In bicollateral type of vascular bundle, 2 phloem patches are found external and internal to the centrally placed xylem in a collateral vascular bundle. Two cambium strips lie between phloem and xylem, eg, Cucurbita. In collateral vascular bundle, xylem and phloem lie together on same radius; xylem being internal and phloem being external. They are of two types - open and closed. When cambium is present between xylem and phloem, it is open type, eg, Dicot and when cambium is absent. It is closed type, eg, Monocot.
In radial vascular bundle, xylem and phloem tissue occur separately on different radii, eg, roots.
In amphicrib type, xylem is surrounded by phloem, also known as hadrocentric, eg, Polypodium, Lycopodium and Selaginella.