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Botanic Garden

Botanic Garden Science Trail


This trail takes approximately 1 hour. Follow the directions below, they will guide you round the lettered posts set out around the garden.

There is an option on the way round to short-cut the trail to half an hour, see post I for details.

This short cut also eliminates some steep steps and some of the more hilly sections of the trail.

To start : You will find post A in front of the Visitor Centre on the right hand side.

A ~ Pampas grass (Cortaderia selloana): razor-edged leaves, once used for making paper.

The grasslands of Chile, Brazil and Argentina are known as the Pampas, and give their name to this handsome grass. The cells along its leaf edge are reinforced with silica, rendering the leaves sharp, so the clump of grass is almost impenetrable and acts as a secure refuge for small animals. Pampas grass is one of a large number of plants that have been used for making paper, which is composed of plant fibers. Most paper is made from wood pulp, but fibrous leaves of many grasses, sedge and rush species have been used. The most famous papermaking plant of all is papyrus sedge (Cyperus papyrus), used by the ancient Egyptians for making papyrus scrolls. You can see a papyrus plant growing in the pond in the greenhouse.

You will find post B in the long border going down the hill to the right hand side of the statues.

B ~ A seed bank in the soil and endangered trees.

In this wild flower border we are trying to recreate the kind of display of wild flowers that was once common around arable fields, before the introduction of efficient modern herbicides for weed control. As every gardener is painfully aware, cultivated soil contains a bank of ungerminated weed seeds that can remain viable for decades, but regular intensive use of herbicides (weedkillers) quickly depletes this seed bank. This is one reason why colourful displays of annual wild flowers are less common than they once were around arable fields. This area of the garden is now being repeatedly re-sown with seeds of corn chamomile, corn marigold, corn cockle, corn flower and corn poppy, which are all allowed to self-seed, building up a soil seed bank that will eventually create a self-sustaining population of these wild flowers. This border also contains examples of some of the world's most endangered trees. These include Malus hupehensis, from Hupei province in China, which has been reduced to fewer than 50 individual tree s in the wild. Sorbus minima is an endemic species of mountain ash that occurs in Britain but nowhere else on Earth, and is an endangered species. One of the major roles of Botanic Gardens like ours is to grow and distribute seeds of endangered species, as an insurance against their accidental destruction in the wild.

Continue down the hill, look out for post C on your right.

C ~ The spindle tree, the broad bean and black bean aphids.

Spindle (Euonymus latifolius) is one of the most beautiful small hedgerow trees in Britain, with vibrant crimson autumn foliage. Its fruits resemble dangling pink lanterns, with four seeds inside that are covered with an orange fleshy layer called an aril. This has evolved to attract the attention of birds that eat and disperse the seeds, which pass through their digestive tract undamaged. The tree's common name relates to the fact that its hard, small-diameter timber was once used for making wooden spindles. Spindle is the winter host of the black bean aphid, which in fests broad beans in summer, and so the tree has been deliberately removed from hedgerows in some parts of Britain where this crop is grown. Many crop plant pests and diseases rely on an alternative host for survival through the winter, when the crop is n o t being grown, and removing the winter host is one way of eliminating the pest, although in this case it also deprives hedgerows of a beautiful small tree. Wheat stem rust fungus spends the winter on barberry (Berberis) bushes, and they have been removed from wheat growing areas. You can find Berberis growing in the Chilean section of the garden (near post F).

A little further down the path you will find post D on your right.

D ~ Hazel (Corylus avellana): coppice, charcoal, water divining and a very strange parasite.

