CHYTRIDIALES 49 



a presentation in sequence of the essential historical facts con- 

 cerning the group. 



The oldest genus recognized at present as a member of the 

 family is Plasmodiophora. It was founded by Woronin (1878) 

 on the causal organism of clubroot of cabbage, P. brassicae Wor, 

 In his discussion of the genus, Woronin indicates clearly that 

 he regarded the organism as an undoubted relative of the Myxo- 

 mycetcs. Incidentally, he concluded that the legume tubercle 

 organism, long known and variously classified, should be placed 

 near it. Other students of the fungi accepted his point of view, 

 and a search for additional "parasitic slime moulds" followed. 

 Several new species were added to Plasmodiophora, and two new 

 monotypic genera Tetramyxa and Sorosphaera were erected. 

 The legume tubercle organism which had already received a 

 number of names {Schinzia leguminosarum Frank, Bacillus 

 radicicola Beijerinck, Rhizohium leguminosarum Laurent, Bactri- 

 dium radicicola Fischer) was now redescribed asPhytomyxa legumi- 

 nosarum by Schroter (1886:134), and a new order, Phytomyxini, 

 was erected for its reception. Because the group (as Phyto- 

 myxinae) was incorporated later by Schroter in the standard 

 work, Engler und Prantl's, Die Nattirhche Pflanzenfamilien, 

 it was generally accepted. It includes there the four genera 

 Plasmodiophora, Phytomyxa, Tetramyxa, and Sorosphaera, repre- 

 sented at that time by seven species, PI. brassicae Wor., PI. alni 

 (Wor.) Moll, PI. elaeagni Schroter, Phy. leguminosarum (Frank) 

 Schroter, Phy. lupini Schroter, T. parasitica Gobel, and S. 

 veronicae Schroter. 



Later, the legume tubercle organism was proved to be beyond 

 question one of the bacteria, and more recent investigations 

 indicate that the root tubercles on Alnus, Elaeagnus, Myrica, 

 and certain other non-leguminous plants are caused by the same 

 species or closely related ones. Consequently, Plasmodiophora 

 alni and PI. elaeagni have disappeared from the Phytomyxinae 

 along with Phijtomyxa. In a review of this situation, Maire 

 and Tison (1909) point out that, since Phytomyxa has been 

 removed, the name Phytomyxinae is no longer appropriate. 

 They use instead Plasmodiophoraceae, and under this heading 

 list the three remaining genera. They follow Schroter in sepa- 

 rating them on the basis of the arrangement of the spores, i.e., 

 Plasmodiophora (spores free from one another), Tetramyxa (spores 

 cUnging together in tetrads), Sorosphaera (spores arranged to 



