324 GENERAL SCIENCE 



water comes to the surface from several feet below and 

 this water is usually sufficient to grow a good crop if it 

 is not permitted to escape by evaporation. In gardens 

 during dry seasons the surface should be raked lightly 

 just after each little shower, so that the surface will not 

 crack. Soil which is not pulverized on the surface and 

 is permitted to crack will dry out very quickly. 



About one-half the volume of ordinary soil is air. This 

 is called soil air, and it is very necessary for growing plants. 

 Cultivation keeps the soil loose and makes room for air, 

 which occupies all the spaces between the little lumps or 

 particles of soil. Soil that is very wet does not have 

 much room for air and most plants do not grow well in it. 

 As excess water is removed air enters. 



Good soils contain a small percentage of decaying plant 

 matter and some animal matter. This plant and animal 

 matter is called humus. It is decomposed and made soluble 

 by the action of microscopic bodies called bacteria and 

 also by small animals living in the soil. These bacteria 

 and small animals cannot live in the soil if there is too 

 much water or if there is not enough water in it. They 

 also need air. Proper cultivation is necessary to make 

 conditions favorable for the growth of these organisms in 

 order to make food available for the growing plants. 



223. Soil in Flower Beds, Pots, and Hotbeds. The 

 soil for flower beds should be enriched with a well-bal- 

 anced commercial fertilizer and some manure or with 

 a large quantity of well-decayed manure. This manure 

 should be thoroughly mixed with the rest of the soil. 

 The soil should be cultivated often enough to keep it 

 loose and well aired or aerated. During dry seasons 

 sufficient water should be added to keep it moist but 

 not wet. 



