76 MANAGEMENT OF THE FORCING-HOUSE. 
caused by the dying of the lower leaves, but it does reach a 
marketable size sooner. It is customary to allow the plants 
to stand as long as they continue to improve, but in case it 
is desirable to cut before that time it will be found that the 
sub-irrigated lettuce will be a week to ten days ahead of the 
other. Should the size to which surface-watered lettuce can 
be grown be set as a standard, and the sub-irrigated cut 
when it reaches that size, it will be found that the latter will 
be ready four to six weeks from the time of planting in the 
beds, and the surface-watered must be allowed to remain 
from six to eight weeks to attain the same size. Whether 
we reckon in this manner, or by the actual weight of the 
crops harvested during the season, there is a gain in one 
season of about one crop by sub-irrigation. Both the yield 
and price vary, of course ; but for a house 20x 100 feet the 
difference in a single season between surface- and sub-irriga- 
tion might safely be estimated at from $50 to $100. The 
latter figure might not be reached, except on very heavy 
clay soil, and on soil specially adapted to lettuce the dif- 
ference might be even less than the lowest, but experience 
has shown that it is more likely to exceed than to fall below 
$50. The difference is likely to be greater with new begin- 
ners than with those of experience, as more skill is required 
to manage a crop by surface- than by sub-irrigation. It is an 
established fact that good head lettuce cannot be grown on 
heavy soil by surface watering, and the same is, in a meas- 
ure, true of all varieties. It is evident, therefore, that sub- 
irrigation greatly enlarges the possibilities of lettuce culture 
under glass. It not only makes the work easier for new 
beginners, but it makes it possible to use soil that would 
otherwise be precluded. More than that, it solves the prob- 
lem of meeting competition from the south, which competi- 
tion bids fair to ruin the business of vegetable forcing at the 
north, unless improved methods are adopted by northern 
gardeners.”’ 
Very similar results with lettuce have been secured by 
Rane, who also found much less trouble with rot in sub- 
