24 COMPARATIVE MORPHOLOGY OF FUNGI 



Psoralea Mutisii and S. aecidioides (Uredo aecidioides) on Amphicarpa in 

 the United States (Gaumann, 1927). 



Still insufficiently known and hence of uncertain position are Microm- 

 yces (Dangeard, 1889) in Zygotonium in western France, Sorolpidium 

 (Nemec, 1911, Guyot, 1927) in the cortical cells of Beta vulgaris (B.mari- 

 tima) in Czechoslovakia and Anisomyxa (Nemec, 1913) in the cortical 

 cells of roots of Plantago lanceolata in Czechoslovakia. All three agree 

 in that their thalli break up into zoosporangial sori and that the zoospores 

 are uniflagellate. The two latter appear to differ from Synchytrium in 

 nuclear relationships. 



Plasmodiophoraceae. — In spite of many studies, there is still much 

 doubt in the decisive points of the life cycle, particularly in regard to the 

 peculiarities of nuclear division and the existence of caryogamy. Usually 

 single organs of phanerogams are stimulated to form tumors within which 

 spores are produced. 



At spore germination, which generally occurs in spring, there arises 

 from each spore an amoeboid zoospore (myxamoeba) with an apical 

 flagellum, which in Spo?igospora combines with the myxamoebae from 

 other spores (Kunkel, 1915) and penetrates the host. In the first stages 

 of the disease, one finds in the protoplasm of the host cell, one or more 

 naked bodies of protoplasm (myxamoebae) which have penetrated (Fig. 

 14, 2). They grow markedly and by repeated promitotic nuclear 

 division become multinucleate (schizont stage) and successively cut off 

 daughter amoebae (meronts) as short blunt processes (Fig. 14, 3). With 

 the divisions of the host cells, where such occur, the amoebae are again 

 divided among the daughter cells; however they are also able to wander 

 independently from cell to cell (Kunkel, 1918). The host cells gradually 

 swell up and the schizogonia of the amoebae proceed until the exhaustion 

 of the reserve stores. 



Then the amoebae of each host cell join to form a plasmodium, and 

 their nuclei extrude a part of their chromatin (Fig. 14, 4 and 5). Their 

 further phases are still insufficiently known. Prowazek (1905) for 

 Plasmodiophora Brassicae, the cause of clubroot of cabbage, and Osborn 

 (1911) for Spongospora subterranea, the cause of powdery scab of potatoes, 

 have claimed that some nuclei come together in pairs and fuse, while 

 the surplus nuclei degenerate and disappear; these statements, however, 

 have not been confirmed. In any case there follows a generative period 

 in which throughout the plasmodia, there occur two synchronous, 

 nuclear divisions, one of which is meiotic (Fig. 14, 7); the plasmodia 

 divide into uninucleate portions, surround themselves with a membrane 

 and develop as spores (Fig. 14, 1, 8). 



These spores are generally comparatively thick walled and very resist- 

 ant to external influences. In Plasmodiophora (Woronin, 1878; Naw- 

 aschin, 1899; Prowazek, 1902, 1905; Maire and Tison, 1909; Favorski, 



