WATER-CONTENT. 



67 



away and disappeared by 1 p. m. At 2, 3, and 5 p. m. passing clouds 

 reduced the light for short periods of time. The humidity was not 

 extremely low, as often happened in the region, since the minimum 

 was 25 per cent at 3 p. m., while the average for the day was over 

 35 per cent. The wind was slight, except between 8 and 9 a. m., when 

 it rose to 2.16 miles per hour. 



The stomata of the plants of plot 1 were closed throughout the 

 series, as was expected from the appearance of the plants. Those 

 of the plants in plot 3 were 17 per cent open at the start and closed 

 completely by 9 p. m. They remained closed until 4 a. m., when the 

 first light of dawn caused them to open slightly, reaching 10 per cent 

 at 5 a. m. Sunrise then caused them to open smoothly and uniformly 

 to maximum at 8 a. m., in which condition they remained until 4 

 p. m., when they started to close. They had decreased only to 85 

 per cent at 6 p. m., but the following hour they closed to 20 per cent. 

 The stomata of plot 2, which had nearly saturated soil, showed 

 stomata open from 10 to 25 per cent throughout the night, but 

 closing completely at 4 a. m. The following hour they opened 20 

 per cent and then more rapidly until maximum was reached at 7 

 a. m. They remained wide open until 2 p. m., when, as usual, the 

 plot was given 2 inches of water. In consequence, they commenced 

 closing immediately and smoothly to 60 per cent at 4 p. m. By this 

 time the water had soaked into the ground and the upper surface 

 was drying slightly. The stomata remained at 60 per cent for an 



9 IO II MT. I 2 34-5 67 8 9 10 II NOW I 234-567 



FIQ. 36. Effect of water-content on movement in upper stomata of alfalfa; 

 irrigated daily with 2 in. of water (A), irrigated 7 days before 

 with 4 in. (B), not irrigated (C). 



hour and then opened to 80 per cent at 6 p. m. The next hour they 

 closed completely. The stomata of the plants of plot 4 were closed 

 at the start of the series and remained closed until 10 p. m. Then 

 they opened very slowly, reaching 9 per cent at 1 a. m., thereafter 

 more rapidly and irregularly to 28 per cent at 5 a. m. As a result of 

 daylight, they opened to 45 per cent at 6 and 70 per cent at 7 a. m. 

 The next hour they closed and remained closed until the end of the 

 series, except for slight irregular openings characteristic of plants 

 operating with deficient leaf -water (fig. 36). 



