Original subtitles

I'm exploring the fascinating world of plants,

from the most bizarre to the most beautiful.

With new technology and in 3D,

we can reveal aspects of their lives

that are otherwise hidden from us.

We can change time

to discover a dynamic world of constant motion.

We can change dimension

to watch them interacting with insects.

We can analyze how they communicate

with color,

with scent,

even heat.

And we can discover how fungi

are not the enemies of plants,

but their essential partners.

And we can watch all these dramas

unfolding in just one unique place,

outside in the gardens

and inside of these spectacular pavilions of glass -

the Royal Botanic Gardens of Kew.

Kingdom of Plants with David Attenborough

Our senses

match what is important to us.

Our eyes can detect just tiny little movements

and see best during the day.

Our ears

can detect the frequencies of the human voice.

But there are many things that are very important to plants

that we can't detect.

This is an exploration

of that hidden world.

Solving The Secrets

Plants may seem passive and inactive,

but, in fact, they move.

These are among the most mysterious -

sundews.

The leaves, like those of other plants,

use sunlight to help them grow.

But their glistening tentacles

get food in another way.

They are traps.

Plants, to grow properly,

needs sunlight

and water,

and minerals and nutrients which they get from soil.

But in some parts of the world,

in swamps and bogs for example.

there are very few minerals and nutrients in the soil.

So plants have to get those things from somewhere else.

And they get them from the bodies of dead animals.

Each tentacle is tipped with a glistening droplet.

It may look like nectar

and, indeed, many insects seem especially attracted to it.

But it's not.

It's a glue.

It not only holds the insect fast,

but clogs up the tiny holes on its flanks

so that it can't breathe.

Time-lapse cameras reveal

that tentacles that are not touched by the insect

now start to bend towards it.

How they detect the insect's presence

we still don't know.

Finally, the sundew begins to fold its whole leave

around its prey.

There will be no escape

from this lethal embrace.

Now, the plant liquefies its victim's internal organs

while it's still alive

and absorbs the nutrients through its leaves.

Other carnivorous plants don't require special photography

to show how fast they can be.

Darwin described this plant

as one of the most wonderful in the world.

It's a native of the coastal plains

of North and South Carolina in America -

the Venus Flytrap.

It catches insects with booby traps.

At the top,

the leaves are baited with a sweet nectar.

But lower down,

there are a few upright bristles -

triggers.

Many things might accidentally touch one of them,

so a single touch has no effect.

But a fly crawling around on the leaves sipping their nectar

is likely to touch more than one of the bristles.

And if it touches two within 20 seconds,

that's different.

It's thought that the trigger hairs work

by releasing a rudimentary electric impulse.

The victim's desperate attempts to find a way out

simply trigger more hairs

and encourage the trap to close even more tightly.

The plant begins to release juices

rich in hydrochloric acid.

It will take ten days to completely digest its meal.

But there's a carnivorous plant

that moves at even greater speeds.

It lives in the hidden underwater world

of lakes and ponds.

It's called Utricularia,

bladderwort.

These tiny wrigglers are mosquito larvae

and they are among its prey.

The bladders that give the plant its name

are not floats.

They, too, are traps.

Each bladder contains a partial vacuum

and has a one-way entrance.

By slowing down the action 240 times,

we can see how they work.

With the slightest touch,

the door flies open inwards,

sweeping the prey inside.

It all happens in less than a millisecond.

Utricularia is the plant world's swiftest killer.

But most plants, of course,

move very slowly indeed.

Our cameras over the year

can show just how dramatic

such seasonal changes are.

It's winter in Kew.

It's so cold and the sun's rays are so feeble

that plants can't grow.

And leaves in winter can be a liability.

A fully-canopied tree

can be uprooted by the winter gales.

And in any case, the flimsy leaves of oaks and beeches

will be destroyed by the frosts.

So many such trees stand naked

and inactive throughout the winter.

