198 Agricultural Bacteriology. 



favor their growth and to seek to establish such in the 

 soil. 



Leguminous plants. It has been known since the 

 days of the early Romans that leguminous plants had a 

 favorable effect on the soil and for this reason they were 

 included in nearly all systems of crop rotation. This 

 favorable effect of the legumes was explained in many 

 ways. Some claimed that because of their deep roots, 

 they were able to reach plant food that was ordinarily 



FIG. 19.- LEGUMINOUS PLANTS. 



Clover growing in soil free from nitrogen. In jar No. 6 the 

 soil is also free from the nodule-forming bacteria; in jar 

 No. 5 the soil contains an abundance of them. 



inaccessible or because of their abundant supply of leaves, 

 they drew more food from the air. It was not until late 

 in the last century that the real reason was discovered. 



It had been noted that many of the leguminous plants 

 often had peculiar nodules or swellings on their roots 

 which were regarded as harmful to the plant, also 'that 

 leguminous plants would grow on sandy soils that were 

 too poor to produce crops of ordinary grains. It was 



