root vascular cylinder differentiation stage The first identifiable region in the differentiating vascular cylinder is the pericycle. In the xylem the differentiation of the tracheary elements begins in a centrifugal direction but is completed in the centripetal direction. The first phloem elements mature before the first xylem elements. PO:0007509 plant_structure_development_stage The stage at which the root vascular cylinder becomes evident. 3 establishment of tissue systems stage