0:00:40 > 0:00:48High in the canopy of the South American rainforest a fruit is falling.
0:00:53 > 0:00:58It has come from a plant sitting on a branch of one of the giant trees.
0:01:08 > 0:01:13Now it will rot and release a thousand seeds.
0:01:13 > 0:01:18To survive, the seedlings must gain a position like their parent's.
0:01:18 > 0:01:24Somehow, they've got to get up into the canopy and the sunshine.
0:01:36 > 0:01:41The shoots that come from the seeds, like all shoots, can sense the light.
0:01:41 > 0:01:44They can see.
0:01:44 > 0:01:48Each, as you might expect, sprouts upwards.
0:01:50 > 0:01:55But now these infant plants behave very strangely.
0:01:55 > 0:02:00They DON'T head for the brightest light. They seek the densest shade.
0:02:00 > 0:02:06And THAT usually lies around the trunk of the nearest tree.
0:02:06 > 0:02:13Each seedling is fuelled entirely by the store of food its parents deposited within the seed.
0:02:13 > 0:02:16That enables it to travel six feet.
0:02:16 > 0:02:23If it doesn't find what it's looking for within that distance, it will die of starvation.
0:02:37 > 0:02:39These have made it to first base.
0:02:39 > 0:02:42They've reached a vertical surface
0:02:42 > 0:02:44a tree trunk.
0:02:47 > 0:02:52As soon as one touches it, its behaviour changes dramatically.
0:02:55 > 0:02:57It starts growing upwards.
0:02:57 > 0:03:01As it does, it puts out its first leaves.
0:03:01 > 0:03:06Now, for the first time, it can manufacture food for itself.
0:03:07 > 0:03:12With each additional leaf, the young plant increases in strength.
0:03:25 > 0:03:30It holds these small circular leaves flat against the bark.
0:03:30 > 0:03:34As it gains height it produces bigger ones.
0:03:46 > 0:03:50And now, 50ft above the forest floor,
0:03:50 > 0:03:56 and many months since it emerged as a slim green shoot from its seed,
0:03:56 > 0:04:02this extraordinary, active plant has changed the shape of its leaves once again.
0:04:02 > 0:04:09They've developed the slits and holes that give it and its relations the name of cheese-plants.
0:04:09 > 0:04:15The small, round, green leaves that were pressed up against this trunk,
0:04:15 > 0:04:17and the stem that bore them,
0:04:17 > 0:04:20have now shrivelled and died.
0:04:20 > 0:04:24The cheese-plant has reached its true home the forest canopy.
0:04:24 > 0:04:27And THESE are its adult leaves.
0:04:27 > 0:04:33Cheese-plant leaves unfurl from pointed spikes like rolled umbrellas.
0:04:33 > 0:04:39But there are many ways of unpacking the green sheets to catch the sunlight.
0:04:44 > 0:04:47These are ferns.
0:05:29 > 0:05:32A tropical Alocasia.
0:05:44 > 0:05:46The needle-shaped leaves of a larch.
0:05:57 > 0:06:02The broad, five-fingered hand of a chestnut.
0:06:06 > 0:06:08Sycamore.
0:06:11 > 0:06:16Leaves are the factories in which plants make their food.
0:06:19 > 0:06:25They're powered by the sunshine, and use the simplest of raw materials
0:06:25 > 0:06:27air, water, and a few minerals.
0:06:27 > 0:06:31The process is the unique talent of plants.
0:06:31 > 0:06:34No animals can do such a thing.
0:06:34 > 0:06:39So all animals too depend, first- or second-hand, on food produced here.
0:06:39 > 0:06:42This is the very basis of life.
0:06:42 > 0:06:46Air seeps into the leaves through pores on their surface.
0:06:49 > 0:06:56It circulates within, and reaches granules containing a green substance chlorophyll.
0:06:56 > 0:07:04It is the key facilitator that uses the sun's energy to bond carbon dioxide to hydrogen from water.
0:07:04 > 0:07:09And produces carbohydrate sugars and starches.
