

FIXATION OF FREE NITROGEN. 151 



which indicate, if not different species or varieties, at any 

 rate different race or nutrition modifications. Beyerinck 

 also concluded that the various papilionaceous bacteria differ 

 more than he had formerly supposed. 



Of the three descriptions of leguminous trees upon which 

 Nobbe experimented, the Robinia and the Cytisus, which are 

 both of the papilionaceous subdivision of the leguminous 

 Order, were susceptible to microbe-infection and nodule- 

 formation on their roots, and showed coincidently gain of 

 nitrogen ; but the Gleditschia, which is not papilionaceous, but 

 of the sub-order Csesalpiniese, was quite indifferent to such 

 infection, although both soil-extracts and pure cultivations 

 from various sources were tried. On the other hand, it was 

 found that the application of calcium-nitrate and ammonium- 

 sulphate gave considerably increased growth. Nobbe observes 

 that the roots of Gleditschia have a very thick covering, which 

 it would be at any rate difficult for the bacteria to penetrate ; 

 but whether the members of this group generally behave 

 differently from the Papilionacese in this respect remains for 

 future investigation to determine. It is at any rate of inter- 

 est to note, that the only leguminous plant outside the papil- 

 ionaceous sub-order which has yet been experimented upon 

 has not been found susceptible to infection, or to have nodules 

 on its roots. 



In 1891, F. Nobbe, E. Schmid, L. Hiltner, and E. Hotter, Physioiogi- 

 commenced various experiments to ascertain the physiologi- ^ '"^rToot- 

 cal meaning of the root-nodules of various wow-leguminous nodules. 

 plants {Eleagnus, Hippophae, and Alnus). Eleagnus sprouts 

 were planted in two pots containing sterilised nitrogen-free 

 sand ; a week afterwards one pot was infected with an extract 

 of Eleagnus soil. The infection had no visible effect during 

 the whole summer, but in the autumn one of the plants 

 began to acquire a somewhat fresher green colour than the 

 others, and in the spring of the following year this plant was 

 unmistakably more vigorous than the others ; it was strong, 

 and had side shoots. All the plants (of both pots) were iso- 

 lated in nitrogen-free sand, when it was seen that only the 

 plant which was benefited by the inoculation had nodules. 

 The non-infected plants were scanty and without side shoots. 

 Only one of the infected plants began to get greener in July 

 1892 ; it had three small oblong nodules when taken up. 



There was no doubt that Eleagnus was enabled by the 

 possession of nodules to utilise free atmospheric nitrogen. 

 The organisms which produced these nodules were obtained 

 in pure cultivations, and were totally different from Bacterium 

 radicicola. 



Here, then, we have experimental evidence of gain of 



