FIXATION OF FREE NITROGEN. 155 



rience in practical agriculture, nor the nitrogen statistics of Little gain 

 soils and crops, points to the conclusion that there is gain of ^e^/S 

 nitrogen to any material extent by the fixation of free nitro- leguminous 

 gen under the agency of microbes within the soil indepen- 9 rowth - 

 dently of leguminous growth. It was our intention to com- 

 mence experiments on this subject at Eothamsted in 1891, 

 but we have not yet been able to do so. 



In 1888, however, Berthelot made numerous experiments 

 with Leguminosse, and in many of them he found very large 

 gains of nitrogen — indeed a much higher range of gain than 

 in his other experiments. That there should be large gain 

 under such conditions is quite consistent with the results 

 which have been recorded of the experiments made at 

 Eothamsted with Leguminosee, and with those previously 

 obtained by Hellriegel and Wilfarth. Further, these results 

 of Berthelot, like those obtained at Eothamsted and by others 

 with leguminous plants, are consistent with well-established 

 facts of agricultural production, and with the nitrogen statis- 

 tics of soils and crops, and serve, with them, to aid the solu- 

 tion of long - recognised problems in connection with the 

 growth of leguminous crops. 



But whether or not it may eventually be established that Lower 

 nitrogen is fixed to any material extent by microbes within °^^^t 

 the soil, independently of leguminous growth, there is evi- food for 

 dence that in soils and subsoils containing organic nitrogen, h ] g ^ s 

 lower organisms may serve the higher plants by taking up or 

 attacking and bringing into a more readily available condi- 

 tion combined nitrogen not otherwise, or only very slowly, 

 available for the higher plants. For example, it is probable 

 that fungi generally derive nitrogen from organic nitrogen ; 

 and in the case of those of fairy rings there can be little 

 doubt that they take up from the soil organic nitrogen which 

 is not available to the meadow plants ; and that on their 

 decay their nitrogen becomes available to the associated 

 herbage. Then in the case of the fungus-mantle observed 

 by Frank on the roots of certain trees, it may be supposed 

 that the fungus takes up organic nitrogen, and so becomes 

 the medium of the supply of the soil-nitrogen to the plant. 

 More pertinent still is the action of the nitrifying organisms 

 in rendering the organic nitrogen of the soil and subsoil 

 available to the higher plants. It may well be supposed, 

 therefore, that there may be other cases in which lower 

 organisms may serve the higher, bringing into a more avail- 

 able condition the combined nitrogen already existing, but in 

 a comparatively inert state, in soils and subsoils. 



It may, then, be considered as fully established, that vari- Points 

 ous Leguminosse acquire a considerable amount of nitrogen by establlshed - 



