Leaves and seeds: the big breakthrough

Even with the water in its roots, a tree still needs to transport it up its trunk to the all-important leaves which manufacture food – and that's a long way in the case of some trees.

For a long time no one could work out how trees did this. Of course, they have no moving parts like heart pumps to do the job for them. It was once thought that external air pressure caused water to flow upwards, as it does when you suck a straw, but air pressure simply isn't strong enough to pump water up a 100ft tree.

The answer is down to the ingenious design of tree leaves which contain millions of tiny perforations, or holes, called stomata. Trees open or close these pores, depending on the weather and conditions of the day. When it is hot, water in the leaves evaporates through the stomata making the sap in the tree trunk more concentrated. This drags underground water upwards through the trunk and into the leaves at the top of the tree. This process is called transpiration.

The tree's final challenge is to find a way of spreading their offspring, even though they cannot walk or move. The earliest species used the wind to spread spores in much the same way as fungi. The problem is that spores need exactly the right conditions to germinate – usually they must land in wet places, such as marshes or bogs. In dry climates, this is a big problem. Then, about 360 million years ago, trees came up with a much better solution. Seeds.

Unlike spores, seeds contain a partly formed tree embryo as well as a substantial food store of sugar, protein and fats. The embryo, with its larder stocked with food, is then encased in a coat (a testa), ready for a sometimes epic journey, using one of a number of alternative transport systems.

Seeds dramatically increase a tree's chances of successful reproduction. They are tougher than spores, they can survive droughts, they take their own food rations with them and some can even float. The first seed-bearing trees were the Cycads which have been traced back to about 270 million years ago – about 40 million years before the first dinosaurs appeared. About 130 species of Cycads are still living today, although many are under threat of extinction owing to the destruction of their habitats. These trees also mastered the art of sexual reproduction, which usually requires the genes of two different trees to combine to make a seed. But that leaves a final, apparently insuperable challenge: how could two different parents mix their genes when they are both, literally, rooted to the ground?

Start your day with The Independent, sign up for daily news emails
Have you tried new the Independent Digital Edition apps?
ebooksA year of political gossip, levity and intrigue from the sharpest pen in Westminster
Arts and Entertainment
a clockwork orange, stanley kubrick
The Tesco Hudl2: An exceptional Android tablet that's powerful, well-built and outstanding value

Life and Style
food + drinkAuthor DBC Pierre presents his guide to the morning after
Sarah Silverman (middle) with sister Reform Rabbi Susan Silverman (right) and sister actress Laura Silverman (left) at Jerusalem's Western Wall for feminist Hanuka candle-lighting ceremony
peopleControversial comedian stages pro-equality Hanukkah lighting during a protest at Jerusalem's Wailing Wall
Arts and Entertainment
The Bach Choir has been crowned the inaugural winner of Sky Arts’ show The Great Culture Quiz
arts + ents140-year-old choir declared winner of Sky Arts' 'The Great Culture Quiz'
Life and Style
food + drink
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Finance Director

£65000 - £80000 per annum: Recruitment Genius: Finance Director required to jo...

Recruitment Genius: Medico-Legal Assistant

£15000 - £25000 per annum: Recruitment Genius: This is a unique opportunity fo...

Ashdown Group: (PHP / Python) - Global Media firm

£50000 per annum + 26 days holiday,pension: Ashdown Group: A highly successful...

The Jenrick Group: Quality Inspector

£27000 per annum + pension + holidays: The Jenrick Group: A Quality Technician...

Day In a Page

Homeless Veterans appeal: 'You look for someone who's an inspiration and try to be like them'

Homeless Veterans appeal

In 2010, Sgt Gary Jamieson stepped on an IED in Afghanistan and lost his legs and an arm. He reveals what, and who, helped him to make a remarkable recovery
Could cannabis oil reverse the effects of cancer?

Could cannabis oil reverse effects of cancer?

As a film following six patients receiving the controversial treatment is released, Kate Hilpern uncovers a very slippery issue
The Interview movie review: You can't see Seth Rogen and James Franco's Kim Jong Un assassination film, but you can read about it here

The Interview movie review

You can't see Seth Rogen and James Franco's Kim Jong Un assassination film, but you can read about it here
Serial mania has propelled podcasts into the cultural mainstream

How podcasts became mainstream

People have consumed gripping armchair investigation Serial with a relish typically reserved for box-set binges
Jesus Christ has become an unlikely pin-up for hipster marketing companies

Jesus Christ has become an unlikely pin-up

Kevin Lee Light, aka "Jesus", is the newest client of creative agency Mother while rival agency Anomaly has launched Sexy Jesus, depicting the Messiah in a series of Athena-style poses
Rosetta space mission voted most important scientific breakthrough of 2014

A memorable year for science – if not for mice

The most important scientific breakthroughs of 2014
Christmas cocktails to make you merry: From eggnog to Brown Betty and Rum Bumpo

Christmas cocktails to make you merry

Mulled wine is an essential seasonal treat. But now drinkers are rediscovering other traditional festive tipples. Angela Clutton raises a glass to Christmas cocktails
5 best activity trackers

Fitness technology: 5 best activity trackers

Up the ante in your regimen and change the habits of a lifetime with this wearable tech
Paul Scholes column: It's a little-known fact, but I have played one of the seven dwarves

Paul Scholes column

It's a little-known fact, but I have played one of the seven dwarves
Fifa's travelling circus once again steals limelight from real stars

Fifa's travelling circus once again steals limelight from real stars

Club World Cup kicked into the long grass by the continued farce surrounding Blatter, Garcia, Russia and Qatar
Frank Warren column: 2014 – boxing is back and winning new fans

Frank Warren: Boxing is back and winning new fans

2014 proves it's now one of sport's biggest hitters again
Jeb Bush vs Hillary Clinton: The power dynamics of the two first families

Jeb Bush vs Hillary Clinton

Karen Tumulty explores the power dynamics of the two first families
Stockholm is rivalling Silicon Valley with a hotbed of technology start-ups

Stockholm is rivalling Silicon Valley

The Swedish capital is home to two of the most popular video games in the world, as well as thousands of technology start-ups worth hundreds of millions of pounds – and it's all happened since 2009
Did Japanese workers really get their symbols mixed up and display Santa on a crucifix?

Crucified Santa: Urban myth refuses to die

The story goes that Japanese store workers created a life-size effigy of a smiling "Father Kurisumasu" attached to a facsimile of Our Lord's final instrument of torture
Jennifer Saunders and Kate Moss join David Walliams on set for TV adaptation of The Boy in the Dress

The Boy in the Dress: On set with the stars

Walliams' story about a boy who goes to school in a dress will be shown this Christmas