204 Agricultural Bacteriology. 



nodule-forming bacteria and even though no inoculation 

 is made some nodules will appear. If the same legume 

 is then grown on the field in a subsequent year, an abund- 

 ant supply of nodules will be produced as the bacteria 

 will persist in the soil for a number of years. 



A large amount of nitrogen is removed from the soil in 

 -any leguminous crop but where the nodules are abundant 

 and much nitrogen has been fixed from the air, the soil 

 is left richer than before because the nodules and roots 

 of the legumes are exceedingly rich in nitrogen. As 

 these tissues decay, the nitrogen is changed to a form in 

 which it can be used by other kinds of plants. In this 

 way the legume has a favorable effect on subsequent crops. 

 The leguminous plants under all circumstances tend to 

 deplete the soil of phosphorous and potassium in the same 

 manner as all other plants. 



Effect of nodules on composition of the plant. The 



presence of the increased nitrogen supply derived from 

 the nodules affects materially the chemical composition 

 of the plant. Plants which have nodules on their roots 

 are found to contain a considerable larger per cent of 

 protein than plants devoid of the nodules. The feeding 

 value of the former is > consequently much greater. 



Nitrogen fixation by bacteria without the aid of 

 plants. With those forms of bacteria that form the 

 nodules on leguminous plants, no fixation of nitrogen is 

 supposed to take place, except in the nodules of the plant. 

 The bacteria are known to exist in the soil for a number 

 of years even though no leguminous plants are grown on 

 the field. It is thus evident that the bacteria must be 

 able to grow in the soil outside of the plant. 



There are found widely distributed in the soil, other 



