The importance of coleoptile tip in phototropic curvature was first experimentally confirmed by

Options

A. Julius von Sachs
B. Charles Darwn and Francis Darwin
C. Boysen - Jenson
D. F.W.Went

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the scientist who first experimentally confirmed the importance of the coleoptile tip in phototropic curvature. Phototropism refers to the growth of plant parts in response to light.

2. **Identifying the Scientists**: The options provided are:
- Julius von Sachs
- Charles Darwin and Francis Darwin
- Boyce and Jensen
- F.W. Went (Fritz W. Went)

3. **Researching F.W. Went's Contribution**: F.W. Went conducted experiments on the coleoptile of plants. He discovered that when the tip of the coleoptile is removed, the plant stops growing towards the light, indicating that the tip is crucial for phototropic response.

4. **Auxin and Its Role**: Went's experiments showed that a substance called auxin, which promotes cell elongation, is produced in the coleoptile tip. When the tip is cut off, auxin cannot be distributed, leading to a cessation of growth.

5. **Experimental Setup**: In his experiments, Went placed agar blocks on the cut tip of the coleoptile to absorb the auxin. When he placed these agar blocks asymmetrically on the cut surface of the coleoptile, he observed that the side with more auxin (the shaded side) grew faster than the illuminated side, causing the plant to bend towards the light.

6. **Conclusion**: F.W. Went's experiments confirmed that the coleoptile tip is essential for phototropic curvature due to the unequal distribution of auxin, which promotes growth on the shaded side.

7. **Final Answer**: The correct answer is F.W. Went.

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