Who discovered that phototropism is the result of presence of more auxin on shaded side than on illuminated side.

Options

A. Galston
B. Boysen-Jensen
C. Went
D. Kogl and Haagen-Smit.

Answer

**Step-by-Step Solution:**

1. **Understanding Phototropism**: Phototropism is the growth of plants in response to light direction. Plants tend to grow towards the light source.

2. **Role of Auxins**: Auxins are plant hormones that play a crucial role in regulating plant growth. They are responsible for cell elongation, which is a key factor in phototropism.

3. **Observation of Avena Coleoptile**: F. W. Wendt conducted experiments on the Avena coleoptile (the shoot of a young grass plant). He observed that when the tip of the coleoptile is cut, the elongation of the plant stops.

4. **Reintroduction of Auxins**: Wendt found that if auxin is applied externally to the cut tip, the elongation of the coleoptile resumes. This indicates that auxins are produced in the tip and are essential for growth.

5. **Distribution of Auxins**: Wendt's experiments showed that auxins are not evenly distributed. When light shines on a plant, auxins move from the illuminated side to the shaded side, resulting in a higher concentration of auxins on the shaded side.

6. **Resulting Growth Direction**: Because there are more auxins on the shaded side, the cells on that side elongate more than those on the illuminated side. This differential growth causes the plant to bend towards the light, demonstrating positive phototropism.

7. **Conclusion**: Wendt concluded that the presence of more auxins on the shaded side than on the illuminated side is the reason for the bending of the plant towards the light source.

**Final Answer**: F. W. Wendt discovered that phototropism is the result of the presence of more auxin on the shaded side than on the illuminated side.

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