THE ABSORPTION OF NITROGEN 197 



made by Lawes and Gilbert it may be well that I should 

 remind you of the views of Liebig on the relation of plants 

 to the soil. Every crop, said Liebig, demanded and 

 took from the soil certain minerals, and the essential 

 mineral present in minimum quantity determined the 

 success or otherwise of the crop in question. Con- 

 sequently the purpose of manuring is to supply the 

 deficiency in minerals, for both the carbon and the 

 nitrogen could be obtained in abundance from the atmo- 

 sphere. After a few experiments had been made, Gilbert 

 dissented from this view, and found himself compelled 

 to support Boussingault. An extensive monograph on 

 the subject appeared in 1861 in the Philosophical Trans- 

 actions of the Royal Society entitled, " The Sources of 

 the Nitrogen of Vegetation ; with special reference to the 

 question whether Plants assimilate free or combined 

 Nitrogen." In this paper Lawes and Gilbert state as the 

 result of their experiments that " we have in no case 

 found any evidence of an assimilation of free or uncom- 

 bined nitrogen." This statement entirely supported 

 Boussingault's conclusions, and so, as you will readily 

 understand, it was — to use an Americanism — " up 

 against " the followers of Liebig to prove their point ; 

 Lawes and Gilbert were not called upon to prove the 

 negative, though they furnished abundant evidence in 

 support of the correctness of their position. 



In the same paper there is another almost side-note 

 which opened up a new aspect of the whole problem of 

 nitrogen assimilation. Let me give it you in full. "In 

 our experiments with leguminous plants the growth 

 was less satisfactory, and the range of conditions possibly 

 favourable for the assimilation of free nitrogen was, 

 therefore, more limited. But the results recorded for these 

 plants, so far as they go, do not indicate any assimila- 

 tion of free nitrogen. Since however in practice legumin- 

 ous crops assimilate from some source so very much more 

 nitrogen than graminaceous ones under ostensibly equal 



