The correct answer is option 'B' - Blackman.

The Law of Limiting Factor is a principle in plant physiology that states that the rate of a physiological process is determined by the factor that is present in the lowest or most limiting amount. This means that even if all other environmental factors are optimal, if one essential factor is deficient or limited, it will determine the rate of the process. The concept of the Law of Limiting Factor was proposed by Frederick Frost Blackman, a British plant physiologist, in the early 20th century.

Blackman's work on photosynthesis and respiration led him to formulate this law. He conducted experiments to understand the factors affecting these processes and found that the rate of photosynthesis or respiration is limited by the factor that is least available or present in the lowest concentration. He observed that increasing the concentration of a limiting factor would increase the rate of the process until another factor became limiting.

Key points:
1. Law of Limiting Factor: The rate of a physiological process is determined by the factor that is present in the lowest or most limiting amount.
2. Proposed by: Frederick Frost Blackman, a British plant physiologist, in the early 20th century.
3. Blackman's work: Conducted experiments on photosynthesis and respiration to understand the factors affecting these processes.
4. Rate limitation: The rate of photosynthesis or respiration is limited by the factor that is least available or present in the lowest concentration.
5. Increasing concentration: Increasing the concentration of a limiting factor would increase the rate of the process until another factor becomes limiting.

The Law of Limiting Factor has important implications in agriculture and plant growth. It helps in identifying and addressing the factors that limit crop productivity. By understanding the limiting factors, farmers and scientists can optimize the growth conditions for plants and improve yields. For example, if a crop is limited by water availability, providing adequate irrigation can help overcome this limitation and enhance crop growth.

In conclusion, the Law of Limiting Factor was proposed by Frederick Frost Blackman. His work on photosynthesis and respiration led him to formulate this principle, which states that the rate of a physiological process is determined by the factor that is present in the lowest or most limiting amount. This concept has significant implications in agriculture and plant physiology.