208 Principles of Plant Culture. 



opened when it is desirable to allow a part of the heat 

 to pass directly into the house. The floor of the bench 

 should not be so tight as to hinder drainage. 



In large commercial establishments, entire glass 

 houses are often devoted solely to propagation. Such 

 houses are usually eleven or twelve feet wide, with low 

 side walls. Sometimes lean-to houses are built for 

 propagation, on the north side of a wall, where direct 

 sunlight is cut off. 



In making the propagating bed, a thin layer of sphag- 

 num moss is usually spread over the floor of the bench 

 and covered to a depth of two to four inches with well- 

 packed, clean, rather coarse sand, brickdust or pow- 

 dered charcoal. Sometimes the whole bed is made of 

 moss. These materials are used because they will not 

 retain an excess of water if the proper provision is made 

 for drainage. Sand is mcst used because it is as a rule 

 readily obtained, but it needs to be selected with care, 

 as it often contains injurious mineral matters. Sand 

 found along the borders of fresh-water streams or lakes 

 may generally be used without washing, but that dug 

 from sandpits should in most cases be exposed to the air 

 for a few weeks, and then be thoroughly washed before 

 being employed for cuttings. The same sand should be 

 used for but one lot of cuttings, as a rule, for it is liable 

 to become infested with fungi that may work havoc 

 with cuttings placed in it. 



369. Methods of Controlling Humidity. Where 

 moisture needs to be controlled with especial care, as in 

 propagating delicate plants from green cuttings, or in 

 herbaceous grafting (393), the planted cuttings or the 



