TRANSPIRATION AND TEMPERATURES 39 



to allow the plant to recover from the shock of handling, to which it 

 had been subjected. 



At the beginning of the experiment the apparatus stood in the shade 

 of a small pitiyon tree with a fitful movement of the air at a temperature 

 of 80° F. During the first few minutes of the observations in which 

 equalization of the negative pressure was in progress, the time in which 

 a unit (100 miUigrams) of water was taken up was as follows : 40, 

 45, 42, 48, 47, 50, 50, 50, 50, 50, 50 seconds, or at the rate 

 of 2 to 2.5 milligrams per second. Half an hour later, at 10.30 

 A. M., after the negative pressure had been equalized tests were made 

 in the open, with the sky clouded, and the air at a temperature of 84" 

 F. The periods in which 100 milligrams were absorbed were 75, 70, 

 80, 85, 85, 90, and 95 seconds, giving a rate of 1.05 to 1.4 milligrams 

 per second. With continued cloudiness, and the air at a temperature 

 of 88° F. beginning at 10.50 A. M., the periods were 75, 75, 60, 70, 

 70, 75 seconds or at a rate of 1.3 to 1.4 milligrams per second. The 

 sun emerging from the clouds the readings of 400 milligrams in 150 

 seconds, 400 milligrams in 210 seconds, and 300 milligrams in 150 

 seconds were taken, giving an average rate of 1.9 to 2.2 milligrams 

 per second. With the return of the clouds immediately afterward the 

 readings were 400 milligrams in 210 seconds, 500 milligrams in 330 

 seconds, 900 milligrams in 600 seconds, or an average rate of 1.9 milli- 

 grams per second, decreasing to 1.5 per second as the effects of the 

 cloudiness were felt. The rate again rose to 1.8 and 1.9 milligrams 

 per second as the sun emerged from the clouds. 



Experiment 2, Artemisia sp. was used in this test. It is a low 

 densely branching shrub with an extensive root system of the deeply 

 penetrating type. It stands nearl}^ inactive throughout the dry season, 

 taking on a quickened growth as demonstrated by the formation of 

 new shoots and reproductive organs within a month after the beginning 

 of the July rains. 



Amain branch with 30 branchlets about 12 inches long was fastened 

 to the potometer at 9 A. M., July 16, with the air temperature 75° F. 

 Readings of 700 milligrams in 17 minutes, 400 milligrams in 10 min- 

 utes were made with the sun obscured by clouds. In sunshine readings 

 of 1,100 milligrams in 25 minutes, 900 in 19 minutes, 500 in 12 minutes, 

 and 500 in 16 minutes were made with an average of .6 to .7 milli- 

 gram per second. The total area of the surface of the branch and 

 leaves was about 960 square inches. 



As a means of comparison similar tests were made with the same 

 piece of apparatus on moisture loving plants in the physiological labo- 

 ratory at the University of Minnesota. 



