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    Have you ever wondered why the roots of the plants always know which way to grow—into the soil but not above it? Some British scientists have recently solved this mystery.    

      It turns out that roots have special hairs that tie them into the soil and help them grow their way past obstacles, a team at the John Inners Center in Norwich reports in the February 29 issue of Journal Science.

    "The key is in the fuzzy(有绒毛的) coat of hairs on the roots of plants," says professor Liam Dolan. "We have found a growth control system that enables these hairs to find their way and to become longer when their path is clear."

    Root hairs explore the soil in much the same way a person would feel their way in the dark. If they come across an obstacle, they make their way around until they can continue growing in an opening. I the meantime, the plant is held in place as the hairs grip the soil.

    The hairs are guided by a clever chemical trick. A protein(蛋白质) at the tip of the root hairs called RHD2 helps them to take calcium(钙) from the soil. Calcium makes the hairs grow, and produce more RHD2, and take more calcium.

    But when an obstacle blocks the hair's path, or the hair reaches the surface of the soil, the cycle is broken and growth starts in another direction.

    This system gives plants the flexibility to explore a complex environment and to live in even the most unpromising soils, says Dolan.

    In poor soils such as in parts of Australia and Africa, native plants have adapted by producing enormous numbers of root hairs. A better understanding of this adaptation will allow scientists to develop hairy rooted crops that can grow in unfriendly environments.

    According to Dolan, "Research in the John Inners Center is taking a breeding approach(育种方法) to increase hair length in wheat but it will be some time before new cultivars(栽培变种) are developed."

    Harper Lee, whose 1961 novel To Kill a Mockingbird on the racial troubles of the American deep south, has died at the age of 89.

    Until last year, Lee had been something of a one-book literary legend. To kill a Mockingbird sold more than 40 million copies around the world and earned her a Pulitzer prize, remaining a towering presence in American literature. Another novel, Go Set A Watchman, was controversially published in July 2015 as a “sequel” to Mockingbird, though it was later confirmed to be Mockingbird's first draft.

    But from the moment Mockingbird was published to almost instant success, the author consistently avoided public attention. Lee had lived for several years in a nursing home near the house in which she had grown up in Monroeville, Alabama—the setting for Maycomb of her famous book. Her neighbor for 40 years, Sue Sellers, said, “She was such a private person. All she wanted was privacy, but she didn't get much. There was always somebody following her around.”

    James Naughtie, BBC Books Editor, commented on the novels of Harper Lee: “I think she stands, particularly among American readers, as someone who shone a light into a very dark place. She was writing at a time when people were beginning to lift the lid on everything in the South which they'd chosen not to understand. That all changed in the 1960s. So I think her status for writing that book in its extraordinarily direct way will remain.

The National Gallery

Description：

    The National Gallery is the British national art museum built on the north side of Trafalgar Square in London. It houses a diverse collection of more than 2,300 examples of European art ranging from 13th-century religious paintings to more modern ones by Renoir and Van Gogh. The older collections of the gallery are reached through the main entrance while the more modern works in the East Wing are most easily reached from Trafalgar Square by a ground floor entrance.

Layout：

    The modern Sainsbury Wing on the western side of the building houses 13th- to 15th-century paintings, and artists include Duccio, Uccello, Van Eyck, Lippi, Mantegna, Botticelli and Memling．

    The main West Wing houses 16th-century paintings, and artists include Leonardo da Vinci, Cranach, Michelangelo, Raphael, Bruegel, Bronzino, Titan and Veronese.

    The North Wing houses 17th-century paintings, and artists include Caravaggio, Rubens, Poussin, Van Dyck, Velazquez, Claude and Vermeer．

    The East Wing houses 18th- to early 20th-century paintings, and artists include Canaletto, Goya, Turner, Constable, Renoir and Van Gogh.

