Fined walls, with an apparatus for temporary coverings of canvas, oiled paper, or woollen nets, are necessary for the perfect production of the finer sorts of peaches and nectarines in all parts of Britain north of Yorkshire. With out the aid of artificial heat, the young wood of these trees is seldom sufficiently ripened, in ordinary seasons, to ensure a supply of good flower-buds for the following year ; and un less the buds be strong and plump, the chance of a crop the ensuing season is proportionally lessened ; and fre quently, after a sufficient quantity of fruit has been brought to full size, unless heat be supp ied artificially, in autumn, maturation is not effected. In the northern parts of the island, therefore, it is always proper to construct a portion of the garden walls with flues : the additional expense of forming the flues, particularly where the inside facing only is of brick, is but trifling ; and little consideration should be attached to the expence of the small quantity of fuel that may be necessary for promoting the setting of the fruit, and for iipening off the young wood in autumn, the time when it is chiefly wanted.
The flues are commonly eighteen or twenty inches deep, and nine inches wide, inside measure, and they make as many turns as the height of the wall will permit. For merly they made only three turns ; but it has been found, that the oftener the flues are returned, provided they draw well, the less heat escapes by the chimney. and consequent ly the more is evolved from the surface of the wall. The sole of the flue to the. length of the first turn, is generally a foot above the level of the border. The front wall dale flue is 44 inches thick, or a brick on bed, without any inside plastering. In some places a wooden trellis covers the wall ; hut in general, the trellis does not extend higher than the first range of the flue, the heat above this not injuring the trees: where neatness is much studied, the trellis rods are sunk into a small recess purposely left in the wall, thus preventing the appearance of bulging, which is otherwise unavoidable.
Soils.
42. The improvement of the soil naturally becomes au object of great importance at the first formation of a gar den ; and its subsequent management, or " keeping in heart," as gardeners term it, is a matter of equal interest.
The various soils distinguished by gardeners and horti culturists consist of the simple earths (as they used to be called) of the chemists, particularly argil, silex and lime, mixed in different proportions. It is well known, that some of the principal offices of the soil are merely mecha nical ; such are, the giving proper support to the vegeta ble by means of its roots, and the supplying these with wa ter in a slow and convenient manner, the superfluous mois ture draining off. A mixture of clay and sand is called loam ; and according as the one or other of these earths predominates, the soil is denominated a clayey or a sandy loam. In the same way, in some counties of England chalky foams are common ; and in other districts, gravelly loams are not unfrequent. When oxide of iron prevails, and renders the clay hard and of a dark brown or red co lour, the soil is called ferruginous loam, or more common ly till. Boggy or heathy soil consists of ligneous particles, or the decayed roots, stems, and leaves of various carices, heaths and sphagna, and the coaly matter derived from these, generally with a slight mixture of argillaceous earth and sand. While the nomenclature of soils remains so im perfect and unsettled as it now is, there seems no proprie ly in enlarging further on the different varieties. Some
judicious remarks on these, and on the principles on which they should be distinguished and named, may be found in the Agricultural Report of Ross and Cromarty, drawn up by Sir George Mackenzie, Bart.
Carbonaceous matter, and certain salts, in small propor tion, are likewise ingredients °in a good soil, plants deriv ing not only support from the soil, and nourishment from the water, and from the decomposition of the water, sup plied by the soil to their roots, but also other peculiar sorts of food from the carbon and salts alluded to.
43. Any substance added to a soil, either to supply a de ficiency, of to rectify what is amiss, is called a manure. The use of manures is, of course, very various. They may be destined to render soil less retentive of rnoisture,•or to make it more retentive ; or they may be calculated to com municate carbonaceous matters or salts. With the former view, clay or argillaceous marl form a suitable manure for a sandy soil, and sand or lime for one that is clayey ; while (lungs and composts of every kind yield the other requisite materials to the soil. For opening clayey soils in gardens, marls are excellent, particularly gravelly marl. Where marls cannot be had, Shelly sand, coal-ashes, or wood-ashes mixed with chips of wood, may be resat ted to. For binding sandy soils, argillaceous marls or calcareous loams are proper ; and the scourings of ditches are often, for this purpose, valuable.
The improvement of cold or sour clay is sometimes ef fected by scorifying it, or burning it, as it is commonly termed. The sward, with two or three inches of the clay adhering to it, is collected in heaps, and brought into a state of red heat, by means of furze, peat, or coals, taking care to add clay on the exterior, so as to confine the fire. Acids and vegetable matters of noxious tendency seem thus to be driven off, and a soil fit for garden culture produced. This is an old practice, which has been lately revived. In Ilitt's Treatise on Fruit-trees, published in 1758, there is a chapter " Of the burning of clay for the improvement of land." 44. The soil of a garden should never be less than two feet and a half deep ; the best gardeners prefer having it fully three feet. The natural soil, therefore, however good, is seldom of sufficient depth. If it be not two feet, a quan tity of earth from the fields is carried in. The cleanings of roads and grass turf of any kind form valuable additions to garden soil. In the course of trenching, a portion of the subsoil is brought to the surface, and gradually meliorated; but to bring up much of it at once, is very injurious. Soil of the usual depth may be trenched two spit (spadeful) deep ; and if this be done every third year, it is evident that the surface which has produced three crops will rest for the next three years ; thus giving a much better chance of constantly producing healthy and luxuriant crops, and with one half the manure that would otherwise be requisite. Nicol insists for the deeper soil, and recommends that, after taking three crops, the ground should be trenched three spit, by which the bottom and top are reversed ; three crops are again to be taken, and the ground trenched two spit, by which the soil which formed the top goes to the middle, and that which lay in the middle goes to the sur face. After other three crops, the ttenching is to be again three spit deep. By thus alternately trenching two spit and three, after intervals of three years, the surface soil is regularly changed, resting six years and producing three ; and an approach is this made to the desirable object of having always a new soil.