FRAME CROPS 393 
Mats and shutters.—In very cold weather, sash alone 
will not keep frost out of the frames; additional protec- 
tion, therefore, is necessary at times. Probably no other 
covering is more effective in guarding against cold than 
rye straw mats (Fig. 134), though the sea grass mats, 
seen in Fig. 135, are most excellent. If better protection 
is required, board shutters placed over the mats and 
manure banked around the outside of the frames will 
take care of the plants when the weather is very cold. 
Growers in the coldest parts of the North, who use 
various methods of heating the frames, often employ mats 
Fig. 135.—Frame cauliflower following a companion crop of lettuce. Note mats 
which are being thoroughly dried before they are stored for the summer. 
and occasionally shutters to conserve the heat. It is not 
uncommon to see both mats and shutters on steam-heated 
frames during the daytime, when there are high winds 
and extremely low temperatures. 
Heating frames.—It is impossible to give any rule for 
the heating of frames. Thousands of frames are used 
without any artificial heating. In the South, the muslin 
or sash-covered frames will keep the plants growing 
throughout the winter. In the North, they may give the 
necessary winter protection to certain crops, and rapid 
