40 



ACIDITY AND GAS INTERCHANGE IN CACTI. 



TABLE 12. Diurnal periodicity of acidity of mature-turgid and mature-flaccid 

 and young joints with leaves of Opuntia versicolor. 



All material was direct from the plant at time of determination. In each group of three 

 the same plant was used. The morning determinations were taken between 9 and 10 

 o'clock; the afternoon determinations between 4 and 5 o'clock. Tucson, Arizona, July 29 

 to 31, 1912. 