0:07:09 > 0:07:16These, dissolved in sap, are then carried from the leaf into the body of the plant,
0:07:16 > 0:07:20even in the night, when the leaf factory has shut down.
0:07:22 > 0:07:27Come the dawn, the sun reappears and the process starts up again.
0:07:27 > 0:07:30BIRDSONG
0:07:43 > 0:07:48In open country in a hedgerow, perhaps
0:07:48 > 0:07:53there is so much light that as the sun climbs higher and higher
0:07:53 > 0:07:56the plant easily gets all it needs.
0:07:58 > 0:08:00In thick forest, it's not so easy.
0:08:00 > 0:08:05A plant growing beneath the canopy has to continually move its leaves
0:08:05 > 0:08:09to catch the shifting shafts of sunlight.
0:08:09 > 0:08:16Above, the trees position their leaves with such accuracy they form a close-fitting mosaic.
0:08:21 > 0:08:28The canopy is so efficient at gathering light that little filters down.
0:08:28 > 0:08:30There ARE leaves, of course.
0:08:30 > 0:08:35This is a sapling of a canopy tree, but it is growing hardly at all.
0:08:35 > 0:08:42It's waiting for one of the adult trees to fall, releasing a flood of light.
0:08:42 > 0:08:47Then it CAN grow, and it'll race upwards to claim the vacant space.
0:08:47 > 0:08:50It can wait 20 years for that chance.
0:08:50 > 0:08:55But until it comes there's not enough light for it to grow further.
0:08:55 > 0:09:00For most, of course, that chance will never come.
0:09:00 > 0:09:02Most will die as saplings.
0:09:02 > 0:09:07But some plants spend their whole lives on the dim forest floor.
0:09:07 > 0:09:10This begonia, for example.
0:09:10 > 0:09:16It produces big leaves, flowers, and sets seeds, all in this dim light.
0:09:16 > 0:09:19How?
0:09:19 > 0:09:22The secret is in the leaves.
0:09:22 > 0:09:26To start with, they have red undersides.
0:09:26 > 0:09:31That means light falling on the leaf surface and going through it,
0:09:31 > 0:09:34is reflected back into the leaf.
0:09:34 > 0:09:42So when sunlight does for a short time fall on the leaf, the plant is able to take maximum advantage of it.
0:09:47 > 0:09:51This species of begonia gathers light differently.
0:09:51 > 0:09:55These patches on their leaves are transparent,
0:09:55 > 0:10:02and act as lenses, gathering the light and focusing it onto the chlorophyll within.
0:10:02 > 0:10:07But plants need something else to make food for themselves.
0:10:07 > 0:10:12They need water and the nutrients dissolved in it.
0:10:12 > 0:10:16And that, of course, they suck up from the ground.
0:10:20 > 0:10:25The roots with which they do so probe downwards, seeking moisture.
0:10:25 > 0:10:32To get that, they place themselves with just as much accuracy as the leaves do when finding light.
0:10:38 > 0:10:44On finding water they put out rootlets, and from them a fur of tiny hairs
0:10:44 > 0:10:52so multiplying many thousands of times the surface area through which water can be sucked in.
0:11:00 > 0:11:07So the soil in a woodland is a tangle of precisely-placed rootlets from many different kinds of plants,
0:11:07 > 0:11:14each individual doing its best to ensure it gets its fair share of moisture.
0:11:14 > 0:11:19If the rainfall is reasonably good for much of the year,
0:11:19 > 0:11:26and if the water in the ground is able to dissolve an adequate amount of nutrients from the soil,
0:11:26 > 0:11:31then some plants will become very big indeed.
0:11:46 > 0:11:51Growing 70ft tall, like this sycamore, brings great advantages
0:11:51 > 0:11:57like overtopping its neighbours so it can get all the sunshine it needs,
0:11:57 > 0:12:02and spreading out a huge surface area of leaves.
0:12:02 > 0:12:06Through their pores it sucks in carbon dioxide.
0:12:06 > 0:12:08It also brings considerable problems.
0:12:08 > 0:12:14As well as carbon dioxide, the leaves need water to make food.
