Travelling The Private Life of Plants

Midwinter and the countryside is so still it seems almost lifeless.

But these trees and bushes and grasses around me are living organisms, just like animals,

with the same sort of problems as animals face in their lives if they are to survive.

They have to fight one another; they have to compete for mates,

and they have to invade new territories.

We are seldom aware of these dramas because plants live on a different timescale.

But these days we have ways of speeding things up visually

and you can see just how dramatic the lives of plants can be.

Condense three months into 20 seconds,

and the desolation of winter quickly warms into the riot of spring.

Speed a week into a minute

and you can sense the urgency with which the ground-living plants race to unfurl their flowers.

Wood anemones nod attentively at the sun as it rises and sets each day.

Above, hazel leaves, moving to the same rhythm,

pulse as they expand to their full size.

Beneath them, the broad leaves of docks are rising from the ground.

Foxgloves gape almost alarmingly as they invite insects to come and collect their pollen.

Strange though it may seem, some plants can move not just their flowers and leaves,

but can travel from place to place.

Take, for example, this bramble.

Of all the woodland plants,

this is one of the most aggressive.

It waves its shoots agitatedly from side to side as if feeling for the best way forward.

And when a shoot settles on its course, it thrusts ahead relentlessly.

The stem's backward-pointing spines give it the grip it needs

to climb over almost anything that stands in its way.

It can advance as much as three inches in a day.

The shoot will put down rootlets

and new territory will be annexed to the bramble's empire.

Other adult plants travel even faster.

The birdcage plant lives in California,

but the desert dunes are always moving and a site becomes exposed,

so the plant must find a new place.

This plant is now dead, but within it there is still life.

These tiny particles are the next generation.

Each contains complete genetic instructions for rebuilding an adult plant like this.

These small grains are the reason most plants do most of their travelling.

Some of these genetic particles are, in fact, microscopic.

Smallest of all belong to fungi.

Fungi are not, to be accurate, plants at all

they belong to a kingdom on their own

but their spores are in many ways similar to seeds.

A single puffball produces so many that someone has calculated that if, for two generations,

every spore grew into an adult, the resultant mass of puffballs

would be 800 times the volume of the earth.

Like the birdcage plant, a puffball can be carried along by the wind,

but the real travelling is done by the spores that are knocked from it in clouds, like smoke.

In autumn, other smaller fungi appear on the woodland floor.

Earthstars.

Their appearance when they emerge gives little hint of how complex they will become.

In the damp autumn air, the earthstars transform themselves.

They open at this time of the year to take advantage of the falling rain.

A drip gives them the energy

to propel their spores into the air.

Flowers also use the wind to transport their seeds

and few do it more successfully than dandelions.

As their petals fall their flower heads, over a period of one or two weeks,

are transformed into wonderfully intricate globes,

each a precise array of a hundred or so seeds, all awaiting the wind.

Their seeds are much heftier than the spores of fungi.

For them to fly, special apparatus is needed.

Each is fitted with its own individual parachute.

It is so efficient that a breeze carries the seeds high into the sky.

In this dense crowd of adult plants,

there's no room for the next generation.

The seeds must get away, and the wind will take them for miles.

Trees have a particular advantage when despatching their seeds by air their height.

The farther it falls, the farther it travels.

And these cottonwood trees

need only provide their seeds with straightforward fluff.

But this, because of their height, is enough to carry them for miles.

Every summer, the waters of the Great Lakes of North America become thickly flecked

with cottonwood seeds around their margins.

A few will wash up on distant shores and germinate.

Most will be lost. But the seeds are so numerous it's of no consequence whatever.

There is much less wind in the tropical rain forest.

The humid air hangs as a mist,

while below, there is seldom even a breath in the air.

A plant here has to give its seeds very good flying equipment indeed.

And none does that better than this liana in Borneo.

Aircraft designers have tried to build a wing as efficient as this this one but failed.

Even the faintest updraught produced by the slightest thermal

is enough to lift this little glider with its seed passenger, and so extend its flight.

Plants preceded humanity in building fixed-wing gliders and not only gliders.

They created helicopters too...

..sycamore seeds.

