No part of the earth is more hostile to life than the frozen wastes around the Poles.
850 miles north of the Arctic Circle, this is Ellesmere Island.
No animal can live permanently on these ice fields
and even plants face big problems,
for the four things they must have are in crippingly short supply.
Water?
Yes, there's a lot of frozen water here,
but water has to be liquid for plants to make any use of it.
Nutrients? There's virtually none in this frost-shattered rock.
Warmth and light? For six months of the year it's dark,
and in the brief summer, as now, the sun doesn't rise high,
and devastating winds can carry away what little warmth it brings. Yet, there ARE plants here.
Some live actually INSIDE the rock.
This thin green line is made by algae - microscopic plants.
They're so small, they can live BETWEEN the grains of this sandstone,
and there, at least, they're out of this desiccating wind.
On the surface of the rocks, there are lichens.
They grow incredibly slowly and may take 50 years to cover a square cm,
but they can survive even if there are only two days a year when it's warm enough for them to grow.
In spite of these bleak conditions, there ARE flowers to be found here.
But you have to look hard to find them.
Here's one.
It's a mustard, but it's
much smaller than its more southerly relatives,
so it can keep out of the crippling wind.
In midsummer, for a few weeks,
enough water melts from the glaciers for streams to flow,
and then, miniature gardens burst into bloom.
The searing wind compels them all to keep close to the ground.
None keeps closer than this. It is, in fact, a tree - a willow.
These are its catkins.
But the trunk grows horizontally,
and it can stretch almost as far along the ground as its more southerly relatives stand above it.
Even so, it still produces enough leaves to sustain a few grazers -
musk ox.
Nothing is wasted up here -
not a moment of sunshine, not the tiniest shelter, not a scrap of food.
When a musk ox dies, its decaying body releases a rich flush of nourishment into the soil,
and tiny gardens appear, in the shelter of its bones.
The Arctic poppy,
like all plants, needs warmth to grow,
but it is unusually efficient at collecting it.
As the midsummer sun skims round the horizon -
360 degrees in 24 hours without setting -
the poppy turns its flowers to track it.
The slanting sun may not be strong, but it is, at least, continuous
during the few weeks of high summer.
The heat the poppy gathers by staring continuously at the sun
enables seeds to develop in each flower before summer comes to an end
and the sun disappears below the horizon for months.
Conditions may be just as severe on the high peaks of the Alps,
2,000 miles to the south, at least during the winter.
But here, spring brings a greater benefit.
The sun rises higher in the sky and is warm enough to melt all but the highest snowfields.
As it melts, it reveals the snowbell, already in flower.
The plant formed its flower buds last autumn,
before the increasing cold shut down all its activities for the winter.
The buds remained dormant until the spring sunshine, through the snow,
triggered them into opening even before the snow had melted.
In summer, the high meadows, newly freed from snow,
fill with flowers.
Because for so much of the time it's so cold, the vegetation here decays only very slowly,
so a peaty soil forms.
But it's only a thin layer over solid rock and boulders
and trees find it very difficult to get root.
Also, avalanches regularly sweep these slopes,
carrying away saplings before they're established.
So, shallow-rooted plants have these parts of the mountains largely to themselves
and in summer, they bring a rich display of colour.
But for every thousand feet you climb, the average temperature drops by about three degrees.
Plants living in the high mountains must be able to survive extreme cold.
It's very important to keep out of the worst of the chilling winds
and many plants here form small rounded humps,
and that brings them a number of advantages.
Growing into the shape of a cushion is a good way of conserving heat
and no plants do it better than these in the mountains of Tasmania.
These are the largest cushion plants in the world.
They grow to over 12 feet across.
Any one square yard contains over 100,000 shoots, so this one cushion around me contains several million.
This rounded shape does more than just reduce wind-chill.
The air temperature around me here, at about 3,500 feet high,
is only a degree above freezing.
But if I put this temperature probe on the surface,
I can see that there it is several degrees warmer.
