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Algae are simple plants which have chlrorophyll and make their own food, but have no true roots, stems or leaves. The largest of the algae are the big seaweesa, but many kinds of algae are tiny. They live in sea water, freshwater, and in damp places. Some are single-celled, and can only be seen under the microscope, although there may be so many of them that they color the water or make a tree trunk’s surface green. Others, such as Spirogyra, consist of a long chain of similiar cells. Such chains may form a green scum on fresh water. Some algae live with fungi, the two combining to form the type of plant known as a lichen. The fungus provides shelter for the algae. Algae make food that the fungus can use.