The Private Life of Plants (1995) s01e03 Episode Script

(SNEEZES) The English summer fills our landscape with lovely flowers, but it comes at a price - hay fever.
For those of us who suffer from it, and I certainly do, our eyes swell, nose runs and we get overcome with fits of uncontrollable sneezing.
The source of our affliction is filling the air all around me - pollen grains.
No bigger than specks of dust, they are astonishingly varied and complex in shape.
Each species of plant has its own characteristic pattern.
They're shed in millions from stamens that tumble out of the grasses' tiny flowers.
As the grains are released, so the wind carries them away.
It's these tiny particles, when they get up our nostrils, that give so many of us such a bad time.
But their proper destination, of course, is not the human nose, it's structures like these, the stigmas of other grass flowers.
When a pollen grain carried by the wind lands on one of these feathery traps, a grass plant is fertilised and can then produce seeds which will grow into other grass plants.
You might think such a method of distributing pollen would be very wasteful and inefficient, but the fact remains that grasses are extraordinarily successful.
They've spread to every continent on earth, and some of them have grown very big indeed.
These, in Nepal, are the biggest of all, standing twenty feet tall.
Human beings, even rhinoceroses, could be moving around in such mammoth meadows and still be totally concealed.
Hazel, like many trees, also relies on the wind to distribute its pollen.
Because pollen is produced in vast quantities and discharged wholesale, it and the structures from which it comes, like these catkins, are regarded as male.
The female structures, the stigmas, grow separately on the hazel as tiny pink sprays.
At the base of each stigma, there's a chamber holding a few eggs - in hazel, only one.
Although many pollen grains may fall on a stigma, only one is needed to fertilise an egg.
The grain develops a microscopic tube, which grows down through the stigma and unites with the egg at the bottom.
This then swells and becomes a hazelnut.
Most plants, however, combine their male and female structures into one flower.
The stigma is usually in the centre, with the pollen-producing stamens clustered around it.
The petals are advertisements to attract animal messengers who will carry the pollen from one flower to another.
Many flowers, like this wild geranium, ripen their male and female structures at different times, to prevent self-fertilisation.
First, the stamens curl back and release pollen from the containers at their tip.
Only then does the white stigma open.
Now it's ready to receive pollen from another plant.
The strange kangaroo-paw flower from Western Australia produces its stamens in a line, like a comb, with the thinner, longer stigma projecting in front of them.
The flowers grow in a spike, and open in succession to offer visiting animals a drink of the sweet nectar that each holds in its depths.
And when a honey-eater reaches down with its beak to collect that nectar .
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it gets pollen over the back of its neck.
And then, when the bird goes to drink elsewhere, the stigma of the second plant is brushed with the pollen from the first.
In South America, hummingbirds are the great nectar-drinkers.
Flowers load them with pollen in similar ways.
The stamens of this one are clustered into a brush.
And on goes the pollen.
Many of these bird-pollinated flowers are red.
This is not just a coincidence.
Unlike insects, which are more sensitive to blue light, birds have a colour vision much like ours, and red draws their attention as quickly as it draws ours.
This South American plant, columnea, at first sight has no bright colours at all.
But look at its leaves from beneath.
They have translucent blotches, and the light shining through them gives them the scarlet brilliance of stained-glass windows.
The flowers, close to the stem, are pale, small and so easily overlooked.
But hummingbirds have learned to recognise that the leaf blotches are signposts.
In some ways, this is an even better way of advertising than using petals.
The red patches are more economically produced, they last longer than petals, and they will advertise a whole succession of flowers.
It's a good guess that a red, robust, trumpet-shaped flower, no matter where you find it, will be bird-pollinated.
These aloes, for example, are in South Africa, and this is a sunbird.
There's another prediction you can make.
Not only are prominent red flowers likely to be pollinated by birds, but they're unlikely to have any scent.
And this aloe hasn't.
The reason why is obvious - birds, with very few exceptions, lack a sense of smell.
Perfume would be wasted on them.
Colour is all they need to attract their sharp-eyed, red-sensitive pollinators.
This aloe, like many in the family, ripens its stigmas at the same time as its stamens.
So you might think the plant would be in danger of fertilising itself.
But aloes have a way of preventing that.
