SOURCE OF THE NITROGEN OF PLANTS. 69 



carbonic acid. In the process of putrefaction,, a 

 quantity of water, exactly corresponding to that of 

 the hydrogen, 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 propor- 

 tion to the quantity of oxygen which they contain ; 

 acids, therefore, yield more carbonic acid than 

 neutral compounds ; while fatty acids, resin, and 

 wax, do not putrify, they remain in the soil without 

 any apparent change. 



The numerous springs which emit carbonic acid 

 in the neighbourhood of extinct volcanoes, must be 

 regarded as another considerable source of oxygen. 

 Bischof calculated that the springs of carbonic acid 

 in the Eifel (a volcanic district near Coblenz) send 

 into the air every day more than 90,000 Ibs. of car- 

 bonic acid, corresponding to 64,800 Ibs. of pure 

 oxygen. 



ON THE ORIGIN AND ASSIMILATION OF 

 NITROGEN. 



We cannot suppose that a plant would 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 

 important question to be solved, therefore, is : 

 How and in what form does nature furnish 



