Upright growth of lodged (horizontal) stem is due to

Options

A. Activity of lateral meristem
B. Accumulation of more auxin on the lower side
C. Accumulation of more auxin on upper side
D. Greater cell enlargement on upper side.

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the reason for the upright growth of a lodged (horizontal) stem.

2. **Identifying Key Concepts**: The key concept here is the role of auxins, which are plant hormones that regulate growth in response to gravity.

3. **Gravitropism**:
- **Positive Gravitropism**: Roots exhibit positive gravitropism, meaning they grow towards gravity.
- **Negative Gravitropism**: Shoots exhibit negative gravitropism, meaning they grow away from gravity.

4. **Auxin Distribution**: In stems that are horizontal (lodged), auxins will accumulate on the lower side due to gravity. This accumulation is crucial for understanding how the stem will respond.

5. **Effect of Auxin on Growth**:
- The auxin on the lower side stimulates cell elongation and growth in that area.
- As a result, the cells on the lower side elongate more than those on the upper side, causing the stem to bend upwards.

6. **Conclusion**: The upright growth of a lodged horizontal stem is primarily due to the accumulation of more auxin on the lower side, which leads to greater cell expansion and growth on that side, pushing the stem upwards.

### Final Answer:
The upright growth of a lodged (horizontal) stem is due to the accumulation of more auxin on the lower side.

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