28 



THE DAILY MARCH OF STOMATAL MOVEMENT. 



per cent at 9 p. m., but opened at once and were wide open the fol- 

 lowing hour. Hence, as in alfalfa, the behavior of the stomata was 

 different in the upper and lower surfaces of the leaves (fig. 10). The 

 striking difference between the two species lies in the widely open 

 stomata of potato throughout the day and most of the night. This 

 behavior indicates that light does not produce opening of stomata 

 in this species. Moreover, though the greatest difference in envi- 

 ronment of the upper and lower stomata is one of light intensity, 

 this can hardly explain the behavior of the lower stomata, since these 

 did not close until darkness set in. If lack of light caused closure, 

 the upper stomata should have closed to even a greater degree, since 

 these were exposed to a greater change in lighting. 



too 



90 

 SO 

 70 

 60 

 60 

 40 

 30 

 20 



10 



5 6 7 8 9 10 1 1 NOON 



Z 2 * 5676 



II MT. I 234 



Fio. 10. Series 10. showing movement in upper (A) and lower (B) stomata 



of potato. 



The tendency of potato stomata to remain continually open is 

 again shown in series 12, started at 1 p. m. on June 21 and continuing 

 to 5 p. m., June 22, 1916. In this case the series was begun on a 

 rainy day and ended on a clear day. The light intensity was not over 

 6 per cent on the afternoon of June 21 until 6 p. m., when the stopping 

 of the rain caused a rise to 13 per cent. The temperature was also 

 low, averaging 46 F. on this afternoon, but rising to 53 F. after 

 6 p. m. The humidity averaged 85 per cent during the afternoon 

 and night. The next day was clear, except for a large passing 

 cloud at 10 and 11 a. m., although some haze due to the rain of the 

 previous day prevented the sunlight from reaching a maximum. The 

 temperature was 40 F. just before daylight, but rose quickly after 

 sunrise, averaging 62 F. during the forenoon. The humidity dropped 

 to an average of 40 per cent during the forenoon, which, however, 

 was high for the region (fig. 11). The behavior of the stomata was 

 essentially identical with that found in series 10. Comparison with 

 the behavior found in alfalfa stomata shows some interesting facts. 



The low light intensity during the rainy afternoon of June 21 

 caused the alfalfa stomata to be almost closed. At 6 p. m., with the 

 increase of light, they opened to 80 per cent, remaining in this con- 



