Sap’s Running

by Stephen R. Swinburne

The Coleman brothers—Nelson, Ralph, and Harold—step out their front door in Vermont. They feel the wind. They feel the sun on their faces. “Sap could be running this morning,” says Nelson.

As they pass 75-year-old sugar-maple trees, sap drips from holes in the trees into metal buckets. They know for sure that today will be a good day for sugaring.

Sap from sugar maples looks like water, but tastes sweet. That’s because it has sugar in it. It also contains minerals from the soil. A 50-foot-high sugar maple has nearly two hundred thousand leaves. All these leaves drink in summer sunshine and make sugar. During winter, sugar is stored in the tree. Running sap in the spring contains the sugar that was made in the tree the summer before.

Every spring, the Colemans tap holes into sugar-maple trees, then hang a bucket under each hole to catch the sap. To make syrup, the sap is heated in big open pans so that most of the water will boil away. The Colemans say it takes about thirty-five gallons of sap to make one gallon of maple syrup.

More than a hundred years ago, scientist Charles Darwin wrote that sap flow was a “most mysterious subject.” Since then, many people have studied how sap flows. Much of the research has been done at the University of Vermont, where sap is still being studied.

Nelson Coleman and his brothers have made maple syrup all their lives. It is a family tradition. They don’t worry too much about why the sap is running in their trees this morning. They’re just glad it is.

The Iroquois Legend of Woksis and Maple Syrup

According to legend, an Iroquois chief named Woksis yanked his tomahawk out of a maple tree one spring day. A bowl sat by the trunk of that tree. As the day warmed, sap dripped from the gash into the bowl. When Woksis’s wife saw the sap in the bowl, she thought it was water. She used it to cook their meal. The sap boiled away, leaving maple syrup. When Woksis tasted the sweetened meat, he loved it. So, boiling sap to make maple syrup began.

What Makes Sap Run?

For years, people have thought that sap rises up from the roots of the sugar-maple tree. It doesn’t. “During the time when sap flows from tap holes, the bulk flow of sap is downward,” says Dr. Tim Perkins. He is a scientist at the University of Vermont.

How does sap flow? During cold nights, maple trees freeze solid. That’s when water rises into the trunk and branches. The water forms frost inside tiny hollow spaces within the tree. In the morning, this frost melts and becomes sap, which flows down the tree.

Scientists say that anyone who cuts down a sugar-maple tree in freezing weather can see this is true. When the weather warms up, sap will flow from the cut end of the trunk—not from the stump.

A student is writing a research report about different kinds of fruit. He wrote an opinion in the report. Read the sentences from the student's report and the directions that follow. 

Many Kinds of Fruit

A fruit is the part of the plant that has the plant's seeds. There are many kinds of fruits. Some that are popular with kids are apples, bananas, grapes, oranges, and strawberries. Sometimes it is confusing to tell if a food is a fruit.

Read the passage and answer the questions.  

What Is a Spacewalk?

Any time an astronaut gets out of a vehicle while in space, it is called a spacewalk.  

The first person to go on a spacewalk was Alexei Leonov. He was from Russia. The first spacewalk was on March 18, 1965. It was 10 minutes long.  

The first American to go on a spacewalk was Ed White. His spacewalk was on June 3, 1965, during the Gemini 4 mission. White's spacewalk lasted 23 minutes.  

Today, astronauts go on spacewalks outside the International Space Station. Spacewalks usually last between five and eight hours, depending on the job.  

The world record for the most spacewalks is held by Russian astronaut Anatoly Solovyev. He has been on 16 spacewalks and spent more than 82 hours outside in space. That's almost 3 ½ days of walking in space! NASA astronaut Michael Lopez-Alegria holds the U.S. record for the most spacewalks. He has done 10.  

Why Do Astronauts Go on Spacewalks?

Astronauts go on spacewalks for many reasons. Spacewalks let astronauts work outside their spacecraft. Astronauts can do science experiments. Experiments can be placed on the outside of a spacecraft. This lets scientists learn how being in space affects different things.  

Spacewalks also let astronauts test new equipment. They can repair satellites or spacecraft that are in space. By going on spacewalks, astronauts can fix things instead of bringing them back to Earth to fix.  

How Do Astronauts Go on Spacewalks?

When astronauts go on spacewalks, they wear spacesuits. Inside spacesuits, astronauts have the oxygen they need to breathe. They have the water they need to drink.  

Astronauts put on their spacesuits several hours before a spacewalk. The suits are pressurized. This means that the suits are filled with oxygen.  

Once in their suits, astronauts breathe pure oxygen for a few hours. Breathing only oxygen gets rid of all the nitrogen in an astronaut's body. If they didn't get rid of the nitrogen, the astronauts might get gas bubbles in their body when they walked in space. These gas bubbles can cause astronauts to feel pain in their shoulders, elbows, wrists, and knees.  

They leave the spacecraft through a special door called an airlock. The airlock has two doors. When astronauts are inside the spacecraft, the airlock is airtight so no air can get out. When astronauts get ready to go on a spacewalk, they go through the first door and lock it behind them. They can then open the second door without any air getting out of the spacecraft.  

How Do Astronauts Stay Safe During Spacewalks?

When on a spacewalk, astronauts use safety tethers to stay close to their spacecraft. Tethers are like ropes. One end is hooked to the spacewalker. The other end is connected to the vehicle. The safety tethers keep astronauts from floating away into space. Astronauts also use tethers to keep tools from floating away. They tether their tools to their spacesuits.  

Another way astronauts stay safe during spacewalks is by wearing a special machine on their backs. This machine uses small jet thrusters to let an astronaut move around in space. If an astronaut were to become untethered and float away, the machine would help him or her fly back to the spacecraft. Astronauts control the machine with a small joystick, like on a video game.  

How Do Astronauts Train for Spacewalks?

One way astronauts train for spacewalks is by swimming. Floating in space is a lot like floating in water. Astronauts practice spacewalks underwater in a large swimming pool. Astronauts train seven hours in the pool for every one hour they will spend on a spacewalk.  

Another way astronauts practice for a spacewalk is by using virtual reality. This is sort of like playing a video game. Astronauts wear a helmet with a video screen inside. They also wear special gloves. A video of what they will see during a spacewalk is shown on the screen inside the helmet. When the astronaut moves, the special gloves allow the movements to be shown with the video. This simulation looks and feels just like a spacewalk.  

A student is writing a report on cheetahs for her class. The student wants to revise a paragraph from the report to give it a stronger conclusion. Read the draft of a paragraph from the report and complete the task that follows.  

Cheetahs are very fast runners. They are the fastest land animals in the world. They can run up to 75 miles per hour! They hunt animals like rabbits and deer. Most cheetahs live in Africa. They are the only big cats that cannot roar. They also cannot climb trees. Cheetahs are smaller than lions and tigers. Their fur is tan with black spots all over. There are only about 10,000 cheetahs left in the world.