Root pressure theory of ascent of sap is unacceptable because

Options

A. Water can ascend without root or root pressure
B. Root pressure cannot explain ascent of sap beyond 10 meters
C. Root pressue is more during early morning then afternoon
D. Root pressure does not occur in spring .

Answer

### Step-by-Step Solution:

1. **Understanding Root Pressure Theory**:
- The root pressure theory, proposed by Priestley, explains that water is pushed up through the xylem vessels due to pressure generated in the root cells. This pressure is created by osmotic action in the cortical cells of the roots.

2. **Evaluating the Options**:
- **Option A**: Water can ascend without root or root pressure.
- This option is correct because experiments have shown that water can move up the xylem even when the roots are removed, indicating that root pressure is not essential for the ascent of sap.

- **Option B**: Root pressure cannot explain ascent of sap beyond 10 meters.
- This statement is incorrect. While root pressure may not be sufficient to explain sap ascent in tall trees, it does not invalidate the theory itself.

- **Option C**: Root pressure is more during early morning than afternoon.
- This statement is also incorrect. Root pressure can vary throughout the day and is not consistently higher in the morning.

- **Option D**: Root pressure does not occur in spring.
- This statement is incorrect as well. Root pressure can occur in various seasons, including spring.

3. **Conclusion**:
- Based on the evaluation of the options, the most acceptable reason for the unacceptability of the root pressure theory is that water can ascend without root or root pressure (Option A).

### Final Answer:
The root pressure theory of ascent of sap is unacceptable because **water can ascend without root or root pressure**.

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