There are over 350,000 kinds of plants in the world. All these continue to struggle to survive against storm, rain, Sun and snow. There are some which die due to severe cold in winters, although before dying their seeds are dispersed on the ground, so that in autumn, they can produce new plants. However, there are some plants, which are able to protect themselves against winter. A coating of ice crystals is called frost. The plants are able to protect themselves against winter frost by a special method. They spread their leaves and flatten themselves against the ground. The warmth in the soil enter their leaves and the plant is protected. Some plants like myrtle and heather allow their upper parts to die but their stem remains alive. The stems acts as storage organs, both above and below the ground. They produce buds and thus preserve their species. Many plants hide themselves under the soil to escape the cold; these include tubers, bulbs and roots, which store their food according to their need. In summers, they push out green leaves and new buds. Sometimes, artificial methods are used to protect plants from frost, e.g., oil heaters called smudge pots are used in the region where citrus fruits are grown. In some places, large fans are used to circulate the air, so that frost is not able to get deposited on the trees.