The Winged Chariot of Time

Flowers that open on the hour

Flowers too have a special “biological clock” which they use to set their internal rhythms and respond to external stimuli. Some flowers open at a particular hour: The great Swedish naturalist Carolus Linnaeus once planted a timekeeping flower bed which he called “Flora’s Clocks.” The blossoms of the convolvulus opened at about 3 a.m., the white lily at 7:00, the marigold at 9:00, and so on for each hour of the day. In many plants, daily rhythms involve not only such particular metabolic processes: the subtle chemistry of photosynthesis, by which they utilize light to manufacture food.