Tyendy Farha, age 14,of Valois, Quebec, Canada, for her question:

How does fungus form?

Patches of mildew seem to come from nowhere. These uninvited guests are members of the plant world. Plants, of course, are living things and all life is handed on from former life. Even those microscopic mold and mildew fungus plants formed from parents like themselves. In small fungi, the details of multiplication are too small for human eyes to observe.

Botanists classify the plant world in large phyla. So far they have identified about 75,000 species in the fungus phylum. Experts on fungus plants are called mycolo¬gists and every year they add a few newly discovered microscopic species to the list. The ten simplest plant phyla are thallophytes, meaning sprout plants. They have no true roots or stems, leaves or flowers. The fungi are thallophytes that have no green chlorophyll either. They come in assorted sizes ranging from the giant, two foot puff¬ball to microscopic single celled species, even smaller than the mold and mildew fungi.

All the simple fungus plants are limited in their wayf of life. But each species has a successful method for handing on life to the next generation. For example, the mushroom plant lives and grows underground. It is no more than a mattress of pale whit¬ish threads called mycelium. When time comes to hand on life, the mycelium sends sprouts above the ground. These chubby umbrellas are the fruiting bodies that we call mushrooms.

They form countless tiny spores, each bearing the life program for the next mushroom generation. The dusty spores grow and ripen in the pills, those feathery folds under the mushroom umbrella. When ripe, the tiny spores break free and let the breezes scatter them to new homes. The big puffball scatters trillions of spores in dusty clouds. Only a very few fungus spores ever come down to eerth on a suitable shady spot where the soil is moist and extra rich. When this happens, a lucky spore swells up and sprouts its first few threads of mycelium down into the food supply. If all goes well, it will grow into a new fungus like its parent.

Molds and other small fungi poke up forests of threads topped with tiny spore cases. Glhen ready, the cases pop open and the ripe spores float off in the air. A few land on suitable spots    such as damp cloth, bread or other human food. They sprout their mycelium on or under the surface. t,)e still do not notice    until they grow their tiny spore cases. Yeasts are single celled fungi that multiply by budding. A well fed mother cell sprouts a bud that forms a daughter cell. Most of the fungus plants form from spores that carry the life program from a parent plant. Some of the one celled fungi form from buds, some from spores. A few have a choice    new fungi can form from buds or spores.

Since fungi have no chlorophyll, they cannot use sunlight to make their basic food from air and water. They depend on food prefabricated by the green plants. Most of them thrive in decaying vegetation. Many molds live on our groceries and certain small fungi live as parasites inside the living cells of plants and animals. No spore or bud can form a new fungus unless it is surrounded by its favorite food.