""STOMATAL RESPONSE TO SUDDEN CHANGE. 63 



that the vertical position of the leaflet greatly lessens the transpiration ; and 

 if the stomata were tightly closed, the same end would be furthered. 



A further consideration of the facts which pertain to plants like the Eu- 

 phorbia* here mentioned leads me to the belief that all is not said on the 

 subject of the regulatory effect of stomata, when we have in mind openings 

 as wide as a micron or more. In view of Brown & Escombe's data it may 

 very well be that the problem of stomatal regulation relates to stomata 

 with very minute openings, and perhaps to larger stomata when nearly 

 closed. There are facts which would seem to exclude the latter, as these 

 minute openings are not found, when the plant is normal, at the times when 

 regulation is supposed to occur. This does not exclude, however, the possi- 

 bility that stomata, the openings of which are beyond the present practical 

 limits of micromeasurement, may not exert a regulatory effect upon trans- 

 piration. Such a problem as this involves a most rigorous physical research 

 of the type of Brown & Escombe, but pushed to far more refined limits and 

 applied extensively to the actual conditions found in the plants themselves. 



*The stoma of this plant measures about 15 by 9 micra; pore, 4 micra long. In water 

 the pore opens to about 1 micron wide. 



