Importance of day length ( photoperiodism ) in flowering of plants was first shown in

Options

A. Lemna
B. tobacco
C. cotton
D. Petunia

Explanation

**Step-by-Step Solution:**

1. **Understanding Photoperiodism**: Photoperiodism refers to the response of plants to the length of day and night, specifically how the duration of light affects flowering. Plants can be categorized based on their light requirements for flowering.

2. **Categorization of Plants**:
- **Long Day Plants**: These plants require more than a certain number of light hours (e.g., more than 8 hours) to flower.
- **Short Day Plants**: These plants require less than a certain number of light hours (e.g., less than 8 hours) to flower.
- **Day Neutral Plants**: These plants do not depend on the duration of light for flowering; they can flower regardless of light duration.

3. **Historical Context**: The phenomenon of photoperiodism was first demonstrated in the early 20th century. Specifically, it was studied by scientists named Garner and Allard in the year 1920.

4. **Experimental Subject**: The specific plant used to study photoperiodism was a variety of tobacco known as "Maryland Mammoth." This variety was crucial in demonstrating how light duration affects flowering.

5. **Findings**: Garner and Allard found that by manipulating light durations, they could induce flowering in Maryland Mammoth tobacco plants during summer or keep them vegetative during winter. This was achieved through artificial darkening or providing extra light.

6. **Conclusion**: Therefore, the importance of day length (photoperiodism) in flowering of plants was first shown in the Maryland Mammoth variety of tobacco by Garner and Allard in 1920.

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