PLASMODIOPHORALES 791 



zoospores; zoospores about 4.5 jx long by 2.5 ;j. wide, pyriform with an 

 orange pigment spot and two lateral oppositely directed flagella. 



Saprophytic in Cystocloniumpurpurascens, in aggregate causing bright 

 orange spots, Sweden. 



There are a number of puzzling features about this fungus. From the 

 description it is difficult to understand the relationship of the plasmodial 

 thallus, which fragments into the spindle-shaped cells, to the sori of 

 sporangia. There is a possibility that two organisms are involved, a 

 Labyrinthula — often found, as was Pyrrhosorus, in decaying algae in 

 marine aquaria — and a Woronina-Wko, fungus to which the sori and 

 zoospores belong. Winge (1913), who points out the resemblance of 

 Pyrrhosorus to Sorolpidium, a parasite of beets, gives the following 

 account of the life history : Infection is presumably caused by the zoo- 

 spore, which penetrates the alga. Inside the host several myxamoebae 

 are found, some small with a single large nucleus, others larger with 

 many small nuclei. Juel thought it possible that the large multinucleate 

 thalli have arisen either by divisions of the single nucleus of the smaller 

 thalli or by the fusion of uninucleate plasmodia. The single large nucleus 

 of the smaller thallus, he believed, has simply enlarged after establish- 

 ment in the alga. The multinucleate Plasmodium may be extensive and 

 penetrate a great number of cells. Eventually it becomes walled and 

 within it are formed either a close aggregation of numerous small uni- 

 nucleated spindle-shaped cells, which round off and become the "spore 

 mother cells, ,, or scattered spindle-shaped cells, which sometimes also 

 eventually become spore mother cells. The closely aggregated, uni- 

 nucleated, naked spore mother cells may frequently have intermixed 

 with them sterile cells which degenerate. Each of the spore mother cells 

 and its nucleus undergoes three successive divisions. In this manner the 

 cell becomes divided into eight biflagellate zoospores, each with two 

 lateral flagella. 



Aleem (1953) identified amoeboid bodies in Ceramium rubrum from 

 Sweden with this fungus but offers no new clues as to its relationships. 



