58 



THE WATER-BALANCE OF SUCCULENT PLANTS. 



The average estimated loss of No. 5 durinsf this winter period was 

 nearly 13 grams daily. 



The preparation was dismounted and the tissues around the more exter- 

 nal part of the clay cylinder were found to be blackened and decayed. 

 Doubtless this disintegration of the tissues had acted to decrease absorp- 

 tion, which, in the beginning of the experiment, was carried on at a rate 

 that would soon have replaced the loss of the previous summer. 



ECHINOCACTUS No. 6. 



On November 7, 1908, a large Echinocactus was taken from the bajada 

 west of Tumamoc Hill, the roots trimmed neatly, and the plant was found 

 to weigh 28.573 kg. It was put on a mounting weighing 1.149 kg., the 

 preparation thus amounting to 29.722 kg. The crown bore 17 ripening 

 fruits, which were carefully noted at each observation, as given below. 

 The preparation was placed in the room with No. 1. 



On December 8, 1909, the weight was found to be 29.310 kg., indica- 

 tive of a loss of 412 grams in 31 days, or a rate of 13 grams daily. The 

 daily rate of No. 1 for the same period was but 1 gram daily. Doubtless 

 some of the excessive rate of No. 6 during this period may be ascribed to 

 loss from the freshly wounded surfaces from which the roots were cut. 

 Other and unknown causes must have contributed to a total action by 

 which the rate of transpiration in the open was thus maintained after 

 being brought under shelter, as was noted in No. 5. 



On May 12, 1909, one fruit had been lost and the weight was now 

 28.360 kg., which indicated an estimated water-loss of about 935 grams in 

 155 days, an average rate of 6 grams daily. 



On June 12, 1909, the weight was 28.055 kg., indicative of a loss of 

 305 grams in 31 days, at a rate of nearly 10 grams daily. 



On August 1, 1909, the weight was 27.585 kg., indicating a loss of 470 

 grams in 47 days, maintaining the rate set up in the arid foresummer of 

 the previous period ; 16 fruits were still present. 



