List of some of the structural part is given below:
Pericycle, pith vascular bundles ad medullary rays
Which is not a part of stele in the primary
Internal structure of dicotyledonae and monocotyledonae roots.

Answer

To answer the question about which structural part is not a part of the stele in the primary internal structure of dicotyledon and monocotyledon roots, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Components**: The question lists four components: pericycle, pith, vascular bundles, and medullary rays. We need to determine which of these is not part of the stele.

2. **Define the Stele**: The stele is the central part of the root that contains the vascular tissues (xylem and phloem) and other associated structures. It is crucial to identify which components belong to this area.

3. **Analyze Each Component**:
- **Pericycle**: This is a layer of cells that is part of the stele. It is located just inside the endodermis and plays a role in the formation of lateral roots.
- **Pith**: The pith is the central part of the root and is also considered part of the stele. It is made up of parenchyma cells.
- **Vascular Bundles**: These include xylem and phloem, which are essential components of the stele, providing transport of water and nutrients.
- **Medullary Rays**: These are strips of parenchyma tissue that extend radially between the vascular bundles. They are involved in the storage and transport of nutrients but are not considered part of the stele itself.

4. **Conclusion**: Based on the analysis, the component that is not part of the stele is the **medullary rays**.

### Final Answer:
**Medullary rays** are not a part of the stele in the primary internal structure of dicotyledon and monocotyledon roots.

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