The term procambium is used to indicate the meristematic tissue that give rise to morphological vascular units. The plants which do not possess secondary growth, all cells of the procambium strand mature and develop into vascular tissue. In the plants which have secondary growth lateron a part of the procambium strand remains meristematic and gives rise to cambium proper. The strips of cambium that arise within collateral bundles are known as fascicular cambium (vascular cambium) and the phellogen as Cork cambium. The intercalary meristems are merely portions of apical meristems that have become separated from the apex during development.