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Sunflowers, like animals, have a circadian rhythm — an internal clock that can be set to the external world. During the day, this system sends messages to the eastern sides of their stems, telling those cells to grow slightly longer, which causes the sunflower to lean westward. At night, the message reverses, and the sunflowers tilt back toward the east. “It’s the first example of a plant’s clock modulating growth in a natural environment and having real repercussions for the plant,” said Stacey Harmer, professor of plant biology at University of California-Davis and senior author on the paper published in the journal Science. Even though they don’t sleep, many plants have “clock genes” similar to those that direct the sleep-wake cycle in animals.

Researchers find Degas’ lost portrait

For decades, a black stain has been spreading across the face of an anonymous woman — the subject of a painting called “Portrait of a Woman” by French Impressionist Edgar Degas. Since the 1920s, its oils have gradually faded, hinting at another portrait hidden underneath. Now researchers in Australia have used a high-tech method called X-ray fluorescence to expose the hidden painting. Over the course of about 30 hours, the researchers watched an elemental map of the hidden portrait emerge on a computer monitor. It seems to be a portrait of Emma Dobigny, a model who was a favored subject.

Mammoths may have been thirsty at end

About 6,000 years ago, St. Paul Island, in the Bering Sea hundreds of miles from what is now the Alaska mainland, was uninhabited except for a few species of small mammals and one big one: woolly mammoths. They had been comfortably living there for a few thousand years. But environmental changes, similar to those in our time, caused the population to die out. Rising seas shrank the island’s size, scientists have found, and saltwater pushed inland, displacing freshwater. The mammoths eventually did not have enough to drink.

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