1890.] On the Question of the Fixation of Free Nitrogen. Ill 



the lower organisms may not serve the higher, in part at least, by 

 taking tip, either directly or indirectly, combined nitrogen; as, for 

 example, fungi take up organic nitrogen from the soil ; or as, it may 

 be assumed, does the fungus in the case of the fungus-mantle 

 observed by Frank on the roots of Cupnliferse, and some other 

 plants ? 



Among the Leguminosse growing in the mixed herbage of grass 

 land, in 1868, nodules were observed on the root-fibres — of Lathy rns 

 pratensis, especially near the surface of the soil ; on the ultimate 

 root-fibres of Trifolium pratense, and on the smaller rootlets of 

 Trifulium repens. 



In the case of red clover growing in rotation on arable land, an 

 abundance of nodules has been found, both near the surface and at a 

 considerable depth. They are generally more or less globular or oval. 

 Some found on the main roots are more like " swellings " than attached 

 tubercles, not, however, encasing the root, but only on one side. The 

 greater number are, however, small, and distributed chiefly on the 

 root-fibres. Observations are, however, needed, as to any difference 

 in character, or relative prevalence, at different periods in the life and 

 growth of the plant, and under different conditions of soil, both so far 

 as mechanical state and porosity, and richness or otherwise in avail- 

 able supplies of combined nitrogen, are concerned. To these points 

 we hope to pay some attention. 



Referring to the main object of the investigation, it will be 

 admitted that the results so far brought forward are abundantly 

 confirmatory of those obtained by Hellriegel, and that the fact of the 

 fixation of free nitrogen in tbe growth of Leguminosse, under tbe 

 influence of microbe seeding of the soil, and of the resulting nodule 

 formation on the roots, may be considered as fully established. 



It appears that, almost concurrently with the experiments made 

 at Rothamsted, M. Breal, of the Physiological Laboratory of the 

 Museum d'Histoire Naturelle, of Paris, has made various experiments 

 on lines suggested by the results obtained by Hellriegel and Wilfarth. 

 He examined the contents of nodules from lucerne rools, and 

 observed rounded grains and bacteria-like filaments. He determined 

 the nitrogen in the root-tubercles from various Papilionacese, and 

 found it much higher in them than in the stalks, leaves, or roots. 

 He germinated peas in a nutritive solution, and added some of the 

 matter from a crushed lucerne root-tubercle. The pea roots became 

 covered with tubercles, and eventually the nitrogen in the plant was 

 about double that in the seed sown. In another experiment he 

 germinated two lupin seeds, inoculated one of them from a living 

 lucerne root- tubercle, and planted both in gravel with a nutritive 

 solution free from nitrogen. Eventually the roots of the inoculated 

 plant were covered with tubercles, whilst those of the other had 



