Leaf midrib. Light micrograph (LM) of a section through the midrib of a leaf from a monocotyledon plant. The midrib (midvein) is the continuation of a leaf's stem along the centre of the leaf. At lower centre is a vascular bundle, which consists of primary xylem (large circles) and primary phloem (green, centre) tissues. Xylem transports water and mineral nutrients from the roots throughout the plant and phloem transports carbohydrate and hormones around the plant. Other, smaller, vascular bundles can also be seen to the left and to the right. The surface (epidermis) of the leaf is covered in a waxy cuticle (red) that helps to prevent water loss.