90 EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. 



though a morning haze prevented maximum from being reached 

 until 1 p. m. (fig. 44). 



The stomata of the field plants of Fouquiera were wide open at 

 the start of the series and remained open until noon. At 1 p. m. 

 they closed to 85 per cent and continued until 20 per cent was re ached 

 at 4 p. m. No further change took place until midnight, when they 



9 IO II NOON I 23456 789 10 II 



56789 10 



FIG. 44. Series 29, weather data for March 15-16, 1918; sunlight (A), tempera- 

 ture (B), humidity (C). 



closed to 10 per cent. At 1 a. m. they opened to 20 per cent and at 



2 to 25 per cent. They remained in this condition an hour and then 

 closed to 5 per cent at 4 a. m. At 5 a. m. they opened to 20 per cent, 

 35 per cent at 6, 50 per cent at 7, and 80 per cent at 8 a. m. At 

 9 a. m. they were again wide open. Watering had no effect upon the 

 stomatal movement exhibited. This movement is apparently in 

 full accord with that found by Lloyd for this species. 



The stomatal movement found in the cut stems of this plant, 

 however, differed greatly. Unlike the cut stems of alfalfa and potato, 

 there was no complete closure. At no time did the stomata show 

 less than 65 per cent opening. As in the field plants, the stomata 

 were wide open at the start and remained at maximum until 1 p. m., 

 when they gradually began to close. At 4 p. m. they were 70 per 

 cent open and then reopened. At 5 they were 80 per cent open, at 

 6, 90 per cent, and at 7 at maximum opening again. At 8 p. m. 

 they closed to 90 per cent, remained in this condition 2 hours, and 

 at 1 1 p. m. closed to 75 per cent. At midnight they were 70 per cent 

 open, at 1 a. m. 65 per cent, and so remained until 4 a. m. At 5 a. m. 

 they reopened to 75 per cent, at 6 to 85 per cent, at 7 to 90 per cent, 

 and to maximum at 8 a. m. They were still wide open when the 

 series closed (fig. 45). 



The behavior of Verbena ciliata was just as striking. As in Fou- 

 quiera, the stomata of the field plants were wide open at the start 

 of the experiment and remained wide open until noon. They then 

 started to close, the process being rather rapid and uniform. At 



3 p. m. they were closed to 15 per cent. After this the rate of closure 





