VARIATIONS OF THE WATER-BALANCE. 



63 



Records taken at several dates between November 8, 1909, and May 13, 

 1910, are given in table 22. 



Table 22. 



"Loss of weight by fruits, 200 gms.; loss of weight by transpiration 

 585 gms., at the rate of 42 gms. daily. 



During- the six months ending May 12, 1909, the average rate of loss was 

 found to be 38 grams daily, and must have been much higher than this 

 during the later part of the period. From the results of the last obser- 

 vation it is to be seen that the rate fell to ISgTams daily during May, 1910, 

 by reason of the depletion of the water-supply. 



The amplitude of fluctuation of which such plants are capable is well 

 illustrated by the summarized observations made on this individual. The 

 original weight, with mounting, 17.339 kg., when taken from the soil 

 November 7, 1908, was decreased by 4.840 kg. by May 12, 1909. After 

 being set out in the soil until October 12, 1909, it absorbed water and 

 made growth, bringing the weight up to 20.370 kg., which is to be con- 

 trasted with the minimum weight of 11.370 kg. The final minimum, as 

 shown in the last observation, was 13.335 kg- at a corresponding season 

 and after equivalent desiccation, so that an actual gain by growth of about 

 1.965 kg. of material between May, 1909, and May, 1910, maybe assumed. 

 The condition of the plant at the last observation indicated that a much 

 greater amount of water might be lost without serious injury. 



ECHINOCACTUS No. 10. 



On November 7, 1908, a healthy Echinocactus growing near the Desert 

 Laboratory was taken up, the roots trimmed, and placed on the base of 

 an upturned tin box. The total weight was 15.040 kg., and the net weight, 

 including 13 ripening fruits, 14.588 kg. The preparation was placed near 

 No. 9, and under practically the same conditions of exposure. 



On December 8, 1908, the weight was found to be 13.130 kg., indicative 

 of a loss of 1.910 kg. during 31 days, or at the rate of 61.6 grams daily. 

 Although much the smallest of the quartet of Nos. 7 to 10, the loss was at 

 a rate 10 times as great as that of No. 8, nearly 4 times as great as that of No. 

 7, and nearly 5 times as great as that of No. 6. But the most startling com- 

 parison is that with No. 1, it having lost water at a rate 60 times as great 



