88 



I'LANL I'KUi'ACiATlON 



brewers' grains, spcul liuijs, ur ulher fcnnenling material 

 is used, as a source of heat. Fresli horse manure is the 

 most popular of such materials. 



2. By horizontal brick or tile flues which carry the 

 gases of fires beneath the benches of a greenhouse or of 

 a hotbed. This method of warming greenhouses is prac- 

 tically obsolete, but for hotbeds, especially for propagat- 



FIG. 76— "SWEAT BOX" FOR PROPAGATING 



High temperature and humidity secured by closing top and lowering burlap 

 curtains below. 



ing sweet potato plants (Fig. 72), it is very popular in 

 Delaware, Maryland and more southern states. 



3. Hot water and steam in iron pipes (Fig. 77) are by 

 far the most popular commercial methods of heating be- 

 cause of their read)^ adaptability to any sized house. 



4. Confining air and heat above the cutting bed by 

 means of glass sash over hotbed-like frames on the 



