450 



PITS AND FRAMES. 



wide, which will afford 

 other parts. They are 



Fig. 629. 



a scale for the 

 heated by hot- 



water pipes to afford atmospheric heat. 

 These are placed in a space between the 

 side of the tank and the front wall, the 

 lower or return pipe resting on the pave- 

 ment or slate covering of the tank. The 

 sides of the front wall and tank being water- 

 tight as well as the bottom, water may be 

 let in, so that the lower pipe may be 

 partly or wholly covered, to give greater 

 humidity to the pits. If dry heat is de- 

 sired, the water is to be withdrawn. The 

 ventilators b b are placed along both sides 

 of these pits, so that the atmospheric air 

 may be warmed before reaching the plants. 

 Bottom heat is obtained by tanks of hot 

 water placed under the beds in which the 

 plants are set. The shoots are trained to 

 a trellis under the glass. Top ventilation 

 is effected by the ridge opening from end 

 to end, upon the principle explained in 

 section Ventilation. The spaces under 

 the tanks c c are to be used for forcing 

 sea-kale and rhubarb during winter, and 

 mushrooms during summer. The passage 

 along the middle may be entered at both 

 ends, which, in summer, will give abun- 

 dance of ventilation. These pits are sunk 

 to the line marked a, presuming the 

 ground be dry. If it is not, they should be 

 kept higher up ; but these are arrange- 

 ments which must be ruled by local cir- 

 cumstances. The roof of this pit may be 

 fixed, and rafters and sashes dispensed 

 with altogether. This pit may also be 

 wrought by fermentation as a bottom 

 heat, and by hot-water pipes for at- 

 mospheric. In this case the tanks 

 would be dispensed with, and the roof 

 constructed of rafters and sashes, as it 

 is necessary to remove them for the pur- 

 pose of making up the beds and removing 

 the decayed material. The hot-water 



pipes are kept clear of the fermenting 

 material, and they are placed in a space 

 formed by laying in a course of pavement 

 or Welsh slate into the wall, allowing it 

 to project 8 inches within the face of the 

 wall. Upon this is set on edge, in a groove, 

 a slip of pavement or slate 12 inches 

 broad, which will form a trough for the 

 pipes to lie in. If this is well jointed, as 

 it ought to be, water may be let in when 

 desired, by a small pipe, and steam will be 

 generated to keep up the genial humidity 

 so essential for the growth of these plants. 

 Ventilation is effected, as in the last ex- 

 ample, both at the side walls and also at 

 the ridge. 



Such a pit as that last described is 

 peculiarly suitable for young pines, for 

 which tank-heated pits are inconvenient, 

 as the plants require to be arranged in the 

 pits according to their heights, and the beds 

 of leaves or tan can be lowered or elevated 

 according to the height of the plants, 

 which beds heated by tanks could not. 



Pits to a very considerable extent might 

 be heated upon the tank system at little 

 expense, if arranged as in fig. 630. The 

 Fig. 630. 



ground-plan is intended to represent four 

 distinct pits, each 50 feet in length, and 6 

 feet wide in the clear. The boiler is to 

 be placed in the middle as at b, or, as is 

 better seen in section fig. 631, with the 



Fig. 631. 



stoke-hole under the level of the walk 

 or passage between them. The floors are 

 to be rendered perfectly level and firm 

 with a coating of concrete, and afterwards 

 covered with cement over their whole 



