ALSO CALLED PHYCOLOGY,

the study of algae, a large heterogeneous group of chiefly aquatic plants ranging in size from microscopic forms to species as large as shrubs or small trees. The discipline is of immediate interest to humans owing to algae's importance in ecology. Certain algae, especially planktonic (i.e., floating or drifting) forms, constitute a vital segment of food chains. In coastal regions many large species of algae are direct food sources for humans. In industry algae are a source of commercially valuable substances such as iodine, agar, carrageenin, alginic acid, and potash. Other algae are used in insulating materials, bricks, scouring powder, and filters. Certain species are used as digestive agents in sewage-oxidation ponds. Some forms of algae are harmful because of their tendency to suffocate other forms of aquatic life in waters used for fishing and recreation.