Lettuce has shallow roots and large
leaves. It grows in four different forms:
head, leaf, romaine, and stem. The
leaves of head lettuce are folded into a
ball. Leaf lettuce has a cluster of curled
leaves. Romaine lettuce has tall, smooth
leaves. Stem lettuce has narrow leaves
and a thick stem.
If lettuce is left to grow, it produces a
long, slender stalk. Small yellow flowers
grow on this stalk. Farmers usually take
lettuce from the field before it grows
flowers. Lettuce must be eaten soon after
being harvested.
Lettuce is a healthy food choice. It is
almost 95 percent water, so it is low in
calories and fat. It also contains fiber
and some vitamins. Lettuce adds flavor
and crunch to salads and sandwiches.
People cook stem lettuce in stews and in
many Asian dishes.
#More to explore
Leaf • Plant • Vegetable
Levee and Dike
Like dams, levees and dikes have a
simple but important job: they hold
back water. People build levees to keep
rivers or lakes from flooding low-lying
land during storms. Dikes are often built
The center leaves of a head lettuce plant
grow in a tight, round cluster.
A levee divides rice paddies (wet
growing areas) in Japan. The
levee also holds the water away
from nearby houses.
BRITANNICA STUDENT ENCYCLOPEDIA Levee and Dike 135
to reclaim, or take back, land that would
naturally be underwater. For example,
dikes may be used to create a new area
of dry land along a seacoast. Levees and
dikes look alike. Sometimes the words
levee and dike are used to mean the
same thing.
Structure
Levees and dikes can be made of dirt,
cement, or stacked stones. They are built
along the edges of the body of water
they hold back. They must be wide
enough so that they will not collapse or
wear away under pressure from the
water. The tops of levees and dikes made
of dirt are often planted with grass to
help hold the dirt together.
History
Levees and dikes have been built for
thousands of years. The ancient Egyptians
built levees for more than 600
miles (966 kilometers) along the Nile
River. People in ancient Mesopotamia
and China also built levees. One of the
largest modern systems of levees runs
along the Mississippi River in the
United States. These levees extend from
southern Missouri to the Gulf of
Mexico, a distance of about 1,000 miles
(1,600 kilometers).
The most famous system of dikes is in
The Netherlands. Much of the
country’s land was once underwater.
Since the 1200s people have built dikes
to reclaim land from the sea. First they
built dikes out in the sea. Then they
pumped out the water between the
dikes and the natural shoreline. More
than 2,500 square miles (6,500 square
kilometers) of The Netherlands is
reclaimed land.
#More to explore
Dam • Flood • Netherlands, The
Lewis, C.S.
The British writer C.S. Lewis is famous
for writing a series of books called The
Chronicles of Narnia. Lewis wrote many
other books, including poetry, science
fiction, and books about Christianity.
Clive Staples Lewis was born on November
29, 1898, in Belfast, Ireland. As a
child, he missed a lot of school due to
illness. In 1916 he went to University
College in Oxford, England. He left
school for a time to fight inWorldWar I
with the British Army. After college, he
became a teacher.
Lewis published many books throughout
his teaching career. Some were about
In 2005
Hurricane
Katrina damaged
levees
protecting
New Orleans,
Louisiana,
which caused
terrible flooding
in the city.
C.S. Lewis
136 Lewis, C.S. BRITANNICA STUDENT ENCYCLOPEDIA
the subjects he taught. He also wrote
about being a Christian. One of his
most well-known Christian books is
called The Screwtape Letters. It was published
in 1942. It is a humorous story
about devils trying to tempt a young
Christian.
In 1950 Lewis wrote one of his most
famous books. It was a children’s book
called The Lion, theWitch, and theWardrobe.
This book was the first of the series
called The Chronicles of Narnia. The
seven books tell the story of four brothers
and sisters. They discover a magical
world called Narnia, where they have
many adventures.
C.S. Lewis died on November 22, 1963.
He had retired from teaching the summer
before.
Lewis and Clark
Expedition
Between 1804 and 1806 a group of U.S.
soldiers and explorers traveled from the
Mississippi River to the Pacific coast and
back. The leaders of this expedition, or
journey, were Meriwether Lewis and
William Clark.
In 1803 the United States had bought a
huge territory west of the Mississippi
River. It was called the Louisiana Territory.
President Thomas Jefferson sent
Captain Meriwether Lewis to find out
what was there. Lewis chose Lieutenant
William Clark to share the leadership.
Lewis and Clark chose men who knew
how to live in the wilderness to go with
them.
Westward Bound
Home base for the group was near what
is now Saint Louis, Missouri. On May
14, 1804, the men started up the Missouri
River in three boats. On August 3
they had their first meeting with Native
Americans, near what is now Council
Bluffs, Iowa.
The group spent the winter in what is
now North Dakota, among the Mandan
Sioux. There a young Native American
woman named Sacagawea joined the
