Linda Mussillo, age 11, of Staten Island, for her question:
How do molds differ from mildews?
Most things in the world of nature have everyday names, which our ancestors gave them long ages ago. In the plant world, some are called molds because they reminded people of moldy, decaying earth. Some are called mildews, or mealdews, because they arrived like the dew, apparently from nowhere, and ruined the mealy cereals. Then came the age of science. Biologists sorted all the living things into related groups and gave them all fancy new scientific names.
What we call molds and mildews are mini members of the plant world. Scientists have identified more than 1,000 different kinds. But they do not classify the molds in one group and the mildews in another, for there is not that much difference between them.
All of them belong in the fungus plant, Eumycophyta, group. This also includes the chubby mushrooms and toadstools. Most scientists class the molds and mildews to¬gether in a special branch of the fungus group. It is called Phycomycetes, a term which means alga fungus. This term suggests that the various molds and mildews are somewhat like the water weed algae and somewhat like the pasty fungi.
The 1,000 or so phycomycetes are subdivided into 240 smaller genera, which is the plural form of genus. Some of these smaller groups are all or mostly molds, others are all or mostly mildews. Some are mixtures of molds and mildews. All of them have the same sort of simplified body plan and all of them feed on foods manufactured by more advanced plants or animals.
Most of those we call downy mildews live like downy fuzz on certain plants. They are parasites that steal their food from the living host plants. Other downy mildews are called saprophytes because they live on decaying organic material. And a few downy mildews live as parasites inside the bodies of living insects.
Most of the powdery mildews live like dusty powder on the surface of certain green plants. There are about 50 of these parasites and they do a great deal of harm. They suck nourishment from roses and apples, peas and peaches and about 1,500 other useful plants.
The various molds also live either as parasites on living plants or as saprophytes on decaying plant and animal material. Those we know best are the so called bread molds that attack whatever scraps of food we leave lying around. The phycomycetes multiply by launching multitudes of infinitesimal spores into the air. The tiny spores drift around and those that settle oa a suitable spot start a new colony. Then a neg¬lected crust becomes a cottony wad of moldy bread.
The downy mildews have been known to change the course of human history. In the 1840's, the major potato crop of Ireland was attacked by Phytophthora infestans alias the potato blight. Many people starved, others left Ireland for new homes in America. At one time, another powdery mildew wiped out all the grape vines of France. The wine business came to a stop until the vineyards were re planted with sturdier vines from the New World.