colonies all around theMediterranean.
Carthage, in North Africa, was a very
successful colony that became a power in
its own right.
Over the centuries a number of foreign
powers controlled all or parts of Phoenicia.
They included Egypt, Assyria, Babylonia,
and Persia. The Macedonians, led
by Alexander the Great, conquered
Phoenicia in 332 BC. In 64 BC Phoenicia
became a part of the Roman Empire.
..More to explore
Carthage Colony Lebanon
Mediterranean Sea
Phoenix
..see Animals, Legendary.
Phoenix
Population
(2000 census),
city, 1,321,045;
(2007 estimate)
1,552,259
Phoenix is the capital of the U.S. state of
Arizona. It is one of the largest cities in
the United States. It lies on the Salt
River within the Sonoran Desert.
Mountains surround the city. Its warm,
sunny climate has made it a popular
vacation spot.
Many people in Phoenix work for the
government. Many others work in tourism,
health care, or other service industries.
Factories in and around Phoenix
make spacecraft, aircraft, electronics,
and computer parts.
Phoenix lies in a dry area. The city
developed as people were able to bring
water there. In ancient times a Native
American people called the Hohokam
lived in the area. They dug canals from
the Salt River to carry water to their
crops.
In modern times there were no towns in
the Phoenix area until the late 1800s. In
1867 a businessman named Jack Swilling
built new water canals in the area.
New farms were soon established there.
Phoenix grew near the farms.
Giant saguaro cacti grow in the Tonto
National Forest east of Phoenix, Arizona.
BRITANNICA STUDENT ENCYCLOPEDIA Phoenix 75
The capital of the Arizona Territory was
moved to Phoenix in 1889. In 1912
Arizona became a U.S. state with Phoenix
as its capital.
Roosevelt Dam was built on the Salt
River in 1911. The dam allowed much
more water to be brought to Phoenix.
The city grew very quickly after that.
#More to explore
Arizona Hohokam Culture
Photography
Using a camera to take photographs is
called photography. A photograph is an
image, or picture, that has been captured
on film or some other material. People
who take pictures are called photographers.
Uses of Photography
Photography is a useful form of communication.
Photographs give information
about people, places, objects, and events
that words may not be able to describe.
Newspapers and magazines have printed
photographs of interesting people and
events since the 1800s. Advertisers and
other businesses use photography to
show people their products. Scientists,
doctors, and police officers use photography
to record important information.
Photography is a form of art as well.
Many museums and galleries display
photographs created by artists.
Finally, photography is a very popular
hobby. People take photographs of
places they visit. They also photograph
important family events, such as birthdays,
holiday celebrations, graduations,
and weddings.
Making Photographs
Photographers use cameras to take pictures.
Traditional cameras use film to
record images. Other cameras, called
digital cameras, use computer chips.
Film is a thin, see-through material. It
has a special coating that goes through
chemical changes when light comes into
the camera from the outside. These
changes create the image. After taking
pictures, the photographer takes the film
out of the camera. Then the photographer
treats the film with more chemicals.
This process is called developing. It
creates a photographic negative. On a
negative, dark areas of the image are
light and light areas are dark. Photographers
create prints, or photographs, by
passing light through the negative onto
A young photographer learns to develop
photographs. The room she works in has
special lighting because ordinary light
would spoil the images on the film.
76 Photography BRITANNICA STUDENT ENCYCLOPEDIA
special paper. One negative can make
many prints.
Digital cameras and cell phones do not
use film. They turn images into electric
signals, which they store on microchips.
People can load images from a digital
camera or a cell phone onto a computer.
Then they may use their computers
printer to print the images. Or they may
send the images to a company that can
print them on special photograph paper.
Cameras have features that allow photographers
to control how the image is
created. One feature is the shutter,
which controls the amount of light that
enters the camera. A photographer can
adjust the shutter to create certain effects
with the light. Another feature is the
lens, which focuses the light. One special
type of lens allows the camera to
capture a wider view than a regular lens
would. Another lens can make objects
far away look much closer than they are.
History
Louis Daguerre of France invented one
of the earliest forms of photography in
1837. Daguerres camera recorded
images on metal plates. His photographs
were called daguerreotypes. The main
problem with daguerreotypes was that
no copies could be made of the original
image.
A few years after Daguerres invention,
British scientist William Henry Fox Talbot
invented a way to produce paper
negatives. This made it possible to print
any number of photographs from a
single negative. Photographers still use
this method today.
Early photography was difficult because
cameras were large and heavy. They
recorded images on stiff plates instead of
film. In the late 1800s the U.S. inventor
George Eastman invented flexible film
and a small, easy-to-use camera. Eastmans
inventions made it possible for
anyone to take photographs.
Before 1907, when color film was
invented, camera film was black and
white. Black-and-white film that developed
itself appeared in 1947. This type
of film was used in a special camera,
called a Polaroid Land camera. The film
came out of the camera after a picture
was taken and revealed an image within
minutes. Color Polaroid film became
available in 1963. Digital cameras
appeared in the 1990s.
#More to explore
Arts Camera Communication
Hobby Light
A photographer prepares to photograph a
woman in his studio in about 1900.
BRITANNICA STUDENT ENCYCLOPEDIA Photography 77
Photosynthesis
Photosynthesis is the process in which
green plants use sunlight to make their
own food. Photosynthesis is necessary
for life on Earth.Without it there would
be no green plants, and without green
plants there would be no animals.
Photosynthesis requires sunlight, chlorophyll,
water, and carbon dioxide gas.
Chlorophyll is a substance in all green
plants, especially in the leaves. Plants
take in water from the soil and carbon
dioxide from the air.
Photosynthesis starts when chlorophyll
absorbs energy from sunlight. Green
plants use this light energy to change
water and carbon dioxide into oxygen
and nutrients called sugars. The plants
use some of the sugars and store the rest.
The oxygen is released into the air.
Photosynthesis is very important
because almost all living things depend
on plants for food. Photosynthesis is also
important because of the oxygen it produces.
Humans and other animals need
to breathe in oxygen to survive.Without
photosynthesis, all Earths oxygen would
be used up.
Some living things other than plants also
make their own food through photosynthesis.
They include certain types of
bacteria and algae.
#More to explore
Energy Plant
Physics
Physics is one of the major branches of
science. People who work in physics are
called physicists. Physicists study matter
and the forces (pushes or pulls) that act
on it. (Matter is what makes up all
physical objects.) Physicists also study
many different forms of energy. The
objects that physicists study range in size
from the tiny building blocks of matter
to huge groups of stars.
Fields of Study
Physics is divided into many fields of
study. Mechanics deals with the effect of
forces on objects and the motions of
objects. Acoustics is concerned with
sound. Optics is the study of light.
Thermodynamics deals with the form of
energy called heat. Electronics and mag-
Green plants such as trees use carbon dioxide,
sunlight, and water to create sugars.
Sugars provide the energy that makes
plants grow. The process creates oxygen,
which people and other animals breathe.
78 Photosynthesis BRITANNICA STUDENT ENCYCLOPEDIA
netism are concerned with a basic property
of matter called electric charge.
Atomic physics concerns the structure of
atoms (the building blocks of matter)
and the forces that act on them. Quantum
mechanics explains the behavior of
very small particlessuch as the particles
that make up an atom.
History
Physics first developed as people began
to wonder about the physical world
around them. The ancient Greeks studied
the motion of objects in the sky and
the physical properties of things on
Earth.
Early in the 1600s the Italian scientist
Galileo studied how all things fall to
Earth at the same speed. At the end of
the 1600s the English scientist Isaac
Newton explained the laws of gravity (a
force) and motion.
In the late 1800s scientists discovered
that tiny particles make up atoms. In
the early 1900s the German-American
physicist Albert Einstein helped to
explain the behavior of these particles.
Einstein also proposed entirely new
ways of thinking about space, time, and
gravity.
#More to explore
Einstein, Albert Electronics Energy
Force Galileo Gravity Heat
Light Magnet and Magnetism
Matter Motion Newton, Isaac
Sound
Picasso, Pablo
Pablo Picasso experimented with many
different styles of painting during his
long career as an artist. His work was a
A young visitor to a science
museum explores an electric
spark generator. Museums can
provide interesting ways to learn
about physics.
Picasso designed a steel sculpture for an
outdoor site in Chicago, Illinois. The sculpture
stands about 50 feet (15 meters) high.
BRITANNICA STUDENT ENCYCLOPEDIA Picasso, Pablo 79
major influence on the development of
modern art. Picasso also created sculpture,
prints, pottery, poetry, and ballet
scenery.
Early Life
Pablo Ruiz y Picasso was born on
October 25, 1881, in Malaga, Spain.
He learned to draw from his father, a
professional art teacher. Picasso held his
first exhibition at age 13 and then
studied at an art academy. But in 1899
he decided to break with his formal
training and join a group of
experimental artists.
Blue and Rose Periods
Picasso was deeply affected by the death
of a close friend in 1901. He began
painting images of death, poverty, and
despair. He used mostly blue tones, so
this part of his career is called his blue
period.
Picasso moved to Paris in 1904. By 1905
he was painting in shades of rose, or
pinkish red, and his subject matter was
less sad. This rose period lasted until
about 1907.
Cubism and Later Styles
With his painting Les Demoiselles
dAvignon in 1907, Picasso touched new
ground. It shows five nude women in
flat, angled shapes. Two of their faces
look like African masks. At the time
many people found the painting
shocking.
Picasso and another painter named
Georges Braque then created a new
style of art called cubism. This style
does not show people or objects in a
realistic way. Instead the subjects are
broken apart into many flat shapes.
Several sides of the same subject might
show at once.
Picasso later used more traditional painting
styles and a less severe style of cubism.
In 1937 he painted Guernica,
which many consider his masterpiece. It
shows images of suffering after the
bombing of the town of Guernica during
the Spanish CivilWar. Picasso continued
to work into his 90s. He died on
April 8, 1973, in Mougins, France.
#More to explore
Painting Sculpture
Pierce, Franklin
Franklin Pierce was was president of the
United States between 1853 and 1857.
Slavery was then an important issue.
Picasso
designed costumes
and
scenery for
five ballets
performed by
a Russian ballet
company.
Franklin Pierce was the 14th
president of the United States.
80 Pierce, Franklin BRITANNICA STUDENT ENCYCLOPEDIA
Early Life
Franklin Pierce was born on November
23, 1804, in Hillsboro, New Hampshire.
His father, Benjamin Pierce,
served as governor of that state. After
graduating from Bowdoin College in
Maine, Pierce studied law. He became a
lawyer in 1827. In 1834 Pierce married
Jane Means Appleton. They had three
sons.
Political Career
Pierce entered the New Hampshire legislature
in 1829. In 1832 he was elected
to the U.S. House of Representatives.
From 1837 to 1842 he served in the
Senate. Pierce then practiced law in
Concord, New Hampshire. During the
MexicanWar (184648) he served
briefly as an officer.
By the 1850s both major political parties,
the Democrats and the Whigs, were
divided over the issue of slavery. In 1852
none of the best-known Democrats
could win enough support to become
the partys presidential candidate. Pierce
was not well known, but the Democrats
eventually compromised by choosing
him. Pierce defeated GeneralWinfield
Scott in the election.
Presidency
As president, Pierce focused on expanding
U.S. territory. In 1853 he unsuccessfully
tried to buy Cuba from Spain. In
the same year, however, the United
States bought almost 30,000 square
miles (78,000 square kilometers) of land
from Mexico in a deal called the Gadsden
Purchase.
Pierce tried to satisfy both sides of the
slavery debate. He appointed Northerners
and Southerners to government
posts. He also signed the Kansas-
Nebraska Act in 1854. The act allowed
the voters in the territories of Kansas
and Nebraska to decide whether to allow
slavery there. Violent clashes broke out
November 23, October 8,
1804 1832 1852 1853 1853 1854 1869
Pierce is
born in
Hillsboro, New
Hampshire.
Pierce is
elected to
Congress.
Pierce is
elected
president.
The United
States tries to
buy Cuba from
Spain but fails.
In the Gadsden
Purchase, the
United States
gains land
from Mexico.
Pierce signs
the Kansas-
Nebraska
Act, which
leads to
violence.
Pierce dies in
Concord, New
Hampshire.
T I M E L I N E
BRITANNICA STUDENT ENCYCLOPEDIA Pierce, Franklin 81
between proslavery and antislavery settlers
in Kansas.
Because of the situation in Kansas, the
Democrats chose another candidate for
president in 1856. Pierce retired to Concord
to practice law. He died there on
October 8, 1869.
..More to explore
Buchanan, James Gadsden Purchase
Kansas-Nebraska Act Slavery
United States
Pierre
Population
(2000 census)
13,876; (2007
estimate)
14,032
Pierre is the capital of the U.S. state of
South Dakota. The city lies on the Missouri
River.
Farmers from the surrounding area go to
Pierre to sell and ship out their cattle
and crops. Many people in the city work
for the government. Tourism also brings
money to Pierre. The regions lakes
attract tourists to the city.
Before 1800 the Arikara Indians had
their capital in the Pierre area. Pierre was
founded in 1880. It was named after the
French fur trader Pierre Chouteau, Jr.
The city grew because it was an important
stop on the railroad used by the
local mining industry. It was also a trade
center for a large area. In 1889 South
Dakota became a U.S. state with Pierre
as its capital.
..More to explore
South Dakota
Pig
Pigs are stout, barrel-shaped mammals.
Some kinds of pigs are wild, while others
are domestic (raised by humans).
Farmers raise domestic pigs for their
The South Dakota state Capitol
in Pierre was finished in 1910.
Piglets stay close to their mother.
82 Pierre BRITANNICA STUDENT ENCYCLOPEDIA
meat, which is called pork, and their fat,
which is called lard. The skin of pigs is
made into leather. Their stiff hair is used
for brush bristles.
Several different names are used to
describe pigs. Both wild and domestic
pigs are also called swine. Domestic pigs
that weigh more than 120 pounds (50
kilograms) are called hogs. That term
can also be used to describe wild or
domestic pigs in general. Before giving
birth a female pig is called a gilt. After
her first litter she is called a sow.
Where Pigs Live
Domestic pigs live on every continent
except Antarctica. Several types of wild
pig are found in Europe, Asia, and
Africa. They live in forests and grasslands.
China has the worlds largest
population of domestic pigs, followed by
the United States.
Physical Features
A pig has a bulky body with short legs.
It has thick skin covered with a coat of
stiff hairs. Pigs range in length from
about 2 to 7 feet (0.6 to 2.1 meters)
long. Domestic pigs can weigh as much
as 700 pounds (320 kilograms). The
largest wild pig, called the wild boar, is
smaller.
A pigs snout ends in a flat, rounded
disk. Pigs use their snout to find food in
the ground and dig it out.Wild pigs
have sharp tusks to dig with, too. They
also use their tusks as a weapon to
defend themselves. Domestic pigs do
not have tusks, but they have tusklike
teeth.
Behavior
In the wild, female pigs live together
peacefully. But males fight, so they usually
live alone.Wild pigs eat a wide variety
of foods, including leaves, roots,
fruit, reptiles, and rodents. Domestic
pigs eat grains and food waste.
A female pig gives birth after a pregnancy
of about four months. The average
litter includes about 10 or 11 baby
pigs, called piglets.
#More to explore
Mammal
Pigeon and Dove
The bird called the domestic pigeon is a
familiar sight on city streets. It is only
one species, or type, of pigeon. About
250 species of pigeons and doves are
found around the world. These birds
make up the scientific family Columbidae.
Often the larger members of the
family are called pigeons, and the
smaller ones are called doves. But there
is no clear distinction between the
The bush pig is an African wild pig that is
known for its long hair.
BRITANNICA STUDENT ENCYCLOPEDIA Pigeon and Dove 83
names. For example, the traditional
dove of peace is a white domestic
pigeon.
Pigeons and doves are found nearly all
over the world. They live in farmlands,
woodlands, deserts, and cities.
Physical Features
These birds have plump bodies with
short necks, small heads, and long
wings. They range in length from about
6 to 33 inches (15 to 84 centimeters).
Many of them are gray, brown, black, or
white. They are strong fliers. On the
ground a pigeon or dove struts about,
bobbing its head up and down.
Behavior
Most pigeons and doves eat mainly
seeds, which they pick up from the
ground. Some types eat leaves or fruit.
Pigeons and doves are the only birds to
feed their young a liquid called milk.
Both parents produce the milk from a
gland in the throat. The parents typically
stay together for as long as they
live.
Relationship to Humans
Pigeons and doves have an excellent
sense of direction. For thousands of
years people have trained pigeons to
carry messages over long distances. A
trained bird can find its way home after
being carried hundreds of miles away.
People also hunt pigeons and doves for
sport. Hunters killed so many passenger
pigeons that this type became extinct, or
died out. The last one died in 1914.
Since then people have tried to limit the
numbers of birds hunted.
#More to explore
Bird
Pilgrimage
A journey to a holy place is called a pilgrimage.
A person who makes such a
journey is a pilgrim. Pilgrimages have
been a part of the worlds major religions
since ancient times.
People go on pilgrimages for many reasons.
Some religions require or encourage
believers to make a pilgrimage as an
expression of faith. People may also
journey to a shrine because they want a
favor, such as a cure for an illness, from
a saint or divine being. Others give
thanks or ask to be forgiven for a wrong
they have done.
The first Christian pilgrims traveled to
Jerusalem, where Jesus died. Those first
The mourning dove is a common bird of
North America.
84 Pilgrimage BRITANNICA STUDENT ENCYCLOPEDIA
pilgrimages took place in the AD 100s.
In later years, Muslims controlled
Jerusalem, which often made the
pilgrimages impossible. Christians
started a series of wars known as the
Crusades partly so that Christian
pilgrims could again travel to Jerusalem.
Modern Christian pilgrimage sites have
included places where people are
thought to have seen visions of the Virgin
Mary. They include Lourdes, France,
and Fatima, Portugal.
Every follower of Islam who can manage
the journey is required to make a pilgrimage
to the holy city of Mecca, Saudi
Arabia, where Muhammad was born.
This pilgrimage is called the hajj. In
Mecca the pilgrim must walk seven
times around a sacred shrine called the
Kabah and touch a black stone in one of
its walls. Muslims believe that this stone
was given to Adam when he was forced
out of the Garden of Eden.
In Hinduism, certain places are considered
holy because of a connection with a
historical event, a legendary person, or a
god. Many Hindu pilgrimage sites lie
along Indias rivers, especially the
Ganges. For Hindus, bathing in a holy
river symbolizes the washing away of sin.
