296 CULINARY GARDENING. BOOK I. 



large vacuity of heated air; d the rubble stone vacuity; e walk 

 in the centre; f earth in which the plants grow; g steam and 

 air tubes; h inner roofing; i surface of the ground, &c. See 

 the plan, sections, and a full description in the " treatise." 



2. Hot-walls. The formation of these consists of two 

 parts: the construction of the flues and furnace in the wall; 

 and the construction and contrivance of a covering of canvass, 

 or netting, to be let down over the trees in severe weather, and 

 during night. The construction of the flues, so as to distribute 

 the heat equally over every part of the wall, is perfectly simple 

 and need not be insisted on. The fronts of these flues should 

 be made at least a brick thick to preserve that heat. The pro- 

 per furnace is that recommended* for hot-houses in connexion 

 with a damper; the great superiority of which in hot-walls I 

 experienced in a striking degree at Mr. Smith's hot-wall, Leith 

 Walk. In contriving the covering of Scotch gauze, or small 

 netting, small rafters must be fixed to the top of the wall, and 

 to the border, about three feet from the roots of the trees. 

 Along the lower ends of these rafters, the roller for containing' 

 the covering must be fixed. By cords and pullies this cover- 

 ing can easily be drawn up to the top of the wall, or rolled 

 down, as occasion may require. Wherever a hot-wall is con- 



* Sold at Cooke's Foundry, Theobald's Road, Holborn, London; and the Edin- 

 burgh Foundry Company, Edinburgh. 



