Foliose lichens are dainty and leaf- like, growing on rocks and trees. They have two growth forms. They grow vertically to the ground or hang from limbs of trees. These lichens are branching and are usually described as being shrubby. A main part of this experiment deals with acid rain.
Acid rain is caused when gases, such as sulphur dioxide and nitrous oxide are released into the air.
These gases mix with water vapor to form sulfuric and nitric acid. When acid rain falls it is dangerous to many parts of the environment. When it gets into rivers it can kill aquatic life and increase the acidity of soil and ground water. Acid rain and pollution are a main factor in the killing of lichens all around the world. Because of their sensitivity to pollution, lichens are very good bioindicators.