58 



HORTICULTURAL MANUAL. 



of starch and plant-food in its cell-structure to aid in 

 starting root and top. If months are required to furnish 

 the needed conditions for growth its contact with moist 

 earth retains its life. But the cutting made from the 

 young and growing parts of the plant must have warm, 

 moist, and more or less confined air where the rays of the 

 sun and rate of evaporation can be controlled. 



63. Controlling Heat and Moisture Various plans have 

 been devised to secure the needed conditions as to light, 

 moisture, heat, and' transpiration. In all of them nearly, 



FIG. 27. Simple propagating bed. 



glass is the covering used, as it is cheap and best combines 

 the essentials needed. Its fault is that it not only admits 

 light and lessens transpiration and evaporation, but it 

 admits the sun's rays that do not return. In other words, 

 the radiant heat of the sun passes through glass and 

 accumulates to such extent that a hot-bed or other struct- 

 ure of limited space under glass may burn and scorch 

 every plant in two hours if the ventilation is neglected. 

 Yet glass is the best covering known, and with a little 

 timely care it answers the purpose well. 



The bottom heat is given in various ways. One of the 



