Microbiology. — "The .-iiinificance of the tubercle bacteria of the 

 PapiUonaceae for the host plant'. By Prof. Hkijkkinck. 



(Communicated in the meeting of April 2G, 1918). 



As (liere is no reason to donbt of f lie accuracy of Hkllrikgki/s ') 

 experiments, it appears certain that the bacteria of the nodules on the 

 roots of the Ijeguininosae are indispensable for the fixation of atmospheric 

 nitrogen by these [)lants. ^) But I shall prove that the theory, at 

 present generally adopted, according- to which this process takes j)lace 

 only within the tubercles, cannot be correct. But previously some 

 remarks on the occurrence of the tubercles and the cultivation of 

 bacteria from them. 



For some plant species such as serradella {Ornithopics sativus) siwd 

 the yellow lupine [Luplniis luteus), it cannot be doubted that only 

 the tubercle-bearing specimens grow vigorously in nitrogen-poor soils 

 and consequently, after the theory, fix the atmospheric nitrogen. It 

 is therefore easy on poor heath fields to find languishing, stunted 

 lupine plants, always devoid of nodules, amid the luxuriantly growing 

 tnbercle-bearing ones. Never did I find theie well-developed lupine 

 or serradella plants quite without them. But the number of lubeicles 

 is of no consequence, it evidently suffices if only few come to 

 development. 



In garden experiments on open sandbeds, without supply of 

 nitrogen, but where inevitably more nitrogen compounds occur than 

 in heath soils, also in peas and beans ( Vicia faba), plants with 

 nodules grow better than those devoid of them. 



In fertile garden soil such as in the laboratory garden at Delft, 

 yellow lupine and serradella do not fully develop, and especially 

 their roots make the impression of sickliness; tubercles do not 

 grow on them, not even when the soil lias been abundantly provided 



^) H. Hellriegel und H. Wilfarth, UntiMsucluingcn über die StickstolTnahrung 

 der Giamineën und Legumiuosen, Zeitschriit fur Riibenzuckerindusliie, Beilageheft 

 November 1888. See fuither the excellent treatise of Hiltner, Bindung von freiem 

 Stickstoff in liöheren Pflanzen, in Handbucli der leclinischen Mykologie, Bd. 3, 

 1903—1905. 



2) For the objective proof that here free atmospheric nitrogen is fixed see, besides 

 Hellrieüel (I. c. p. 191), ScHLösiNG et Lauhknt, Fixation de I'azole libre par les 

 plantes, Ann. de I'institut Pasleur, Tome 6, pag. 65, 1892. 



