62 



THE CAEBOHYDRATE ECONOMY OF CACTI. 



less CO 2 at 40 than did A at 28, which had been exposed to air-tempera- 

 tures. C, on the other hand, evolved a relatively large amount of CO 2 at 

 28 after having been kept at 12. Kichards * found that the maximum 

 carbon dioxid production for Opuntia versicolor was quite definitely at 

 45. The analyses are given in table 27. 



TABLE 27. Analysis of joints of Opuntia phceacantha which had "been exposed to 

 different temperatures. Values in percentages of the dry material. 



The results from another series are given in table 28. 



Here the plants contained a relatively large amount of monosaccharides 

 and disaccharides to begin with. There were three sets of Opuntia joints : 

 One was analyzed immediately and represents the condition of the joints at 

 the end of the arid autumn, when the low temperatures had already affected 

 the carbohydrate content, but before the winter rains caused a further 

 decided increase in the simpler sugars. Of the two other sets of joints one 

 was kept for 35 days at 28 in the dark and the other for the same length 

 of time at 12. The analyses are given in table 28. 



TABLE 28. Analysis of joints of Opuntia phceacantha, original conditon and after 

 being kept for 35 days at 28 and 12, in percentages of the dry material. 



The proportional values of the various groups of carbohydrates are given 

 in table 29. 



1 RICHABDS, H. M. Acidity and gas interchange in cacti. Carnegie Inst. Wash. Pub. 

 No. 209, p. 49, 1915. 



