3.5.3. Slime molds

The slime molds are difficult to classify. In body form, slime molds resemble protozoa, but their method of reproduction somewhat resembles a fungus. The body of a slime mold is usually a brightly colored, jellylike network of cytoplasm called a plasmodium. The plasmodium has no cell walls but many nuclei. It creeps by amoeboid movement over the ground and dead logs. Like an amoeba, the plasmodium engulfs microscopic prey and digests the food in food vacuoles.

When its food supply runs short, the plasmodium separates into tiny mounds of cytoplasm that develop into fungus like sporangia. The spores produced in these sporangia may be scattered to new areas where food is more plentiful. Slime mold spores grow into either flagellated or amoeba-like cells. A new plasmodium develops when two flagellated cells fuse or when a mass of the amoeba-like cells join and form the larger organism.

3.5.4. Club fungi

The class Basidiomycetes contains about 25,000 species, including mushrooms, shelf fungi, puffballs, rusts, and smuts. Basidiomycetes are called club fungi because they produce spores on club-shaped, microscopic structures called basidia. The basidia develop within the fruiting body.

Mushrooms. The most common club fungi are mushrooms. What you think of as a mushroom is the spore-producing structure of an underground mycelium. The mushroom first develops as a tight mass of hyphae called a button. A stemlike structure known as the stipe pushes the button above ground. There the button opens into a cap, the fruiting body of the mushroom. The underside of the cap contains thin sheets of tissue, or gills, to which the basidia are attached. Within each basidium are two haploid nuclei that fuse to form a diploid nucleus. This nucleus undergoes meiosis, and the resulting haploid nuclei produce four basidiospores. Each basidipspore is capable of developing into a new mushroom.

Some kinds of mushrooms are edible, but others are poisonous. Because some poisonous mushrooms resemble harmless ones, you should never eat wild mushrooms. For example, even a small portion of the "destroying angel", Amanita bispo-rigera, can be lethal. A toxin in this mushroom damages the liver so severely that death results.

Rusts and Smuts. Rusts and smuts are parasitic club fungi that cause severe damage to cereal and vegetable crops. Rusts and smuts produce spores, but not in mushroom like fruiting bodies. The mycelia spread throughout the host plant, destroying the plant’s cells while producing billions of basidiospores.

The life cycle of wheat rust involves two alternate hosts. In the spring, the fungal spores infect young wheat plants. In the summer, a second cycle of spore production infects barberry plants. The disease can be controlled by destroying all barberry bushes growing near wheat fields.

Corn smut produces large deformed growths on ears of corn. The life cycle of corn smut involves only one host. Corn smut can be eliminated by burying or burning the infected plants before the fungi produce spores.