264 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



bacteria are apparently also capable of taking up atmos- 

 pheric carbon dioxide or carbon dioxide in solution and 

 utilizing the energy secured by oxidation of inorganic com- 

 pounds to assimilate the carbon dioxide into their own 

 protoplasm. Such organisms have already been noted 

 among the so-called nitrifiers, the energy secured by oxida- 

 tion of ammonia, for example, being in part used for the 

 reduction of carbon dioxide and the production of organic 

 carbon compounds. 



Microorganisms in general (as well as animals) possess 

 the ability to break down complex compounds of carbon, 

 securing growth energy by their oxidation, and giving off 

 carbon dioxide continuously. In the main, therefore, the 

 carbon cycle consists in manufacture of carbon compounds 

 by green plants and their oxidation not only by these plants 

 but also by animals and microorganisms. 



Under certain anaerobic conditions, microorganisms may 

 attack carbon compounds, evolving hydrogen and carbon 

 dioxide. In general the carbohydrates have the empirical 

 formula CnH^nOn- ^ * s apparent, therefore, that if free 

 hydrogen gas is given off together with carbon dioxide that 

 there will be a residuum of carbon. Apparently changes 

 of this kind have been responsible for the formation of peat 

 and of coal. 



Production of Carbon Dioxide in Soil by Microorgan- 

 isms. Practically all of the aerobic bacteria and many of 

 the anaerobic bacteria produce carbon dioxide in the decom- 

 position of carbonaceous material. It is, therefore, constantly 

 being produced in the soil, and is of considerable significance 

 there. A large proportion of the carbon dioxide evolved 

 escapes in the air, some portions are dissolved in the soil 

 water and in part may be taken up by plant roots. It is 

 evident that the soil solution must, under most conditions, 

 be practically a saturated solution of carbon dioxide. This 

 exerts a marked solvent action upon many of the minerals 