The cushion acts as a solar panel, absorbing heat from the sun
so that, even on very cold days, provided it's not covered with snow,
it can photosynthesise and grow.
The plants that form these spectacular cushions come from several different families -
sedges and rushes, daisies and dandelions.
One cushion may contain several species, tightly packed together and growing to the same height.
For one kind to grow higher than those around it would be suicidal.
In the New Zealand Alps, one of these cushion-forming species
also protects itself by developing a blanket of hair.
Its colonies form conspicuous white humps on the mountainside.
New Zealand farmers, whose flocks can stray up onto these slopes,
call such cushions "vegetable sheep".
This tall pillar, growing on Mount Kenya,
also covers itself in a blanket.
It's a giant lobelia.
Its long leaves are fringed with dense hairs.
Its flowers are hidden away from the frost beneath this downy covering.
Bright petals are no use if they can't be seen,
and these are just simple tubes.
The lobelia's pollinator, a sunbird, knows where they are and how to reach them.
During the day, it can get quite warm,
for Mount Kenya stands almost exactly on the equator.
But at 14,000 feet, once the sun goes down, it gets bitterly cold
and then the lobelia will have real need of its hairy blanket.
There are other giants here too - tree groundsels,
relatives of the little yellow weed in European gardens.
They have a different way of dealing with the cold nights.
Their dead leaves remain on the stem, so that they act like lagging
and prevent the liquids in the pipes inside the trunk from freezing solid.
Conditions here can change with extraordinary speed.
One moment the equatorial sun is blazing down from a cloudless sky,
the next, a chilling wind begins to blow and the great mountain collects a cloud cover.
As well as the tree groundsel,
there's another groundsel that grows close to the ground like a cabbage.
As night falls, it makes its own preparations for surviving the bitter cold.
The most precious and vulnerable part of the plant is the bud in its centre from which all growth comes.
That must be protected at all costs,
and folding the thick leaves over it does the trick.
The temperature has now fallen by as much as 30 degrees.
Water in the muddy swamps is beginning to freeze. As it does so,
it expands and the ground begins to heave.
It's impossible for small plants to remain rooted under these conditions.
The Mount Kenya moss doesn't even try.
It grows into balls that are lifted up by the ice pinnacles and it rolls around during the night.
The sun returns, the temperature rises,
the threat of death by freezing has passed,
and the cabbage groundsels stretch out their leaves to catch the light
and start making food once more.
The ice in the swamps melts
and the streams flow again.
This is just as well, for now the plants, baking under the sun, are beginning to lose a lot of water
by evaporation from their leaves.
And severe water loss is the other disaster that can kill hardy plants.
If the sap-filled vessels in the tree groundsels' trunks had frozen,
their leaves would now be baked dry.
Here we are...still in Africa,
but about 14,000 feet lower down.
I'm on the southern edge of the Namib Desert.
Here, plants can't get water, not because it's frozen, but because rain hardly ever falls -
only about one or two inches a year.
Most of the time, it's bone dry...
and devastatingly hot.
Yet, almost unbelievably, there are trees standing out in the sands,
totally unsheltered, with no signs of moisture anywhere around them.
Water storage is the trick here.
These green succulent leaves are full of it,
and so are these bloated branches.
The local bushmen used to hollow out these branches and use them as containers for their arrows,
which is why this tree is called the quiver tree.
Its branches are covered with a blindingly white powder which reflects the heat,
and its leaves have thick rinds with few pores
which minimises water loss through evaporation.
The trunk, even of an old tree,
remains smooth and impermeable.
But even the quiver tree can't seal itself off completely.
Living involves breathing and some water vapour is inevitably lost in that process.
But this tree has a way of reducing that.
Self-amputation. It can cut off a leaf rosette and seal the stump.
This branch will never grow leaves again.
The tree will just survive with fewer leaves
and put out new shoots when conditions improve.
Most of the plants in this desert, however, are less conspicuous,
and there are rather more of them than you might suppose.
This little plant has fused its leaves together in pairs
to form cones, which is why it's called Conophytum.
