200 



PRINCIPLES OF PLANT CULTURE 



Although affording no bottom heat (362), the cold- 

 frame may be used for propagating many plants from 

 cuttings. It is also serviceable in connection with the 

 propagating bed (368) for " hardening off " young plants 

 grown from cuttings in the latter, as well as for growing 

 many plants from seed. Set over a pit in the earth, 

 the coldframe makes an excellent place (cold pit) for 

 wintering half-hardy plants. 



365. The hotbed (Fig. 97) differs from the coldframe in 

 having bottom heat (362), which is usuaUy supplied by 

 the fermentation of moist vegetable material, as horse 



manure, leaves, 

 refuse hops or 

 tan bark. The 

 material in- 



FiG. 97. — Cross-section of hotbed in pit. 

 frame is banked up a little with earth. 



The 



tended for heat- 

 ing, if fresh, 

 should be 

 thrown into a 

 pile of sufficient 

 size to generate 

 heat several days before it is desired for use ; and unless 

 already moist, it should be moderately sprinkled with 

 water. In order that all the material may reach the same 

 stage of fermentation, the mass should be made into a new 

 pile after the heating starts vigorously, as is indicated by 

 vapor rising from the heap, and the outer part of the mass 

 should be placed in the center of the new pile. Leaves 

 ferment slower than the other materials above named, 

 and hence may often be advantageously mixed with 

 them to lengthen the period of fermentation. 



Heat is economized by placing the fermenting mate- 

 rial in a pit in the ground, but hotbeds are often made 



