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, 

 as lettuce generally does, are most 

 commonly grown in solid beds, that 

 is, on the earth. Those 

 crops requiring bottom 

 heat must be grown on 

 benches. The height of 

 these benches above the 26. Iron 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 feet 

 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 10 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. 