A yearly bathing festival for hundreds of
thousands of pilgrims takes place on the
Ganges near Allahabad.
The pilgrimage centers of Buddhism are
tied to the life of the Buddha. The most
important pilgrimage site for Buddhists
is Bodh Gaya, in northeastern India.
This is where the Buddha is said to have
become enlightened (or awakened to the
truth about life). Most Buddhist countries
now have their own shrines at
which pilgrims gather.
#More to explore
Crusades Ganges River Jerusalem
Mecca
Pima
The Pima are Native Americans who live
in southern Arizona. They call themselves
the Akimel Oodham. The Pima
are related to the Tohono Oodham
people. They are probably descendants
of the ancient Hohokam Indians.
The Pima traditionally lived in round,
one-room houses. The houses had pole
frames and walls of grass and mud. The
Pima were farmers who built canals
(artificial waterways) to carry river water
Hindu pilgrims bathe in the Ganges River in
India.
In ancient
times Jewish
men were
expected to
make
pilgrimages to
Jerusalem
during three
yearly
festivals.
BRITANNICA STUDENT ENCYCLOPEDIA Pima 85
to their fields. They grew corn, squash,
pumpkins, kidney beans, tobacco, and
cotton. They gathered cactus fruits and
other wild plants. They also fished and
hunted small animals, including
jackrabbits.
Spanish explorers arrived in the land of
the Pima in the 1690s. The Spanish
taught the tribe how to grow barley and
wheat and how to raise sheep and cattle.
In 1853 the tribes land became part of
the United States. Then whites began
settling there. They changed the direction
of rivers to water their own fields.
The Pima eventually lost much of their
land. They kept one reservation on the
Gila River and another on the Salt River.
At the end of the 20th century there
were about 8,500 Pima living in the
United States. Most lived on the tribes
reservations in Arizona.
#More to explore
Hohokam Culture Native Americans
Tohono Oodham
Pine
Pines are believed to be among the oldest
trees on Earth. Some can live as long
as 6,000 years. There are 90 species, or
types, of pine. They are most common
in the mountains.
Pines vary widely in size. Some are only
a few feet tall. Others grow taller than
200 feet (61 meters). Pines have thin
leaves that are called needles. Pines are
evergreens, which means that they do
not lose their leaves in autumn. Pines
contain a liquid called resin. It fights
infection. Pines burn easily because of
their resin.
Pines belong to the group of trees called
conifers, which means that they produce
cones. Both male and female cones grow
on a pine tree. Usually the male cones
grow on the lower branches of the tree.
Male cones are less than 1 inch (2.5
centimeters) long. They are smaller than
the female cones. Female cones are usually
called pinecones.
Pima women used curved sticks to play a
game.
Pine trees grow in Tongass National Forest
in Alaska.
86 Pine BRITANNICA STUDENT ENCYCLOPEDIA
In spring or early summer pollination
occurs. In this process the male cone
releases tiny grains called pollen. The
pollen is then carried by the wind to the
female cone. Over the next several years
the female cone makes seeds. These
seeds can become new plants.
Pine trees are a major source of timber.
Their wood is used in construction and
to make paper. The resin of pine trees is
used to make paints, turpentine, and
varnishes. Pine oil can be used as medicine.
#More to explore
Conifer Tree
Pineapple
Pineapples are sweet, juicy fruits. They
grow on a plant with the scientific name
Ananas comosus. Ananas means excellent
fruit in an Indian language from South
America. Pineapples are native to warm
regions of the Americas.
Pineapples now grow in tropical (warm)
areas around the world. The leading
producers of pineapples include Thailand,
the Philippines, India, China, Brazil,
and the U.S. state of Hawaii.
Pineapples grow on plants that have
leaves shaped like long swords. The
plants also have purple flowers and
smaller leaves. As they grow, these flowers
and leaves join together to form the
pineapple fruit.
A ripe pineapple looks like a cactus. The
outer peel is very tough. It has sections
that look like eyes. Each eye is formed
from one flower. A group of leaves grows
out of the fruits top. These leaves are
called the crown. The inside of the fruit
is fleshy and yellow.
Some pineapple plants do not produce
seeds. In such cases, new plants are
grown from cuttings, or pieces of the
plants. Farmers prepare for planting by
laying a covering of heavy paper or plastic
over the soil. Then they plant the
cuttings through holes in the covering.
The covering protects the young plants.
Pineapples can be eaten fresh or canned.
In some areas people use them in baked
desserts. Pineapple leaves contain a silky
fiber. In the Philippines people weave
the fiber into a delicate fabric called pina
cloth.
#More to explore
Fruit
Christopher
Columbus and
other early
explorers
found the
pineapple
growing in the
West Indies.
A pineapple fruit rises out of a
cluster of sword-shaped leaves.
BRITANNICA STUDENT ENCYCLOPEDIA Pineapple 87
Pioneer Life
Pioneers were men, women, and children
who started new lives on the U.S.
frontier in the 1800s. After a long journey
from the East, they built simple
homes and small farms. They often lived
miles from any neighbors and worked
hard every day to survive.
MovingWestward
Pioneers had different reasons for moving
westward. Many settlers went west
during the California gold rush of 1849.
Others wanted a piece of free land,
which the U.S. government began giving
away in the 1860s. Some groups
were looking for religious freedom.
Many former slaves wanted to start a
new life after the CivilWar ended in
1865.
The trip west was difficult. Many pioneers
traveled in covered wagons pulled
by horses, mules, or oxen. They often
followed well-worn paths such as the
Oregon Trail or the Santa Fe Trail.
Along the way, pioneers and Native
Americans sometimes fought. Many
pioneers died from accidents and disease.
In 1869 railroads linked the East
andWest coasts. However, pioneers used
the wagon trails until about 1880.
Pioneer Settlements
Early pioneers made houses out of sod,
or bricks of dirt and prairie grass. Others
lived in dugouts, or spaces dug out of a
hillside or the ground. Still others made
houses out of logs and mud. Most
homes had dirt floors, a fireplace, and a
chimney. The simple furniture was usually
made of wood.
Towns developed only as more people
settled in the area. This meant that pioneer
families had to do everything on
their own. They grew crops and raised
farm animals for milk, eggs, and meat.
In the winter they hunted and ate preserved
food, including beans and grains.
Pioneers also made their own clothes out
of wool, flax, old cloth, and leather.
#More to explore
American CivilWar Gold Rush
Oregon Trail Santa Fe Trail
Pirate
Pirates are criminals who attack ships at
sea. The most famous pirates sailed the
seas from the late 1500s to the early
1800s. A common symbol of piracy was
the Jolly Rogera black flag with a
white skull and crossbones.
Many of the ideas that people have
about pirates have come from books and
Pioneers on the prairies built houses out of
sod if they could not find trees to use for
wood.
88 Pioneer Life BRITANNICA STUDENT ENCYCLOPEDIA
movies. These tell of lives of adventure
and buried treasure. The stories are a
mix of fact and fiction. For example,
there are many colorful stories about
characters named Henry Morgan, Captain
Kidd, and Blackbeard. The stories
are mostly made up, but the characters
were actual people, and they were
pirates.
A Pirates Life
Real pirates used ships that were small
and swift. They could attack much
larger, better-armed ships. Armed with
swords and pistols, they went aboard the
other ship. Pirates not only stole a ships
cargothey also took the ship itself.
Pirates sold the ships that they captured
or made them into pirate ships. Sometimes
pirates held the ships passengers
or crew for ransom. This means that
they demanded money before they
would release their captives.
Some pirate crews obeyed strict rules on
their ships. Death could be the punishment
for stealing another mans share of
the loot. Women were not allowed on
board pirate ships. However, there were
some women pirates. They disguised
themselves as men in order to join pirate
crews.
History
In ancient times pirates from Phoenicia,
Greece, and Rome threatened ships in
the Mediterranean Sea. About a thousand
years ago some of the Viking warriors
in northern Europe committed
piracy.
Pirates are now criminals throughout the
world. However, there was once a legal
form of piracy called privateering. Privateers
were privately owned ships that
had a governments permission to attack
an enemys cargo ships. The privateers
owners and crew got to keep the cargo
they captured.
During the 1500s many Spanish ships
carried treasure from Mexico back to
Europe through the Caribbean Sea.
They were attacked by pirates and by
privateers such as the Englishman Sir
Francis Drake. Caribbean pirates of the
1600s were known as buccaneers.
In the Mediterranean Sea, dangerous
pirates received support from countries
along the Barbary Coast of North
Africa. These countries were called pirate
states. The British, French, and U.S.
Buccaneers
were originally
French,
Dutch, and
English sailors,
many of whom
had left their
countries to
escape the
law.
Blackbeard was an English pirate of the
early 1700s. His real name was Edward
Teach.
BRITANNICA STUDENT ENCYCLOPEDIA Pirate 89
navies ended piracy in this region in the
early 1800s.
Piracy and privateering decreased in the
1800s and 1900s, but it still exists. For
example, pirate attacks are still a threat
to shipping in the South China Sea and
off the northern coast of Africa near
Somalia. Modern pirates do not sail the
seas on pirate ships. Instead they attack
from the coast using speedboats and
small gunboats.
#More to explore
Drake, Francis
Pitcher Plant
Most plants get the nutrients that they
need from soil. Pitcher plants also get
nutrients by catching and digesting
insects. For this reason they are called
carnivorous, or meat-eating, plants.
There are several different species, or
kinds, of pitcher plant. Some are related
to the Venuss-flytrap, another carnivorous
plant. Many types of pitcher plant
grow in North and South America, but
some species grow in other parts of the
world.
Pitcher plants have structures shaped
like pitchers, bowls, or trumpets. In
some types the structures make up the
whole of the plants leaves. In other
types the structures are just part of the
leaves. In these types the structures grow
at the ends of stringlike parts called tendrils.
The purple, or common, pitcher
plant has green to reddish leaves and
purple-red flowers. The yellow, or trumpet,
pitcher plant has green, trumpetshaped
leaves and bright yellow flowers.
Most types of pitcher plant catch and
digest prey in a similar way. Glands in a
plants pitcher produce nectar. Nectar is
a sweet, sometimes sticky liquid that
attracts insects. Once an insect crawls
into the pitcher, it falls into a pool of
enzymes, or digestive juices. These
enzymes dissolve the insects soft parts.
The plant then absorbs the soft parts
through the walls of the pitcher.
#More to explore
Insect Plant Venuss-flytrap
Pizarro,
Francisco
Francisco Pizarro was a Spanish explorer
and adventurer. He conquered the Inca,
who had established an advanced
Pitcher plants have special
leaves that they use to trap
insects.
90 Pitcher Plant BRITANNICA STUDENT ENCYCLOPEDIA
civilization in South America. Pizarro
also founded the city of Lima, now the
capital of the South American country
Peru.
Francisco Pizarro was born in Trujillo,
Spain, in about 1475. His father was an
army captain. As a young man Pizarro
explored Central America.
Pizarro heard stories of a large and
wealthy empire in South America. In
1523 he made a plan to take the Inca
lands for Spain. Few people believed he
could succeed. Early expeditions failed,
but in 1531 he reached the lands of the
Inca in what is now Peru.
On November 15, 1531, Pizarro and his
men entered the Inca city of Cajamarca.
The Spaniards had better weapons and
easily defeated the Incas. Pizarro and his
men took gold and silver from the Inca
and killed their emperor. Pizarro went
on to take control of all of Peru.
In 1535 Pizarro founded the city of
Lima. The city was the center of Pizarros
new government. But there was
trouble between Pizarro and another
Spaniard named Diego de Almagro.
Almagros followers killed Pizarro on
June 26, 1541.
Plague
In the 1300s a disease called the plague
killed about 25 million people in
Europe. The plague became known as
the Black Death because of the black
patches that appeared on a victims skin.
Today people commonly use the word
plague in two ways. They use it to refer
to the disease itself. They also use it to
mean a large outbreak of any dangerous
disease. In the second case plague has
the same meaning as the word epidemic.
An old illustration shows a doctor
visiting a patient infected with
the plague.
Francisco Pizarro
BRITANNICA STUDENT ENCYCLOPEDIA Plague 91
Plague is caused by tiny living things
called bacteria. It is mostly a disease of
rats. Fleas that bite infected rats pick up
the plague bacteria. They then spread it
to other rats or to people through bites.
Infected people sometimes spread the
disease to others when they cough.
Once inside a persons body, the plague
bacteria enter the bloodstream. They
travel to the liver, spleen, kidneys,
lungs, and brain. Fever, weakness,
headache, and shaking chills quickly
develop. The most common form of
plague, called bubonic plague, also
causes swelling in a persons lymph
nodes. (The lymph nodes help to
protect the body from disease.) Swollen
nodes are called buboes, which is why
this form is called bubonic plague.
Pneumonic plague mostly infects the
lungs. Septicemic plague mainly infects
the bloodstream.
Outbreaks of the plague are now rare.
Because cities are cleaner than they used
to be, there are fewer infected rats and
fleas to spread the disease.
#More to explore
Bacteria Disease, Human Epidemic
Flea Rat
Planets
Planets are large natural objects that
orbit, or travel around, stars. Eight planets
orbit the star called the sun. In order
from the closest to the sun, these planets
are Mercury, Venus, Earth, Mars, Jupiter,
Saturn, Uranus, and Neptune. The
solar system is the collection of the sun
and the objects that orbit around it,
including the eight planets.
Planets differ from other objects such as
comets, asteroids, and meteors. In general,
planets are the largest objects in the
solar system after the sun. Most of them
orbit the sun in a path shaped like a
circle. They also have an atmosphere, or
a layer of gases surrounding them. Most
of the planets have at least one moon.
However, scientists have long debated
what makes a planet a planet. For many
years most people believed that there
were nine planets in the solar system.
This number included Pluto, which was
discovered in 1930. Pluto is a planetlike
object that is usually beyond Neptune.
But Pluto orbits the sun in a different
way than the eight planets do. Plutos
orbit overlaps the orbit of Neptune.
Also, Pluto is much smaller than the
eight planets. In 2006 a large group of
scientists decided to make a new category
for Pluto and similar objects in
the solar system. They called the objects
dwarf planets.
Types of Planets
There are two main types of planets in
the solar system. The four planets nearest
the sunMercury, Venus, Earth, and
Marsare called inner planets. They are
rocky planets about the size of Earth or
somewhat smaller. Jupiter, Saturn, Uranus,
and Neptune are called gas giants.
They are made up mostly of gases and
have no solid surfaces. They are all much
larger than Earth. Also, the gas giants
each have many moons and a system of
Rats traveling
aboard ships
have spread
plague to all
areas of the
world.
92 Planets BRITANNICA STUDENT ENCYCLOPEDIA
rings. Saturns rings are the largest and
best known.
Motion
Planets move in two ways. Each planet
travels around the sun in a path called
an orbit. The time it takes a planet to
complete one orbit is equal to a year on
that planet. For example, Earth completes
one orbit every 365 days, so a year
on Earth is that long.
Each planet also rotates, or spins about
its center. As the planet spins, it turns
different sides toward and then away
from the sun. In one day, a person on
the planet would see the sun appear
overhead, then set, then rise overhead
again.
On most planets, a day is roughly equal
to the time it takes the planet to complete
one rotation. For example, Earth
completes one rotation in about 24
hours, and a day on Earth lasts 24
hours. Mercury and Venus are different
because they spin slowly. By the time
they complete one rotation, they have
traveled very far in their orbit. A different
part of the planet is then facing the
sun. Therefore their day is not yet complete.
It takes much longer for the same
part of the planet to face the sun again.
Other Planets
In the 1900s scientists began to discover
planets outside the solar system. These
planets orbit around stars other than the
sun. It is difficult to tell much about
such planets because they are so far
away. Scientists can find them by looking
for certain tiny changes in the position
and light of stars. These changes
occur when a planet travels around a
star.
#More to explore
Earth Jupiter Mars Mercury
Neptune Saturn Solar System Sun
Uranus Venus
Mercury, Venus, Earth, and Mars are rocky planets. They are closer to the sun than Jupiter,
Saturn, Uranus, and Neptune, which are gas giant planets.
BRITANNICA STUDENT ENCYCLOPEDIA Planets 93
Plankton
Countless tiny living things float and
drift in the worlds oceans and other
bodies of water. These living things, or
organisms, are known as plankton. They
include plants, animals, and other kinds
of organisms. Plankton have an important
place in the food chain that supports
fish and other sea creaturesand
the people who eat them.
Types of Plankton
Plankton that is made up of plants or
plantlike organisms is called phytoplankton.
These organisms are often no
larger than a single cell. For example, a
single-celled type of algae, called a diatom,
is a common form of phytoplankton.
Phytoplankton floats near the
surface of the water. Like other plants it
uses sunlight to produce energy and
then releases the gas oxygen. This process
is called photosynthesis.
Plankton that is made up of animals or
animal-like organisms is called zooplankton.
Some of these organisms,
such as miniature crustaceans and
protozoans, are very small. Others, such
as jellyfish, are larger. Some fishes and
shellfish begin their lives as eggs or tiny
larvae. These eggs and larvae are also
zooplankton.
Besides phytoplankton and zooplankton,
bacteria and fungi float in the
worlds waters. These living things may
also be considered plankton.
Importance
Plankton is very important to life on
Earth. Phytoplankton produces much of
the oxygen that people and animals need
to survive. Plankton is also a major
source of food. Zooplankton feeds on
phytoplankton. In turn, fish and other
larger animals eat the zooplankton.
Many types of whale feed on zooplankton.
The huge whales catch the tiny
plankton by using a series of filters,
called baleen, in their mouths.
#More to explore
Algae Crustacean Food Chain
Photosynthesis Protozoan
Plant
Hundreds of thousands of different species,
or kinds, of plant grow on Earth.
Some plants are so tiny that people can
hardly see them. Others are trees that
grow as tall as skyscrapers.
Most plants have several things in common.
They need sunshine, water, and air
to grow. They are not able to move
around. Their cells have stiff walls made
of a tough material called cellulose. All
An almost transparent zooplankton is seen
in an enlarged view.
94 Plankton BRITANNICA STUDENT ENCYCLOPEDIA
green plants use the suns energy, water,
and a gas called carbon dioxide to make
their own food. This process is called
photosynthesis.
Where Plants Grow
Plants grow nearly everywhere on Earth.
Most plants grow in soil. They get the
water and nutrients they need from the
soil. But some plants do not need soil.
