Virginia creeper stem. Polarised light micrograph of a cross-section through a stem from a Virginia creeper (Parthenocissus tricuspidatus). The primary epidermis has sloughed off and been replaced by an outer cork layer (white-brown). The next layer is the cortex (red and blue), which surrounds the vascular cylinder. The outer vascular layer is a broken ring of phloem (red, topped with yellow fibres). The next ring is xylem tissue (yellow). The pith (centre) is composed of large parenchyma cells (blue). Magnification: x14 when printed at 10 centimetres across.