546 



had been employed for the increased growth of the cereals, the 

 nitrogen in the immediate increase of produce had amounted to little 

 more than 40 per cent, of that supplied, and that in the increase of 

 the second year after the application, to little more than one-tenth 

 of the remainder. Estimated in the same way, there had been in 

 the case of the meadow grasses scarcely any larger proportion of 

 the supplied nitrogen recovered. In the leguminous crops the pro- 

 portion so recovered appeared to be even less ; whilst in the root 

 crops it was probably somewhat greater. Several possible explana- 

 tions of this real or apparent loss of the nitrogen supplied by 

 manure are enumerated. 



The question arises what are the sources of all the nitrogen of 

 our crops beyond that which is directly supplied to the soil by arti- 

 ficial means ? The following actual or possible sources may be 

 enumerated: the nitrogen in certain constituent minerals of the 

 soil ; the combined nitrogen annually coming down in the direct 

 aqueous depositions from the atmosphere ; the accumulation of 

 combined nitrogen from the atmosphere by the soil in other ways ; 

 the formation of ammonia in the soil from free nitrogen and nascent 

 hydrogen ; the formation of nitric acid from free nitrogen ; the 

 direct absorption of combined nitrogen from the atmosphere by 

 plants themselves ; the assimilation of free nitrogen by plants. 



A consideration of these several sources of the nitrogen of the 

 vegetation which covers the earth's surface showed that those of 

 them which have as yet been quantitatively estimated are inadequate 

 to account for the amount .of nitrogen obtained in the annual pro- 

 duce of a given area of land beyond that which may be attributed 

 to supplies by previous manuring. Those, on the other hand, which 

 have not yet been even approximately estimated as to quantity 

 if indeed fully established qualitatively offer many practical 

 difficulties in the way of such an investigation as would afford results 

 applicable in any such estimates as are here supposed. It appeared 

 important, therefore, to endeavour to settle the question whether or 

 not that vast storehouse of nitrogen, the atmosphere, affords to 

 growing plants any measurable amount of its free nitrogen. More- 

 over, this question had of late years been submitted to very extended 

 and laborious experimental researches by M. Boussingault, M. Ville, 

 and also to more limited investigation by MM. Mene, Roy, Cloez, 



