62 



THE RELATION OF DESERT PLANTS TO 



Experiment XL This experiment was carried out with three Boer- 

 havias just coming into flower. The record was begun at 6 h 30 m p.m., 

 August 16, and discontinued at 9 l '30 m p.m., August 17. The total leaf 

 area of the three plants was 82.6 sq. cm. The average rate of water 

 loss from all three plants for the whole period was 0.7052 gram, or 

 0. 0085 gram per square centimeter of leaf surface. The usual curves are 

 given in figure 16. The period of the experiment was not long enough 

 to warrant any discussion further than to state that a single maximum 

 is shown at about 10 a.m., with a temperature of 79.5 F. and an 



evaporation rate of 0.035 

 gram. Minima are not 

 definitely shown within 

 the period. 



Experiment XII. The 

 subject was a single flow- 

 ering plant of Boerhavia 

 in a Stender dish standing 

 in the shade. The record 

 extended from 6 h 30 m p.m., 

 August 16, to 9 h 30 m p.m., 

 August 17. The leaf area 

 was not obtained. The 

 hourly rate of water loss 

 from the entire plant for 

 the whole period was 

 0.1926 gram. 



The ratio curve for this 

 plant need not be pre- 

 sented. It shows a max- 

 imum having a rate of 

 relative transpiration of 



0.158 at 7p.m., with a temperature of 73.5 F., and an evaporation rate 

 of 0.011 gram. Minima are not certainly indicated by the curve. 



Experiment XIILThe subjects were three flowering Boerhavia 

 plants standing in the shade. The record extended from 10 p.m., 

 August 18, to 8 h 30 m a.m., August 21, when wilting occurred. The total 

 area was 63.193 sq. cm. From 6 p.m. August 19 to the end of the 

 experiment the entire culture transpired at the average rate of 0.5860 

 gram per hour, or 0.0093 gram per hour per unit leaf surface. Only a 

 few weighings were made and a curve could not be constructed. 



Experiment XIV. The subject was a single plant of Boerhavia 

 standing in bright sunshine. The record extended from 6 a.m. to 



FIG. 15. Curve of relative transpiration for a plant 

 of Boerhavia, August 16-17, 1904. 