But eventually,

the sun begins to rise higher and higher in the sky.

The day is getting warmer

and spring arrives.

Light and heat sensitive molecules inside plant cells

are the triggers of germination and flowering.

Timing is critical.

Bloom too early and frost can kill a plant.

Too late and they can be swamped by the growth of its rivals.

The first scent flowers are bulbs.

The beds in front of Kew's Palm House

are transformed as they burst into color.

Then, trees join the race.

Cherries

and magnolias.

Their flowers last just long enough to attract pollinators

and then they will fall.

Meanwhile in the woods,

bluebells begin to appear.

They must grow fast

if they are to collect their share of the spring sunshine

before the canopy develops over head

and cuts it off from them.

But in some parts of the world,

spring and summer may last only a few weeks.

And the plants that live there

have to complete their annual activities very swiftly.

Kew makes special arrangements for them.

This is the garden's newest glass house.

It's the Alpine House.

Inside grow plants from the mountains

where spring and summer not only brief

but bitter.

This house has been built to replicate alpine conditions

and it does it with this strange shape.

Deep below ground,

there is a labyrinth of concrete passages

where the air is very cold.

And as the temperature up here warms,

so that cold air is drawn up through vents

and flows over the plants on ground level.

Then it warms still further,

rises and escapes through vents of the top.

And when the sun is really strong,

it's got a further trick up its sleeve.

It's usually the melting snow

that stimulates alpine plants to bloom.

But here, technology creates such continuous conditions

that alpines flower without it.

The alpine Allium,

Roscoea, a Himalayan plant

which is closely related to ginger,

and sempervivum,

a plant so hardy,

it can root in tiny cracks between the rocks.

Mountain plants, it's true, are nearly all tiny,

but they have the beauty and fascination of jewels.

However, flowers did not evolve to please our eyes.

Their function is to please insects.

Nobody can be exactly sure how insects view the world,

but it's certainly rather different from the way we do.

We can see a part of the spectrum from red,

which is a long wavelength light,

through orange, yellow,

and green and blue to violet,

which is short wavelength light.

But insects can see even shorter wavelength still.

They can see ultraviolet.

And we can use special cameras

to reveal just what information

that sensitivity to ultraviolet light reveals.

We can move from how we see the world

to how insects might see it.

By looking at flowers in this way,

we can begin to understand their true purpose.

This flower,

to our eyes, it seems to have uniformly plain pedals.

But the insect looking at it in ultraviolet,

each pedal has a white tip,

so there is a circle of white

drawing attention to the bull's eye,

which is there for the insect can find pollen.

This flower which, to our eyes, appears to be in plain blue.

The ultraviolet light has white pedals

with lines running down it all the way around

pointing towards the center.

And this is the common fox glove

with, to our eyes,

nothing more than a few random markings on its throat.

But to an insect, there are more.

These white lines probably act as landing lights

which guide it to the nectar.

Most important structures are often the most vivid colored.

The nectaries glow brightly.

As does the pollen.

The four-o'clock flower blooms at dusk

and has fluorescent pollen

that attracts night flying moths.

This sensitivity to ultraviolet

is just one way in which plants communicate with insects.

Plant don't rely solely on color

to attract their insect pollinators.

They also produce smells.

In fact, as I stand here,

I'm surrounded by a swirling vortex

of perfumes of many kinds.

Unhappily,

the human nostrils can only detect

about five percent of them.

Insects do very much better.

We can imagine microscopic droplets of these volatile oils

suspended in the air.

Many insects have antennae

that are extraordinary sensitive to them.

Some can detect concentration of

just a few parts per billion.

As a consequence,

insects can smell a flower from as much as a mile away.

But messages can also travel in another direction.

Some insects can communicate with plants.

They do it with sound.

Some flowers are extremely fussy

about their pollinators.

This is Gustavia

from the Amazon rainforests.

Here are its flower buds.

