Have you ever wondered why trees  and other plants in the countryside  always seem to lookbetter than  those found in towns and cities?  One of the reasons for this may be  pollution. Air Pollution and gases like  sulphur dioxide, can actually slowly  poison the plants in towns ! What Is A Lichen? A lichen is a partnership between a  fungus and an algae. They both  work together to live in places that  they may not be able to survive on  their own ! About 18,000 to 20,000 types of  lichen have been identified. The algae part of the lichen provides food to the fungus using  photosynthesis. Lichens look a little like mosses: both are small and grow on trees or  rocks as well as on the ground. Mosses are made up of slender, green stems with tiny, transparent, green leaves. Lichens, however, come in many forms: paint-like rusts; scalloped,  wrinkled sheets; lacy patterns, bushy tufts; untidy strands of black or  green "hair"; but they never have leaves. You may not have known that: Lichens are widely used as  environmental indicators. If air is very badly polluted with sulphur  dioxide there may be no lichens present, just green algae may be  found. If the air is clean, shrubby, hairy and leafy lichens become  abundant. A few lichen species can tolerate quite high levels of  pollution and are commonly found on pavements, walls and tree bark  in urban areas. The most sensitive lichens are shrubby and leafy while the most  tolerant lichens are all crusty in appearance. The centre of large towns and cities may not have any lichen at all. As  you move away from the centre towards the countryside you will first  see grey-green crusty lichens, next leafy lichens and then shrub like  lichen. A simple rule to remember is that the more the lichen sticks out, the cleaner the air.. Lichen Jungle Pictures (Copyright C.Gourlay 2003) Very Clean Air ....   Shrubby green lichen, numerous types Clean Air....   Leafy green lichen, numerous types Slightly Dirty Air  Flat rounded lichens, green, yellow, black or orange Quite Dirty Air  Patches of crusty orange or grey-green lichens NO LICHENS................................ Very Dirty Air   ACTIVITIES FOR YOU TO DO!  Conduct a survey to study lichens around your school or in your  garden. If you dont have a garden ask your parents to take you on a  walk to the local park or woods.Walk around and keep your eyes open  ! Make a note of the types of lichens you can see : Example of a Lichen Recording Chart:  -------------------------------------------------------------------------------- Colour: Shrubby surface? Leafy surface? Orange, yellow or black? Granular surface? White, frost-like surface? Ridged surface? Rough surface? Smooth surface? Veined surface? What kind of texture does our lichen's surface have? Other observations. -------------------------------------------------------------------------------- Now What?  Compare your results with the diagram above showing which type of  lichens you have found. Can you tell what the air pollution is like in the areas that you studied  the lichens? NOTE: Some places that do not have any lichens are not  necessarily polluted, you may just not have found them or  other factors may mean that they may not grow there. Try  another nearby area or park/ woods.

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