210 VEGETABLE FORCING 
be made to determine the merits of the seed. Germina- 
tion trials should be made from time to time, and the seed 
may be sown thicker, if necessary, in order to obtain a 
satisfactory stand of plants. 
Soil—Most of the large lettuce-forcing establishments 
are located where the soil contains considerable sand, 
and this is especially true regarding greenhouses devoted 
to the culture of head lettuce. Cos lettuce seems also to 
require soil that contains a fairly large percentage of 
sand. Grand Rapids lettuce is grown with entire success 
in practically all classes of soils, including the heaviest 
with the smallest proportion of sand. The general ad- 
vantages of sand for greenhouse use have been discussed 
in Chapters III and V, and these should be fully con- 
sidered in connection with the selection and preparation 
of soils for the forcing of lettuce. Greater weight of 
Grand Rapids may be obtained in heavy soils, but, not- 
withstanding this fact, growers prefer soils that are not 
too heavy. 
For the production of head lettuce, the soil must be 
well aerated. This can be accomplished to a great ex- 
tent by the liberal use of stable manure and sometimes 
by mixing muck with the soil. Experienced growers, 
however, claim that one or both of these materials cannot 
entirely take the place of sand. An open, porous soil is 
essential, though it is possible to make it too light and 
fluffy. 
Beach made some interesting experiments at the New 
York Station; they were reported in Bulletin 146. Soils 
of various composition were used, but reference will be 
made to only two. What is referred to as the Geneva 
clay loam contained 3.32 per cent fine gravel, 5.20 per 
cent coarse sand, 20.71 per cent medium sand, 43.43 per 
cent fine sand, 0.94 per cent very fine sand, 7.96 per cent 
silt, 1.64 per cent fine silt and 9.86 per cent clay. The 
Geneva sandy loam contained 0.51 per cent fine gravel, 
0.69 per cent coarse sand, 9.49 per cent medium sand, 