The balance between the weight of the seed and the length and width of the wing is perfect.

A slightly heavier seed or a shorter and narrower wing

and the whole thing would fall like a stone.

The tri-star plant produces a revolving seed with six blades

and aircraft designers have yet to copy that.

Or this.

Plants also use explosives...

..jet propulsion.

This is a squirting cucumber.

And this Himalayan balsam.

Its seed capsules are pumped full of liquid to such a pressure

that the slightest touch makes them explode.

The force is so great

that seeds can be shot away for as much as fifteen feet.

Mesembryanthemum seed heads are opened by rain.

It's the sudden absorption of water

that powers their opening.

Once open, they expose a screen as taut as a trampoline.

Raindrops bounce off it, taking the seeds with them.

Water provides many plants with the power they need for travelling.

It can shift really heavy, bulky ones.

Beside many tropical rivers, there hangs the biggest of all seed pods the sea bean.

These huge containers house one of the most successful of all vegetable travellers.

There is a groove between each seed, so that each can fall away in its own separate packaging.

One by one, the sea beans start on their voyages.

This one is setting off down a small river in Africa.

After a few miles perhaps even a few hundred miles

the seed arrives at the mouth of its river and makes its way to the sea.

It can voyage through groups of islands and out into the open sea

to ride the great ocean currents for as much as a year and still remain alive.

Its protective packaging

may become so frayed and tattered that it disintegrates and releases the seed.

But it's not a disaster, for the seed is able to float by itself.

Many, doubtless, are lost at sea. But some eventually reach another and maybe a distant coast.

One has landed on a tropical beach in northern Australia,

I've no idea where it came from. It could be from a tree a few miles up the coast,

or from another continent. Sea beans land on the coast of Europe, having come with the Gulf Stream.

Of course it's too cold for them there and they seldom germinate,

but if they land in the tropics, they will almost certainly grow. There's one on this very beach.

So, some plants send their seeds by sea, some by air.

But most, in fact, use living couriers.

Animals with hairy coats

are easily conscripted.

The burdock uses hooks hundreds of them.

And very effective they are.

Eventually the burrs are licked off,

picked off, or shaken off.

If the burdock is lucky,

that will happen some distance from where the adult plant grew.

Trousers will serve just as well as hairy coats,

and shoes as hooves or paws.

Here, in southern Africa, there is a creeper that uses not hooks but spikes.

These things are called by the local people 'devil thorns' and you can see why.

If an animal or human trod on that with a naked foot it would be very painful.

But if you think that's bad, what about this?

This is the seed case of the grapple plant.

Animals with cleft hooves or relatively soft pads

can be crippled by the grapple plant, but the bony, scaly feet of ostrich

are particularly tough.

They can carry this vicious hitchhiker for many miles

without any ill effects.

But there's another way of treating messengers.

Instead of relying on chance encounters with them,

you can tempt them with rewards.

Many plants in these dry heathlands

engage ants as carriers by attaching ant food to their seeds.

If a seed lies out in the open for long here,

a mouse or some other rodent will eat it. If it's to survive,

it must get below ground quickly.

And the ants take it there.

The fleshy bit at the end is all the ants want.

So the seed has now reached a safe resting place

just below the surface of the ground.

Plants bribe us too. And they make us fit in with THEIR timetable.

This blackberry, for example, is not yet ready for my services.

But as the flesh around the seeds sweetens, it announces the fact by changing colour.

The blackberry's seeds will be more widely distributed

if the plant is visited by a succession of different messengers

so its berries do not all ripen simultaneously.

Birds find them irresistible,

and quickly spot them. For black is a very conspicuous colour. And so, too, is red.

Birds see colour the same way as we do.

What is vivid to them is vivid to us.

So rowans and yews, strawberries and plums,

cherries and hawthorns, use red or black to summon birds to collect their fruit.

Tropical figs produce much smaller fruit than their European relative,

and they turn yellow. Even so, their message is widely understood.

A tropical fig tree in fruit is a huge bonanza in the forest.

All kinds of diners come to the tree.

As well as fruit-eating birds, they attract all kinds of mammals

monkeys, squirrels and gibbons.

