102 EFFECT OF STOMATAL MOVEMENT UPON TRANSPIRATION. 



by the stomata. When the stomata are wide open or nearly wide 

 open, transpiration is the result of the action of the factors of evapo- 

 ration alone, since the stomata in nowise interfere with the action. 

 As the stomata close, the influence of the factors is lessened, but 

 until closure has reduced the apertures to 50 per cent or less, stomatal 

 regulation is still largely overshadowed by the control exerted by 

 them. When closure is almost complete, the regulation of water-loss 

 by the stomata is very close and the effect of the factors over- 

 shadowed by the effect of even very small changes of the opening. 





