LETTUCE 283 



from 6 to 10 inches below the level of the surface of the beds, 

 and also at intervals of from 12 to 16 feet parallel with the long 

 axis of the house. 



In the early years of the extensive cultivation of lettuce under 

 glass, flat-roofed, shedlike houses, with the long slope toward the 

 south, were the type chiefly used. These houses were 4 or 5 feet 

 high at the eaves on the south side, with a ridge 12 or 14 feet 

 high, and a short span to the north with a wall of boards from 

 8 to 10 feet in height, as shown in figure 22, page 73. Houses 

 of this type have been constructed to cover as much as 3 acres 

 of land. While this was previously the prevailing type of structure 

 for forcing lettuce, the even-span house on the ridge-and-furrow 

 plan with solid benches is the type now preferred by the best 

 lettuce growers. 



Planting under glass. The seed is sown broadcast or in drills 

 in the benches of a house, where a few degrees of bottom heat can 

 be maintained. As soon as the lettuce has developed its first true 

 leaves to the length of J- inch or less, it is transplanted to an inter- 

 mediate house, where the plants are set 3 by 3 inches apart and 

 grown until the leaves begin to crowd. If only a small crop is to 

 be grown, the young plants are set in thumb pots and remain 

 there until the roots fill the pots and the leaves are 3 inches or 

 more in length. From the intermediate house or from the thumb 

 pots the plants go to the finishing house, where they are set 

 10x10 or 12x12 inches apart, the distance depending upon 

 the type of lettuce grown. Cutting lettuce of the Grand Rapids 

 type is usually set closer, 9x9 inches. Head lettuce, such as 

 Tennis Ball and Big Boston, are set at the wider distances. 



Soil for greenhouses. The soil for the seed bed should be a rich 

 sandy-loam compost. The soil for both the intermediate house and 

 the finishing house should be a rich clayey-loam compost contain- 

 ing enough sand and organic matter to prevent it from becoming 

 puddled under heavy watering. As a rule, in the lettuce-forcing 

 sections, if the soil in the houses is of a heavy, clayey nature, it 

 can be easily and satisfactorily modified to meet requirements by 

 the* addition of well-composted manure and sand. The soil for 

 large houses with solid beds is not prepared like potting soil ; it 

 is prepared in place upon the bed itself. The soil at the start is 



