Leaf venation in a giant rhubarb plant (Gunnera manicata). Photosynthesis is carried out by chlorophyll-containing green cells within leaves. These cells require water and nutrients from the soil, and the sugars they produce are used throughout the plant for its growth. These materials are moved through the leaf and plant by the veins seen here. The veins branch and sub-divide so that no cell is more than a short distance from a supply of food and water.