The law of limiting factors was proposed by

Options

A. R. Emerson
B. Robert Hill
C. D. Amon
D. F.F. Blackman

Answer

### Step-by-Step Solution:

1. **Identify the Question**: The question asks who proposed the law of limiting factors in photosynthesis.

2. **Review the Options**: The options provided are:
- R. Emerson
- Robert Hill
- D. Ammon
- F. F. Blackman

3. **Recall Relevant Information**: The law of limiting factors is a principle in plant physiology that states that the rate of a process (like photosynthesis) is limited by the factor that is in the shortest supply.

4. **Identify the Correct Answer**: F. F. Blackman, a plant physiologist, proposed the law of limiting factors in 1905. He emphasized that the rate of photosynthesis is limited by the slowest factor, which can include carbon dioxide concentration and temperature.

5. **Conclude the Answer**: Therefore, the correct answer to the question is **F. F. Blackman**.