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No part of the earth is more hostile to life than the frozen wastes around the Poles.

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850 miles north of the Arctic Circle, this is Ellesmere Island.

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No animal can live permanently on these ice fields

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and even plants face big problems,

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for the four things they must have are in crippingly short supply.

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Water?

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Yes, there's a lot of frozen water here,

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but water has to be liquid for plants to make any use of it.

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Nutrients? There's virtually none in this frost-shattered rock.

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Warmth and light? For six months of the year it's dark,

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and in the brief summer, as now, the sun doesn't rise high,

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and devastating winds can carry away what little warmth it brings. Yet, there ARE plants here.

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Some live actually INSIDE the rock.

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This thin green line is made by algae - microscopic plants.

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They're so small, they can live BETWEEN the grains of this sandstone,

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and there, at least, they're out of this desiccating wind.

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On the surface of the rocks, there are lichens.

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They grow incredibly slowly and may take 50 years to cover a square cm,

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but they can survive even if there are only two days a year when it's warm enough for them to grow.

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In spite of these bleak conditions, there ARE flowers to be found here.

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But you have to look hard to find them.

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Here's one.

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It's a mustard, but it's

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much smaller than its more southerly relatives,

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so it can keep out of the crippling wind.

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In midsummer, for a few weeks,

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enough water melts from the glaciers for streams to flow,

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and then, miniature gardens burst into bloom.

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The searing wind compels them all to keep close to the ground.

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None keeps closer than this. It is, in fact, a tree - a willow.

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These are its catkins.

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But the trunk grows horizontally,

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and it can stretch almost as far along the ground as its more southerly relatives stand above it.

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Even so, it still produces enough leaves to sustain a few grazers -

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musk ox.

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Nothing is wasted up here -

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not a moment of sunshine, not the tiniest shelter, not a scrap of food.

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When a musk ox dies, its decaying body releases a rich flush of nourishment into the soil,

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and tiny gardens appear, in the shelter of its bones.

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The Arctic poppy,

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like all plants, needs warmth to grow,

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but it is unusually efficient at collecting it.

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As the midsummer sun skims round the horizon -

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360 degrees in 24 hours without setting -

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the poppy turns its flowers to track it.

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The slanting sun may not be strong, but it is, at least, continuous

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during the few weeks of high summer.

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The heat the poppy gathers by staring continuously at the sun

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enables seeds to develop in each flower before summer comes to an end

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and the sun disappears below the horizon for months.

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Conditions may be just as severe on the high peaks of the Alps,

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2,000 miles to the south, at least during the winter.

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But here, spring brings a greater benefit.

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The sun rises higher in the sky and is warm enough to melt all but the highest snowfields.

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As it melts, it reveals the snowbell, already in flower.

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The plant formed its flower buds last autumn,

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before the increasing cold shut down all its activities for the winter.

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The buds remained dormant until the spring sunshine, through the snow,

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triggered them into opening even before the snow had melted.

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In summer, the high meadows, newly freed from snow,

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fill with flowers.

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Because for so much of the time it's so cold, the vegetation here decays only very slowly,

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so a peaty soil forms.

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But it's only a thin layer over solid rock and boulders

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and trees find it very difficult to get root.

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Also, avalanches regularly sweep these slopes,

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carrying away saplings before they're established.

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So, shallow-rooted plants have these parts of the mountains largely to themselves

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and in summer, they bring a rich display of colour.

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But for every thousand feet you climb, the average temperature drops by about three degrees.

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Plants living in the high mountains must be able to survive extreme cold.

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It's very important to keep out of the worst of the chilling winds

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and many plants here form small rounded humps,

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and that brings them a number of advantages.

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Growing into the shape of a cushion is a good way of conserving heat

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and no plants do it better than these in the mountains of Tasmania.

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These are the largest cushion plants in the world.

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They grow to over 12 feet across.

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Any one square yard contains over 100,000 shoots, so this one cushion around me contains several million.

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This rounded shape does more than just reduce wind-chill.

