THE GENERAL CHEMISTRY AND PHYSICS OF PLANT- LIFE. 255 



by Engelmajtn's interesting bacterial experiments, which confirmed 

 the old theory of Lommel. We shall now return to the nitrogenous 

 foods. 



The following are natural sources of nitrogenous compounds. 



1. The electric spark passing through dry air produces NO; this 

 immediately unites with the O of the atmosphere and forms NO, ; 

 the latter unites with water to form nitric acid : 



NO 



O NO, 

 H 



NO, 



HO 



2. In various processes of combustion ammonium nitrite and 

 ■ammonium nitrate are formed (NH.NO, , NH^NO,). 



3. Ever since animal creation the decay of animal substances 

 has been the source of important nitrogenous compounds, especially 

 NH3 (ammonia). Connected with this process of ammonia-forma 

 tion is 



4. The production of saltpetre (potassium nitrate), as follows : 

 NH3 takes up O in the presence of an alkali ; that is, the oxidation 

 of NH3 forms a nitrate, as KNO, , NaNOj ; the latter occurs very 

 plentifully in Chili. 



The formation of albuminous substances in the plant has already 

 been discussed. 



Mineral Food-substances. — The essential minerals are K, Ca, 

 Mg, Fe (S and P were mentioned above). The agricultural impor- 

 tance of phospliate of lime, of the sulphates, and of the lime-salts are 

 well known. CI, Na, and Si are useful, though not necessary. 



The true use of K. that is, of its compounds, is still unknown; 

 it always seems to be concerned in the translocation of plastic 

 materials. It is probable that Ca plays a part in the formation of 

 cell-walls. Mg seems to be distributed much in the same manner 

 as K. Of Fe we know definitely that it is necessary to the forma- 

 tion of chlorophyll. (This seems to be the reason why fungi can do 

 without it.) 



According to the recent investigations of F. W. Schimpee, Ca 

 serves as a vehicle for the mineral acids, especially phosphoric and 

 sulphuric acid ; it furtliermore prevents poisoning by preventing 

 the accumulation of acid calcium oxalate.' 



Flora, 1890. 



