Vascular bundle. Coloured scanning electron micrograph (SEM) of a section through a vascular bundle from an Aconitum sp. plant, showing: palisade tissue (green, top), chloroplasts (green dots), vascular tissue (curled tubes), and a tracheid (blue). Cell nuclei are red. A vascular bundle is a part of the transport system in vascular plants. The transport itself happens in vascular tissue, which exists in two forms: xylem (containing tracheids) and phloem. Magnification: x600, when printed 10 centimetres wide.