|MadSci Network: Botany|
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of a few reasons why it may be beneficial for stomata to be restricted mainly to the lower epidermis but there may not be published experimental studies that have determined how big the benefits are for each of these. 1.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
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