The stem shows three regions in its primary structure. They are epidermis, cortex and stele.
In the stele a limited number of vascular bundles are present in the form of a ring.
The bundles are conjoint, collateral, endarch and open.
A vascular bundle consists of phloem towards outside, xylem towards inside and a strip of fascicular cambium between xylem and phloem.
The process of secondary growth in the intrastelar region can be discussed under the following headings:-
Formation of cambial ring
Formation of secondary tissues
Formation of secondary medullary rays
Formation of annual ring
Sap wood and heart wood