140 



THE ROTHAMSTED EXPERIMENTS. 



Hellriegel's 

 results con- 

 clusive and 

 all-import- 

 ant. 



Recent 

 trials at 

 Rotham- 



grew in it luxuriantly, and nodules were abundantly de- 

 veloped on their roots. 



Further particulars of the experiments of Hellriegel and 

 Wilfarth, and also of the results and conclusions of Berthelot, 

 Deh^rain, Joulie, Deitzell, Frank, Emil von Wolff, and At- 

 water, as well as some of the later experiments of Boussin- 

 gault which have a bearing on the present aspect of the 

 question, will be found in our paper in the Philosophical 

 Transactions, vol. 180 (1889), B. A short account is also 

 given of the experiments of Breal in our paper in the 

 Proceedings of the Royal Society, vol. 47, 1890. It may be 

 added that A. Petermann found gain with lupins, but doubted 

 whether it was entirely due to root-nodule action, or whether 

 it was from the combined or the free nitrogen of the air. 

 (Bull. Stat. Agron. Gembloux Belg., March 1890.) 



Thus, then, not only did Hellriegel and Wilfarth get nega- 

 tive results with plants of other families than the Legu- 

 minosse, as all experience would lead us to expect, but they 

 obtained positive results with the Leguminosse, in regard to 

 the source of the whole of the nitrogen of which experience 

 showed that there was a " missing link." Such results were 

 obviously of fundamental and of far-reaching importance; 

 and it seemed desirable that the subject should be further 

 investigated with a view to their confirmation or otherwise. 

 Accordingly, it was decided to take it up at Rothamsted, and 

 it was hoped to commence experiments in 1887, but it was 

 not possible to do so until 1888. In that year a preliminary 

 series was undertaken, and the investigation has been con- 

 tinued each year since, and is, in fact, not yet completed 

 (1894). 



It is proposed to give a brief account of the conditions, and 

 of the results, of these recent experiments made at Rothamsted, 

 which do show a fixation of free nitrogen. But, before 

 doing so, it will be well to call attention to those of the 

 earlier experiments, which did not indicate any fixation ; as 

 the well-defined difference in the conditions under which such 

 different results were obtained will bring clearly to view what 

 are the conditions under which fixation does, and what are 

 those under which it does not, take place. 



Earlier Experiments which did not show Fixation of Free 

 Nitrogen. 



Experiments on the subject were commenced at Rotham- 

 sted in 1857; they were continued for several years, and the 

 late Dr Pugh took a prominent part in the inquiry. 



The soils used were ignited, washed, and re-ignited pumice 



