EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. 99 



Two weeks before the experiment, three plants were transplanted 

 into the metal containers, watered, and left to establish themselves. 

 Since they were planted in soil of known water-content, and weighed 

 before watering, they were readily brought to the desired water- 

 content at the start of the experiment. Twelve large plants were 

 also placed in earthenware pots with the same water-content. Since 

 the low water-content of the dry containers of the alfalfa series 

 caused more closure than desired, the containers in this case were 

 started at 14 per cent and fell to 10 per cent at the end. No watering 

 was done during the series, since this tends to produce localized 

 regions of high water-content. The containers were weighed each 

 hour, immediately after collecting the strips. 



At 6 p. m., when the series started, the stomata were 30 per cent 

 open, and 10 per cent at 7 p. m. During the hour, the rate of water- 

 loss was 50 mg. per minute. At 8 p. m. the stomata closed to 1 

 per cent and the rate fell to 11.25 mg. At 9 p. m. the stomata 

 practically closed, a few slightly open in the upper surface making 

 the average 0.5 per cent. The rate of water-loss as a result fell to 

 5.45 mg. per minute during the hour. At 10 p. m. the stomata 

 opened to an average of 5 per cent and the rate rose to 8.00 mg. per 

 minute. At 11 p. m. further opening to 10 per cent occurred and the 

 rate rose to 15.00 mg. At midnight the average opening decreased 

 to 7 per cent and the rate of loss decreased to 10 mg. per minute. 

 At 1 a. m. average opening decreased to 1 per cent, but a great in- 

 crease of evaporation caused a slight increase of water-loss to 10.91 

 mg. As the stomata continued at nearly complete closure during 

 the following hour, the rate dropped to 4.62 mg. per minute. At 3 a. m. 

 the average opening increased to 2.5 per cent and the water-loss rose 

 to 7.27 mg. per minute. At 4 a. m. the stomata opened to 10 per 

 cent, and in consequence a great decrease in evaporation caused 

 but a slight decrease in the rate of water-loss to 6.15 mg. The next 

 hour it rose to 10.91 mg. per minute. From 5 to 6 a. in. the stomata 

 closed from 3.0 per cent to 0.2 per cent, the rate of evaporation fell, 

 and hence the water-loss fell to the minimum of 3.65 mg. per minute. 

 The lower stomata then opened, while the upper remained closed, 

 bringing the average to 32 per cent. As evaporation dropped still 

 lower, the increase of water-loss was only 11.67 mg. The stomata 

 remained at this opening another hour and the rate of water-loss 

 rose to 41.43 mg. per minute. Opening to 75 per cent caused a rise 

 to 52.73 mg. per minute, and to a maximum of 120 mg. on the 

 following hour, as the evaporation rate rose very much, in spite of 

 the fact that the stomata began to close again. However, the 

 greatest water-loss occurred during the hour the stomata were at 

 their widest opening for the series. Closure to 15 per cent at 11 a. m. 

 caused the rate to decrease to 78.33 mg. The stomata opened again 

 to 18 per cent at noon, causing the rate also to rise to 83.33 mg. 



