THE YEAST OF THE SOIL. 17 



to kill not only the weeds, but to make the soil light and friable, to 

 admit the air, to encourage the circulation of moisture through the 

 soil, and to make it an acceptable medium for the roots of the crop. 

 The modern theory includes the old and also recognizes the necessity 

 of making the conditions as favorable as possible for the growth 

 of bacteria. Thorough cultivation also conserves the moisture 

 of the soil by means of a fine mulch on the surface, which prevents 

 the moisture from evaporating into the atmosphere. 



In the West, where they carry on "dry farming," that is, farming 

 without irrigation, where there is little rainfall, they have been 

 successful in raising large crops by continuous cultivation, keeping 

 the surface like a dust heap which, strange to say, not only retains 

 the moisture, but, by means of capillary action, draws it up from 

 lov.er levels. Mr. Hale, the celebrated peach grower of Connecti- 

 cut, keeps horse cultivators going practically all the time in his 

 orchards, during the growing season, not only to keep down weeds, 

 but to conserve moisture. He calls it "horse-leg irrigation." Thus 

 the modern farmer cultivates not for the purpose solely of killing 

 weeds and of admitting warmth and air into the soil, but to encour- 

 age the growth of bacteria, as well as the distribution and conserva- 

 tism of soil moisture. 



The Sap of the Soil. 



We frequently hear farmers speak of the "sap of the soil," a 

 phrase which expresses a great deal. All cultivated plants take up 

 their food in dilute solution. The sap of a tree or plant circulates 

 throughout its system of trunk, branches, and leaves, carrying with 

 it the nourishment necessary for its upbuilding. This sap has been 

 absorbed from the soil through the roots of the plant and is more or 

 less charged with plant food ingredients which were either applied 

 in a soluble form or were rendered soluble through bacterial action 

 in the soil, or through the digestive process which takes place in 

 contact with the roots of plants. Manure or commercial fertilizers 

 enrich the sap of the soil by supplying additional quantities of 

 available plant food. Bacteria, as we have seen, help to break down 

 the organic forms of plant food and render them soluble for the sap 

 of the soil to absorb. 



