56 



THE WATER-BALANCE OF SUCCULENT PLANTS. 



ECHINOCACTUS No. 4. 



On March 6, 1908, a small plant near the Desert Laboratory was taken 

 up and placed on a rock pedestal, as in the case of No.- 3. 



On November 5, 1908, shrinkag^e had occurred as in No. 3, and the 

 weight was found to be 795 grams. 



On December 8, 1908, the weight had increased to 838 grams, showing 

 an increase of 43 grams in 33 days. The tentative suggestions applied to 

 No. 3 are the only explanations that may be offered for this very notice- 

 able change. 



On May 21, 1909, the weight was found to be 752 grams, indicative of a 

 loss of 82 grams in 182 days. 



On June 15, 1909, the weight appeared to be 756 grams, an apparent 

 gain of 4 grams in 24 days, although the entire amount might be due to 

 error and the use of a different scale in making the determination. 



On August 1, 1909, the weight was found to be 728 grams, showing a loss 

 of 28 grams in 47 days, at a rate of nearly 0.6 gram daily, which is not far 

 below that of No. 3 during the same period in the constant-temperature 

 room, although the latter had a weight over six times as great. 



On October 16, 1909, the weight was 700 grams, showing a loss of 28 

 grams in 76 days. 



The rate was now scarcely half that shown in the early summer. 



Several records taken between November 8, 1909, and February 25, 

 1910, are given in table 17. 



Table 17. 



The preparation was now removed to the dark-room, with the temperature 

 at 58° F., and the relative humidity 62 per cent. 



On February 27, 1910, no change of weight could be detected. 



On March 3, 1910, the weight had increased to 678 grams, denoting an 

 increase of 2 grams in the 6 days in the dark-chamber. The preparation 

 was now brought into a well-lighted and ventilated room. 



On March 22, 1910, the weight was 670 grams, a loss of 8 grams in 19 

 days. The rate was greater than before being taken into the dark-room, 

 by reason of the advance of seasonal conditions. 



On April 21, 1910, the weight was 664 grams, a loss of 6 grams in 30 

 days, a daily rate of 0.2 gram. 



