PLASMODIOPHORALES 



healtliy cells, with the result that conspicuous ex- 

 cresences and galls are usually formed. However, 

 only two species are economically important as para- 

 sites. Plasmodiophora Brassicae and Spongospora 

 subterranea are destructive pathogens of crucifers 

 and potatoes, respectively, and cause the diseases 

 commonly known as club root and powdery scab. 



While these diseases had been recognized since 

 early times, their causative agents were not identified 

 until the latter part of the 19th century. The discov- 

 ery of P. Brassicae in hypertrophied roots of cruci- 

 fers by Woronin in 1 877 may be said to have initiated 

 the study of the Plasmodiophorales as a distinct 

 group of organisms. A second genus, Tetramiixa, 

 was found by Goebel in 1881, and in the same year 

 Zopf created a new family, Plasmodiophoraceae, in 

 the zoosporic Monadineae to include these genera. 

 Two additional genera, Spongospora and Soro- 

 sphaera were reported by Brunchorst and Schroeter 

 in 1886, but the relationship of the former genus was 

 not generally recognized until much later. Schroeter 

 ignored Zopf's classification and created a new or- 

 der, Phytomiixini, with one family, Phytomyxaceae, 

 to include these genera as well as the legume tubercle 

 organism which he redescribed as Phiitomijxa legii- 

 minosarum. Inasmuch as Schroeter's Phytomyxinae 

 was later ('97) incorporated in Engler and Prantl's 

 Die Natiirlichen Pflanzenfamilien, it was widely 

 recognized and accepted. Phiitomyxa as well as 

 Plasmodiophora Alni and P. Elaeagni were excluded 

 by Tubeuf and Smith ('97) and other pathologists in 

 their discussions of the parasitic slime molds, but 

 Schroeter's order and family names nonetheless con- 

 tinued to be used. In 1909 Maire and Tison made an 

 extensive review and study of these doubtful species 

 and showed again that P. legiiminosarum, P. Alni, 

 P. Elaeagni, Tylogonus Agavae, and Pseudocommis 

 J'iiis have little or nothing in common with the true 

 plasmodiophoraceous species. Since Phyiomi/.ra had 

 already been excluded, they pointed out that the 

 name Phytomyxaceae was no longer appropriate. 

 They accordingly adopted Zopf's Plasmodiopho- 

 raceae to include Plasmodiophora, Tetraviy.ra, and 

 Sorosphaera and listed Schroeter's Phytomyxinae 

 pro parte and Delage's Protomyxideae zoosporideae 

 as synonyms. Apparently unaware of ]\Iaire and Ti- 

 son's studies, some protozoologists nevertheless still 

 continue the use of Schroeter's Phytomyxinae or 

 some modification of this name. 



In the meantime, Sporomyra and Peliomyces had 

 been added to the group, and following Maire and 

 Tison's first paper, Ligniera, MoUiardia, Sorodiscus, 

 Ostenfeldiclla, Cystospora, Tremaiophlyciis, Clath- 

 rosorus, Memhranosorus, Polymy.ra and Octomyxa 

 were successively discovered and included in the 

 Plasmodio])]ioraceae. However, many of these gen- 

 era have eitlier been merged or excluded entirely, so 

 that the order includes at present comparatively few 

 valid genera. The group as a whole was finally raised 

 to ordinal rank by Cook ('28, '33), following a sug- 

 gestion made by Schwartz in 191 K 



Taxonomically, the Plasmodiophorales have been 

 bandied back and forth by protozoologists and my- 

 cologists for more than half a century, and few work- 

 ers are in agreement about tlie taxonomic position 

 and relationships of this order. Its members have 

 been included at various times in the Mycetozoa, 

 Monadineae, Proteomyxa, Rhizopoda, and Chytri- 

 diales. Some mycologists, particularly Gwynne- 

 V^aughan, Barnes, and Cook ('33), have maintained 

 that the Plasmodiophoraceae are not fungi and have 

 arisen along independent lines from more primitive 

 forms. However, the rediscovery within the last two 

 decades of zoosporangia in this order and the ob- 

 servations that biflagellate heterocont zoospores are 

 produced in such sporangia and also from resting 

 spores indicate a closer affinity with the simple fungi 

 than was formerlv believed to exist. 



Glossary 



Akaryote stage, a nuclear stage in which little or no 



chromatin is visible in the nucleus. 

 Binuclearity hypothesis, the theory that the micro- 

 and macronuclei of infusoria contain the idio- and 

 • trophochromatin, respectively, and that the ordi- 

 nary nucleus of higher forms is accordingly a dual 

 "amphinucleus. ' 

 Blepharoplast, the basal granule at the point of in- 

 sertion of each flagellum. 

 Capillitium, sterile filamentous, simple, branched, or 

 net-like tubes or fibers formed among spores in a 

 sporogenous body. 

 Chromidia, trophochromatin granules which are ex- 

 truded from tlie nucleus into the cytoplasm. 

 Chromidia hypothesis, the theory that the nuclei of 

 rhizopods and other similar organisms contain 

 idio- and trophochromatin. the latter of which is 

 extruded into the cytoplasm as chromidia and de- 

 generates or plays a dominant role in the differ- 

 entiation of specialized structures. 

 Chromidial stage, a nuclear stage during which the 



trophoeliromatin is extruded into the cytoplasm. 

 Cruciform stage, equatorial ring stage of promitosis 

 in the Plasmodiophorales during which the nu- 

 cleole is elongate and forms a cross with the chro- 

 matin ring. 

 Cystosorus, a more or less compact aggregate of 



cysts or resting spores. 

 Eucarpic, only a portion of the tliallus transformed 

 into a reproductive organ; remainder of thallus 

 vegetative. 

 Extramatrical, outside of host, matrix, or substra- 

 tum. 

 Double-anchor stage, anaphase stage of promitosis 

 in the Plasmodiophorales during which the arched 

 daughter chromatin bands and nucleoli are con- 

 nected by a chromatic strand and form a figure re- 

 sembling a double anchor. 

 Dumb-bell stage, more or less synonymous with 

 double-anchor stage of promitosis. 



