A section through a leaf of the Christmas rose, Helleborus niger, viewed using a scanning electron microscope. The leaf's upper surface is at the top. Below are the flat, rectangular cells of the epidermis, with the long vertical palisade cells beneath them. Palisade cells contain round chloroplasts (coloured green here). These are the site of photosynthesis, a complex set of reactions that use the energy of the sun to combine carbon dioxide and water to make carbohydrates such as sugar and cellulose. The image is magnified 4,000 times.