Primary xylem :
(i) It is developed from procambium.
(ii) There are no medullary or any rays in primary xylem.
(iii) It is concerned with the growth of the primary plant body.
(iv) It is associated with the formation of patches in-side the vascular bundle around the pith.
Secondary xylem :
(i)It is developed from vascular cambium.
(ii)There are rays in the secondary xylem.
(iii)It is concerned with the secondary growth of the plant.
(iv)It constitutes the continuous cylinder around the pith.