Stomata are often confined to the lower epidermis, and the parenchyma is differentiated into palisade cells and spongey mesophyll. The extra thickness of sun leaves is made up of extra layers of palisade cells by comparison with shade leaves of the same plant. The mesophyll is honeycombed with air space, allowing access of CO2 to the individual cells. Vascular bundles also run through it, in close parallel lines in many monocots or branching extensively in dicots. Individual mesophyll cells are never far from a xylem vessel for water supply or a sieve tube for export of sugar.
Leaves have a number of anatomical and physiological adaptations to conserve water.
For example pine needles have a much reduced surface area by comparison with lilac, and a thicker cuticle. A similar effect is achieved in plants with densely hairy leaves. In a sense they have taken on the nutrient absorbing functions of roots. All rights reserved.