Werewolves aren鈥檛 the only thing the moon is supposed to affect (Image: Perry Mastrovito/Corbis)
The movement of plant leaves may be partially governed by the gravitational pull of the moon, just like ocean tides.
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Some plants鈥� leaves rise and fall during the day-night cycle, mostly in reaction to light in their environment. But plants grown in the dark have similar cycles, which hints that something else 鈥� generally accepted to be a form of internal circadian clock 鈥� may be at work as well.
To investigate further, Peter Barlow of the University of Bristol, UK, looked at data recorded from the 1920s onwards on the leaf movement of beans and other plants. He matched these with computer estimates of the gravitational influence of the moon at the time and location of these experiments.
The two data sets don鈥檛 match exactly, says Barlow, but generally, when the lunar tide turns, so too do the leaf movements. 鈥淵ou鈥檝e got a zero rate of change in gravity, and that seems to be the trigger for movement in the plant鈥檚 cells,鈥� he says. 鈥淚f you look at enough of these correlations, they all seem to be strong enough to make you believe they might be causal.鈥�
Barlow also looked at data from plants on the International Space Station, and found they followed a 90 minute cycle rather than a 24 hour one. Because the ISS orbits Earth every 90 minutes, its position relative to the moon is changing on a faster cycle, so this makes sense, he says.
It鈥檚 not clear exactly how the moon could influence this change, but Barlow believes it has to do with the movement of water within the plant. Ocean tides are produced by a combination of the sun and moon鈥檚 gravity and Earth鈥檚 rotation, creating bulges of water on opposite sides of the planet. For plants, Barlow says water movement in the pulvinus, the 鈥渏oint鈥� where leaf meets stem, could be responsible.
Planting by the moon
Some gardening folklore suggests that planting crops according to the phases of the moon will give you a better harvest, but there is little scientific evidence to back this up. 鈥淚t鈥檚 not really accepted in mainstream science,鈥� says Barlow, who hopes his paper will encourage people to revisit the idea.
Earlier this year, of Stockholm University in Sweden did discover a rare plant called Ephedra foeminea whose pollination is governed by the full moon. 鈥淯nfortunately, scientific work on lunisolar impact on biological systems has sometimes been almost ridiculed, and the field has probably been hampered by unjustified scepticism,鈥� she says. 鈥淭herefore, well-conducted and interesting papers like this are very important.鈥�
There is still scepticism, of course. 鈥淲e definitely cannot exclude that the gravitational effect of the moon and the sun could effect this water-driven movement,鈥� says of the University of Lausanne, Switzerland. But he adds that other forces like temperature would overpower this effect, and there is also genetic evidence for a circadian clock. 鈥淚 am quite sceptical about the great importance of this phenomenon.鈥�
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