154 



THE ROTHAMSTED EXPERIMENTS. 



Boussin- 



gault's 



results. 



Berthelot's 

 results. 



Other re- 

 sults. 



nitrogen by Leguminosae under the influence of microbe- 

 infection of the soil, and nodule-formation, is due to fixation 

 by organisms within the soil itself independently of the sym- 

 biosis. It is obvious, too, that so far as free nitrogen may be 

 fixed by microbes within the soil, independently of connection 

 with a higher plant, the resulting nitrogenous compounds 

 should, directly or indirectly, be available to plants generally 

 whether leguminous or non-leguminous. 



On this point it may be remarked that, from the results of 

 vegetation experiments made by Boussingault in 1858 and 

 1859, in mixtures of rich soil and sand, he concluded that free 

 nitrogen had been fixed within the soil by the agency of 

 mycodermic vegetation ; and that the nitrogenous products 

 which remained within it were largely in the form of organic 

 detritus. Subsequently, however, he considered that there was 

 not satisfactory evidence that free nitrogen is fixed within the 

 soil under the influence of the development of the lower or- 

 ganisms. It is, nevertheless, of interest to observe that those 

 of his results in 1858 and 1859 which showed any material 

 gain of nitrogen, either in the vegetable matter grown or in 

 the soil, were obtained with Leguminosse ; and that, in the 

 case in which there was the greatest gain in the plants them- 

 selves, he records that there were numerous tubercles on their 

 roots. In one other case in which, however, only sand was 

 used as soil, and the gain in the plant was but small, he also 

 observed tubercles on the roots. It is at any rate very sig- 

 nificant, when viewed in the light of recently acquired know- 

 ledge, that in all the cases of gain the plants grown were of 

 the leguminous family, and that in some of them nodules 

 were observed on the roots. 



Again, Berthelot's experiments showed fixation of free 

 nitrogen by the agency of microbes within the soil, both in 

 the absence of higher vegetation, and also coincidently with 

 the growth of non-leguminous plants. He further considered 

 that such fixation takes place to an extent which would be an 

 important source of nitrogen to our crops. As referred to 

 above, Boussingault's experiments of 1858 and 1859 showed 

 fixation within the soil which he then attributed to the 

 agency of mycodermic vegetation. The fact of such fixation 

 within the soil, under the influence of lower plants, has also 

 been confirmed by the recent results of some other experi- 

 menters. Thus, M.M. Schloesing fils and Laurent have shown 

 fixation in bare soil, and in soils growing various non-legu- 

 minous plants, when certain Lichens and Algae were developed, 

 but not when their occurrence was prevented. Hellriegel has 

 also found fixation coincidently with the growth of certain 

 Algse. Nevertheless, it may be observed that neither expe- 



