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Animals can move from place to place, but plants cannot. When an animal is under attack, it can run away
or fight back. Plants certainly cannot run away, and they have no teeth and claws. But plants can defend (保护)
themselves by using both physical and chemical ways.
Some plants have their own ways to keep animals away. For example, the leaves of the holly (冬青) plant
have sharp prickles (刺) that stop grass-eating animals. Holly leaves on lower places have more prickles than
leaves on upper places. This is because the lower leaves are easier for most animals to reach.
Some plants, such as the oak tree (橡树), have thick and hard leaves that are difficult for animals to eat.
Some grasses may contain a sandy material, eating such grasses wears down the animal's teeth.
Many plants also have chemical defenses. Some plants produce chemicals that taste bitter or cause an
unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals.
When a worm (虫子) bites a tobacco leaf (烟叶), the leaf produces a chemical smell.
Many plants depend on both physical and chemical defenses. A certain plant in China, for instance, has
prickly leaves, and each prickle has poisonous water (毒液). Only one experience with this kind of plant will
teach an animals to stay away from it is the future.
1. Can plants move from place to place?
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2. Can plants defend themselves by physical ways or by chemical ways?
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3. Why lower holly leaves have more prickles than upper ones?
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4. How does tobacco defend itself against an attack from a worm?
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5. What kind of experience will teach an animal to stay away from a plant in the future?
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