THE PROPAGATION OF PLANTS 



199 



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 essential to success. Since light 

 is necessary to food preparation (58), such a structure 

 must be roofed with glass or some other more or less 

 transparent material. 



364. The coldframe (Fig. 96) 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, covered 

 with glazed win- 

 dow sash. Mus- 

 lin or paper is 

 sometimes used 

 instead of glass, 

 and these materials may be rendered waterproof and less 

 opaque by painting with linseed oil or some similar material. 

 The frame is usually 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 

 with 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 mat or blankets, while excessive sun 

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

 paper-covered frames require no shading. 



Fig. I 



6. — Coldframe, with sash lifted for venti- 

 lation. 



