1. Trees are plants that survive year after year and have a single main stem composed entirely of wood. Some kinds grow to only ten feet, Others attain heights of more than 350 feet. These giants also have stems that are as much as 100 feet in circumference (圆周).
2. Over 25,000 different species of tree grow around the wood, except near the North and South Poles. They all belong to one of two possible groups. They are either coniferous (松类的) or deciduous (落叶的). Coniferous trees are evergreens (常绿的), such as pine or fir, which bear needlelike foliage (叶子) all year long. Many deciduous trees have broad leaves, which they usually shed each year at the beginning of the cold season.
3. Trees provide people with a host of oils, drugs glues, candy, cloths, fuels, and well over 10,000 wooden products. Some have unique qualities that make their wood valuable for special purposes. One particular type of tree, for example, is used to make fishing rods because it is not strong but unusually flexible. Queensland walnut is used by the electrical industry in Australia, because it is almost as good an electrical insulator as rubber. One of the world most unusual trees is the teak (柚木). It is one of the heaviest of all woods, and it has the largest leaves of any tree. These enormous leaves are two feet square and their surface is so tough and coarse that cabinetmakers in India use them as sandpaper. Teakwood itself is so heavy that when a teak tree is first cut down it will not float in water. It takes three years for the ten or fifteen-ton trunk to dry out enough so it will not sink.
4. Of all the world"s billions of living trees, the tallest is a giant redwood in California. It towers 368 feet. This redwood tree is anchored and nourished by a massive root system. It extends over three full acres.