0:12:14 > 0:12:19And water in the leaf can easily evaporate through the pores.
0:12:19 > 0:12:24Indeed, 90% of the water sucked in by the roots
0:12:24 > 0:12:29is lost through the surface of the leaves at the top of the tree.
0:12:29 > 0:12:36But pumping water up here, to this height, can cause considerable problems.
0:12:56 > 0:13:01To pump this jet of water 70ft up in the air here,
0:13:01 > 0:13:05it takes that huge, noisy engine down there.
0:13:05 > 0:13:11But this tree pumps up about a hundred gallons every hour,
0:13:11 > 0:13:15and manages to do so in total silence.
0:13:18 > 0:13:20How?
0:13:22 > 0:13:26The answer is to be found in the tree's trunk.
0:13:26 > 0:13:29The central part of this is wood.
0:13:29 > 0:13:34Around the outside of this pillar there are ranks of hair-thin pipes.
0:13:34 > 0:13:41Those immediately beneath the bark carry the food-laden sap down from the leaves.
0:13:50 > 0:13:55Farther inside the trunk there's another set of tubes.
0:13:55 > 0:14:00These are the ones that carry the water up.
0:14:00 > 0:14:05They are continuous pipes that extend the whole length of the trunk.
0:14:16 > 0:14:23As water evaporates in the leaves above, the threads of it are pulled up the tubes into the branches,
0:14:23 > 0:14:27and, ultimately, into the leaves themselves.
0:14:27 > 0:14:31Some of it is used in the food-making process.
0:14:31 > 0:14:36The rest evaporates through the leaf pores as vapour.
0:14:45 > 0:14:49Of course, leaves can't absorb water directly.
0:14:49 > 0:14:55Water lying on their surface can cause problems as it clogs up the pores.
0:14:55 > 0:15:00So some leaves have shapes which help to reduce that problem.
0:15:16 > 0:15:21Plants in the tropical rainforests have particular difficulties.
0:15:21 > 0:15:26For here the rain drenches down in torrents.
0:15:30 > 0:15:35They have to be tough to withstand the pounding.
0:15:38 > 0:15:42They must have gutters to carry away the water.
0:15:58 > 0:16:01Many have pointed tips at the end,
0:16:01 > 0:16:05ensuring water doesn't linger on the leaf
0:16:05 > 0:16:09and doesn't obstruct air passing through the pores.
0:16:11 > 0:16:15Others use dense hairs to keep their pores free.
0:16:20 > 0:16:24But rainfall is the least of the dangers that threaten leaves.
0:16:58 > 0:17:03Leaves are breakfast, lunch, supper for the proboscis monkeys in Borneo.
0:17:03 > 0:17:06They eat pretty well nothing else.
0:17:06 > 0:17:13Maybe a few flower petals now and then, perhaps a little fruit, otherwise entirely leaves.
0:17:13 > 0:17:17But leaves have a drawback as food. They're not very nutritious.
0:17:17 > 0:17:25So these monkeys have to spend hours and hours and hours every day stripping the trees of their leaves.
0:17:41 > 0:17:46The leaf sap, loaded with starch and sugars, is certainly nutritious.
0:17:46 > 0:17:53The problem comes from the walls of the cells enclosing the sap. They are made of cellulose.
0:17:53 > 0:17:58The digestive juices of mammals can't deal with it. But bacteria can.
0:17:58 > 0:18:02And those animals that eat a lot of leaves
0:18:02 > 0:18:10have to sit around after feeding to give time for the bacterial colonies in their stomachs to work.
0:18:10 > 0:18:17Despite these drawbacks, lots of mammals, and even some birds and reptiles, have taken to this diet.
0:18:17 > 0:18:22But in fact, such big leaf-eaters are in the minority.
0:18:23 > 0:18:28The plants' most numerous attackers by far are insects.
0:18:28 > 0:18:35Around me in this Borneo rainforest there are millions of tiny mouths munching away invisibly.