The white surface of each cone is the skin of last year's leaf,
and the plant is now waiting for the rains to arrive.
Let's see what happens if I make them arrive earlier.
One of the greatest of all water reservoirs is the saguaro cactus
that grows in Arizona and New Mexico.
One of these giants can hold several tons of liquid.
They don't risk losing any water through the leaves - they have none.
Instead, the task of making food has been taken over by the stem
which has become green with chlorophyll and keeps its pores well-protected in grooves.
The 50-foot columns are crowned with flowers.
The pleats in the trunks enable the plants to expand rapidly
and suck up rain falling in a sudden storm before it evaporates in the heat and disappears.
Such a store of liquid is very precious. Lots of desert animals would raid it if they could.
They can't because cacti, like other desert succulents, defend themselves with spines.
The other way of protecting yourself against robbers
is to hide underground.
You might THINK that these are pebbles.
You would be wrong.
This...is a window plant.
These little studs are the flat tops of the pillar-like leaves.
And these tops are transparent. They allow the light to pass through
where it's transmitted by a row of crystals to the bottom of the leaf where there's green pigment.
So although this little plant is several inches under the ground,
it can catch the sunlight and turn it into food.
And in the driest times of all, when sandstorms blow across the Namib,
it may be covered up completely.
Many plants take refuge underground during the hottest part of the year
and survive as bulbs and tubers, swollen with food and water stores,
gathered during the good times.
Underground is undoubtedly the coolest place to be,
but it's not necessarily the safest.
Mole rats.
They burrow ceaselessly,
searching at random for their food.
Some of the bulbs they eat immediately,
but others they take away and stack in special larders.
Being carried away and put in store is not necessarily a disaster for the plants.
The mole rats seldom eat all their reserves
and some larders get forgotten.
Then the bulbs sprout and benefit from doing so in a new location.
This plant is totally dead.
It didn't store its food underground in bulbs. It adopted a very different and very drastic strategy.
It condensed its entire life into a few short weeks.
And its last act was to release into the sand a few hundred seeds.
They're easy enough to find.
And there are some.
They can wait here, in this hot sand, apparently lifeless, for years...
even 20 years.
But when the rains DO come, their moment arrives.
One day, the land is so dry that the withered plants crunch to pieces underfoot.
Two or three weeks later... and it's ablaze.
Arid lands around the world, not only here in South Africa,
but in Australia and Arizona, all respond to rain
by rapidly producing dazzling displays of colour.
The sudden flush of flowers and leaves attracts lots of plant-eaters.
For them, too, the pressures of desert-living are momentarily relaxed.
It may seem a paradox that some of the harshest environments should produce such unrivalled glories.
But the desert soil will not remain moist for long after rain
and in that short time, plants must grow leaves AND produce seeds.
So the need for pollination is urgent.
The most brilliant flowers have the best chance of attracting an insect.
This is competitive advertising at its most intense.
So, a few days of rain once every year or so
are enough to enable plants to survive in the driest areas on earth.
THUNDER
And this is one of the wettest places on earth.
Here, it rains almost every day and sometimes for days on end.
I'm in South America, on the top of an immense sandstone plateau,
9,000 feet high, five miles across,
surrounded by huge vertical cliffs.
This is Mount Roraima.
Plants cut off up here from the hot rainforest below
adapt to their surroundings in their own individual way.
So there are species here that occur nowhere else in the world.
The rains produce torrents that cascade over the edge of the plateau
and form some of the highest waterfalls on earth.
Much of this extraordinary landscape is naked rock.
Only here and there do clumps of plants manage to get a root-hold,
and even when they succeed, life is difficult.
Lack of nutrients is the big problem.
Streams wash away everything in their path and flow over bare rock.
Only in a few places does a little gravelly sediment accumulate.
So many of the plants here have to have ways of augmenting their food.
And some of them do it by eating animals.
This is about the simplest way
in which a plant can catch and eat an insect.
This is the marsh pitcher and this particular species lives only on Mount Roraima.
There are four others, which only live on other mountains near here.
