198 Principles of Plant Culture. 



afford the most protection, when located to form the north 

 wall of the house. In houses extending north and south, 

 the south end is usually glazed above the height of the 

 side walls. 



367. Heating Devices for the Greenhouse are of various 

 kinds. The "smoke flue' 7 is simplest and cheapest in 

 first cost. It consists of a flue extending from the furnace, 

 which is placed somewhat below the floor level, length- 

 wise through the house, preferably rising gradually to a 

 chimney at the opposite end; or the flue may cross the 

 farther end of the house and return at the other side, to 

 a chimney built directly upon the furnace. The latter 

 method usually gives better draft, since the warmth from 

 the furnace stimulates an upward current of air through 

 the chimney. The flue should be of brick for the first 25 

 feet from the furnace, as a safeguard from fire. After 

 this it may be of cement, or of vitrified drain- pipe. 



Greenhouses of the better class are now almost invari- 

 ably heated with steam or hot water, or with a combina- 

 tion of the two. Pipes from a boiler located beneath 

 the. floor level, extend nearly horizontally about the 

 house, below the benches, returning to the boiler; or 

 the main feed pipe extends overhead to the farther end 

 of the house, where it connects with a system of return 

 pipes beneath the benches. While the steam- or hot- 

 water heating costs much more at the outset than the 

 smoke-flue system,* it is generally found not less eco- 

 nomical and far more satisfactory in the long run. Where 



* In round numbers, the cost of the smoke-flue may be estimated at ten 

 per cent of the whole outlay required in a house heated by this method, 

 while in one heated with hot water or steam, the cost of the heating appa- 

 ratus is not far from fifty per cent of the whole. 



