192 Princtples of Plant Culture. 
the outset than the sinoke 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 
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 (362a), the space beneath the 
bench is boxed in with boards. Horizontal doors are, however, 
provided which may be 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 
usually eleven or twelve feet wide, with low side walls. 
Sometimes lean-to houses are built for propagation, on the 
north side of a wall, where direct sunlight is cut off. 
In making the propagating bed, a thin layer of sphagnum 
moss is usually spread over the floor of the bench, and 
covered to adepth of two to four inches with well-packed, 
clean, rather coarse sand, brickdust or powdered charcoal. 
Sometimes the whole bed is made of moss. These materials 
are used because they will not retain an excess of water if 
the proper provision is made for drainage. Sand is most 
used because it is as a rule readily obtained, but it needs to 
be selected with care, as it often contains injurious mineral 
matters. Sand found along the borders of fresh-water 
*In round numbers, the cost of the smoke flue may be estimated at ten per 
eent. 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. 
