46 THE WATER-BALANCE OF SUCCULENT PLANTS. 



plant had received no water included the most rig-orous part of the dry fore- 

 summer, with a relative humidity rarely exceeding 25 per cent, and stand- 

 ing at 7 to 10 per cent during the greater part of many days. Maximum 

 temperature of 112" occurred and the tissues exposed to the sun doubtless 

 reached 140° F. or even higher on some days. 



The summer rainy season now came on and the air was relatively moist 

 at times, but no water- vapor was taken in, since it has been shown by 

 Prof. V. M. Spalding that desert plants in general do not absorb water 

 in measurable quantity from the air. On November 4 the plant was ex- 

 amined and found to have developed three small roots which depended 

 downward among the large, loose stones of the support, but did not reach 

 the soil. All the cut surfaces had become calloused and the plant appeared 

 to be in a healthful condition, although subjected to the severest rigors 

 of the desert for six months. 



The difference between conditions in the open air and in an inclosed room, 

 not heated, being but little, except as to wind effects at this time of the 

 year, the plant was now removed to the laboratory. Its length was found 

 to be 148 cm. and the maximum distance between the center of any ridge 

 and the nearest one to it was 10 cm. It now weighed 32.518 kg. and was 

 set in a mounting, for convenience in handling, that brought the total 

 weight to 32.933 kg. December 8, 1908, 33 days later, the preparation 

 weighed 30. 783 kg. , showing a loss of 2 .050 kg. , or a rate of 62 grams daily. 

 On May 15, 1909, a year from the beginning of the experiment, an exam- 

 ination was again made. The length had shrunk from 148 to 140 cm., the 

 ridges now showing a maximum separation of but a trifle over 4 cm. and 

 the weight having fallen to 28.750 kg., giving a rate of loss for the period 

 of 23 grams daily. 



This plant had lost over 4 kg. of water in an inclosed room at compara- 

 tively low temperature during the six months ending in May, 1909, this 

 being accompanied by shrinkage in both length and diameter. 



The apical portion of the stem, 20 cm. long, was removed, and a complete 

 section 33 cm. long was then taken for examination in the chemical labor- 

 atory. The sap expressed from the tissues gave the following data: 



Specific gravity of sap as extracted i.03SS 



Acidity calculated as H2SO4 grams per 100 c.c. . .163 



Total solids in sap Do 9.622 



Ash-content of sap Do 2.754 



The tissues were distinctly moist to the touch, and the stump of the 

 plant, about a meter in length, was set in the soil under a lath shelter and 

 seemed normal in March, 1910. As may be seen, the proportion of inor- 

 ganic material was about 2.76 times as great as the normal (see data of 

 normal plant, page 47), indicating that the plant had lost over 57 percent 

 of its original weight, which may be estimated at 50.44 kg., and had given 

 off about 63 per cent of the water originally held in its tissues. 



