2004. M'Phail's frame (fig. 563.) consists of two parts, the frame (a a) and lights (b), which are of wood, and not different from those used for growing cucumbers, or other similar purposes; and the basement (c d) on which the frame is placed consists of flues of brickwork, with the outer wall uniformly perforated, or, as it is commonly called, pigeon-holed, as shown at f. Against these perforated flues linings of dung are formed, the steam of which enters the flue, and heats the earth (e e e) in the centre of each light The chief objections to this plan are the first cost and the greater consumption of dung, which some allege is required to keep up the proper heat. Its advantages are, that hot dung may be used without any preparation, by which much heat is gained; and, that in the winter months, when a powerful artificial heat is required, which (in the case of common hotbeds) is apt to burn the plants, they are here in the coldest part of the soil, and cannot possibly be injured by any degree of heat which can be communicated by dung.
