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Short-day plants flower at which point in the year, and on what cue?
AIn spring, when darkness falls below a critical length
BIn spring, when daylight falls below a critical length
CIn late summer and early fall, when days lengthen
DIn late summer and early fall, when nights lengthen
Answer & Solution
Correct answer: D. In late summer and early fall, when nights lengthen
1. A plant reads season from the length of the night, which is why short-day plants are also called long-night plants.
2. Short-day plants flower in the late summer and early fall, when nights exceed a critical length.
3. Long-day plants, also called short-night plants, flower in spring when darkness is less than a critical length.
4. So the cue for a short-day plant is lengthening nights rather than lengthening days.
5. Flowering in day-neutral plants is not regulated by day length at all.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 30 "Plant Form and Physiology", section 30.6 Plant Sensory Systems and Responses_
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