200 INTRODUCTION TO GENERAL SCIENCE 



This is the incalculable amount of bacteria present. These 

 bacteria serve many purposes of disintegration and decay, 

 and are also able to abstract the nitrogen of the air, and 

 change it into nitrates, which are then readily absorbed by the 

 plants. A little later we will take up a more complete study 

 of bacteria in relation to plant growth. 



References : 



1. 1601 : 36-37. The Soil a Laboratory. 



2. 1601 : 76-88. Chemical Constituents of the Soil. 



3. 1601 : 101-106. Store of Plant Food. 



4. 1605 : 109-113. Plant Food in Soils. 



5. Farmers' Bulletin, No. 342:5-10. Conservation of Soil 



Resources. 



a. 1602 : 39. Make-up of Rich Soil. 



6. 1606 : 18-22. The Organic Elements and Agents. 



c. 1606 : 25-28. Resources of the Soil. 



d. 1610 : 35-36. Natural Strength of Soils. 



e. 1611:141-142. Soil Bacteria. 



/. 1612 : 62-70. How Plant Food is Preserved. 



g. 1612 : 71-78. Getting Acquainted with Plant Food, 



Chemical Analysis. 

 h. 1713 : 149-150. The New Theory of Liebig. 



143. KINDS OF SOILS 



Soils are classified according to the labor which is required 

 to work them properly and in respect to their water-holding 

 capacity. Thus graded, soils are called heavy, compact, 

 sandy, light, porous, cold, and warm. There is another 

 classification which is due to the composition of the soils; 

 namely, gravelly, loamy, swamp, peat, or humus soils. 



References : 



1. 1205:19-22. The Soil. 



2. 1503:91-92. Kind of Soil Favorable to Evaporation. 



