30 TIIKORIES OX THE ABSORPTION OF NITROGEN 



lation and plants have absorbed nitrates when no nodules 

 were present. 



(3) This formation occurred wherever addition to steri- 

 lized soils was made by a fresh infusion of sandy earth in 

 cultivation. No formation took place when the infusion had 

 been sterilized, and from this we can deduce that the forma- 

 tion is due to the presence in the soil of an organized 

 ferment. 



(4) The formation of nodules was accompanied by a gain 

 in nitrogen, occurring during growth, which could not be 

 attributed to the original nitrogen content of the soil. 



The following experiment conlirmed the two scientists' 

 statements : — 



Eight vessels i"eceived an equal amount of nitrogen. The 

 first four were sterilized and nothing was added. The plants 

 in these did not grow beyond a limit corresponding to the 

 original amount of nitrogen placed at their disposal. 



The four reinaining vessels received the same amount of 

 nitrates with the addition of an earthy infusion. The plants 

 in these grew normally and showed a gain in nitrogen ex- 

 ceeding the amount in the nitrates, while the total amount 

 of dry matter was by no means in strict relation to the 

 nitrogen content of the soil. 



Franck carried out an experiment to refute this, but it 

 was defective, and did not prevent Hellriegel and Wilfarth 

 from asserting that the formation of tubercles rested on 

 the facultv these plants have of deriving nitrogen from other 

 sources than those afforded by nitrates or other nitrogenous 

 compounds in the soil. 



These assertions remained uncontradicted by any experi- 

 ment, not even by those of Rantemberg and Kulm showing 

 that Leguminos^e which had been grown in water were pro- 

 vided with nodules which in no way increased their gain 

 in nitrogen. 



Indeed, the possession of assimilating organs does not 

 necessarily ensure luxuriant growth in the plant, for they 



