WALLS, ESPALIER-RAILS, AND TRELLIS-WORK. 137 



extensively, there are commonly one or more small frames with single 

 lights for raising seedlings, and others of two or three lights for winter 

 or early spring crops ; the smallness of the frame allowing a greater 

 command of the heating material beneath it, by the application of out- 

 side casings of warm dung. The back, front, and ends of frames are 

 generally permanently fixed together by tenons and mortices, and by 

 being nailed to posts in the four inner angles ; but in some cases the 

 buck and sides are fastened together by keyed iron bolts, which readily 

 admit of separating the frame into pieces, and laying these away under 

 cover, and in little space, when not required for use. From the short 

 duration of frames, and from the great quantity of dung required to 

 heat them, as well as from the waste of heat incurred in preparing the 

 dung, frames are now, in most British gardens, being replaced by pits, 

 which may be called fixed frames, with brickwork substituted for wood. 



Fixed Structures used in Horticulture. 



The fixed structures required in gardens are chiefly walls, espalier- 

 rails, trellis and lattice-work, and structures for containing growing 

 plants. 



Walls, Espalier-rails, and Trellis-work. 



Walls are used for the protection of gardens, and also as furnishing 

 surfaces on which fruit-trees and ornamental plants may be trained, 

 with a view to producing increase of temperature and protection from 

 high winds : they may be considered in regard to direction, material, 

 height, foundation, coping, and general construction. 



Walls constructed merely for boundaries take the direction indicated 

 by the form of the ground to be enclosed; but those built pur- 

 posely 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 secon- 

 dary 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 fre- 

 quently 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, 



