Lori Hancock, age 10, of Imperial Beach, California, for her question:

Why do they harvest kelp?

If you make a list of the largest plants, it will certainly include the tallest trees. Chances are, you would never think of adding a seaweed to your list of giant vegetation. But you should. The seaweed called kelp happens to belong in the group of world's largest plants.

There are many varieties of kelp seaweeds and the biggest of them cluster in underwater groves off our Pacific shores. Some types are 200 feet long and specimens of even 260 feet have been dragged up from their watery homes. However, the kelp is not harvested alone. As a rule, it is dragged ashore with a large assortment of other seaweeds. For the ocean, like the land, has a large variety of plant life, and all or most of these other plants are also useful items in the seaweed harvest. The massive kelp just happens to make up the bulk of the ocean crop.

Kelp and other seaweeds have been used to fertilize the farms of France and Ireland, England and Scotland for centuries. As well as being the name for a seaweed,~the word kelp refers to the ashes of dried and burned seaweeds, which gives us a hint as to how these natural fertilizers were prepared. They were first dried and,ioasted. This process caked the seaweeds into a thick, gummy mass. The hot mass was sprinkled with water to break it into manageable pieces. The fragments were spread around to enrich the soil with chemical plant foods. Twenty tons of seaweed yielded about one ton of kelp ash containing about 200 pounds of plant invigorating potassium sulfate.

Early in the last century, kelp ash was found to be rieh in iodine. The same 20 ton haul of seaweed also yielded about 20 pounds of this germ killing medicine. In recent years our clever chemists have extracted still more useful chemicals from the kelp harvest. Several factories in southern California got busy processing the rich ocean vegetation to make food for cattle. The kelp industry tested this fodder by adding it in ten per cent helpings to the menus of dairy cattle. And those kelp eating cows gave more milk than any other cattle in the world.

For ages the people of Asia have used kelp type seaweeds to create jellified soups and other delicately flavored dishes. Our clever chemists separated the jellifying chemical from kelp and named it algin. They found that algin has a talent for holding different liquids together. We use it in ice cream to stop the water in the milky mixture from separating. Without algin, our ice cream would be spiked with frozen needles of glassy ice. Algin also is an ingredient in chocolate milk, puddings and many more of our creamy smooth desserts and salad dressings.

In World War I, kelp was used to make explosive ammunition and also to make iodine to purify the wounds that the ammunition caused. Nowadays we make explosives from other chemicals and much of our iodine comes from brine wells of salty water. But half rotted kelp is richer in plant food than barnyard manure, and most of the harvest is needed as fertilizer. The same harvest also yields a dividend of creamy, nourishing food for the human family.