Each one will only open for a few hours

and in that time, it has to be visited

by a particular kind of bee,

the buzzes with a particular musical note.

Of course, there aren't bees like that

flying around here in London.

We have ways of deceiving Gustavia

with a tuning fork.

All we have to do now

is to wait for the flowers to open.

A tuning fork that resonates

at exactly the pitch of Gustavia's bee

will cause the stamens to vibrate.

The motion releases the pollen

that would otherwise remain locked fast in the flower.

The bee gains

because it has exclusive access to a nutritious food source

and therefore favors it.

And the plant has a courier

who is almost certain to deliver the pollen to the right address.

We've highlighted Gustavia's pollen cloud

because the grains are so fine,

they are impossible to see with the naked eye.

But there is a way to examine even the tiniest pollen grain

with an electron microscope.

The colors are artificial,

but these pollen grains are minute.

This is cedar pollen

magnified 7,000 times.

Each grain contains a tiny bundle of the particular DNA

that will fertilize the flower

produced by another individual of the same species.

But it has to get to such a flower

Some plants use animals as couriers.

This mountain ebony pollen is sticky

and clings to the fur of bats.

Eelgrass pollen carries a bundle of pheromones

that will suspend the grains in water

at just the depth at which the plant's flowers bloom.

The wind-disperse pollen grains produced by pines

drift through the air with the help of tiny air sacks.

Looking at the grains through a microscope

reveals how astonishingly complex their shapes can be.

Each is unique to one particular species of plant.

Only grains of that shape and right DNA

will fertilize the flowers of the species that produce it.

A pollen grain, when it arrives on such a flower,

doesn't swim like the sperm of an animal.

Instead, as the illustration shows,

it produces a tube

which grows down into the ovary

at the very center of the flower.

With each new season,

new worlds reveal themselves.

In late spring,

the longer days and stronger sunlight

cue the emergence of leaves.

The gardens are transformed.

Each plant arranges its leaves,

so that there is the minimum of overlap between them.

They grow to fill all the available space

ensuring that every ray of light

is harnessed by the green chlorophyll inside them.

Up here in this walkway through the treetops,

you can see the process as it happens.

In just a few weeks,

the trees close themselves in green.

The amount they produce of leaves and shoots is extraordinary.

In just one acre,

it can weigh four tons.

During the long warm days of summer,

leaves of all shapes and sizes grow in great abundance.

And it's not just plants that depend on them.

The rich foliates provide hidden habitats

for whole communities of tiny insect herbivores

and their predators.

For many, leaves are food.

Blackflies get what they need

by stabbing their needle-like mouth parts

into the veins of leaves and stems

and extracting the sap.

They don't even need to suck.

The pressure inside the plant

is enough to squirt the sap into their stomachs.

Mealybugs are also sap drinkers.

They produce a waxy powder from their skin,

which most predators dislike,

so that they are able to drink unmolested out in the open.

Snail rip through the vegetation

rasping off mouthfuls with a long file-like tongue.

A single snail can consume

a fifth of the weight of its body, shell and all,

in a single day.

So insects and other small creatures,

some helpful, some harmful,

flourish through the summer.

This is the time when most of them reproduce.

And they do so with staggering speed.

Female aphids mate and lay eggs like other insects,

but they also produce clones,

babies that hatch from unfertilized eggs.

And the clones themselves,

even before they leave the female's body,

are already pregnant with other clones.

Such telescope generations

enable aphids to infest a whole plant

in a matter of hours.

But aphids are themselves food for others

and assemblies like these don't go unnoticed

by other insects.

Among the most ferocious,

are the many kinds of ladybird

and their lavae.

This is the young of a ladybird called Cryptolaeumus

and it eats virtually nothing

but Mealybugs and aphids

when young and as an adult.

This is a fasting moving young of a hoverfly.

This larva of a lacewing is totally blind,

but it doesn't need to see.

It has an acute sense of smell

and is specially sensitive to the pheromones produced by aphids.

