Assertion: Parenchyma and collenchyma tissues act as mechanical tissue to plants.
Reason: Parenchyma and collenchyma form an important part of the bark of trees.

Options

A. Both Assertion and Reason are true and Reason is correct explanation of the assertion.
B. Both Assertion and Reason are true but Reason is not the correct explanation of the assertion.
C. Assertion is true, but Reason is false.
D. Assertion is false, but Reason is true.

Explanation

### Step-by-Step Solution:

1. **Identify the Assertion and Reason**:
- Assertion: "Parenchyma and collenchyma tissues act as mechanical tissue to plants."
- Reason: "Parenchyma and collenchyma form an important part of the bark of trees."

2. **Evaluate the Assertion**:
- Parenchyma is primarily involved in storage functions and does not provide mechanical support.
- Collenchyma, on the other hand, does provide mechanical support due to its thickened cell walls.
- Therefore, the assertion that both parenchyma and collenchyma act as mechanical tissues is **incorrect**.

3. **Evaluate the Reason**:
- Both parenchyma and collenchyma are indeed found in the bark of trees.
- This statement is **correct**.

4. **Conclusion**:
- The assertion is false while the reason is true.
- Therefore, the correct answer is that the assertion is false but the reason is true.

### Final Answer:
- The correct option is: "Assertion is false but Reason is true."