56 



ACIDITY AND GAS INTERCHANGE IN CACTI. 



TABLE 29. Respiration in relation to acidity. Opuntia versicolor. 



Samples were taken during the morning and afternoon, directly from the plant in the open. 

 The respiration in darkness was determined by the Pettenkofer apparatus and at the same 

 time the acidity was recorded. The acidity is given in cubic centimeters of N /10 alkali and 

 the respiration rate in milligrams of COa per hour. The material used was of the previous 

 season's growth and turgid. The experiments were conducted at Tucson, Arizona, in 

 July 1912. 



TABLE 30. Respiration in relation to acidity. Opuntia versicolor. 



Similar to the preceding series, except that the material used was young. The joints were 

 very turgid and had well-developed leaves. The work was done at Tucson, in July 1912. 



