STOMATAL RESPONSE TO SUDDEN CHANGE. 



55 



During a i5-minute interval, after nearly 7 hours' exposure to darkness, the 

 average opening of the stomata increased from 2.5 micra to 3.5 micra. This 

 increase was due to the opening of the closed stomata, those having the wider 

 openings being scarcely affected. The failure of stomata already partially 

 open to increase their dimensions may not indicate lack of physiological 

 response, but rather that the mechanical advantage in closed stomata is 

 greater, and that, therefore, the result is more quickly expressed. The rate 

 of transpiration at the close of the same interval of exposure to light (15 

 minutes) was nearly trebled. The average transverse linear dimensions of 

 the stomata increased in the same period somewhat less than one -third. 

 Otherwise stated, transpiration ratio, 2.9; that of diffusion capacity, 1.3. 



4 - 



la.m. 2 



II 



12m. 6pjn. 7 



FIG. 19. Curves for experiments 48 to 53, inclusive. Fouquieria splendenf. Curves are arranged 

 so as to intersect but seldom. 



