. Carnegie Institution of Washington publication. DAILY MOVEMENT IN ALFALFA. 19 the next hour and a half, and was still 98 per cent at 2 p. m. In the meantime the stomata started to close and reached total closure at 2 p. m. At 3 p. m. they had begun to open again, and at 4 p. m. were 80 per cent open, the maximum for the afternoon (fig. 3). This closure at 2 p. m. was very puzzling. At the time it was believed that some mistake had been made, that inadvertently a functionless leaf. uu 90 80 70 60 50 4-0 30 20 !0 / — £" \ £ /• / \ (S / • /- ^^*" "CT — — „ -• — . _ ,: \ IB
. Carnegie Institution of Washington publication. DAILY MOVEMENT IN ALFALFA. 19 the next hour and a half, and was still 98 per cent at 2 p. m. In the meantime the stomata started to close and reached total closure at 2 p. m. At 3 p. m. they had begun to open again, and at 4 p. m. were 80 per cent open, the maximum for the afternoon (fig. 3). This closure at 2 p. m. was very puzzling. At the time it was believed that some mistake had been made, that inadvertently a functionless leaf. uu 90 80 70 60 50 4-0 30 20 !0 / — £" \ £ /• / \ (S / • /- ^^*" "CT — — „ -• — . _ ,: \ IB % /- ^? • / f i) / ..-••*' 9 IO II NOON I E 3 4- 5 Fro. 2.—Series 1, showing movement in upper stomata of alfalfa (A), lower stomata of barley (B), sunlight (C). Fio. 3.—Series 2, showing movement in upper stomata of alfalfa (A), sunlight (B), temperature (C), humidity (D). had been stripped at 2 p. m. or a vial of badly diluted alcohol had been used. No other explanation seemed probable, as the plant was not wilted, and an examination of the soil showed that there was sufficient moisture. The next day another series was made of the same plants and for the same length of time. The morning started very cloudy, but it slowly cleared during the late forenoon. However, in the early afternoon a haze appeared which thickened until it was rather cloudy again at 5 p. m., when the series ended. An entirely different behavior was observed, and one that had no direct relationship to changes in light and only a superficial one to changes in relative humidity. The stomata were 60 per cent open at the start of the series, 80 per cent at 10 a. m., and 85 per cent at 11 a. m. At noon they had closed to 70 per cent, but had opened slightly the next hour and reached maximum at 2 p. m., remaining in this condition to the end of the series (fig. 2). The one similarity in the two series is the mid-day closure. However, this occurred 2 hours earlier in the second than in
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