extensive with each other; or rather, that superior extent is generally found, on the side of the Roots.

In the more confined parts of the forest, the reverse of this usually takes place, from the warmth generated by shelter, and the injurious effects of evaporation being obviated. Here Roots, and especially Fibres, are of far less extent and strength, and also fewer in number, than in open positions; and hence the risk, arising from thickets or close plantations being too suddenly laid open, as above mentioned. The want of a stronger system of Root, in such cases, is sufficiently accounted for by the reasonings already given, and by a deficient supply of the descending sap.

Further; Roots are materially determined in their form, by the nature of the soil, in which they grow, and the different nature and character of the Trees. Their developement is most luxuriant in ground, that is neither too loose, nor too dense. In stiff and poor soils, they are spare and scraggy; whereas, in such as are at once deep and loose, the minutest Fibres both expand and elongate with facility, and render the mouths, that search for food to the plant, almost innumerable. * This is remarkably exemplified in the Beech and the Sycamore, and, still more, in the Ash, of which the

* Du Hamel, Phys. des Arbres, T. I. p. 82.

fibrous Roots sometimes amount to millions. Such soils, accordingly, furnish the best rooting ground, and are always favourites with the planter. To fit Trees, however, for removal to situations of great exposure, the Roots may, by artificial methods, be multiplied to a degree far beyond what can be accomplished by unassisted nature; and thus, by art discreetly employed, the business of vegetation, that is, the circulation of the sap, is prevented from standing still, during the extreme violence, which Transplanting, in its best form, must inflict.

FOURTHLY; Extent, Balance, and Closeness of Branches.-Branches, like the roots and stem, are classed among the Conservative Organs. They are divisions of the trunk originating generally in the upper extremity, but often, likewise, along the sides. The primary divisions are again subdivided into secondary divisions, and these again into divisions still smaller, till they terminate, at last, in slender twigs or spray. In point of external form and structure, Branches resemble the trunk from which they issue; but, in point of insertion, distribution, and direction, they exhibit considerable variety, furnishing a ground of distinction, occasionally assumed by botanists, in the discriminating and characterizing of species. Like the stem and root, Branches encrease in width, by the accession of new layers, and in length, by the addition of new

shoots; but they are not formed merely by means of an horizontal extension of the longitudinal tubes of the stem, but each Branch is, as it were, a distinct individual. Hence, the stem is to the Branch what the soil is to the Plant, the source of nourishment and stability.

Branches may properly be considered as among the most important parts of Trees, as they certainly are the most beautiful. One of the most obvious offices they have to perform, is to support the Leaves; and the leaves, by a respiration perceptible and imperceptible, and by the action of the atmosphere, as above noticed, elaborate the sap sent up by the roots, and convert it into juice fitted for nutrition. The ascent of the sap from the roots seems to be considerably assisted, by a proper number of Side-Branches, distributed along the stem; and the general health and vigour of the Tree are, in the same way, encreased; so that it will ultimately attain a greater size, than if deprived of such Branches, or very sparingly supplied with them. During the descent of the Proper juice, on the other hand, as has been seen, each Branch is nourished by the sap prepared by itself; and the surplus quantity, beyond what s so employed, goes to the encrease, first, of the stem,

Grew, Anat. of Plants, p. 28.-Du Hamel, T. I. p. 93.Keith, vol. I. p. 48-51.-Vol. II. pp. 255, 256.

and, in the end, of the roots.

From the experi

ments made by the most accurate observers, we further find, that the solid texture of the wood depends on the quantity of the descending sap, and, in a great measure likewise, on the slowness of its descent; both of which objects are materially promoted by the lateral Branches. But, should they exceed the due number, requisite for those important purposes, retaining too much of the sap which they prepare, and affording too scanty a supply to the stem, they may, in ordinary cases, be considered as robbers, and should be curtailed by pruning, within proper limits.

In this view, it will be perceived, that judicious Pruning is a work of far greater nicety and difficulty, than is generally believed, and that it should not be permitted, unless under the superintendence of some scientific person. It is true, it has been shown (and, I think, satisfactorily, by the ingenious Mr Pontey), that severe pruning must augment the actual weight of the stem, and, as he specially argues, the value of the tree. But great doubts may be entertained, whether, in some cases, this writer, meritorious as he is, may not have proceeded on an erroneous principle in his theory; and that his practice in pruning has been carried

Knight on the Sap of Trees, Philosoph. Trans. 1803, 1804. Mirbel, Anat. et Phys. Veget. Art. 6.

to a height, sanctioned by neither science nor experience.

Branches, besides giving to Trees both beauty and nourishment, serve to balance them properly; and, by throwing themselves out on every side, aid the Trees in withstanding the wind, in whichever way it may blow. Most Trees, if not prevented by adverse circumstances, have, at first, a leading shoot, which tends perpendicularly upwards, and is invested with a preeminence over the other branches. Having reached the height, which the soil and situation admit, the central shoot loses its preeminence. The sap, required to give it superior vigour, seems then to fail, and it gradually disappears among the other shoots. Meanwhile, the plastic powers of the Trees soon multiply the branches of the top, which gradually obtains a rounded form, and beconies what the nurserymen call" clump-headed." But this sort of head, so desirable for picturesque purposes, may also be procured by judicious treatment, as will be seen in the sequel, and with sufficient room for expansion, during the youthful age of the Tree, and while the central shoot yet maintains its preeminence, and the power of reaching its greatest height.

It is pleasing to observe, in this place, how beauty and utility coincide in the same object. In

*NOTE III.