96 



Wetenschappen" in Haarlem in 1904 ')). The said point of view may 

 be found, however, in one of BEIJERINCK'S latest writings 2 ), which 

 certainly must be counted among the most remarkable. This writing 

 deals exclusively with the "significance" for the plant of the bacteria 

 in the nodules. 



BEIJERINCK stated emphatically that he did not doubt that proof 

 has been established by HELLRIEGEL, by SCHLOSING, and by LAURENT 

 (1892), that the nodule bacteria are indispensable for furnishing the 

 Leguminosae with the power to fix atmospheric nitrogen. He does 

 doubt seriously, however, whether in the prolonged tests which were 

 done to prove this nitrogen fixation under sterile conditions, after 

 inoculation with a pure culture, there has not occurred some conta- 

 mination of the soil with other bacteria, among which there may have 

 been free-living nitrogen fixers. 



Furthermore, in 1908 BEIJERINCK observed the highly important 

 fact (which seems indeed to be insufficiently known) that nodules 

 which are isolated from the plant can fix no elementary nitrogen; 

 even large quantities of these nodules appear incapable of fixing 

 traces of nitrogen. This fact has been recently confirmed by one of the 

 writer's pupils, G. J. A. GALESTIN 3). 



Finally BEIJERINCK brought forward many observations from na- 

 ture, from which it appeared that the presence of only a few nodules 

 on the roots of some Leguminosae is sufficient for a satisfactory 

 development of these plants. This number was so small, for instance, 

 in a vigorous specimen of Robinia pseudo-acacia, which grew in poor 

 heath soil, that, in BEIJERINCK'S words, "nobody would attribute to 

 them any direct significance for such a large tree, had not the fixa- 

 tion of nitrogen in the nodules become an inveterate belief". 



Rightly, BEIJERINCK concluded in 1918: "Hence, the at present 

 generally accepted explanation of the peculiar behaviour of the Pa- 

 pilionaceae cannot be correct. New researches, especially with Phaseo- 

 lus, are desirable". 



Much research in this field was done also in the years after 1918, but 

 up till now, BEIJERINCK'S problem still awaits an answer. 



!) L'influence des microbes sur la fertilite du sol et la croissance des vegetaux su- 

 perieurs, Archives neerlandaises des sciences exactes et naturelles, ser. 2, 9, VIII- 

 XXXVI, 1904 (Verzamelde Geschriften 4, 249-265). 



2 ) The Significance of the tubercle bacteria of the Papilionaceae for the host plant, 

 Proc. of the Section of Sciences, Kon. Akad. van Wetenschappen Amsterdam 21, 

 183-192, 1918 (Ver-zamelde Geschriften 5, 264-271). 



3 ) Wordt bij de assimilatie van luchtstikstof door Leguminosen elementaire stik- 

 stof door de wortelknolletjes geabsorbeerd ?, Chemisch Weekblad 30, 207-209, 1933. 