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The air temperature around me here, at about 3,500 feet high,

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is only a degree above freezing.

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But if I put this temperature probe on the surface,

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I can see that there it is several degrees warmer.

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The cushion acts as a solar panel, absorbing heat from the sun

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so that, even on very cold days, provided it's not covered with snow,

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it can photosynthesise and grow.

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The plants that form these spectacular cushions come from several different families -

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sedges and rushes, daisies and dandelions.

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One cushion may contain several species, tightly packed together and growing to the same height.

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For one kind to grow higher than those around it would be suicidal.

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In the New Zealand Alps, one of these cushion-forming species

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also protects itself by developing a blanket of hair.

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Its colonies form conspicuous white humps on the mountainside.

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New Zealand farmers, whose flocks can stray up onto these slopes,

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call such cushions "vegetable sheep".

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This tall pillar, growing on Mount Kenya,

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also covers itself in a blanket.

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It's a giant lobelia.

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Its long leaves are fringed with dense hairs.

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Its flowers are hidden away from the frost beneath this downy covering.

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Bright petals are no use if they can't be seen,

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and these are just simple tubes.

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The lobelia's pollinator, a sunbird, knows where they are and how to reach them.

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During the day, it can get quite warm,

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for Mount Kenya stands almost exactly on the equator.

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But at 14,000 feet, once the sun goes down, it gets bitterly cold

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and then the lobelia will have real need of its hairy blanket.

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There are other giants here too - tree groundsels,

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relatives of the little yellow weed in European gardens.

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They have a different way of dealing with the cold nights.

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Their dead leaves remain on the stem, so that they act like lagging

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and prevent the liquids in the pipes inside the trunk from freezing solid.

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Conditions here can change with extraordinary speed.

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One moment the equatorial sun is blazing down from a cloudless sky,

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the next, a chilling wind begins to blow and the great mountain collects a cloud cover.

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As well as the tree groundsel,

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there's another groundsel that grows close to the ground like a cabbage.

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As night falls, it makes its own preparations for surviving the bitter cold.

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The most precious and vulnerable part of the plant is the bud in its centre from which all growth comes.

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That must be protected at all costs,

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and folding the thick leaves over it does the trick.

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The temperature has now fallen by as much as 30 degrees.

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Water in the muddy swamps is beginning to freeze. As it does so,

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it expands and the ground begins to heave.

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It's impossible for small plants to remain rooted under these conditions.

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The Mount Kenya moss doesn't even try.

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It grows into balls that are lifted up by the ice pinnacles and it rolls around during the night.

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The sun returns, the temperature rises,

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the threat of death by freezing has passed,

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and the cabbage groundsels stretch out their leaves to catch the light

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and start making food once more.

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The ice in the swamps melts

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and the streams flow again.

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This is just as well, for now the plants, baking under the sun, are beginning to lose a lot of water

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by evaporation from their leaves.

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And severe water loss is the other disaster that can kill hardy plants.

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If the sap-filled vessels in the tree groundsels' trunks had frozen,

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their leaves would now be baked dry.

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Here we are...still in Africa,

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but about 14,000 feet lower down.

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I'm on the southern edge of the Namib Desert.

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Here, plants can't get water, not because it's frozen, but because rain hardly ever falls -

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only about one or two inches a year.

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Most of the time, it's bone dry...

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and devastatingly hot.

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Yet, almost unbelievably, there are trees standing out in the sands,

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totally unsheltered, with no signs of moisture anywhere around them.

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Water storage is the trick here.

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These green succulent leaves are full of it,

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and so are these bloated branches.

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The local bushmen used to hollow out these branches and use them as containers for their arrows,

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which is why this tree is called the quiver tree.

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Its branches are covered with a blindingly white powder which reflects the heat,

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and its leaves have thick rinds with few pores

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which minimises water loss through evaporation.

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The trunk, even of an old tree,

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remains smooth and impermeable.

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But even the quiver tree can't seal itself off completely.