Plants called epiphytes grow on hard
surfaces, such as other plants or rocks.
They get most of the water and nutrients
they need from rain and the air.
Still other plants float in water. A few
species of plant live on and get their
nutrients from other plants.
Types
All plants belong to one of two main
groups, vascular plants and nonvascular
plants. Vascular plants have special tissues,
called xylem and phloem, that
carry water and food throughout the
plant. Vascular plants also have roots,
stems, and leaves. Vascular plants
include herbaceous plants, shrubs, and
trees. Herbaceous plants have soft stems.
Shrubs and trees have woody stems.
Nonvascular plants do not have xylem
or phloem. They also lack true roots,
stems, and leaves. Nonvascular plants
include mosses, liverworts, and hornworts.
They are generally small and grow
in moist places.
Reproduction
Plants reproduce, or make more of their
kind, either by seeds or spores. Seeds
and spores are small structures that
develop on plants and then fall off. They
then may grow into new plants. Seeds
are larger and more complex than
spores.
Most vascular plants reproduce by seeds.
Most seed-bearing plants grow flowers.
Fruits grow from the flowers, and seeds
grow inside the fruits.
Other vascular plants do not grow flowers
or fruits. For example, the plants
Most plants grow flowers of some kind. The
flowers are where the plant produces its
seeds.
Plants called conifers have cones that contain
the plants seeds.
BRITANNICA STUDENT ENCYCLOPEDIA Plant 95
called conifers form their seeds inside
cones. Conifers include pines, spruces,
firs, and similar trees and shrubs.
Nonvascular plants reproduce by spores.
A few kinds of vascular plants, such as
ferns, also reproduce by spores.
Sometimes plants can reproduce without
spores or seeds. Stems, leaves, or other
parts of a plant may grow into new
plants. For instance, strawberry plants
grow runners, or stems that creep along
the ground. These stems may form roots
and grow into new plants.
Importance
Without plants, no other living thing
could survive. Plants provide food for
people and animals. They also make the
oxygen that other living things breathe.
They produce the oxygen as part of the
process of photosynthesis.
Human beings use plants in countless
ways. They get many foods, drinks, and
flavorings from plants. They build
homes from wood and many other parts
of plants. People also burn wood for
heat and energy.
Many of the fibers used to make cloth
come from plants, especially cotton. A
type of cloth called linen is made from
the flax plant. Other useful things made
from plants include medicines, paper,
chewing gum, cork, rubber, and cocoa
butter.
A bean is the seed of a bean plant. When the seed germinates, or starts to grow, small
parts inside the seed grow into the root and stem. Most of the seed is used for food by the
young plant. When the plant grows green leaves it begins to make its own food by
photosynthesis.
96 Plant BRITANNICA STUDENT ENCYCLOPEDIA
People also use flowers for decoration.
They plant trees and flowers in their
yards and in large formal gardens.
#More to explore
Conifer Fern Fibers Flower
Garden Leaf Moss Photosynthesis
Root Seed Tree
Plastic
A plastic is a kind of material that is
made by people and can be formed into
almost any shape. Most plastics are
strong, long-lasting, and lightweight.
They resist damage by water, heat,
chemicals, and electricity. In addition,
plastics can be made in many colors.
Plastics have countless uses. Manufacturers
often use plastics in place of more
expensive materials. In nylon stockings,
for example, plastic takes the place of
silk. In vinyl house siding, plastic takes
the place of wood. In many automobile
parts, plastic takes the place of metal.
Making Plastics
Most plastics are made from chemicals
that come from petroleum (oil), natural
gas, or coal. Heating these chemicals
causes them to break down into molecules.
(Molecules are groups of two or
more atoms, which are the tiny building
blocks of everything.) Scientists then
join these molecules into chains. These
chains make up plastics. Different combinations
of molecules form different
kinds of plastic.
Plastics can be made into almost any
shape by heating them at a high temperature.
The heat softens the plastic,
which can then be poured into a mold.
As the plastic cools, it hardens. When
reheated, some types of plastic will
soften again. The plastic can then be
made into new shapes. Other types of
plastic will stay hard even when
reheated.
History
In 1869 JohnWesley Hyatt, a U.S.
inventor, made the first plastic. He
called it celluloid because he made it
from a plant material called cellulose. In
1909 a U.S. chemist named Leo H.
Baekeland developed the first plastic
made completely from synthetic
(human-made) materials. Baekeland
named the new material Bakelite. Scientists
have developed many more plastics
since then.
#More to explore
Molecule Petroleum
Some plastics
can be
recycled by
being ground
up and made
into such
products as
plastic lumber
and filler for
down jackets
and sleeping
bags.
Women sort plastic containers
for recycling.
BRITANNICA STUDENT ENCYCLOPEDIA Plastic 97
Plate Tectonics
The theory, or idea, of plate tectonics
says that Earths outer layer, or crust, is
made up of large, moving pieces called
plates. All of Earths land and water sit
on these plates. Under the plates is a
layer of melted rock called magma. The
plates float on top of the magma.
Plate Movements
As the plates move they come into
contact with each other.One of three
things happens at these plate boundaries.
First, the plates may move past each
other in opposite directions. Second, the
plates may crash into each other. In this
case the edge of one plate may slide
under another plate and be destroyed.Or
the two edges of the plates may rise up
and form mountains. Third, magma may
rise to the surface and force the plates to
move apart. As the rising magma cools, it
hardens to create new crust.
Earthquakes and volcanoes often happen
along plate edges. Many happen around
the plate under the Pacific Ocean.
Continental Drift
The plates have moved across Earths
surface for hundreds of millions of years.
As the plates move, the continents on
them move, too. This movement is
called continental drift.
Scientists think that all the continents
were once joined together in one big
continent. This supercontinent, called
Pangaea, had formed by about 250 million
years ago. Pangaea lay across a plate
boundary. Slowly, Pangaea broke apart
at this boundary. Rising magma filled in
the space, which eventually became the
floor of the Atlantic Ocean.
One piece of Pangaea included parts of
what are now North America, Europe,
and Asia. This piece, called Laurasia,
98 Plate Tectonics BRITANNICA STUDENT ENCYCLOPEDIA
drifted north. The other piece of Pangaea
included parts of what are now
Antarctica, Africa, South America, and
Australia. This part, called Gondwanaland,
drifted south. Eventually Laurasia
and Gondwanaland broke apart, too.
The continents then slowly moved to
the places they are now.
The continents continue to move today.
Scientists believe that in about 250 million
years they will join together again.
#More to explore
Continent Earth Earthquake
Mountain Volcano
Platypus
The platypus is an unusual mammal of
eastern Australia and Tasmania. The
platypus and its relatives the echidnas
are the only mammals that lay eggs.
The platypus also looks odd. It has a
bill and webbed feet like a duck and a
flat tail like a beaver. The platypus is
sometimes called a duckbill. Its
scientific name is Ornithorhyncus
anatinus.
The platypus has a squat body with
short legs. It is about 15 to 24 inches
(38 to 60 centimeters) long, including
the tail. It has thick brown fur. Its eyes,
ears, and nostrils close underwater.
Male platypuses have a sharp spur on
each back foot. The spurs are connected
to glands that make poison. The males
use their spurs to fight each other, especially
during mating season. The poison
can cause great pain.
When
European scientists
first saw
stuffed platypuses,
they
thought they
were fake.
They changed
their minds
only after seeing
live platypuses.
The plates that make up Earths crust are all different shapes and sizes.
BRITANNICA STUDENT ENCYCLOPEDIA Platypus 99
The platypus lives in and near rivers and
lakes. It eats insects, worms, shellfish,
fish, frogs, mollusks, and tadpoles. The
amount of food it eats every day is
almost equal to its own weight.
About two weeks after mating, a female
platypus lays one to three eggs. The
babies hatch about 6 to 10 days later.
Like other mammals, the mother feeds
her babies with milk.
#More to explore
Echidna Mammal
PLO
#see Palestine Liberation
Organization.
Plum
Plums are small fruits that may be sweet
or tart. People have eaten them since
ancient times. Some grow on trees that
are also valued for their beauty.
There are many varieties of plum. They
grow in Europe, Asia, and North
America. The leading producers of
plums are China, the United States,
Germany, and Romania. Most of the
plums grown in the United States come
from California.
Plums grow on trees and shrubs. These
plants come in many sizes, shapes, and
colors. Some shrubs are only 3 feet (1
meter) tall. Certain trees can be 33 feet
(10 meters) high. Their leaves may be
green, green with red or purple, or reddish
purple.
Most plum trees have thorny twigs.
These twigs are called spurs. Groups of
flowers grow on the spurs. They may be
white, pink, or red. The flowers develop
into the fruits, or plums.
Some plums are as small as a cherry.
Others are larger than a hens egg. Their
skin may be yellow, green, red, or dark
purple. Sometimes the skin has a whitish
coating. At the center of the fruit is a
The platypus uses its strong front limbs for
swimming as well as for digging.
Plums are popular fruits that are eaten fresh
or baked into pies and pastries.
100 PLO BRITANNICA STUDENT ENCYCLOPEDIA
hard stone, or pit. Inside the pit is a
seed. Cherries, peaches, and apricots are
other fruits that have pits.
Many people eat plums fresh. The fruits
are also made into jams, pastries, and
drinks. Some types of plums are dried to
make prunes.
#More to explore
Apricot Cherry Peach
Pluto
Pluto was considered the smallest planet
in the solar system until 2006. In that
year a large group of scientists decided
that Pluto was not a true planet. They
voted to call Pluto a dwarf planet
instead. Pluto is very far from Earth. It
is difficult to observe from Earth, even
with the most powerful telescopes.
Pluto orbits, or travels around, the sun
at an average distance of about 3.6 billion
miles (5.9 billion kilometers). It is
usually farther from the sun than the
planet Neptune. However, Plutos path
around the sun is shaped like an oval,
not a circle. Its distance from the sun
varies greatly as it orbits. About every
228 years Plutos orbit takes it closer to
the sun than Neptune. This last
occurred from 1979 to 1999.
Plutos oval orbit, small size, and other
unusual features make it unlike the eight
planets. In the 1990s scientists discovered
a ring of millions of small, icy
objects. These objects orbit the sun
beyond Neptune. Pluto seems to be
similar to some of them.
Physical Features
Plutos diameter, or distance through its
center, is about 1,430 miles (2,300 kilometers).
This is less than half the diameter
of the smallest planet, Mercury.
Scientists think that Pluto consists of
rocky material and frozen gases. Some
areas of Plutos surface are very bright,
while others are dark. The bright regions
are probably a frozen gas called nitrogen.
Pluto is so far from the sun that it
receives only a little sunlight. Scientists
believe that the average temperature on
its surface is about .387° F (.233° C).
Orbit and Spin
Like the planets, Pluto has two types of
motion: orbit and spin. Pluto completes
one orbit around the sun every 248
Earth years. That means that a year on
Pluto lasts 248 Earth years. Pluto spins
about its center slowly. It completes one
rotation in about 6.5 Earth days, so a
Pluto day lasts about 6.5 Earth days.
Pluto is very difficult to photograph clearly
because it is so small and so far away.
BRITANNICA STUDENT ENCYCLOPEDIA Pluto 101
Pluto is tilted so that it spins nearly on
its side.
Moons
Pluto has three known moons: Charon,
Nix, and Hydra. Pluto and Charon are
closer in size than any of the planets and
their moons.
Observation and Exploration
In 1930 U.S. astronomer Clyde Tombaugh
discovered Pluto with the use of a
telescope. Scientists believed that Pluto
was the ninth planet in the solar system.
In 2006 the United States launched a
spacecraft, called New Horizons, to
explore Pluto. The journey to Pluto was
expected to take about nine years. Later
in 2006 scientists decided that Pluto
should be called a dwarf planet rather
than a planet. This brought the number
of planets down from nine to eight.
#More to explore
Neptune Planets Solar System
Pluto, god
#see Hades.
Plymouth
Colony
Plymouth Colony was the first lasting
English settlement in New England. It
was located on the site of the modernday
city of Plymouth, Massachusetts.
The city lies on Plymouth Bay, 37 miles
(60 kilometers) southeast of Boston.
Plymouth was founded by people called
Puritans. The Puritans were an English
religious group that practiced a strict
form of Protestant Christianity. They
disagreed with some practices of the
Church of England. Some Puritans were
called Separatists because they wanted to
separate themselves from the Church of
England. The Separatists who left
England and founded Plymouth are
now known as the Pilgrims.
The Pilgrims crossed the Atlantic Ocean
on a ship called the Mayflower. They
reached Cape Cod in November 1620.
It took them until December 21 to
decide where to settle. They named the
chosen site Plymouth because the Mayflowers
voyage had started in Plymouth,
England. According to tradition, the
Pilgrims landed on Plymouth Rock on
December 26.
Winter had already set in when the Pilgrims
landed. They were short of food.
Many became ill. More than half the
Pilgrims did not survive the first winter.
The Pilgrims who did survive got help
Pluto is only
about twothirds
as large
as Earths
moon.
An old picture shows the landing of the Pilgrims
at Plymouth Rock.
102 Pluto, god BRITANNICA STUDENT ENCYCLOPEDIA
from Native Americans who lived
nearby. The Wampanoag people taught
the Pilgrims how to plant crops, fish,
and hunt.
Between 1630 and 1640 the Plymouth
colonists made a good living by trading
with the new Massachusetts Bay Colony.
In 1691 Plymouth Colony became a
part of the Massachusetts Bay Colony.
..More to explore
Colony Massachusetts Bay Colony
Mayflower Puritans Wampanoag
Pneumonia
Pneumonia is an inflammation, or swelling,
of tissue in the lungs. An infection
usually causes this inflammation. Pneumonia
makes breathing difficult and
even painful.
The main symptoms, or signs, of pneumonia
are coughing, fever, chest pain,
and shortness of breath. People with
pneumonia may also have headaches,
sweating, and confusion.
Pneumonia is not a single disease. Many
things, including bacteria, viruses, and
fungi, can infect the lungs and cause
pneumonia. The infection can spread to
others when the infected person coughs
or sneezes.
Substances called vaccines can prevent
some forms of pneumonia.Washing
ones hands may also help to stop infections
that lead to pneumonia. In addition,
people should always cover their
mouth when sneezing or coughing.
Treatment for pneumonia includes taking
medicines that fight the infection
and getting plenty of rest. Some people
with pneumonia may need to go to a
hospital for drugs and extra oxygen.
With medical treatment, most people
recover from pneumonia within a few
weeks.
..More to explore
Cough Lung Vaccine
Pocahontas
Pocahontas may be the most famous
Native American in history. She helped
to make peace between Native Americans
and the English colonists of
Jamestown, Virginia.
Pocahontas was born in about 1595.
Her father, Powhatan, was a powerful
Indian leader. Pocahontas was about 12
years old when she first met the colonists.
The English leader John Smith
Doctors find pneumonia by looking at chest
X-rays. The lung at left is infected.
Viruses cause
about half of
all cases of
pneumonia.
BRITANNICA STUDENT ENCYCLOPEDIA Pocahontas 103
later claimed that young Pocahontas
saved his life. Smith said that Powhatans
men took him prisoner and were
going to kill him. But Pocahontas got
her father to free him.
The story has become part of American
folklore, but it may not be true. Smith
liked to tell tales. Nevertheless, Pocahontas
was helpful. She brought food to the
settlers as their supply ran low. She also
warned them of possible Indian attacks.
Smith returned to England in 1609.
Relations between the settlers and
Powhatan grew worse. Pocahontas probably
stopped visiting her English friends.
In 1613 an English sailor took Pocahontas
prisoner. The sailor hoped that
Powhatan would release some English
prisoners in return for Pocahontas. He
took Pocahontas to Jamestown. The
colonists taught her Christianity. In
1614 Pocahontas married a colonist
named John Rolfe. The wedding began
eight years of peace between the Native
Americans and the colonists.
In 1616 the Rolfes sailed to England.
The king and queen welcomed Pocahontas.
But while in England Pocahontas
caught the disease smallpox. She died
in Gravesend, England, in March 1617.
..More to explore
Native Americans
Podgorica
Population
(2007 estimate)
174,000
Podgorica is the capital of Montenegro.
The city is located in the southern part
of the country, on a plain surrounded by
mountains.
Although it is a very old city most of the
buildings in Podgorica are less than 100
years old. Much of the city was
destroyed duringWorldWar II (1939
45). Only a clocktower, a mosque, and a
few houses survived. Today Podgorica is
a modern city that is home to several art
galleries, theaters, and museums.
Podgoricas economy is based on services
such as banking, government, and telecommunications.
Factories process aluminum
and produce medicines.
Pocahontas
104 Podgorica BRITANNICA STUDENT ENCYCLOPEDIA
The earliest records for the city show
that the site was a caravan stop during
ancient times. The city was first called
Podgorica in 1326. In 1474 it became
part of the Turkish Ottoman Empire.
Four hundred years later Podgorica was
awarded to Montenegro after a war
between Turkey and several states,
including Montenegro.
The city was occupied by Austria during
WorldWar I (191418). After the war
Montenegro became part of the Kingdom
of Serbs, Croats, and Slovenes.
That later became Yugoslavia.
Podgorica suffered major damage during
WorldWar II. After that war the city
was renamed Titograd in honor of Josip
Broz Tito. Tito was the Communist
leader of Yugoslavia from 1945 to 1980.
After the collapse of Communism in
1992 the city once again became
Podgorica. When Montenegro became
an independent country in 2006
Podgorica remained its capital.
..More to explore
Montenegro Yugoslavia
Poetry
Poetry is a type of literature, or artistic
writing, that attempts to stir a readers
imagination or emotions. The poet does
this by carefully choosing and arranging
language for its meaning, sound, and
rhythm. Poetry has many forms and
styles. Poems may tell a story or express
feelings. They may be serious or funny.
One thing that makes poems different
from other types of writing is their
structure. The words of a poem are
arranged in lines and groups of lines,
called stanzas. For example, here is the
first stanza of the poem From a Railway
Carriage, about an exciting train ride,
by Robert Louis Stevenson:
Faster than fairies, faster than witches,
Bridges and houses, hedges and
ditches;
And charging along like troops in a
battle,
All through the meadows the horses
and cattle:
All of the sights of the hill and the
plain
Fly as thick as driving rain;
And ever again, in the wink of an eye
Painted stations whistle by.
