F.Skoog and coworkers added the following substance in addition to auxins in their experiments.

Options

A. Leaf extract
B. Root extract
C. Yeast extract or coconut milk
D. Malt extract

Answer

**Step-by-Step Solution:**

1. **Understanding the Context**: F. Skoog and his co-workers were conducting experiments related to plant growth, specifically focusing on the role of auxins in plant tissue culture.

2. **Identifying the Experiment**: In their experiments, they observed the formation of callus tissue in tobacco plants when they added certain substances to a nutrient medium that already contained auxins.

3. **Substances Used**: The substances they added included yeast extract, vascular tissue extract, and coconut milk. These substances were crucial for promoting cell proliferation and differentiation in the callus tissue.

4. **Discovery of Kinetin**: During these experiments, they discovered a substance called kinetin, which was associated with rapid cell division in areas such as root tips and shoot buds.

5. **Choosing the Correct Option**: Among the given options (Leaf extract, Root extract, Yeast extract, Malt extract), the correct substance that Skoog and his co-workers added to auxins in their experiments is **Yeast extract**.

**Final Answer**: The substance added by F. Skoog and co-workers in addition to auxins in their experiments is **Yeast extract** (Option 3).

---