The Significance of the tubercle bacteria of the 

 Papilionaceae for the host plant. 



Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen, Amster- 

 dam, Vol. XXI, 1918, p. 183192. Verscheen onder den titel De beteekenis der 

 bakterien van de Papilionaceenknolletjes voor de voedsterplant in Verslagen Kon. 

 Akademie van Wetenschappen, Wis-en Natuurk. Afd., Amsterdam, Deel XXIV, 1918, 



biz. 1456 1465. 



A s there is no reason to doubt of the accuracy of H e 1 1 r i e g e 1's *) experiments, 

 j> JL it appears certain that the bacteria of the nodules on the roots of the Legu- 

 minosae are indispensable for the fixation of atmospheric nitrogen by these plants 2 ). 

 But I shall prove that the theory, at present generally adopted, according to which 

 this process takes place 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 (Ornithopus sativus) and the yellow 

 lupine (Lupinus luteus), it cannot be doubted that only the tubercle-bearing specimens 

 grow vigorously in nitrogen-poor soils and consequently, after the theory, fix the atmo- 

 spheric nitrogen. It is therefore easy on poor heath fields to find languishing, stunted 

 lupine plants, always devoid of nodules, amid the luxuriantly growing tubercle-bearing 

 ones. Never did I find there well-developed lupine or serradella plants quite without 

 them. But the number of tubercles 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 has been abundantly 

 provided with the concerned bacteria. Whether the latter die in the soil or are not 

 attracted by the roots of the plant is not yet clear. Most other leguminous plants, such 



! ) H. Hellriegel und H. Wilfarth, Untersuchungen iiber die Stickstoffnahrung 

 der Gratnineen und Leguminosen, Zeitschrift fur Rubenzuckerindustrie, Beilageheft 

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

 Stickstoff in hoheren Pflanzen, in Handbuch der technischen Mykologie, Bd. 3, 1903 1905. 



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

 Hellriegel (1. c. p. 191), Schlosing et Laurent, Fixation de 1'azote libre par le's 

 plantes, Ann. de 1'Institut Pasteur, Tome 6, pag. 65, 1892. 



