360 ACCELERATING VEGETATION. 



hotbed, it is employed in the open garden as a surface-mulching, to 

 keep in heat or moisture. 



Preparation of Materials for Hotbeds. The object being to get rid 

 of the violent heat which is produced when the fermentation is most 

 powerful, it is obvious that preparation, whether of leaves, tan, or 

 stable-dung, must consist in facilitating the process. For this purpose 

 a certain degree of moisture and air in the fermenting bodies are 

 requisite ; and hence the business of the gardener is to turn them over 

 frequently, and apply water when the process appears impeded for 

 want of it, and exclude rain when it seems chilled and retarded by too 

 much water. Recent stable-dung generally requires to lie a month in 

 ridges or beds, and to be turned over in that time thrice before it is fit 

 for cucumber-beds of the common construction ; but for linings or 

 casings to any description of hotbed or pit, no time at all need in 

 general be given, the dung being formed at once into linings. Tan and 

 leaves require in general a month to bring them to a proper degree of 

 heat ; but much depends on the state of the weather and the season of 

 the year. Fermentation is always most rapid in summer ; and if the 

 materials are spread abroad during frost, it is totally impeded. In 

 winter, the process of preparation generally goes on under cover from 

 the weather, in the back sheds, which situation is also the best in 

 summer, as full exposure to the sun and wind dries the exterior 

 surface too much ; but where sheds cannot be had, it will go on very 

 well in the open air. 



M'Phail's hotbed or pit consists of two parts, the frame and lights of 

 which are of wood, and not different from those used for growing 

 cucumbers, or other ordinary purposes, and the basement on which the 

 frame is placed, which is flues of brickwork, with the outer wall uni- 

 formly perforated, or, as it is commonly called, pigeon-holed. Against 

 these perforated flues, linings of dung are formed, the steam of which 

 enters the flue, and heats the earth enclosed. The chief objections to 

 this plan are the first cost and the greater consumption of dung which 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. 

 Fig. 328 is a section of a pit on this principle, with some improve- 

 ments : a a is the surface of the ground ; b #, excavations for the dung- 

 casings, 2J feet deep, 18 inches wide at bottom, and 2 feet wide at the 

 ground's surface ; the greater width at top being to prevent the dung 

 from shrinking from the sides of the excavation as it sinks ; c is the 

 outer perforated wall, a brick in width ; d, the inner wall of brick set 

 on edge, and tied to the outer wall with occasional cross bricks ; e is a 

 layer of billet-wood, one foot in thickness, to admit of the heat penetrating 

 from each side, or the same object may be effected by a layer of loose 

 stones : f, a covering of faggot-wood, over which a layer of turf or litter 

 is placed to prevent the soil from sinking into and choking up the 



