BIFLAGELLATAE 



PLASMODIOPHORALES 



Although the Plasmodiophorales is not ordinarily considered a 

 group of primarily aquatic fungi, over half the species in Cook's 

 (1933b) and Karling's (1942d) accounts of the order, and in subsequent 

 literature, are obligate parasites of aquatic vascular plants, Characeae 

 or aquatic fungi. The discovery in recent years of plasmodiophoraceous 

 fungi on Phycomycetes has proved particularly fruitful in clarifying the 

 concepts of life histories and relationships. On such hosts their devel- 

 opment, reproductive activity, and so forth, can most readily be follow- 

 ed. Some have regarded the Plasmodiophorales as Phycomycetes 

 (Fitzpatrick, 1930; Sparrow, 1943). Others assigned them a vague po- 

 sition between the Myxomycetes, Protozoa, and Phycomycetes. Still 

 others classed them as a family of the Myxomycetes. Schroeter (1885, 

 1893) placed them in the Phytomyxinae, a group of organisms more 

 animal-like than plant-like. Gaumann (1926) and Gaumann and Dodge 

 (1928) originally thought them to be Archimycetes, a group separate 

 and coequal with the Phycomycetes (see Martin, 1932, 1940; Karling, 

 1942d). 



While the Plasmodiophorales are not chytrids, their inclusion in the 

 Phycomycetes seems increasingly justified by the evidence. A phycomy- 

 cetous sporangial stage has been clearly demonstrated in species of 

 Sorodiscus (Goldie-Smith, 1951), Spongo\pora (Kole, 1954), Woronina 

 (Goldie-Smith, 1954), Octomyxa (Couch, Leitner, and Whiffen, 1939; 

 Pendergrass, 1948, 1950), and Polymyxa (Ledingham, 1939; Sparrow, 

 1947b). Protomitosis 1 and the formation of a heterocont type of zoo- 

 spore (one with two unequal flagella) have been proven typical for 

 valid members of the order. The presence of these in Woronina poly- 

 cystis (Goldie-Smith, 1954) substantiates, therefore, the earlier transfer 

 of that genus (and family) to the Plasmodiophorales (Sparrow, 1943). 



Karling (1942d), while he did not commit himself specifically as to 



1 See Nawaschin (1899) and Home (1930). 



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