Mushrooms are produced by certain fungi. Some people love them (mycophiles); other folks are afraid of them (mycophobes). Either way, most people would agree that mushrooms are some of nature’s most unusual and interesting life forms.
What is a Mushroom?
Mushrooms are fungi. To be considered a fungus, an organism must (1) be eukaryotic; (2) grow by extending filamentous cells called hyphae, or by budding; (3) obtain nutrients by absorption, (4) have no chlorophyll, and (5) reproduce via spores.
Mushrooms are the reproductive structures produced by members of the division of fungi known as the Basidiomycota (also called the Basidiomycetes). The purpose of a mushroom is to produce and release spores. Most people consider morels to be mushrooms also, although they are Ascomycetes which generate spores in a different way.
A fungus spends most of its time underground or in decaying wood and these surroundings are not ideal for the dispersal of spores. A fungus needs to make large numbers of spores and it needs to disperse them efficiently so as to increase the probability that the spores will find new sources of nutrients to exploit. The mushroom serves this purpose well by rising above the substrate to get its spore producing apparatus into the air.
How Mushrooms Grow
Mushroom-producing fungi perform valuable roles in ecosystems. They are decomposers, responsible for recycling dead organic matter -- notably wood -- back into molecular form to be used over and over again by other organisms as nutrients. Most are beneficial, but a few are parasitic on living trees.
Mushroom formation is triggered by some combination of environmental conditions. Usually a cool spell accompanied by adequate moisture (rain) is needed.
Mushrooms begin as promordia, which are little bumps of cells that appear at the place from which a mushroom is to develop. If the moisture is sufficient and the humidity high enough, the promordia go on to produce fully developed mushrooms.
The Structure of Mushrooms
The basic parts of a mushroom (technically known as a basidiocarp) are the stipe (stem), the pileus (cap) and either lamellae (gills) or tubes which are covered (or lined in the case of tubes) with reproductive cells call basidia from which spores are produced. The spores are usually actively ejected from the gill or tube surface to float downand out of the cap, to where even the slightest breeze is enough to transport them far and wide.
The number of spores that can be produced by a large mushroom is truly astounding, having been calculated in the trillions. The total number of spores released on a daily basis on earth is astronomical. So why is the world not overgrown with mushrooms? Fortunately for the rest of the living things on earth, only a tiny fraction of all these spores end up in a place suitable for germination and growth. But fortunately for the mushroom-producing fungi, enough do find suitable conditions and nutrient sources, to be able to keep up with all the decomposition work that has to be done.
References
Buller, A.H.R, Researches on Fungi, Hafner Pub. Co., 1958
Miles, P.G, Chang, S., Mushroom Biology: Concise Basics and Current Developments, World Scientific Publishing Company, 1997
Philip McIntosh - The author holds a B.Sc. in Botany and Chemistry and an M.A in Biology and he has thirty + years of experience in science and industry.
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