Opening Hours：

    The Gallery is open every day from 10 am. to 6 pm. (Fridays 10 am. to 9 pm.) and is free, but charges apply to some special exhibitions.

Getting There：

    Nearest underground stations: Charing Cross (2-minute walk), Leicester Square (3-minute walk), Embankment (7-minute walk), and Piccadilly Circus (8-minute walk).

    Even if trees cannot walk, they are still on the move.

    In parts of the Arctic, entire forests are moving northward. Across the Arctic, temperatures are rising faster than anywhere else in the world. As that happens, the tree line that marks where forests stop and the treeless tundra (冻原) starts has been shifting northward. Trees growing along the tree line must protect themselves from the cold wind. To dothis, plants tend to grow horizontal (水平的) branches low to the ground. The energy it takes for trees to grow this way means they don't have enough energy to make seeds.

    But as Earth's climate has been warming, trees no longer have to just grow horizontally. Many can instead grow up toward the sky. This takes less energy. And with all that leftover energy, these trees have started producing more seeds. This happens especially in places where white spruce (白云杉) grows.

    White spruce, which is a North American tree, is quite able to produce a lot of seeds, which can move long distances in the wind. When wind­blown seeds end up on the tundra beyond the tree line, they eventually can sprout(发芽) new trees. This explains how a forest can move. Of course, the process would work only if the tundra were warm enough. But in recent years, the whole planet has been warming.

    New trees will provide shelters for some snow. Keeping the sun's rays from making the white surface disappear. Instead, the trees absorb the sun's heat. This warms the surrounding air. The extra warmth encourages even more trees to produce seeds. That further boosts a forest's ability to expand. In addition, more trees will trap more snow, preventing much of it from being blown away. Snow can trap heat in the soil below, which encourages trees to grow. The recent rise of temperatures has helped more trees grow past the tree line. People worry about impacts on the animals that depend on frozen conditions for food and shelter.

    Membership

    All you need to do is fill out the order form at the bottom of the page, select your first order from our book list and then post the completed form back to us.

    Special offers for new members

    As a special offer, you may choose any reduced-price books from our new members' book list, to the value of 100 yuan in total. Tick the box on your form to order a free watch. Join before the end of this month and you receive another free book carefully chosen by our staff. Order an audio-book from the many on offer, at half the recommended retail price.

    When you've joined

    As a member you get around 50% off the publisher's price of every book you buy, and what's more, they come straight to your door. Your free club magazine arrives once a month to keep you up to date with the latest best-sellers we've added to our list. On the Internet, you can find all our titles for the year at our exclusive members' website. Our website also has a book swap service where members can request or offer books for exchange.

    Being a member

    All you have to do is order four books during your first year. After that, you can decide on the number of books you wish to take. In each of your monthly club magazines, our experienced staff choose a "Book of the Month" for you, which is offered at an extra-special price. If you do not want this book, just say so in the space provided on the form and send it back to us. We always send the book if we do not receive this form.

    Once we receive your order, your books are delivered within one week. And remember, you have up to a fortnight to decide if you wish to keep the books you have ordered. If they aren't what you expected just end them back!

    Stephen Hawking was a famous physicist. He was born in 1942. He died at his home on March 14h, 2018 in Cambridge, Britain.
    As one of the well-known physicists on space and time in the world, Hawking devoted his whole life to discovering the secrets of the universe, and he is called the King of the Universe. Since he was 21 years old, Hawking had been badly ill, but he didn't give up his hope of living. He went on to study at Cambridge University after graduating from Oxford University. In 1965, he got a doctor's degree. Then he worked as a professor at Cambridge University.

    Hawking was known for his work with black holes. He also wrote several popular science books. Although he didn't live as freely as others, he still felt he was happy and he was thankful to life. When Hawking was invited to China, he made speeches in some famous universities.

    From Stephen Hawking's whole life, we learn that no matter how bad life is, we should not lose hope. As he once said," Life is not fair, you just have to do the best you can in your own situation."