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



465. The common hotbed frame is a bottomless box, commonly six feet 

 wide, and three, six, or eighteen feet in length, formed of boards from one 

 to two inches in thickness. The height at the back may be two feet, and 

 in front one foot. The bottom should be level, so that the sides and the 

 sashes laid on the frame may slope from back to front. A three-light or 

 three-sashed frame is divided by two cross bars or rafters, so as to leave a 

 space between them from two feet nine inches to three feet for the width 

 of the sash. It is placed either on the open ground, or on a mass of 

 heating material, according to the purpose for which it is wanted, and, ex- 

 cepting for particular purposes, facing the sun. As the great object of frames 

 is to increase temperature without excluding light, the soil on which they 

 are placed, or the dungbed or other means of heating which they cover, 

 ought to be as dry as possible, either naturally or by artificial drainage ; and 

 the glass ought to be clear, and so glazed as to permit as little air as possible 

 to escape between the laps. When common crown glass is used, small panes 

 are found to be less liable to breakage than large ones of this kind of glass ; 

 but when the sheet window-glass is used, from its greater thickness, the 

 panes may be two or three feet in length, without much danger of breakage. 

 The boards used for the frame should be of the best red deal ; and if, after 

 being prepared for fitting together, they are thoroughly dried on a kiln, and 

 afterwards soaked with train-oil in the manner which we have described (452 ) 

 for preparing wooden props, the duration of the frame will be greatly in- 

 creased. All frames and sashes, when not in use, should be kept in an open 

 B\vy shed, and there raised from the ground a few inches by supports of bricks 

 or other suitable materials. In gardens where cucumbers and melons are 

 grown 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 outside 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 back 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 that dung, frames are now, in most British gardens, being re- 

 placed by pits, which may be called fixed frames, with brickwork substi- 

 tuted for wood. 



SECT. III. 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. 



Subsect. 1. Walls, Espalier-rails, and Trellis-work. 



466. 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. 



