Moulds, those dusty little spots often found spreading over bread, cheese, books, and other things in the home, cause the loss of millions of dollars to our economy every year and, even worse, may be a menace to your health. To deal with them successfully we must understand what moulds are and exactly what they are doing.
Moulds are microscopic, plant-like organisms, composed of long filaments called hyphae. Mould hyphae grow over the surface and inside nearly all substances of plant or animal origin. Because of their filamentous construction and consistent lack of chlorophyll they are considered by most biologists to be separate from the plant kingdom and members of the kingdom of fungi. They are related to the familiar mushrooms and toadstools,differing only in not having their filaments united into large fruiting structures. For our purposes here, we shall consider as moulds only fungi that are commonly encountered n the home and laboratory and that can be easily grown and studied.
When mould hyphae are numerous enough to be seen by the naked eye they form a cottony mass called a mycelium. It is the hyphae and resulting mycelia that invade things in our homes and cause them to decay.
Reproduction in fungi is complex and involves a great diversity of structures. At the most fundamental level we can say that most moulds reproduce by spores. Spores are like seeds; they germinate to produce a new mould colony when they land in a suitable place. Unlike seeds, they are very simple in structure and never contain an embryo or any sort of preformed offspring. Spores are produced in a variety of ways and occur in a bewildering array of shapes and sizes. In spite of this diversity, spores are quite constant in shape, size, colour and form for any given mould, and are thus very useful for mould identification.
The most basic difference between spores lies in their method of initiation, which can be either sexual or asexual. Sexually initiated spores result from a mating between two different organisms or hyphae, whereas asexual spores result from a simple internal division or external modification of an individual hypha. the recognition of a mating and subsequent spore formation is often difficult for an observer,and is usually reserved for patient specialists. However, for practical purposes one can learn to recognize certain indications of the sexual process, namely, the four kinds of sexually determined spores that appear in mould fungi: (1) oospores, (2) zygospores, (3) ascospores, and (4) basidiospores.
