90 



PLASMODIOPHORALES 



naked plasmodium-like thalli, zoocysts, and sporo- 

 cysts. When aggregated the latter two structures are 

 comparable with the loose sporangio- and cystosori 

 found in plasniodiophoraceous and woroninaceous 

 species. Aphelidiopsis, Gymnococcus, Pseudosporop- 

 sis and Amylophagits may be taken as examples, and 

 for the sake of more concrete comparisons drawings 

 by de Bruyne and Scherffel of the zoospores and 

 some developmental stages of these genera have been 

 brought together in Plate 17. The zoospores of Pseu- 

 dosporopsis sp. {Bodo filobosus Stein, fig. 7-10), 

 Amylophagiis algarum (fig. \\-\2).P.rotatoriorhim 

 (fig. i3). and Aphelidiopsis epithe7nine (fig. li),like 

 those of the Plasmodiophora, Octomyxa, etc., have 

 two unequal flagella at the anterior end. In B. c/lo- 

 hosus and A. cpithemiae the short flagellum extends 

 forward and the longer one backward in swimming, 

 while in the other species the relative positions are 

 reversed. The zoospores may become amoeboid, and 

 engulf solid food particles (fig. 7, 8), and include a 

 well-defined contractile vacuole. In tiie latter two 

 characteristics they appear to differ sharply from 

 the zoospores of the Plasmodioijhoraceae, but as has 

 been noted before the zoospores of Polymyxa gra- 

 minis and the young plasmodia of /,. J unci are said to 

 engulf algae and particles of food. 



In all these species, except A. epithemiae and 

 Gymnococcus Cladophorae, the developing thallus 

 becomes invested with a membrane and forms one 

 zoocyst or zoosporangium (fig. 19). There is no 

 cleavage into segments and development of a spo- 

 rangiosorus, according to Scherffel. In A. epiihe- 

 miae, on the other hand, the type of development is 

 more like that of the Plasmodioplioraceae. The con- 

 tent of the zoospore enters the host, leaving the 

 empty spore case on the outside, feeds upon the host 

 protoplasm, and develops into an oval vacuolate thal- 

 lus (fig. 15) which appears to be naked or devoid of 

 a well-defined membrane. At maturity this plasmo- 

 dium-like thallus cleaves into from 2 to 8 segments 

 (fig. 16) which round up, form tliin membranes, and 

 become zoocysts. These vary greatly in size and in 

 the number of zoospores they produce. Small zoo- 

 cysts may form only 3 to 4. zoospores. No exit papillae 

 for the emission of zoospores are developed, and at 

 maturity the wall deliquesces and disappears (fig. 

 17) freeing the zoospores simultaneously. In G. Cla- 

 dophorae, however, the wall is thicker, more perma- 

 nent, and remains after the zoospores have emerged 

 (fig. 18). No exit papillae are present here also, and 

 the zoospores doubtless bore through the sporan- 

 gium wall as in A. algarum (fig. 20). Scherffel did 

 not observe resting spore formation, but his illus- 

 trations (fig. 22) suggest that they may be formed 

 in the same manner as the zoocysts. They lie free in 

 the host cell without an enveloping membrane. In P. 

 rotatoriorum as many as 8 resting s])ores are formed 

 in a sporocyst (fig. 21), but in this species they are 

 held together by a membrane. Germination of the 

 resting spores has not been observed. 



It is to be particularly noted that the type of nutri- 

 tion in these species is animal-like. The zoospores. 



amoebae, and developing thalli engulf chlorophyll 

 granules, starch grains, oil globules, etc., apparently 

 digest them in the food vacuoles, and extrude the 

 waste material shortly before sporogenesis. No con- 

 clusive evidence of this type of nutrition has been 

 found in the Plasmodiophoraceae, and this appears 

 to be one of the chief differences between these two 

 groups of organisms at present. 



Comparison on the basis of sexuality, time and 

 place of meiosis, alternation of generations, etc., 

 cannot be made, because very little is known about 

 these processes in the Proteomyxa. No good evidence 

 of fusion of amoeboid or motile gametes has been ob- 

 served in the biflagellate species. Likewise no evi- 

 dence of schizogony, "promitosis," "akaryosis" or 

 anj^ other reported cytological characteristics of the 

 Plasmodiophoraceae have been observed, but so far 

 Pseudosporopsis, Aphelidiopsis, and other similar 

 genera have not been intensively studied from fixed 

 and stained material. It is accordingly premature to 

 draw conclusions on these grounds. 



The belief that the Plasmodiophoraceae are re- 

 lated to Protozoa, exclusive of the Proteomyxa which 

 have already been discussed, stems primarily from 

 the views of the protozoologists who have included 

 this family among the primitive animals. Proto- 

 phythologists in general have opposed this view on 

 the grounds that the Plasmodiophoraceae are fungi. 

 There are, nonetheless, certain specific structural, 

 developmental and cytological similarities among 

 the Rhizopoda and Sporozoa on which this belief is 

 based. The suggested relationship with the Sporozoa 

 relate to similarities in life cycles and asexual repro- 

 duction by schizogony, while in the Rhizopoda, ex- 

 clusive of the Proteomyxa, it concerns the occurrence 

 of "promitosis" and the extrusion of chromidia. The 

 Sporozoa are spore-forming parasites of animals, 

 some species of which may cause marked hyper- 

 trophy of the host cell and form galls or cysts. In 

 certain species of the Myxosporidiae the spores give 

 rise to amoebula which penetrate the host tissue, 

 grow in size, and undergo schizogony, cutting off 

 uninucleate schizonts. Each schizont develops into 

 a multinucleate amoeboid plasmodium or trojiho- 

 zoite and divides into sporonts at maturity. The lat- 

 ter grow in size as their nuclei divide several times, 

 become sporoblasts, and form a variable number of 

 spores, which are usually liberated as the host tissue 

 degenerates, and cause secondary infection. In these 

 respects certain sporozoan species resemble the Plas- 

 modiophoraceae, but further than this the similarity 

 is not very striking. However, the occurrence of schi- 

 zogony is particularly noteworthy. This is a common 

 and widespread method of asexual propagation in 

 the Sporozoa, and has also been reported to occur in 

 most genera of the Plasmodiophoraceae. That its oc- 

 currence in both groups together with the production 

 of numerous spores indicates jihylogenetic relation- 

 ship is, however, highly questionable and doubtful, 

 as Maire and Tison ('09) have already pointed out. 

 The contention that the Plasmodioiihoraceae show 

 affinities to the strictly amoeboid Rhizopoda or 



