Stem section. Coloured scanning electron micrograph (SEM) of a section through a stem of a woody dicotyledon plant. This stem consists mainly of secondary xylem tissue (dark brown, centre), a thin layer of secondary phloem tissue (not clearly seen) surrounding the xylem, and an outer cork (cream). The xylem contains many vessels that transport water and mineral nutrients from the roots throughout the plant. The phloem transports carbohydrates and plant hormones around the plant. The cells of the cork are reinforced with lignin, which helps to maintain structural support. Magnification: x20 when printed 10 centimetres wide.