ASSIMILATION OF NITROGEN 



65 



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

 carried out by Sachs, c by Schlosing^ and by Adolf Mayer. 6 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 100 cu. m. of air contains, on the 

 average, only 2.4 mg. of ammonia. 



§2. The Nitrogen of the Soil. — The nitrogen of the soil 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 will 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 usually 

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

 various nitrates generally 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 1 kg. of soil contained the following amounts of 

 nitrogen: 



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 



c Sachs, J., as cited by Robert Hoffman, Ueber die Aufnahme des Kohlensauren Ammoniaks 

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



d Schloesing, Th., Sur l'absorption de l'ammoniaque de l'air par les vegetaux. Compt. 

 rend. Paris 78: 1 700-1 703. 1874. Also see: Atwater, W. O. Ueber die Assimilation von 

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

 1885.— Ed. 



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

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



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

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