What is correct sequence
(a) xylem-cambium-medulla
(b) cortex-endodermis-pericycle-xylem
(c) cambium-xylem-cortex
(d) None of the above

Answer

To determine the correct sequence of plant structures from the given options, we need to analyze the internal structure of a dicot stem. Here’s a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Understanding Dicot Stem Structure**:
- The internal structure of a dicot stem consists of several layers, starting from the outermost layer to the innermost.
- The sequence typically begins with the epidermis, followed by the cortex, endodermis, pericycle, phloem, xylem, and finally the medulla.

2. **Analyzing Each Option**:
- **Option (a)**: xylem-cambium-medulla
- This sequence is incorrect because cambium is not positioned between xylem and medulla in a typical dicot stem structure.

- **Option (b)**: cortex-endodermis-pericycle-xylem
- This sequence is correct. The cortex is followed by the endodermis, then the pericycle, and finally the xylem.

- **Option (c)**: cambium-xylem-cortex
- This sequence is incorrect as the cambium is not located before the xylem in the internal structure of a dicot stem. The cortex is actually outside of the cambium and xylem.

- **Option (d)**: None of the above
- Since we have identified option (b) as correct, this option is not valid.

3. **Conclusion**:
- The correct sequence is found in option (b): cortex-endodermis-pericycle-xylem.

### Final Answer:
**(b) cortex-endodermis-pericycle-xylem**