Their stigmas can recognise their own pollen, and will only accept pollen from other plants.
Proteas, another South African plant family, Iike aloes produce a multitude of small flowers clustered together.
But they pack them even more closely, so that several hundred tiny florets form a single, spectacular bouquet.
Those in the centre may produce stamens and stigmas and nectar, while those around the outside are sterile and serve only as advertisements.
So proteas produce spectacular flower-heads of great variety, and offer their pollinating birds a large number of individual sips of nectar.
But a few are different.
This, too, is a protea, and although at first sight it might be difficult to believe, it too is in full bloom.
But the flowers are not perched conspicuously on top, they're down here.
They're brown, they point downwards and in the evening they develop a yeasty smell.
They're obviously not suited for pollination by birds.
But to discover what does pollinate them, you have to watch them after dark.
(CHIRPING OF INSECTS) A little bush mouse.
The banquet won't last long, for the flowers will soon be over.
Then the mouse will go back to its normal diet of seeds.
But by that time, it will have carried pollen from one plant to another, on its nose, which is all the protea requires as payment for the meal.
The durian tree of Borneo also blooms at night, and is also tended by nocturnal mammals fruitbats.
They rival birds in their effectiveness as pollinators, for they too will fly great distances in search of food.
Mammals were the most recent group in the animal kingdom to evolve.
Before them, the reptiles ruled, and some of them, doubtless, in the time of the dinosaurs, were conscripted by plants, as some are still today.
The giant gecko of New Zealand is one.
The islands' only native mammals are bats, so plants have limited candidates for the job of courier.
The gecko has been recruited by the pohutakawa tree.
Dawn in Madagascar.
Madagascar split away from the eastern flank of Africa 40 million years ago, and it's been isolated ever since.
Because of that, it has plants today that are found nowhere else.
The spectacular traveller's palm is one of them.
It produces its flowers in sprays between the leaves of its great fan.
They're drab, stiff, almost leathery structures.
You have to be pretty strong to pull these hefty petals apart to reach the nectar they conceal.
But the island not only has unique plants, it has unique animals.
Lemurs.
They have all the strength that is necessary.
There are many kinds of lemur, but only a few have taken to nectar feeding.
The black lemur is one.
Its name is misleading, for though the males are black, the females are brown.
They have much longer tongues than their relatives, nectar teetotallers, and that enables them to drink from the palm's deep nectaries.
Being dusted with pollen is only half the duties the plant requires from the lemur.
The other is to deliver the pollen to another traveller's palm.
The nearest may be miles away.
But the lemurs move great distances.
Having drained the nectar from one palm, they set off to try and find another.
Only when they've drunk from a second traveller's palm will they have completed the task given to them by the first.
But the most widely-used messenger service is supplied neither by mammals, birds nor reptiles, but by insects.
In many ways, they provide the cheapest and most efficient courier service of all.
A plant like this Indian balsam can summon them with quite small, economically-produced flowers.
Each individual messenger, such as this bumble-bee, will do its work for quite a modest payment of nectar.
And the balsam constructs its flowers in a way that ensures that no one gets a drink without being given a load.
It holds the nectar deep in the flower, so the bee has to go right inside to get it.
The stamens hang from the roof of the entrance, so that an arriving bee brushes them with its back.
When all the pollen has gone, the stamens loosen so that a departing messenger knocks them off.
And that exposes the stigma, so the next thirsty bee that arrives for a drink will make not a collection but a delivery.
Dozens of pollen grains get caught on the sticky stigma, many more than are needed.
And when the flower's function is over, the petals fall.
Then the egg chamber at the base of each flower quickly swells and becomes a capsule full of seeds.
Many plants have found that it pays to have an exclusive courier service, so a messenger doesn't deliver its package to the wrong address, a different kind of flower, where it'll be useless.
This gentian, growing on the Cape in South Africa, has adopted that policy.
The reward it offers its employees is edible pollen, and carpenter bees pack great quantities of it into baskets on their legs.
The stamens appear to offer yellow pollen to all comers, but that is an illusion.
These yellow structures are hollow tubes, and the pollen is secure inside.
A beetle attracted by the sight is totally baffled.
So how do the bees manage to collect such large loads of pollen? Well, if you listen very carefully when one arrives, you can hear the answer.
