AGRICULTURAL BOTANY 



157 



with linseed oil to render it waterproof. The frame is placed so as to 



have a south slope. Occasionally the sun's rays are so hot that a 



covering must be thrown 



over the glass if glass is 



used, but if muslin or 



paper is used, none is 



necessary. The frame 



must also be additionally 



protected in freezing 



weather. 



A hotbed is like the 

 cold frame except that 

 it has heat beneath it, 

 this heat being produced 

 by the fermentation of 

 manure, leaves, or tan 

 bark used as a founda- 

 tion. This foundation 

 may be put into a pit 

 two or two and one 

 half feet deep dug in 



FIG. 78. Cold Frames, 

 the ground or may be placed on top of the ground. The cuttings 



FIG. 7g. Section of a Hotbed. 



require a temperature of about 90 degrees, and as the fermentation 

 sometimes produces a much greater degree of heat than this, care 



