AMONG SCHOOL GARDENS 



"vegetable soil". The most common types of 

 nearly pure humus are the leaf mold of the woods, 

 or the rich, soft, friable earth, still showing its 

 origin, found at the bottom and under the edges 

 of every old woodpile. From this almost clear 

 vegetable soil, humus in varying quantities runs 

 through the different varieties of soil mentioned, 

 almost entirely disappearing in the coarser sands 

 and gravel. It is of the utmost importance to 

 plants because it not only largely furnishes them 

 food, but through the chemical changes it is con- 

 stantly undergoing, it helps to break up the more 

 insoluble mineral constituents of the soil into fmer 

 particles, and thus tends constantly to increase 

 both the supply of plant food and the area over 

 which and through which the tiny root fibers can 

 make their way. Herein lies one of the values of 

 well-rotted, coarse barnyard manure over the ar- 

 tificial fertilizers. The manure helps the plants 

 mechanically as well as chemically. 



So important is the humus that its relative 

 quantities determine the division of soils ac- 

 cording to their productivity.* A good loam, 

 ^an excellent soil for most growth, is approxi- 

 mately one-third gravel, one-third clay and one- 

 third humus. To this, land in a farming country 



* There is still another division of soils according to their forma- 

 tion. Their names tell their story, — sedimentary soil, transported 

 soil, alluvial soil, glacial soil and wind-formed soil. On the leeward 

 side of arid lands and deserts the soil, carried there by the wind, is 

 often very fine and fertile. 



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