Which of the following sequences is the correct arrangement of tissues in the anatomy of a young dicotyledonous stem from the inside to the outside ?

Analyze the question: You are asked for the order of tissues in a young dicot stem, starting at the centre (inside) and moving outward to the surface.

Concept: In a young dicot stem, the vascular bundles are arranged in a ring. Within each bundle the xylem lies on the inner side, the phloem on the outer side, and the cambium sits between them. This is called a collateral, open bundle.

Order from the inside to the outside:

1. Pith (central region, made of parenchyma)
2. Xylem (towards the centre)
3. Cambium (a thin layer of meristematic cells)
4. Phloem (towards the outside)
5. Cortex (parenchyma, and just under the epidermis the collenchyma)
6. Epidermis (outermost layer)

Checking the options:

• A: Puts phloem before cambium and xylem. This is wrong because phloem is outside the cambium, not inside it.
• B: Starts with xylem and has no pith. It also includes the endodermis, which is not a distinct feature here, and it leaves out the parenchyma and phloem order properly. Wrong.
• C: Pith, xylem, cambium, phloem, then collenchyma, parenchyma and epidermis. The vascular sequence is correct. The cortex order (collenchyma, then parenchyma) is slightly off, since collenchyma is normally just beneath the epidermis, but this is the only option with the correct pith, xylem, cambium, phloem order.
• D: Puts phloem before xylem, which is reversed. Wrong.

Note on option C: Strictly, the cortex parenchyma lies inside the collenchyma, so a perfect sequence would read "parenchyma, collenchyma, epidermis." Option C swaps those two.

Answer: C

Tip: Remember "X-C-P": Xylem, Cambium, Phloem. From the centre outward, xylem comes first, then cambium, then phloem. Xylem is "inside", and phloem is "outside" in a dicot stem.