Leaf midrib. Coloured scanning electron micrograph (SEM) of a section through the midrib of a leaf from a Camellia sp. plant. The midrib (midvein) is the continuation of a leaf's stem along the centre of the leaf. Within the midrib is a vascular bundle (yellow), composed of xylem (centre) and phloem (outer) cells, which transport water and carbohydrates around the plant respectively.