208 Principles of Plant Culture. 



almost invaiiably heated with steam or hot water, or 

 with a combination of the two. Pipes from a boiler lo- 

 cated beneath the floor knel, 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 sys- 

 tem of return pipes beneath the benches. While the 

 steam or hot-water heating costs much more at the out- 

 set than the smoke-flue system, it is generally found 

 not less economical and far more satisfactory in the 

 long run. Where the pipes need to make many turns, 

 steam is usually more satisfactory than hot water. 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. 



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 he 

 opened when it is desirable to allow a part of the heat 

 to pass directly into the house. The floor of the bench 

 should not be so tight as to hinder drainage. 



In large commercial establishments, entire glass houses 

 are often devoted solely to propagation. Such houses are 