Rhythm
Poets use patterns of rhythm to create
various effects. Some syllables, or parts
of words, in a line receive more emphasis,
or stress, than others. For example,
in the phrase hedges and ditches, the
hedg and ditch sounds are stressed
more than the other sounds. The stressing
of certain syllables creates a rhythm.
A poems rhythm is called its meter.
Sound
Poets also use patterns of sound. Some
poems rhyme, or use two or more words
that end with the same sound, such as
hat and bat. A poem may repeat
sounds in many other ways. For
example, in high as a kite, the long i
sound is repeated. In a stroke of luck,
the k sound is repeated. A group of
The words of
songs can
sometimes be
studied as
poetry.
BRITANNICA STUDENT ENCYCLOPEDIA Poetry 105
words can also start with the same
sound, as in a dark and dangerous day.
Form
Some poems follow strict patterns of
meter, sound, and length. For instance,
the sonnet is a form of poetry that consists
of 14 lines of 10 syllables each. It
also follows a set pattern of rhythm and
rhyme. Haiku is a form of poetry with
three lines. Each line has a fixed number
of syllables: five syllables in the first and
third lines and seven syllables in the
second line.
Some poems do not use any set form.
Instead they use rhythms that are closer
to those of everyday speech. These
poems are known as free verse. However,
the poet may still carefully arrange the
sounds and rhythm.
..More to explore
Literature Nursery Rhyme Writing
Poison
A poison is a substance that causes harm
when it enters the body or touches the
skin. Certain household cleaners are
poisons. Parts of certain plants are poisons.
The venoms in certain snakes, spiders,
insects, fish, and other animals are
poisons. Foods that have spoiled also
may have poisons in them.
Some poisons, such as the oil on the
leaves of poison ivy, cause rashes or pain.
Other poisons, such as those in certain
molds and mushrooms, cause serious
illness or death.
Some poisons can harm people in seconds.
Others can build up over days,
weeks, or months and then harm
people. For example, a person feels the
sting of a poisonous scorpion right away.
But if a person regularly breathes in
paint dust that has lead in it, the lead
will gradually build up in the body. The
damage will happen slowly.
A person who thinks someone has been
poisoned should immediately telephone
a poison control center or emergency
call center. The person should be ready
to explain what happened and wait for
instructions. Doctors can treat many
types of poisoning.
Still, people should learn to identify
poisons in order to prevent poisoning. It
is especially important to keep medicines,
household cleaners, and other
poisonous substances out of the reach of
children.
..More to explore
Food Poisoning
The skull-and-crossbones symbol
is often used as a warning
that something is poisonous.
106 Poison BRITANNICA STUDENT ENCYCLOPEDIA
Poland
The Republic of Poland is a country in
eastern Europe. The outline of Poland
often changed during its history. At
times it did not exist at all when foreign
powers took control of the land. In the
late 20th century Poland led the fight
against Communism, a strict form of
government, in eastern Europe. Polands
capital is Warsaw.
Geography
Poland borders Germany, the Czech
Republic, Slovakia, Ukraine, Belarus,
Lithuania, and Russia. The Baltic Sea
lies to the north.
Most of Poland is low and flat. Hills
and mountains rise in the south. The
Tatra Mountains, on the border with
Slovakia, are the highest range. Polands
main rivers are the Vistula and the
Oder. Both flow northward into the
Baltic Sea.
Poland has warm summers and cold,
snowy winters. The mountains get the
most rain and snow.
Plants and Animals
Forests cover about one quarter of the
country. Larch, beech, oak, birch, pine,
and spruce are common trees. The animals
of the forests include deer, wild
pigs, beavers, and elk. Bears, wildcats,
and chamois (goatlike animals) roam the
mountains. Small numbers of wisent, or
European bison, live in the east.
People
Most of Polands people are Poles. They
speak Polish, a language related to Czech
and Slovak. Small numbers of Ukrainians,
Germans, and Belarusians also live
in the country. The main religion is
Roman Catholicism. More than half of
the population lives in cities and towns.
Economy
Services such as banking, communications,
and tourism are the fastestgrowing
parts of Polands economy.
Manufacturing is also important. Factories
make food products, machinery,
transportation equipment, iron and
steel, and chemicals. The country also
mines coal, sulfur, copper, and silver.
Agriculture is a small part of the
economy, but many Poles still work as
farmers. The main crops include pota-
BRITANNICA STUDENT ENCYCLOPEDIA Poland 107
toes, wheat, and sugar beets. Farmers
produce pork, eggs, and dairy products
as well.
History
People called Slavs came to what is now
Poland more than 3,000 years ago. The
written history of Poland begins in the
AD 900s. At that time the Piast dynasty
(ruling family) gained power in the
region. The Piast ruler adopted
Christianity in 966.
The Piast dynasty ruled Poland until the
1300s. In 1386 Polands Queen Jadwiga
married Wladyslaw II Jagiello, the grand
duke of Lithuania. The marriage united
Poland and Lithuania, which were
known together as the Commonwealth.
The marriage also started the Jagiellon
dynasty. The Jagiellon rulers controlled
Hungary and Bohemia (now part of the
Czech Republic). They fought off powerful
enemies.
Weakened Poland
After the Jagiellon dynasty ended in
1572, weak kings ruled the Commonwealth.
In the 1600s the Commonwealth
fought costly wars with Sweden,
Russia, and Turkey.
In 1772 Russia, Prussia (part of Germany),
and Austria each took part of the
Commonwealths territory. The three
powers divided the land again in 1793.
After a third division in 1795, Poland no
longer existed as a separate state.
The Poles formed a new Polish kingdom
in 1815, but the Russians controlled it.
The Poles revolted against Russian rule
several times. Russia responded by
stamping out Polish culture. For
example, Russia ordered that Polish
schools use the Russian language.
Rebirth of Poland
WorldWar I (191418) led to the
rebirth of Poland. The war weakened
Children wear traditional clothing at a ceremony
in Poland.
Tourists visit an old monastery of
the Roman Catholic church in
Poland. A monastery is a home
for monks.
Facts About
POLAND
Population
(2008 estimate)
38,111,000
Area
120,728 sq mi
(312,685 sq km)
Capital
Warsaw
Form of
government
Republic
Major cities
Warsaw, Lodz,
Krakow,
Wroclaw, Pozna!
108 Poland BRITANNICA STUDENT ENCYCLOPEDIA
Russia, Austria, and Germany. Poland
became an independent republic in
1918.
WorldWar II
Germany and Russia (by then part of
the Soviet Union) still wanted parts of
Polands land. In 1939 the two countries
secretly agreed to divide Poland between
them. In September 1939 Germany
invaded western Poland. The invasion
startedWorldWar II. Soon the Soviet
Union took over the east.
In 1941 Germany turned against the
Soviet Union and took over all of
Poland. The Nazis of Germany killed
about 3 million Polish Jews. This was
part of a massacre called the Holocaust.
Communism
The Soviet Union drove the German
army out of Poland in 1945. After the
war Poland lost its eastern lands to the
Soviet Union. However, it gained German
lands in the west. Meanwhile, the
Soviet Union set up a Communist government
in Poland. Secret police
arrested and sometimes killed people
who disagreed with the government.
In 1980 an electrician named Lech
Walesa helped bring together almost 10
million Polish workers into an organization
called Solidarity. It protested the
Communist government. In 1981 the
government made the group illegal.
Modern Poland
After more protests the government
made Solidarity legal in 1989.
Communism soon collapsed. In 1990
Poland electedWalesa president. He and
later leaders worked to improve the
economy. Poland joined the European
Union in 2004.
#More to explore
Communism European Union
Holocaust Lithuania Warsaw
WorldWar II
966 1386 177295 1918 1939 1945 1989
Poland adopts
Christianity.
Poland and
Lithuania unite.
Russia, Austria,
and Prussia
take Polands
land; Poland
ceases to exist.
Poland is
reborn as an
independent
republic.
Germany
invades
Poland.
Poland
becomes a
Communist
country.
Polands
Communist
government
falls.
T I M E L I N E
BRITANNICA STUDENT ENCYCLOPEDIA Poland 109
Polar Exploration
Polar exploration is the exploration of
the lands around the North and South
poles. The poles are the coldest and
most remote regions on Earth. The
North Pole is in the Arctic Ocean,
which is covered by a huge, floating ice
sheet. The South Pole is on land, in the
frozen continent of Antarctica.
Some early polar explorers used dogsleds
or went on foot. This was dangerous, as
huge cracks in the ice could swallow
dogs, sleds, and people. Other explorers
used ships. This also was dangerous, as
floating ice could wreck the ships. Later
explorers used icebreakers (ships that can
cut through ice), dirigibles (aircraft that
float like balloons), airplanes, and snowmobiles.
Reasons for Polar Exploration
People made early polar explorations for
a number of reasons. Some people
wanted the fame that would come from
being the first to reach an unknown
land. Others were hoping to discover
shorter sailing routes from Europe to
eastern Asia. Still others sought to get
rich from whale and seal hunting. More
recently, people began exploring the
polar regions to gather scientific information.
Many adventurous explorers
died or risked their lives trying to
achieve these goals.
Exploring the Arctic
Native peoples have lived in the regions
around the Arctic Ocean for thousands
of years. The first outsider to reach the
Arctic was probably an ancient Greek
named Pytheas. He reached Norway or
Iceland in about 300 BC. The Vikings of
Norway traveled to Iceland and Greenland
in the 800s and 900s.
By the 1500s the Dutch and the English
were venturing to the Arctic in search of
trade routes. In 187879 a Swedish
explorer, Baron Adolf Erik Nordenskiold,
sailed from Europe through the
Arctic Ocean to the Pacific Ocean. This
route was called the Northeast Passage.
In 1905 the Norwegian explorer Roald
Amundsen became the first to sail
through the Northwest Passage. This
was a route through the Arctic from the
Atlantic Ocean to the Pacific Ocean.
The U.S. explorer Robert E. Peary
claimed to be the first person to reach
the North Pole, in 1909. Peary, Mat-
On May 1,
1986,
members of
the Steger
International
North Pole
Expedition
reached the
North Pole
assisted only
by dogs.
Matthew Henson (center) waves from the
North Pole in 1909. With him stand other
members of the group led by Robert E. Peary.
110 Polar Exploration BRITANNICA STUDENT ENCYCLOPEDIA
thew Henson, and four Eskimo (Inuit)
made the last part of the trip on
dogsleds. Some people later questioned
whether Peary really did reach the pole.
In 1926 Amundsen and two companions
flew over the North Pole in a dirigible.
In 1937 pilots from the Soviet
Union flew an airplane to the United
States over the North Pole. In 1958 a
U.S. submarine became the first ship to
cross the North Pole under the Arctic ice
sheet.
Exploring Antarctica
Several explorers first saw Antarctica in
1820. People first landed on the continent
in 1895. British explorers Robert F.
Scott and Ernest Henry Shackleton each
led expeditions there in the early 1900s.
Scott reached the South Pole on January
18, 1912. He had hoped to be the first
to do so. However, Roald Amundsen
and four companions had reached the
pole a month earlier, on December 14,
1911. Scott and his men died on their
return trip.
In 1928 the U.S. explorer Richard E.
Byrd set up a base on an ice shelf on
Antarcticas coast. Byrd made the first
flight over the South Pole in 1929.
Meanwhile, many countries were
becoming interested in the scientific
study of Antarctica. During 195758
scientists from several countries set up
50 bases throughout Antarctica for scientific
research. In 1959 a number of
countries signed the Antarctic Treaty.
This agreement preserves the entire Antarctic
continent for scientific research.
#More to explore
Amundsen, Roald Antarctica Arctic
Ocean Eskimo Henson, Matthew
Peary, Robert E.
Police
The police are people whose job is to
make sure that citizens follow the law
and do not harm others. Police officers
work for the governments of towns,
cities, counties, states, and countries.
Police Today
The police have many tasks. First, they
patrol, or keep watch over, streets and
neighborhoods. Most police officers
patrol in cars. But sometimes they patrol
on foot, on horseback, on motorcycles,
or on bicycles. Second, police go to the
scenes of crimes and emergencies to
catch criminals and to help victims.
Third, police investigate, or study,
crimes to find out who committed
Ross Island is in the Ross Sea, just off the
coast of Antarctica. Several explorers have
used the island as a base.
BRITANNICA STUDENT ENCYCLOPEDIA Police 111
them. Police fight many types of crimes.
One of the most serious is terrorism.
(Terrorists use violence to try to affect
peoples beliefs or ways of life.)
Some police officers wear uniforms.
Others work in everyday clothing, called
plain clothes. Many police officers carry
handcuffs, a notebook, and a two-way
radio. Some also carry a handgun. Some
use a stun gun or pepper spray to stop
criminals without seriously harming
them. Some officers travel with specially
trained police dogs.
Police officers whose main job is investigating
crimes are called detectives.
Detectives usually work in plain clothes.
They talk to witnesses, or people who
may know something about the crimes.
They also talk to suspects, or people
they think may be guilty of the crimes.
Detectives sometimes use hidden microphones
or cameras to record the conversations
and actions of suspects.
At the scene of a crime, detectives look
for evidence, or clues to help them figure
out who committed the crime. Evidence
includes fingerprints, footprints,
bits of cloth, blood, hair, and anything
else that the criminal may have left
behind. When they find the person who
they think committed the crime, they
arrest that person. The person may then
be put on trial to determine if they did
commit the crime. During the trial, the
detectives and other police officers often
talk about the evidence they gathered
when they were investigating the crime.
History
Ancient peoples, including the Sumerians,
the Egyptians, and the Babylonians,
had police forces. Their job was
mostly to make sure that the people
followed the rulers orders. Emperor
Augustus of Rome put together a large
and well-organized police force in 7 BC.
Police officers block off a street in London,
England, while they investigate terrorist
attacks.
A police officer at a crime scene
brushes powder on a door in the
hope of finding fingerprints.
Police use fingerprints to identify
criminals.
112 Police BRITANNICA STUDENT ENCYCLOPEDIA
Over the centuries other cities and
countries set up police forces.
By the 1800s police were using many
modern tools and methods to do their
jobs. Police first used telephones in
Washington, D.C., in 1878. Fingerprinting
was introduced in the 1890s.
Police first rode in cars in the United
States in 1899. In the 1920s police
started using ballisticsthe study of
bullets to match them to the gun that
fired them. In the 1930s police began
using small two-way radios to communicate
with each other. Today police
depend on computers to keep records
and to search for information while solving
crimes.
#More to explore
Crime Government Law
Polio
Polio, called poliomyelitis in full, is a
disease caused by a tiny germ called a
virus. In the past, polio attacked many
children and left them paralyzed, or
unable to move their muscles.
The first symptoms, or signs, of polio
can be very mild. In fact, many people
who get the disease feel fine. Others
think they have caught a cold. In serious
cases people complain of having pains in
their neck, back, and legs. The pains are
a sign that the polio virus has attacked
the spine. The spine has nerves that control
the muscles of the body. If the virus
damages those nerves, the muscles
become weak.
Some people recover their muscle
strength.Others become permanently
paralyzed. If the virus damages the nerves
controlling the leg muscles, the person
can no longer walk. If the virus attacks
the nerves controlling the lungs, the
person cannot breathe without the help
of a machine. There is no cure for polio.
As recently as the 1950s polio affected
thousands of people in the United
States. Polio affected mostly children,
but some adults got it as well. The U.S.
president Franklin D. Roosevelt was
paralyzed by polio as an adult.
In the early 1950s the medical researcher
Jonas Salk made a substance called a
vaccine to protect people from the virus
that causes polio. Polio has disappeared
from most countries because almost
every child is vaccinated.
#More to explore
Disease, Human Salk, Jonas Virus
A child wears a brace on a leg
that has been affected by polio.
BRITANNICA STUDENT ENCYCLOPEDIA Polio 113
Political Party
Political parties are groups of people that
work to be in charge of a government.
The main way in which a political party
gains power is through the election of its
members to office. Office is a word for
a government positionfor example,
the presidency or a seat in a legislature
(lawmaking body). In many countries
the party with the most members in the
legislature has great control over the government.
Government leaders are the most powerful
members of political parties. But
ordinary voters may belong to political
parties, too. Party members usually have
similar beliefs about the role of government
and how it should be run.
The number of political parties differs
from country to country. Some countries
have several parties, and all of them
may be represented in the government.
Many European countries have three or
more major political parties.
Other countries function with only two
major parties. In the United States the
two main political parties are the Democratic
Party and the Republican Party.
Other parties, called third parties, may
exist in such a system. However, most
people support either of the two main
parties. It is almost impossible for third
parties to gain power.
Still other countries have one-party systems.
China, Cuba, and several African
countries have such systems. There all
members of the government must
belong to the same party. People might
form opposing parties, but their candidates
may not run for office. Opposing
parties may even be illegal. Such groups
are sometimes called underground
political parties.
#More to explore
Government Legislature Voting
Polk, James K.
James K. Polk was the 11th U.S. president.
During his term the United States
won a war with Mexico and gained
much land along the Pacific coast and in
the Southwest.
Early Life
James Knox Polk was born on
November 2, 1795, in Mecklenburg
County, North Carolina. He was the
eldest child of Samuel and Jane Knox
Polk. At age 11 he moved with his
In the United
States, the
Republican
Partys symbol
is an elephant.
The Democratic
Partys
symbol is a
donkey.
A portion of a ballot from a U.S.
presidential election shows candidates
from large and small
political parties.
114 Political Party BRITANNICA STUDENT ENCYCLOPEDIA
family to Tennessee. He graduated in
1818 from the University of North
Carolina.
Polk then returned to Tennessee and
studied law. In 1820 he started a law
practice in Columbia, Tennessee. Four
years later he married Sarah Childress.
They had no children.
Political Career
A Democrat, Polk was elected to the
Tennessee legislature in 1823. A year
later he was elected to the U.S. House of
Representatives. He served there for 14
years, including four years as speaker
(leader) of the House. In 1839 Polk was
elected governor of Tennessee. He failed
to win reelection in 1841 and again in
1843.
Presidency
The Democrats planned to choose Polk
to run for vice president in 1844. A dispute
over the presidential candidate,
however, led the Democrats to ask Polk
to run for president instead. In the election
Polk defeated Henry Clay of the
Whig Party.
As president, Polk settled a fight over the
Oregon Territory. The United States and
Great Britain both claimed the land.
November 2, June 15,
1795 1824 1839 1844 1846 1848 1849
Polk is born in
Mecklenburg
County, North
Carolina.
Polk is elected
to the U.S.
House of
Representatives.
Polk becomes
governor of
Tennessee.
Polk is elected
president.