It attacks its prey

by impaling them on a large hook in its mouth

and then sucking them dry.

And it has an unquenchable appetite.

It could eat up to 600 aphids before it's adult.

Most predators aren't fussy about the plants they live on

as long as there is prey to hunt.

But one predator

has formed a special partnership with a plant

that looks rather like the insect-eating sundew.

This plant,

which is called Roridula,

also catches insects

which get stuck to these sticky hairs on its leaves.

Oddly enough,

Roridula can't digest insect bodies.

Instead, it gets help

from one particular kind of insect called capsid bug,

which lives nowhere else but on Roridula.

And the capsid bug runs around

on these leaves without getting stuck

because its body is coated with a non-stick substance.

And the capsid bug

goes and feeds on the bodies of the insects

the Roridula has caught.

And when an insect lands and is caught,

the capsid bug runs across,

sticks its mouth part into the insect body

and sucks it dry.

Then it produces droppings which fall to the ground

and those can feed Roricula.

The carefully controlled conditions

inside Kew's glass houses

certainly suit plants.

But equally,

they suit insects.

So something has to be done to keep pests in check.

One way is to introduce predators -

Asian water dragons.

They exists on a diet of mealworms

and cockroaches.

They quickly learn that daily hosing down

will drive the cockroaches out of the cracks

where they hide during the day.

There are also more subtle ways of controlling pests

that visitors seldom notice.

These cards have been coated with microscopic eggs

of a wasp.

When they hatch,

the young wasps go off and search for their favorite prey -

aphids.

This one has discovered aphid pupae.

It selects its target

and injects it with an egg of its own.

When the larva hatches within its host,

it will eat it alive,

just as others have done before it.

These are the dried out husks of victims -

aphid mummies.

Kew is starting its next great seasonal transformation -

autumn.

Plants growing outside

without the protection of the glass houses

must get ready for the bad conditions that are coming.

Trees prepare to lose their leaves.

The green chlorophyll inside them

begins to break down to be reabsorbed.

The bright colors are byproducts of the process.

As the leaves fall,

a new world reveals itself

from beneath the soil.

Fungi.

Fungi can't photosynthesize

because, unlike plants, they have no chlorophyll.

In fact, they are more closely related to animals

and are made of chitin,

the material insects use for their skeletons.

These are the fruiting bodies of a fungus.

Their function is to produce dust-like spores

which are then blown away through the woodland

to grow elsewhere.

But these are only a tiny part of the fungus.

Most of the body of the fungus

is beneath the ground,

a tangle of tiny treads

which extend for hundreds of yards.

through the forest.

And we are now begin to realize

that those threads are essential

to the growth and health

of many of the woodland plants.

The length of these threads is almost unbelievable.

One specimen in America

was found to extend across nearly four square miles.

That's an area 16 times bigger

than Kew Gardens itself.

Technically speaking,

it's the largest known living organism on the plant.

Most fungi make a living

by feeding on the dead tissues of other organisms,

both plant and animal.

They produce powerful chemicals

that enable them to break down

about 90 percent of all organic matter,

including leaves and wood.

In doing this,

they release the nutrients to the soil

that plants need to fuel their new growth in the spring.

So fungi are essential links

in the cycle of life.

But some fungi establish partnerships with plants

while the plants are still alive.

And they are just as important.

This is the Lucombe Oak.

It germinated from an acorn in the year 1762

and is one of the oldest plants in Kew.

It's roots are covered with a fungus.

But that's not a friction.

That's the reason why this tree was able to live for so long

because the fungus can do something

that the oak tree can't.

It can extract nitrogen directly from the soil

and then the oak tree collect it from the fungus.

And in return, the fungus takes sugars

from the sap in the roots of the oak tree.

So it's a mutually convenient arrangement,

an symbiotic relationship.

In fact, we now know

that around 90 percent of the species of plants on the earth

depend upon fungi one way or another.

