. Carnegie Institution of Washington publication. 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 7h 30m it was 9 per cent, 28 per cent at 8, and 43 per- cent at 8h 25m a. m. At 9 it reached 55 per cent, but deepening haze prevented a rapid increase in i
. Carnegie Institution of Washington publication. 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 7h 30m it was 9 per cent, 28 per cent at 8, and 43 per- cent at 8h 25m 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 11 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 stom
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