(BUZZING SOUND CHANGES) By vibrating more slowly than usual and making a deeper buzz, the bee shakes the tube with just the right frequency to make the pollen spurt out of a tiny hole at the top.
I can show you the sort of vibration that's required with this tuning fork.
There.
You might think the long stigma projecting to one side would collect pollen sprayed around so extravagantly, but there's no danger of the flower fertilising itself.
The stigma doesn't become receptive until all the flower's own pollen has gone.
There's another advantage to this strategy.
A bee can't tell by sight whether a yellow stamen has pollen inside it or not.
So those flowers with no pollen left but newly receptive stigmas get a pollen delivery without having to pay for it.
Honeysuckle rewards its employees not with pollen but with nectar.
It keeps the payments at the end of long tubes formed by the petals, so a long tongue is needed to get it out.
The hummingbird hawkmoth has one.
To get the last drops, the moth has to probe to the full length of its tongue, and that compels it to brush the stamens with its underside.
The flowers go on producing nectar well after their stamens are exhausted and shrivel.
So the moths go on drinking from them, but now they brush pollen off their undersides, onto the stigma.
Some flowers make drinking even more difficult for their couriers.
This small iris grows in South Africa.
Each flower has a hugely elongated tubular base.
The tiny entrance to it is indicated with exemplary clarity and accuracy by these white arrows on the petals.
And here is the only tongue that can reach that nectar.
It belongs to a hoverfly.
It's not so much a tongue as a fine tube, but in proportion to body length, it's one of the longest feeding implements in the animal kingdom.
The clear markings are particularly important because the tongue is so long that even in the lightest wind, the end blows about.
An extra thrust is needed to get the last drop.
The iris only flowers for a few weeks, so what does the hoverfly collect with its phenomenal tongue at other times? Well, after this iris is over, this different blue flower opens.
It's produced by another species of iris.
There's a succession of plants that bloom on the veldt in the next few months, so that the hoverfly is kept fed throughout its short adult life.
The hoverfly collects pollen on the front of its broad head and on the back of its neck.
Butterflies, on the other hand, tend to accumulate it around the base of the tongue.
They don't hold their tongue needle-straight like the hoverfly - they curve it and, sometimes, most remarkably, they can put a sharp bend in it.
This butterfly has got pollen not only on its tongue but all over its legs as well.
Pollen, however, is valuable stuff.
In terms of calories, it costs a lot for the plant to produce.
The crassula flower on which this South African mountain pride butterfly is feeding releases its pollen so lavishly that the butterfly gets it all over its tongue.
The mountain pride lives in the hills around the Cape.
Several red flowers grow here, and the butterfly, unusually among insects, has a particular liking for that colour, which elsewhere seems almost the prerogative of birds.
Not only are there red crassulas, there are also red gladioli, and they too squander pollen on the butterfly most lavishly.
But there's one flower that has done something about that and loads its pollen onto the mountain pride butterfly in a much more accurate and therefore economical way.
And it grows at the head of this spectacular gorge.
And this is it, a red orchid.
It's got a vessel at the back which is full of nectar, and the butterfly knows exactly where it is.
Orchids have a special way of rationing their pollen.
They parcel it up into a pair of packets called pollinia.
Here, they're hidden at the back, behind those two white knobs at the top.
The white lump at the bottom is the stigma.
Like other orchids, this one provides its visitors with a landing platform.
There's only one position in which a butterfly can stand in order to reach the nectar.
As the mountain pride pushes forward to get the last drop, a pad from one of those white knobs is glued onto its back legs.
And as the butterfly moves again, it pulls out the yellow pollinia.
When it visits its next flower, it must once again alight on the landing platform in precisely the same position, and that now causes the pollinia to be dragged across the stigma.
That, too, is sticky.
The orchid has been fertilised.
Here in South Africa in spring, the veldt is covered with as spectacular a display of flowers as can be found anywhere in the world.
Some are advertising meals of pollen, some drinks of nectar.
And those aren't the only treats on offer.
This flower, a relative of the snapdragon, has a more unusual product, a nutritious oil, which it holds at the end of two long spurs.
Only one customer, this bee, has the right equipment for collecting it.
Its front legs are specially elongated and thickly covered with hair which mops up the oil.
In South America, a group of orchids offers an even more unusual and sophisticated product.
