EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. 85 



August 25 there was 65 per cent light at noon, which decreased to 

 53 per cent at 2 p. m. At 3 p. m. the intensity had increased to 

 60 per cent and then decreased uniformly until sundown at 7 p. m. 

 The sun rose above the mountains shortly after 6 a. m. August 26, 

 but clouds prevented the light from reaching more than 4 per cent 

 at 7 a. m. At 7 h 30 m it was 9 per cent, 28 per cent at 8, and 43 per- 

 cent at 8 h 25 m a. m. At 9 it reached 55 per cent, but deepening 

 haze prevented a rapid increase in intensity for a time. At noon the 

 haze began to clear, and at 1 p. m. the light reached 88 per cent, the 

 maximum during the period of the experiment (fig. 40). 



All the plants, except the heavily watered field plants, suffered 

 from excessive water-loss. The cut stems had open stomata from 

 10 a. m. until 1 p. m., when the lower stomata started to close, 

 reaching 15 per cent at 2 p. m., while no change occurred in the upper. 

 At 3 p. m. the upper closed to one-half of their maximum, while the 

 lower opened to 25 per cent. The upper closed to 40 per cent and the 

 lower to 20 per cent at 4 p. m. At 5 p. m. the lower closed to 10 

 per cent and the upper to 20 per cent. At 6 p. m. the lower opened 



100 



10 



NOON I Z 3 a. 56 789 10 II MT I 334567 89 10 II NOON 



FIG. 40. Series 20, weather data for August 25-26, 1916; sunlight (A), temper- 

 ature (B), humidity (C). 



to 20 per cent, while the upper remained in the same condition. At 

 7 p. m. the upper opened to 25 per cent and the lower closed to 10 

 per cent. At 8 p. m. the lower stomata closed, while the upper were 

 20 per cent open. At 9 p. m. the upper closed to 15 per cent and at 

 10 p. m. closed completely. At this time, however, the lower opened 

 3 per cent, and 5 per cent at 1 1 p. m. By midnight all closed, except 

 occasional stomata in both surfaces, producing 1 or 2 per cent opening 

 throughout the rest of the night. At 6 a. m. the upper stomata opened 

 10 per cent, and 20 per cent at 7 a. m. At 9 a. m. the lower opened 

 5 per cent, while the upper remained in the same condition. At 10 

 a. m. the lower closed to 2 per cent, in which condition they remained 

 until noon. The upper closed to 15 per cent at this time, then to 

 5 per cent at 11 a. m. and remained in this condition until noon. 

 At 1 p. m. the stomata of both surfaces closed completely^(fig. 41). 



