SOURCE AND ASSIMILATION OF NITROGEN. 85 



gen, is again formed by extraction of oxygen from 

 the air ; while all the oxygen of the organic matter 

 is returned to the atmosphere in the form of carbonic 

 acid. Vegetable matters can emit carbonic acid, 

 during their decay, only in proportion to the quan- 

 tity of oxygen which they contain ; acids, therefore, 

 yield more carbonic acid than neutral compounds ; 

 while fatty acids, resin, and wax, do not putrefy; 

 they remain in the soil without any apparent change. 

 The numerous springs which emit carbonic acid 

 in the neighborhood of extinct volcanoes, must be 

 regarded as another means of compensating for the 

 carbonic acid absorbed and retained by plants dur- 

 ing life, and consequently as a source by which 

 oxygen is supplied to the atmosphere. Bischof 

 calculated that the springs of carbonic acid in the 

 Eifel (a volcanic district near Coblenz) send into 

 the air every day more than 99,000 lbs. of carbonic 

 acid, corresponding to 71,000 lbs. of pure oxygen. 



CHAPTER V. 



ON THE ORIGIN AND ASSIMILATION OF NITROGEN. 



We cannot suppose that a plant could attain 

 maturity, even in the richest vegetable mould, with- 

 out the presence of matter containing nitrogen ; 

 since we know that nitrogen exists in every part of 

 the vegetable structure. The first and most impor- 

 tant question to be solved, therefore, is : How and 

 in what form does nature furnish nitrogen to vege- 

 table albumen, and gluten, to fruits and seeds 1 



This question is susceptible of a very simple solu- 

 tion. 



Plants, as we know, grow perfectly well in pure 

 charcoal, if supplied at the same time with rain- 

 water. Rain-water can contain nitrogen only in 

 two forms, either as dissolved atmospheric air, or as 



8 



