Their walls are often wavy or sinuate. It is unknown, what induces this shape during development, since the explanations given by the existing hypotheses seem insufficient. Elongated epidermis cells can be found at organs or parts of organs that are elongated themselves, like stems, leaf petioles, leaf veins or leaves of monocots . 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.