Scientists have long known that plants have a day-to-night cycle. Some trees close their leaves in the evening. Most flowers open up their petals in the morning.But these observations have largely been made only in experiments with potted plants. Now, a team of scientists has used a laser scanner to measure trees’ daily cycles in the wild, and they’ve discovered that trees sleep. “Our results show that the whole tree droops during night, which can be seen as position change in leaves and branches,” Eetu Puttonen, a scientist at the Finnish Geospatial Research Institute and lead author of the new study, said in a statement. Silver birch leaves drooped to their lowest point a couple of hours before sunrise and became upright again a few hours later. It isn’t yet clear whether the sun or the plants’ internal rhythm spurs the movement. The findings were recently published in the journal Frontiers in Plant Science.