Xylem plant cells. Coloured scanning electron micrograph (SEM) of xylem cells from a black nightshade (Solanum nigrum) leaf. The xylem transports water and mineral nutrients from the roots throughout the plant. The walls of the xylem vessels are strengthened with lignin (dark brown), a woody substance that helps to support the plant. Magnification: x3300 when printed at 10 centimetres wide.