THE CHEMICAL PROCESSES IN PLANT RESPIRATION 143 



acids or from intermediate products of the synthesis of pro- 

 tein/ and the oxidation of the common plant acids represents 

 a process which is more like "protein respiration" than "sugar 

 respiration. " 



7. THE COORDINATION OF THE VARIOUS PROCESSES IN 



PLANT RESPIRATION 



From the previous statements it is evident that the normal 

 oxygen respiration of plants consists of various stages and so 

 represents a complicated process. The smooth course of proc- 

 esses as complicated as are those of alcoholic fermentation or 

 oxygen respiration is really to be traced to a remarkable coor- 

 dination of the reaction velocities of the several stages. This 

 is demonstrated by various known cases of disturbance of the 

 coordination in the case of plant respiration. According to 

 the ratio of the reaction velocities of the two most essential 

 processes, the primary anaerobic cleavage and the subsequent 

 oxidation, the following types of plant respiration are possible: 



First Case. — The amount of zymase in the plant cells is 

 extremely large in comparison with the quantity of the oxidis- 

 ing enzymes. For that reason the velocity of the primary 

 cleavage of sugar is greater than the velocity of the subsequent 

 oxidation. Consequently, part of the sugar attacked by the 

 enzymes of fermentation cannot be entirely consumed, even 

 with free access to oxygen. The labile, intermediate products 

 of the alcoholic fermentation become changed, under aerobic 

 conditions, into the stable form of alcohol and COo, since the 

 activity of the oxidising enzymes does not suffice to effect a 

 complete oxidation of all the products of fermentation. 



This is a solution of the problem of the effect of oxygen on 

 fermentation by yeast. Nageli- and Brown, ^ on the basis of 

 calculations not entirely free from objections, assumed a stim- 

 ulatory effect of oxygen on alcoholic fermentation but other 

 investigators such as Hoppe-Seyler, Pedersen, Hansen, and 



' For the formation of acids during the germination of plants cf. Windisch und Dietrich. 

 Wochenschr. f. Brauerei. 35: 159- 1918; Liiers, H. Biochem. Z. 104: 30. 1920. 

 - Nageli, C. v. Theorie der Garung. 1879. P. 18. 

 'Brown, A. Jour. Chem. Soc. (London) i: 369. 1892. 