It, too, is an oil, but not an edible one.
The customers for whom it's produced are tiny iridescent bees.
But only males visit the flowers.
The oil is very waxy, and the bees have to scrape it from a pad at the back of the flower.
It's not a food, it's a perfume, and the male bees use it to attract females during their courtship rituals.
Each species of bee needs its own exclusive brand, so each species of orchid tailors its product to match the taste of its own particular customers.
But it doesn't come for free.
The surface of the orchid around the oil pad is particularly slippery, and the males have a lot of trouble keeping their foothold.
One slip, and he falls down a chute to collide with a sticky knob.
It fastens onto him so securely that, when at last he struggles free, he pulls the yellow pollinia away with him.
Another orchid in this group imposes its will on customers in a different way.
That white rod is a trigger.
Small bees are not heavy enough to operate it.
But this one is altogether heftier.
And in a fraction of a second, the orchid dumps its cargo onto it.
Some plants produce a reward that only one animal seems to like, or could even reach.
This tropical fig tree in northern Australia has a relationship with a wasp that is so complex that it's very difficult to imagine who initiated it or who is getting the better of the bargain.
The fig tree carries its flowers inside these small green knobs.
They never see the light of day.
The only way to reach them is through this tiny hole in the centre.
Within, the cavity is lined by both male and female flowers.
Each is little bigger than a pinhead.
But some of the female ones have been parasitised.
Weeks ago, a minute female wasp crawled in through the entrance hole and laid her eggs inside their ovaries.
Now those eggs are about to hatch.
First to emerge are male wasps, but they're difficult to recognise as such, for they have long, worm-like bodies and no wings.
They will never fly, they won't even leave this chamber.
They're searching for those parasitised female flowers that contain unhatched female wasps.
A male, having found what he seeks, mates with the female while she's still inside the tiny flower.
He crawls away and will soon die.
His work is over.
Now the females begin to hatch.
They are more recognisable as wasps, for, although they are barely bigger than mosquitoes, they do at least have wings.
They head for the exit hole.
To reach it, they have to pass the fig's male flowers, and they get loaded with pollen as they go.
Out into the open air they fly, to look for another fig tree in flower.
If they find it, they will force their way into the little globular flower capsules and so fertilise the fig.
Their reward for that service will be to use the fig's flower chamber as a nursery for the next generation.
Some plants, however, do not give their pollinators any reward of any kind.
In the warmer parts of Europe lives a whole group that bamboozle their pollinators into thinking they're going to get a sensational reward, a sexual one.
They're little orchids, and their flowers reproduce remarkably closely the signals that enable a male bee or wasp to recognise a female of the same species.
Several have blue patches.
One is fringed with what looks like fur.
A wasp's wings, in the right light, do flash iridescent blue, and its abdomen is covered with thick brown fur.
A female wasp also pumps out an identifying perfume.
But the orchid does the same, and the result is irresistible.
As the male wasp nuzzles forward in his attempts to mate, he butts the pollinia, which stick to him like yellow horns.
He seems well aware that something has happened to him, but there's nothing he can do about it, and he flies off to try his luck elsewhere.
Which is what the orchid requires, because this time he deposits the pollen on another bogus female.
The hairs on many such orchids run downwards, as though the female is sitting head-up.
But some reproduce her clinging head-down, and then the male must land that way if he wants to mate.
And he will get the pollen stuck to his rear.
This one, too, seems fully aware that he's got more than he bargained for.
The orchid's mimicry is so convincing and enticing that sometimes a flower will attract a whole scrum of sex-crazed suitors.
Some are trying to get to the orchid and will inadvertently deliver the pollen.
Other males, as there seems to be a full house, attempt to mate with one another.
In the heathlands of Western Australia, orchids perpetrate an even more complex sexual charade.
This time, the victims are a particular group of wasps known as the thynnids.
In spring, the female thynnid emerges from the sandy soil where she's been feeding on beetle grubs.
She's now ready to mate.
If you burrow, it's difficult to develop wings, and she has none, so she can't travel far.
But the males can, for they feed by hunting and do have wings.
They will have to come to her.
Once settled, she begins to emit a message of perfume detectable a long way downwind.
Then she waits, and usually not for long.