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Living involves breathing and some water vapour is inevitably lost in that process.

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But this tree has a way of reducing that.

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Self-amputation. It can cut off a leaf rosette and seal the stump.

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This branch will never grow leaves again.

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The tree will just survive with fewer leaves

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and put out new shoots when conditions improve.

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Most of the plants in this desert, however, are less conspicuous,

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and there are rather more of them than you might suppose.

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This little plant has fused its leaves together in pairs

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to form cones, which is why it's called Conophytum.

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The white surface of each cone is the skin of last year's leaf,

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and the plant is now waiting for the rains to arrive.

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Let's see what happens if I make them arrive earlier.

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One of the greatest of all water reservoirs is the saguaro cactus

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that grows in Arizona and New Mexico.

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One of these giants can hold several tons of liquid.

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They don't risk losing any water through the leaves - they have none.

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Instead, the task of making food has been taken over by the stem

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which has become green with chlorophyll and keeps its pores well-protected in grooves.

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The 50-foot columns are crowned with flowers.

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The pleats in the trunks enable the plants to expand rapidly

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and suck up rain falling in a sudden storm before it evaporates in the heat and disappears.

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Such a store of liquid is very precious. Lots of desert animals would raid it if they could.

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They can't because cacti, like other desert succulents, defend themselves with spines.

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The other way of protecting yourself against robbers

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is to hide underground.

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You might THINK that these are pebbles.

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You would be wrong.

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This...is a window plant.

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These little studs are the flat tops of the pillar-like leaves.

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And these tops are transparent. They allow the light to pass through

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where it's transmitted by a row of crystals to the bottom of the leaf where there's green pigment.

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So although this little plant is several inches under the ground,

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it can catch the sunlight and turn it into food.

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And in the driest times of all, when sandstorms blow across the Namib,

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it may be covered up completely.

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Many plants take refuge underground during the hottest part of the year

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and survive as bulbs and tubers, swollen with food and water stores,

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gathered during the good times.

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Underground is undoubtedly the coolest place to be,

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but it's not necessarily the safest.

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Mole rats.

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They burrow ceaselessly,

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searching at random for their food.

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Some of the bulbs they eat immediately,

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but others they take away and stack in special larders.

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Being carried away and put in store is not necessarily a disaster for the plants.

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The mole rats seldom eat all their reserves

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and some larders get forgotten.

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Then the bulbs sprout and benefit from doing so in a new location.

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This plant is totally dead.

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It didn't store its food underground in bulbs. It adopted a very different and very drastic strategy.

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It condensed its entire life into a few short weeks.

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And its last act was to release into the sand a few hundred seeds.

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They're easy enough to find.

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And there are some.

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They can wait here, in this hot sand, apparently lifeless, for years...

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even 20 years.

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But when the rains DO come, their moment arrives.

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One day, the land is so dry that the withered plants crunch to pieces underfoot.

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Two or three weeks later... and it's ablaze.

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Arid lands around the world, not only here in South Africa,

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but in Australia and Arizona, all respond to rain

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by rapidly producing dazzling displays of colour.

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The sudden flush of flowers and leaves attracts lots of plant-eaters.

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For them, too, the pressures of desert-living are momentarily relaxed.

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It may seem a paradox that some of the harshest environments should produce such unrivalled glories.

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But the desert soil will not remain moist for long after rain

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and in that short time, plants must grow leaves AND produce seeds.

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So the need for pollination is urgent.

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The most brilliant flowers have the best chance of attracting an insect.

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This is competitive advertising at its most intense.

232
00:26:16,9600 --> 00:26:21,4800
So, a few days of rain once every year or so

233
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are enough to enable plants to survive in the driest areas on earth.

234
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THUNDER

235
00:26:48,4800 --> 00:26:54,0400
And this is one of the wettest places on earth.

236
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Here, it rains almost every day and sometimes for days on end.

