THE CHEMICAL PROCESSES IN PLANT RESPIRATION 1 23 



understood through the fact that the relative value of various 

 sources of carbon depends on the ease of conversion into fer- 

 mentable sugars. Kostychev^ has identified as glucose the 

 sugar formed from tartaric acid, glycerine, quinic acid and 

 lactic acid. Fructose appears to accumulate on mannite 

 solutions. 



In this way fermentable sugars represent the usual material 

 for respiration. However, there seems to be another kind of 

 plant respiration — that at the expense of the protein of the 

 protoplasm, a type found in starving cells. At the same time 

 it must be emphasized that this has nothing to do with that 

 assumed in Detmer's theory. Detmer assumes a dissociation 

 and oxidation of protoplasmic protein even under conditions 

 in which a direct analysis shows only the consumption of sugar. 

 A destruction of the protein material in the presence of sugar 

 is purely hypothetical, whereas Detmer attempts to explain the 

 normal type of plant respiration by this theory. Actually a 

 noticeable respiration of protein only occurs with a deficiency 

 of sugar, as in etiolated bean leaves.- Respiration is thereby 

 considerably weaker than under normal circumstances. 



Kostychev and Afanassjewa^ have found that Aspergillus 

 niger, fed with peptone as a source of carbon, behaves peculiarly. 

 In the absence of oxygen neither sugar nor alcohol is formed in 

 peptone cultures. Afterwards these cultures are to all appear- 

 ances generally free from zymase, since they do not ferment 

 added sugar. It has already been pointed out that zymase is 

 formed in these cultures only after a brief exposure to air in the 

 presence of sugar. 



Since peptone cultures of Aspergillus niger liberate CO2 in the 

 absence of oxygen but form neither sugar nor alcohol, we may 

 suppose that the oxygen respiration of these cultures is peculiar 

 and differs in principle from the normal sugar respiration. On 

 the strength of these results Kostychev assumes that there are 

 two kinds of plant respiration — "sugar respiration" and 

 "protein respiration." The former is the usual type and 

 proceeds by means of the participation of enzymes of alcoholic 



' Kostytschew, S. loc. cit. 



- Palladin, W. Rev. gen. de bot. 5: 449. 1893; 6: 201. 1894; 13: 18. 1901. 



'Loc. cit. 



