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THE NODULE ORGANISM OF THE LEGUMINOS^. 

 By R. Greig Smith, M.Sc, Macleay Bacteriologist. 



(Plates li.-lii.) 



It has been for a long time known to agriculturists that a 

 leguminous crop enriches the soil to a considerable extent, and it 

 is customary to sow a crop of beans, clover, or other leguminous 

 plant as a preparation for wheat, which makes a great demand 

 upon the soil nitrogen. It was the general feeling that the 

 Leguminosie could gain nitrogen from the air, but how this 

 occurred was not understood. 



In the middle of the century Boussingault, Villes, Lawes, 

 Gilbert and Pugh studied the question, and although Villes 

 certainly showed a gain of nitrogen in some of his plant experir 

 ments, yet the later investigations of the Rothamsted experimen- 

 ters showed that neither the Leguminosa? nor any other plant 

 could utilise the nitrogen from any source other than the soil. 

 With the exception of Berthelot, who about 1876 doubted this 

 conclusion, the matter \aby practically dormant until Hellriegal 

 and Wilfarth in 1886 published their classical researches upon 

 the fixation of nitrogen. These authors showed that when crop 

 plants were grown with a sufficiency of minerals the produce was 

 proportional to the amount of nitrogenous manure in the soil. 

 This law, however, did not hold for the Leguminosee, which grew 

 independently of nitrogenous manuring; indeed some of the largest 

 crops of peas were obtained from soils which had received no 

 nitrogen whatever. But they also showed that when the legumi- 

 nous plant reached the "sick " period — that is, when the growing 

 plant had exhausted all the cotyledonary nitrogen and appeared 

 pale green in colour — it either took on a new lease of life or died, 

 depending upon whether nodules appeared upon the roots. With 

 the death of the plant there was no formation of nodules and no 