The male carries her away and will mate with her in mid-air.
This, however, is plainly not, to our eyes, a wingless female wasp, it's a tiny orchid.
But it does carry the signals which indicate "female wasp" to a male wasp.
And not only that, it backs those visual signals with a perfume that is virtually identical, chemically, to the smell emitted by a female wasp.
And the two things between them are quite enough to delude a poor male.
Watch.
He tries to fly away with her.
But how is this helping the orchid? The answer lies in the ingenious mechanical construction of the flower.
The purple part is the bogus female.
The other half has a little cup, with the pollinia attached to another of those sticky pads.
A black head and a furry body is all, apparently, you need to disguise yourself as a female.
This simplified mock-up is attached to the other part of the flower by a delicate but strong hinge.
When the male tries to carry off what he assumes is the female, he's thrown upwards by the force of his own exertions towards the cup and the pollinia.
But the male's position has to be absolutely correct.
In spite of the enthusiasm with which this one tries to mate, he isn't clinging in exactly the right way.
Perhaps this time the orchid will be luckier.
Obviously, there's little wrong with this orchid's mimicry - two males are trying to get at it.
There.
The pollinia are attached to his back.
But the most punishing of fertilisation techniques used by plants involve not sexual deception but imprisonment, penal servitude.
Gull colonies in the Mediterranean, as anywhere else in the world, are busy, noisy places, full of activity, as parent birds come and go, tending their chicks.
They're also messy, smelly places, with droppings, half-digested fish and dead bodies lying about all over the place.
In short, for flies and ants they are very heaven.
And beside some gull colonies, you may find one of these.
This is not an image of a sexy, seductive female animal.
The mimicry is more gruesome.
This is a bogus corpse, mimicking rotting flesh covered with hair and giving off the putrid smell of carrion.
It's the dead horse arum.
Blow-flies find this highly attractive.
They need to find a hole to get into a corpse, and this seems to be one.
Within are a whole cluster of tiny flowers.
Those at the top are male, but they're not yet ripe.
Below is a barricade of spines, and below them, the female flowers.
Some of the flies have already visited a flower like this, and are carrying cargoes of pollen.
Down here, in a real corpse, they might have found rotting flesh on which to feast and lay eggs, so that later their maggots could also feed, but they find nothing.
As they continue to search, pollen brushes off them onto the stigmas.
The spikes discourage them from getting out.
By now it's getting dark, and flies don't fly at night.
They're stuck.
During the night, the male flowers suddenly shed their pollen.
And during the night, too, the spikes of the barricade shrivel.
So by the morning, the flies are free to go.
And each takes with it a load of pollen from the male flowers.
One of the most extraordinary of these insect-enticers Iives here in the tropical rainforest of Sumatra.
It only flowers once in a thousand days, and when the flower develops, it only lasts three days.
So very few people have seen it, but here it is.
Technically, it's a whole group of flowers clustered around this, but you could be justified in regarding it as one flower.
And if you do that, this is the biggest flower in the world.
It's related to the dead horse arum, but it's nine feet tall and three feet across.
It's Amorphophallus titanum, the titan arum.
The function of this great spike in the middle is to produce a smell .
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and if you smell it, it smells very strongly of bad fish.
This apparently attracts insects, which come along here and go down into this great funnel to the small flowers that grow at the base.
Until this film was taken, no one was sure what insects pollinated the titan arum.
As we watched, we saw that, without doubt, the job was done by tiny sweat bees.
Like other arums, the male flowers form a band at the top.
Below them, the female flowers, with long, yellow-tipped stigmas.
The bees seemed to find some reward on the stigmas, for they crawled all over them, distributing the pollen they had brought with them.
But why should the titan arum produce the biggest bloom in the world to attract such tiny pollinators? To be effective, these bees must bring pollen from another bloom.
But as the plant is rare and only flowers once in three years, the nearest may be miles away.
It's not easy to spread perfume over such distances in the still air of the rainforest.
Perhaps the best way is to disperse it from the top of a towering spire, Iike smoke from a factory chimney.
We tend to assume that flowers are here to gladden our hearts.
They're not, of course.
Plants produced flowers long before humanity appeared, to summon mammals, birds, and, above all, insects.
And though they sometimes are given some payment, they are the servants.
The masters are the plants.