Hazel is a woodland shrub which is traditionally managed by coppicing - a technique that involves cutting it down to ground level once every five or six years. This stimulates the formation of buds on the stool, which develop into fast-growing straight stems. This small diameter timber was once used in many rural crafts, including charcoal burning and the production of hurdles. By coppicing hazel in rotation a continuous supply of poles could be produced. The tree also produces edible nuts, and varieties selected for their large fruits are still grown in a few places in Kent, in plantations known as platts. Hazel rods are used by water diviners, for finding hidden water supplies. Hazel is also the host of a strange parasitic flowering plant called toothwort (Lathraea squamaria), which is quite common around hazel roots in spring throughout north east England. Toothwort appears as a ghostly white flower spike, with no leaves and no green chlorophyll. It produces a sucker-like structure called a haustorium, which penetrates hazel roots and draws off nutrients.

Follow the path down hill, look out for the steps down into the woodland garden, on your left, round the corner. Half way down the steps you will find post E.

E ~ Underground associations (Gunnera manicata)

Many plants only thrive when their roots link up with other symbiotic organisms in the soil, which help to supply them with essential nutrients. For example, many forest trees form mutually beneficial associations with soil fungi, called mycorrhizal associations, which help the tree's roots to absorb phosphorus. Gunnera has roots that play host to microscopic blue-green algae, which convert atmospheric nitrogen into a soluble form of nitrogen that the plant can use for growth.

Go back up to the main path, either by the steps you came down or by following the parallel lower path in the woodland. Bear left down the track at the gates and fence, look out for post F on the right by the single kissing gate.

F ~ Grafting (Horse chestnut species)

There is usually a close relationship between the size and vigour of a plant's root system and the amount of growth that it makes above ground. The most spectacular example of this can be seen in bonsai trees, where regular restriction of root growth produces a miniature version of a tree. Grafting onto rootstocks of different vigour is a way of controlling the growth of plants, and many fruit trees for small gardens are grafted onto dwarfing rootstocks to produce more compact trees. Sometimes it is necessary to graft exotic trees that grow poorly in adverse climates and soils, onto rootstocks of common species that are better adapted to local growing conditions. This buckeye (a North American relative of the horse chestnut) has been grafted onto a horse chestnut rootstock. As with most such grafts, you can see a 'step' at the point of grafting, due to unequal growth rates of the stock and scion. In this case the rootstock has sprouted a horse chestnut shoot. This horse chestnut will have palmate leaves with seven 'fingers' in summer - the buckeye only has five 'fingers'. Buckeyes are so-called because their large brown seeds resemble the eyes of deer, or buck as they are known in North America.

Horse Chestnut- Aesculus hippocastanum and Buckeye - Aesculus flava.

Nearby look out for post G tucked under a large spreading tree.

G ~ Walnut (Juglans regia): A tree for a God.

Walnut trees have always been valued for their hard, fine-grained and beautifully figured timber, which is used in high quality products like furniture veneers and gun stocks. The tree was also once important as a source of brown dye, extracted from the fleshy coating of the hard-shelled nuts. The Roman writer Pliny recommended walnut oil as an excellent cure for baldness and the Latin name of the tree - Juglans - reflects the Romans' esteem for it, derived as it is from the words Jovis (the god Jove) and glans (nut). Most flowers have male parts (stamens) and female parts (the stigma and ovary) within a single flower, but in some species they are physically separated to promote cross-pollination. Walnuts produce separate male and female flowers on the same tree - an arrangement known as monoecy. Other trees have separate male and female flowers on separate trees, an arrangement known as dioecy. Examples of trees that show dioecy are Willow, Holly and the next tree on the trail, Monkey Puzzle, ours happens to be a male tree.

Post H is at the base of the tall Monkey Puzzle tree.

H ~ A tree that outlived the dinosaurs - Monkey puzzle (Araucaria araucana)

There may now be more monkey puzzles surviving in Britain than in its native South America, because the tall straight trunk of this tree produces perfect planks of a highly desirable wood. A s a result, the species has been over-exploited in the wild and is now protected under the Convention for International Trade in Endangered Species. Monkey puzzle is an ancient species that would have been a familiar sight in the Cretaceous landscape in which dinosaurs roamed. Many surviving plants from that period have tough leathery foliage, thought to have evolved as a deterrent to large herbivorous dinosaurs, which in turn may have continued to increase in size so that their elongated guts could process such indigestible material. Monkey puzzles exist as separate male and female trees, and produce edible seeds.

