The upper epidermis is covered by a layer of waxy substance called cutin which is secreted by the epidermal cells. This substance further protects the leaf from dehydration. As an additional protection mechanism, epidermal cells in some plants secrete fluids, oils and poisonous substances and might contain soft hair called mullein.
Palisade mesophyll: the palisade parenchyma lies just next to and below the upper epidermis and contains oval and elongated cells closely packed together. These cells are thin walled and the primary site for photosynthetic reaction. They contain small structures called chloroplasts in large numbers that bear chlorophyll- the key ingredient for photosynthesis.
Spongy mesophyll: the spongy parenchyma is a layer of loosely packed irregular cells lying between two layers of palisade cells. They also contain chloroplasts although they are fewer in number as compared to the palisade parenchyma. The intracellular spaces between cells allows for efficient exchange of gases.
Air spaces: air spaces are actually the intracellular spaces between the spongy parenchyma cells and bear communication with the air chambers behind the stomata. They facilitate inflow and outflow of gases.
Stomata: the se are pores scattered throughout the epidermis (more on the lower epidermis). The stomata allow for the interchange of gases for respiration and photosynthesis. ...