Ethylene is a hydrocarbon plant hormone, in the form of gas. It controls the ripening of fruits, opening of flowers, and falling of leaves. Plants produce ethylene themselves, but cultivators use this hormone to quicken the ripening of fruits to produce more to sell in the market. Ethylene basically can be produced from any part of the plant and plays an important role in agriculture and the maturation of plants. The picture above shows an ripened (sort of) apple due to the effects of ethylene production.