Becky Knight, age 14, of Charleston, W. Va

Are molds the same as mildews?

We tend to think of these busy blotches only as nuisances. They attack our food and many of our favorite plants. In warm, wet places, especially in the rainy tropics where they thrive most abundantly, they destroy fabrics, books and even leather. But the molds and mildews lead a double life, for they also play a vital role in the scheme of nature. They help break down complex substances into simple chemicals which are returned to the soil to feed new generations of plants.

Molds and mildews have bothered mankind since the beginning of settled civilization. Therefore they were named long before science had a chance to study, name and classify them. The word mold came from an older word for earth, which shows that our name‑giving ancestors were very thoughtful. For a moldy loaf of bread will finally become a bit of dust to enrich the soil. The word mildew comes from older words meaning spoiled meal or flour. The ancients built granaries to protect their crops from these sneaky invaders.

In everyday language, we can say that a slice of bread is either moldy or mildewed. But science can recognize this particular blotch of blue or grey, green or yellow as being different from countless other varieties of mold and mildew. Bread may be attacked by several different molds. A certain mildew feeds only on grapes, another only on lilacs. Some are parasites, feeding only on living things. Others, like the bread molds, are saprophites, feeding on non‑living plant or animal material.

A good many of the mildews are parasites, but not all of them. Most, though not all, of the molds are saprophites. That slice of bread is almost certain to be moldy. Science groups some of the molds and mildews in the Phycomycetes plant class, meaning the alga‑like fungi. others are grouped in the class Asomycetes, the sac fungi. Many of the tiny plants are so much alike that it takes an expert with special equipment to tell them apart.

All of the molds and mildews are fungus plants, midget cousins of the pasty mushroom. The fungi have no chlorophyll with which to make their own food from air, light and moisture, They depend upon prefabricated food made by green plants and sometimes by animals. This is why we find them thriving happily on slices of bread, on living leaves, on grapes and sometimes in the tissues of living animals.

A mold or mildew starts life as a dusty spore, too small to be seem It spreads out a mesh of fine, pale threads into a warm, moist food supply, such as a slice of bread. This mesh is the plant body, called the mycelium. Soon it sprouts a lawn of tiny spikes, each topped with spore capsule. Under a microscope, a grimy blotch of mold looks like a miniature garden, for the dainty spore capsules may be shaped like flowery pour‑pours, fans, feathers or fronds.