The rhinoceros hornbill, with its huge beak,

has to be a bit of a juggler.

Now comes the important part.

Dozens of fruits containing hundreds of seeds are ferried miles away in the hornbill's crop.

The flesh of the fruit will be digested

and the seeds will be voided in a distant place in the forest.

All forest canopies, however, do not have such a rich variety of fruit eaters as in Borneo.

In New Guinea, there are very few mammals and no monkeys at all.

The biggest creature on the ground is not an antelope or a great ape.

It's a bird the cassowary.

Both male and female cassowaries have vividly coloured wattles, and the similarity between them

and the fruits may not be coincidence.

The wattles serve as social signals between the birds.

Did plants adopt the same colours to call the birds' attention to their fruit?

Or did the cassowaries make themselves more attractive to their mates

by reminding them of a good meal? No-one can say for sure.

What is certain is that cassowaries have no difficulty finding objects with these colours among the leaves.

Visual signals, however, have their limitations as advertisements.

In thick forest, you just can't see them unless you are quite close.

But there is another medium smell. It's less precise, but it works over greater distances.

In Borneo, one fruit produces a smell so pungent

that a sensitive nose can detect it from half a mile away.

And some people like the taste of that fruit so much that they walk miles to find it.

And so will others.

This is it the famous durian.

I have to say that the smell, to my nostrils at any rate, is fairly disgusting.

Like an open sewer with just a dash of coal gas.

That's the rind. It's the advertisement. This is the fruit.

That's very different.

It's really pretty good.

A kind of... slimy caramel creme, perhaps, would describe it.

But if all Europeans aren't instantly durian addicts, all orang-utan are.

Animals may carry seeds for long distances in their stomachs,

but most get rid of them at random.

For some plants, that is simply not good enough.

The trewia tree in the forests of Nepal has a particular problem.

Their seeds cannot germinate in deep shade.

They have to be taken into a clearing if they are to stand a chance

and one animal will do that for them,

the great Indian rhinoceros.

It's so fond of these fruits

that they're called, locally, 'rhino apples'.

The rhinos usually feed in the forest during the heat of the day,

but in the cool of the evening they habitually move out into open grasslands.

The grasslands are created by monsoon floods that, every few years,

wash away parts of the forest. Rhinos visit them for the rich grazing.

And out here, on regularly used communal middens,

they perform the last of their daily duties.

And there, neatly deposited with a ration of fertilising manure,

are the seeds of the trewia.

So young trewias sprout on the rhinos' dunghills.

Other trees will grow, and the forest will colonise the grasslands.

Then the trewia fruit, once more, will have a problem, and rely on the rhino to solve it.

Sadly, this magnificent animal

is getting rarer and rarer.

Over millions of years of evolution, the trewia tree has established a link with it.

But if the great Indian rhinoceros becomes extinct,

the trewia itself may disappear from the grasslands and riverbanks of southern Nepal.

In Africa, elephants similarly have become crucial partners for acacias.

That may seem surprising, for they are only too obviously great destroyers of acacias.

For when other food is short, they will use their great strength

to knock the trees down to eat their branches.

But without elephants, some species of acacia would barely survive.

Lots of animals come to feed on acacias.

Inside the pods, the seeds are threatened

by serious enemies. These beetle grubs hatched from eggs

injected into the pods.

They will now eat all the seeds unless they are stopped.

Monkeys eat pods, seeds and grubs chewing it all thoroughly.

The acacia gets little benefit from providing THEM with meals.

But elephants are different.

They greatly relish the seed pods which are highly nutritious.

They go to considerable trouble

to pick up these fiddly little things.

But they don't grind up their food into such a fine mash as monkeys do.

And having fed, they move on.

They may walk for several miles before, having digested their meals, getting rid of the remains.

These acacia seeds,

have spent at least 24 hours inside an elephant's stomach.

This has killed stone dead those beetle grubs.

The elephant's digestive juices have disinfected these seeds

just as efficiently as a farmer dressing his seeds with insecticides.

Ninety percent of acacia seeds in elephant dung germinate.

Those in pods that are left uneaten on the ground will be killed by beetle grubs.