Kew cares for fungi

just as it does for plants.

A special underground world has been created for them.

Here, thousands of different species

are preserved in boxes.

This is the fungarium.

There are more specimens of fungi here

than anywhere else in the world,

one and a quarter million of them.

And such has come

from all over the world, here to Kew,

in order to study them.

The fungarium contains specimens that Kew has collected

through out the course of its 400-year history.

They are stored for their potential value

in science and medicine.

Perhaps the most famous is this one.

This is Penicillium,

a mold from which we get penicillin.

Here's another which is able to digest oil.

And scientists are working to see

whether it could be used for in cleaning up oil spills.

But fungi can also be very sinister.

This caterpillar has a fungus

growing from its head.

It's a species of Cordyceps,

a tropical fungus

that has developed a gruesome power.

They can infect the brain of an animal.

One infects ants

and causes ants to climb up a grass stem,

tamp its jaws on the top,

and there, high up on the plant,

the fungus kills it.

A long fruiting body then bursts out of the ant's brain.

This elaborate behavior

enables the fungus to rise high above the ground

and shower its spores over great distances

and so reach new victims.

The world of plants is still full of secrets

even though we have so many different ways

of investigating their lives.

One of the most famous species

has been something of a mystery until only a few years ago.

It may look like a tree,

but in reality, this is just a single giant leaf.

It's called the titian arum

and it's a record breaker.

But not because of what you see now.

In a week or so,

that green stem and the leaflets that go on top

will die, and rot,

and disappear.

But beneath the surface of the soil,

there is a gigantic tuber,

and it's from that

that the record breaker will emerge.

This extraordinary event

occurs just once every seven years.

It will take two months to complete.

But this new growth is neither a trunk,

nor a leaf.

It's the bud of the biggest flower in the world.

As it grows day after day,

a huge spire, the spadix,

rises from the center of the developing flower.

And then one evening as darkness falls over the forest,

the giant flower opens.

This, surely, is one of the most astonishing of blooms.

I first saw one of these amazing flowers

growing in the wild in the tropical rainforest of Sumatra.

But why are they so big?

Well, the function of the flower, like all flowers,

is to attract pollinator.

And this plant gives off the smell of rotting flesh.

But it does something else.

Something you can see with a heat sensitive camera.

This remarkable device

reveals something astonishing.

The white areas at the base of the spire

are significantly hotter

than the surrounding plant.

It's heating up.

At its hottest,

the spire can reach 37 degrees centigrade,

the same temperature as the body of a mammal.

And as it warms, something else happens

inside the flower at the base of the spire.

Hundreds of smaller structures begin to produce stringy pollen.

The titan arum is readying itself

for the arrival of pollinating insects.

Tiny sweat-bees and probably carrion beetles as well

are attracted by a combination of the powerful smell and the heat.

Other flowers that smell of carrion also produce heat.

So it seems that what is happening

is that they are mimicking the warmth

of the body of recently dead animal.

But the hot air

produced in pulses from the top narrow spire

must have a different function.

At night,

a layer of cold air, still air,

forms between the forest canopy and the forest floor.

But the spire of the titan arum

producing the pulses of warm air

pierces that barrier

so that the smell of the titan arum

spreads out of the top of the canopy

far and wide.

so attracting insects,

pollinating insects, from a long way away.

If we could imagine such a spectacle,

it would look something like smoke from a chimney

discharging heat into the night sky.

It remains in bloom for just two days.

And then, it closes.

Science has given us a glimpse

into a hitherto unseen world.

However, our journey of discovery has only just started.

As technology advances,

so will our understanding

of the hidden world of plants.

The final frontier of plant discovery

is in the dry zone.

In deserts,

plants use an extraordinary adaptations

in order to survive

by day and by night.

And as we will discover,

new research into plants' astonishing time capsules of life -

their seeds -

could ensure that no plant

need ever become extinct again.