ORDER PLASMODIOPHORALES 



33 



Fig. 8. Plasmodiophorales. (A) Spore balls of Spongospora subterranea (Wall.) 

 Lagerheim. (B-E) Plasmodiophora brassicae Wor. (B) Biflagellate zoospores. (C) 

 Amoebae in root hairs. (D) Young plasmodia in root cortex. (E) Host cell filled with 

 spores. (F) Sorosphaera veronicae Schroet. (A, after Osborn: Ann. Botany, 25(98) :327- 

 341. B, after Ledingham: Nature, 133(3362) :534. C-E, after Chupp: Cornell Univ. 

 Agr. Sta. Bull, 387 :421-452. F, after Palm and Burk: Arch. Protistenk., 79(3) :263-276.) 



flagella have not been determined in this species. The foregoing authors 

 beheve that the swarm cells unite by twos and that the resulting amoeboid 

 zygotes are the origins of the large plasmodia which give rise to the resting 

 spores. The zygotes and young plasmodia arising from them may possibly 

 unite to form larger plasmodia. These are slowly amoeboid and at least 

 in their younger stages seem to be able to pass from cell to cell of the host. 

 The young plasmodia apparently may undergo division. As growth of the 

 parasite progresses, the host cells multiply hyperplastically and the 

 infected cells undergo hypertrophy. Eventually the cell contents of the 

 invaded cells are almost completely exhausted and the cell is practically 

 filled by the Plasmodium. The nuclei of the latter then undergo two 

 rapidly succeeding divisions which are believed to be meiotic, although 

 cytologic studies have not definitely proved this. Then the protoplasm 

 rounds up into uninucleate spores around each of which a dark chitin 

 wall is secreted. There is no enclosing membrane around the mass of 

 spores which lie free in the host cell. Upon decay of the root the spores 

 are set free. In the laboratory they are brought to germination only with 

 difficulty. The wall cracks open and the zoospore emerges with the two 

 flagella in advance of the cell body. At this stage, the author has observed 

 the two flagella on the living zoospore before it has escaped from the 

 spore wall, so that there is no doubt as to the correctness of Ledingham's 



