AEROBIC AND ANAEROBIC RESPIRATION. 



69 



acid disintegration which was advanced by the writer in an earlier paper/ 

 The acidity of these cacti in the morning is due essentially to the presence 

 of malic acid. The photolysis of malic acids yields through the loss of two 

 molecules of carbon dioxid from the carboxyl groups one molecule of ethyl 

 alcohol. 



COOH 

 CH 2 

 CHOH 

 COOH 



CH 3 



2CO a +| 



CH a 



OH 



As the photolytic disintegration of the malic acid proceeds there is thus 

 an accumulation of ethyl alcohol. 



Under anaerobic conditions there is a very active production of alcohol 

 in the cacti. In table 33 are given the results of analyses of plants of 



TABLE 33. Acidity and alcohol content of Opuntia versicolor after 

 being kept in air and oxygen-free atmosphere. 



Opuntia versicolor which were kept in an atmosphere freed of oxygen in the 

 manner previously described. 



The normal amount of alcohol is very small in Opuntia versicolor. In 

 the course of normal respiration in the dark this quantity does not increase, 

 although the acidity rises very much. When kept in an atmosphere freed 

 of oxygen large quantities of alcohol are formed; there is also some acid 

 formation, but this is not nearly so great as in air. It is very noticeable 

 that due to the higher rate of sugar consumption under anaerobic condi- 

 tions, the water-content of plants kept under such conditions is finally much 

 higher than in those kept in air. 



* SPOEHB, H. A. Blochem. Zeitsch., 57, 106, 1913. 



