44 



THE DAILY MARCH OF STOMATAL MOVEMENT. 



and cloudless, the behavior of the stomata was practically normal, 

 in spite of the low light intensity in the greenhouse, and the fluctua- 

 tions in opening and closing coincide with those of light intensity. 

 At the outset, the stomata were closed and did not open until after 

 sunrise. At 6 a. m. they were only 5 per cent open, but the next hour 

 they had opened to 50 per cent and at 8 a. m. were wide open. They 

 remained at maximum until noon and then started to close slowly. 

 At 2 p. m. they were still 80 per cent open, but with the sudden drop 

 in light intensity at this time they closed to 50 per cent in the next 

 hour. Then, as the light decreased very little for a time, the stomata 

 closed only to 30 per cent in the next 2 hours. At 6 p. m. they closed 

 to 10 per cent, as there was less than 1 per cent light in the green- 

 house, and completely by 7 a. m. They remained closed all night. 



100 

 90 

 60 

 70 

 60 



50 



40 

 30 

 20 

 10 



B 



4 5 6 7 8 9 10 II NOON I 2 3 4 5 6 7 8 9 10 II MT. 



234. 



FIG. 26. Series 26, showing movement in lower stomata of wheat growing 

 in the greenhouse (A); light intensity outside (B), inside (C). 



The stomatal movement of wheat in this series may be considered 

 somewhat representative of all cereals under the most favorable con- 

 ditions. The small amount of light causing opening is not remark- 

 able for plants grown in a greenhouse, and hence adjusted to operate 

 under conditions of reduced light intensity. The plants in the Great 

 Salt Lake region did not show this type of movement, which is not 

 strange, as the average daily minimum humidity for June, July, and 

 August 1916 was only 10 per cent. The behavior of the individual 

 stomata was different in this series. In those made at Salt Lake 

 City only part of the stomata opened, thus making the average open- 

 ing for all rather low. Then, as closure began, some stomata closed 

 slightly, others completely, and some not at all. As time went on, 

 a larger proportion of closed stomata were found, until finally all 

 were closed. In the greenhouse series, however, far the larger number 

 showed the same degree of opening in each strip, and less than a 

 fifth of their number varied from this average, and most of these 

 only a little. This adds evidence to the belief that, in the series made 

 during less favorable conditions, some remained closed throughout 

 the 24-hour period, while others showed all the opening that occurred. 



