for my specimens of this knot, and the informa-tion concerning it; a part of a knot of the same species, with some of the surrounding wood, is in the model room of the Admiralty. Somerset House.

It appears extremely clear likewise, that the beautiful East Indian wood, called both Kiabooca and Amboyna, is, in like manner, the excrescence of a large timber tree. Its character is very similar to the burr of the yew-tree, but its knots are commonly smaller, closer, and the grain or fibre is more silky. The Kiabooca has also been supposed to be cut from around the base of the cocoa-nut palm, a surmise that is hardly to be maintained although the latter may resemble it, as the Kiabooca is imported alone from the East Indies, whereas the cocoat-nut palm is common and abundant both in the eastern and western hemispheres.* (See Kiabooca in the Catalogue.)

The bird's-eye maple shows in the finished work the peculiar appearance of small dots or ridges, or of little conical projections with a small hollow in the centre, (to compare the trivial with the grand, like the summits of mountains, or the craters of volcanoes,) but without any resemblance to knots, which are the apparent cause of ornament in woods of somewhat similar character, as the burrs of the yew and kiabooca, and the Russian maple (or birch tree): this led me to seek a different cause for its formation.

On examination, I found the stem of the American bird's-eye maple, stripped of its bark, presented little pits or hollows of irregular form, some as if made with a conical punch, others ill-defined and flattened like the impression of a hob-nail; suspecting these indentations to arise from internal spines or points in the bark, a piece of the latter was stripped off from another block, when the surmise was verified by their appearance. The layers of the wood being moulded upon these spines, each their fibres is abruptly curved at the respective places, and when cut through by the plane, they give, in the tangental slice, the appearance of projections, the same as in some rose-engine patterns, and the more recent medallic glyptographic or stcrco-graphic engravings, in which the closer approximation of the lines at their curvatures, causes those parts to be more black, (or shaded,) and produces upon the plane surfaces, the appearances of waves and ridges, or of the subject of the medal.

* I have a beautiful specimen of a Burr, found occasionally upon the teak, which is fully equal in beauty to the Amboyna, but a smaller figure; I owe it to the kindness of Dr. Horsfield of the India-House.

Mr. G. Loddiges considers the burrs may occur upon almost all old trees, and that they result from the last attempt of the plant to maintain life, by the reparation of any injury it may have received.

The short lines observed throughout the maple wood, between the dots or eyes, are the edges of the medullary rays, and the same piece of wood when examined upon the radial section, exhibits the ordinary silver grain, such as we find in the sycamore, (to which family the maple tree belongs,) with a very few of the dots, and those displayed in a far less ornamental manner.

The piece examined measured eight inches wide, and five and a half inches radially, and was apparently the produce of a tree of about sixteen inches diameter; the effect of the internal spines of the bark was observable entirely across the same, that is through each of the 130 zones of which it consisted. The curvature of the fibres was in general rather greater towards the center, which is to be accounted for by the successive annual depositions upon the bark, detracting in a small degree from the height or magnitude of the spines within the same, upon which the several deposits of wood were formed. Other woods also exhibit spines, which may be intended for the better attachment of the bark to the stem, but from their comparative minuteness, they produce no such effect on the wood as that which exists, I believe exclusively, in the bird's-eye maple.