Asserion : Long distance flows of photoassimilates in plants occurs through seive tubes
Reason : Mature seive tubes have parietal cytoplasm and prforated seive plates

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

### Step-by-Step Solution

1. **Understanding the Assertion**: The assertion states that long-distance flow of photoassimilates in plants occurs through sieve tubes.
- **Explanation**: Sieve tubes are part of the phloem tissue in plants, which is responsible for the transport of nutrients, particularly the products of photosynthesis (photoassimilates), from the leaves to other parts of the plant.

2. **Understanding the Reason**: The reason given is that mature sieve tubes have parietal cytoplasm and perforated sieve plates.
- **Explanation**: Mature sieve tubes are specialized cells that lack a nucleus and have a unique structure. They contain parietal cytoplasm (cytoplasm located at the periphery of the cell) and are characterized by perforated sieve plates. These sieve plates allow for the movement of photoassimilates from one sieve tube to another, facilitating long-distance transport.

3. **Evaluating the Relationship**: We need to determine if the reason correctly explains the assertion.
- **Analysis**: The presence of parietal cytoplasm and perforated sieve plates in mature sieve tubes is indeed crucial for the long-distance transport of photoassimilates. The perforations in the sieve plates allow for the efficient flow of nutrients through the phloem.

4. **Conclusion**: Both the assertion and the reason are correct, and the reason provides a valid explanation for the assertion.
- **Final Answer**: Therefore, the correct option is that both the assertion and reason are true, and the reason is the correct explanation for the assertion.