INTRODUCTION 19 



from a solution of the particular soil to be inoculated. 

 Whatever method is employed, it is necessary to prepare 

 the cultures from nodules of the same species of plant for 

 which the culture is intended. 



Beginning with the introduction of nitragin, many 

 hundreds of inoculation experiments have been performed. 

 There can be no question of the importance of nodules 

 to the plants, as the difference between inoculated and 

 uninoculated plants is often markedly apparent. Any 

 superiority of artificial cultures over natural inoculation 

 has thus, far not been realized. Artificial inoculation for 

 reasons not ascertained is less certain than natural soil 

 inoculation. Artificial cultures have the advantage of 

 cheapness and convenience, but thus far the uncertainty 

 attending their use on uninoculated soil has more than 

 counterbalanced these advantages. 



From theoretical considerations, there is abundant 

 reason to believe that. methods will yet be perfected to 

 secure reliable inoculation by artificial cultures of espe- 

 cially efficient strains of the nodule bacteria. 



15. Dependence of legumes on root nodules. Many 

 legumes will grow normally in a fertile soil without root 

 nodules. In this case, however, the plant is less rich in 

 nitrogen. Thus, Hopkins analyzed cowpeas grown at the 

 Illinois Experiment Station, comparing plants with and 

 without nodules. The former were three times as large 

 and contained 3.9 per cent nitrogen and the latter but 2.2 

 percent. At Amarillo, Texas, in 1908, plots of cowpeas 

 of several varieties planted in fertile virgin soil were 

 entirely devoid of nodules, although their growth was ap- 

 parently perfectly normal. 



On the other hand, alfalfa seems to be dependent under 

 some conditions on root nodules for existence. In Mary- 



