[48] In fairness, it may be proper to explain, that the greater part of the trees we have thus cultivated have been of _Pyrus_, although we commenced the practice with common forest trees—yet the pear and apple vary nothing from the oak and ash in the primary stage of life, in as far as respects the extension—we can also profit fully as much by raising apple timber of proper fast grown variety, as by any other timber; and have it in our power to sell this timber to machine-makers at double the price of oak of the same size. [49] We think Sir Henry would find some of the failures of which he owns he cannot well ascertain the cause, but occurring especially in beech and oak, to be owing to a number of the lower roots, which are by far the tenderest, being bruised by the weight of the tree itself, when he turns it repeatedly over from the one side to the other, in order, by throwing in earth beneath it, to raise the root on a level with the surface of the field, the whole weight of the incumbent mass resting upon these soft roots. The oak, and still more the beech, are exceedingly susceptible to injury from cutting or bruises, and die far inward from the laceration. The wounded lower roots, especially when any vacuity is left not filled close in with earth, where mouldiness might generate in a dry situation, or when soaking in moisture for a part of the season, will become corrupted; the putrefaction thence gradually extending upward into the bulb, will contaminate the whole, and the second or third year after planting, the tree will be dead. [50] We understand freezing the earth around the bulb is an old practice. [51] We particularize the oak, cork-tree of arid warm Spain, and much of the timber of New Holland. Owing to the hot parching air in the latter place, the epidermis becomes dried to such a degree, that contracting by the drought, and bursting by the swelling of the enveloped stem, it peels off like the old skin of a serpent, and is often seen hanging upon the tree in large shreds like tattered garments. In several kinds of trees, we have counted regular annual rings of desiccated bark; in some kinds this appeared a growth or deposition, in others, mere parched exuviæ. Trees attain some age before the _exuviæ_ commence; the _deposit_ begins the first season, even in sheltered situations. The cork-tree, and the small-leaved elm, shew the greatest annual deposit of dry bark. The former does, and the latter is said to belong to warm arid countries; both form a better nonconductor of heat than any other dry bark we are acquainted with—infinitely better than the bark exuviæ of trees which approach the polar regions. [52] We do not pretend to explain how it is, that one kind of climbing plant follows the sun in its convolutions, and another traverses his course. There surely cannot be any thing in a habit acquired in the southern hemisphere.