Cold-frame, with sash lifted for ven- 



2U4 Principles of Plants Culture. 



plants, as the willow, grape and currant, are readily 

 propagated from cuttings out of doors. Some struc- 

 ture, 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 essen- 

 tial to success. 

 Since light is 

 necessary to 

 food prepara- 

 tion (58), such 

 a structure must be roofed with glass or some other 

 more or less transparent material. 



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

 ture of this kind. It consists of a frame or box with- 

 out bottom, usually shallower on one side than on the 

 other, covered with glazed window sash.* The frame 

 is generally placed so that its shallower side faces the 

 south, thus giving its cover a southward slope. It has 

 no provision for artificial heat, though when covered 

 Avith glass, the temperature within the frame is much 

 increased during sunshine, owing to the property pos- 

 sessed by glass for confining the heat rays. The cold- 

 frame should be protected in freezing weather by an 

 additional cover of mats or blankets, while excessive 

 sun heat should be avoided by shading (235). Muslin- 

 or paper-covered frames require no shading. 



♦ Musliu or paper is sometimes used instead of glass, and these 

 materials may be rendered waterproof and less opaque by painting 

 with linseed nil or some similar material. 



