Importance of day length (photoperiodism) in flowering of plants was first shown in
(a) Cotton
(b) Petunia
(c) Lemna
(d) Tobacco

Options

A. Cotton
B. Petunia
C. Lemna
D. Tobacco

Answer

To solve the question regarding the importance of day length (photoperiodism) in the flowering of plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Photoperiodism**:
- Photoperiodism refers to the physiological reaction of organisms to the length of day or night. In plants, it significantly influences flowering and other developmental processes.

2. **Historical Context**:
- The concept of photoperiodism was first studied by researchers in the early 20th century, specifically by scientists named Garner and Allard.

3. **Key Experiment**:
- In their experiments around 1920, Garner and Allard focused on a specific variety of tobacco known as the Maryland mammoth. They discovered that the flowering of this tobacco plant could be manipulated by altering the light exposure (day length).

4. **Conclusion**:
- Based on the historical studies conducted by Garner and Allard, it was established that the importance of day length in flowering was first demonstrated in the tobacco plant.

5. **Final Answer**:
- Therefore, the correct answer to the question is (d) Tobacco.