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Medical Plants - Реферат

The plant kingdom is rich and varied. There are some 500,000 different species of plants. Plants have different "natural homes" (habitats). Cultivated plants from the garden differ greatly from the plants growing in the field or in the meadow. Some plants are familiar to you. You feast your eyes on modest bell-flowers, timid violets, bright poppies, luxuriant roses, fragrant lilac, long clusters of showy coloured flowers of hollyhock and evergreen leaves of ivy.
Don't gather meadow and field flowers into bouquets. Some of them are rare species. Many plants produce poison that can kill or sicken people that come in contact with the plant. Touching poison ivy (a shrubby or climbing plant that has small, greenish berries and leaflets in groups of three) causes a severe, itching skin rash; eating certain holly berries (a shrub or a tree having evergreen leaves with pricky edges and bright-red berries) causes vomiting; chewing a stem of hemlock (a poisonous plant with featherlike leaves and flat clusters of small whitish flowers) can kill an adult.
The best rule for dealing with plants is: never eat or chew any wild plant.
But some of the chemical plants are used to produce medicines that ease human suffering and cure serious illnesses. Medical plants and some poisonous ones serve as a raw material for medicines.
A plant with a slender cluster of fragrant bell-shaped white flowersis called lily of the valley. It is a raw material for extracts to cure heart diseases. A bitter medical drug made from the dried juice of aloe (a tropical plant with thick, spiny-toothed leaves) is used to stimulate the digestive tract. The juice extracted from fresh leaves is used for applications on fester wounds and abscesses.
A North American shrub with yellow flowers that bloom in late autumn or winter is called witch hazel. A spicy-smeliing liquid made from the bark and leaves of this plant and rubbed on the skin relieves an open injury or wound pain. Early Native Americans were good at using various herbs and plants for medical purposes. The Hurons had a cure from scurvy (a disease caused by lack of fresh fruit and vegetables). They made a tonic from the bark and needles of an ever green tree that carried massive dozes of vitamin C. The Incas used a colourless substance from certain cinchona (a South American tree) barks to cure malaria. Bitter drugs or chemicals derived from quinine are used to treat malaria nowadays.
Over 200 years ago, doctors prepared medicines from the bark of willow trees. The bark contains a chemical that can ease or reduce fevers. The willow bark contains salicylate, an active ingredient of aspirin.