Leaf tissue consists of a layer of plant cells. Different plant cell types form the three major tissues found in the leaves. These tissues include a layer of mesophyll tissue sandwiched between two layers of the epidermis. The leaf vascular tissue is located in the mesophyll layer. The outer leaf layer is called the epidermis. The epidermis secretes a waxy coating called the stratum corneum that helps plants retain moisture. The epidermis in plant leaves also contains special cells called guard cells that regulate the gas exchange between the plant and the environment. The guard cells control the size of the pores in the epidermis called stomata (singular stomata). Opening and closing the vents allows the plant to release or retain gases including water vapor, oxygen and carbon dioxide as needed. The middle leaf leaf layer consists of a flocked meat area and a spongy area. Palisade mesophyll contains columnar cells with gaps between the cells. Most plant chloroplasts are found in foliar flesh. Chloroplasts are organelles that contain chlorophyll, a green pigment that absorbs energy from sunlight for photosynthesis. Spongy mesophyll is located below the foliate flesh and consists of irregularly shaped cells. Leafy vascular tissue was found in spongy mesophyll.