Stele
ஸ்டீல் (மைய உருளை)
Stop confusing the cortex with the stele. The endodermis is the boundary, not the structure. If you cannot identify the pericycle, you have already lost the question.
The idea
The stele comprises all tissues internal to the endodermis. This includes the pericycle, vascular bundles, and the pith. In roots, the pericycle initiates lateral roots. In stems, the arrangement of these vascular bundles defines the plant's structural integrity.
Why it matters
It serves as the central conducting and structural core of the plant axis, housing the vascular tissues responsible for transport.
NEET lens
NEET focuses on the components of the stele. Remember: Pericycle + Vascular Bundles + Pith = Stele. Do not include the endodermis in your count; it is the boundary, not part of the stele.
Clinical significance
In humans, vascular organization is analogous to the stele's role in nutrient transport. Failure in vascular differentiation leads to systemic transport collapse, similar to how xylem and phloem failure in plants results in immediate tissue necrosis.
Introduction
The stele is the central cylinder of vascular tissue in roots and stems, consisting of pericycle, vascular bundles (xylem + phloem), and pith (if present).
Core concept
Components: Pericycle (outermost layer of stele), vascular tissue (xylem + phloem), pith (if present). In root: pericycle gives rise to lateral roots (endogenous origin), xylem is exarch, xylem and phloem alternate. In stem: xylem is endarch, vascular bundles with cambium (dicot) or no cambium (monocot).
Go deeper
Types of stele (evolutionary series): Protostele (simplest — xylem core), Siphonostele (hollow cylinder, pith in center), Dictyostele (dissected siphonostele), Eustele (vascular bundles in ring — most dicots), Atactostele (scattered bundles — monocots).
From Class 10
You know roots have xylem and phloem inside. The central vascular cylinder of a root is called the stele.