Peter M. Vishton

We had an infrared camera so we could see that.

Even the plants, I would bet this is true with your house plants as well, they look like they're stationary, but they're almost always moving.

They just move very, very slowly.

So you look at lots and lots of these three-day cycles.

The Mimosa pudica plant, but lots of plants are what we call foragers.

They forage for light.

They're kind of like if you're in a crowd watching a show up on stage, you sort of move around so that you can see what's going on on the stage.

The plants are doing that all the time to try and get clear of the other plants to get more light.

This slow sort of movement where they're jostling around, that doesn't just happen when the sun's up, it happens in the hours leading up to when the sun comes up.

So at night they get relatively still, but as you get closer and closer to the onset of the light, they start moving around more and more.

The thing we found was not right away, but after about 15 days, after five or six of these three-day cycles where it was dark, on the days when it was going to be dark, the plants didn't move around as much.

They stayed relatively still.

They remembered!

That's suggesting to us they had counted, oh, we've had two days with light, so now it means it's going to be dark for a long time.

So let's kick back.

Let's conserve our resources.

We'll jostle tomorrow when we can anticipate the light.

That is a really hard question.

The first question that almost, if I talk to a botanist, if I talk to a real plant scientist, the first thing they ask me is, well, how are they doing it?

What genes are being expressed selectively that make this happen?