6* 



PLASMODIOPHORALES 



appearance. Very shortly thereafter progressive 

 cleavage (fig. 15) begins and delimits the individual 

 resting spores which remain in continuity as clusters 

 (fig. 16). The resting spores are usually uninucleate, 

 and in germination each gives rise to one zoospore 

 (fig. 21 ) which is similar in size, shape and structure 

 to those formed in the zoosporangia. 



Polymyxa is strikingly similar to Ligniera in size 

 and shape of its cystosori, size, shape and arrange- 

 ment of resting spores, and by its failure to cause 

 hypertrophy of the host. It differs primarily by the 

 shape and size of its zoosporangia, but this differ- 

 ence may be only specific instead of generic. The 

 lack of schizogony in Polymyxa, which Ledingham 

 cited as an additional difference, may not prove to be 

 of great significance, since its presence in Ligniera 

 also is still quite doubtful. 



P. GRAMINIS Ledingham, I.e.; 1939. Canadian Jour. 

 Res. C, 17:50. PI. 1-3. 



Resting spores spherical, polygonal, 4-7 /tt ; con- 

 tents hyaline and ref ringent ; inner wall hyaline, 

 outer wall smooth, yellowish-brown. Zoosporangia 

 lobed. oval, uteriform and irregular; exit tubes of 

 variable length. Zoospores broadly spindle-shaped, 

 ovate, pyriform, I— .5 jj. in diameter; flagella 16—20 jx 

 and 4— .5 /x long respectively ; zoospores emerging 

 fully formed and swimming directly away ; rolling 

 over and over while in motion, intermittently amoe- 

 boid. Plasmodium variable in size and shape, often 

 filling host cell, amoeboid in shape and motion. 



Parasitic in the roots of Triiicum aestiz'iivi, T. 

 durum, Hordeum vulgare, and Secale cereale in 

 Canada. 



Ledingham found similar resting spores in roots 

 of species of Agropyron, Scolochloa, Rumex, and 

 Impatiens, but since no sporangia were present, he 

 was uncertain about the relation of this fungus to 

 P. graminis. He reported further that species of 

 Juncus and Poa in which Ligniera parasites occur 

 failed to become infected when grown witli parasit- 

 ized wheat roots. He accordingly regarded P. grami- 

 nis as an obligate parasite. Truscott ('34) also re- 

 ported what he believed to be P. graminis in roots of 

 strawberries in Canada. 



DOUBTFUL GENERA 



Under tliis title are presented four genera about 

 which there has been much disagreement and con- 

 troversy. Rhi-omyxa, Sorolpidium, and Anisomyxa 

 occur in the roots of higher plants, do not cause hy- 

 pertrophy, and form cvstosori of indefinite size and 

 shape. In these characters they resemble Ligniera 

 and are regarded by most recent investigators as 

 synonyms of this genus. Trematophlyctis, however, 

 parasitizes leaves and petioles and causes marked 

 hyixrtrojjhy. There is very little evidence in Patouil- 

 lard's account to warrant inclusion of this genus in 

 the Plasmodiophoraceae, but inasmuch as Palm sub- 

 sequently reported it to be "an undoubted member of 



this family" a brief description of its life cycle is 

 herewith presented. The present writer is in agree- 

 ment with Maire and Tison's, Ciuyot's, Cook's, and 

 Barrett's interpretation of Rhisomyxa, Sorolpidium 

 and Anisomyxa, but further intensive study may pos- 

 sibly reveal distinct generic differences. For this rea- 

 son thev are described and figured separately, so that 

 research students may judge independently the evi- 

 dence of identity and relationships of these genera. 



RHIZOMYXA 



Borzi, 1884. Rhizomyxa, nuova ficomicete, Mes- 

 sina. 



(plate 12, fig. 23-30) 



Plasmodia partly or completely filling host cell, 

 variable in size and shape ; forming at maturity 

 either single large zoosporangia or sporangiosori 

 composed of small zoosporangia. or cystosori ( ?). 

 Cvstosori and resting spores poorly known or doubt- 

 ful. 



R. HYPOGEAE Borzi, I.e., pi. 1, 3. 



Sporangiosori one or more in a cell, spherical, 

 ovoid, irregular, elongate, sometimes made up of lin- 



PLATE 12 

 Pnlymy.ra graminis 



(All figures, except 30 and -21, after Ledingham; fig. (i, 7, 

 8, 17, 19 and il drawn from photographs.) 



Fig. 1-3. Biflagellate heterocont uninucleate zoospores. 



Fig. 4. Large binucleate tetraflagellate zoospore. 



Fig. j. Living, amoeboid zoospores. 



Fig. 6. Zoospore on surface of root hair. 



Fig. 7. Zoospores after entrance Into root hair. 



Fig. 8. Stained zoospore inside of cortical cell shortly 

 after penetration. 



Fig. 9-11. Stages in development of zoosporangial thalli. 



Fig. 12. Mature zoosporangia with exit tubes passing 

 through adjacent cells. 



Fig. 13. Naked myxamoeba during period of active 

 growth. 



Fig. 14. Segments or meronts formed by division of Plas- 

 modia. 



Fig. 15. Same cell as in fig. 13 after meronts have coa- 

 lesced to form a large plasmodium. 



Fig. K). Plasmodium just I'.rior to cleavage into incipient 

 cystosori. 



Fig. 17. Cleavage of plasmodium into cvstosori. 



Fig. \S-2\. Variations of cystosori. (Fig. .'0 and 2\ 

 drawn from material presented by Ledingham.) 



Fig. 22. Zoospore from resting sjiore stained in Into. 



Hhh(>myx<t hypogeae 



(.\11 figures after Borzi) 



Fig. 23. Zoospore. 



Fig. 2\, 2o. Germination and infection stages. 



Fig. 2ti. Plasmodia within liost cells. 



Fig. 2", 2S. Sporangiosori and sporangia. 



Fig. 29. Emergence of zoospores. 



Fig. 30. Zoospores from sporangia. 



