184 



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 legnminons plants, such as clover, Vicia, peas and Viciafaba, 

 bear also in fertile soil many nodules, and it is not easy to tind 

 specimens wholly devoid of them, unless the soil has been previously 

 sterilised. 



On the roots of Genista amjlica and Genista pilosa, growing on 

 poor heath fields, I found after long seeking oidy very few tubercles, 

 although they, and in particular the former, bore many pods with 

 good seeds; the tubercles are, however, never quite absent. When 

 sown in my garden at Delft or brought there as plants, they die 

 after some few years. On the other hand, Genista tinctoria thrives 

 as well at Delft as along the higlnvay of Zutphen to Vorden and 

 at both places bears a small number of nodules. 



For Robinia pseudo-acacia the favoui-able influence oï B. radicicola 

 only on the young plant, has been stated by Nobbk. ') As to fnll- 

 grown specimens on poor heath soil at Gorssel I could after long 

 digging find but few tubercles, while at a small distance, bnt on 

 somewhat better soil more tubercles occurred, but still so Utile 

 numerous, that nobody would attribute to them any direct signifi- 

 cance for such a large tree, had not the fixation of nitrogen in the 

 tubercles become an inveterate belief. Sarothanmus vulgaris and 

 Ulex europaeus behave in the same way as Robinia. On Phase- 

 olus vidgaris on saridy soils I found but few nodules, and then only 

 on thin rootlets and nearly always enclosed by plant remains; in 

 the pure sand the nodules are very rare. In garden soil at Delft 

 Phaseolus produces no nodules, but it does in a there arranged 

 sandbed; Lupinus luteus and Serradella behave likewise. 



When comparing the various mentioned plants, all noted in 

 agriculture for their power of ameliorating the soil, as they contain 

 in their dry substance nearly double the quantity of Jiitrogen found 

 in other plants, for example the grasses, we come to the conclusion 

 that only for lupine and serradella the number and weight of the 

 tubercles is of some significance in regard to the whole weight of 

 the plant. For other species they are of so little volume that even 

 if within them free nitrogen were fixed with great intensity, oidy 

 an extremely little quantity of fixed nitrogen could be expected, whilst 

 in reality this amount is very considerable. Hence the theory, at 

 present generally accepted, after which the fixation takes place in the 



1) HiLTNER I.e. Also BiisGEN, Bau und Leben unserer Waldbaume, 2te Aufl., Pag 

 246, 1917. 



