198 HISTORY OF BOTANY 



circumstances of supply of combined nitrogen, it is 

 desirable that the evidence of further experiments with 

 these plants under conditions of more healthy growth 

 should be obtained/' 



In Valerius Cordus's Historia Plantarum this sentence 

 occurs : " The root of the lupine is slender, woody, 

 white and without useful properties, parted into a few 

 slender fibres upon which there grow small tubercles." 

 These words were written three centuries before the 

 Rothamsted researches were published, and it is strange 

 that no one during all these years made any effort to 

 explain why leguminous plants only should possess these, 

 seemingly, pathological swellings. 



The next step in advance was taken by the French 

 chemist Berthelot, who, in 1876, drew attention to the 

 fact that, although plants did not absorb free nitrogen 

 from the air directly, a constant fixation of atmospheric 

 nitrogen was taking place in the soil and also in the air 

 under the influence of silent electric discharge. In 1885 

 he associated the fixation of nitrogen in the soil with the 

 presence of micro-organisms, and in the following year 

 Hellriegel and Willfarth showed that the formation of 

 nodules on the roots of Leguminosae was intimately 

 connected with the absorption of nitrogen by such 

 plants ; so that at last, after three centuries of waiting, 

 Cordus's discovery came into its own. These results 

 Gilbert reluctantly accepted, even explaining his failure 

 (in 1861) to demonstrate the fixation of nitrogen by 

 Leguminosae by admitting that he had calcined the 

 soil in which his experimental plants had been culti- 

 vated. 



The root nodules were investigated in 1887 by Marshall 

 Ward, who traced their origin to a microfungus which 

 enters the root hair from the soil and causes hypertrophy 

 of the cortical cells, and in the folio whig year Beijerinck 

 isolated the bacterium concerned and named it Bacillus 

 radicicola. The whole life-history of the organism was 



