Section IV. FUNGI
Fungi are members of the Plant Kingdom Mycetae (Fungi). Outstanding features
of these eucaryptic microorganisms are the presence of cell walls, the lack of motility,
and the absence of photosynthesis. Some exist as parasites on other living organisms
whereas others are saprophytes, living on the remains of dead plants or animals. The
term "fungi" includes the molds, yeasts, mildews, rusts, smuts, mushrooms, and
toadstools. This group of organisms includes not only pathogenic species, but also
several of important economic value. Molds of the genera Aspergillus and Penicillium
are used in the manufacture of antibiotics. Certain molds of the same class are used in
the production of cheese (Camembert, Roquefort, and so forth.). Yeasts are used in the
production of alcoholic beverages and the baking industry. Edible mushrooms are
considered a delicacy by connoisseurs of fine foods.
2-17. MORPHOLOGY OF FUNGI
a. General. Fungi vary widely in size and shape, from unicellular, microscopic
organisms to multicellular forms easily seen with the naked eye. Individual cells range
from 1 to 30 . Microscopic fungi exist as either molds or yeasts or both. Internally,
fungal cells are fairly typical eucaryotic cells.
b. Molds. The molds form large multicellular aggregates of long branching
filaments, called hyphae. There are vegetative hyphae and reproductive hyphae.
Spores are borne on the reproductive hyphae. (Fungal spores should not be confused
with bacterial spores that are resistant bodies formed for bacterial survival rather than
reproductive purposes.) Spore size, shape and structure are used in the classification
and identification of fungi. The tube-like hyphae are responsible for the fluffy
appearance of the macroscopic mold colony. The hyphae and other structures combine
to form an elaborate network called a mycelium.
c. Yeasts. These are large (5 to 8 ), single-celled organisms that rarely form
filaments. Most yeasts reproduce by the asexual process of budding. Yeast colonies
are usually characterized by a smooth surface similar to that of many bacteria.
2-18. PHYSIOLOGY OF FUNGI
a. Nutrition. Most fungi contain complex enzymes and other chemical
substances which, when diffused into the host, break down the complex substances
available--wood, vegetation, leather, bread, and so forth--into simpler substances that
can be used for food. The chemical products of digestion are, therefore, completed
outside of the organism, and the fungus absorbs the end products.
b. Reproduction. Fungi reproduce sexually or asexually, or both, depending
upon the species and the environmental conditions. As the name implies, sexual