50 DREER’S VEGETABLES UNDER GLASS. 
the mercury is very low is it safe to allow the sashes to 
remain closed during the day time, and even then it is a dan- 
gerous thing to do if the sun shines on the glass. Free ven- 
tilation is the safe rule. Snow must be removed and the 
walks or alleys between the ranges of glass kept open, so 
that the beds can be properly examined every day. 
Watering the cold frames is not necessary in winter 
time, and but seldom in the early spring. 
The Philadelphia truckers and market gardeners do not, 
as a rule, cover their cold frames at night with ‘‘lids”’ 
(shutters) or mats. Private gardeners and amateurs, on the 
other hand, will find it to their advantage to do so. It 
hastens the maturity of the lettuce and several days can be 
gained in the crop. 
The Philadelphia cultivators are, however, careful to 
build high board fences on the north and northwest sides of 
their glass to keep off the cold winds; and this plan is 
worthy of imitation. Indeed, it is essential to success. The 
height of four or five boards is sufficient here. New Yorkers 
use six boards, and the Boston ‘‘ market farmers” employ 
seven boards (laid sidewise) in the construction of their 
screens or wind breaks. The Boston men, indeed, build a 
wind fence for each row or ‘‘string’’ of frames. For in- 
stance, they put up a seven-foot fence (seven boards), lean- 
ing toward the north. At its base, on the sunny side, they 
set the cold frames, or ‘‘boxes,’’ or ‘‘strings.’’ ‘Then they 
allow a considerable space (perhaps forty feet) before build- 
ing another fence so that the shadow may not fall upon the 
glass in the rear. Many of these wind fences or breaks are 
yet to be seen in New England, and still have their uses, 
although the Yankee lettuce growers for the most part seem 
to have equipped themselves with forcing houses. 
Hor Bep CuLTuRE OF LETTUCE. The hot bed culture 
of lettuce is not very widely practiced on a commercial scale 
