HOUSEHOLD BACTERIOLOGY 



Nitrogen 

 Traps 



Enrich 

 the Soil 



Inoculating 

 the Soil 



It fertilizes the ground in which it has been sown as 

 well as any manure." The lupine and vetch are also 

 mentioned in ancient writings as enriching the soil and 

 supplying the place of fertilizers. 



On the roots of these leguminous plants, clovers, 

 alfalfas, peas, beans, etc., are seen little nodules which 

 have been found to be filled with bacteria. Fig. 29. 

 If these "nitrogen traps" are absent or are removed 

 the plants are less vigorous. Fig. 30 shows the com- 

 parative size of two plants of a variety of pea; (a) 

 grown on soil containing the proper kind of bacteria ; 

 (b) grown in the same conditions and soil, but with- 

 out the bacteria. The nitrogen is stored up in the 

 knots, swellings, or nodules on the roots. 



Not only do these nitrifying bacteria thus feed the 

 plants which carry them, but also when the plants de- 

 cay they enrich the soil in which the plants grow. Soils 

 "run out," as the farmers say, that is, there is not plant 

 food enough to sustain luxuriant vegetable life. Here 

 is a place for the legumes to supply with their tiny 

 balls of bacteria the nitrogen which has been with- 

 drawn. In some way, not understood, the clover or 

 similar plant in company with the bacteria stores up 

 nitrogen from the air, which is finally returned to the 

 soil when the decomposition bacteria have accom- 

 plished their work, thus making the soil richer in 

 nitrogen. 



When the proper kind of nitrifying bacteria are not 

 present, the scientist comes to the aid of the farmer 



