The vascular system of dicotyledonous stem consists of a large number of vascular bundles arranged in ring between cortex and pith. Each vascular bundle is conjoint i.e., xylem and phloem both are present in the same radius. They are usually collateral, i.e., the phloem lies towards the outerside of xylem (e.g., Helianthus) or bicollateral, i.e., the phloem is present on either side of xylem (e.g., Cucurbita). In some cases, the vascular bundles are concentric type as in case of Begonia, Rumex, etc., they are amphivasal type, i.e. the phloem lies in the centre surrounded by xylem. The vascular bundles are open, i.e., cambium is present between the xylem and phloem.