`2:4`-D causes

Options

A. Delay in senescence
B. Bolting
C. Increase in branches
D. Increased growth of all parts.

Answer

**Step-by-Step Solution:**

1. **Understanding 2,4-D**:
- 2,4-D is a type of plant growth hormone, specifically classified as an auxin. It is primarily used as a herbicide to control broadleaf weeds.

2. **Mechanism of Action**:
- 2,4-D mimics the natural plant hormone auxin. When applied, it induces uncontrolled growth in the plants, leading to various physiological effects.

3. **Effects of 2,4-D**:
- The primary effect of 2,4-D is the stimulation of increased growth in all parts of the plant. This uncontrolled growth can eventually lead to the death of the plant.

4. **Evaluating the Options**:
- **Option 1: Delay in senescence**: This is incorrect as 2,4-D does not delay senescence.
- **Option 2: Bolting**: This is also incorrect; bolting is caused by gibberellins, not 2,4-D.
- **Option 3: Increase in branches**: This is incorrect; 2,4-D does not specifically lead to an increase in branching.
- **Option 4: Increased growth of all parts**: This is correct as 2,4-D causes uncontrolled growth in all parts of the plant.

5. **Conclusion**:
- The correct answer is **Option 4: Increased growth of all parts**.

---