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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."

    The brain of an insect isn't very big. But insects are somehow still able to make lots of important decisions. Bees, ants and roaches(蟑螂) build hives(巢穴)with thousands of workers doing specialized work. The jobs are done without a head or even a plan. How do insects manage this?

    To solve the mystery, scientists in Belgium spent months building robotic roaches and then putting them among real roaches. The final goal of the research is to find out how the simple behavior of individuals gives rise to a collective decision. The roach is a good starting point for trying to answer the big question because its social system is simple enough for scientists to study.

    The first step was to build robots that real roaches would accept as their own. Although the robotic roaches don't look much like the real thing, they have similarities with them in three key ways: they naturally head toward dark areas, they are influenced by the behavior of other roaches, and even more importantly, they smell like roaches.

    The next step was getting the robotic and real roaches to work together on common tasks. In experiments, the robots would collectively head towards a dark place, copying the behavior of natural roaches. That got the researchers wondering: if you program the robotic roaches to go woward the lighted place, would the real roaches follow, going against their natural instincts.(本能) ?

    They will – it turned out. Many of the real roaches followed the robots to a lighter shelter. But influence turned out to be a two- way street. On occasion, the real roaches were able to override the programming of the robot roaches and get them to turn into dark hiding places. Being social creatures, both the robotic and natural roaches were paying attention to and following the example set by others.

    In theory, it would be possible to create a robot that could influence collective decision-making in humans. To do this, researchers would have to invent a robot that people would accept. Fortunately, the technology isn't there yet.

    Rent control, like all other government-mandated（强制执行的）PRICE CONTROL,is a law placing a maximum price, or a "rent ceiling," on what landlords may charge tenants（房客）.It is a program designed to stop rents from rising rapidly and is used mainly in large urban areas where there are more people than housing. In cities with rent control, the city government sets the maximum rent that a landlord can charge for an apartment. Supporters of rent control argue that it protects people who are living in the apartments. Their rent cannot increase; therefore, they are not in danger of losing their homes. However, almost all the critics conclude that rent control is destructive. They say after a long time, rent control may have negative effects.

    In a 1990 survey of 464 people published in the May 1992 issue of the American Economic Review,93% of US respondents agreed that a ceiling on rents reduces the quantity and quality of apartments available. Landlords are too cautious (perhaps too smart) to put their faith in rental apartments because they know that the rental-controlled apartments cannot increase their profits. Therefore, they invest in other businesses where they can increase their profits. They do not invest in new buildings which would also be rent-controlled. As a result, new apartments are not built. Many people who need apartments cannot find any.

    Some theorists argue that the minimum wage law can cause problems in the same way. The federal government sets the minimum that an employer must pay workers. The minimum helps people who generally look for unskilled, low-paying jobs. However, if the minimum is high, employers may hire fewer workers. They will replace workers with machinery. The price, which is the wage that employers must pay, increases. Therefore, other things being equal, the number of workers that employers want decreases. Thus, critics claim, an increase in the minimum wage may cause unemployment. Some poor people may find themselves without jobs instead of with jobs at the minimum wage.

    Supporters of the minimum wage say that it helps people keep their dignity, Because of the law, workers cannot sell their services for less than the minimum. Furthermore, employers cannot force workers to accept jobs at unfair wages.But the supporters make a big error. They fail to realize that it is possible for such a law to increase wages beyond the value of what the workers contributes.

    Economic theories predict the results of economic decisions such as decisions about farm production, rent control, and the minimum wage. The predictions may be correct only if "other things are equal". Economists do not agree on some of the predictions. They also do not agree on the value of different decisions. Some economists support a particular decision while others criticize it. Economists do agree, however, that there are no simple answers to economic questions.

    Directions Choose a book from the list below and bring it to class by the due date. You will have approximately one trimester，from September 14 to November 16，to read the book and complete your report. It is okay to switch your book if you do not like your original choice. Students are encouraged to check out the book of their choice from the public library.

    The purchase of a book is optional.

An Edinburgh inventor has created a fully biodegradable bottle that is made from paper and a secret combination of plant materials, and it could help save the planet's oceans from plastic pollution and can also be eaten by sea creatures.

The Edinburgh-based Durham University chemistry graduate James Longcroft started a non-profit bottled water company two years ago. He wanted to put all his profits into a charity that provided clean drinking water to countries in Africa.

However, after concerns about the environmental impact of plastic bottles, Mr. Longcroft decided the Edinburgh and London-based company, Choose Water, should go plastic-free. So he came up with a new type of water bottle—a waterproof paper bottle.

"The outside is made from recycled paper, but the inside has to be waterproof, and provides strength so the bottle would keep its structure, and keep the water fresh," Mr. Longcroft said.

When the bottle is thrown in the ocean the degrading process begins within hours leaving the bottle totally degraded (分解)within weeks. The steel cap breaks down within a year.

Mr. Longcroft now believes these novel bottles could revolutionise the industry and says the cost of producing the bottle is around 5 pence more than one made from single-use plastic.

"The main difficulty we face is breaking into a saturated (饱和的)market and competing with an old industry," he said. "Changing an industry will be a big uphill battle, but with the support from the public, we will change the way we look at bottled water."

Researchers warn that eight million tonnes of plastics currently find their way into the ocean every year which will stay in the environment for centuries.

"We really want to get our bottles on shelves and into people's hands as soon as possible—if we can stop even one plastic bottle ending up in the environment it will be worth it," said Mr Longcroft.