0:18:35 > 0:18:43To give you some idea of the lengths to which an insect will go in order to get a vegetarian meal in safety,
0:18:43 > 0:18:45look at this.
0:18:45 > 0:18:50It's a damaged leaf, but where's the creature that's doing the damage?
0:18:56 > 0:18:58This is it a tiny caterpillar.
0:18:58 > 0:19:01It's soft. It's defenceless.
0:19:01 > 0:19:05It's an excellent mouthful for many a bird.
0:19:05 > 0:19:09To survive, it must take steps to protect itself.
0:19:18 > 0:19:23It starts by making a semi-circular cut into the leaf from the margin.
0:19:34 > 0:19:40When the cut is only half complete, it starts from the other end.
0:19:40 > 0:19:42It spins silk across the hinge.
0:19:42 > 0:19:45That, as it dries, contracts,
0:19:45 > 0:19:50helping the caterpillar pull it over to form a roof.
0:19:50 > 0:19:58To make its tent more commodious it cuts a pleat, pulls it across, and now it's got a little wigwam.
0:20:02 > 0:20:10The whole process only takes a few hours and is usually done at night when there are no birds around.
0:20:10 > 0:20:12The caterpillar can feed in safety,
0:20:12 > 0:20:18shaving off the soft surface layers of the leaf out of sight of hungry birds.
0:20:18 > 0:20:21And at significant cost to the plant.
0:20:47 > 0:20:54The damage and loss inflicted on plants by animals both large and small is huge and never-ending.
0:20:54 > 0:20:59Plants do what they can to defend themselves.
0:20:59 > 0:21:03Some develop long, ferocious, needle-sharp spines.
0:21:03 > 0:21:07These APPEAR sufficient to deter anything.
0:21:07 > 0:21:09But not so.
0:21:09 > 0:21:14This tongue is so mobile it can pick the soft leaves BETWEEN the spines.
0:21:14 > 0:21:20This hide is so tough even the sharpest spines don't puncture it easily.
0:21:20 > 0:21:27And these rubbery lips seem able to survive the most prickly of mouthfuls.
0:21:36 > 0:21:39The attacker is a giraffe.
0:21:39 > 0:21:46It can reach 15ft above ground. It's the tallest of all living animals.
0:21:57 > 0:22:05Such intensive grazing means it's difficult for plants to grow bigger than stunted bushes.
0:22:05 > 0:22:10Thanks to their thorny defences some acacias manage to grow to maturity.
0:22:10 > 0:22:16Then they develop the umbrella shape so characteristic of the East African grasslands.
0:22:16 > 0:22:21Now, at last, the acacia has some parts even a giraffe can't reach.
0:22:21 > 0:22:26The branches up at the top, in the centre.
0:22:26 > 0:22:33There the acacia can save precious energy and reduce the scale of its thorny armaments.
0:22:33 > 0:22:38On the outside, the thorns are as long and dense as anywhere.
0:22:38 > 0:22:43But in the middle of the crown there are no thorns whatsoever.
0:22:43 > 0:22:48The techniques employed by plants to defend themselves are very varied.
0:22:48 > 0:22:51Some involve very refined armaments.
0:22:51 > 0:22:56This is one of the commonest plants of the European countryside.
0:22:56 > 0:23:00In summer, many might think it TOO abundant.
0:23:00 > 0:23:05Beneath its leaves, it produces sprays of tiny flowers.
0:23:05 > 0:23:10We all recognise nettles, and have been able to since our youth,
0:23:10 > 0:23:14for the very good reason they have painful stings.
0:23:14 > 0:23:19But this sting is actually quite a complex weapon. Watch.
0:23:21 > 0:23:23Ow.
0:23:24 > 0:23:30It's a hollow hair made from silica, the mineral from which we make glass.
0:23:30 > 0:23:32And it's filled with poison.
0:23:32 > 0:23:37Its tip is so sharp a mere touch cuts our skin,
0:23:37 > 0:23:44and so fragile, it then breaks releasing poison into the wound, resulting in a painful swelling.
0:23:44 > 0:23:49Young humans learn to avoid nettles. So do young rabbits.
