Many tulip species originate from Southwest and Central Asia, where summer temperatures can be extremely high. As a survival mechanism, these plants become dormant in the hot summer months, moving below ground as bulbs. Plants that produce underground storage organs as a way of storing food for the next growing season or to escape adverse environmental conditions are known as ‘geophytes’. After flowering in the cooler spring months, their leaves wither and die off, meaning no parts of the plant remain above ground during the dormant period. Consequently, the remaining underground bulb cannot detect the length of the day by sensing light, so instead it relies on its ability to sense changes in temperature, starting to grow only once a set period of cold (i.e., winter) has passed. Sensing seasonal rhythms often requires environmental cues as well as activity of the circadian clock.
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