Typical mesomorphic leaf of a dicot: General view

Collenchyma forms abaxial rib in major veins

Transverse section of a thin dorsiventral (bifacial) leaf from a mesomorphic plant (one that grows typically in temperate regions with average moisture), lilac (Syringa vulgaris), showing typical arrangement of tissues. In the mesophyll, palisade parenchyma is oriented toward the adaxial (upper) surface, and the spongy parenchyma (stained green) toward the abaxial (lower) surface.

In the major vein, the xylem of the vascular bundle is oriented toward the adaxial surface. The collenchyma associated with the bundle rises above the abaxial surface of the lamina in the form of a prominent rib.