96 PHYCOMYCETEAE 



to simpler vegetative structure they perforce become very similar. 

 Sparrow (1943) includes these simple or simplified forms in five famihes 

 in two orders (not coinciding entirely with the famihes recognized by 

 Karling). 



The author follows Sparrow in part in his distinction of three famihes 

 to which he adds doubtfuhy the Woroninaceae and Thraustochytriaceae. 



Woroninaceae : fungus remaining naked and amoeboid for a considerable time, 

 forming a " Plasmodium "(?)■ Eventually separating into several segments 

 which produce cell walls and become zoosporangia or the whole "Plas- 

 modium" enlarging to form a single zoosporangium with its wall in close 

 contact with the host wall. Zoospores preformed in the zoosporangia. Clusters 

 of angular or single round resting spores may be formed. Parasitic in algae 

 and fungi. 



Olpidiopsidaceae: one-celled, free in the host cell and early producing a cellu- 

 lose wall. Zoospores preformed in the zoosporangium. Resting spores formed 

 sexually or by parthenogenesis. Parasitic in algae or fungi. 



Sirolpidiaceae: forming a linear series of zoosporangia, occasionally a single, 

 elongated zoosporangium. Zoospores preformed in the zoosporangium. 

 Sexual stage unknown. Parasites in marine algae. 



Lagenidiaceae: one-celled or more often a short, constricted or unconstricted, 

 unbranched or branched row of cells, each of which becomes a zoosporangium 

 or gametangium. Zoospores completing their development in a vesicle at 

 the opening of the exit tube. Oospores formed within the female gametan- 

 gium. Parasitic in algae (mainly fresh-water forms) or microscopic animals 

 or roots of grasses. 



Thraustochytriaceae: resembling Rhizophydium. Parasitic upon marine algae. 

 Zoosporangium epibiotic, obpyriform, attached to a branched endobiotic 

 rhizoidal system. Zoospores formed in the zoosporangium but not motile, 

 and set free by the dissolution of the apical portion of the wall, as angular 

 cells, from which after some time the biflagellate motile stage emerges. 

 Zoosporangia proliferating after the discharge of the zoospores. A family of 

 very doubtful relationship. 



Family Woroninaceae. In this family of possibly three genera the 

 zoospores encyst on the external surface of the host and empty their 

 contents into the host cell through a slender tube, the empty spore walls 

 remaining attached for some time. Within the host cell the uninucleate 

 fungus remains naked and amoeboid and grows, accompanied by multi- 

 phcation of the nuclei, until it largely fills the cell. Eventually this 

 plasmodium-like structure separates into a group of several segments 

 around each of which a cellulose wall is produced. The zoospores produced 

 in these sporangia escape through exit tubes, those further inside the 

 sorus emptying through those nearer the surface. The zoospores are 

 biflagellate anteriorly. Instead of producing zoosporangia the naked 

 fungus mass may divide into very numerous small angular resting spores, 

 also with cellulose walls, which are clustered together in more or less 

 definite compact cystosori of a few to many spores. Each resting spore 



