[A]: Dicot stem shows secondary growth.
[R]: Tissue system is not differentiated in di- cot stem.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To analyze the statements provided in the question, we will break down the assertion and reason step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "Dicot stem shows secondary growth."
- In dicotyledonous plants, secondary growth is a common phenomenon that occurs due to the activity of the cambium, a type of lateral meristem. This growth leads to an increase in the thickness of the stem.

2. **Understanding the Reason (R)**:
- The reason states that "Tissue system is not differentiated in dicot stem."
- This statement is incorrect. In dicot stems, the tissue system is indeed differentiated. The stem consists of various types of tissues including epidermis, cortex (which contains collenchyma and parenchyma), vascular bundles (which include phloem and xylem), and pith.

3. **Analyzing the Relationship**:
- Since the assertion (A) is true (dicot stems do show secondary growth), and the reason (R) is false (the tissue system is differentiated), we conclude that the correct answer is that A is true but R is false.

4. **Conclusion**:
- Therefore, the final answer to the question is: C (A is true but R is false).