1915] LONG—GROWTH IN CACTI 497 
The swelling of the /ess acid sample is much the greater, and the 
difference is too great to be explained on the ground of increased 
osmotic pressure due to the day’s transpiration. This result 
corresponds to those recorded above which had to do with pieces 
of the plant in acid and neutral solutions, and may be interpreted 
as possibly throwing light on the varying diurnal growth rate. 
DESERT LABORATORY 
Tucson, Ariz. 
