This cross section of the stem axis shows the outer cell layer (epidermis, marked in black colour), the cortex (marked in orange colour), the medulla (marked in dark brown colour) and the regenerative tissue (cambium, marked in red colour) between cortex and medulla. The vascular bundles are containing transport systems for water and mineral nutrients on the one hand (xylem, marked in blue colour) and for carbohydrates and various organic substanes on the other hand (phloem, marked in green colour). (Structure and positioning of the vascular bundles differ from each other regarding different plants).