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Problem : What is deceptive about calling various plants short-day, long-day, or day-neutral?

The flowering of these plants is actually related to the night rather than the day. Duration of uninterrupted darkness hours, scientists have found (after labeling the plants), is the factor that leads to photoperiodism in plants.

Problem : Define photoperiodism.

An organism's response to the length of day and night within a 24-hour period (photoperiod); in many plants, this phenomenon determines when flowering will occur.

Problem : Define and give some examples of day-neutral plants.

Day-neutral plants are independent of photoperiod when it comes to the onset of flowering; they can produced flowers in seasons of short nights as well as long. Examples of day-neutral plants are tomatoes, sunflowers, dandelions, rice, and corn.

Problem : Why do scientists think there might be a flowering hormone in plants? What have they termed this hypothetical hormone?

Scientists speculate that a flowering hormone (called florigen) exists because photoperiod is detected by leaves and must send a signal regarding the duration of nighttime hours over to the buds. Signals such as this are usually sent by hormones.

Problem : What is the leaf pigment that detects the duration of day and night?

Phytochrome.
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