Fern rhizome. Polarised light micrograph of a cross-section through a rhizome from a male Dryopteris felix-mas fern. This is the central area of the rhizome, surrounded by bands of outer supporting fibres (red). In this central area are meristeles (oval areas) made up of vascular tissue. The meristele layers are: a single layer of endoderm cells (deep green); the cells of the pericycle and phloem (light green); and the large, open vessels of xylem (orange). Magnification: x100 when printed at 10 centimetres across.