Tucked away behind the Monkey Puzzle you will find a secret dell, where you will find post I. 

I ~ Microclimate, frost and rhododendrons

This part of the garden, surrounded by old Rhododendron ponticum bushes, has a sheltered, relatively frost-free microclimate where we can grow frost-sensitive species such as tree ferns and the Chilean flame bush (Embothrium coccineum). Frost kills plants when spiky ice crystals form inside their cells, rupturing the cell wall and allowing the cell sap to leak out - which is why plants that have been killed by frost sometimes look as though their have been reduced to a watery pulp. Rhododendron ponticum was introduced as an ornamental shrub, probably from Spain or possibly from the Middle East. It has become naturalised in parts of the British countryside and in some places, such as Snowdonia, has become a major weed, smothering native vegetation. Garden introductions that have escaped into the wild have caused major environmental damage in many parts of the world, and the escape of alien species into natural ecosystems is now recognised worldwide as a threat to native wildlife.

Come out from the dell, bearing left, and you will find a post marking the way to some steep steps down the woods to post J. ( If you wanted to avoid the steps, it is possible to miss out some posts and continue the trail from post S. To get to post S from here go past the two ponds, up to the gazebo. To the right you will see post S.)

J ~ Circulating water (beech, Fagus sylvatica)

While you are standing under this beech, contemplate these statistics. In high summer this tree will bear about 170,000 leaves, with a surface area of around 675 square metres. Evaporation from their surface will draw up about 220 litres of water per hour from the roots, and release it as water vapour into the atmosphere, where it will form clouds and eventually fall as rain, many miles from where you are standing. That volume of water consumption is equivalent to the content of about ten typical car petrol tanks, every hour. Plants are prodigious users of water, and in doing so play a major role in regulating our climate. Even a sunflower uses 17 times more water than a human does every day.

Continue down the steps and turn left to post K.

K ~ A woody grass with suicidal tendencies (bamboo)

The native grasses in Britain are minute compared with their tropical cousins, the bamboos. Some South East Asian bamboos grow to well over the typical h eight of a telegraph pole. Their woody stems are an important building resource in Asia, used for constructing buildings and for scaffolding. Bamboos tend to flower infrequently, but when they do they often flower in synchrony and then all die at once.

Continue along the path, crossing the stream, post L can be found in the group of trees on the left, by the corner.

L ~ Tough wood, delicately folded leaves (hornbeam, carpinus betulinus)

Hornbeam is a slow growing tree that produces very hard wood, so was once used for durable rural implements like wooden rake teeth and gear wheels for windmills and water mills. When its buds burst in spring the foliage is beautifully pleated, revealing the way in which the compressed, fully-formed leaf tissue was folded in t h e bud all through the winter, ready to be inflated by rising sap in spring. The pattern of leaf folding has been studied by mathematicians interested in biomimetics - the science of copying natural mechanisms for technological purposes. These studies have suggested ways in which large solar panels used by spacecraft might be more efficiently folded during the early stages of flight, before they are deployed.

Continue left along the path and back up the hill, look out for the steep stone steps on the right, in this bankside you will find post M.

M ~ Witches take the blame, but a fungus is the culprit

The weird growths on this birch tree are commonly called witches' brooms, but they're really caused by a tiny fungus called Taphrina, which is a close relative of the fungus that causes peach leaf curl disease. In birch (Betula pendula) it causes a proliferation of buds, which extend into a mass of small twigs. Eventually these witches brooms can weigh several kilogram's and have a hard core of wood with a distorted grain pattern, which was once highly valued by wood turners in Russia for the production of beautifully figured wooden bowls.

Go up the steps, as they level out watch out for post N.

