Propagation by Cuttings. 207 



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 vitri- 

 fied drain-pipe. 



Greenhouses of the better class are now almost in- 

 variably heated with steam or hot water, or with a com- 

 bination of the two. Pipes from a boiler located be- 

 neath 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 the pipes need to make many turns, steam is 

 usually more satisfactory than hot water. 



368. The Propagating Bed. A certain part of the 

 greenhouse is usually set apart for propagating plants 

 from cuttings. The propagating bed is made upon the 

 ordinary greenhouse bench, directly over the flue or 

 heating pipes. To furnish the bottom heat (362 a), the 

 space beneath the bench is boxed in with boards. Hori- 

 zontal doors are, however, provided which may be 



* In round numbers, the cost of the smoke-flue may be esti- 

 mated 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 apparatus Is not far from fifty 

 per cent of the whole. 



