Capillarity theory was proposed by

Options

A. Unger
B. Sachs
C. Bohm
D. Mac Dougal

Answer

**Step-by-Step Solution:**

1. **Understanding Capillarity Theory**: Capillarity theory explains the mechanism of water transport in plants, particularly through the xylem vessels. It is based on the principles of surface tension and adhesive forces.

2. **Key Components of the Theory**: The theory highlights two main forces:
- **Surface Tension**: This is the tension created by the liquid molecules at the surface, which helps in pulling the water upward.
- **Adhesive Forces**: These are the forces between the water molecules and the walls of the xylem vessels that assist in the upward movement of water.

3. **Role of Xylem**: The xylem vessels in plants act like fine capillary tubes. The finer the xylem vessels, the greater the rise of water due to the combined effects of surface tension and adhesive forces.

4. **Identifying the Proposer of the Theory**: The question asks who proposed the capillarity theory. The options provided are:
- Unger
- Sachs
- Boehm
- McDougall

5. **Evaluating the Options**:
- **Unger**: While he was a notable plant physiologist, he did not propose the capillarity theory.
- **Sachs**: Known for his contributions to plant physiology, but not specifically for this theory.
- **Boehm**: He is recognized as the scientist who proposed the capillarity theory.
- **McDougall**: He contributed to plant physiology but not specifically to the capillarity theory.

6. **Conclusion**: Based on the evaluation, the correct answer is Boehm, who proposed the capillarity theory.

**Final Answer**: The capillarity theory was proposed by Boehm.

---