N ~ Long-lasting leaves: pine, heather, juniper and mahonia.

Several of the plants in this part of the garden, such as the Scots pine, heather, juniper and Mahonia are evergreens. Typically, leaves of evergreen conifers live for about four years before they are shed. This strategy, of holding on to foliage through winter, allows the leaves to begin photosynthesising again at the earliest possible opportunity in spring, making maximum use of the short growing season in temperate climates at high latitudes. The Mahonia leaves have a shorter life because they often become infected with Mahonia rust, a fungus that causes the vibrant red and yellow colours on the leaf surface and often causes the leaves to be shed prematurely. ab The roots of heather and of many conifers form a mutually beneficial partnership with benign fungi, called a mycorrhizal association. The fungal hyphae that spread out from the tree roots help it to absorb minerals like phosphorus, and in return the fungus may receive sugars from the tree roots. This association accounts for the fact that m any toadstools are found close to trees in woodlands. ab If you crush a small piece of juniper foliage between finger and thumb you may notice a familiar aroma if you are partial to a gin and tonic - juniper berries are an essential ingredient in the manufacture of gin, and this is one of many plants that provide natural food flavourings.

Continue up the rest of the steps, follow the path ahead and bear left at the crossroads. Along this path you will find post O.

O ~ Long life, from a relative of ivy

This Chinese bush, Acanthopanax, is a close relative of ivy and is one of several sources of ginseng, a traditional Chinese medicinal plant said to promote health and long life. The flowers and fruit of Acanthopanax closely resemble those of ivy. W e must have some very old and healthy rabbits in the Botanic Garden, because they often dig down and nibble the roots.

A little further along the path you will see post P.

P ~ An indicator for climate change (foxglove tree - Paulownia tomentosa)

One way to monitor climate change is to follow the way in which plant species respond to shifts in the length and timing of seasons, a study known as phenology. Bud burst, flowering and leaf colour change are particularly sensitive to the kinds of changes in seasons that might be triggered by global warming. Paulownia tomentosa is at just about the northern limit of its climatic tolerance in Durham, and for the first decade of its life this specimen struggled to survive. In recent years, with milder, wetter w inters, its growth has noticeably improved and in 2001 it flowered for the first time. As our climate becomes milder, many cold- sensitive exotic species will grow better in British gardens.

Follow along the path, and cross straight over the tarmac path, look our for post Q under the spreading tree in front of you.

Q ~ Owzat! Willow and its uses.

Willow (Salix) is a fast-growing tree of riverbanks and damp soils, and has had many uses. (Salix is the latin name for willow, and comes from the Celtic Sal, near and lis, water). Cricket bat willow, a distinctive form of the white willow, Salix alba, is the traditional source of timber for our national sport. Willow bark contains salicylic acid, the active ingredient of aspirin, and was the source of t h e painkiller until the drug was synthesised artificially in the laboratory. Today coppiced willow is becoming increasingly important as a source of renewable energy. It grows rapidly, producing large quantities of biomass that can be used as an energy source. Willow is one of the easiest woody plants to root from cuttings - just stand a twig in a bottle of water for a few days and it will quickly produce a mass of white roots. There are over 300 species of Willow in the world, this species, Salix matsudana is from China and is commonly known as the Peking Willow.

Look to your left and you will find post R in the stand of trees.

R ~ A living fossil (dawn redwood - Metasequoia glyptostroboides)

Living fossils are organisms that were once only known from fossils, and so were thought to be extinct, but which have since been discovered living in the wild. Dawn redwood, once only known as a fossil, was discovered in 1944 in Sichuan Province in China. It is unusual amongs t conifers in shedding its leaves in winter. Living fossils are especially valuable because they give us an insight into the ancestry of present day species. More recently, two more living fossil conifers have been discovered - the Wollemi pine in a remote gorge in Australia in 1994 and an entirely new living fossil conifer genus, related to the familiar garden leylandii cypress, in the mountains of Vietnam in 2002.

