Marion Harrington, age 8, of Portland, Maine, for his question:

WHAT EXACTLY ARE ALGAE?

Thousands of different plants grow on the land, all rooted to the spot. The algae are special plants that belong in the water. They float in the sunshine near the surface, so they need no roots to anchor them down. Most of them live in the sea, but many types live in freshwater ponds and streams. Some of the smaller algae invade our fishbowls and cloud the. water with misty green.

The large alga types are floating seaweeds and water weeds. But most of them are too tiny to be seen one by one. Millions of these midgets color the water green or brown or sometimes red. All algae use sunlight to make their own food from gases and water. As they perform this miracle, they add breathable fresh oxygen to the air  and the breezes blow it around the world.