How a Leaf Changes Color in Fall

There is a transparent waxy layer called the cuticle that covers a leaf but admits sunlight. This layer helps prevent the evaporation of water from leaf cells. Palisade parenchyma cells (looks like a row of stakes) in the leaf's upper half shown in the illustration receive direct rays from the sun.
Stoma are pores on leaf bottoms that allow movement of air into leaf while veins support the leaf and carry water and food back out and into the rest of the tree. Loosely packed cells on the bottom half of leaves permit air containing carbon dioxide (for photosynthesis) to move inside the leaf.