Magnolia stem. Coloured environmental scanning electron micrograph (ESEM) of a transverse section through the stem of a Magnolia sp. plant. 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).