Sago cycad leaf. Coloured scanning electron micrograph (SEM) of a transverse section through a sago cycad (Cycas revoluta) leaf. At centre is the vascular bundle, consisting of phloem (rusty brown), protoxylem (green) and tracheids (brown) vessels. The phloem transports carbohydrates and plant hormones around the plant. The protoxylem transports water and mineral nutrients from the roots throughout the plant. Tracheids are xylem vessels with thickened walls and so also provide structural support. The hairs on the surface of the leaf help to prevent water loss.