188 Principles of Plant Culture. 
364. The Cold=-Frame (Fig. 92) is the simplest struc- 
ture of this kind. It consists of a frame, or box without 
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 giv- 
ing its cover a southward slope. It has no provision for 
artificial heat, though when covered with glass, the temper- 
ature within the 
frame is much 
increased during 
sunshine, owing 
to the property 
possessed by 
Fic. 92. Cold-frame, with sash lifted for ventilation. glass of 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 (236). 
Muslin- or paper-covered frames require no shading. 
Although affording no bottom heat (362a), the cold-frame 
may be used for propagating many plants from cuttings. It 
is also serviceable in connection with the propagating bed 
(368), for ‘hardening off’? young plants grown from cut- 
tings in the latter, as well as for growing very many plants 
from seed. Set over a pit in the earth, the cold-frame 
makes an excellent place (cold pit) for wintering half-hardy 
plants. 
365. The Hotbed differs from the cold-frame in having 
bottom heat (362a), which is usually supplied by the fer- 
mentation of moist vegetable material, as horse manure, 
* Muslin 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. 
