VARIATIONS OF THE WATER-BALANCE. 67 



On Aug:ust 1, 1909, 85 c.c. of water were necessary to replace loss from 

 water-system, after which the weigfht of the entire preparation was found 

 to be 25.445 kg-., indicative of a loss of 355 grams in 47 days, at a rate of 

 nearly 7.5 grams daily. 



On October 1, 1909, 135 c.c. of water were necessary to replace loss in 

 water-system, after which the preparation weighed 25.215 kg., showing a 

 loss of 720 grams in 88 days, at a rate of over 8 grams daily. The column 

 of water in the inverted U-tube was broken. 



On October 5, 1909, the U connection with a vessel of water was 

 removed to the top of the bougie, cleaned and fitted with soft wax, filled 

 with water, and a g-lass cover put on, which was sealed by the wax. The 

 preparation now weighed 23.410 kg. 



On October 16, 1909, 35 c.c. of water were needed to refill the bougie to 

 zero. After this was done the weight of the preparation was 23.410 kg., 

 or exactly the same as 11 days earlier. The loss from the outer surfaces 

 of the plant had therefore been balanced by the amount withdrawn from 

 the clay cylinder. 



In order to test the behavior of an Echinocactus freshly taken from 

 the soil, a specimen with the main root bent at right angles was taken up 

 on February 18, 1910, and it was found to weigh 49.390 kg. After trim- 

 ming, the greatest diameter, measured in the plane of the bent root, was 

 41.3 cm. and the greatest length 58.5 cm. The plant was now supported 

 in its original position on a base of loosely piled rocks, where it would be 

 exposed to the full effects of the sun and wind. 



On May 12, 1910, the weight had decreased to 36.900 kg., showing a 

 loss of 12.490 kg., or nearly 25 per cent of the total in 84 days, at a daily 

 rate of 148.7 grams. This was the most rapid depletion noted during the 

 entire investigation. The length had decreased from 58.5 cm. to 56 cm., 

 and the thickness from 41.3 cm. to 37 cm. The shrinkage therefore was 

 equivalent to a hollow cylinder with closed ends, the walls of which were 

 22 mm. in thickness, the ends 33 mm. in thickness, with a length of 58.5 

 cm. and a diameter of 41.3 cm. 



OPUNTIA SP. 



The flattened joints of Opuntia are known to carry a water-balance and 

 to exhibit such slow transpiration that joints have survived in dry rooms 

 for many months, or even as long as 2 or 3 years, and it was deemed 

 important to ascertain the rate of loss of water for brief periods. This was 

 done with great care by Mrs. E. S. Spalding. Terminal joints of plants 

 growing near the Desert Laboratory were taken, being cut off at the nar- 

 rowest part of the constriction by which they were joined to the part below. 

 The cut surfaces were sealed with grafting-wax and exposures arranged 

 as below. Table 24, on the following page, is a record of the losses in No. 1 . 



