The epidermis of the leaf has unique features that aid in the survival of the plant. We are going to take a look into some of these unique features inside the lower epidermis of the leaf, starting with the outer protective layer of the epidermis. It’s waxy to help prevent water loss, and that wax or cutin will be increase with light intensity. The cuticle protects the leaf’s photosynthesizing cells. These cells must face many environmental dangers including bacteria, fungi, viruses, and of course insects and animals. The cuticle is the first line of defense.
The most important structure on a leaf’s lower epidermis is the mouth shaped opening called the stoma. There are many stomata on each leaf, so tiny that they are up to one million per square centimeter. They are natural openings in the leaves that regulate the gas exchange (CO2 in, O2 out) and along with the cuticle, help prevent water loss. The guard cells are kidney-shaped cells that surround the stoma that regulate the opening and closing of the stomata. Once the guard cells are open, the cells within the leaf responsible for photosynthesis are in contact with the surrounding atmosphere.
Just above these stomata and guard cells is a spongy layer of loosely packed ball-shaped cells with many air pockets. This layer is pretty straight forward in its name, it’s called the spongy layer. The air pockets allow for gas exchange between different areas of the leaf. Within the spongy layer, there are a few other components. Along the air pockets in the spongy layer are vascular bundles containing xylem and phloem. These bundles are also called veins. These veins are where the movement of water and food occurs. Xylem moves the water and dissolved minerals up from the roots, while the phloem moves the food resulting from photosynthesis throughout the plant.