The Private Life of Plants (1995) s01e01 Episode Script

Travelling

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.
And they have to face very much the same sort of problems as animals face throughout their lives if they're to survive.
They have to fight one another, they have to compete for mates.
They have to invade new territories.
But the reason we're seldom aware of these dramas is that plants, of course, live on a different time-scale.
But these days we have ways of speeding things up visually, and then you can see just how dramatic the lives of plants can be.
Condense three months into twenty 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 they 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 invading 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.
Before long, the shoot will put down rootlets, and then new territory will have been annexed for the bramble's empire.
Other adult plants travel even faster.
The bird-cage plant lives in California, but the desert dunes are always moving and a sheltered site can suddenly become intolerably 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 is a miracle of packaging.
Each, after all, contains complete genetic instructions for rebuilding an adult plant like this.
And it's precisely because these grains are so small that it is in this form that most plants do most of their travelling.
Some of these genetic particles, in fact, are microscopic.
The smallest of all belong to fungi.
Fungi are not, to be accurate, plants at all.
They belong to a kingdom all their own.
But the particles they produce, called spores, are in many ways similar to seeds.
A single puffball produces so many 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 bird-cage plant, it can be carried along by the wind.
But the real long-distance travellers are the spores that are knocked from it in clouds, like smoke.
In autumn, other, smaller fungi appear on the woodland floor.
Earth-stars.
Their appearance just after they emerge above ground gives little hint of how complex they will become.
As damp autumn airs blow through the leafless woods .
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the earth-stars begin to transform themselves.
(THUNDER) They open at this time of year to take advantage of the falling rain.
A drip gives them all the energy they need 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.
The device is so efficient that a breeze will carry the seeds high into the sky.
In such a dense crowd of adult plants as this, 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 dispatching their seeds by air - their height.
The farther a seed has to fall, the longer it takes to reach the ground and the further it can travel.
And these cottonwood trees need do no more than 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 seeds from the cottonwoods growing around their margins.
A few will reach a distant shore and germinate.
Most will be lost.
But the cottonwoods produce seeds in such numbers that the loss is of no consequence.
There is much less wind in the tropical rainforest.
Even above the canopy, the humid air hangs as a mist.
Below, there is seldom even a breath of air.
If a plant is to exploit its height here, it 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 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 exact and 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 .
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or this.
Plants also use explosives .
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jet propulsion.
This is a squirting cucumber.
And this, Himalayan balsam.
Its seed capsules are full of liquid at such a pressure, the slightest touch makes them explode.
(FIREWORK NOISES) 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 by their dry tissues 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.
Provided the seeds are given the right equipment, it can shift really heavy, bulky ones.
Beside many a tropical river 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's a groove across the pod between each seed, so that each can fall away independently 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, or even a few hundred miles, the seed arrives at the mouth of its river and makes its way through the mangroves 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 even this is no disaster, for the seed is able to float by itself.
Many, doubtless, are lost at sea, but some eventually reach another, maybe distant, coast.
This one has landed on a tropical beach in northern Australia.
But I've no idea where it came from.
It could be from a tree just up the coast, or from another continent.
Sea-beans are the great success story of seed distribution.
Every year they land on the coasts of Europe, brought by the Gulf Stream from the Caribbean.
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 standing up ahead 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'll 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's a creeper that uses not hooks but spikes, waiting for you to tread on them.
These things are called by the local people devil thorns, and you can quite see why.
If you trod on that with your naked foot, whether you're human or animal, it must be very painful.
But if you think that's bad, what about this? (THREATENING MUSIC) 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 hitch-hiker for many miles without any ill effects.
But there's another way of treating messengers.
Instead of relying on chance encounters, you can entice them with tempting rewards.
Ants are indefatigable workers.
Many plants in the dry heathlands of southern Africa engage them as carriers, by attaching a small reward of ant food to the end of 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, the rest is of no interest to them.
The seed has a safe resting place and an ideal position to germinate, just below the surface of the ground.
Plants bribe larger animals, too, including us.
And what's more, they force us to fit in with their timetable.
This blackberry, for example, is not yet ready for my services, so its fruits are still sour.
But as the seeds complete their development, the flesh around them sweetens and announces the fact by changing colour.
The seeds will be more widely distributed if the plant is visited by a succession of messengers than if it's stripped on a single visit by just one.
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 in much the way 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, unusually, as they ripen 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, in order to eat such small fruit with such a huge beak, has to be a bit of a juggler.
Now comes the important part, as far as the fig is concerned.
Dozens of fruits, containing hundreds of seeds, are ferried away in the hornbill's crop for many miles.
The flesh of the fruit will be digested, then the indigestible bits, including the seeds, will be voided in a distant place in the forest.
Not all forest canopies, however, have such a rich variety of fruit-eaters to serve as messengers as there are in Borneo.
In New Guinea, there are very few mammals and no monkeys at all.
The biggest creature on the forest floor is not an antelope or a great ape, it's a bird - the cassowary.
Both male and female cassowaries have vividly coloured wattles.
The similarity between them and the fruits which are its main food may not be mere coincidence.
The wattles serve as social signals between the birds.
