Xylem is always in direct contact with phloem in the vascular bundles of
I.   Dicot stem    
II.  Gymnosperm stem     
III. Dicot leaf     
IV. Monocot stem

Xylem and phloem are in close contact in the vascular bundles of dicot leaf and monocot stem. They are described as closed vascular bundles. In the vascular bundles of dicot stem and gymnosperms stem, the xylem and phloem, though present in the same radius, possess cambium in between xylem and phloem and hence described as open vascular bundles.