SPORE DISCHARGE AND DISSEMINATION 353 



SUMMARY 



Many fungi have no means of forcibly discharging their spores but must 

 depend upon the physical and biotic factors in nature for liberation and 

 dissemination of spores. Others possess special mechanisms for dis- 

 charging their spores away from the fruiting structures which bear them. 

 In most cases this violent discharge depends upon high osmotic pressure 

 within certain cells of the fungus. Increased osmotic pressure usually 

 is a result of the digestion of glycogen to soluble sugars. 



Many coprophilous fungi, such as Pilobolus, Ascobolus, Sordaria, and 

 Pleurage, forcibly discharge their spores for some distance toward the 

 source of light. In nature this adaptation is of great advantage to the 

 fungus in its dissemination by animals, which ingest the spores with the 

 vegetation. Some Discomycetes exhibit a puffing of the spores when 

 many asci discharge their spores simultaneously. 



In Pilobolus, Basidiobolus, and Entomophfhora the sporangia are forcibly 

 abjected from the sporangiophores. Ascospores may be ejected either 

 simultaneously or successively from the ascus. The ascus may elongate 

 to reach the surface of the ascocarp and discharge its spores, or the asci 

 may become detached in some Pyrenomycetes and, after being forced 

 through the ostiole, may explode to release the spores. In other species 

 the ascus walls are deliquescent, and the ascospores ooze out of the 

 ostiole. 



The basidiospores of most Basidiomycetes are forcibly discharged by a 

 mechanism which is not well understood. A drop of liquid is extruded at 

 the tip of the sterigma just prior to discharge and is believed to affect the 

 process in some way. The peridioles of Cijathus and Sphaerobolus may 

 be thrown several feet away from the fruit bodies. The latter fungus 

 exhibits a unique catapult action by a portion of the fruit body. Other 

 mechanisms act in the forcible discharge of the aeciospores of many rusts 

 and the sporangia of Peronospora. 



Air currents are the most common agent of dissemination of dry spores. 

 Spores borne in a sticky, malodorous, or sweet matrix are well adapted to 

 insect dissemination. Some fungi, such as Septobasidium, have estab- 

 lished a symbiotic relationship with certain insects, which are the sole 

 agents of dissemination. 



REFERENCES 



Andersen, A. L., W. B. Henry, and E. C. Tullis: Factors affecting infectivity, 



spread and persistence of Piricularia oryzae, Phytopathology 37: 9-4-110, 1947. 

 Brefeld, O.: Botanische Untersuchungen iiber Schimmelpilze, Heft 4, Verlag von 



Arthur Felix, Leipzig, 1881. 

 *Buller, A. H. R.: Researches on Fungi, Longmans, Roberts and Green, London. 



Vol. I, 1909; Vol. II, 1922; Vol. Ill, 1924; Vol. VI, 1934. 

 Couch, J. N. : The Genus Septobasidium, The University of North Carolina Press, 



Chapel Hill, 1938. 



