Jenny McElwain

speaker

162 appearances 1 recordings 1 series first heard Jul 2026 last heard 2 Jul

Jenny McElwain’s voice in public audio — every appearance, attributed to the second.

Trend

recordings per month · last 12 months

Recordings per month over the last 12 months — 1 in all, peaking in Jul 2026 with 1.

Appearances

newest first · ▶ plays the moment

In Our Time · The Evolution of Trees · 2 Jul 2026 podcast

And if you think of a tree, it can be woodless, it can have wood.

Trees have worked out many ways of becoming a tree.

So what is wood?

Wood is a tissue made up of lots of cells and those cells are really complex and they are hollowed out and they really look like straws in their simplest form.

So they have a hollow centre and then the cell wall of the straw is thickened with a polymer that is called lignin.

And lignin enables that tree to self-support and not fall down and not rely on other structures to lean on.

So if the tree has lignin, we call it wood.

Actually, the Greek for wood is called xylem.

And that's what those wood cells are called, xylem.

Yeah, so we kind of always think trees are ubiquitous today, so we kind of think they've always been here.

But if you look deep into evolutionary time using fossil plants, between about 460 million years ago and 390 million years ago, the world was treeless.

And in actual fact, plants are just coming onto the Earth's surface out of water and photosynthesising, so they're green.

So if you could imagine you would be walking in a world where you'd see lots of bare rock, very little soil.

And the plants are leafless.

They are rootless and there are no trees.

So the highest plants are kind of brushing your ankle, touching your knee, but there's no massive tree structures on the earth before the advent of trees.

Yeah, that's right.

So evolutionary groups that have evolved in the earliest phase of the earth are mosses, liverworts.

There's also ferns.

So these plants all reproduce by spores.

Showing 21–40 of 162 · page 2 of 9