Polk settles the
Oregon
dispute.
The Mexican
War ends;
the United
States gains
land.
Polk dies in
Nashville,
Tennessee.
T I M E L I N E
James K. Polk was the 11th president of the
United States.
BRITANNICA STUDENT ENCYCLOPEDIA Polk, James K. 115
Polk proposed dividing the territory at
the line of 49° north latitude (the 49th
parallel). After refusing, Britain finally
accepted Polks offer. In 1846 the
United States received the part of
Oregon south of the 49th parallel.
Polk also gained Texas and much of the
Southwest for the United States. In
1845 the United States admitted Texas,
formerly part of Mexico, as a state. That
action caused the MexicanWar of
184648. After the United States
defeated Mexico, it bought more Mexican
land. That territory included parts
of what are now Arizona, California,
Colorado, Nevada, New Mexico, and
Utah.
Retirement
At the end of his term in 1849, Polk
retired to his home in Nashville, Tennessee.
He died soon afterward, on June 15,
1849.
#More to explore
MexicanWar Oregon United States
Pollen
Pollen is the substance that causes plants
to form seeds. New plants then can grow
from the seeds. Both flowering plants
and conifers (plants that grow seeds
inside cones) make pollen. A grain of
pollen is so tiny that it is best viewed
through a microscope.
Pollination
The male parts of a plant, called stamens,
make pollen grains. These grains
contain sperm cells. The female parts of
a plant, called pistils, contain egg cells.
During pollination, pollen grains travel
from the male parts to the female parts.
There, a sperm cell from the pollen joins
with an egg cell. The fertilized cell then
develops into a seed.
Some plants have only male or only
female parts. They need help transporting
pollen between plants. This is called
cross-pollination. Other plants have
both male and female parts. They can
pollinate themselves. This is called selfpollination.
Pollen travels in many ways.Wind,
water, and animals can carry it. Many
plants have fragrant or colorful flowers
to attract birds or insects (especially
bees). These animals come to drink a
sweet liquid called nectar. While an animal
drinks the nectar, pollen from the
flower sticks to its body. The animal
Polk was 49
years old
when he
became president.
He was
the youngest
U.S. president
up to that
time.
A plant can pollinate itself if it has both stamens
and pistils.
116 Pollen BRITANNICA STUDENT ENCYCLOPEDIA
carries the pollen to other flowers when
it moves on for more food.
Hay Fever
Some people have an allergic reaction
when they breathe in pollen. They may
sneeze, get a stuffy nose, or have itchy
eyes. This condition is known as hay
fever. People with hay fever suffer most
during seasons when there is a lot of
pollen in the air.
#More to explore
Allergy Conifer Flower Plant Seed
Pollution
Pollution happens when the environment
is contaminated, or dirtied, by
waste, chemicals, and other harmful
substances. Pollution is a problem all
over the world. But it is especially bad in
large cities with a lot of industries and
automobiles. There are three main forms
of pollution: air, water, and land.
Air Pollution
Wildfires, volcanoes, and industrial
chemicals cause some air pollution. But
most air pollution comes from burning
fossil fuels. These include coal, oil, and
natural gas. Factories, electrical plants,
and automobiles burn these fuels for
power. The burning of fossil fuels may
release solid particles, such as ash and
soot, into the air. It also may release
harmful gases. This type of pollution
may be seen in the form of smog over
Most plants depend on a carrier, such as a bee, to bring pollen to them from another plant.
The smokestacks of chemical plants send
pollution into the air.
BRITANNICA STUDENT ENCYCLOPEDIA Pollution 117
big cities. The word smog is a combination
of smoke and fog. Smog-filled
air is hazy, or hard to see through.
Air pollution may cause such diseases as
cancer and asthma. Air pollution also
leads to acid rain, or polluted rain that
can harm living things. In addition, air
pollution may be a cause of global
warming, which is a steady rise in
Earths average temperature. Finally, air
pollution damages a part of the
atmosphere called the ozone layer. The
ozone layer is important because it
protects Earth against harmful rays
from the sun.
Water Pollution
Some causes of water pollution are easy
to see. People dump garbage and sewage
into creeks, rivers, ponds, lakes, and
oceans. Factories or cities sometimes
release oils, poisonous chemicals, and
other wastes into water.
Other causes of water pollution are not
so direct. The use of chemicals in farming
is one example. Farmers use some
chemicals as fertilizers, or substances
added to soil to help crops grow. They
use other chemicals as pesticides or herbicides.
These are substances that kill
pests or weeds. When these chemicals
seep into the ground, they may make
the groundwater unfit to drink. Chemicals
also may drain into rivers and lakes,
where they can harm fish and other
forms of life.
Land Pollution
Littering, or tossing garbage on the
ground, is a form of land pollution. Litter
is unpleasant to look at. It also can
destroy the habitats, or homes, of plants
and animals.
The buildup of dangerous chemicals in
the ground is another form of land pollution.
The chemicals may come from
farms or factories. These chemicals can
spread to plants and animals. They may
even harm people who eat the contaminated
plants and animals.
Controlling Pollution
Many governments, environmental
groups, and ordinary people are working
to control pollution. Governments have
passed laws to keep people from releasing
dangerous chemicals into the environment.
Some companies and people
are trying to use fewer fossil fuels.
Instead they are getting power from the
sun, wind, water, and other energy
sources that produce less pollution.
Many communities use recycling to
reduce pollution. Recycling is the process
of making new products out of used
Workers clean a seacoast that is coated
with oil spilled by a tanker ship.
118 Pollution BRITANNICA STUDENT ENCYCLOPEDIA
writer who helped him to describe his
travels in a book. Polo was released from
prison in 1299. He returned to Venice,
where he died on January 8, 1324.
#More to explore
China Mongol Empire Venice
Pomo
The Pomo are Native Americans of
northern California. There are about 72
separate tribes grouped together as
Pomo.
Pomo along the coast of the Pacific
Ocean traditionally lived in cone-shaped
homes made from the wood and bark of
redwood trees. The Pomo farther inland
lived in larger rectangular houses built
from poles, brush, and grass. The Pomo
fished and hunted deer, birds, and small
animals. They also gathered and ate
many types of wild plants.
Spanish explorers may have visited the
Pomo in 1542. In 1811 or 1812 Russian
fur traders founded Fort Ross in Pomo
territory. The Russians forced the Pomo
to hunt sea animals and give them the
animals furs.
A few years later Spanish priests built a
mission in the area. They got some
Pomo to live and work at the mission.
The Spanish often treated the Pomo
harshly. In addition, many Pomo died
from smallpox and other diseases
brought by the Spanish.
Gold was discovered in California in
1848. Thousands of U.S. settlers rushed
to the area, taking Pomo lands. The settlers
killed many Pomo. They forced
other Pomo to work in mines as slaves.
At the end of the 20th century there
were about 5,000 Pomo living in the
United States.
#More to explore
Missions, Spanish Native Americans
Pompeii
Pompeii was an ancient city in southern
Italy. In AD 79 a volcano called Mount
Vesuvius erupted close by. Thousands of
people died, and the city was buried.
Archaeologists later cleared away much
of the rubble. They uncovered ruins that
gave historians a look at life in the
Roman Empire.
The Ancient City
People lived in the Pompeii region in
prehistoric times. The Romans took
control of Pompeii in about 290 BC.
An old photograph shows a
Pomo woman gathering seeds
into a basket.
120 Pomo BRITANNICA STUDENT ENCYCLOPEDIA
They brought Roman architecture and
culture to the city.
Mount Vesuvius began to erupt on
August 24, AD 79. The eruption lasted
for several days. Poison gases from Vesuvius
choked many people. Then volcanic
stones and ashes covered the city. When
the eruption ended, Pompeii was buried
to a depth of 19 to 23 feet (6 to 7
meters).
The Archaeological Site
The debris protected Pompeii from vandals
and the weather for hundreds of
years. An Italian architect discovered the
ruins in the late 1500s. Archaeologists
began excavating, or digging out, the
city in 1748. The work at Pompeii and
Herculaneum, another city buried by
Vesuvius, marked the start of modern
archaeology.
The early excavations were not well
organized. Many early diggers were
interested only in finding treasure. After
1860, however, archaeologists made sure
that the work was done in an orderly
way. By the 1990s about two thirds of
the city had been excavated.
Historians have learned a lot about the
Roman world from the excavations.
They can walk down streets and look at
temples, public baths, houses, and
shops. The digging uncovered charred
nuts and fruits in market stalls and
loaves of bread in bakeries. Historians
have also learned about life in Pompeii
from statues and pictures.
#More to explore
Archaeology Rome, Ancient
Vesuvius, Mount
Ponca
The Ponca are Native Americans of
Oklahoma and Nebraska. They once
lived along the coast of the Atlantic
Ocean, but they later moved west.
The Ponca lived in earth-covered lodges.
They fished, hunted, and gathered wild
plants for food. In spring and autumn
they lived in portable tepees while hunting
bison (buffalo).
By the late 1600s the Ponca were living
in what is now Minnesota.Warfare with
the Sioux people forced the Ponca to
move even farther west. They settled in
southwestern Minnesota and the Black
Hills of South Dakota.
The ancient
city of Stabiae
was also
destroyed by
the eruption of
Mount
Vesuvius.
Many of the buildings that were excavated
in Pompeii are now open to the public. On
display in one room is a plaster cast of one
of the people who died in the city. The
people who excavated Pompeii discovered
that the ashes that covered the city made
molds of some of the people who died
there. Scientists later made models from
those molds.
BRITANNICA STUDENT ENCYCLOPEDIA Ponca 121
By the early 1800s diseases brought by
white settlers had reduced the tribe from
about 800 people to about 200. In 1877
the U.S. government forced the Ponca
to move to Indian Territory (now Oklahoma).
Some Ponca left Indian Territory
and traveled north on foot for 600 miles
(965 kilometers) to eastern Nebraska.
The Ponca who settled in Nebraska
became known as the Northern Ponca.
The Ponca who stayed in Indian Territory
became known as the Southern
Ponca. By the late 20th century the
number of Ponca had grown to more
than 3,000.
#More to explore
Kaw Native Americans Omaha
Osage Quapaw
Ponce de Leon,
Juan
Juan Ponce de Leon was an early Spanish
explorer of the Americas. He was the
first European to visit Florida. He is also
famous for his search for the legendary
Fountain of Youth.
Ponce de Leon was born in 1460 in the
Spanish province of Leon. He may have
sailed to the Americas with Christopher
Columbus in 1493. In 1502 he helped
to conquer the island of Hispaniola, in
the Caribbean Sea. In 1508 he founded
Puerto Ricos earliest European settlement.
In 1509 he became governor of
the island.
While in Puerto Rico, Ponce de Leon
heard about an island where a spring
flowed with water that kept people
young. In March 1513 he went looking
Standing Bear was a Ponca chief. In 1879
he went to court to challenge the U.S. governments
treatment of his people. The court
ruled in his favor. The case was very important
to the cause of Native American rights.
Juan Ponce de Leon
122 Ponce de Leon, Juan BRITANNICA STUDENT ENCYCLOPEDIA
for the island. He landed on the mainland
of North America, though he
thought he was on an island. He named
the territory Florida.
Ponce de Leon had landed near what is
now Saint Augustine, in the northeastern
part of the state. He did not find the
fountain so from there he traveled south
along the coast. He continued through
the chain of islands called the Florida
Keys to Floridas west coast. On the way
he discovered the Gulf Stream, a warm
ocean current that flows northward.
Ponce de Leon returned to Spain in
1514. The king gave him permission to
start colonies in the areas he had visited.
In 1521 Ponce de Leon sailed again to
Florida. He was wounded in an attack
by Native Americans. His crew took him
to Havana, Cuba, where he died.
#More to explore
Americas, Exploration and Settlement of
the Florida Puerto Rico
Pontiac
Pontiac was a Native American chief of
the Ottawa people. He is best known for
leading a war to stop the British from
taking control of the Great Lakes area.
The war is now called PontiacsWar.
Pontiac was born in about 1720 in what
is now Ohio. Little is known of his early
life. By 1755 he had become a chief.
At first Pontiac was friendly to British
settlers. But he soon realized that they
were trying to take control of his peoples
land. In 1762 he asked other
Native American tribes in the region to
help stop the British. He planned surprise
attacks on British forts. In 1763
Pontiac himself tried to capture a fort on
the site of Detroit, Michigan. He was
defeated after five months of fighting.
In all, Pontiacs forces attacked 12 forts
and captured 8 of them. They also
destroyed many British settlements.
After a few years of war Pontiac grew
tired. He agreed to a peace treaty with
the British in 1766. On April 20, 1769,
Pontiac was killed by a Peoria Indian in
what is now Cahokia, Illinois.
#More to explore
Native Americans Ottawa
Pony Express
The Pony Express was a service that
delivered mail on horseback between
Missouri and California. The service
Pontiac
BRITANNICA STUDENT ENCYCLOPEDIA Pony Express 123
lasted for only about a year and a half in
the early 1860s. Nevertheless, the Pony
Express is well remembered in the stories
of the AmericanWest.
Starting in the 1840s many people
moved to the western United States.
Mail from the East took a long time to
reach theWesterners. It took about a
month for a letter to travel from New
York to California by sea. A stagecoach
service from Saint Louis, Missouri, to
San Francisco, California, took 24 days.
A company called Russell, Majors, and
Waddell decided to set up a horseback
mail service from Saint Joseph, Missouri,
to Sacramento, California. The
route was about 1,800 miles (2,900 kilometers)
long. Along the way there were
157 stationsone about every 10 to 15
miles (16 to 24 kilometers).
A rider carried about 15 pounds (7
kilograms) of letters in a pouch. He
changed horses at every station. After 6
to 8 stations a new rider took over.
Only the pouch of mail traveled the
entire distance. This usually took about
10 days.
The first mail pouch left Saint Joseph on
April 3, 1860, and arrived in Sacramento
on April 13. The service was
closed down after a telegraph system was
completed in October 1861. The Pony
Express lost only one load of mail, even
though the riders faced outlaws,
unfriendly Native Americans, and rough
country. The most famous Pony Express
The Pony Express crossed the Rocky Mountains and the Sierra Nevada on the route
between Missouri and California.
124 Pony Express BRITANNICA STUDENT ENCYCLOPEDIA
rider was William Cody, who later
became known as Buffalo Bill.
#More to explore
Cody,William Frederick Postal Service
Telegraph
Pope
The pope is the head of the Roman
Catholic church. The office or institution
associated with the pope is called
the papacy. The pope rules the church
much as a king rules a country.
Duties
The pope does many things. He has an
organization called the Roman Curia to
help him. The pope decides the churchs
position on issues. He makes church
laws. He has the power to call ecumenical
councils, which are general meetings
that decide church policy. The pope also
appoints clergymen called bishops and
assigns them to regions called dioceses.
A bishop is in charge of all the Catholic
churches within his diocese.
The pope himself is the bishop of Rome,
Italy. He rules Vatican City, which lies
within Romes borders but is a separate
country. Vatican City is all that remains
of the Papal States, a region of Italy that
the popes ruled from 756 to 1870.
Elections
The pope is elected to his position. Only
the highest-ranking bishops, who are
called cardinals, have votes. After a pope
dies, all the cardinals under age 80
gather in a building called the Sistine
Chapel. There they secretly vote for a
new pope. White smoke from the chapel
chimney is the signal that a new pope
has been elected.
History
Catholics consider Saint Peter, who died
in about AD 64, to be the first pope.
Peter was one of the 12 disciples, or first
followers, of Jesus Christ. Since then
there have been more than 260 popes.
During theMiddle Ages, which lasted
from about AD 500 to about 1500,
unhappy cardinals sometimes chose their
own popes. These unofficial popes are
now known as antipopes. Beginning in
1378, during a period called the Great
Western Schism, there were popes in
Avignon, France, and in Rome. By 1417,
however, the cardinals had agreed on one
pope. Since then, every pope has lived in
Rome.
#More to explore
Roman Catholicism Vatican City
The pope blesses a gathering of people in
Vatican City.
BRITANNICA STUDENT ENCYCLOPEDIA Pope 125
Poplar
Poplars are fast-growing trees. People
like them for their beauty and the shade
they provide. Aspens and cottonwoods
are types of poplar. Poplars are closely
related to willows.
Poplars grow in many parts of North
America, Europe, Asia, and North
Africa. Many grow in moist, wooded
areas or near water. Poplars come in
many shapes and sizes. At up to 200 feet
(60 meters), the Western balsam poplar
is one of North Americas tallest trees.
Other types grow only to about 100 feet
(30 meters).
Flowers appear on all poplars. The flowers
develop pods filled with tiny seeds.
These pods will open and the fluffy
seeds will float to the ground. Poplar
leaves are oval, heart-shaped, or round.
The top of the leaf is light or dark green.
The underside is fuzzy and either a
lighter green or silvery color. Poplar
leaves flutter in the gentlest breeze.
Poplars have soft wood that is used to
make furniture, particle board, and
paper. Although it is useful in some
ways, the poplar tree can also cause
problems. The roots are always looking
for water. If poplars are planted too close
to water pipes or sewer lines, their roots
will clog them. In addition, poplars have
more insect damage, disease, and rotting
than many other trees.
#More to explore
Aspen Tree Willow
Poppy
Poppies are flowers that are valued for
their brilliantly colored blossoms with
papery petals. They are grown as garden
plants and also for their seeds.
Poppies grow in mild climates throughout
the world. Most species, or types, of
poppy grow best in sunny areas with
moist soil. Some, however, can grow in
rocky deserts.
Some kinds of poplar grow tall and narrow.
California poppies grow wild in a meadow.
126 Poplar BRITANNICA STUDENT ENCYCLOPEDIA
Poppies come in different sizes. Some
are tiny plants that grow near the soil.
Others grow to more than 15 feet (4.6
meters) in height. The leaves may be
green or bluish green. Some leaves,
stems, and the pods that hold the seeds
are hairy.
Poppy flowers are shaped like cups and
have four to six petals. They may be red,
orange, yellow, pink, blue, lilac, or
white. Some species have a dark blotch
at the center of the flower. Poppies do
not give off a strong smell.
Most types of poppies have only one
flower on each stem. The flowers close at
night and open in the morning. When
the soil is dry, the seed pod opens and
many small seeds fall to the ground.
One type of poppy produces seeds that
have a nutty taste when dried. The seeds
are used for baking breads and desserts.
In addition, medicine to relieve pain can
be made from the same poppy.
