LEGUMINOUS PLANTS AND NITROGEN. 



unable to use the nitrogen of the air ; that they 

 must have a supply of nitrogen-containing 

 bodies in the soil ; and that nitrification makes 

 these useful to plants. There is, however, a 

 remarkable exception in -as-much as plants 

 belonging to the pea and bean order (Leyu- 

 mutoseaf) are able to thrive even in soils con- 

 taining no nitrogen. It has been found that this 

 interesting and important property is due to the 

 prese nee of great numbers of bacteria (microbes 

 or germs) which inhabit small nodule* or 

 swellings to be found on the roots of plants of 

 this order. The bacteria living in these swell- 

 ings are able to feed on the nitrogen of the air 

 and pass on this nitrogen to the plants in con- 

 nexion with w r hich they live. They thus ena- 

 ble these plants to use the nitrogen of the air. 

 Now, as nitrogen is the most expensive con- 

 stituent of plant food, this property, possessed 

 by leguminous plants, .of using and building up 

 into their own structures nitrogen from the air, 

 is of great value to the cultivator. He is able to 

 grow crops of beans and peas upon soils which 

 are too poor in nitrogen to produce remunera- 

 tive crops of other kinds. When the bean 

 crop is reaped the roots which remain in the 

 ground, together with the leaves, stems, etc., 

 may be returned to the soil to increase its 

 nitrogenous store. The result is that the soil 



