Plant leaves may move due to Moon’s gravitational pull

New Scientist : For the past two millennia, the leaves of plants have been known to move relative to daytime and nighttime. The movement, observers thought, had to do with light exposure at different times of the day. However, plants grown in a constantly light or dark environment also maintain a similar movement cycle. To find out why, Peter Barlow of the University of Bristol studied data gathered over the past century. He found that to a certain degree leaf movements are synchronized with the gravitational forces exerted by the Sun and Moon. The reason may be the movement of water within the plants, Barlow says. Much as ocean tides are produced by the Sun’s and Moon’s gravity in combination with Earth’s rotation, so too might water be pushed and pulled within the joint where leaf meets stem. However, other factors, such as temperature and the circadian clock, are almost certainly at play.