Popular Music
Popular music is any type of music that
a large number of people enjoy. Popular
music, also called pop, is usually topselling
music created by professional
musicians.
Popular music is different from folk
music. Folk music is the traditional
music and songs of common people.
Popular music is also different from classical
music, which is often more formal
or artistic.
Types of Popular Music
There are many types of popular music.
Some of the best-known types are rock,
country, rap, rhythm and blues (or
R&B), dance music, the blues, jazz, and
reggae. People throughout the world
listen to these forms of popular music.
Other popular music is known mainly
in a certain country or region. Often
this kind of popular music is based on
the traditional music of the area. If this
type of music gains popularity around
the world, people call it world music.
It is very common for popular music to
be popular for only a short time. New
songs regularly replace hit songs. Even
types of popular music lose popularity.
The styles of ragtime, vaudeville, big
band, soul, funk, and disco are no
longer as popular as they once were.
However, some songs and styles have
remained popular for many years.
History
Popular music developed out of many
styles of religious, folk, and classical
A popular music act draws a large crowd
at an outdoor concert in Australia.
BRITANNICA STUDENT ENCYCLOPEDIA Popular Music 127
music. In the 1800s concert bands and
traveling musical groups brought popular
music to more and more people.
In the late 1800s and early 1900s the
United States became an important center
of popular music. Songwriters in
New York City wrote many popular
songs. African Americans created jazz
and other new forms of popular music.
In the early 1900s phonograph records
appeared, so people could listen to
music in their homes. Soon the first
radio stations began broadcasting
orchestras playing popular songs.
Rock and roll, a mixture of country and
blues music, appeared in the 1950s.
Rock and roll became wildly popular
with young people. Rock is still the bestknown
form of popular music.
In the late 20th and early 21st centuries
radio, television, movies, and the Internet
helped popular music to grow and to
change. These inventions made it possible
for millions of people to hear a
single song at the same time. They also
helped to make popular music into the
huge business that it is today.
#More to explore
Blues Country Music Jazz Music
Rap Rock Music World Music
Porcupine
Porcupines are rodents with sharp spines
called quills. The quills are stiff hairs
about 3 inches (7.5 centimeters) long
that act as armor to protect the porcupine.
Many people believe that porcupines
can shoot their quills, but this is
not true.
Porcupines live in Europe, Africa, Asia,
and throughout the Americas. Some
porcupines live on the ground and others
live in trees. They sleep in caves, in
holes in trees or on the ground, or in
hollow logs.
Porcupines are stout, short-legged animals.
They often move slowly. Their
color ranges from grayish brown
through dark brown to blackish. The
quills are generally white with black tips
or bands of yellow, orange, or black.
Some porcupines have more than
30,000 quills.
When threatened, a porcupine may
grunt and stamp its back feet in warning.
It also sticks up its quills and rattles
them. The quills come off easily and can
stick in the enemys skin. The quills can
seriously hurt or even kill other animals.
Porcupines are basically plant eaters.
Some like to eat the layer beneath bark
A porcupine drinks at a water hole in Africa.
The first
important U.S.
popular songwriter
was
Stephen Foster
(182664).
He wrote Oh!
Susanna,
Swanee
River, and
many other
songs that
people still
know.
128 Porcupine BRITANNICA STUDENT ENCYCLOPEDIA
and can damage trees. Others eat roots
and fruit and can ruin crops.
..More to explore
Rodent
Porpoise
Porpoises are the smallest members of the
large group of animals called whales.
People often confuse porpoises with their
close relatives, the dolphins. Porpoises
and dolphins have a similar appearance,
but a porpoise is usually smaller and
chubbier than a dolphin. It also has a
shorter and more rounded snout.
There are six species, or types, of porpoise.
Most live in the oceans and seas
north of the equator. The harbor porpoise
is one of the most common species.
It lives in the northern parts of the
Atlantic and Pacific oceans. South of the
equator, porpoises live along the coast of
South America and in the area of the
East Indies.
Porpoises grow to no more than 7 feet
(2 meters) long. The skin is smooth,
usually with a color pattern combining
black, white, and gray. Porpoises have
two flippers on their sides, and most
have a triangle-shaped fin on the back.
Porpoises are mammals and not fish.
Porpoises have lungs and need to come
to the waters surface to get air. They
breathe through a single nostril, called a
blowhole, on the top of the head.
Porpoises generally swim together in
small groups of two to four. About 10 to
12 months after mating, a female porpoise
gives birth to a single offspring
called a calf. The harbor porpoise usually
lives for about 6 to 10 years, but other
types live longer.
..More to explore
Dolphin Mammal Whale
Port
..see Harbor.
Port-au-Prince
Population
(2003 census),
city, 703,023;
urban area,
1,977,036
Port-au-Prince is the capital of Haiti, an
island country in the Caribbean Sea. It
is the largest city in Haiti by far. It lies
on a bay of the Gulf of Gonave. The city
The harbor porpoise got its name because it
is often seen in bays and harbors.
BRITANNICA STUDENT ENCYCLOPEDIA Port-au-Prince 129
has suffered from many fires and violent
conflicts.
Haiti is a poor country. Many people in
Port-au-Prince do not have jobs. Factories
in or near the city process foods and
make clothing. Shipping also brings
money to Port-au-Prince. The city is
Haitis main port.
The French founded Port-au-Prince in
1749. At the time France ruled what is
now Haiti as a colony. They made Portau-
Prince the capital of the colony in
1770. Earthquakes damaged the city
twice in the 1700s.
In 1804 Haiti became an independent
country. Port-au-Prince was its capital.
In the late 20th and early 21st centuries
Port-au-Prince was sometimes the site of
fighting. Several times rebel groups overthrew
or tried to overthrow the government
of Haiti in the city.
..More to explore
Haiti
Port Louis
Population
(2007 estimate)
148,940
Port Louis is the capital of Mauritius, an
island country in the western Indian
Ocean. It is on the countrys main
island, which is also called Mauritius.
Port Louis is the countrys largest city
and main port. It lies between mountains
and a harbor.
Shipping goods through the port is
important to the economy of Port Louis.
Industries in the city make clothing,
food products, and ships. Tourism also
brings money to Port Louis.
The French founded Port Louis in about
1736. It was a port for ships traveling
Haitians dance during a parade in Port-au-
Prince.
The waterfront of Port Louis, Mauritius, is
popular with tourists.
130 Port Louis BRITANNICA STUDENT ENCYCLOPEDIA
around southern Africa on the route
between Europe and Asia. The British
took control of the island in the 1800s.
The port became less important after the
Suez Canal was opened in 1869. It let
ships travel between Europe and Asia
without sailing around Africa. In 1968
Mauritius became an independent country
with Port Louis as its capital.
..More to explore
Mauritius
Port Moresby
Population
(2004 estimate)
337,900
Port Moresby is the capital of Papua
New Guinea, an island country in the
Pacific Ocean. The city lies along a harbor
on the island of New Guinea.
Factories in PortMoresby make food
products and process oil. The city has a
port on the harbor. Shipping goods
through the port brings money to the city.
Port Moresby began after the British
captain John Moresby explored the harbor
in 1873. A settlement grew along
the harbor. In the 1880s the British took
control of the area. They made Port
Moresby their base on New Guinea.
Australia took control of the area in the
early 1900s. DuringWorldWar II
(193945) Australia had a military base
at Port Moresby. The Japanese tried to
capture the city. Port Moresby was damaged
by bombing but was later rebuilt.
Papua New Guinea became an independent
country in 1975. Port Moresby was
made its capital.
..More to explore
Papua New Guinea
Port of Spain
Population
(2006
estimate), city,
49,800; (2004
estimate), urban
area, 264,000
Port of Spain is the capital of Trinidad
and Tobago, an island country in the
Caribbean Sea. The city lies on the coast
Some of the houses in Port Moresby, Papua
New Guinea, stand on stilts over the water.
BRITANNICA STUDENT ENCYCLOPEDIA Port of Spain 131
of the island of Trinidad. It is the countrys
main port.
Unlike other places in the Caribbean
islands, Port of Spain is not dependent
on tourism. Instead, the city has many
different industries that contribute to its
economy. Port of Spain is a center of
manufacturing, business, and trade. Factories
in Port of Spain make drinks, processed
foods, clothing, and other
products. Shipping goods through the
port also brings money to the city.
Port of Spain was originally a small
Native American fishing village. The
Spanish took control of the island of
Trinidad in the 1500s. In 1784 they
made Port of Spain the capital of Trinidad.
Great Britain took over Trinidad in
the late 1700s.
A large fire damaged Port of Spain in the
early 1800s, but it was rebuilt. Trinidad
and Tobago became an independent
country in 1962. Port of Spain was its
capital.
#More to explore
Trinidad and Tobago
Porto-Novo
Population
(2004 estimate)
234,300
Porto-Novo is the capital of Benin, a
country in western Africa. It lies on the
coast along a pool of water connected to
the Atlantic Ocean. Benins lawmakers
meet in Porto-Novo. However, the presidents
office and most other government
offices are in Cotonou, the countrys
largest city.
Porto-Novo lies within a farming area.
The farmers sell their products in the
city.
A people called the Allada founded the
town in either the late 1500s or the early
1700s. The Portuguese also established a
trading post there. In the 1700s they
made Porto-Novo a center of the slave
trade. The Portuguese shipped Africans
out from the city to the Americas for use
as slave labor.
The French conquered the region in the
late 1800s. They made Porto-Novo the
capital of their colony of Dahomey. In
1960 Dahomey became an independent
country. Porto-Novo was its capital. In
1975 the country was renamed Benin.
#More to explore
Benin
The president of Trinidad and Tobago lives
in a fine house in Port of Spain, on the
island of Trinidad.
132 Porto-Novo BRITANNICA STUDENT ENCYCLOPEDIA
Portugal
Portugal is a small country on the western
edge of Europe. About 500 years ago
Portuguese sailors were some of the first
Europeans to explore the world. Portugals
capital is Lisbon.
Geography
Portugal sits on the Iberian Peninsula, a
piece of land in southwestern Europe. It
shares the peninsula with Spain, which
lies to the north and east. The Atlantic
Ocean lies to the west and south. The
Azores and the Madeira islands are also
part of Portugal. They lie far off the
mainland, in the Atlantic Ocean.
Northwestern Portugal is hilly and rainy.
The northeast is mountainous and drier.
It contains the mainlands highest
mountain range, the Estrela Mountains.
Southern Portugal has low plains and
gentle hills. In general, Portugals winters
are mild and humid, and the summers
are warm and dry.
Plants and Animals
Forests of oak, beech, chestnut, and pine
trees grow in the north. The south has
shrubs, grasses, and small groups of cork
oak and other trees. Animals include
foxes, rabbits, hares, goats, and deer.
Wolves live in the Estrela Mountains.
People
Most of Portugals people are Portuguese.
There are small groups of Africans,
Brazilians, and other Europeans.
Portuguese is the national language. The
main religion is Roman Catholicism.
Most people live in cities and towns,
mainly in the north.
Economy
Services and manufacturing are important
parts of Portugals economy. Ser-
Portugal has a long seacoast and many
beaches.
BRITANNICA STUDENT ENCYCLOPEDIA Portugal 133
vices include tourism, banking, and
health care. Manufacturers make clothing,
shoes, machinery, vehicles, cork and
wood products, and other goods. Portugal
sells many of those goods to other
countries.
Farming is a small part of the economy.
However, Portugal is famous for its port
and Madeira wines, which are made
from local grapes. Other crops include
potatoes, tomatoes, olives, and grains.
History
Iberian peoples settled in what is now
Portugal more than 7,000 years ago.
Celtic peoples began to arrive about
3,000 years ago. Ancient Rome ruled
the Iberian Peninsula from the 100s BC
to the AD 400s. Germanic peoples controlled
much of the land until Muslims
invaded in 711.
The Muslim invasion left only northern
Portugal in Christian hands. In 1179 the
kingdom of Portugal was established
there. It expanded as it reconquered the
Muslim-held lands. The reconquest was
done by about 1250.
Age of Discovery
The kingdom of Portugal soon became
one of Europes great powers. At the
same time the Portuguese forced many
Jews to become Christians or to leave
Portugal.
In the 1400s Portuguese explorers began
sailing to Africa, India, Indonesia,
China, the Middle East, and South
America. Bartolomeu Dias and Vasco da
Gama discovered new routes from western
Europe to Asia. In 1500 Pedro Alvares
Cabral claimed Brazil for Portugal.
By the 1500s Portugal had a huge overseas
empire.
Foreign Control
Spain took over Portugal in 1580. A
Portuguese revolution forced out the
Spanish in 1640. France attacked Portugal
in the early 1800s. The Portuguese
royal family escaped to Brazil. In 1821,
after France was defeated, the Portuguese
king returned to Portugal.
Modern Portugal
Portugal overthrew its monarchy in
1910. The military seized power in
1926. A dictator (a leader with absolute
power) ruled the country for many years
after that. Portugal finally held free elections
in 1976. Today Portugal is a member
of the European Union.
..More to explore
Dias, Bartolomeu European Union
Gama, Vasco da Lisbon
Portuguese folk dancers perform a traditional
dance.
Facts About
PORTUGAL
Population
(2008 estimate)
10,649,000
Area
35,580 sq mi
(92,152 sq km)
Capital
Lisbon
Form of
government
Republic
Major cities
Lisbon, Porto,
Amadora, Braga,
Coimbra
134 Portugal BRITANNICA STUDENT ENCYCLOPEDIA
Poseidon
Poseidon was the god of the sea in
ancient Greek mythology. According to
legend, he was one of the 12 chief gods
who lived on Mount Olympus.
Poseidon also was said to have a palace
under the sea. Poseidons main symbols
were the dolphin and the trident (a
three-pronged spear). The name
Poseidon means husband of Earth or
lord of Earth. The ancient Romans
called Poseidon by the name of
Neptune.
According to legend, Poseidon was the
son of Cronus and Rhea, who were
Titans. The Titans were a race of giants
who once ruled the world. Poseidon had
two brothers, Zeus and Hades. Together
they defeated the Titans and took power.
Zeus became the supreme ruler on
Earth, and Hades became the lord of the
underworld. Poseidon became the ruler
of the oceans.
The ancient Greeks believed that
Poseidon could use his trident either to
stir up storms at sea or to calm the
waves. He also used his trident to
shatter rocks. Because of this, he
became known as the god of
earthquakes.
The Greeks also honored Poseidon for
creating the horse and giving it to
humans. He was the father of the
winged horse called Pegasus. Poseidons
own horses had golden manes and
pulled his chariot over the sea. In
ancient works of art Poseidon is sometimes
shown riding on the backs of dolphins
or carrying his trident.
#More to explore
Hades Mythology Titans Zeus
In ancient Greek mythology, Poseidon was
the god of the sea.
BRITANNICA STUDENT ENCYCLOPEDIA Poseidon 135
Postal Service
A postal service is a system used to send
mail (letters and packages) from one
place to another. Today people can send
mail nearly anywhere in the world.
How Postal ServicesWork
People pay for using postal services in
several ways. Senders may pay by putting
a stamp on the mail. They may also
take their mail to the post office and pay
a clerk or a postage machine. Heavier
mail costs more to send. People mail
their letters and packages by placing
them in a mailbox or taking them
directly to the post office.
At the post office, postal workers sort
the mail by size. Letters go through a
machine that cancels the stamps. This
means that the machine prints lines over
the stamps so that they cannot be used
again. The machine also prints the date,
the time, and the place of stamping.
This is called the postmark.
Postal workers then sort the mail according
to its destination (the place where it
is going). They may sort it by hand or
with the help of machines.
Postal workers send the mail to its
destination by truck, train, ship, or
airplane. Postal services around the
world cooperate so that mail can even
travel between countries. At the
destination, letter carriers deliver the
mail to each address. Many letter
carriers travel on foot or in small mail
trucks.
History
Postal services have been an important
method of communication for thousands
of years. Egypt had a postal service
in about 2000 BC. The Chinese used
riders on horseback to deliver mail by
about 1000 BC. For hundreds of years
governments sent almost all mail.
Then, in the AD 1200s, trade between
faraway countries began to increase. To
communicate about trade, groups of
Modern postal services have machines to
sort the mail.
Many letter carriers deliver mail
on foot.
136 Postal Service BRITANNICA STUDENT ENCYCLOPEDIA
business owners and bankers set up their
own private postal services. Towns,
workers groups, religious groups, and
universities also set up ways to send and
receive messages.
In the 1500s and 1600s most private
postal services went out of business.
National governments took over most
postal services. One famous private service
that emerged later was the Pony
Express. It delivered mail on horseback
in the western United States in the early
1860s.
National governments still run most
postal services. Since the early 1970s
private companies have also offered
some services, especially the delivery of
packages. In the 1990s many people
began to send faxes and e-mail instead of
written letters. However, people today
still use postal services, especially when
they want to send important or private
information.
#More to explore
Communication Pony Express Stamp
Potato
The potato is one of the main food
crops of the world. It grows well in cool
climates. Potatoes are often boiled, fried,
or baked. They are served whole or
mashed, cut up into fries, or made into
potato chips.
The potato belongs to the nightshade
family of plants, which also includes
eggplant, tomatoes, and garden peppers.
The scientific name of the potato is
Solanum tuberosum. It is not related to
the sweet potato.
The potato plant can grow to 20 to 40
inches (50 to 100 centimeters) high. It
bears white or purplish flowers. The
leaves are about 8 to 12 inches (20 to 30
centimeters) long and divided into parts
called leaflets.
The stems of the potato plant grow
underground. The ends of the stems
thicken to form potatoes. The potatoes
have buds, or eyes, that can grow into
new potato plants. The skin of a potato
varies in color from brownish white to
deep purple. The inside is usually white
or yellow, but it can be purple.
Indians of South America might have
grown potatoes as early as 1,800 years
ago. Spanish explorers of the Americas
brought potatoes back to Europe in the
1500s. By the end of the 1600s potatoes
were the major food crop in Ireland. In
the 1840s disease ruined the potato crop
Potatoes are thick, underground
stems of a potato plant.
BRITANNICA STUDENT ENCYCLOPEDIA Potato 137
in Ireland. A famine resulted. More than
a million people died from starvation or
diseases related to the famine.
#More to explore
Famine Sweet Potato Tomato
Potawatomi
The Potawatomi are a Native American
people who traditionally lived near the
Great Lakes. Their lands included parts
of what are now the states of Michigan,
Wisconsin, Illinois, and Indiana. They
were closely related to their neighbors,
the Ottawa and the Ojibwa.
