66 



THE WATER-BALANCE OF SUCCULENT PLANTS. 



Table 23. 



*Cloudy, cool. 



Hitherto the preparation had stood in a gflass-house at a temperature 

 practically the same as in the open air, but without as much exposure to 

 air-currents. It was now removed to an inclosed room, and, the fitting 

 seeming" to be in good condition, it was not disturbed. The tubing was 

 refitted and a receiver for water arranged to exclude evaporation from the 

 surface of the water in it. The entire preparation was placed on a bal- 

 ance and found to weigh 26.110 kg. on May 13. 



On May 17, 18 c.c. of water had been taken up, but the whole prepara- 

 tion now weighed but 26.065 kg., giving a transpiratory loss of 47 c.c. in 

 4 days. 



On May 21, 15 c.c. of water had been taken up, the preparation weigh- 

 ing 26.025 kg., indicative of a transpiration amounting to 40 c.c. of water 

 in 4 days. 



On June 5, 1909, the amount of water was not noted, but when the 

 receiver was filled to zero the preparation weighed 25.935 kg., indicative 

 of a transpiratory loss (net) of 90 c.c. in 15 days, which was slightly less 

 than the estimated rate for the previous period. 



On June 15, 1909, 22 c.c. of water was necessary to replace loss from 

 receiver, and the whole preparation, after this was done, weighed 25.800 

 kg., indicative of a total loss of 160 c.c. of water in 10 days. 



The transpiration at this time was greater than the amount taken up by 

 the artificial absorptive apparatus, although not as great as the capacity of 

 this device when it was first arranged. The contact with the fluid by this 

 apparatus when freshly put in place might well furnish better facilities for 

 taking in water than the root-system itself. But little doubt exists that in 

 the natural condition in the open air the echinocacti in the Tucson region 

 lose more water than they take from the soil during May and June, this 

 period being the arid foresummer, with its high temperatures, low relative 

 humidity, and great wind-flow. 



