86 EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. 



The stomata of the potted plants were wide open at the start and 

 remained open an hour. The lower stomata then closed completely 

 by 3 p. m., while the upper stomata closed to 20 per cent at 5 p. m. 

 No further change took place in either surface until after 7 p. m. 

 At 8 p. m. the upper started to reopen slightly, reaching 30 per cent 

 at 10 p. m. At midnight further opening again took place, the upper 

 showing 50 per cent opening. At 1 a. m. the lower showed 20 per cent 

 opening, and the upper 80 per cent; at 2 a. m. the lower were half 

 open and the upper at maximum. At 3 a. m. the stomata of both 

 surfaces were wide open, and so remained to the end of the series. 



1 00 

 90 

 80 

 70 

 60 



\ 



50 



30 

 20 



10 



A; 



z 



NOON I 



10 II MT. 1 



8 9 10 II NOON I 



FIG. 41. Series 20, showing movement in upper (A) and lower (B) stomata of 

 potted potato plants, and in upper (C) and lower (D) stomata of 

 cut potato stems. 



The stomata of the watered field plants were wide open until 

 4 p. m., when the lower began to close. At 5 p. m. the upper also 

 showed closure to 80 per cent, while the lower were but 40 per cent. 

 At 6 p. m. the lower were closed and the upper were 50 per cent 

 open. At 7 p. m. the upper closed to 30 per cent, and at 8 p. m. closed 

 completely. At midnight the upper showed 50 per cent opening, 

 and complete opening the following hour. The lower were but 30 

 per cent open at midnight, 60 per cent at 1 a. m. and wide open 

 at 2 a. m. They remained at maximum to the end of the series. 

 The unwatered field plants had closed stomata when the series 

 began. At 2 p. m. the lower opened 10 per cent, closed to 5 per cent 

 at 3, and opened to 15 per cent at 4 p. m. At this time the upper 

 opened to 20 per cent, and to 30 per cent at 5 p. m., while the lower 

 closed to 5 per cent at this time. At 6 p. m. the lower closed com- 

 pletely and the upper to 15 per cent. At 7 p. m. both were closed, 

 but at 8 the upper reopened 5 per cent. At 9 p. m. the lower opened 

 10 per cent, while the upper reached 25 per cent. At 10 p. m. both 

 surfaces showed 20 per cent opening, and closure at 11 p. m. At 

 midnight the stomata of the upper surface opened 25 per cent, those 

 of the lower 10 per cent, and at 1 a. m. the upper reached 60 per cent 

 and the lower 30 per cent. At 2 a. m. the upper were 80 per cent 

 open, but closed to 70 per cent the following hour. In the mean- 



