44 



ACIDITY AND GAS INTERCHANGE IN CACTI. 



TABLE 18. Acidity in diminished and increased oxygen supply of old and young joints of 



Opuntia versicolor. 



Acidity is shown in terms of cubic centimeters of N /10 KOH per cubic centimeter juice. 

 Experiments kept in darkness. Tucson, Arizona, July 1912. 



1 Material for this and three subsequent experiments were collected several days before using. 

 Kept in dark, relatively cool place. 



2 Material for this and all subsequent experiments were freshly collected. 



TABLE 19. Acidity in diminished and increased oxygen supply in Opuntia versicolor, material 



taken at time of low acidity. 



Material was taken at time of low acidity to test the effect of the conditions upon possible 

 rise of acidity. The experiments were kept in darkness. The series was carried through 

 in July 1912 at Tucson. (For further details see table 18.) 



TABLE 20. Acidity in diminished and increased oxygen supply, with material exposed to 



diffuse light during daytime. 



The material (Opuntia versicolor) exposed to diffuse light during daytime. The experi- 

 ments were made in July 1912 at Tucson. (For further particulars see preceding series.) 