237
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I'm in South America, on the top of an immense sandstone plateau,

238
00:27:04,6000 --> 00:27:08,1600
9,000 feet high, five miles across,

239
00:27:08,1600 --> 00:27:11,6000
surrounded by huge vertical cliffs.

240
00:27:11,6000 --> 00:27:14,3600
This is Mount Roraima.

241
00:27:19,1200 --> 00:27:23,8400
Plants cut off up here from the hot rainforest below

242
00:27:23,8400 --> 00:27:28,3600
adapt to their surroundings in their own individual way.

243
00:27:28,3600 --> 00:27:33,4000
So there are species here that occur nowhere else in the world.

244
00:27:33,4000 --> 00:27:39,2000
The rains produce torrents that cascade over the edge of the plateau

245
00:27:39,2000 --> 00:27:43,2400
and form some of the highest waterfalls on earth.

246
00:27:46,6800 --> 00:27:50,7200
Much of this extraordinary landscape is naked rock.

247
00:27:50,7200 --> 00:27:55,8000
Only here and there do clumps of plants manage to get a root-hold,

248
00:27:55,8000 --> 00:28:00,3200
and even when they succeed, life is difficult.

249
00:28:00,3200 --> 00:28:03,1600
Lack of nutrients is the big problem.

250
00:28:03,1600 --> 00:28:09,2400
Streams wash away everything in their path and flow over bare rock.

251
00:28:09,2400 --> 00:28:14,2800
Only in a few places does a little gravelly sediment accumulate.

252
00:28:14,2800 --> 00:28:19,4000
So many of the plants here have to have ways of augmenting their food.

253
00:28:19,4000 --> 00:28:23,3600
And some of them do it by eating animals.

254
00:28:25,6400 --> 00:28:28,2400
This is about the simplest way

255
00:28:28,2400 --> 00:28:32,2800
in which a plant can catch and eat an insect.

256
00:28:32,2800 --> 00:28:39,2800
This is the marsh pitcher and this particular species lives only on Mount Roraima.

257
00:28:39,2800 --> 00:28:45,0800
There are four others, which only live on other mountains near here.

258
00:28:45,0800 --> 00:28:47,5600
And this is how they do it.

259
00:28:49,4400 --> 00:28:52,4400
The leaf, in the shape of a tube,

260
00:28:52,4400 --> 00:28:55,4800
is covered by downward-pointing hairs -

261
00:28:55,4800 --> 00:29:00,6800
easy to slide down, very difficult to climb up. One slip,

262
00:29:00,6800 --> 00:29:05,0400
and it's drowning and dissolution for the insect.

263
00:29:05,0400 --> 00:29:09,0400
And then digestion by the plant.

264
00:29:12,4400 --> 00:29:16,8800
The pond in a bromeliad is usually safe for aquatic insects,

265
00:29:16,8800 --> 00:29:22,3600
but a bladderwort is hunting inside Roraima's bromeliads.

266
00:29:31,1600 --> 00:29:34,0800
Not content with prey in THIS pond,

267
00:29:34,0800 --> 00:29:39,0400
the bladderwort is looking for new hunting grounds elsewhere.

268
00:29:49,1200 --> 00:29:53,0800
It explores with long, sensitive tendrils.

269
00:29:59,6000 --> 00:30:02,5600
It has found another bromeliad.

270
00:30:06,1200 --> 00:30:09,7200
And descends into this new territory.

271
00:30:17,5200 --> 00:30:20,3600
Now it prepares to hunt.

272
00:30:32,5600 --> 00:30:38,3600
Its traps - the bladders from which it gets its name - are tiny capsules.

273
00:30:38,3600 --> 00:30:44,1200
Glands inside them extract water, so creating a partial vacuum.

274
00:30:54,6000 --> 00:30:58,8000
Each bladder has a little door fringed with bristles.

275
00:30:58,8000 --> 00:31:03,3600
A mosquito larva has only to touch one of these triggers

276
00:31:03,3600 --> 00:31:08,8800
and the door will implode and sweep the prey inside.

