Bamboo stem. Coloured scanning electron micrograph (SEM) of a section through a xylem vessel in a bamboo (family Gramineae) stem. The xylem transports water and mineral nutrients from the roots throughout the plant. The walls of the xylem vessels are strengthened with lignin (grey loops), a woody substance that helps to support the plant. Magnification: x1150 when printed at 10 centimetres wide.