Children fortunate enough to have lived near ocean beaches where seaweeds are cast ashore by the surf have often enjoyed stamping on the bladders ("floats") of kelps to hear the distinct popping sound as they break. Some have collected and pressed beautiful, feathery red seaweeds, and others who have waded around the shores of freshwater lakes or in slow-moving streams have encountered slimy-feeling pond scums. All who have kept tropical fish in glass tanks have sooner or later had to scrape a brownish or greenish algal film from the inner surfaces of the tank, and those who have lived in homes with their own swimming pools have learned that the plaster of the pool soon acquires colored algal patches on its surface if chemicals are not regularly added to prevent them from appearing.
Although some of the seaweeds have flattened, leaflike blades, algae have no true leaves or flowers. They are involved in our everyday lives in more ways than most people realize (see the discussion in the section "Human and Ecological Relevance of the Algae," which begins on page 344). Seaweeds and some pond scums, fish-tank films, and colored patches in swimming pools include but a few of the numerous kinds of algae all assigned to Kingdom Protista. The algae are grouped into several major phyla based on the form of their reproductive cells and combinations of pigments and food reserves.
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