PLANT PROPAGATION 



cerned heat is the only important one. For though all 

 these agents produce the same effect (arousing the ac- 

 tivity of enzymes or ferments, chemically or physically, 

 to change and make available the stored plant food, 

 especially that near the buds), heat is the most active, 



most normal, and most 

 easily and economically 

 applied. Therefore, the 

 plant grower, while in- 

 terested in the abnor- 

 mal agents, applies 

 heat under proper con- 

 trol to secure a healtliy 

 growth where he 

 knows it is needed first 

 of all. 



Cuttings after being set in the propagating bed always 

 begin to grow at the part most favorably placed as to 

 temperature. That is, if a stem cutting be placed so its 

 upper end is in an air temperature appreciably higher 

 than that of the soil, growth will begin in the upper buds. 

 With no cuttings is this so apparent as with cuttings of 

 immature wood, grown in a greenhouse. \Vhen bottom 

 heat is lacking and the air warmed, even only by sun 

 heat, the buds expand into new stems and leaves ; but 

 few or usually no roots are produced. Such conditions 



FIG. 79 ONE "LIGHT" FORCING FRAME 

 The sash lifts for ventilation 



FIG. 80 HOTBED "KNOCKED DOWN" TO SHOW CONSTRUCTION 



