194 Principles of Plant Culture. 



c Abundant moisture is important in growing plants 

 from cuttings, because moisture favors root development 

 (89), and water is essential to cell growth (63). The 

 amount of water required varies considerably with differ- 

 ent plants and conditions. 



With cuttings containing leaf tissue (377, 382), trans- 

 piration (75) must be reduced to the minimum until 

 roots are formed, because water cannot be taken up freely 

 without root-hairs (101). For such cuttings, therefore, 

 the air as well as the soil must be kept abundantly moist 

 (369), and the direct rays of the sun must be intercepted 

 by shading (236). 



363. Methods for Controlling Temperature. The alter- 

 nations of temperature in the open air are unfavorable 

 to the development of cuttings, though many plants, as 

 the willow, grape and currant, are readily propagated 

 from cuttings out of doors. Some structure, therefore, 

 that may confine warmth radiated from the earth or 

 artificially generated, or that may when necessary shut 

 out a part of the solar heat, is always of great assistance 

 in propagating plants from cuttings, and in many species 

 is essential to success. Since light is necessary to food 



preparation (59) ? 

 such a structure 

 must be roofed 

 with glass or some 

 other more or less 

 transparent ma- 



FiG.93. Cold-frame, with sash lifted for ventilation, terial. 



364. The Cold-Frame (Fig. 93) is the simplest structure 

 of this kind. It consists of a frame or box without 

 bottom, usually shallower on one side than on the other, 



