SDP plants flower when the days are shorter. They need less than the critical duration of light (about 8-10 hours) and a continuous dark period (about 14-16 hours) to flower. Thus, both light and dark period are very critical for SDP plants and has to be continuous. So, option d is correct.

Short Day Plants and the Critical Period

Short day plants are a type of plants that require a specific duration of darkness, or a critical period of darkness, in order to initiate and maintain their flowering process. This critical period of darkness is crucial for the activation of the plant's photoperiodic response, which is the ability to sense and respond to the duration of day and night.

The Critical Period for Short Day Plants

The critical period for short day plants is the duration of darkness that is required for the initiation of flowering. During this period, the plant needs to be exposed to uninterrupted darkness for a specific number of hours in order to trigger the flowering process. The length of this critical period differs among different species of short day plants.

Factors Influencing the Critical Period

1) Light: Short day plants require a specific duration of darkness to initiate flowering. If they are exposed to light during the critical period, it can disrupt the flowering process and delay or inhibit flower formation.

2) UV Rays: UV rays are a part of the light spectrum and their presence can also affect the flowering process of short day plants. Exposure to UV rays during the critical period may interfere with the plant's ability to perceive the duration of darkness and disrupt the photoperiodic response.

3) Dark/Night: The critical period for short day plants is primarily determined by the duration of uninterrupted darkness. During this period, the plant's internal clock is triggered by the absence of light, signaling the initiation of flowering.

4) Both A and C: The critical period for short day plants is influenced by both light and darkness. While darkness is essential for initiating flowering, exposure to light during this period can interrupt the process. Therefore, both light and darkness play crucial roles in determining the critical period for short day plants.

Conclusion

In summary, the critical period for short day plants is the duration of uninterrupted darkness required to initiate flowering. Light and darkness both play important roles in determining this critical period. Exposure to light or UV rays during the critical period can disrupt the photoperiodic response and delay or inhibit flower formation in short day plants.