RESPIRATION OF PLANTS 



101 



and water. This supposition has been abandoned because 

 during respiration alcohol is oxidized less readily than sugar. 

 The process is now commonly supposed to take place in the 

 following way: Under the influence of zymase, which is always 

 present in cells, some intermediate products of alcohohc fermenta- 

 tion are formed first; the subsequent fate of these products is 

 varied. Alcohol and carbon dioxide are formed from them when 

 oxygen is lacking. In the presence of oxygen, they break down 

 to carbon dioxide and water before alcohol has been formed. 



The interrelations between anaerobic and normal respiration 

 in the presence of oxygen may be represented in the following 

 scheme, according to Blackman: 



Normal hexoses 



i 



Activation in presence of phosphoric acid 



i 



[Active hexoses| 



i 



Glycolase 



i 



Intermediate products — 

 pyruvic acid, aldehydes 



Further disintegration in 

 an anaerobic medium 



i 



Oxidation in an aerobic 

 medium 



i 



CO2 + alcohol 



CO2 + H2OI 



According to this scheme, based principally on the works of 

 Palladin and Kostytchev and their coworkers, respiration must 

 be viewed as the sum of fermentative processes, which may be 

 divided into three phases: (1) The activation of normal inactive 

 sugars and their transformation into an active form, realized 

 in the presence of phosphoric acid and the enzyme phosphatase; 

 (2) glycolysis, i.e., the disintegration of active hexoses with the 

 formation of very unstable intermediate products of the type 

 of pyruvic acid, glyceric aldehyde, etc., brought about by 

 enzymes of a desmolytic character; and (3) oxidation of these 

 products by oxygen of the surrounding medium through oxida- 

 tion enzymes. 



