DAILY MOVEMENT IN POTATO. 



29 



dition until 7 p. m. They then closed gradually until 9 p. m. They 

 remained closed until 4 a. m., when they showed slight opening. 

 At 5 a. m. they were 20 per cent open and at 6 a. m. half open. At 

 7 a. m. this had increased to 90 per cent and at 8 a. m. to maximum. 

 The stomata remained in this condition for an hour, but at 10 a. m. 

 they had closed to 60 per cent, at 11 a. m. to 50 per cent, and at 



Ram 

 trace 



Rain 

 [tmcs 



JULY Z7, 1816 



\ 



9 10 I ' NOON 133*5676910 



4T. I Z34.S6789IOII 



FIG. 11. Series 12, weather data for June 21-22, 1916; sunlight (A), humidity (B), 



temperature (C). 



noon they opened again to maximum. This forenoon closure is 

 coincident with decrease in light caused by the passing cloud. The 

 stomata remained in this condition 3 hours, closing to 70 per cent 

 at 4 p. m. and to 45 per cent at 5 p. m., when the series ended (fig. 12). 



wo 



8O 

 60 

 70 

 60 

 60 

 40 

 3D 



eo 



IO 



C/ 



234-56 7 8 9 IO M MT. I 2 3 



5 6 7 & 9 10 It NOON I 2 3 * 



Fio. 12. Series 12, showing movement in upper (A) and lower (B) stomata of potato, 

 and upper stomata of alfalfa (C). 



The relation of stomatal movement in alfalfa to changes in light 

 is distinct in this series. Evaporation was low and the water-content 

 high as results of the rain, which explains why movement in the 

 stomata of alfalfa was related to light alone. But neither the low 

 light intensity on the afternoon of June 21 nor the darkness of 

 night caused any closure whatever in the upper stomata of potato. 

 The lower closed for an hour at 9 p. m., this being the only closure 

 observed. The conclusion is inescapable that light has no direct 

 effect upon stomatal movement in the potato. 



