CHYTRIDIALES 53 



When several myxamoebae exist together in the same host cell, 

 and continue to grow, it might be expected that they will finally 

 come into actual contact, and being naked fuse. They have 

 been stated to do so in some species, and certain writers have 

 termed the apparently united and homogeneous mass, which 

 tends to fill the host cell, the plasmodium. Other investigators 

 deny that fusion is complete, and maintain that mitosis is simul- 

 taneous only in a given myxamoeba, not throughout the entire 

 host cell. In Spongospora according to Kunkel (1915: 273) the 

 uninucleate myxamoebae which escape from the various spores 

 composing a spore ball may lie in such close contact that "they 

 seem to fuse and cannot be distinguished as separate bodies." 

 He states further that such " baby plasmodia " may come together 

 to form larger ones, and that infection of the host is effected by 

 the penetration of the multinucleate "plasmodium" between 

 the cells of the tuber. In the Myxogastres where the term Plas- 

 modium was first used by Cienkowski an as yet unexplained 

 phenomenon of mutual attraction exists between the motile cells. 

 They are drawn together, and multiple cell fusions result in 

 the formation of an enlarging naked amoeboid protoplast. This 

 body is termed a plasmodium not merely because it is naked and 

 multinucleate, but more essentially because it is formed by 

 multiple fusion of uninucle'ate motile cells which are drawn 

 together by mutual attraction. To the writer it does not seem 

 that such a true plasmodium has been found in any of the Plas- 

 modiophoraceae. In those species of the family in which a 

 fusion is conceded by all workers to be lacking, and in which the 

 nuclei of the mature multinucleate myxamoeba clearly arise 

 through repeated division from the nucleus of the infecting zoo- 

 spore, the use of the term plasmodium seems wholly unjustified. 



In attempting to indicate the bases on which it seems desirable 

 to incorporate the Plasmodiophoraceae in the fungi rather than 

 in the Myxomycetes it is necessary to deal in generahzations 

 on account of inadequate data. Enough is known concerning 

 the group, nevertheless, to warrant the attempt. In the 

 character of the zoospore and in the unusual type of vegetative 

 mitosis the Plasmodiophoraceae are unlike other known fungi. 

 The zoospore seems to resemble that of the Myxogastres, the 

 nuclear division to some extent that of certain Protozoa. In 

 the absence of capillitium and so called "sporangial" walls, 

 in the absence of a true plasmodium, and in the presence of para- 



