VARIATIONS OF THE WATER-BALANCE. 



69 



except that the time was a month later than that when the weig-hings of No. 

 2 were made, so that the temperature was higher and the air probably drier. 

 Table 26 gives the rates of transpiration of the two. 



♦Original weight of No. s> 140.38s gms. 

 fOriginal weight of No. 6, 206.070 gms. 



In the 37 days during- which the weighing-s were being made, No. 5 lost 

 one-ninth and No. 6 one-tenth of its entire weight, while it required No. 

 2, which was left indoors, 77 days to lose one -tenth of its weight. 



MICRAMPELIS FABACEA. 



On November 10, 1908, a large tuber of Micrampelis fabacea which had 

 been taken from the ground at Carmel, California, packed in straw, and 

 shipped to Tucson, was weighed after lying in a shaded room for a month, 

 and found to give 28.834 kg., and with a suspension harness 28.950 kg. 

 This was now placed in a room with a sahuaro and several echinocacti, being 

 subjected to the same conditions. 



On December 8, 1908, the weight was found to be 26.208 kg., showing 

 a loss of 2.742 kg., at a rate of 94 grams daily. 



On May 15, 1909, the weight was only 18.570 kg., indicative of a loss 

 of 7.630 kg., at a rate of 48 grams daily. Although the tuber had lost 35 

 per cent of its weight, or nearly 45 per cent of its total water-balance, its 

 tissues were still moist, cool to the touch, and alive. The growing-points 

 were capable of sending up vines. This plant would, however, rarely be 

 subjected to the temperatures and evaporating action of the Arizona desert 

 in its native habitat. When exposed to conditions of this character the 

 rate of water-loss was such that its desiccation would have ensued much 

 more quickly than in the cacti on which the observations were made. 



On October 19, 1909, the tuber having been allowed to dry out during 

 the summer, it became very hard and showed huge cracks. The weight 

 was now found to be 7.625 kg., showing a loss in weight of about 73.4 

 per cent, which would probably be increased to 75 per cent by the ordinary 

 methods of analysis in the laboratory. 



