DAILY MOVEMENT IN SUGAR-BEET. 33 



is high, the potato with its stomata open throughout the day can 

 produce much more photosynthate than alfalfa, which has the 

 stomata closed for a considerable portion of the working period. 



THE DAILY MOVEMENT IN SUGAR-BEET. 



The stomata and epidermal cells of sugar-beet are unique in being 

 similar on both surfaces of the leaf. This is in marked contrast to 

 the epiderm of alfalfa or potato leaves, where the stomata and cells 

 of one surface are distinctly unlike those of the other. For this 

 reason, as well as because of its importance as a crop plant in the 

 region about the Great Salt Lake, this plant was included in a number 

 of series. The first of these was No. 11, started at 11 a. m. June 19, 

 1916, and ended at noon June 20. The weather conditions of these 

 two days were characterized by increasing humidity, high tempera- 

 ture, and cloudy nights, which culminated in a rain on June 21. 

 Throughout this period passing light clouds cut down the sunlight, 

 but at no time to the point where the stomata were affected. The 

 temperature ranged from 80 F. at 3 p. m. June 19 to 55 F. just 

 before dawn on June 20. A dense layer of clouds formed during the 

 evening of the 19th and persisted until after sunrise. This condition 

 was responsible for the warm night and resulted in the high humidity 

 of the following day (fig. 16). The light was not as great or the 

 temperature as high this second day as on the first. 



At the start of the series the upper stomata had just started to 

 close, while the lower showed but 30 per cent opening. The lower 

 surface reached a minimum of 5 per cent for the afternoon at 1 p. m. 

 and remained in this condition for an hour. The upper had closed 

 to 10 per cent at 2 p. m. At 3 p. m. both surfaces showed the stomata 

 opening; at 4 p. m. the lower had opened to 40 per cent, while the 

 upper had only reached 20 per cent. The next hour the lower had 

 opened to 50 per cent, but the upper, increasing the rate of opening 

 very much, reached 80 per cent. This was the time of greatest 

 opening in either surface that afternoon. The following hour the 

 lower stomata were unchanged, but the upper had closed slightly, 

 and then more rapidly until nearly all were closed at 10 p. m. The 

 lower stomata closed to 10 per cent at 8 p. m. and then began to 

 open, reaching a maximum for the night of 70 per cent at 11 p. m. 

 At this hour the upper stomata had opened slightly and reached 

 15 per cent at 1 a. m. After 11 p. m. the lower stomata had gradually 

 closed, this change being completed at 3 a. m. The upper stomata 

 reached the minimum of 7 per cent at the same time. The next hour, 

 although the light of approaching dawn was very faint, the upper 

 stomata had opened 60 per cent and were wide open at 5 a. m., about 

 20 minutes before the sun rose over the mountains. The lower 

 stomata, however, were still closed at 4 a. m. and showed only 5 per 



