This cross section of a root shows the outer cell layer (rhizodermis, marked in red colour), the root cortex (marked in orange colour), the central cylinder (marked in brown colour) and the cell layer separating cortex and central cylinder (endodermis, marked in black colour). The central cylinder contains the vascular system for the transport of water and mineral nutrients on the one hand (xylem, marked in blue colour) and of carbohydrates and various organic compounds on the other (phloem, marked in green colour).