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Synopsis Plants are essential to the balance of nature and in people's lives. Green plants, i.e. those possessing chlorophyll, manufacture their own food and give off oxygen in the process called hotosynthesis, in which water and carbon dioxide are combined by the energy of light.

Plants provide many useful drugs. Some of these plants have been used as medicines for hundreds of years. The bark of the cinchona tree was used 400 years ago to reduce fever. It is still used to make quinine, a drug used to treat malaria and other diseases. Another drug, called digitalis, is used in treating heart disease. It is made from the dried leaves of the purple foxglove plant. The roots of the Mexican Yam are used in producing cortisone, a drug useful in treating arthritis and a number of other diseases.