Plants which form flowers only when the day length exceeds 12 hours are called:

Plants which form flowers only when the day length exceeds 12 hours are called:

• A. short-day
• B. long-day
• C. day-neutral
• D. long-blooming

Answer: (B)

Photoperiodism governs when many plants flower by sensing how long the day is. Some plants need long days to flower; these are long-day plants. When daylight exceeds a certain threshold—around 12 hours for many species—these plants initiate flowering. The exact threshold varies by species, but the pattern is the same: longer days trigger flowering in long-day plants. In contrast, short-day plants flower when days are shorter than their threshold, and day-neutral plants flower regardless of day length. So, flowering only after day length passes the 12-hour mark fits the behavior of long-day plants.

Photoperiodism governs when many plants flower by sensing how long the day is. Some plants need long days to flower; these are long-day plants. When daylight exceeds a certain threshold—around 12 hours for many species—these plants initiate flowering. The exact threshold varies by species, but the pattern is the same: longer days trigger flowering in long-day plants. In contrast, short-day plants flower when days are shorter than their threshold, and day-neutral plants flower regardless of day length. So, flowering only after day length passes the 12-hour mark fits the behavior of long-day plants.