Continue forwards and straight in front of you in the woodland garden you will see post S.

S ~ Mutants in the garden - corkscrew hazel (Corylus avellana 'Contorta')

Many garden plants are natural mutants, selected and propagated for their unusual or aesthetically pleasing characteristics. Corkscrew hazel is a natural mutant of wild hazel, carrying a mutation that produces contorted shoots and distorted leaves. The original mutant was discovered in Gloucestershire in 1870, and the plant is still widely grown for the sculptural qualities of its branches in winter and spring. The mutation causing the abnormal growth is not transmitted via the seeds, so the plant can only be grown from cuttings, or via grafts onto normal hazel rootstocks. So every single plant in cultivation - and there must be hundreds of thousands of them - is a clone (an exact genetic copy) of the original Gloucestershire plant. Scottish music hall star Sir Harry Lauder (1870-1950) is reputed to have carried a curly walking stick made from contorted hazel.

Post T can be found at the gazebo shelter to your left.

T ~ Lichens: Co-operation is the key to survival.

Lichens, like those growing on the stones on the footbridge, are a combination of two mutually beneficial organisms - an alga and fungus - linked together in a symbiotic association. Lichens are early colonisers of bare rock surfaces and most are slow growing. By measuring the growth rate and the diameter of the lichen it is possible to calculate how old it is. Lichens absorb nutrients from rain water over their whole surface, and this makes them very sensitive to atmospheric pollution. During the industrial revolution lichens disappeared from the centre of major cities, but modern improvement in air quality has allowed them to return. Some brightly coloured lichens have been used as a source of dye - notably for Harris tweed - and there are some excellent examples of these lichens growing on the rope edging of the cornfield annual border near the visitor centre. Some mosses, like those growing on the gazebo roof, are also good colonisers of bare surfaces, where they can be subjected to long periods of drought during dry summers. They survive on moisture that condenses as dew on the fine points of the leaves, and often have a cushion-like growth form that can retain moisture. 


Head back past the last post and go back out of the woodland garden, heading left up the grassy hill to join the tarmac path up the hill. Near the top of the hill go left up the paved path, post U is on the right.

U ~ + Laburnocytisus adami: A crazy, mixed-up plant.

This unusual plant, +Laburnocytisus adami, is not one species but two, whose tissues have mingled together as a result of grafting. The two parent species are Laburnum (Laburnum anagyroides) and broom (Cytisus purpureus), and the plant produces three kinds of flowers - yellow ones resembling the Laburnum parent, purple ones that originate from Cytisus tissue and bronze flowers that are a mixture of both. Technically the plant is known as a graft chimaera. It originated in the nursery of Monsieur Adam near Paris in 1825.

Continue along the paved path and where it meets the tarmac path bear left to find post V on your left in the New Zealand collection.

V ~ Alien invasions from Down-Under - pirri-pirri bur

The tiny ground-hugging plant romping through this bed of New Zealand plants is pirri-pirri bur, Acaena species. Visitors to Holy Island's sand dunes will also be familiar with this plant, which has rapidly colonised the dune system there. It has spiky seeds that catch in the fur of rabbits and the socks, trousers and shoe-laces of day trippers, who have spread the seed so effectively that this little alien is now a nuisance on the island. The plant is sold as a garden ground-cover ornamental, but was first introduced into Britain on wool fleeces imported into Tweedside from New Zealand. It is not known whether the Holy Island population established from the wool-import hitchhiking seeds, or from a garden escape, but the alien invader now threatens to smother some of the native sand dune plants. Other Acaena species in our collection : Acaena novae-zelandiae, Acaena fissistipula and Acaena buchananii.

Now go into the Alpine Garden hidden behind the holly hedge to find post W. 