0:23:49 > 0:23:52This one knows leaves are edible.
0:23:52 > 0:23:58It has yet to learn that SOME can defend themselves.
0:23:58 > 0:24:03The nose has a little protective fur. And that hurt!
0:24:05 > 0:24:08It's better to stick to grass!
0:24:13 > 0:24:21With such an effective armoury, nettles grow unmolested, and rapidly establish themselves in thickets.
0:24:21 > 0:24:28But there are two kinds of nettles growing here. The kind on the right is slightly different.
0:24:28 > 0:24:32Its leaves look like those of a stinging nettle,
0:24:32 > 0:24:40but its white tubular flowers look quite different from those small brown ones of the true nettle.
0:24:42 > 0:24:47In fact, this is a relative of mint and thyme. This is the dead-nettle.
0:24:47 > 0:24:50And it has no sting of any kind.
0:24:50 > 0:24:55But even an adult rabbit doesn't apparently know the difference.
0:24:55 > 0:24:58It certainly doesn't risk a sting.
0:24:58 > 0:25:03The dead-nettle, without the trouble of producing poisoned hypodermics,
0:25:03 > 0:25:06has found protection in mimicry.
0:25:07 > 0:25:09And this is another mimic.
0:25:14 > 0:25:19A tortoise in the southern African desert looks for a juicy mouthful.
0:25:19 > 0:25:27But it walks over as good a one as it might find all day, feeding instead on a few shrivelled leaves.
0:25:30 > 0:25:37The pebble plant mimics surroundings so accurately it even varies its colour to match that of the gravel.
0:25:37 > 0:25:40Few animals even notice it.
0:25:42 > 0:25:49The passion flower uses mimicry to defend itself in perhaps the most extraordinary way of all.
0:25:49 > 0:25:53It's pestered by heliconias butterflies
0:25:53 > 0:25:58because its leaves are the favourite food of heliconias caterpillars.
0:25:58 > 0:26:04So the female butterflies always lay their eggs on the plants
0:26:04 > 0:26:12in order that their youngsters when they hatch will find their favourite food immediately in front of them.
0:26:12 > 0:26:15The egg is a bright yellow globe.
0:26:24 > 0:26:26There's another one.
0:26:29 > 0:26:33The caterpillars are particularly voracious.
0:26:33 > 0:26:40They'll tackle leaves, stems, shoots and buds pretty well every part of the passion flower.
0:27:02 > 0:27:09Because her young need so much food a female heliconias won't lay where there are eggs already.
0:27:09 > 0:27:12Before she starts she makes a survey.
0:27:12 > 0:27:17This female has decided NOT to lay here.
0:27:17 > 0:27:23Hardly surprising the leaves are already covered with "eggs".
0:27:23 > 0:27:31Except they're NOT eggs. These yellow spots are imitations, fakes, produced by the plant as a deterrent.
0:27:31 > 0:27:37This species of passion flower produces even more convincing "eggs" on the leaf stalks.
0:27:37 > 0:27:43Surely one of the subtlest of strategies based on mimicry.
0:27:45 > 0:27:49Bracken has adopted a rather more straightforward defence.
0:27:54 > 0:28:02You might think a nutritious-looking carpet of leaves like this would show signs of damage by grazers.
0:28:03 > 0:28:05I can see none.
0:28:05 > 0:28:10The fact is that bracken is full of a cocktail of toxins so powerful
0:28:10 > 0:28:15that any mammal that eats it, such as rabbit or cattle,
0:28:15 > 0:28:19is liable to go blind or get cancer.
0:28:19 > 0:28:27When they're young, the leaves are packed with cyanide which deters most things, including insects.
0:28:27 > 0:28:35As the plant matures it starts to synthesise more complex poisons that deter almost every living creature.
0:28:35 > 0:28:43And as a result, the plant sprawls unchecked and covers vast areas of European hillsides.
0:28:46 > 0:28:51Ferocious spines, painful stings, poisonous sap, near-perfect disguise.
