42 



THE DAILY MARCH OF STOMATAL MOVEMENT. 



no time dropped below 20 per cent. Except for the passing of some 

 thin and hazy clouds, the sunlight was nearly normal, and at no 

 time was the light reduced to an extent sufficient to affect the stomata. 

 The weather data are shown in figure 16. At the beginning of the 

 series the stomata of wheat, barley, and oats were closed and showed 

 no opening until 6 a. m., June 20. Maximum opening for the morn- 

 ing occurred at 7 a. m., and was 21 per cent in wheat, 16 per cent in 

 oats, and 17 per cent in barley. Total closure occurred in all three 

 at nearly the same time and was complete at 11 a. m. (fig. 24). In 



NOON I 



89 10 II MT. I 



56789 10 II NOON I Z 



FIQ. 24. Series 11, showing movement in lower stomata of wheat (A), oats (B), and barley (C). 



comparing these results with those obtained in series 10, it will be 

 observed that the stomata of wheat showed very little difference in 

 behavior, those of oats opened more widely than on June 8, while those 

 of barley opened to twice the width and remained open 2 hours 

 longer. The chief difference in weather conditions during the two 

 series was in temperature, the maximum on June 20 being 76.5 F., 

 while the maximum of June 8 was 88. In addition, the humidity 

 was not as low and the evaporating power of the air was correspond- 

 ingly less. Wheat was therefore but little affected by the higher 

 temperature of the preceding series, barley showed the greatest 

 effect, and oats occupied an intermediate position. 



The stomatal movement in millet (Setaria italica germanica) was 

 essentially the same as in wheat, the only difference being a slightly 

 wider opening at 7 a. m. in millet. The stomatal movement in corn, 



NOON I Z 34 56 789 10 II MT. I 234 5 6 "7 8 9 10 II NOON I Z 



FIQ. 25. Series 11, showing movement in lower stomata of corn (A) and millet (B). 



however, was distinctly different. The stomata were 50 per cent open 

 at noon on June 1 9 when the series started. They closed gradually and 

 completely by 3 p. m. However, they immediately began to open 

 and at 6 p. m. reached 15 per cent, the maximum for the afternoon. 

 They then closed as slowly as they had opened, completing the move- 





