FINDING AND MAKING SOIL 195 



doing this very work and that, if given possession of 

 the soil, they would not exhaust it of nitrogen, but 

 would increase the nitrogen that is the most im- 

 portant plant food. 



Here we have the most wonderful of all facts con- 

 cerning your little garden, or your larger fields, that 

 by planting peas and beans, or sowing clover and 

 alfalfa you are not exhausting your land except 

 in the way of phosphorus and potash. Then it was 

 found that this specific power of legumes was due to 

 nodules on the roots and that these nodules were 

 the home of bacteria of a peculiar sort. Hereto- 

 fore bacteria had not carried to the mind of the crop 

 grower any pleasant suggestion. They were sup- 

 posed as a rule to be associated with disease, but now 

 bacteria began to be thought of as a beneficent 

 agency. 



Bacteria subdivide to multiply, and the Kansas Ex- 

 periment Station reports that it estimates over one 

 billion six hundred millions in a single gram of soil. 

 As you go down into the earth bacterial life decreases, 

 until it ceases entirely below six feet. As four-fifths 

 of the air is nitrogen, the bacteria have a big field 

 to work in. They transform it and then turn it over 

 to the plant as food. Why ? We do not know why, 

 any more than we know how. But we do know that 

 it is done in connection with the little appendages 

 called tubercles or nodules on the roots of the 

 legumes. If you will carefully dig a young clover 

 .(not pull it), and plunge the roots into warm water, 