Did plants exploit that by adopting the same colours to call attention to their fruit? Or was it the other way round? Do the cassowaries attract 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 scattered among the leaves.
Visual signals, however, have their limitations as advertisements.
In thick forest you just can't see them unless you're quite close.
But there's another medium for messages, smell.
It may not be so precise, but it works over much 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 will walk for miles to find it.
And so will others.
Durian! (THEY SPEAK IN A LOCAL LANGUAGE) This is it, the famous durian.
I have to say, the smell, to my nostrils at any rate, is fairly disgusting.
An open sewer with a dash of coal gas is a fair description.
But that comes from the rind, that's the advertisement.
This is the fruit and .
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and that's very different.
In fact, it's really pretty good.
A kind of a slimy caramel cream, perhaps, would be a description of this.
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 largely at random, and for some plants, that is simply not good enough.
The fruits of the trewia tree that grow in the forests of Nepal have a particular problem.
Their seeds cannot germinate and grow in deep shade.
They have to be taken out of the forest into a clearing to stand a chance.
There is one big animal that 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 in the heat of the day, but in the cool of the evening, they habitually move out onto the open grasslands that fringe the rivers.
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 in open country on the rhinos' dunghills.
In due course, other trees will grow up around them and the forest will colonise the grasslands.
And then the trewia fruit, once more, will have a problem, and once more 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, there's a great risk that the trewia itself will disappear from the grasslands and river-banks of southern Nepal.
In Africa, elephants, similarly, have become crucial partners for acacias.
That may seem surprising, for they're only too obviously great destroyers of acacias.
When food is short, they use their bulk and strength to knock the trees down to eat their branches.
But without elephants, some species of acacia would barely survive.
Each year, acacias produce huge crops of seeds, and lots of animals come to feed on them.
Inside the pods, the seeds are threatened by serious enemies.
These - little beetle grubs that hatched from eggs injected into the pods.
They will now eat all the seeds, unless they're stopped.
Monkeys eat pods, seeds and grubs, chewing the whole lot very 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, and they go to considerable trouble to pick up what must be, to them, very 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 well walk several miles before, having digested their huge meals, they get rid of the remains.
These acacia seeds have spent at least 24 hours inside an elephant's stomach.
That hasn't harmed them, but it has killed stone dead those beetle grubs.
In fact, the elephant's digestive juices have disinfected these seeds just as efficiently as a farmer does when he dresses his seeds with insecticide.
90% of acacia seeds in elephant dung germinate.
Those in pods left uneaten on the ground will nearly all be killed by beetle grubs.
So acacia seeds eaten by an elephant have not merely been transported, they've been saved from near-certain death.
Some seeds, however, are so well protected that it seems nothing could eat them.
These capsules, themselves as hard as cannon-balls, contain the individually armoured 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 has a way of protecting its seeds from the only animal that can penetrate 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 exactly suits the Brazil nut.
It prudently buries what it can't eat at once, to save it for another time.
But it doesn't have a perfect memory.
It loses track of what it's buried, 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.
And then, like the agouti, the bird hides them, one by one, as provisions to help it through hard times.
But unlike the agouti, it regularly carries the seeds away from the forest, up onto open ground, perhaps because there it can more easily memorise landmarks, to help it find the seeds again months later.
And some of these places suit the young trees very well.
One by one, the bird brings them up from its crop.
It buries them at just the right depth that suits the seed.
And it carefully fills in the hole to conceal its treasure from other seed-eaters.
So the seeds of the arolla pine are carried far from the parent tree and planted with all the care a human forester might give them, not only in high alpine meadows, but in places humans might find very difficult to reach, 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 50 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 to help it climb up here, no clinging roots like ivy.
Its colonies manage to advance up the wall from crack to crack in an entirely different way.
As the petals of its flowers fall off, the seeds within the capsule beneath begin to develop.
And then the toadflax behaves in a most remarkable fashion.
It finds the nearest crack and plants its seeds itself.
So, one way or another, plants get their seeds to the best places to germinate.
But they have another question to settle - what is the best time to do so? These proteas growing here on the southern tip of Africa have had their seeds ready and waiting inside the seed pods for several years now.
Why haven't they released them? Well, the best moment to do so is about to arrive.
There are several species of protea here, and they 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 that protea seeds can germinate, because these seed-heads have to be burnt before they will release their seeds.
And an hour or so after scorching, the heads open.
All around lies a rich ash which will make an excellent and nutritious bed for the seeds.
Protea seeds can remain inert and apparently lifeless for many years, and then spring into life when the right conditions arrive.
Not all seeds can do that.
Some will die after two or three years, whatever the conditions.
But others are able to remain alive for astonishing periods.
One of the most remarkable examples comes from an archaeological site here in Japan.
2,000 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 were also among the first people in Japan who knew how to plant and reap rice.
And they stored their harvests in small pits in the ground.
In one of those pits they found some seeds like these.
These are rice grains.
They're black and 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.
But 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 only survived as that one, lone seed in an archaeological ruin? It's too early to know the answer, but whatever it is, this is surely a marvellous example of the fact that plants, with their seeds, are not only extraordinary travellers in space, but incomparable travellers in time.