14 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



etc. The course of growth of joints Nos. i, 2, and 3 at Tucson 

 and of Nos. 4, 5, 8, and 12 at Carmel iUustrate the widely ranging 

 intensities of environmental conditions at the first-named place 

 and the equable climate of the second. 



Fig. I. Measurement of variations in length of mature joint of Opuntia with 

 precision auxograph. The mercurial thermometer may be read at convenient intervals 

 for actual temperature of the joint while air temperatures are recorded by a thermo- 

 graph. 



The record of No. 5 {Opuntia Blakeana) of the auxanometric 

 series may be used as a guide to the discussion of the growth 

 phenomena of a Hat joint of opuntia. This joint was put in 

 bearing with an auxanometer kner on March 27, 191 5, when 

 its length was 17 mm. With the exception of brief intervals 

 necessary for readjustment of instruments, the history of the 

 developmental enlargement of this joint to ten times this length 

 was comi^letely recorded for a period of 63 days. At the end of 

 this pericjd the net increase in length became very small and the 

 variations in length were of the type displayed by a mature joint. 



