68 BOTANICAL GAZETTE [yuLy 
retaining and lifting water, while sandy soils possess this property to a 
much less degree. 
Since the natural soils dealt with in the paper cited differ chemically 
as well as physically, clay being largely composed of alumina and sand of 
silica, it seemed wise actually to test by field cultures the hypothesis above 
referred to. It was desirable that in these cultures the several soils should 
at the start be chemically the same, while their physical properties alone 
should differ. To this end crushed quartz, containing 99.8 per cent. pure 
silica, was obtained in three sizes or grades. - The particles of the finest 
grade have an average diameter of 0.02™™; those of the medium 0.6™™5 
and those of the coarse 1.15™™, To these different sands were added 
mineral salts which should supply the essentials for plant growth. The 
proportion of the ions to the volume of soil was made approximately the 
same as it was found to be in natural fertile soils by Taylor and Mooney.’ 
The salts actually used were KH,PO,, Ca(NO,)., MgSO,, NaNO,. and 
CaCl. All three grades of sand were treated exactly alike. 
Three ordinary apple barrels were chosen for the cultures. These 
7 U. S. Dept. of Agric., Bureau of Soils, Bull. 22:37. 1903. 
2 a ARERR 
