PKOP AG ATION. 261 



such can generally be bought ready made. The 

 front of the frame should be about a foot high, 

 and the back from four to six inches higher 

 than the front, according to the width of the 

 frame ; in other words, there should be just 

 slope enough to shed water. It is a very com- 

 mon mistake to make the slope quite steep. 

 The frame may be made of common rough 

 boards, or it may be made of worked boards, 

 and painted, and put together with screws and 

 hooks, so as to be taken apart : there are vari- 



Fig. 107. 



ous ways of making them. A good idea of the 

 frame and sash, with its fastenings, etc., may be 

 got from Fig. 107. 



A covering of some kind must now be pro- 

 vided to protect the plants at night, and pre- 

 vent the loss of heat. For this purpose, straw 

 mats are commonly used, as they are conven- 