277
00:31:08,8800 --> 00:31:11,7600
The glands pump out water,

278
00:31:11,7600 --> 00:31:15,2400
so the bladderwort starts its meal

279
00:31:15,2400 --> 00:31:20,6800
and resets its trap which is ready for another customer in two hours.

280
00:31:28,4400 --> 00:31:33,7600
Roraima also has sundews. Like sundews elsewhere,

281
00:31:33,7600 --> 00:31:38,2400
they catch insects in a way that is a family speciality.

282
00:31:42,6800 --> 00:31:48,4400
The drops on the leaf hairs are not sweet, but still attract insects.

283
00:31:48,4400 --> 00:31:53,1200
They are, however, extremely sticky -

284
00:31:53,1200 --> 00:31:56,2800
as any inquisitive insect discovers.

285
00:32:00,4400 --> 00:32:06,5200
The hairs move swiftly. One can turn 180 degrees in less than a minute.

286
00:32:06,5200 --> 00:32:11,8800
So even though an insect may have been caught by only one or two hairs,

287
00:32:11,8800 --> 00:32:16,4400
others nearby quickly fold over it and soon it is held fast.

288
00:32:43,2000 --> 00:32:50,2400
The sundew species on Roraima, like the bladderwort and carnivorous pitcher,

289
00:32:50,2400 --> 00:32:52,8800
occur only on these plateaus.

290
00:32:54,3200 --> 00:33:01,7600
Indeed, about a third of the species on the mountain have evolved here and are found nowhere else.

291
00:33:02,9600 --> 00:33:10,2800
The water sluicing over these rocks has caused problems for Roraima's plants by washing away nutrients.

292
00:33:17,9200 --> 00:33:23,6400
After leaving the mountain, it joins the biggest river of all, the Amazon,

293
00:33:23,6400 --> 00:33:26,2800
and then, lying in swamps and lakes,

294
00:33:26,2800 --> 00:33:29,3600
it will create different problems.

295
00:33:29,3600 --> 00:33:33,9600
But again, there are plants that have solved them.

296
00:33:39,3600 --> 00:33:46,8800
Access to light is the great problem here. Those plants that can command the surface can rule the lake,

297
00:33:46,8800 --> 00:33:52,2400
and none does so on a greater scale and more aggressively than this -

298
00:33:52,2400 --> 00:33:55,0400
the giant Amazon water lily.

299
00:34:04,2000 --> 00:34:08,2400
Its gigantic leaves are armoured with spines

300
00:34:08,2400 --> 00:34:13,2400
that protect them against any fish that might try to eat them.

301
00:34:28,7200 --> 00:34:33,7600
Their huge form is kept outstretched and floating on the surface

302
00:34:33,7600 --> 00:34:38,2000
by a lattice of buoyant, air-filled struts.

303
00:34:43,8400 --> 00:34:48,0000
The crinkles in the surface swiftly flatten out

304
00:34:48,0000 --> 00:34:51,7200
as the leaf expands to its full size.

305
00:34:58,5600 --> 00:35:04,0000
The edges are turned up so that the leaf can shoulder aside any rivals.

306
00:35:06,2400 --> 00:35:10,6800
Fully grown, a single leaf is six feet across.

307
00:35:10,6800 --> 00:35:17,7200
Virtually no other plants can live in the black, shaded water beneath these leaves.

308
00:35:17,7200 --> 00:35:23,0400
They cover the surface so completely and their girders are so strong,

309
00:35:23,0400 --> 00:35:25,9600
that birds, like the lily-trotter,

310
00:35:25,9600 --> 00:35:31,7200
can spend their entire lives walking around on them, collecting insects.

311
00:35:31,7200 --> 00:35:37,2400
The giant lily's flowers are on an equally monumental scale.

312
00:35:37,2400 --> 00:35:39,6800
They're about a foot across.

313
00:35:51,2000 --> 00:35:54,2400
The life of any one bloom is short.

314
00:35:54,2400 --> 00:35:59,1600
It opens in the evening and gives off a strong perfume.

