In autumn , leaf fall occurs because

Options

A. Formation , of abscission layer at the base of leaves
B. Leaf becomes heavy
C. Leaf does not remain green
D. Of low temperature

Answer

### Step-by-Step Solution:

1. **Understanding the Context**: In autumn, many deciduous plants shed their leaves. This process is known as leaf fall or abscission.

2. **Identifying the Mechanism**: The leaf fall occurs due to the formation of an abscission layer at the base of the leaves. This layer is a specialized layer of cells that develops in response to environmental changes, particularly as daylight decreases and temperatures drop during autumn.

3. **Evaluating the Options**:
- **Option 1**: Formation of abscission layer at the base of leaves - This is the correct answer as it directly relates to the physiological process that leads to leaf fall.
- **Option 2**: Leaf becomes heavy - While leaves may become heavy with moisture, this is not the primary reason for leaf fall.
- **Option 3**: Leaf does not remain green - This is a consequence of the abscission process, not the cause.
- **Option 4**: Low temperature - While low temperatures can trigger the process, they do not directly cause leaf fall.

4. **Conclusion**: The correct answer is **Option 1: Formation of abscission layer at the base of leaves**. This layer effectively cuts off the supply of nutrients and water to the leaf, leading to its eventual detachment from the plant.