THE CHEMICAL PROCESSES IN PLANT RESPIRATION lOI 



means of various transformations, pyruvic acid, which is then 

 spKt by carboxylase into acetaldehyde and carbon dioxide. 

 CH3— CO— COOH = CH3— CHO + COo 

 The acetaldehyde is then reduced to ethyl alcohol. Hence 

 it is clear that in alcoholic fermentation the CO2 and alcohol 

 do not arise simultaneously. This explains how the ratio 



comes to be abnormal in some plants. It can be so 



CO2 



C2H5OH 



because the acetaldehyde either unites with other substances 

 or becomes inaccessible before reduction through the eventual 

 formation of aldol or by similar alterations. These side reac- 

 tions could also be brought about through the checking of the 

 reducing forces which, in the case of normal fermentation, 

 induce a change of aldehyde to alcohol. This checking could 

 be evoked by means of oxidising agencies and indeed by the 

 oxidation of the hydrogen necessary for the formation of the 

 alcohol. The circumstance is worthy of note that particularly 

 in plants in which there are powerful oxidative processes and in 



r CO2 



which loosely bound oxygen is contained, the value of p;;tj"qjj 



is found to be abnormal in the absence of oxygen. In actual 



CO 



practice the ratio t^Tt^t? for aerobic molds is always the same 



as for normal yeast fermentation. On the other hand, a con- 

 siderable part of the sugar consumed by molds in the absence 

 of oxygen is not made into CO2 and alcohol but into other sub- 

 stances, the nature of which has not been estabhshed at the 



present time. 



CO 



The abnormal size of tt^et^li in the case of the anaerobic 



C2XI5UXI 



working-up of sugar may often be traced to the fact that in 

 some plants acetaldehyde, the intermediate step in the forma- 

 tion of alcohol, is not reduced to alcohol but is consumed 

 in another manner. 



Apparently all cases in which neither the working-up of sugar 

 nor the presence of zymase is demonstrable are to be explained 

 otherwise. Thus Kostychev and Afanassjewa^ found that 



1 Kostytschew, S. und M. Afanassjewa. Jahrb. f. wiss. Bot. 60: 628. 1921; (f- also 

 Kostytschew, S. Z. f. physiol. Chem. iii : 236. 1920. 



