92 EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. 



curred until after 1 a. m. At 2 a. m. they opened to 60 per cent, to 

 70 per cent at 3, and to 80 per cent at 4 a. m. At 5 a. m. they had 

 closed to 55 per cent, but opened to 70 per cent at 6, and to 90 per 

 cent at 7 a. m. At 8 a. m. they were wide open, and remained open 

 to the end of the series (fig. 46). 



a 10 ii NOON 



Fig 47. Series 29, showing stomatal movement (A) and transpiration 

 (B) in cut stems of Fouquiera splendens. 



There was no close correlation between stomatal movement am 

 transpiration in either species. The maximum transpiration-rate 

 for Fouquiera occurred between noon and 1 p. m., and was clearly 

 the result of low humidity and maximum sunlight at the time when 

 the stomata were still open. After this time the rate fell, in spite of 

 the fact that the light was still at maximum and humidity less, owing 

 to partial closure of the stomata. The fall was not rapid, however, 

 until between 4 and 6 p. m., when the humidity rose somewhat and 

 sunlight fell off rapidly. But as the stomata at no time closed to 

 less than 65 per cent, their effect upon the water-loss of the plant 

 was mostly overshadowed by that of humidity and sunlight, as well 

 as air-temperature and wind (fig. 47). 



In Verbena the maximum rate of transpiration was reached be- 

 tween 11 a. m. and noon, an hour earlier than in Fouquiera. The 

 rate was only slightly less on the following hour, as there was but 

 little closure. The rapid fall in the rate occurred at the same time 

 as in Fouquiera and was clearly the result of changes in the physi- 

 cal factors and not of stomatal movement. Just as in Fouquiera, 

 the fact that the stomata of cut stems never closed sufficiently to 

 cause close regulation of transpiration allowed the water-loss to 

 be controlled almost completely by the factors of evaporation (fig. 48). 



Throughout his investigation, Lloyd (1908) apparently made no 

 parallel series of observations upon the stomatal movement in cut 