0:28:51 > 0:28:56Plants seem to have evolved every conceivable defence for their leaves,
0:28:56 > 0:29:02which have to spread wide to catch the light, and so are very visible.
0:29:02 > 0:29:07But this sensitive mimosa, common beside tropical roadsides,
0:29:07 > 0:29:12has the most radical, and certainly the most dramatic solution, of all.
0:29:24 > 0:29:27One touch makes it fold its leaflets.
0:29:29 > 0:29:33Another tap and it flops to the ground.
0:29:33 > 0:29:39How does that help? Well, watch how a hungry grasshopper gets on.
0:29:39 > 0:29:43Obviously, there's a splendid meal ahead(!)
0:29:47 > 0:29:51But before it even takes a bite...
0:29:53 > 0:29:56the meal vanishes.
0:30:24 > 0:30:33This ability to move fast is used by one astonishing plant to turn the tables on animals.
0:30:33 > 0:30:38It grows here in this swampy pine forest in northern Carolina.
0:30:38 > 0:30:43Animals don't eat IT. IT eats animals. And there's one right here.
0:30:46 > 0:30:48Watch.
0:30:58 > 0:31:01This is Venus's-flytrap.
0:31:01 > 0:31:06Its traps are the ends of its leaves. One or two hairs act as triggers.
0:31:07 > 0:31:10Here comes a meal.
0:31:14 > 0:31:18Touch the hair, and the trap is sprung.
0:31:20 > 0:31:22There's now no escape.
0:31:24 > 0:31:29The beetle's struggles stimulate the plant to close the trap more tightly.
0:31:29 > 0:31:34It now produces digestive acids from glands on the leaf's inner surface,
0:31:34 > 0:31:39which first kill and then dissolve its victim's body.
0:31:39 > 0:31:44Growing in the same Carolina swamp there is another carnivorous plant.
0:31:44 > 0:31:47These are the trumpet pitchers.
0:31:47 > 0:31:54They, like the Venus's-flytrap, find so little nutriment in this impoverished soil
0:31:54 > 0:31:58they supplement it with the bodies of animals.
0:31:58 > 0:32:01Their traps are also formed from leaves,
0:32:01 > 0:32:09but leaves that have been folded lengthways to make a vertical tube which fills with water.
0:32:15 > 0:32:21These spectacular trumpets may LOOK like flowers, but, of course, they're not.
0:32:21 > 0:32:28Though, in a sense, this bright yellow top to them serves the same purpose as a petal.
0:32:28 > 0:32:31It advertises a delicious reward.
0:32:31 > 0:32:33The reward itself is under here.
0:32:36 > 0:32:39Sweet nectar.
0:32:39 > 0:32:46But if an insect comes to collect it and strays into the mouth of the trumpet, it's doomed!
0:33:01 > 0:33:08The inside of the throat of the trumpet is covered with microscopic, downward-pointing spines.
0:33:11 > 0:33:15As long as it stays on the rim the ant is all right.
0:33:15 > 0:33:18But if it strays off it...
0:33:18 > 0:33:22it falls into a pond of water and drowns.
0:33:22 > 0:33:28The tiny corpse dissolves, and the marsh pitcher absorbs the resulting soup.
0:33:31 > 0:33:36And where one ant goes others are likely to follow.
0:33:52 > 0:33:56The marsh pitcher attracts other animals too.
0:33:56 > 0:34:04This frog hopes to eat some insects before the pitcher, but if it loses its footing the plant will eat IT.
0:34:08 > 0:34:12Marsh pitchers have comparatively simple traps.
0:34:12 > 0:34:17The pitcher plants proper, producing more elaborate ones,
0:34:17 > 0:34:20live on the other side of the world.
0:34:23 > 0:34:27The HQ of the pitcher plants are in South-East Asia.
0:34:27 > 0:34:34There are 76 different species, 30 of which grow only on the island of Borneo.
0:34:34 > 0:34:41They include the biggest of them all, a truly spectacular plant, appropriately called Nepenthes rajah,
0:34:41 > 0:34:45that grows only on this great mountain, Kinabalu.
