788 AQUATIC PHYCOMYCETES 



Even in it, however, a considerable number of the cystosori are some- 

 what circular in outline and one- or two-layered. The answer to the 

 question of what is the correct generic concept of Sorodiscus still awaits 

 critical study and evaluation. 



KEY TO THE SPECIES OF SORODISCUS 



On Cham S. karlingii, p. 788 



On filamentous Phycomycetes (Pythium) S. cokeri, p. 789 



Sorodiscus karlingii Cook 



Arch. Protistenk., 80: 207. 1933 



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



"Cystosori numerous, up to 400 in a cell, quite variable in size and 

 shape, often oval, elongate and disc-shaped, 1 5-30 \x x 45-70 \x, occa- 

 sionally almost spherical, 10-35 \x in diameter, irregular, or reduced to 

 tetrads, triads, diads and rarely monads ; consisting of from 1 to 200 

 spores; enveloping membrane unknown. Resting spores polygonal and 

 angular, 4-9 [x, when pressed together in large sori, spherical, oval and 

 ellipsoidal when single or in small groups, 5-23 :ji in diameter, uni- or 

 multinucleate with hyaline smooth walls and surmounted by one and 

 occasionally two fairly thick caps; germination unknown. Plasmodia 

 one to several in a cell, multinucleate, and up to 90 \x in diameter; 

 schizogony unknown. Zoosporangia and zoospores unknown" (Kar- 

 ling, 1942d). 



Parasitic in Chora contraria and C. delicatula, causing marked hyper- 

 trophy, Karling (1928c: 485, figs. 1-9; 1942d: 50, pi. 8), Chara sp., 

 (Michigan) United States. 



The species may be quite abundant in the lakes in Lower Michigan 

 in some years. 



Because of the variations in shape of the cystosori and the lack of a 

 common surrounding membrane, Karling (1942d) retains the species in 

 Sorodiscus only provisionally. The Michigan material in spite of var- 

 iations in the shape and size of the cystosori fits well enough into 

 Sorodiscus as now defined. 



