PLANT REPRODUCTION 165 



be placed in such a strong light that it wilts or becomes 

 light green and yellow. 



Plant-food contents of soil for cuttings. When cuttings 

 are placed in soil, they have no power of absorbing plant 

 food from it. They must first develop a delicate root-sys- 

 tem. The development of this system is retarded if there 

 is a large amount of decaying organic matter in the soil. 

 The cutting should have this food in a diluted form, just 

 as an infant requires dilute nitrogenous substances during 

 the earlier years of its development. This nourishment is 

 given the developing roots through the water which is 

 applied. Therefore, the medium in which cuttings are 

 placed should contain little plant-food. 



131. Controlling environment of the cuttings. To 

 give cuttings the conditions best suited for the develop- 

 ment of roots, special cases or rooms should be provided. 

 These are propagating cases, or special propagating houses. 

 The environmental conditions, such as soil temperature 

 and the like, can then be more accurately controlled. 



Soil temperature. Soil temperature is controlled in 

 propagating houses by means of additional pipes placed 

 underneath the benches. In older propagating houses, 

 these pipes were generally inclosed by boarding the front 

 of the area under the benches. Usually this area had doors 

 to permit ventilation and heat regulation. This produced 

 close, confined air conditions which fostered the develop- 

 ment of disease in cuttings. It is considered better to have 

 a flange on the lower side of the board which fronts the bed, 

 or to have a drop curtain for retaining the heat as it rises 

 from the pipes underneath the propagating benches. 



That the heat may not be too intense at the base of the 

 cuttings, the bottom of the bench is often made of tiles or 

 bricks, and the pipes are placed six or eight inches below 



