68 THE CARBOHYDRATE ECONOMY OF CACTI. 



few drops of toluene, the bottle was immediately attached to the aeration 

 train. The alcohol was removed from the juice by forcing a stream of air 

 through the solution and absorbing the alcohol which is thus distilled over 

 in concentrated sulphuric acid. 



The arrangement was as follows : The air passed first through a solution 

 of sulphuric acid and potassium bichromate, then through a safety bottle, 

 whereupon it was forced through the plant juice, another small safety bottle, 

 and then through two small absorbing cylinders containing concentrated 

 sulphuric acid. The air was passed through this train for 24 hours. The 

 sulphuric acid was then transferred to a distilling flask connected with a 

 condenser and receiving vessel. By means of a dropping-funnel a 2 per 

 cent solution of potassium bichromate was added to the sulphuric acid. 

 The warm mixture in the distilling flask was allowed to stand for 15 to 20 

 minutes in order to complete the oxidation of the alcohol to acetic acid, and 

 then distilled until no more acid came over. A thermometer was kept in the 

 solution and the temperature was not allowed to rise over 112. It was 

 found that at higher temperature there is danger of sulphuric acid being 

 carried over. The solution can be distilled until the distillate is neutral to 

 litmus by adding 25 c. c. of boiled water from time to time to prevent the 

 solution from becoming too concentrated. The distillate was made up to a 

 definite volume and titrated with 0.1 normal potassium hydroxide. 



As has been stated, the nocturnal respiration of the cacti is characterized 

 by the formation of acids. This acidification is the result of restricted 

 oxygen supply. The question arises, then, whether under these conditions 

 there is also formation of alcohol that is, whether the course of respiration 

 is so affected as to radically change the mode of the process. For this 

 purpose Opuntia versicolor joints were collected in the morning and in the 

 evening, and acidity and alcohol determinations made in the usual manner. 

 The results are given in table 32. 



TABLE 32. Diurnal variations in the acidity and alcohol content of Opuntia versicolor, 



May 7-8. 



There is evidently no accumulation of alcohol in these plants during the 

 night time coincident with the nocturnal acidification. It seems highly 

 improbable that this form of respiration can be regarded as being of intra- 

 molecular nature. It was observed, however, that there was a distinct 

 increase in the alcohol-content of these plants after they had been exposed 

 to sunlight for some time. This fact serves to substantiate the theory of 



