ASSIMILATION OF NITROGEN 6 1 



Experiments upon the assimilation of ammonia from the air by leaves were 

 carried out by Sachs," by Schlosing'' and by AdoH Mayer. = The upper parts 

 of the plant were isolated from the soil and received the ammonia as the car- 

 bonate, in solution. All the plant parts so treated exhibited a higher nitrogen 

 content than the corresponding organs in the controls without ammonia thus 

 supplied. This kind of nitrogen assimilation is of almost no importance under 

 natural conditions, however, since the ammonia content of the air is exceedingly 

 small. According to Schlosing a volume of loo cu. m. of air contains, on the 

 average, only 2.4 mg. of ammonia. 



§2. The Nitrogen of the Soil. — ^The nitrogen of the soU occurs as organic 

 compounds, ammonium salts and nitrates.-'' The experiments of Boussingault 

 and those of many agricultural chemists have shown that ordinary plants 

 (with the exception of certain forms, especially the legumes, which wiU be dis- 

 cussed later) obtain their nitrogen exclusively from the soil, and that all three 

 kinds of nitrogen compounds of the soil are beneficial to plants. Soils poor 

 in nitrogen, and thus unproductive, can often be made productive by addition 

 of any of these three forms of nitrogen compounds, but this result can be 

 best and most quickly attained by the addition of nitrates. Therefore, the 

 various nitrates serve as the best source of nitrogen for higher plants. 



The question arises whether all nitrogen compounds of the soil are taken 

 up directly by the plant or first undergo some alteration. In order to answer 

 this question we must consider some of the properties of soils. 



According to Boussingault i kg. of soil 'contained the following amounts of 

 nitrogen : 



Kind op N-compound 



Source of Soil 



LlEBERAUENBERG 



, Nancy 



Me^tais 



Organic nitrogen 



Nitrogen of ammonium salts 

 Nitrate nitrogen 



grams 



^.lOI 



o.oig 

 0.029 



Most of the soil nitrogen thus has the form of organic compounds, which are 

 decomposition products from the decay of animal and plant materials. The 

 nitrogen of ammonium salts forms the smallest part. The ammonia of the soil 

 is derived partly from the decomposition of organic nitrogenous compounds 



" Sachs, J., as cited by Robert Hoffmann, Ueber die Aufnahme des Kohlensauren Ammoniaks 

 der Luft durch die Pflanzenblatter. Jahresb. Agrikulturchem. 3 : 78-80. 1862. — Ed. 



^ Mayer, Adolf, Ueber die Aufnahme von Ammoniak durch oberirdische Pflanzentheile. 

 Landw. Versuchsst. 17 : 329-397. 1874. — Ed. 



' Schloesing, Th., Sur I'absorption de I'ammoniaque de I'air par les v6g6taux. Compt. 

 rend. Paris 78.: 1700-1703. 1874. Also see: Atwater, W. O. Ueber die Assimilation von 

 Stickstoff aus der Atmosphare durch die Blatter der Pflanzen. Landw. Jahrb. 14: 621-632. 

 i88s.—Ed. 



' Nitrites also occur, but in small amount. — Ed. 



