ORDER PLASMODIOPHORALES 35 



Burk (1933), is a very doubtful genus. Zoosporangia are known but 

 further study is needed to determine whether the zoospores are truly 

 uniflagellate anteriorly as reported or biflagellate. 

 Polymyxa: spores in irregular clusters in the roots of grasses, zoosporangia with 

 long necks are abundant, zoospores from the resting spores as well as 

 those from the zoosporangia are anteriorly biflagellate and heterocont 

 (Ledingham, 1939). Sexual reproduction has not been observed. Hyper- 

 trophy of the host cells is not brought about. 



Several other genera have been ascribed to this family but Karling 

 (1942) is doubtful as to the correctness of their assignment here {Sorol- 

 pidium, Anisomyxa, Trematophlyctis, Sporomyxa, Peltomyces, Cystospora). 



The relationship of the four orders — -Myxogastrales, Acrasiales, 

 Labyrinthulales, and Plasmodiophorales — described in the foregoing, is 

 not admitted by all. Sparrow (1943) places the last named order in his 

 group Biflagellatae, in which he also includes the Saprolegniales, Lepto- 

 mitales, Lagenidiales, and Peronosporales. The author admits the simi- 

 larity of Octomyxa and Polymyxa to Woronina, which he includes in the 

 Lagenidiales. It is possible that with further study of these and some 

 other genera now assigned to the Plasmodiophorales they may be found 

 to have cell-wall composition and flagellar structure that will compel 

 their removal from their present position. Be that as it may, the order 

 stands or falls by its type species Plasmodiophora hrassicae. Therefore it is 

 with this species that comparisons must be made. 



In these four orders the resting spores possess a cell wall whose chief 

 component is chitin in Plasmodiophora but is not definitely determined 

 in the other groups. Upon germination a naked amoeboid uninucleate cell 

 is set free, which may lack flagella (Acrasiales, Lahyrinthula of the 

 Labyrinthulales) or which may have one or two anteriorly attached 

 flagella (Myxogastrales, Labyrinthomyxa of the Labyrinthulales, and 

 Plasmodiophora). Where two flagella are present they are both of the 

 w^hiplash type, neither being of the tinsel type. Sexual reproduction where 

 reported (Myxogastrales and Plasmodiophora) is by the union of two 

 myxamoebae or two flagellate swarm spores. The vegetative body of the 

 organism is a Plasmodium or a more or less loose aggregation of myxa- 

 moebae. Eventually this separates into naked uninucleate spores around 

 which a spore wall is produced. Because of the naked vegetative body of 

 Plasmodia! nat^ure the zoologists have included these four groups among 

 the Protozoa. The protozoologist Kudo (1946) places these four groups 

 in Phylum Protozoa, Class Sarcodina, including the Labyrinthulales in 

 his Order Proteomyxa, and the other three in his Order Mycetozoa. 



The genus Reiiculomyxa has recently been described by Miss Nauss 

 (1949). The organism consists of a central multinucleate Plasmodium 

 with radiating, forking, and anastomosing branches which appear to be 

 the chief organs for the capture of the food particles upon which it lives. 



