CHAPTER 2 THE NATURE OF FUNGI WITH SPECIAL EMPHASIS ON MUSHROOMS Synopsis This chapter aims to give a basic understanding of fungi, their structure and mode of growth with specific emphasis in the mushroom fungi. The role of mushrooms in nature is outlined with reference to the main forms of nutrition. The historical uses of psychotropic mushrooms in early forms of religion are outlined together with the use of other mushrooms as items of food and medicine. Introduction Mycology is concerned with the study of the Fungi, the term being derived from the Greek word mykes, meaning a fungus. The Fungi were, until comparatively recent times, regarded as members of the Plant Kingdom but are now recognized as a very distinct and separate group of organisms. They are eukaryotes having welldefined membrane-bond nuclei with a number of definite chromosomes and, as such, clearly distinguishable from bacteria. They are heterotrophic, requiring organic carbon compounds of varying degrees of complexity which distinguishes them from plants which manufacture their own organic food by photosynthesis. All but a few fungi have well-defined cell walls through which all their nutrients must pass in a soluble form and, in this respect, they differ from animal cells which lack defined cell walls. The number of species of fungi is a matter of speculation but recent estimates have strongly suggested that their numbers could be well in excess of 1.5 million. The fungi show immense differences in size, structure and metabolic activities. The smallest, such as the yeasts, grow as loose aggregates of single detached microscopic cells while most fungi exist as microscopic filaments or hyphae which extend at the tip, branching and fusing (anastomosing) to form a complex mycelium or network. As such mycelial networks increase in size they become visually 12 apparent and, indeed, in some cases the mycelia form large complicated structures exemplified by the large fruit bodies known colloquially as mushrooms. While many fungal species do grow and function in aqueous environments, the vast majority, by the nature of their apical growth patterns, are best adapted to growth over and through solid substrates, especially in terrestrial environments. Fungi function extensively in the soil environment breaking down dead organic matter but can also extensively grow in plants, animals and man causing decay and disease. Many fungi negatively attack manufactured products of all kinds including foodstuffs, fabrics, leather, timber, cosmetics, pharmaceuticals, aviation fuel etc., while, on the other hand, they make a huge contribution in biotechnology producing wines, beers, spirits, fermented food products such as cheeses, antibiotics, industrially-important organic acids and now many other important medicinal compounds. In themselves many edible mushrooms form the basis of huge commercial processes. In mycology, as in other sciences, increased knowledge has resulted in complexity and, eventually, the division of the science into a number of branches with the resultant increase in specialization. What is termed pure mycology concerns the detailed structure, cytology and modes of development of fungi while taxonomic studies examine structure with a view to classifying fungi so as to show relationships and facilitate identification of the myriad of types. Medical mycology deals with the fungi which cause diseases in man and as well as the toxic effects of mycotoxins, fungal metabolites formed by filamentous fungi growing mainly in cereal grains and oilseeds. Several of these mycotoxins are now recognized as powerful carcinogens of man. Such cancer-forming mycotoxins present in the human diet deserve greater awareness in the medical profession.