Re: Why are there more stomates in the lower epidermis than in the upper one.

Not all leaves have more stomata on the lower epidermis than the upper 
epidermis. Waterlily leaves have virtually all stomata on the upper surface of 
their floating leaves for an obvious reason. Many upright leaves, such as corn 
and wheat, have about equal numbers of stomata on the upper and lower 
surfaces. 

You can think of a few reasons why it may be beneficial for stomata to be 
restricted mainly to the lower epidermis but there may not be published 
experimental studies that have determined how big the benefits are for each of 
these.

1. Stomata on the upper surface may have a higher transpiration rate than 
stomata on the lower surface, which are shaded and more protected from drying 
winds. There seems to be data supporting this idea.

2. Stomata on the upper surface may be more susceptible to entry by disease-
causing microbes.

3. Stomata on the upper epidermis may get clogged more easily by water.

4. Stomata on the upper surface may allow more mineral nutrients to be washed 
out of the leaf during heavy rains.

5. Stomata on the upper epidermis may get clogged more easily by dust.

References


Re: density of stomata and the effect this has on transpiration


Re: DO STOMATES OCCUR ON THE UPPER & LOWER LEVEL OF MESOPHYTES & XERIPHYTES?



Leaf Stomata as Bioindicators of Environmental Change