Apical dominance is due to

Options

A. critical day length period
B. photoperiodism
C. phototropism
D. auxins

Answer

### Step-by-Step Solution:

1. **Understanding Apical Dominance**:
- Apical dominance refers to the phenomenon where the growth of the main (apical) bud inhibits the growth of lateral (axillary) buds. This results in the plant growing taller rather than bushier.

2. **Identifying the Factors**:
- The question lists several factors: critical day length period, photoperiodism, phototropism, and auxin. We need to determine which of these is responsible for apical dominance.

3. **Analyzing Each Factor**:
- **Critical Day Length Period**: This relates to photoperiodism, which is the plant's response to the lengths of day and night. It influences flowering but does not directly cause apical dominance.
- **Photoperiodism**: This is the overall response of plants to light and dark cycles, affecting flowering and growth but not specifically related to apical dominance.
- **Phototropism**: This is the growth response of plants towards light. While it affects plant growth, it does not regulate apical dominance.
- **Auxin**: This is a plant hormone that plays a crucial role in regulating growth. It promotes cell elongation and is specifically known to inhibit the growth of lateral buds, thus maintaining apical dominance.

4. **Conclusion**:
- Based on the analysis, the correct answer is auxin, as it is the hormone responsible for maintaining apical dominance by inhibiting the growth of lateral buds.

### Final Answer:
Apical dominance is due to auxin.

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