Since flowers possess both male and female parts, some flowers can fertilize themselves— or fertilize another flower on the same plant—which is called self-pollination. Or the ovules of one flower may be fertilized by the pollen of a different flowering plant of the same species, a method called cross-pollination.
The wind, water, insects, and other animals help to carry pollen from one flower to another. Crosspollination usually produces a better plant: the offspring of cross-pollination possesses the genetic traits of two parents, which may give it new characteristics that will help it survive in an always-changing environment. Cross-pollination is so desirable, in fact, that many flowering plants have developed different ways to keep selfpollination from happening. In the flowers of a spiderwort plant, for example, the stamens are ready to release pollen grains before the pistils are ready to accept them, so the pollen has to travel to other spiderwort plants in search of a ripe pistil.
Muscles are attached to bones by tendons, the longest and strongest of which is called the Achilles tendon in your heel. This thick band of tissue attaches the muscles of the calf to the heel bone and is the key to the foot’s ability to flex.
The Achilles tendon allows you to push off of your foot when walking or running. In ancient Greek myth, the hero Achilles died from a wound to his heel, so the popular expression “Achilles heel” often refers to a physical weakness or limitation.
Dinosaurs probably communicated both vocally and visually. Large meat eaters like Tyrannosaurus rex, with its loud roar, or a Triceratops shaking his head, would have made its intentions very clear. The chambered head crests on some dinosaurs such as Corythosaurus and Parasaurolophus might have been used to amplify grunts or bellows. Mating and courtship behavior and territory fights probably involved both vocal and visual communication. Scientists believe that the sounds created by dinosaurs like Parasaurolophus were so individual that each had a slightly different tone. They also believe that these dinosaurs had different calls, ranging from low rumbles to high-pitched notes, which they used for different situations.
In ancient times, small doses of the plant were used to relieve pain, with a great risk of poisoning. One species, Conium maculatum, was used to carry out the death sentence in ancient times. The Greek philosopher Socrates was condemned to death in 329 B.C.E.; he killed himself by drinking a potion made from hemlock. The hemlock plant was introduced to North America from Europe, and has often been mistaken for a pretty garden plant. All parts of the weedy hemlock plant are poisonous, especially leaves and seeds. Hemlock is a member of the wild carrot family, and it grows along roadsides and waterways in North America.
Most birds fly. They are only incapable of flight during short periods while they molt, or naturally shed their old feathers for new ones. There are, however, several birds that do not fly, including the African ostrich, the South American rhea, and the emu, kiwi, and cassowary of Australia. The penguins of the Southern Hemisphere are also incapable of air flight. They have feathers and insulation for breeding purposes, but use a different form of motion: their sleek bodies “fly” through the ocean using flipper-like wings. All of these flightless birds have wings, but over millions of years of evolution they have lost the ability to fly, even though they probably descended from flying birds. These species may have lost their ability to fly through the gradual disuse of their wings. Perhaps they became isolated on oceanic islands and had no predators; therefore, they had no need to fly and escape danger. Another possibility is that food became plentiful, eliminating the need to fly long distances in search of food.
Bats, which are most active at night, have eyesight that ranges from very good to very poor. However, they rely primarily on echolocation to “see” in the dark. Echolocation is the transmission of sound waves to locate objects, including food, and to detect obstacles in an animal’s path. These sound waves travel out away from the bat and then bounce off objects and surfaces in the bat’s path, creating an echo. The echo returns to the bat, giving it a sense about the object’s size, shape, direction, and distance. This high-frequency ultrasound is higher than the range of human hearing and usually comes from the bat’s mouth. A few species emit sounds from their noses, freeing their mouths for eating at the same time.
Scientists have learned that earthquakes occur in a number of definite zones, mainly where there are deep trenches in the ocean bed with groups of islands nearby, such as around the Pacific. In these zones, seismologists (people who study earthquakes) try to guess whether stress is building up underneath the surface. If the area has been dormant (quiet) for a long time, it may be that an earthquake is about to happen. They also use seismometers to detect the tiny shock waves that occur right before an earthquake. It is estimated that there are 500,000 detectable earthquakes in the world each year. Of these, 100,000 can be felt, and 100 of them cause damage.
With the most common coffeemaker, the drip coffee machine, hot water drips down freely onto ground coffee beans to make coffee. The water inside the machine’s water bucket is heated as it passes along a heat-resistant tube. The tube goes into the drip area and releases heated water, just below boiling temperature (212 degrees Fahrenheit [100 degrees Celsius]). The water is heated by a heating element (a resistive heating coil that gives out heat when electricity is passed through it). The heating element has direct contact with the water inside the water bucket, and also heats the heating pad on which the glass coffee container is rested. Today, most models of coffee machines are either semi-automatic or automatic. Buttons and switches have replaced the manual coffee straining and lever-pushing of espresso machines. And some machines now have special features, such as built-in coffee bean grinders and froth makers.
During colonial times the U.S. Navy used the oak tree’s hard wood to build its ships. The U.S.S. Constitution received its nickname, “Old Ironsides,” during the War of 1812 because its live oak hull was so tough that British war ships’ cannonballs lit erally bounced off it. Because the Constitution was built before shipbuilders learned to bend or steam wood into shape, the live oak’s long, arching branches were used as braces to connect the ship’s hull to its deck floors. Throughout the years, oak wood has been used as lumber, railroad ties, fenceposts, veneer, and fuel wood. Today it is manufactured into flooring, furniture, and crates.
The gravity of the moon is one-sixth that of the earth; hence the weight of a person on the surface of the moon will be one-sixth of his actual weight on earth.