So acacia seeds eaten by an elephant have not merely been transported, but saved from near-certain death.

Some seeds, however, are so well-protected that it seems that nothing could eat them.

These capsules, as hard as cannon-balls,

contain the individual seeds the nuts

of the Brazil-nut tree.

Even a fall of a couple of hundred feet doesn't crack them.

Only one animal has the equipment to open them the agouti.

The agouti has two pairs of front teeth that are as sharp as chisels

and they enable it to gnaw a hole into the capsule and get at the seeds.

But the Brazil-nut tree protects its seeds from the only animal

that has penetrated its armour.

It presents it with 15 or 20 nuts far more than an individual agouti could eat in one sitting.

And the agouti has a habit which suits the Brazil nut. It buries what it can't eat, for later.

What it doesn't have is a perfect memory. It loses track.

And a significant proportion of the nuts survive to sprout.

The Alpine nutcracker a kind of crow is an even more obliging partner for the arolla pine.

The bird knows exactly how to open the cones and pick out the ripe seeds.

Each one is swallowed, but it doesn't go into the stomach. It's stored in the crop,

while the bird tackles the next.

Then, like the agouti, the bird hides them, one by one, as provisions for hard times.

But, unlike the agouti, it carries the seeds away from the forest onto open ground,

perhaps because there it can more easily memorise landmarks

to help it find the seeds again months later.

These places suit the young trees very well.

One by one, the bird brings them up from its crop.

It buries them at a depth that suits the seed.

Then it fills in the hole to conceal its treasure.

So the seeds of the arolla pine are carried far from the parent tree

and planted with all the care that a human forester might give them,

not only in high alpine meadows,

but even high up on the mountain ridges.

Yet some plants succeed in reaching seemingly inaccessible sites

without the help of any animal

and entirely by their own exertions.

A crack in a wall fifty feet above the ground is not easy to reach.

But the ivy-leaved toadflax, nonetheless, manages to get there.

It has no suckers like Virginia creeper or clinging roots like ivy.

Its colonies manage to advance up the wall, from crack to crack,

in an entirely different way.

As the petals fall off, the seeds in the capsule beneath begin to develop.

Then the toadflax behaves in a most remarkable way.

It finds the nearest crack and plants its seeds itself.

So, plants manage to get their seeds

to the best places to germinate. But what is the best time?

These protea growing here on the southern tip of Africa

have had their seeds inside the seed pods for several years now.

The time to release them is about to arrive.

The several species of protea growing here all depend upon the arrival of seasonal fires.

The fire has killed all the adult plants on this land,

so this is an excellent time for seeds to germinate. There are no established competitors.

In fact, it's the ONLY time protea seeds can germinate,

because these seed heads have to be burnt to release their seeds.

An hour or so after scorching, the heads open.

All around lies a rich ash,

which makes a nutritious bed for the seeds.

Protea seeds can remain inert and apparently lifeless for many years

and then spring into life when conditions are right. Some will die after 2 or 3 years.

But others are able to remain alive for astonishing periods.

One of the most remarkable examples comes from an archaeological site here in Japan.

Two thousand years ago a small settlement,

with buildings like these, stood at a place called Asada.

The people who lived here in such houses

had only just begun to master the art of working metal. They also knew how to plant rice.

They stored their harvest in small pits.

In one of those pits they found some seeds, like these.

These are rice grains obviously dead.

But this is a magnolia seed.

Scientists took away that strange, ancient seed, planted it and it grew.

At first it looked like Magnolia kobus, the wild species that still grows in Japanese woods.

Then, in its tenth year,

it produced its first flower buds. These, when they opened, would reveal exactly what it was.

Magnolia kobus today, typically, has six petals on its flowers.

But this flower has an extra petal seven.

And this has eight.

Is this a consequence of its long sleep, or were all Magnolia kobus 2,000 years ago variable like this?

Or could it be that this is an ancient species

that has survived as that one lone seed?

It's too early to know the answer to those questions,

but this is surely a marvellous example of the fact that plant seeds

are not only extraordinary travellers in space, but incomparable travellers in time.

Subtitles by Wilma Campbell BBC Scotland 1995