In most dicot plants the xylem is concentrated in the innermost region of the central cylinder.
When a cross-sectional view of the root is observed, the protoxylem occupies an area in the shape of a cross or star, the ends of which touch the pericycle.
The protofloema is found in the vertices formed by the "arms" of the cross. Between protoxylem and protofloema there is a primary meristem called procambium. The remaining spaces within the central cylinder are filled with parenchyma.
In monocotyledonous plants, the center of the root is occupied by a medulla consisting of the medullary parenchyma and the woody and liberian vessels are arranged around it.