6 THE WATER-BALANCE OF SUCCULENT PLANTS. 



laboratory building-. The results of some series of measurements are ex- 

 pressed in the dia^ams (figs. 2 to 15) in which the movements of the ribs 

 were calibrated to one sixty-fourth of an inch, the amount of the ramfall 

 being expressed in vertical heavy lines. 



RAINFALL 



BY MONTHS, IN INCHES 

 I90a-TOTAL I7.A25 



1909 



JAN, FEB. MAR. APR. MAY JUME JULY AUG. SEP. OCT. NOV. DEC. I JAN, FEB. MAR, 



Fig. 1. — Curve of precipitation at Desert Laboratory, 1908-09. 



The flat opuntias, to which reference will be made later, were measured 

 with calipers; and although it was found to be impossible by this means 

 to obtain a high degree of accuracy, it was nevertheless possible to secure 

 data of value for comparison. 



