Maiden hair tree stem. Coloured scanning electron micrograph (SEM) of a section through a maidenhair tree (Ginkgo biloba) stem. At centre is the pith, which consists of soft, spongy parenchyma cells. Outside of this is the secondary xylem, which transports water and nutrients around the plant. The next ring consists of secondary phloem, which transports carbohydrates and hormones around the plant. Outside of this are the cortex, periderm and bark (brown).