184 PLANT PHYSIOLOGY 



CO2 + 2H2S = CH2O + H2O + 2S. 



There is no liberation of oxygen during this process. Besides 

 nitrifying and sulphur bacteria, there is a series of microorgan- 

 isms, the iron bacteria, which obtain energy from the oxidation 

 of ferrous iron. These bacteria also were originally described 

 by Vinogradsky. They oxidize ferrous ion Fe++ to ferric ion 

 Fe+++. Most organisms of this group belong to filamentous 

 types, such as the genera Leptothrix, Crenothrix, etc. Their 

 role in nature is exceedingly important. Their activity explains 

 the formation of bog iron ore, large accumulations of iron oxide 

 that occur in marshes and lakes. Some of these bacteria, how- 

 ever, are capable of using organic substances and thus in contrast 

 to nitrifying bacteria do not represent obligate autotrophic 

 organisms. Many of them are capable of oxidizing not only 

 ferrous but also manganous ions. 



43. The Chemical Reactions of Photosynthesis. Theories of 

 Baeyer, Willstatter, and Warburg. — Although the equation for 

 photosynthesis can be written thus, 



6CO2 + 6H2O -> C6H12O6 + 6O2, 



and although no intermediate compounds have been demon- 

 strated, still this simple equation must undoubtedly proceed 

 through several steps. This is confirmed by the great com- 

 plexity of the carbohydrates formed, which certainly cannot 

 arise directly from such simple substances as CO2 and H2O; and 

 further, the picture of photosynthesis is obscured by the diffi- 

 culty of the reduction of such a stable compound as carbon 

 dioxide. It has already been seen what great difficulties the 

 analysis of the separate respiratory reactions involves. Photo- 

 synthetic reactions are still more comphcated, for, in addition, 

 light energy participates in the dynamics of the chemical proc- 

 esses. It is not surprising that as yet there is very little known 

 of the separate phases of the process of photosynthesis and that 

 there are several theories that are not completely coordinated. 



One of the facts that should form the basis of every theory 

 of photosynthesis is the nearly complete equality always observed 

 in the volumes of the gases, oxygen and carbon dioxide, inter- 

 changed in photosynthesis. 



Carbohydrates must always be the products of photosynthesis, 

 because the proportion O2 to CO2 can be equal to unity only 



