I02 PLANT RESPIRATION 



peptone cultures of Aspergillus niger give off COo in the absence 

 of oxygen but do not produce the smallest amount of alcohol. 

 In this case the lack of formation of alcohol is probably due to 

 the absence of zymase, because peptone cultures of Aspergillus 

 niger do not work up added sugar in the absence of oxygen. 

 After a short stay on sugar solutions with access to oxygen pep- 

 tone cultures do produce considerable amounts of zymase and 

 so gain the power to ferment energetically sugar to CO2 and 

 alcohol in the absence of oxygen. It can hardly be doubted 

 that in the cases before us the anaerobic respiration took 

 place in the absence of sugar at the expense of the cleavage 

 products of the protein and so presented an entirely different 

 process from alcoholic fermentation. In other plants also 

 there occurs, under certain conditions, such a cleavage of 

 COo from nitrogenous products of protein hydrolysis sim- 

 ultaneously with alcoholic fermentation that the total excre- 



CO2 



tion of CO2 is considerably increased and the ratio ^^^-r-r^yTj 



attains an abnormal value. 



2. THE NATURE OF THE OXIDATION PROCESSES IN PLANT 



CELLS 



Before we seek to define more closely the connection of the 

 anaerobic cleavage processes with the subsequent oxidation of 

 the cleavage products, the foundations of biological oxidation 

 in plant cells must be discussed. 



It is acknowledged that Lavoisier was the first to prove that 

 oxidations are to be traced to the fixation of oxygen. Later 

 investigations by various workers showed that autoxidations at 

 the expense of molecular oxygen often introduce compHcated 

 processes, because the absorption of atmospheric oxygen by 

 autoxidisable substances is not uncommonly accompanied by 

 the oxidation of compounds which of themselves do not fix 

 molecular oxygen at all or only very slowly. Thus phosphine 

 is quickly oxidised by atmospheric oxygen. With it there 

 easily occurs a simultaneous oxidation of indigo white which 

 of itself proceeds slowly and incompletely. Analogous phenom- 