The Potawatomi built large, barkcovered
houses. They also built smaller,
dome-shaped homes called wigwams.
They grew corn and squash and gathered
berries, seeds, and wild rice. They
fished and hunted deer, bison (buffalo),
elk, and small animals.
French explorers entered Potawatomi
lands in 1634. The tribe gave the French
furs in exchange for metal tools, beads,
cloth, and guns.
In the 1830s the U.S. government
forced the Potawatomi to give up much
of their land. Some of the tribe fled to
Canada. Most Potawatomi moved to a
reservation in what is now Kansas. The
Kansas Potawatomi became known as
the Prairie Band. In the late 1860s some
of the Kansas Potawatomi moved to
Indian Territory (now Oklahoma). They
became known as the Citizen Band.
At the end of the 20th century there
were about 16,000 Potawatomi in the
United States. Most lived in Kansas,
Oklahoma, Michigan,Wisconsin, and
Indiana. A small group lived in Canada.
#More to explore
Native Americans Ojibwa
Pottery
Pottery is the art of making objects of
clay. The clay is shaped and then fired
(baked at a high temperature) to harden
it. The items created in this way also are
called pottery. Like brick and tile, pottery
is a type of ceramic, a material made
from nonmetallic minerals.
Ancient peoples all around the world
made pottery. Pottery was a useful
invention because it could carry water or
store food. Yet it also became a form of
art and a way to tell stories through its
paintings. Archaeologists study ancient
pottery because it provides clues as to
A Potawatomi dancer wears traditional
clothing.
138 Potawatomi BRITANNICA STUDENT ENCYCLOPEDIA
how people lived, what they believed in,
how they fought, and what they ate.
Today factories mass-produce many
kinds of pottery. But potters around the
world still handcraft fine pieces that are
more like works of art.
Types of Pottery
There are three basic types of pottery
earthenware, stoneware, and porcelain.
Earthenware is the simplest and oldest
form of pottery.Water can soak through
earthenware even after it is fired. But
when earthenware is coated with a substance
called a glaze, liquid cannot soak
through. The glaze is melted under high
heat to form a glassy surface.
Liquid cannot soak through stoneware
and porcelain even when they are left
unglazed. If a glaze is applied, it is only
for decoration. Stoneware is very hard.
Porcelain is smooth, light, and thin, and
usually light can shine through it. Both
stoneware and porcelain originated in
China more than 1,000 years ago. China
has been a leading center of pottery
since ancient times. Many people still
call porcelain china.
How Pottery Is Made
One of the simplest ways to make pottery
is with long ropes of clay. The potter
coils these ropes on top of each other
to make a bowl or vase shape. Then the
potter smooths the surface.
In another method, called slip casting,
the potter pours liquid clay into a mold.
The clay then hardens into the desired
shape. Slip casting is useful for making
pottery in flat or unusual shapes.
Pottery is often made on a potters
wheela round, flat surface that spins
around. The potter puts a chunk of clay
on the wheel and then shapes the
spinning clay into a pot or other
rounded object. Because the wheel
spins, it is easy for the potter to keep
the sides even.
Chinese porcelain vases from the late
1600s or early 1700s are decorated with
scenes of daily life.
Ancient Greeks of the Minoan civilization
made decorated pots in about 1700 BC.
BRITANNICA STUDENT ENCYCLOPEDIA Pottery 139
When the pottery is dry, it is ready to be
fired. The potter places it in a kiln, or
high-temperature oven. Earthenware
may need a temperature of 1,400° F
(760° C), while stoneware or porcelain
may need 2,700° F (1,480° C).
After firing, the hardened pottery can be
glazed and painted. Glazes are made of
ground minerals that produce different
colors. Paint may be applied either
under or over the glaze. After glazing
and painting, the pottery is often fired
again so that the glaze hardens and
becomes shiny.
#More to explore
Ceramics Clay Decorative Arts
Sculpture
Poultry
Poultry are birds that people raise for
meat, eggs, and feathers. Domesticated
(tame) chickens, turkeys, geese, and
ducks are poultry. People learned how to
raise poultry thousands of years ago.
Raising poultry at home meant that a
family always had eggs and meat to eat.
Today raising poultry is one of the
largest agricultural, or farming,
businesses in the world. Poultry are
usually raised inside large, modern
buildings. A building may have as many
as 70,000 birds. But some farmers allow
their birds to roam free during the day.
These birds usually roost, or sleep,
inside. They also come inside to lay
their eggs. Farmers feed their birds
special diets. They control the diseases
and keep away the predators that may
harm the birds.
Poultry come in many different colors
and sizes. Kinds of poultry are grouped
together by breed. A breed is a group of
birds that share certain traitsfor
example, feather color, egg color, and
their type of comb. (A comb is the
fleshy growth on the head of a
chicken.)
#More to explore
Chicken Duck Goose Turkey
A man in India makes pottery on a wheel
he spins with his foot.
A woman sprays disinfectant to kill germs in
a large chicken house in India.
140 Poultry BRITANNICA STUDENT ENCYCLOPEDIA
Powell, Colin
Colin Powell was an important military
and political figure in the United States
in the late 20th and early 21st centuries.
He was a general in the Army. He also
served as secretary of state to President
GeorgeW. Bush.
Colin Luther Powell was born on April
5, 1937, in New York City. His parents
were immigrants from Jamaica. Powell
studied geology at the City College of
New York. He graduated in 1958 and
became a U.S. Army officer.
Powell earned medals while serving in
the VietnamWar in the 1960s. He then
rose in the ranks of the Army. He was
often assigned to help high officials in
Washington, D.C.
In 1989 Powell became the countrys
top military officer, with the title of
chairman of the Joint Chiefs of Staff.
Powell became well known as a commander
in the Persian GulfWar of
1991.
Powell retired from the Army in 1993.
Many people wanted him to run for
president in 1996, but he chose not to
run. In 2001 President Bush appointed
Powell as secretary of state. Powell
became the first African American to
hold that position.
Powells biggest challenge as secretary of
state was to get other countries to support
a U.S.-led invasion of Iraq, which
began in March 2003. Powell retired as
secretary of state in January 2005.
..More to explore
Bush, GeorgeW. Persian GulfWar
Prague
Population
(2007 estimate)
1,188,126
Prague is the capital of the Czech
Republic, a country in central Europe.
The city lies on the Vltava River. It is
the largest city in the Czech Republic.
Prague is a beautiful city known for its
buildings and cultural life. The city has
many historic churches and palaces. Its
most famous landmark is the ancient
Colin Powell
BRITANNICA STUDENT ENCYCLOPEDIA Prague 141
castle of Hradcany. The Charles Bridge
is a stone bridge built in the 1300s.
Each spring Prague hosts an international
festival of classical music. The city
has two world-class orchestras and many
theaters.
Economy
Industries in Prague are very important
to the economy of the Czech Republic.
Most people in the city work in industries
that provide services, such as tourism,
banking, and trade. Manufacturing
also brings money to Prague. Factories
in the city make machinery, chemicals,
food products, and electronics.
History
Prague dates back to at least the 800s.
The rulers of the country called Bohemia
made it their capital in the 900s.
The city became one of Europes major
centers of trade and culture.
In 1918 an independent country called
Czechoslovakia was created in central
Europe. Prague was its capital.
German troops controlled Prague from
1939 to 1945, during World War II. A
few years later Czechoslovakia became a
Communist country. The Soviet Union
invaded Prague in 1968 to make sure
that the country stayed Communist. In
1989 Pragues citizens held large
protests against Communism. Soon
afterward Communism ended in
Czechoslovakia.
In 1993 Czechoslovakia broke into two
separate countries, the Czech Republic
and Slovakia. Prague became the capital
of the Czech Republic.
..More to explore
Czech Republic
Praia
Population
(2005 estimate)
111,500
Praia is the capital of Cape Verde, an
island country off the northwest coast of
Africa. It is the largest city in Cape
Verde. It lies on Sao Tiago, the countrys
largest island.
Praia has a port on the Atlantic Ocean.
Ships load up there with foods, shoes,
clothing, and other products for sale
overseas. Factories in the city process
fish.
Arched bridges span the Vltava River in
Prague, Czech Republic.
142 Praia BRITANNICA STUDENT ENCYCLOPEDIA
No one lived on the islands of Cape
Verde in ancient times. The Portuguese
began settling the islands in the 1460s.
They first settled the town of Ribeira
Grande, which became the first capital.
They later moved the capital to Praia.
This was partly because Praias harbor
was safer for ships involved in the slave
trade. The slave trade became a major
part of the citys economy. Slavery
ended on the islands in 1876.
Cape Verde became an independent
country in 1975. Praia remained its
capital.
#More to explore
Cape Verde
Prairie Dog
Prairie dogs are rodents that bark like
dogs. They belong to the squirrel family.
Prairie dogs are known for their large
underground colonies. Sometimes called
towns, these colonies have many rooms
and tunnels.
There are five species, or types, of prairie
dog. The best known are the black-tailed
prairie dog and the white-tailed prairie
dog. Prairie dogs live on prairies in western
North America.
Prairie dogs have plump bodies and
short legs. Their claws are long and powerful.
Not including their tails, prairie
dogs are about 11 to 13 inches (28 to 33
centimeters) long. They can weigh
almost 4 pounds (2 kilograms). Most
prairie dogs have yellowish brown fur.
Prairie dogs are active in the daytime.
During winter, three of the species
hibernate. This means that they stay
inactive until spring.
A female prairie dog gives birth to a
litter of up to 10 young. After about two
years the male young are driven away.
They move to new colonies. Females
usually stay.
Prairie dogs eat grass. Sometimes they
leave little grass for cattle. For this reason
some people consider prairie dogs a
pest.
Other people think prairie dogs are very
important. They say that many animals
depend on the prairie dog. Foxes, coyotes,
badgers, and hawks eat prairie
dogs. Rabbits and snakes live in holes
dug by prairie dogs.
#More to explore
Rodent Squirrel
The largest
prairie dog
colony ever
seen was in
Texas. It contained
about
400 million
prairie dogs.
A black-tailed prairie dog can look out over
prairie grass when it stands upright.
BRITANNICA STUDENT ENCYCLOPEDIA Prairie Dog 143
Pregnancy
#see Gestation.
Prehistoric Life
Long before people appeared on Earth,
other forms of life existed. Many of
these living things are now extinct,
meaning they have died out completely.
The period when they lived is called
prehistory, or prehistoric times.
Everything that people today know
about prehistoric plants and animals
comes from fossils. Fossils are the
remains or traces of early life-forms.
They are often found in rocks.
Precambrian Life
The earliest life-forms developed during
the earliest period of Earths history,
called Precambrian time. Precambrian
time began with the formation of
Earths crust, about 4 billion years ago.
It ended about 543 million years ago.
Scientists do not know exactly when
life-forms first appeared, but the oldest
known fossils are more than 3 billion
years old.
The first life-forms had only one cell.
They included early types of bacteria,
algae, and protozoans. Living things
with more than one cell began to appear
late in the Precambrian. All life at this
time lived in Earths oceans.
Paleozoic Life
The next period of Earths history is
called the Paleozoic era. It lasted from
about 543 million years ago to about
248 million years ago. At first, all living
things were in the oceans. By the end of
the era, plants and animals also lived on
land.
Over hundreds of millions of years, life spread through the seas and over Earths surface.
144 Pregnancy BRITANNICA STUDENT ENCYCLOPEDIA
Ocean Life
Early Paleozoic animals were similar to
the jellyfish, sponges, and worms that
live in oceans today. Other animals in
the oceans were arthropodsthe early
ancestors of crabs, insects, and spiders.
Arthropods called trilobites were common
sea animals. They were oval and
often measured 6 to 7 inches (15 to 18
centimeters) long. Trilobites became
extinct by the end of the Paleozoic era.
The first fish appeared about 450 million
years ago. These animals did not
look much like fish today. They had
armorlike shells and no jaws. Later fish
developed jaws, a backbone, and fins.
Life on Land
By about 400 million years ago early
plants had started growing on land. By
the end of the Paleozoic era there were
forests of large, treelike ferns. Huge
swamps also developed near the equator.
In general, northern lands were dry and
warm. Ice sheets covered the south.
Meanwhile, some of the arthropods in
the oceans went through changes that let
them live on land. They eventually
evolved, or developed, into the first centipedes,
insects, and spiders. Some fish
also developed body parts that allowed
them to live on land. They became
amphibians, or animals that live both in
water and on land.
Reptiles evolved from amphibians by
about 300 million years ago. Reptiles
were the first animals with a backbone
to live entirely on land.
Mesozoic Life
The Mesozoic era followed the Paleozoic
era. It lasted from about 248 million
years ago to about 65 million years ago.
The first life-forms were very simple. Later forms were more complicated and more varied.
BRITANNICA STUDENT ENCYCLOPEDIA Prehistoric Life 145
Large reptiles called dinosaurs dominated
the land during this era. Some dinosaurs
fed on palmlike plants and evergreen
trees, which grew well in the mild to
warm climate.Other dinosaurs preyed
on other animals. Large reptiles also lived
in the oceans and flew in the air.
Mammals evolved from reptiles during
the Mesozoic era. The earliest mammals
appeared by 200 million years ago. They
were small, shrewlike creatures.
Birds also appeared during the Mesozoic
era. They evolved from reptiles by about
150 million years ago. The earliest birds
had wings and feathers like modern
birds. But they also had teeth and claws.
All dinosaurs became extinct by about 65
million years ago. But other reptiles,
including the ancestors of snakes, turtles,
crocodiles, and lizards, survived. Birds,
mammals, insects, flowering plants, and
other life-forms also survived.
Cenozoic Life
The next period in Earths history is the
Cenozoic era. It began about 65 million
years ago and continues today.
Many mammals developed during this
era. The first horses, rhinoceroses, pigs,
hippopotamuses, camels, deer, giraffes,
sheep, cattle, and apes appeared. By
about 4 million years ago the ancestors
of humans, called hominins, had
appeared. Early forms of humans developed
between 2 million and 1.5 million
years ago.
Between 1.8 million and 10,000 years
ago large ice sheets covered much of
Earth. During four periods, known as
ice ages, glaciers moved across the northern
half of the planet. Long warm periods
separated the ice ages. During this
time such huge mammals as woolly
mammoths, mastodons, and sabertoothed
cats roamed the land. But by
the end of the ice ages, most of the huge
mammals had died out.
Early humans hunted mammoths and
other animals. They made and used
stone weapons and tools. For this reason
this period of prehistory is known as the
Stone Age. The Stone Age ended at different
times in different places. It ended
as humans began to farm, settle in villages,
and make tools out of metal.
About 5,000 years ago humans began to
write. Prehistory then ended, and
human history began.
#More to explore
Dinosaur Earth Evolution Fossil
Human Origins Mastodon and
Mammoth Stone Age
Presley, Elvis
Elvis Presley was a famous popularmusic
star in the United States. He was
one of the first musicians to sing and
play rock music. For this he is often
called the King of Rock and Roll.
Elvis Presley was born on January 8,
1935, in Tupelo, Mississippi. His family
was very poor. In the late 1940s the
Presleys moved to Memphis, Tennessee.
As a young man Elvis enjoyed many
Many animals
died out in
historical
times. They
include the
dodo bird of
Mauritius and
the passenger
pigeon of
North
America.
146 Presley, Elvis BRITANNICA STUDENT ENCYCLOPEDIA
different kinds of music, including gospel,
blues, and country.
In 1953 Presley went to Sam Phillips
music studio to make a recording for
his mother. Phillips had recently started
the Sun Records label. He liked
Presleys singing. In 1954 Presley made
his first recordings for Sun, including
Thats All Right Mama, which
became a local hit.
In 1955 Presley began recording with
RCA Victor, a major record label. Presleys
early hits included Dont Be
Cruel, All Shook Up, and Hound
Dog. He released his first number-one
record, Heartbreak Hotel, in 1956.
Presley became an actor in 1956. His
first movie, Love Me Tender, was released
in that year. He went on to star in more
than 30 films.
In 1958 Presley entered the U.S. Army.
In 1960 he returned to the United States
and continued recording, performing,
and acting. In the 1970s Presley had
problems in his personal life. When not
performing, he spent almost all of his
time at Graceland, his mansion in Memphis.
Presley died on August 16, 1977.
#More to explore
Popular Music Rock Music
Pretoria
Population
(2005 estimate),
urban area,
1,282,000
The country of South Africa has three
capitalsPretoria, Cape Town, and
Bloemfontein. Pretoria is home to the
presidents office and many other government
offices.
Pretoria lies on the Apies River. The city
is famous for its jacaranda, a type of tree
that has purple flowers.
Most people in Pretoria work for the
government or in trade, banking, or
other service industries. Factories in the
city make metal products, processed
foods, cars, and other products.
A people called the Boers founded the
city in 1855. The Boers were descen-
Elvis Presley
BRITANNICA STUDENT ENCYCLOPEDIA Pretoria 147
dants of earlier Dutch settlers. The city
was named Pretoria after Andries Pretorius,
a Boer leader.
In 1910 the country of South Africa
was created. Pretoria became one of its
capitals.
In 2000 Pretoria became a part of the
Tshwane Metropolitan Municipality.
The municipality governs Pretoria and
surrounding cities. Tshwane was named
after an African chief who lived in the
area before the Boers arrived.
#More to explore
Bloemfontein Cape Town South
Africa
Primate
The primates are a group of mammals
that includes some of the most intelligent
animals. The major kinds of primates
are humans, apes, monkeys,
tarsiers, lemurs, and lorises. There are
more than 300 species, or types, of primate.
These different types have many
physical features in common. For this
reason scientists believe that they may
share a common ancestor.
Where Primates Live
Humans live nearly everywhere in the
world.Most other primates can be found
in hot and warm regions of Central and
South America, Africa, and Asia.
Nonhuman primates often live in trees.
Physical Features
Some primates are small, and others are
large. One type of mouse lemur weighs
only about an ounce (35 grams). On the
other hand, a gorilla may weigh 600
pounds (270 kilograms).
The bodies of primates share many common
features. For instance, primate
brains are large compared to the size of
their bodies. The brains of humans,
apes, and monkeys are especially large
and complex. Primates also have eyes
that face forward. The view from one
eye overlaps the view from the other eye.
This helps primates judge the depth and
distance of what they see. Special nerve
endings in the hands and feet give primates
a good sense of touch.
