EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. 81 



The difference in the stomatal movement of the cut stems and the 

 watered field plants was striking. The watered plants showed 15 

 and 20 per cent opening from 10 p. m. until 1 a. m., and closure from 

 then to dawn. This was largely the result of the slight rain which 



1O II MT. I 2 3 4- 5 6 7 8 9 10 II NOON I 23456789 IO 



FIG. 37. Series 17, weather data for August 8-9, 1916; sunlight (A), 

 temperature (B), humidity (C). 



too 



90 

 60 

 70 

 60 

 60 



30 

 20 

 10 



V -. . 



' \ ^ 



A 



\ 



la II MT. I 2 3 4 5 6 7 8 9 10 II WON 12345678910 



FIG. 38. Series 17, showing average movement of alfalfa stomata in watered 

 (A) and unwatered (B) field plants, and in cut stems (C). 



too 



90 



80 

 70 



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PIG. 39. Series 17, showing stomatal movement (A), and transpiration (B) 

 in cut stems of alfalfa; humidity (C). 



occurred after 10 p. m. The cut stems had closed stomata at 10 p. m., 

 but they opened slowly to 10 per cent at 1 a. m. and then began 

 closing. At 3 a. m. this was complete. The next hour, however, 



