PLANTS, WITH GLASS ROOFS. 



187 



be unequal for the slowness of the circulation in consequence of the 

 water-troughs being necessarily on a dead level. Mr. Glendinning's 

 pit, however, may be heated by any mode, not even excepting a smoke- 

 flue. Fig. 153 is a section of this pit, showing : 



Fig. 153. 



Cross section of a pit to be heated on Corbetfk 

 system, or by smoke-flues. 



f, f, Glass roof, g, Bark pit. 



h, Back path. 



I, Pit for dung casing, fc, 

 Drain. Hinged cover of 

 ledged boards to protect 

 the dung from the rain 

 and wind. 



m, Ground line. 



TO, Suspended shelf for straw- 

 berry pots. 



o. Slate shelf for pots. 



P, Stink-trap communicating 

 with the cross-drain (3), 

 which leads to the main or 

 barrel-built drain (Jfc). 



r, Corbett's hot- water appa- 

 ratus. 



s, Hollow wall of bricks on 

 edge. 



Pits or low houses have been formed with glass on all sides, and span 

 roofs (see ' Gard. Mag.,' vol. vii. p. 290) ; but from the great quantity 

 of glass in proportion to the surface of floor enclosed, they become 

 too expensive for general purposes, and, unless furnished with a warm 

 covering, the extensive surface of glass occasions an injurious degree of 

 radiation. 



The greenhouse is a light, airy structure, with a glass roof at an 

 angle of 35 or 40 with the horizon, and upright glass in front and at 

 the ends ; and with the means of heating sufficient to keep out frost 

 and in humid weather to dry up damp. The plants are grown in 

 pots placed on a stage, or range of shelves rising one above another 

 from a path in front, to within six or seven feet of the upper angle of 

 the back wall. Between the front path and the upright glass, there is 

 a broad shelf on a level with the lowest shelf of the stage, for small 

 plants that require to be near the light. All the front and roof sashes 

 are made to move, because it is frequently necessary to admit a free 

 circulation of the external atmosphere ; and coverings are seldom 

 applied, because a very little fire-heat is found to exclude the frost. 

 This is the common or normal form of the greenhouse, when it is 

 placed against a wall, or the side or end of a dwelling-house, and 

 lacing the south or some point between south-east and south-west ; 

 but much more elegant forms, of the curvilinear or ridge and 

 furrow kind, may be adopted, and where the expense of fire-heat 

 is not an object, it may face the east or west, or be constructed of 

 glass on all sides. For placing against a wall in a flower-garden, we 

 should prefer a curvilinear structure, with ends of the same kind, 

 and an architectural entrance, either in the back wall, as in fig. 127, 

 p. 155, or in front ; but against a dwelling-house, and on a small 



