Dicotyledon vascular bundle. Coloured scanning electron micrograph (SEM) of a section through a vascular bundle from a dicotyledonous plant. 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, larger vessels) and phloem (containing sieve tubes, smaller vessels). Magnification: x800, when printed 10 centimetres wide.