40 THE CONSTRUCTION OF THE FORCING-HOUSE. 
for all purposes. Indeed, I should prefer glass 12 inches 
wide to that which is 18 inches wide. 
Beds and benches.—Those plants 
which thrive best without bottom heat, QE 
as lettuce generally does, are most WY 
commonly grown in solid beds,—that 
is, on the earth. Those 
crops requiring bottom , 
heat must be grown on Y4yy 
benches. The height of —--_ 
these benches above the 45, sron cleat in a gutter-board. 
ground must be deter- 
mined wholly by circumstances. The first thing to con- 
sider is to secure sufficient head room for the plants, or, in 
the instance of low plants, to get them near to the glass. 
Benches will run from a foot to three feet above the ground. 
They are handiest when the extreme height is about two féet 
and the width not over three and a half or four feet. The 
depth of the bed (that is, of the soil) varies with different 
operators from 5 to to inches. As a rule, with good soil, 
6 or 7 inches of earth is sufficient. A greater body of 
earth is likely to make a too continuous growth, with 
consequent loss of earliness, and it requires more care 
in the watering if it should become hard or somewhat 
impervious to water. Benches are ordinarily built of 
common lumber. One-inch hemlock boards, in single 
thickness, will last about three winters if the soil is removed 
in the summer. Cracks of a half inch or a little more 
should be left between the boards, and it is then not neces- 
sary to place drainage material—as broken crocks or 
clinkers—on the bottoms of the beds. With shiftless 
watering, however, no amount of drainage material can 
insure safe results. 
HEATING. 
Steam and hot water.— Modern forcing-houses are 
heated by either steam or hot water in wrought-iron pipes, 
