WALLS, ESPALIER-RAILS, AND TRELLIS- WORK. 177 



467. Direction and material. — Boundary walls take the direction indi- 

 cated by the form of the ground to be enclosed ; but walls built purposely 

 for training trees, in the interior of a garden, are varied in direction according 

 to the aspects which are considered most desirable. A wall in the direction 

 of east and west, gives one side of the wall fully exposed to the sun for the 

 finer fruits, or for fixing against it glass structures : while the north side of 

 the wall may be employed for inferior fruits, for retarding crops, as well of 

 fruit against the wall, as, in some cases, of vegetables on the border. A wall 

 in the direction of north and south furnishes two good aspects for the second- 

 ary fruits, such as apricots, plums, and the finer pears. Walls have been 

 built in a curvilinear direction, but no advantage has been found from them 

 excepting a saving of material, in proportion to the length of the wall, the 

 curves having the same effect in resisting lateral pressure as buttresses ; but 

 walls in situations exposed to high winds, built with projections at right 

 angles, of the height of the wall and the width of the border, but somewhat 

 sloped down from back to front, have been found beneficial in checking the 

 course of the wind when in a direction parallel to the wall. Screen walls of 

 this kind are frequently built at the exterior angles of the walls of kitchen- 

 gardens ; and sometimes they occur at distances of from 100 to 200 feet along 

 walls having a south aspect ; and in the case of east and west winds they 

 are found very beneficial. Walls with piers at regular distances, allowing 

 room for one trained tree between every two piers, have also been found 

 beneficial from the shelter afforded by the piers, which at the same time 

 greatly strengthen the wall, and admit of its being built thinner. In general, 

 however, a straight wall, without projections of any kind, is most conve- 

 nient, most suitable for training, and for protecting by temporary copings, 

 and most agreeable to the eye. 



4G8. The materials of walls are brick, stone, mud, and wood ; but the first 

 is by far the best. Brick retains warmth, in consequence of its much 

 greater porosity than stone ; forms a very strong wall wdth comparatively 

 little substance, from the rectangular shapes of the bricks, and the firnmess 

 with which mortar adheres to them ; and it is the best of all walls for training 

 on, from the small size of the bricks and the numerous joints between them. 

 Add also, that from the porosity of the bricks, nails may even be driven 

 sufficiently far into them to hold branches, as securely as nails driven into the 

 joints. Stone walls are good in proportion as they approach to brick walls. 

 For this reason, if the stone is not naturally porous and a bad conductor of 

 heat, the walls should be built of extra thickness, and the stones should not 

 be large, nor so rough as to make coarse joints, The warmest walls of this 

 kind are such as are of sufficient thickness to allow of the interior of the 

 wall being built without mortar, in consequence of which much air is re- 

 tained, and heat is not readily conducted from the warm side of the wall 

 to the cold side. A stone wall, with a facing of bricks on the warm side, 

 forms the next best wall to one entirely of brick ; and next to this, a stone 

 wall stuccoed, plastered over with a mixture of stone lime and sharp sand, 

 or coated over with Roman cement of good quality. Walls formed of earth 

 or mud are still better non-conductors than brick walls; but though they are 

 warm, yet as surfaces for training trees on they are attended with several 

 disadvantages. They cannot conveniently be built high, and whatever may 

 be their height, they require the coping to project farther than is beneficial 

 to the plants trained on them at any other season than in early spring ; and 



