Bryce Kendrick, Sidney-by-the-Sea, British Columbia, Canada
Fungi, broadly defined, (1) are eukaryotic, (2) have no plastids or photosynthetic pigments, (3) are therefore heterotrophic (unable to make their own food from inorganic components), (4) are osmotrophic (absorb rather than ingest food), (5) are often opportunistic and capable of exploiting manydifferent substrates, (6) are never amoeboid at any stage, (7) almost always live inside branching networks of microscopic, apically extending, tubular structures known as hyphae, (8) almost all reproduce by unicellular or multicellular spores, (9) generally have haploid somatic nuclei, and (10) mostly do not produce flagellate cells. Mycology is the branch of science that studies these organisms.Introductory article
. What are Fungi, and How Do We Study Them? . Milestones in the History of Mycology
What are Fungi, and How Do We Study Them?
Although the taxonomy of organisms at the highest levels is not yet universally agreed upon, in this essay fungi are classiﬁed in two biological kingdoms, which are here called Chromista and Eumycota, though other authorities namethem Stramenopila and Fungi, respectively. This essay follows a taxonomic scheme proposed by Patterson and Sogin (1993), which recognizes two domains (Prokaryota and Eukaryota) and seven kingdoms (the prokaryotan Archaea (or Archaebacteria) and Eubacteria (or Bacteria),
and the eukaryotan Protozoa, Chromista, Plantae, Animalia and Eumycota (or Fungi) (Figure 1). Let us ﬁrst examine the basichyphal modules of which fungi are composed. The ﬁrst hypha (germ tube) arises when a spore germinates. This tube, usually between 3 and 10 mm wide, has walls made largely of chitin (in the eumycotan fungi) or cellulose (in the chromistan fungi). The ﬁrst hypha soon branches, again and again, as it grows out radially, exploring its immediate surroundings (Figure 2). Almost all exchange of materials –secretion of enzymes, absorption of nutrients – takes place at or near the numerous hyphal tips, because behind the tip the walls
Chromista Plantae Animalia Plant chloroplasts Cyanobacteria Eubacteria Agrobacterium Plant mitochondria Enterobacteria Prokaryota Sulfolobus Thermoplasma Methanobacteria Fungi Myoplasma
Myxostellida Entamoebae ProtozoaKinetoplastids Euglenoids Microsporidians Trichomonads Diplomonads
Figure 1 A diagram of relationships among the 7 kingdoms of living organisms. What we call fungi make up Kingdom Mycota, and also form a part of Kingdom Chromista (after Patterson and Sogin, 1993).
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Fungi and theHistory of Mycology
Figure 2 A young fungal colony, arising from a spore at the centre, and spreading radially outward by producing repeatedly branching hyphae. There are already 388 hyphal tips in the drawing, and this number increases very rapidly as the colony grows.
soon become relatively impermeable. In some fungi the interior of the hyphae is continuous (coenocytic), but in most it ispunctuated at regular intervals by perforated crosswalls or bulkheads called septa, which strengthen the hypha and may also regulate nuclear migration. The advantages of this life form may be expressed succinctly as follows. The fungal hypha, with its strong, waterproof, chitinous (or cellulosic) wall, the repertoire of enzymes it can secrete at its growing tip, and the hydrostatic pressures it canbring to bear, is ideally suited for actively penetrating, exploring and exploiting solid substrates in a manner that the bacteria, chief competitors of the fungi,
cannot match. Fungi have evolved biochemical versatility, because in many cases they must be opportunistic, in order to be able to survive on a variety of food substrates. Almost any organic substrate is vulnerable to one fungus or...