Stalk of Polypodium vulgare, at 10x Magnification Polypodium vulgare, This is a cut of a fern frond. On the outside are lignified cells (red) to give the fern frond stability. Inside (green, white) is the pulp. There are two vascular bundles. Each vascular bundle is surrounded by a bundle sheath (brown). , 10x by Eckhard Völcker