SOILS 51 
in pipes, the sandy soils are handled with the greatest 
ease. There is always danger of injuring the physical 
properties of heavy soils when either steam or formalin is 
used for sterilization, 
(14) Sandy soils have a wider adaptation to greenhouse 
vegetables than do the heavier types. 
So important is sand in greenhouse soils that it is often 
transported long distances and mixed with the heavier 
soils that must be used. The financial returns from 
greenhouse crops probably justify the practice; and yet it 
is better to select soils, if possible, which make this 
expenditure unnecessary. There is an increased tendency 
to mix muck with various types of soils to be used for the 
forcing of vegetables. This practice deserves considera- 
tion wherever a supply of muck is easily available. Both 
light and heavy soils seem to be improved by its addition. 
Although special emphasis has been given to the im- 
portance of coarse-grained soils, there are numerous 
examples of success on heavy types. When a first-class 
market is easily accessible, no one should hesitate to 
engage in vegetable forcing simply because a light soil is 
not available. 
Structure.—This term applies to the arrangement of the 
mineral matter of the soil. In some instances, as in fine 
silts, the particles aré in such intimate contact that the 
soils are very compact; they form a mass that is not 
easily penetrated by roots. This condition is most un- 
satisfactory to aeration, surface evaporation, tillage, soil 
sterilization, seed sowing and transplanting. Soils of un- 
favorable structure for vegetable forcing can be greatly 
modified by proper cultural methods. Tillage may be the 
means of breaking up the soil into granular masses, and 
lime may cause the particles to flocculate, while the fiber 
of stable manures separates the soil into small masses. 
It is important, however, to avoid if possible the selection 
of soils of compact structure for the forcing of vegetables. 