And this is how they do it.
The leaf, in the shape of a tube,
is covered by downward-pointing hairs -
easy to slide down, very difficult to climb up. One slip,
and it's drowning and dissolution for the insect.
And then digestion by the plant.
The pond in a bromeliad is usually safe for aquatic insects,
but a bladderwort is hunting inside Roraima's bromeliads.
Not content with prey in THIS pond,
the bladderwort is looking for new hunting grounds elsewhere.
It explores with long, sensitive tendrils.
It has found another bromeliad.
And descends into this new territory.
Now it prepares to hunt.
Its traps - the bladders from which it gets its name - are tiny capsules.
Glands inside them extract water, so creating a partial vacuum.
Each bladder has a little door fringed with bristles.
A mosquito larva has only to touch one of these triggers
and the door will implode and sweep the prey inside.
The glands pump out water,
so the bladderwort starts its meal
and resets its trap which is ready for another customer in two hours.
Roraima also has sundews. Like sundews elsewhere,
they catch insects in a way that is a family speciality.
The drops on the leaf hairs are not sweet, but still attract insects.
They are, however, extremely sticky -
as any inquisitive insect discovers.
The hairs move swiftly. One can turn 180 degrees in less than a minute.
So even though an insect may have been caught by only one or two hairs,
others nearby quickly fold over it and soon it is held fast.
The sundew species on Roraima, like the bladderwort and carnivorous pitcher,
occur only on these plateaus.
Indeed, about a third of the species on the mountain have evolved here and are found nowhere else.
The water sluicing over these rocks has caused problems for Roraima's plants by washing away nutrients.
After leaving the mountain, it joins the biggest river of all, the Amazon,
and then, lying in swamps and lakes,
it will create different problems.
But again, there are plants that have solved them.
Access to light is the great problem here. Those plants that can command the surface can rule the lake,
and none does so on a greater scale and more aggressively than this -
the giant Amazon water lily.
Its gigantic leaves are armoured with spines
that protect them against any fish that might try to eat them.
Their huge form is kept outstretched and floating on the surface
by a lattice of buoyant, air-filled struts.
The crinkles in the surface swiftly flatten out
as the leaf expands to its full size.
The edges are turned up so that the leaf can shoulder aside any rivals.
Fully grown, a single leaf is six feet across.
Virtually no other plants can live in the black, shaded water beneath these leaves.
They cover the surface so completely and their girders are so strong,
that birds, like the lily-trotter,
can spend their entire lives walking around on them, collecting insects.
The giant lily's flowers are on an equally monumental scale.
They're about a foot across.
The life of any one bloom is short.
It opens in the evening and gives off a strong perfume.
During the night, it closes
and it stays closed for the whole of the next day, slowly flushing pink.
On its second evening, it opens again.
Then it closes for the last time.
Why does it behave in this extraordinary way?
It's a way of avoiding any chance of being fertilised by its own pollen.
The perfume it produces on its first evening attracts beetles.
They bring pollen from other lilies,
so this flower is about to be fertilised.
But then, the lily closes its petals.
The beetles will be held captive inside for 24 hours.
The following evening, the beautiful prison opens its gates
and the inmates are free to go.
The flower has given the beetles its own pollen during their long stay.
Now red and odourless, the flower is no longer attractive to beetles,
so they'll search for white flowers on another plant,
carrying the pollen and bringing about cross-fertilisation.
Its mission completed, the flower withdraws back to its watery world.
As swiftly-flowing streams enter the still water of a lake,
so they slow down and shed their load of sediment.
So, day after day, the lake fills up.
As the water gets shallower,
so it becomes possible for different, bigger plants to grow in it.
The trees in the forefront of this invasion, here in the southern United States,
are likely to be swamp cypresses.
The bases of their trunks are broad and cone-shaped, so they can squat firmly on the lake floor.
But they also make an ever-widening platform for themselves
to get a head start on their competitors.
Mud will be deposited wherever the current that is carrying it slows down.
Cypresses encourage that to happen around them by growing their roots into flanges and spires.