315
00:35:59,1600 --> 00:36:02,1600
During the night, it closes

316
00:36:02,1600 --> 00:36:07,2000
and it stays closed for the whole of the next day, slowly flushing pink.

317
00:36:07,2000 --> 00:36:11,4000
On its second evening, it opens again.

318
00:36:16,6000 --> 00:36:19,6000
Then it closes for the last time.

319
00:36:21,2400 --> 00:36:25,4000
Why does it behave in this extraordinary way?

320
00:36:25,4000 --> 00:36:31,1600
It's a way of avoiding any chance of being fertilised by its own pollen.

321
00:36:31,1600 --> 00:36:36,1600
The perfume it produces on its first evening attracts beetles.

322
00:36:40,6800 --> 00:36:44,3600
They bring pollen from other lilies,

323
00:36:44,3600 --> 00:36:48,2000
so this flower is about to be fertilised.

324
00:36:52,5200 --> 00:36:55,3600
But then, the lily closes its petals.

325
00:36:56,6000 --> 00:37:02,3200
The beetles will be held captive inside for 24 hours.

326
00:37:08,0000 --> 00:37:13,1600
The following evening, the beautiful prison opens its gates

327
00:37:13,1600 --> 00:37:15,6800
and the inmates are free to go.

328
00:37:22,0000 --> 00:37:27,4400
The flower has given the beetles its own pollen during their long stay.

329
00:37:29,0000 --> 00:37:34,0800
Now red and odourless, the flower is no longer attractive to beetles,

330
00:37:34,0800 --> 00:37:38,4800
so they'll search for white flowers on another plant,

331
00:37:38,4800 --> 00:37:43,4000
carrying the pollen and bringing about cross-fertilisation.

332
00:37:48,4400 --> 00:37:54,2800
Its mission completed, the flower withdraws back to its watery world.

333
00:38:08,6400 --> 00:38:14,1200
As swiftly-flowing streams enter the still water of a lake,

334
00:38:14,1200 --> 00:38:19,6000
so they slow down and shed their load of sediment.

335
00:38:19,6000 --> 00:38:23,4800
So, day after day, the lake fills up.

336
00:38:23,4800 --> 00:38:26,1200
As the water gets shallower,

337
00:38:26,1200 --> 00:38:31,0800
so it becomes possible for different, bigger plants to grow in it.

338
00:38:32,2000 --> 00:38:39,1600
The trees in the forefront of this invasion, here in the southern United States,

339
00:38:39,1600 --> 00:38:41,7600
are likely to be swamp cypresses.

340
00:38:41,7600 --> 00:38:48,9600
The bases of their trunks are broad and cone-shaped, so they can squat firmly on the lake floor.

341
00:38:53,0800 --> 00:38:58,6000
But they also make an ever-widening platform for themselves

342
00:38:58,6000 --> 00:39:02,6800
to get a head start on their competitors.

343
00:39:02,6800 --> 00:39:09,2000
Mud will be deposited wherever the current that is carrying it slows down.

344
00:39:09,2000 --> 00:39:16,5200
Cypresses encourage that to happen around them by growing their roots into flanges and spires.

345
00:39:16,5200 --> 00:39:20,5600
But the problems of a freshwater swamp are tiny

346
00:39:20,5600 --> 00:39:26,5600
compared with those of the coastal, salty swamps where mangroves live.

347
00:39:29,5600 --> 00:39:35,2400
EERIE ANIMAL NOISES Here, I am close to the sea

348
00:39:35,2400 --> 00:39:38,3200
and the ground is even more unstable.

349
00:39:38,3200 --> 00:39:43,3600
So the mangroves that grow here have to take more extreme measures

350
00:39:43,3600 --> 00:39:49,4000
in order to stand upright, and they develop this tangle of prop roots.

351
00:39:49,4000 --> 00:39:55,6000
Twice in every 24 hours, their land is invaded by the sea.

