124 PLANT RESPIRATION 



fermentation. The latter is only started after stoppage of the 

 supply of carbohydrates, and takes place without manifestation 

 of the enzymes of fermentation. The chemical side of the 

 material transformations which proceed thereby is at present 

 wholly unknown. Peptone cultures of molds are a favorable 

 research material to use in the study of protein respiration, 

 since they are entirely free from sugar yet are not studied in 

 the starving condition. 



4. THE NATURE OF THE CONNECTION BETWEEN THE AN- 

 AEROBIC CLEAVAGE PROCESSES AND THE SUBSEQUENT 

 OXIDATION OF THE CLEAVAGE PRODUCTS 



This question can only be discussed in relation to the "sugar 

 respiration" since the chemical side of "protein respiration" 

 is still entirely unknown. 



It is hardly to be doubted that in the case of plants which 

 respire at the expense of sugar, anaerobic respiration is essen- 

 tially an alcoholic fermentation. It has been pointed out already 



CO 



that the value of ^^r j r\T^ often does not correspond to that 



LoIlsUrl 



of alcoholic fermentation by yeast. In all these cases there 



is a surplus of CO2. In extreme cases the formation of alcohol 



is entirely suppressed. These conditions may be explained as 



follows : 



I. Protein respiration takes place simultaneously with sugar 

 respiration. In peptone cultures of Aspergillus niger all the 

 CO2 produced in the absence of oxygen is due to protein respira- 

 tion. With some other plants probably part of the CO2 is 

 formed from cleavage products of proteins in the absence of 

 oxygen. 



CO2 



II. The abnormal value of ^ Vj r\u depends on the fact that 



(^2il5Uri 



either part of the alcohol formed disappears as a result of ester 

 formation and similar processes, or the preliminary stage of 

 alcohol formation is somewhat irregular and consequently 

 products other than ethyl alcohol appear. . 



It is thus evident that the first phase of sugar respiration is 

 usually nothing but alcoholic fermentation. Now Kostychev^ 



1 Kostytschew, S. Biochcm. Z. 15: 164. 1908; Jour. d. russ. hot. Ges. 1: 182. 1916. 



