774 AQUATIC PHYCOMYCETES 



This order contains only one family, the Plasmodiophoraceae, par- 

 asites of terrestrial and aquatic flowering plants and fresh-water algae, 

 Phycomycetes, and Isoetes. 



PLASMODIOPHORACEAE 



Characters those of the order. 



As in the first edition the Plasmodiophoraceae includes Woronina, 

 which was placed by Minden (1915) and later authors in a separate 

 family of the Chytridiales, the Woroninaceae. Rozella septigena Cornu, 

 in the sense of Fischer (1882), and R. simulans Fischer may yet be found 

 to be referable to the Plasmodiophoraceae (see the delineation of the 

 zoospores of R. septigena by Tokunaga, 1933a). They are, however, 

 given here under Rozellopsis (pp. 924, 925) of the Olpidiopsidaceae. 



No original taxonomic treatment of the genera and species of the 

 parasites of aquatic vascular plants can be attempted. The reader is 

 referred to the monographs by Cook (1933b) and Karling (1942d) for 

 details of these and other species. 



KEY TO THE AQUATIC GENERA OF THE PLASMODIOPHORACEAE 1 



Parasitic in the hyphae of aquatic Phycomycetes and in filaments of 

 Vaucheria; zoosporangia globose 

 Infected parts of the host segregated by cross walls; resting spores 

 either linearly or irregularly grouped or aggregated to form a 



somewhat globose mass Woronina, p. 775 



Infected parts of the host not segregated by cross walls; resting spores 



grouped predominantly in eights Octomyxa, p. 782 



Parasitic in aquatic vascular plants and Chara; zoosporangia variously 

 shaped 

 Resting spores scattered, without definite arrangement in the host 



cells ; infected parts of the host strongly hypertrophied 



Plasmodiophora, p. 783 



Resting spores more definitely aggregated; infected parts of the host 

 with or without hypertrophy 



Resting spores in irregular groups; host not hypertrophied 



Ligniera, p. 784 



Resting spores in groups of two and four; host hypertrophied . . . 



Tetramyxa, p. 785 



Resting spores in two layers, forming a flat ellipsoidal plate; host 



hypertrophied Sorodiscus, p. 787 



Resting spores forming spherical or ellipsoidal, usually hollow 



masses; host hypertrophied Sorosphaera, p. 790 



1 Note that the key is not strictly dichotomous. 



