178 HATCH EXPERBIENT STATION. [Jan. 



proofs of the special claims of these crops as nitrogen gather- 

 ers when compared in that direction with grain crops. 



The subsequent important discovery of the real cause of 

 the exceptional behavior of these crops by Hellriegel and 

 others has given not only a satisfactory explanation of pre- 

 vious observations in practical agriculture but has also im- 

 parted, for economical reasons, an increased interest in the 

 study of successful methods of raising clovers, etc., without 

 the aid of a liberal supply of nitrogen-containing manurial 

 substances. 



Hellriegel and his co-laborers established by careful obser- 

 vation the fact that leguminous plants, like clovers, beans, 

 vetches, lupines, etc., with the assistance of certain micro- 

 organisms (root bacterium) found in the soil, can utilize the 

 elementary nitrogen of the air for the formation of nitrogen 

 plant food fit for the support of their growth. 



These micro-organisms fasten themselves upon the roots 

 of the clover, etc., penetrate the epidermis and form in the 

 course of their growth swellings, nodules or tubercles, of 

 varying size and shape. Their presence and growth in the 

 tissue of the roots of this stated class of plants is considered 

 an essential condition for the conversion of the elementary 

 nitrogen of the air into suitable nitrogen plant food. The 

 recognition of the circumstance that their presence or ab- 

 sence in the soil controls the results in a material degree, 

 even under otherwise favorable conditions, has turned the 

 attention of progressive agriculturists towards the study of 

 the circumstances which secure success. 



Quite prominent among the more recent results of investi- 

 gation in this direction are the observations that a variety of 

 root bacterium exists ; that some infest the roots of one kind 

 of leguminous plant while others thrive upon other kinds : that 

 is to say, some leguminous crops ma}' fail to give satisfactory 

 returns where others prosper on account of the presence or 

 absence of the right variety of root bacterium, or of suitable 

 condition of the soil for their vigorous development. 



These results caused the introduction of various modes of 

 infecting the soil, wherever found necessary, with the de- 

 sired kind of bacterium germ, before seeding down the new 

 crop. A very common method consisted in scattering a 