352
00:40:11,0000 --> 00:40:15,0000
Estuary mud is particularly fine and sticky.

353
00:40:15,0000 --> 00:40:19,5200
Aerating it is impossible and when the tide is out,

354
00:40:19,5200 --> 00:40:24,0400
the mangroves breathe through pores on their prop roots.

355
00:40:24,0400 --> 00:40:28,0800
But when the tide is IN, they can't do that.

356
00:40:28,0800 --> 00:40:32,6800
In effect, they hold their breath for several hours.

357
00:40:36,8000 --> 00:40:42,2000
Eventually, the tide begins to turn, and as the water ebbs away,

358
00:40:42,2000 --> 00:40:46,6400
the mangroves slowly begin to breathe again.

359
00:40:46,6400 --> 00:40:50,6800
Submersion is longest at the edge of the sea.

360
00:40:50,6800 --> 00:40:55,8800
It's the first part to be covered and the last to be exposed.

361
00:40:55,8800 --> 00:41:03,3200
Here the mangroves sprout fields of snorkels, each with pores through which the roots can take in air.

362
00:41:07,2400 --> 00:41:12,2800
It's especially tricky for young plants to get started here.

363
00:41:12,2800 --> 00:41:15,0800
The adult trees deal with that

364
00:41:15,0800 --> 00:41:20,0800
by keeping hold of their young until the very last moment.

365
00:41:40,8400 --> 00:41:46,8400
This long spike, green though it is, is, in fact, a root.

366
00:41:46,8400 --> 00:41:51,8800
The seed has germinated while it's still attached to the tree.

367
00:41:51,8800 --> 00:41:59,0800
And now, the young plant is about to stake its claim for territory in a quite literal way.

368
00:41:59,0800 --> 00:42:03,5600
A shoot that falls when the tide is out may stick in the mud.

369
00:42:09,5200 --> 00:42:14,6000
If the water is too deep, the shoot won't reach the bottom.

370
00:42:14,6000 --> 00:42:17,5200
But all is by no means lost.

371
00:42:17,5200 --> 00:42:20,4400
The young plant simply floats away.

372
00:42:21,8400 --> 00:42:26,0800
Like this, it may be carried into a different estuary.

373
00:42:28,3200 --> 00:42:31,2800
There, when the tide goes out,

374
00:42:31,2800 --> 00:42:37,0400
it may snag its tip in the mud. So it ends up far from its parents

375
00:42:37,0400 --> 00:42:42,6000
and colonises newly-formed mud flats on the very margins of the sea.

376
00:42:50,0800 --> 00:42:55,1200
Rocky coasts present plants with yet other problems.

377
00:42:55,1200 --> 00:43:02,3200
The rocks are firm enough. The perils are the pounding waves and the surging currents.

378
00:43:02,3200 --> 00:43:09,7600
No flowering plant has evolved a solution to the difficulties of living here. But algae have.

379
00:43:09,7600 --> 00:43:13,8000
They have the simplest structure of all plants.

380
00:43:13,8000 --> 00:43:20,0000
They've never developed rigid stems, but here, the water provides support.

381
00:43:20,0000 --> 00:43:23,9200
Their holdfasts grip the rock so firmly,

382
00:43:23,9200 --> 00:43:29,4000
that in a strong current, the rock's more likely to break than the plant.

383
00:43:36,2000 --> 00:43:39,0800
They have long, cable-like stems

384
00:43:39,0800 --> 00:43:43,5200
that are rubbery and flexible but immensely strong.

385
00:43:43,5200 --> 00:43:49,3600
The great blades in which they make their food are kept near sunlight

386
00:43:49,3600 --> 00:43:52,2800
by huge, gas-filled floats.

387
00:43:57,2000 --> 00:44:00,0000
Such algae can reach immense lengths.

388
00:44:00,0000 --> 00:44:04,0800
They can grow in waters almost 100 feet deep,

389
00:44:04,0800 --> 00:44:11,2000
but because they stream out in the current, their total length can be several times that.

