AMONG SCHOOL GARDENS 



the clay in solution can be decanted off. The 

 water in both is then evaporated and each in 

 turn weighed to constant weight or to within one 

 thirty-second of an ounce thereof. Soil grains 

 of silt run from one-twentieth to one one-hun- 

 dredth of a millimeter in diameter, and of clay 

 from one five-thousandth to one ten-thousandth.* 

 To complete the experiment, the weights of the 

 gravel and of each of the sand residues should be 

 found. Each of the varieties found in soil may 

 be put in a small vial, neatly labeled with name 

 and percentage, and mounted on a card. If 

 humus and water of the determined weights be 

 also placed in vials, the card will be a complete 

 exhibit of the garden soil in its physical charac- 

 teristics and approximate supply of plant food. 



At first thought, it would seem as if the finer 

 clay would furnish more plant food. It does hold 

 more. The soil grains of a cubic foot of coarse 

 sand will spread over one-fourth an acre, while 

 those in the same amount of finest clay will 

 spread over four acres. Consequently, the clay 

 with its myriads of film surfaces will hold more 

 water. But clay soils are so compact that water 

 stagnates in them, cutting off the air that should 

 go to the roots, tending to sour the ground and to 

 develop in it mold and fungus disease. On top, 



* The experiment can be shortened by a determination of the 

 water, the humus, all the sands, and the clay and silt in one mass. 

 Plants will not grow in over 80 per cent of sand, or over 60 per cent 

 of clay. 



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