VARIATIONS OF THE WATER-BALANCE. 53 



weight was seven times that of No. 2. Some of the excessive loss of No. 

 2 may be attributed to the fact that freshly-cut and hitherto unexposed sur- 

 faces were exposed to the action of dry air. 



On February 13, 1909, the weight was found to be 4.966 kg., indicating 

 a loss of 99 grams in 66 days, which is to be compared with a transpiration 

 of 232 grams by No. 1, which was now showing a decrease, presumably 

 owing to its long exposure to the evaporating action of the air. 



The preparation was now removed to the constant-temperature dark- 

 room, which stood at a temperature of 56° F. at this time. 



On August 1, 1909, the temperature had risen to 75° F., the maximum 

 of the year. The weight was found to be 4.872 kg., indicating a loss of 94 

 grams in 138 days in a chamber with no air-currents and a comparatively 

 high relative humidity (80 to 90 per cent). This would give a rate of 0.7 

 gram daily. 



On October 16, J.909, the weight was found to be 4.77 kg., indicating a 

 loss of 102 grams in 76 days. The temperature had now fallen to 71° F. 

 No new spines, as a result of growth, were to be seen in the apical region. 

 A registering hygrograph placed in the room for 48 hours gave a relative 

 humidity of 88 and 89 per cent. 



The actual amount of water-vapor in the air of the chamber probably does 

 not vary much during the year, and the relatively slight variation in the 

 temperature would make fairly constant conditions. The rate of loss was 

 therefore practically constant during a period of 8 months, showing that 

 transpiration in this case is a very direct reaction to external conditions. 



On February 19, 1910, the weight was 4.736 kg. and the thermometer 

 reading was 56° and 57° F., with humidity unchanged. 



The total loss of this plant during a year (371 days) amounted to 220 

 grams, or about 4.4 per cent of the original weight, when placed in the 

 constant- temperature chamber. 



On February 21, 1910, the weight was found to be 4.728 kg., after which 

 the preparation was set out in the open. 



On February 23, 1910, the weight was 4.716 kg., a loss of 12 grams in 

 2 days, which is not an excessive increase over the rate displayed in the 

 moist atmosphere of the equable dark-room. The exposure had resulted 

 in the blanching of the surfaces on the southern side of the plant. 



On March 23, 1910, the weight was 4.292 kg., a loss of 424 grams in 28 

 days, a rate of 15 grams daily. The blanched surfaces were now tinged 

 with red and the general condition of the plant was good, despite the great 

 length of time it had been deprived of water and the abrupt change from 

 equable conditions to the desiccating effects of the wind and sun. 



On April 21, 1910, the weight was 3.865 kg., a loss of 427 grams in 29 

 days, a rate of 15.7 grams daily. 



On May 13, 1910, the weight was 3.412 kg., a loss of 453 grams in 22 

 days, a daily rate of 20.6 grams. 