390
00:44:13,7600 --> 00:44:18,2800
One species has fronds that measure over 300 feet,

391
00:44:18,2800 --> 00:44:22,9600
about as long as the tallest of land-living trees.

392
00:44:22,9600 --> 00:44:30,4800
These thickets can, with justice, be regarded as the marine equivalents of terrestrial forests.

393
00:44:30,4800 --> 00:44:34,5200
Farther out to sea, the water becomes so deep

394
00:44:34,5200 --> 00:44:41,4800
that even these giant algae can't maintain a hold on the sea-floor and still reach the light.

395
00:44:42,5200 --> 00:44:45,0800
The open water of the deep ocean

396
00:44:45,0800 --> 00:44:49,0800
is the domain of the simplest plants of all -

397
00:44:49,0800 --> 00:44:52,0800
the microscopic single-celled algae.

398
00:44:56,1200 --> 00:45:01,1600
These, perhaps the least considered by humanity of all plants,

399
00:45:01,1600 --> 00:45:05,2000
have the four essentials of life in abundance.

400
00:45:05,2000 --> 00:45:09,7200
The water around them never drops much below freezing,

401
00:45:09,7200 --> 00:45:13,2400
they are always within reach of sunlight,

402
00:45:13,2400 --> 00:45:18,2800
they're provided with nutrients as currents bring plenty of rich ooze,

403
00:45:18,2800 --> 00:45:22,7600
and they have colonised not only salt water, but fresh.

404
00:45:38,5200 --> 00:45:43,0800
These simple plants are the basis of all life in water,

405
00:45:43,0800 --> 00:45:47,6400
just as higher plants are the basis of all life on land.

406
00:45:47,6400 --> 00:45:55,2000
Two thirds of the earth's surface is covered by water - most of it is out of reach of flowering plants.

407
00:45:55,2000 --> 00:46:02,7200
So floating algae, in the seas and lakes, play a greater part in enriching our atmosphere with oxygen

408
00:46:02,7200 --> 00:46:06,6800
than all the land-based plants put together.

409
00:46:11,8800 --> 00:46:14,9600
So we end as we began -

410
00:46:14,9600 --> 00:46:18,0000
with the simplest of plants - algae.

411
00:46:18,0000 --> 00:46:22,1200
Between them, plants, whether simple or complex,

412
00:46:22,1200 --> 00:46:29,6400
like these growing in the rainforest on the coast of tropical Australia, have colonised the whole planet.

413
00:46:29,6400 --> 00:46:36,2800
They live, not only in favourable environments, but on frozen rocks of the Polar lands

414
00:46:36,2800 --> 00:46:40,2000
and in the searingly hot sands of the deserts.

415
00:46:40,2000 --> 00:46:44,6800
They've developed ways of surviving fire and hurricanes.

416
00:46:44,6800 --> 00:46:49,6400
They can withstand animal attacks and can even eat animals themselves.

417
00:46:49,6400 --> 00:46:52,8800
But one thing plants CAN'T withstand

418
00:46:52,8800 --> 00:46:56,8000
and that's the determined onslaught of human beings.

419
00:46:56,8000 --> 00:47:04,2400
Ever since we arrived on this planet, we have cut them down, dug them up, burnt them and poisoned them.

420
00:47:04,2400 --> 00:47:07,4400
Today, we're doing so more than ever.

421
00:47:07,4400 --> 00:47:14,5200
Even this small, precious patch of rainforest in northern Queensland is under threat.

422
00:47:18,1200 --> 00:47:21,2000
We destroy plants at our peril.

423
00:47:21,2000 --> 00:47:25,7200
Neither we nor any other animal can survive without them.

424
00:47:25,7200 --> 00:47:32,5200
The time has now come for us to cherish our green inheritance, not to pillage it.

425
00:47:32,5200 --> 00:47:36,2000
For without it, we will surely perish.

426
00:48:12,0000 --> 00:48:16,6400
Subtitles by Gillian Frazer BBC Scotland 1995