178 WALLS, ESPALIER-RAILS, AND TRELLIS- WORK. 



they require a trellis on which to fasten the plants. Nevertheless the vine 

 and the peach have been successfully grown against such walls at various 

 places in the neighbourhood of Paris, though they are now rapidly giving 

 way to stone walls. These walls are commonly built without mortar, ex- 

 cepting to close the outside joints, or to plaster over the surface of the wall 

 as a substitute for a trellis, which is always used when this is not done. 

 The grapes at Thomery, near Fontainebleau, are chiefly grown on trellised 

 walls of this kind ; and the peaches at Montreuil, near Paris, are chiefly on 

 stone walls stuccoed. Walls formed of boards are frequent in the north of 

 Europe, where timber is abundant ; but, except when the boards are five or 

 six inches in thickness, they are very cold. In Holland, and more particu- 

 larly in Sweden, when such walls form the backs to hothouses, they are 

 thatched from top to bottom. In Britain, were it not for the expense of 

 the material, boarded walls might in many cases be adopted instead of brick ; 

 more especially in the case of walls built in the direction of north and south, 

 because in them the air is of nearly the same temperature on both sides : 

 whereas in an east and west wall, the heat produced by the sun on the south 

 side is being continually given out to the much colder north side. Boarded 

 walls two or three centuries ago afforded the only means, in the neighbour- 

 hood of London, of forcing the cherry, the only fruit which at that time was 

 attempted to be produced out of season. The boarded wall or fence was 

 placed in the direction of east and west, the cherries planted against it on 

 the south side, and casings of hot dung on the north, close to the boards. To 

 derive the full advantage from the south side of an east and west wall, it 

 ought to be of greater thickness than a south and north wall under the same 

 circumstances ; because, from the much greater cold of the north side, the 

 south side is continually liable to have the heat abstracted from it in that 

 direction. A south and north wall, on the other hand, can never become 

 so hot on either side as an east and west wall does on the south side ; and as 

 it receives its heat equally on both sides, so it loses it equally. Where a 

 south and north wall is thin, and consequently cold, it might become worth 

 while, when it was desirable to retain as much heat on the south side as 

 possible, to thatch it on the north side during the winter and spring months. 

 The great advantage of coverirfg with some protecting material the north 

 sides of walls in spring, when trees are in blossom, may be inferred from the 

 case of trees trained against dwelling-houses, which invariably set their 

 blossoms better than trees against unprotected garden-walls. 



469. The height of garden-walls may vary according to the object in view, 

 but it is rarely necessary to be more than twelve or fifteen feet, or less than 

 six feet. In kitchen-gardens the highest wall is generally placed on the 

 north side, as well to protect the garden from north winds as to admit of a 

 greater surface for training on exposed to the full sun, and to form, if ne- 

 cessary, a back sufficiently high for forcing-houses. The east and west 

 boundary walls are commonly made two or three feet lower than the north 

 wall, and the south wall somewhat lower still. The usual proportions in a 

 garden of three acres are 17, 14, and 12 ; for gardens of one acre, 14, 12, and 

 10 ; that part of the north wall against which the forcing-houses are placed 

 being in small gardens raised somewhat higher than the rest. Twelve 

 feet is found to be a sufficient height for peach and apricot trees ; but for 

 pears and vines it may be one half more ; and indeed for vines there is 

 scarcelv anv limit. 



