Question

The essential distinction between long-day and short-day plants is that flowering in long day plants is promoted only when the day length exceeds a certain duration, called the ______________.

• A. critical day length
• B. short-long day length
• C. long-short day length
• D. photoperiod

Answer 1

Answer: (A)

The period of daylight appears to initiate flowering in long-day plants or inhibit flowering in short-day plants. In actual fact, long-day plants will not flower if the dark period exceeds a certain maximum and conversely short-day plants will not flower unless the dark period exceeds a certain minimum. These periods are termed critical dark periods and must be continuous to have effect.