EXPERIMENTAL DATA ON ACIDITY DETERMINATION. 



39 



TABLE 10. Diurnal range of acidity in turgid joints of previous season's growth, 



Opuntia versicolor. 



Acidity was taken at 2-hour intervals over a period of 26 hours. Two series were run, at 

 Tucson, April 11, 12, 1911, the material having all been collected at the same time and ex- 

 posed to the light and air. The day was clear and bright throughout, with a maximum of 

 28.5 C. at 3 h 30 m p. m. on April 11 and a minimum of 15.5 C. at 5 h 30 m a. m. on April 12. 

 The acidity is given in terms of N /10 alkali per gram fresh weight and pure juice, per cubic 

 centimeter. 



TABLE 11. Diurnal periodicity of turgid joints at least 1 year old from irrigated 



plant of Opuntia versicolor. 



The material had been collected 24 hours before use and had been placed in the dark con- 

 stant-temperature room at a temperature of 23 C., to accumulate as high an acidity as 

 possible. The acidity is expressed in terms of N/10 alkali per cubic centimeter of pure, 

 freshly extracted juice. After the first determination at 5 h 30 m a. m. the joints were placed 

 in full sunlight under as natural conditions as possible. The three series were made from 

 different plants, at Tucson, July 27, 1913. 



