196 



FIXED STRUCTURES FOR GROWING 



supply of dry heat M^ill immediately be obtained, which may be rendered 

 moist at pleasure by pouring on water. Another mode of obtaining an imme- 

 diate extra supply of heat from a dung-bed is, by beddiiig in it, when first 

 made, an iron pipe of three or four inches in diameter, with the two extremi- 

 ties turned up, and covered by flower-pot saucers. The length of the tube 

 may be nearly equal to that of the bed, and the one end must be sunk a few 

 inches deeper than the other, as in fig. 154. It is evident that by taking off 



the covers of this pipe 

 there will be a draught 

 created in it, in conse- 

 quence of its sides being 

 heated by the dung ; and 

 an extra degree of heat 

 will by this means be 

 brought into the atmo- 



Fig. 134. Section of a dung-bed, with a tube for supplying hot air. gpj^gj.g j^g^^ This 



plan might also be adopted for putting the air of a plant-bed in motion, 

 without the admission of the external air. 



490. Fermenting materials and fire-heat combined. — In pits and low-forcing 

 houses heated chiefly by dung, provision is frequently made for the supply of 



extra heat, by the addition of smoke-flues or hot- water pipes. 



Fig. 135 is a 



Fig. 135. Pinery heated by dung linings. 



perspective elevation and section of a house, jn which a bed of leaves within 

 is heated by a dung lining placed on the outside of a pigeon-holed wall, and 



extm heat is provided for by 



three turns of a flue, one above 

 the other, in the back path: 

 a is the pit in which the dung 

 lining is placed and covered 

 with a hinged shutter ; &, the 

 surface of the bed of leaves, 

 in which pine-apples, or cu- 

 cumbers, or melons may be 

 grown, or strawberry plants or 

 flowers forced ; c, door ; d^ 

 flues ; e, front pigeon-holed 

 wall ; and /, end pigeon-holed 

 wall. Fig. 136 shows a mode 

 of applying dung under a bed 

 of soil without coming in im- 

 mediate contact with it, and 

 by which no heat whatever 

 produced by the dung is lost ; 

 a is the bed of soil in which 



Section of a vinery heated by dung' 



