DAILY MOVEMENT IN SUGAR-BEET. 



35 



On July 20, 1916, thirty leaves of sugar-beet were carefully twisted 

 so as not to injure them and left clamped with their lower surfaces 

 turned upward. In the following discussion upper and lower sur- 

 face are used to describe the respective surfaces of the leaves, regard- 

 less of the actual position in which they were placed. On July 26, 

 1916, series 16 was started at 9 a. m. and continued until 11 a. m. 

 the following day. Among the sets of epiderm collected were two 

 of sugar-beet, one from the upper and lower surfaces of normal 

 leaves, and one from the two surfaces of the reversed leaves. This 

 was to determine how much of the difference in the behavior of the 

 stomata in the two surfaces of the leaves was due to physical factors 

 and how much to the internal structure of the leaves. 



The weather conditions were rather favorable for growth. Two 

 light showers occurred on the afternoon of the 26th at 3 h 15 m and 

 4 h 10 m p. m. Each lasted but a minute or two, and there was not 

 sufficient precipitation to measure. They did not reduce the light 

 sufficiently to produce any change in the behavior of the stomata. 

 The temperature and humidity were high on both days. The 26th 



JUNE 21 



JUNE ZZ 



i PM. z 3 4- 5 6 



8 9 



FIQ. 18. Series 16, weather data for July 26-27, 1916; sunlight (A), temperature (B), humidity (C). 



especially was a still, hot day, oppressive because of the high humidity, 

 with clouds hanging over the mountains and the valley in brilliant 

 sunshine. There were fewer clouds on the day following, and 

 these disappeared as they drifted away from the mountains (fig. 18). 

 The curves for the two sets of sugar-beet leaves are shown in figure 

 19. The upper epiderm of the reversed leaves produced the same 

 stomatal curve as the lower epiderm of the normal leaves. The 

 lower epiderm of the reversed leaves did not show exactly the same 

 etomatal movement as in the upper stomata of the normal leaves, 

 but the behavior was essentially similar, demonstrating that most 

 of the difference between the upper and lower stomata of the normal 

 leaf is the result of a different environment. The slightly slower 

 opening and earlier closing of the lower stomata of the reversed leaves 



