The epidermises of the leaf's upper- and undersurface may be of different structures. The wall of epidermal cells that constitute the leaf's surface are often thicker than that of the other walls. Aquatic plants have usually thin walls. The wall of many seeds becomes stronger during ripening and may fill nearly all of the cell's lumen so that the protoplast is driven out and degenerates. The basic epidermal cells of most species are devoid of chloroplasts.
Exceptions are some ferns and several aquatic or shade plants.
Epidermis cells secrete a cuticle , that covers all epidermal surfaces like an uninterrupted film. It may either be smooth or structured by bulges, rods, filaments, folds , or furrows. Nevertheless is the folding of the cuticle not always caused by cuticular rods or filaments. There are cases where it is merely the expression of the bulging of the cell walls below. It may be necessary to analyze cross-sections of the cuticle and the underlying epidermal cells to find the actual cause.