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 



9 IO II NOON I 



34-5 



FIG. 2. Series 1, showing movement in upper stomata of alfalfa (A), lower stomata of barley 



(B), sunlight (C). 

 FIG. 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 the first and involved only 15 per cent change in 



