PROCEEDINGS OF THE COTTESWOLD CLUB II3 



considerably more than was supplied. Other observers, 

 Frank, Joulie, Strecker, etc., had attained similar results. 

 Atwater and JouHe concluded that the supply of Nitrogen 

 was from the free element in the atmosphere, but how 

 obtained remained an open question. Others gave hy- 

 pothetical explanations. 



Hellriegel and Wilfarth felt that their experiments com- 

 pelled them to reject the several hypotheses advanced in 

 explanation of the phenomena furnished by peas and other 

 Leguminous plants, and to look for the true solution of the 

 problem in the relationships now known to subsist 

 between certain lowly-formed organisms in the soil and the 

 roots of the higher plants with which they appeared to be 

 symbiotically associated. The unexplained but constant 

 irregularity exhibited by the peas which had found new 

 sources of Nitrogen might be accounted for on the 

 hypothesis that very greatly varying numbers of micro- 

 organisms engaged in the work would by the law of 

 probabilites be present in the experimental pots. The 

 possession by the Leguminosse of tubercules on their 

 roots, already well known to botanists, and the relation- 

 ship between these tubercules and certain Bacteroid 

 organisms contained in them suggested a line of enquiry, 

 and a hypothesis that the tubercules and their contents 

 were associated with the absorption of the Free Nitrogen 

 of the air. 



On this line Hellriegel and Wilfarth carried out a new 

 set of experiments, with both cereals and Leguminous 

 plants of various species during the years 1886 and 1887. 

 The methods were precisely as before, except that the 

 sand in one set of pots was carefully sterilized, and in 

 another set was watered with a solution of soil extract. 

 This extract was prepared by taking some ordinary soil in 

 which Leguminous plants were healthily growing, and 

 washing it thoroughly with distilled water, the supposition 

 being that the solution, after filtration of large particles 



H 



