SIMPLE LIFE 



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ancient than flagellates and the fungi might have 

 evolved from the bacteria. This creates a problem 

 because the archaic protistans often are believed to 

 have been flagellates. However, bacterial origin of the 

 fungi was suggested long before the fossil indication. 

 In fact, many botanists include the bacteria and true 

 fungi in the same phylum; however, any relationship 

 between the two groups seems too remote to make a 

 single-phylum grouping meaningful. In addition, 

 joining the bacteria with the fungi would minimize 

 the importance of the Monera. 



Although there is some disagreement about the 

 true status of the Eumycophyta, there appears to be 

 adequate evidence for placing the three classes that 

 follow into a single phylum. Not only do the struc- 

 tures of the three groups show close relationship and 

 the possibility of straight-line evolution from Phyco- 

 mycetes to Ascomycetes to Basidiomycetes, but the 

 fossil record implies the same temporal sequence in 

 the three classes. 



Like the slime molds, true fungi lack both chloro- 

 phyll and the process of photosynthesis. For this 

 reason, many fungi are found in areas of darkness, for 

 example, underground and in caves. Other fungi are 

 quite inconspicuous, and neither their structures nor 

 other indications of their presence are likely to be 

 noticed. Still others are noted mostly by their ef- 

 fects upon the plants or animals they parasitize. 

 Most of the conspicuous algal fungi have the ap- 

 pearance of molds and are found either upon dead 

 plants and animals in water or upon dead insects and 

 organic remains on land. For details of the sac and 

 club fungi, one should study the synopses of the 

 classes. 



Structure: generally simple and usually multicellu- 

 lar (cellular organization), but also species with one 

 to many nuclei and typically not filamentous (uni- 

 cellular); multicellular forms mostly filamentous, the 

 hair-like filaments sometimes organized into moldy- 

 looking masses or visible fruiting bodies; fruiting 

 bodies normally spherical, oval, or shaped like a 

 pear, funnel, cup, umbrella (toadstools or mush- 

 rooms), hoof, cushion, disc, club, branching tree or 

 coral, or quite irregular; filaments spread over sub- 

 strate or branch within living or dead organic mat- 

 ter; usually without any tendency toward tissue 

 formation. 



Cells are distinct or without cell walls, so nuclei are 

 in a continuous cytoplasm; when distinct, cells may 

 have one to many nuclei; nuclei complete and com- 



plex; cytoplasm without photosynthetic pigments; 

 cell walls often absent; when present, they are 

 usually chitinous, sometimes having cellulose; 

 flagellae absent, or one or two in some Fhycomy- 

 cetes spores. 



A single filament is called a hypha; a mass of 

 hyphae, a mycelium. 



Fruiting bodies are usually limited to sexual spore 

 production, but asexual spore-producing types are 

 known. 



.\utrition: parasitic or saprophytic; both types 

 found throughout the phylum. 



Reproduction: asexual occurs by fragmentation, 

 budding, mitosis, and spore production; sexual re- 

 production and parthenogenesis also occur. 



Life cycle: very complex (Figures 8.11, 8.13, and 

 8.15); probably all types occur; generally there is an 

 alternation of haploid and diploid phases (if not gen- 

 erations) and a true diplobiontic cycle; many fungi 

 have an asexual cycle associated with a sexual cycle, 

 both cycles stemming from and generally returning to 

 a vegetative stage (often a mycelium). 



In the asexual cycle a vegetative stage (usually a 

 mycelium) forms spore-producing structures; spore- 

 producing structures form asexual spores; asexual 

 spores produce the vegetative stage or transform 

 directly into gametes. 



In the sexual cycle the vegetative stage usually 

 forms structures which directly or indirectly form 

 gametes; then gametic fusion (fertilization) or 

 parthenogenesis occurs, followed later by nuclear 

 fusion and zygote formation; then the zygote may go 

 into either a resting-spore or a sporangium stage 

 prior to meiosis and the vegetative structure de- 

 velopment; or these stages are accompanied by the 

 development of a fruiting body; and finally, some 

 fruiting-body hyphae produce sexual spores which 

 germinate into a filament mass (vegetative 

 mycelium) ; still other variations occur. 



The sexual cycle usually contains a perfect stage, 

 one in which structures (often fruiting bodies) re- 

 lated to zygote formation and meiosis occur. Fungi 

 without such a stage are grouped as Imperfect 

 Fungi. 



Occurrence: widespread as parasites on plants and 

 animals and as saprophytes on organic remains; in- 

 clude about 1300 Phycomycetes, about 15,000 

 Ascomycetes, and about 15,000 Basidiomycetes. 



Although the fungi include the most conspicuous 

 protistans, some are microscopic, unicellular or 



