VARIATIONS OF THE WATER-BALANCE. 



47 



A second young- plant, specimen No. la, was taken from the soil near 

 the Desert Laboratory on October 22, 1909, and the root-system neatly cut 

 away, after which it was fitted to a metal stand weighing 7.315 kg-., the 

 whole preparation giving a draft of 52.640 kg., which would make a net 

 weight of 45.325 kg. for the plant. It was then put in a laboratory room. 

 The data obtained are shown in table 13. 



The plant with its mounting was now removed to the open, where it 

 was exposed to the full action of wind and sun. The conditions of expos- 

 ure were such as to be fairly equivalent to those of a plant on a rocky slope 

 during the same period. . 



On May 13, 1910, the gross weight of this plant had fallen to 42.675 kg. 

 by a loss of 5.535 kg. The rate of depletion was 117 grams daily in No- 

 vember, immediately after it had been taken from the soil; 7 grams daily 

 during December; 15.5 grams daily during January; 5.5 grams daily dur- 

 ing the early part of February indoors; and 66.5 grams daily in the open 

 during a period of 83 days from February 19 to May 13, 1910. A compari- 

 son with the results pre-viously described shows that the rate of loss in the 

 open was between two and three times as great from plants in the open as 

 from others in shaded rooms. It is of interest to note that the rate of de- 

 pletion from the sahuaro in the open was less than that of an Echinocactus 

 taken up at the same time. 



Table 14. — Analyses of sahuaro trunks at different dates. 



Specimen. 



No. I 



No. 2 (2.5 meters high) 

 No. 3 (3 meters high) . 

 No. 4 



Specific 

 gravity 

 of sap. 



1.023 

 1.022 

 1.020 

 I.0145 



Acidity 



as H2SO4 per 



100 c.c. 



0.187 



•ISO 

 .181 

 .1619 



Total 



solids per 



100 c.c. 



gms. 

 S-924 

 S-3S2 

 4.512 



3-434 



Asli- 



content per 



100 c.c. 



gms. 



I-SS6 

 1.740 

 1.724 

 1.002 



A terminal section of a trunk of a plant which was growing in the open 

 was obtained late in the foresummer, June 15, and the analysis yielded 

 the data shown in table 14, opposite the line No. 1. 



A heavy rain on June 26, 1909, ended the dry foresummer and two 

 small sahuaros were taken, two days later, to the chemical laboratory for 