But the problems of a freshwater swamp are tiny
compared with those of the coastal, salty swamps where mangroves live.
EERIE ANIMAL NOISES Here, I am close to the sea
and the ground is even more unstable.
So the mangroves that grow here have to take more extreme measures
in order to stand upright, and they develop this tangle of prop roots.
Twice in every 24 hours, their land is invaded by the sea.
Estuary mud is particularly fine and sticky.
Aerating it is impossible and when the tide is out,
the mangroves breathe through pores on their prop roots.
But when the tide is IN, they can't do that.
In effect, they hold their breath for several hours.
Eventually, the tide begins to turn, and as the water ebbs away,
the mangroves slowly begin to breathe again.
Submersion is longest at the edge of the sea.
It's the first part to be covered and the last to be exposed.
Here the mangroves sprout fields of snorkels, each with pores through which the roots can take in air.
It's especially tricky for young plants to get started here.
The adult trees deal with that
by keeping hold of their young until the very last moment.
This long spike, green though it is, is, in fact, a root.
The seed has germinated while it's still attached to the tree.
And now, the young plant is about to stake its claim for territory in a quite literal way.
A shoot that falls when the tide is out may stick in the mud.
If the water is too deep, the shoot won't reach the bottom.
But all is by no means lost.
The young plant simply floats away.
Like this, it may be carried into a different estuary.
There, when the tide goes out,
it may snag its tip in the mud. So it ends up far from its parents
and colonises newly-formed mud flats on the very margins of the sea.
Rocky coasts present plants with yet other problems.
The rocks are firm enough. The perils are the pounding waves and the surging currents.
No flowering plant has evolved a solution to the difficulties of living here. But algae have.
They have the simplest structure of all plants.
They've never developed rigid stems, but here, the water provides support.
Their holdfasts grip the rock so firmly,
that in a strong current, the rock's more likely to break than the plant.
They have long, cable-like stems
that are rubbery and flexible but immensely strong.
The great blades in which they make their food are kept near sunlight
by huge, gas-filled floats.
Such algae can reach immense lengths.
They can grow in waters almost 100 feet deep,
but because they stream out in the current, their total length can be several times that.
One species has fronds that measure over 300 feet,
about as long as the tallest of land-living trees.
These thickets can, with justice, be regarded as the marine equivalents of terrestrial forests.
Farther out to sea, the water becomes so deep
that even these giant algae can't maintain a hold on the sea-floor and still reach the light.
The open water of the deep ocean
is the domain of the simplest plants of all -
the microscopic single-celled algae.
These, perhaps the least considered by humanity of all plants,
have the four essentials of life in abundance.
The water around them never drops much below freezing,
they are always within reach of sunlight,
they're provided with nutrients as currents bring plenty of rich ooze,
and they have colonised not only salt water, but fresh.
These simple plants are the basis of all life in water,
just as higher plants are the basis of all life on land.
Two thirds of the earth's surface is covered by water - most of it is out of reach of flowering plants.
So floating algae, in the seas and lakes, play a greater part in enriching our atmosphere with oxygen
than all the land-based plants put together.
So we end as we began -
with the simplest of plants - algae.
Between them, plants, whether simple or complex,
like these growing in the rainforest on the coast of tropical Australia, have colonised the whole planet.
They live, not only in favourable environments, but on frozen rocks of the Polar lands
and in the searingly hot sands of the deserts.
They've developed ways of surviving fire and hurricanes.
They can withstand animal attacks and can even eat animals themselves.
But one thing plants CAN'T withstand
and that's the determined onslaught of human beings.
Ever since we arrived on this planet, we have cut them down, dug them up, burnt them and poisoned them.
Today, we're doing so more than ever.
Even this small, precious patch of rainforest in northern Queensland is under threat.
We destroy plants at our peril.
Neither we nor any other animal can survive without them.
The time has now come for us to cherish our green inheritance, not to pillage it.
For without it, we will surely perish.
Subtitles by Gillian Frazer BBC Scotland 1995