Tree fern frond midrib. Coloured scanning electron micrograph (SEM) of a section through the midrib of a frond of a tree fern (Dicksonia antarctica). At centre is the vascular bundle, which consists of xylem (red) and phloem (brown within red) tissues. Xylem transports water and mineral nutrients from the roots throughout the plant and phloem transports carbohydrate and hormones around the plant. The surface of the leaf is covered in a waxy cuticle (green) that helps to prevent water loss.