0:34:45 > 0:34:48And they're all around me.
0:34:55 > 0:35:04I guess...this one...contains oh, two or three pints...of liquid.
0:35:04 > 0:35:10It's so big that it catches not just insects, but even small rodents.
0:35:10 > 0:35:16And one was recorded that had in it the body of a drowned rat.
0:35:16 > 0:35:22So if ever there was a carnivore among plants, this is it.
0:35:24 > 0:35:31The traps of this Asian family of pitcher plants are, once again, modified leaves.
0:35:31 > 0:35:36But they're not simply folded into a tube. The process is more complex.
0:35:36 > 0:35:43A shoot appears that looks just the same as those that turn into normal leaves.
0:35:48 > 0:35:55Over a period of several days flanges develop near the end, opening to form a leaf blade.
0:35:57 > 0:36:02But then the tip of the midrib continues to grow.
0:36:14 > 0:36:19Once it touches the ground it begins to inflate.
0:36:44 > 0:36:49The lid opens to expose the plant's lethal pond.
0:37:06 > 0:37:13Some of the bigger species may produce half a dozen of these huge elegant traps.
0:38:04 > 0:38:09The shape and placing of the pitchers varies between species.
0:38:09 > 0:38:12But essentially they're all the same.
0:38:12 > 0:38:14They attract their prey with nectar,
0:38:14 > 0:38:19they have slippery sides so many of their visitors tumble into them,
0:38:19 > 0:38:25and the fluid within contains juices which actively dissolve the bodies.
0:38:34 > 0:38:42So leaves, either by catching insects or by absorbing gases and harnessing the energy of sunlight,
0:38:42 > 0:38:45manufacture food for a plant.
0:38:45 > 0:38:48But leaves are delicate structures.
0:38:48 > 0:38:50This plant
0:38:50 > 0:38:54the giant arum of Borneo
0:38:54 > 0:38:58develops the biggest undivided leaf of all.
0:38:58 > 0:39:03It can have a surface area of up to 3 square metres 34 square feet.
0:39:03 > 0:39:10The arum keeps these vast leaves outstretched by pumping the cells within them full of water.
0:39:10 > 0:39:17If there's not enough water, or if it freezes and bursts the cell walls, the leaf will collapse.
0:39:17 > 0:39:24Neither is likely to happen in a tropical rainforest, which is why immense leaves develop.
0:39:24 > 0:39:29But elsewhere in the world plants don't have it so easy.
0:39:38 > 0:39:43In northern lands where the winters can be very severe,
0:39:43 > 0:39:48many trees have to take drastic measures to protect themselves.
0:39:48 > 0:39:53As the days grow shorter and colder, and autumn approaches,
0:39:53 > 0:39:58the trees prepare to cut their losses and suspend their activities.
0:40:02 > 0:40:09They start to shut down their food factories and withdraw the valuable chlorophyll from the leaves.
0:40:09 > 0:40:16As the green pigment drains away, waste products that have accumulated over the year are revealed,
0:40:16 > 0:40:20and the leaves begin to change colour.
0:40:20 > 0:40:25In New England and the Appalachian Mountains, day after day,
0:40:25 > 0:40:30whole hillsides of maples and aspens begin to flush red.
0:41:28 > 0:41:32As the leaves dry out, they are sealed off.
0:41:32 > 0:41:37A hard corky partition develops within the base of the leaf stalks.
0:41:37 > 0:41:42Now the slightest breath of air will detach them.
0:42:10 > 0:42:14The loss is great, but it's not total.
0:42:14 > 0:42:16The falling leaves will soon decay.
0:42:16 > 0:42:21That releases much of the nutriments used in constructing them.
0:42:21 > 0:42:28And in spring, the trees through their rootlets just below the earth's surface
0:42:28 > 0:42:32will be able to reclaim what they've lost.
0:42:32 > 0:42:38So by the time winter grips the land the trees are reduced to skeletons.
0:42:38 > 0:42:40Growth has virtually stopped.
0:42:40 > 0:42:44The processes of life barely tick over.