W ~ The secret's in the name (Saxifraga species)

Latin names may be hard to pronounce but they all have a meaning that often tells you something useful about the plant. Alpine saxifrages are all in the genus Saxifraga, which means 'stone-breaker' - an allusion to their tendency to grow in the tiny amounts of soil that accumulate in the gaps between shattered rocks. Other plant names have a less formal origin. For example, the Latin name of the cactus Lobivia is an anagram of its country of origin, Bolivia. Come out of the Alpine garden and go towards the greenhouse.

On the lawn out side the greenhouse in the right hand corner bed you will find post X.

X ~ Ferns and horsetails: spores: invisibility, fine fossils and gold prospecting.

Ferns and horsetails are primitive plants that reproduce by producing microscopic, wind-blown spores that are carried long-distances in the wind. Legend has it that fern spores could make you invisible, as Shakespeare noted in his play Henry IV, when Gadshill remarks that "we have the receipt of fern-seed, we walk invisible". No one knows where this superstition comes from, although it may have something to do with the fact that microscopic s p ores can land anywhere and produce a new plant, as if by magic, in unlikely places like gutters, high above the ground. The spores germinate into a flat, membranous structure called the prothallus, about the size of a little finger nail. This carries female cells in minute flask-shaped structures called archegonia, and also releases swimming male cells that fertilise them. The whole process requires plenty of moisture, so ferns tend to be found in damp places. Horsetail stems and leaves are full of hard silica, which means that they rot slowly and tend to form exceptionally fine fossils. This also makes the stems abrasive and accounts for their other common name - scouring rushes. Horsetails tend to accumulate heavy metals like gold in their tissues, so some prospectors believed that a flourishing patch of horsetails was a likely place to begin digging for heavy metals.

Post Y is in the next bed in the left hand corner.

Y ~ Scratch and sniff botany (rosemary, lavender and bay)

The aromatic compounds that you can smell when you crush the foliage of these plants probably act as natural pest deterrents, keeping caterpillars at bay. Humans find the scents and flavours attractive, and use them as food additives and in perfumery. Plants are full of an enormous range of natural chemicals. Some, like the toxic alkaloids in deadly nightshade, are lethal in high doses but have valuable medicinal effects when used in tiny amounts. Plants have been synthesising this natural cocktail of chemicals for mi l lions of years. So far we have only identified and learned to use a small fraction of the total, that might include many more useful medicines, but nevertheless about 40 per cent of the proprietary medicines that you can buy from your local chemist contain natural plant extracts.

The last post Z is located in the bed outside the cactus house, on the right hand side of the path on the way back up to the visitor center.

Z ~ Grasses: lawn-mowing, and a Hollywood myth.

This collection of grasses shows the elegant and attractive form of many species. Grasses that are used for football pitches, golf courses and lawns grow in an unusual way. New tissues in plants are formed from clusters of cells called meristems, and grasses have two kinds of meristem. Intercalary meristems between their leaves are responsible for producing creeping growth across the soil surface. Leaves themselves grow from meristems at their bases, so the oldest part of a grass leaf is its tip. This means that you can mow lawns (and cows and sheep can graze pastures) without killing the plant, which just produces more leaves from its meristems and creeping shoots. If you have watched Hollywood dinosaur movies like The Lost World, you may have noticed Velociraptors lurking in the long grass. This is a little bit of cinematographic liberty-taking, because grasses evolved long after the dinosaurs were extinct. Velociraptors would really have had to hide behind large ferns and giant cycads.

You will find a Cycad in our Tropical House.

Well done, that's the end of the science trail, we hope you enjoyed it !

If you would like to know more about any of the plants mentioned here, or about any other plants you see in the garden, please contact a member of the Botanic Garden staff, or :

Dr. Phil Gates Lecturer in Botany,
School of Biological and Biomedical Sciences,
Durham University,
South Road

This trail is written by Dr. Phil Gates from our School of Biological and Biomedical Sciences and funded by the BBSRC, Biotechnology and Biological Sciences Research Council.