Tell us about it.

It's 500 million years ago, so nobody can say no, can they? Plants colonised land probably somewhere around 500 million years ago, maybe slightly more recently than that.

And the fossils of the first plants have no leaves.

And for 50 million years, plants were little short things, mainly stem roots.

And there was stomata on the stems themselves, I believe.

Wait, how do you know this? We know this from fossils.

And in particular, there's a wonderful... deposit of fossils at a little village called Rhynie, just south of Aberdeen.

That's another B minus for other.

A- and, and what sort of, um, sensors do they have o- on, on them, uh, leaves? And, and how does that vary from plant to plant? I mean, can they sense chemicals in the environment that are toxic? C- uh, can they sense, um, uh, predators?

They sense predators in, in, in a couple of ways.

I mean, one is when they bury their jaws into the, into the leaf.

This sets off all sorts of, uh, chemical alarms which raise the, the, the concentration of nasty chemicals that will slow down the rate at which things like caterpillars can, can digest the food.

So that's one thing which a lot of plants do.

And some of those chemicals are, are vaporized.

They actually escape through the little pores in the leaf called stomata.

Mm.

Right.

There's no image.

There's no, no, no, no image capture going on in a plant.

It is, of course, sensitive to light, and plants will bend towards the light very obviously.

There are occasionally, by the way, plants that will actually bend away from light towards darkness.

That's another story.

So plants don't hear in the way that listeners to this podcast are hearing what I'm saying, but they do have a sense of touch that's mediated by these little hairs called trichomes, and certain frequencies vibrate those trichomes.

So, you know, what's going on there? Why do they produce such a vast degree of these different aromatic compounds? You know, what do we know about what the kind of, you know, evolutionary purpose of those is?

[chuckles]

... or on the way to the pub or the way back or, or, or so- some informal setting.

Um, I remember we were just walking and, and he said, he looked up at a tree and he said, "Why do trees have so many leaves?" Now, this was, I mean, his, his own PhD.

He-- I think he, he was originally an engineer.

He did genetics on Drosophila.

He was a theoretical biologist.

Uh, but he, he, he was a key bird watcher and a, and, and, and something of a naturalist.

Mm-hmm.

Tell me about Rhamney Chirp.

Ah, Rhamney Chirp.

It contains the most exquisite fossils of some of the earliest land plants, and they were preserved in a hot spring, or a series of hot springs, about...

I hope I get the time right, it's about 430 million years ago.

It's a mecca for paleobotanists and, you know, anybody interested in the, in the history of life really, uh, because you can see these, under a microscope, when, in a properly prepared rock specimen, you can see these tiny little plants, and they're sort of, their, their, their bodies are like tu- little, little tubular stems, and they've got rather primitive branches.

No leaves.

No leaves.

You know, it's a-