PLASMODIOPHO RALES 787 



to form tetrads of resting spores. Zoosporangia and zoospores unknown" 

 (Karling, 1942d: 37). 



A monotypic genus, members of which are parasitic on and cause 

 hypertrophy (galls) of marine vascular plants. 



SPECIES IN AQUATIC VASCULAR PLANTS 



Tetramyxa parasitica Goebel 



Loc. cit. 



Parasitic in Ruppia spp., Zannichellia spp., and Potamogeton panor- 

 mitanus (see recent paper by Luther, 1950, for numerous records of 

 occurrences and hosts). 



SORODISCUS Lagerheim and Winge 

 Arch. f. Botanik, 12(9): 23. 1913 

 (Fig. 59 A-D, p. 786) 

 Membranosorus Ostenfeld and Petersen, Zeitschr. Bot., 23: 17. 1930. 



Cystosori usually flat, oval, disc-shaped and composed of one or two 

 layers of spores pressed closely together, often variable in size and shape, 

 rarely hollow spheres, occasionally an elongate and irregular linear se- 

 ries of spores or reduced to tetrads, triads, diads and rarely monads ; 

 soral membrane doubtful or lacking; resting spores polygonal, angular 

 and urn-shaped or oval and almost hemispherical with hyaline smooth 

 or spiny outer walls, apical collar and cap present or lacking, remaining 

 attached or separating at maturity, producing one or possibly more 

 than one zoospore in germination; zoosporangia thin-walled, spherical 

 or ovoid (in S. cokeri) ; zoospores with one short anterior flagellum and 

 a long posterior one, discharged after the deliquescence of papillae; 

 Plasmodia one to several in a cell, large or small, schizogony lacking or 

 doubtful in some species. (Modified from Karling, 1942d: 46.) * 



Parasites of aquatic vascular plants, Characeae, and Pythium. 



Karling's (loc. cit.) diagnosis of the genus was sufficiently broad to 

 allow for the inclusion of Sorodiscus {Membranosorus) heter anther ae, a 

 species which is somewhat variable with respect to type of spore mass. 



1 Modified in the light of Goldie-Smith's (1951) findings. 