0:42:55 > 0:43:03This alternation of growing in summer and shutting down in winter leaves its mark in a tree's trunk
0:43:03 > 0:43:06annual rings.
0:43:06 > 0:43:10The white wood are large cells formed in summer,
0:43:10 > 0:43:17and the dark wood, small dense cells laid down more slowly in autumn and winter.
0:43:17 > 0:43:25So by counting the rings I can be absolutely certain that this beech tree lived for over 200 years.
0:43:25 > 0:43:27That's longer than any animal lives.
0:43:31 > 0:43:38The record for longevity, however, is much greater than THAT, and is held elsewhere.
0:43:53 > 0:43:59Here, 10,000ft up in the White Mountains of eastern California,
0:43:59 > 0:44:04grow the oldest living things on earth the bristle-cone pines.
0:44:06 > 0:44:09This part is already dead.
0:44:10 > 0:44:14But here, there is life and growth.
0:44:14 > 0:44:20Those rings in the trunk tell us exactly how old these trees are.
0:44:20 > 0:44:26Because the conditions are extreme and it gets very cold in winter,
0:44:26 > 0:44:28some years there's little growth.
0:44:28 > 0:44:33As a consequence, the rings are very much more close together.
0:44:33 > 0:44:37This is a cross-section of one tree.
0:44:37 > 0:44:41The outermost ring is the year in which it died 1958.
0:44:41 > 0:44:45Count 100 rings inwards - 1858.
0:44:45 > 0:44:49Another century 1758.
0:44:49 > 0:44:56Around here is the ring it was developing when Columbus arrived on this continent in 1492.
0:44:56 > 0:45:01It was in the full vigour of youth when the Pharaohs were ruling Egypt.
0:45:01 > 0:45:10So we can be sure when the first human farmers were just beginning to plant seeds for themselves,
0:45:10 > 0:45:14this ancient ravaged tree was just sprouting.
0:45:14 > 0:45:17It's over 4,000 years old!
0:45:18 > 0:45:23Pine leaves are very different from the leaves of oak and maple.
0:45:23 > 0:45:29Instead of being broad and flat, and easily damaged by frost,
0:45:29 > 0:45:32they are needle-shaped and tough.
0:45:32 > 0:45:37Instead of having pores all over the flat surface as oak and maple do,
0:45:37 > 0:45:43The pores are restricted to a groove running the length of the needle.
0:45:43 > 0:45:47It's partly filled by a tough, waxy deposit.
0:45:49 > 0:45:53Beneath that there are lines of small pores
0:45:53 > 0:45:56Few compared with those on an oak leaf.
0:46:02 > 0:46:09Even at the height of summer leaves like these can't manufacture food as swiftly as broad leaves do.
0:46:09 > 0:46:15On the other hand, needle-producing trees don't discard them every year.
0:46:15 > 0:46:20They keep them much longer with all the energy saving that implies.
0:46:20 > 0:46:24The conifer's policy is "slow, but sure".
0:46:24 > 0:46:30And it's produced not only the oldest plants, but OTHER record holders.
0:46:32 > 0:46:38And this is the most massive living thing on earth
0:46:38 > 0:46:40the giant sequoia.
0:47:02 > 0:47:09They don't live as long as bristle-cone pines, but almost over 3,000 years.
0:47:09 > 0:47:11They grow up to 300ft tall.
0:47:11 > 0:47:19And every year they put on as much wood as there is in a 60ft tree of normal proportions,
0:47:19 > 0:47:24so that the really big ones weigh over a thousand tons.
0:47:51 > 0:47:58Although they may be loaded with snow for months in the winter, and baked dry in the summer,
0:47:58 > 0:48:05the conifers have produced the largest and the longest-living of all organisms on earth.
0:48:05 > 0:48:10Like all plants they have done it with the simplest of ingredients
0:48:10 > 0:48:12water and minerals from the earth,
0:48:12 > 0:48:17carbon dioxide from the atmosphere, and light.
0:49:01 > 0:49:06Subtitles by Carolyn Donaldson BBC Scotland, 1994