Most primates have thumbs that can
bend to meet the other fingers. This
allows them to grasp things with their
hands. All primates except humans have
big toes that can bend and grip in this
way, too. Most types also have flat nails
on their fingers and toes rather than
claws.
Pretoria has many tall buildings and several
large parks.
148 Primate BRITANNICA STUDENT ENCYCLOPEDIA
Feeding and Reproduction
Primates eat a variety of plants and animals.
These may include fruits, flowers,
leaves, birds eggs, insects, and other
small animals.
Over the course of their lives, female
primates tend to have fewer young than
other animals do. Most primates give
birth to one baby at a time. The babies
take a long time to grow into adults.
Primates must take care of their young
for much longer than other animals do.
Deep emotional bonds often develop
between mother and child.
Primates Under Threat
While the human race keeps getting
larger, some other primates are in danger
of dying out. Human activities such as
logging and farming have destroyed the
habitats of some primates. Hunting is
another threat to many species.
#More to explore
Ape Lemur Loris Mammal
Monkey Tarsier
Primates have many features in common. In general, they have large brains, eyes that face
forward, and thumbs that can bend to meet the other fingers.
BRITANNICA STUDENT ENCYCLOPEDIA Primate 149
Prince Edward Island
Prince Edward Island is Canadas
smallest and most crowded province.
The British named the
island after Prince Edward, a son of
King George III. The capital is Charlottetown.
Geography
Prince Edward Island is on the east coast
of Canada. The province of Nova Scotia
lies south and east of the island. It protects
the island from the Atlantic Ocean.
The Confederation Bridge connects
Prince Edward Island to New Brunswick,
to the west. Bays cut deeply into
the long, narrow island. Most of the
island is a gently rolling plain with soil
that is good for growing crops. Tiny
islands dot the coastline. Sandy beaches
attract tourists in the summer.
People
Most of the people of Prince Edward
Island are Canadians of Scottish,
English, Irish, or French heritage. Some
are descended from Loyalists (American
colonists who did not want independence
from Great Britain) who settled
on the island after the American Revolution.
There are small numbers of American
Indians and people with other
European or Asian ancestors.
More than half of the people live in
rural areas. Still, the island has more
people per square mile than any other
Canadian province. The port city of
Charlottetown is the islands center of
government, business, and culture. It is
also home to the University of Prince
Edward Island. Every summer the city
stages a musical based on the childrens
novel Anne of Green Gables, which is set
on Prince Edward Island.
Economy
Government services are the largest part
of Prince Edward Islands economy.
Finance, health care, and retail services
The red cliffs of East Point line
the shore at the eastern end of
Prince Edward Island.
150 Prince Edward Island BRITANNICA STUDENT ENCYCLOPEDIA
are also important. Technological and
scientific services are growing, as is tourism.
Manufacturing, especially food
processing, is the chief industry.
Farmers grow potatoes, grains, and vegetables.
They also raise cattle, pigs, and
poultry. Fishers catch lobsters, oysters,
fish, and other seafood. The provinces
forests provide wood for lumber and
paper.
History
In early times Micmac Indians from the
mainland used the island for fishing,
hunting, and planting. The Italian
explorer John Cabot may have become
the first European to see the island in
1497. The French explorer Jacques
Cartier definitely saw the island in 1534.
Another French explorer, Samuel de
Champlain, claimed the island for
France in 1603. Settlers from France did
not arrive until 1720. French speakers
from the mainland also set up small
communities on the island. The French
called the island Ile Saint-Jean.
In 1758 British forces occupied the
island, and most of the French settlers
left. The British governed the island as a
part of Nova Scotia. In 1769 they made
the island a separate colony. They later
renamed it Prince Edward Island.
In 1864 representatives of several provinces
met on the island, at Charlottetown,
to discuss a plan of confederation,
or union. A new country called
the Dominion of Canada was formed in
1867. For its early role in the union of
Canada, the island is sometimes called
the Cradle of Confederation. However,
Prince Edward Island did not join the
union until 1873.
At that time many of the islands landowners
lived in England. They charged
rent to their tenants, or the people living
on the land. A law passed in 1875 made
it possible for tenants to buy the land.
However, the islands economy
remained poor. Many people moved
away to find work.
Many changes came to Prince Edward
Island in the 1900s. Roads, cars, ferries,
a radio station, and air service arrived by
the 1950s. Tourism helped the economy
to grow. The Confederation Bridge to
the mainland opened in 1997.
..More to explore
American Revolution Cabot, John
Canada Cartier, Jacques
Champlain, Samuel de New
Brunswick Nova Scotia
The Confederation Bridge crosses the
Northumberland Strait to connect Prince
Edward Island with New Brunswick. The
bridge is 8 miles (12.9 kilometers) long.
Facts About
PRINCE EDWARD
ISLAND
Flag
Population
(2006 census)
135,851
Area
2,185 sq mi
(5,660 sq km)
Capital
Charlottetown
Motto
Parva sub Ingenti
(The Small Under
[the Protection of]
the Great
When Prince
Edward
Island
Became a
Province
1873
BRITANNICA STUDENT ENCYCLOPEDIA Prince Edward Island 151
Printing
Printing is a way to make many identical
copies of texts and images on paper.
Printing began as a way to speed up the
process of making copies of books. At
first this was a very slow process because
it involved copying the text by hand.
With the invention of a machine called
the printing press, printing became
faster and easier. Modern printing by
computers can produce hundreds of
pages in minutes. People use printing to
create books, magazines, money, stamps,
maps, posters, billboards, and labels.
Printing Methods
The most common type of printing is
electronic printing. It is also known as
computer or digital printing. In this
method, a writer, editor, or designer
creates pages on a computer screen.
Next, laser printers (photocopiers controlled
by laser beams) use heat and
powdered ink to form an image of the
page on a sheet of paper.
Most books are printed from printing
plates. In this method, printers transfer
the image of several pages to a metal or
plastic plate. They may do this by computer
or by hand. Next they place the
plate in a printing press and put ink on
it. Then they feed paper into the printing
press. The press transfers the ink
onto the paper.
On older kinds of printing plates, all the
words and pictures are reversed, as if
seen in a mirror. On some older plates,
the words and pictures are raised above
the surface of the plate. Ink applied to
the plate sticks to the raised areas. On
other plates, the words and pictures are
engraved on, or cut into, the plate. Ink
then collects in the cut-out areas.
On newer kinds of printing plates, the
image is flat. Special ink sticks to the
image but not to the rest of the plate.
The inky image is transferred onto a
An artist of the 1800s imagined Johannes
Gutenberg and a printer in their workshop.
A huge press prints many copies
of a newspaper on a long roll of
paper. Other machines will cut
the roll into sheets.
152 Printing BRITANNICA STUDENT ENCYCLOPEDIA
sheet of rubber. The rubber sheet then
prints the image onto paper. Because the
image is transferred twice, the words and
pictures on the plate do not have to be
reversed.
History
By the AD 700s people in China were
using carved wooden blocks to make
prints. They applied ink to the block
and then pressed the block onto paper.
This technique was used to make the
Diamond Sutra in 868. It is the first
known printed book.
In the 1400s in Germany, Johannes
Gutenberg invented a printing press that
could make copies of whole pages of
text. Gutenberg arranged type (metal
blocks with raised, reversed letters on
them) on a tray. He rubbed ink on the
raised surface of the type. He then used
the machine to press a sheet of paper
against the inky type. Gutenbergs
invention could easily print many copies
of a pageand even copies of a whole
book.
The printing press created a communication
revolution. Before this time,
people copied books by hand. It was a
slow process, so there were few books
available. After the invention of the
printing press, more books could be
printed and sold. Printing also led to the
creation of newspapers.
#More to explore
Book and Bookmaking
Communication Gutenberg,
Johannes Newspaper
Prism
A prism is a piece of glass or other seethrough
material that has several flat
sides, called faces. Many prisms have
three long faces in between two triangleshaped
ends. However, prisms can be
made in many forms and shapes. People
use prisms to bend light.
Light travels through space in the form
of waves. Scientists use an idea called
wavelength to describe these waves.
Some light waves have long wavelengths,
while others have short wavelengths.
Each wavelength produces a different
color of light.
Usually all the wavelengths of light
blend together to form white light. But
when light enters a prism, it bends.
Light waves of different wavelengths
bend by different amounts. The longest
wavelengths bend the least. The shortest
wavelengths bend the most. This
bending separates the light waves so
each color can be seen. This band of
colorsred, orange, yellow, green, blue,
indigo, and violetis called a
spectrum.
A prism shows that white light is actually a
combination of many colors.
BRITANNICA STUDENT ENCYCLOPEDIA Prism 153
Prisms may be found in binoculars,
microscopes, and many other instruments.
They help to bend the light that
enters these instruments toward the
viewers eyes. Scientific instruments
called spectroscopes use prisms to separate
the energy given off by light
sources, such as stars. Each chemical
that makes up a star produces a different
wavelength of light. Scientists can measure
the different wavelengths to tell
what the stars are made of.
..More to explore
Light
Prison
Prisons are buildings that hold people
who have been convicted, or found
guilty, of serious crimes. Of all the
worlds countries, the United States and
China have the most known prisoners.
Purposes of Prisons
Prisons serve three main purposes. They
punish criminals by taking away their
freedom. They also keep dangerous
criminals off the streets. Finally, prisons
can help to rehabilitate prisoners, or
make them into better people. Prisons
do this by giving prisoners an education,
job training, or help in getting over the
problems that caused them to commit
crimes. These problems may include
emotional problems, mental problems,
or the abuse of drugs or alcohol.
Types of Prisons
Maximum-security prisons hold people
who have been convicted of the most
serious crimesfor example, murder or
hurting someone with a gun, a knife, or
another deadly weapon. Prisons built to
hold less dangerous criminals are called
minimum-security prisons. Jails are prisons
for people who committed small
crimes or people waiting for a trial.
There are separate prisons for men and
women.
History
Until the 1700s most prisons were not
used for punishment. Instead of prison,
common punishments included death
and banishment (sending a person out
of the country). Prisons mainly held
people who could not pay their bills,
people waiting for a trial, and guilty
people waiting to be given their sentences,
or punishments. By the 1900s,
however, most prisons held convicted
criminals.
The conditions in early prisons were
horrible. Disease, violence, and abuse
were common. In the late 1700s reformers
(people who work for change) in the
United States and Great Britain began to
look for ways to improve prisons. By the
1900s many prisons offered prisoners
Prisoners live in small rooms called cells. rewards for good behavior, education,
154 Prison BRITANNICA STUDENT ENCYCLOPEDIA
and job training. Reformers today continue
to work for safer and more effective
prisons around the world.
..More to explore
Crime
Pristina
Population
(2004 estimate)
165,840
Pristina is the capital of Kosovo. It is
located in the east-central part of the
country.
Pristina is a cultural center for ethnic
Albanians, who make up most of the
population of Kosovo. A museum in the
city teaches about the history and people
of the area. Southeast of the city is the
Gracanica Monastery. It was built in the
1300s and contains interesting frescoes,
or wall paintings. The monastery is a
religious center for Serbian Orthodox
Christians.
The economy of Pristina relies on services,
including trade, health care, government,
and businesses that are related
to tourism. Lead, silver, and zinc are
mined in mountains near Pristina.
Pristina has a long history. It was the
capital of all of Serbia, which included
Kosovo, until 1389. In that year the
Turkish Ottoman Empire conquered
Serbia. Serbia and Kosovo then developed
different identities. Serbian leaders
made Belgrade their capital.
Serbia eventually gained independence
from the Ottomans and regained
Kosovo. But by the late 1900s Kosovo
wanted independence from Serbia. During
fighting in the late 1900s and early
2000s several cities in Kosovo were
heavily damaged. Pristina did not suffer
as much damage. Many people moved
to the city because of that. Kosovo
declared its independence from Serbia in
2008 with Pristina as its capital.
..More to explore
Kosovo
Prometheus
In ancient Greek mythology Prometheus
was a god of fire. He was also a trickster
and a master craftsman. Prometheus was
one of the Titans. The Titans were
giants who once ruled the world.
In one story Zeus, the chief god, had
Prometheus and his brother Epimetheus
create the animals and people.
Epimetheus made the animals first. He
gave them all the best qualities, such as
strength and speed. He also protected
them with fur and feathers.
Epimetheus then realized that he had
little left to give people. He asked
Prometheus for help. Prometheus stole
fire from the gods and gave it to
humans.
BRITANNICA STUDENT ENCYCLOPEDIA Prometheus 155
Zeus saw what Prometheus had done
and became angry. He had Prometheus
tied to a rock. Every day an eagle ate
Prometheus liver. Every night he grew a
new liver for the bird to eat the next day.
Eventually the hero Heracles (or Hercules)
freed him.
Zeus also punished humans after
Prometheus gave them fire. Zeus sent
the first woman, named Pandora, to
Earth. Her curiosity is said to have
brought troubles into the world.
#More to explore
Heracles Mythology Pandora Zeus
Protective
Coloration
Some animals have special colors or
markings called protective coloration.
These markings protect animals from
predators, or animals that will eat them.
Some markings are a kind of camouflage,
meaning that they help the animal
blend in with its surroundings. Others
help scare predators away by making the
animal appear dangerous.
Camouflage
Many animals have body colors that
match their usual surroundings. This
helps them to hide from predators.
Snowshoe hares, for example, have
white fur in winter to blend in with
snow. For the rest of the year their fur
is brown, to match the ground. Insects
known as walkingsticks are long, thin,
and green or brown. Their color and
shape make them look like parts of the
plants on which they feed. Some
animals, such as cuttlefish, can even
In ancient Greek mythology, Prometheus
stole fire from the gods and gave it to
humans.
156 Protective Coloration BRITANNICA STUDENT ENCYCLOPEDIA
change their color and pattern to match
their surroundings.
Spots, stripes, and other color patterns
help to mask the true shape of some
animals. For example, the stripes on
zebras make it hard for predators to tell
exactly where each zebra is. But patterned
fur also helps some predators.
The spots or stripes of many big cats
help them to hide as they move closer to
their prey.
Warning Colors
Some animals use color to warn others
not to bother them. These animals often
have poison or other weapons to defend
themselves. Some poisonous snakes and
frogs are brightly colored. Bees, which
are known for their stings, often have
bold stripes of yellow and black. Predators
may avoid these animals because
they have learned to associate bright
colors with pain.
Some harmless animals have the same
colors as dangerous or bad-tasting animals.
These colors trick predators into
staying away. This type of coloration is
called mimicry.
How Coloration Develops
Animals gain helpful traits through a
process called natural selection. If an
animal happens to be born with such a
trait, it is more likely than others to survive.
It therefore has a better chance of
having offspring. If the animal passes on
the trait, the offspring, too, will have a
better chance to survive. They can pass
on the marking or coloring to their own
offspring. After many generations, the
entire population has the useful trait.
#More to explore
Animal Mimicry
Protestantism
With more than 400 million followers,
Protestantism is the second largest
branch of Christianity. Protestantism is
divided into many different churches.
The first Protestant churches broke away
A toads coloring allows it to blend in with
a clump of leaves.
Women serve as ministers in some Protestant
churches. Other Protestant churches
accept only men as ministers.
BRITANNICA STUDENT ENCYCLOPEDIA Protestantism 157
from Roman Catholicism, the largest
branch of Christianity.
Beliefs and Practices
Although many Protestant churches
have different beliefs, all Protestants
reject Roman Catholicism and the
power of its leader, the pope. They base
their beliefs on the Christian Bible.
Most believe that getting to heaven
requires only faith in God, not any specific
actions. They think that each
believer, not just priests, can spread
Gods teachings.
Most Protestant churches hold worship
services on Sundays. Protestants perform
only two of the sacraments, or rituals,
practiced by Roman Catholics: baptism
and Communion.
History
In the 1500s some Roman Catholics
began to disagree with their church. At
first they wanted only to change, or
reform, parts of the church. Their movement
became known as the Reformation.
But the leaders of Roman
Catholicism strongly opposed such
changes. Soon some people broke away
to form new churches. Members of the
new churches became known as Protestants.
The first Protestant churches to
form were the Lutheran church, the
Church of England, and the Reformed,
or Presbyterian, churches.
Catholics and Protestants fought wars
over religion in the 1500s and 1600s.
Protestantism remained strong, however,
and spread throughout Europe and its
colonies.
In the 1600s and 1700s some Protestants
thought that Protestantism was
still too close to Roman Catholicism.
Some of them formed new Protestant
groups, such as Congregationalists, Baptists,
Quakers, and Methodists.
In the 1800s missionaries spread Protestantism
further in the Americas, Africa,
Asia, and Oceania. New Protestant
churches continued to form in the
1800s and 1900s. Meanwhile, beginning
in the 1900s, some Protestants worked
to build unity with all Christians.
#More to explore
Bible Christianity Reformation
Roman Catholicism
Protist
Protozoans, algae, and slime molds
belong to a group of living things called
A layer of slime mold covers leaves and a
wet log.
Three leaders
of the Reformation
were
Martin Luther,
John Calvin,
and King
Henry VIII of
England.
158 Protist BRITANNICA STUDENT ENCYCLOPEDIA
protists, or protoctists. Protists are not
animals, plants, fungi, or bacteria. Many
protists are so small that people can see
them only through a microscope.
There are thousands of different species,
or types, of protist. Many types live in
water, both in oceans and in freshwater.
Others live on land. Some, called parasites,
live inside the bodies of animals.
Some types are solitarythey do not
form groups with other protists. Other
types form groups called colonies.
Most protists are unicellular, which
means that they have just one cell. Some
protists are made up of clusters of cells.
But a protist never has more than one
type of cell.
Some protists act like animals. For
example, some types of protozoan move
around and feed on other living things.
Other protists act more like plants.
They make their own food through a
process called photosynthesis, just as
plants do. Many plantlike protists are
called algae.
The protists called slime molds can act
like animals or like fungi (such as mushrooms).
Sometimes slime molds move
around as unicellular creatures, as protozoans
do. But at other times slime mold
cells gather together. They form a slimy
layer that moves across forest floors or
other surfaces. This slime feeds on
decaying plants and other living things.
Sometimes small stalks grow out of the
slime. The stalks release spores, as fungi
do. These spores are tiny units that turn
into new slime mold cells.
#More to explore
Algae Cell Living Thing Protozoan
Protozoan
Protozoans are simple organisms, or
living things. They belong to a group of
organisms called protists, which are neither
plants nor animals. Most protozoans
are so tiny that they can be seen only
with a microscope. Amoebas and paramecia
are types of protozoan.
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