HOTHOUSES. 8 1 



inclination. By making a low pitch, the hot air is more evenly dis- 

 tributed. In houses having a high pitch, the hot air accumulates at 

 the top of the house, and as the tendency of plants is for the sap 

 to flow to the spot where the greatest heat exists, the lower portions 

 of such plants will suffer. 



These glass buildings may be divided into two classes, viz., the 

 lean-to houses and the span-roof houses. The former are mostly 

 used for vineries and peach-houses, and are the most economical ; 

 the latter are generally used for stoves, forcing- houses, pits, etc. 

 Various examples are given, showing the different combinations 

 alluded to. (See Plan Q.) Wood alone is preferable to iron in such 

 constructions, but a combination of iron and wood is advantageous. 

 The plates, sills, mullions, rafters, and posts should be constructed of 

 wood ; but purlins, strengthening tie-rods, bars, brackets, etc., may be 

 made of iron. 



The houses should be built of best yellow or red deal with oaken 

 sills. This woodwork should be well seasoned, free from defects, 

 and painted two coats before being fixed, and two after. All joints, 

 tenons, mortises, should be primed before fixing. Plate glass is 

 preferable for front lights of a conservatory. The glass for growing- 

 houses should be best 21 oz. English sheet. The front lights and 

 the roof lights should be opened by lever simultaneous opening gear. 

 This gear is constructed by running, through small bearings fixed to 

 each mullion, a rod, to which are fixed at proper intervals the ends 

 of elbow joints ; the other ends being attached to the bottom rails 

 of the lights. When the rod is caused to revolve, the whole of the 

 elbow joints are straightened and the sashes thus opened. In con- 

 servatory work, sometimes the vertical sashes are hung from the 

 top, and sometimes at the sides. They are opened by set-opens, 

 which are brass or iron arms, having holes, which are dropped on to 

 vertical pins. Fresh air should be made to enter as near the 



M 



