St John's wort leaf. Light micrograph of a section through a St John's wort (Hypericum sp.) leaf. The leaf's midrib is at left, with the vascular bundle at its centre. The vascular bundle consists of xylem and phloem tissues, which transport water and carbohydrates around the plant respectively. The layer of cells across top is the upper epidermis (purple), with a palisade mesophyll layer (dark red) beneath it.
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