VARIATIONS OF THE WATER-BALANCE. 



51 



ECHINOCACTUS No. 1. 



On March 4, 1908, a large plant in good condition growing among vol- 

 canic rocks near the stone reservoir of the Desert Laboratory on Tumamoc 

 Hill, at an altitude of about 800 meters, was taken up without injury, the 

 roots cut away cleanly, and the base seated on a wooden ring padded with 

 excelsior. This preparation was now placed on a platform scale in a ven- 

 tilated room in the laboratory. The gross weight was found to be 42.743 

 kg., or about 42 kg. net. A continuous record of the weight was kept for 

 16 months, and as it is the most complete of any series, the data are given 

 in full in table 15. The close observation to which this individual was 

 subjected made it evident that weights taken at longer intervals would 

 meet the requirements of the present investigation. It is to be noted that 

 a change of the preparation was made at the beginning of 1909, for which 

 a correction is necessary to show the difference between the earliest and 

 final weights. 



Table 15. — Record of weight of Echinocactus No. 1 for 16 months. 



*By adjustment of mounting. 



tBy adjustment of scale and mounting. 



tRoom heated. 



The specimen was dead when examined on September 20, 1909. 

 The daily rate of loss has been given in the nearest integer, except in 

 instances where the smaller differences were of critical value, as in calcu- 



