PBOPAGATION BY INARCHIXG. 59 



simplest forms of combining the confined air and bot- 

 tom heat is shown at Fig. 27. The box is about two feet 

 deep with glass over the top. The water over the lamp is 

 ill a sheet-iron tray supported as shown. The sand shown 

 is held up by placing in a shallow wooden box. "With a 

 little practice and experience cuttings can be rooted in a 

 small way in this frame with about as much certainty as in 

 a greenhouse cutting-bench. 



The principle is the same in the private house, conserv- 

 atory or the great commercial greenhouse. But in these 

 cases the heating of the houses in winter and the needed 

 bottom heat of the cutting-bench are given by steam- or 

 hot-water pipes. 



64. Why Cuttings Need Bottom Heat. In section (60) 

 the reasons why grape and other cuttings are put in solar 

 hot-bed in inverted position are given. If most heat is given 

 at the base of the cutting it favors the emissson of roots, 

 while the top buds are relatively dormant. In the same way 

 if green cuttings are inserted in sand warmer than the air 

 above, it favors the more rapid callusing and rooting of the 

 base, while the parts in the air show less active cell forma- 

 tion. Even rooted plants in the open air during the grow- 

 ing season are in most if not all countries favored with a 

 warmer soil than the average temperature of the air. But 

 as stated in (19), exposed soil in interior climates often gets 

 much hotter than the air. In this case the branches and 

 leaves will give off moisture faster than the roots can supply 

 it. In the same way the soil of the cutting-bench may get 

 too hot under artificial conditions as well as too cold. 



65. The Hot-bed. The use of the hot-bed for growing 

 seeds of subtropical and other seeds is noted in prior sec- 

 tion (12). At the home place, and in commercial gardens, 

 the hot-bed is used mainly for growing tomato, egg-plant, 

 pepper, flowers, and many other plants. Even where large 



