A cross-section of a leaf shows that it is a complex organ built of several different kinds of specialized tissues. The 3D leaf cross-section diagram shows cuticle, epidermis, palisade mesophyll, vein, lower epidermis, stomata, and spongy mesophyll. A leaf is made of many layers that are sandwiched between two layers of tough skin cells called the epidermis, which also secretes a waxy substance called the cuticle. Among the epidermal cells are pairs of sausage-shaped guard cells. Gases enter and exit the leaf through the stomata. Most food production takes place in elongated cells called palisade mesophyll. Viens, on the other hand, support the leaf and are filled with vessels that transport food, water, and minerals to the plant.