•IIYI.OUKNY AM) HKI.ATIDN.SIl ll'S 



85 



diajiranis rfjircsoiitiiiji the life oyi'lcs of tin- I'l.is- 

 niodi(i|)lioraU's in Chapter III an- compartd with 

 those of the Myxoinycctts tliese siniilaritii's bci'onif 

 iiioro strikinir. .Most rciciit workers in hotli iiroii])s 

 aftree that tlie dijjhiiil phase is initiated liy the fusion 

 of anioehoid or motile ijainetes and karyo-ianiy and 

 extends to the time of the last two nuelear divisions 

 preecding sporojjenesis during whieh reduetion oe- 

 curs. while the haploid phase ineludes the sjiores, 

 zoospores, amoebae, and g.-imetes. However, the 

 presenee of :i zoosporanjri.-il st.-ige in the Plasmodio- 

 Jihorales and the possibility th;it tlie zoosporangia 

 may be gametangia eoni|)lie.ites the situation, and 

 until more is known about this developmental ))hase 

 it is impossible to say how elose the Plasmodiopho- 

 rales and Mycetozoa are to each other. 



PlASMODIOPHORALES AN-D CllVTRIDIALES 



As has been noted in the historieal review, the sug- 

 gested relationship of the Plasniodiophorales with 

 the Chytridiales involves principally the families 

 Woroninaceae. Synehytriaceae. and certain members 

 of the Olpidiaceae. Reports of relationship with the 

 Synehytriaceae are based ])riiuarily on tlie fact that 

 the thallus in this family functions as a prosorus and 

 segments into a number of zoosporangia as in some 

 genera of the Plasniodiophorales. It must be noted, 

 however, that this thallus is haploid in the Synehy- 

 triaceae. according to Curtis, Kusano, Kohler and 

 others, while in the Plasniodiophorales it is believed 

 by numerous workers to be di]jloid. Outside of the 

 formation of sporangiosori in both families, there is 

 little or no further similarity. The presence of pos- 

 teriorly uniflagellate zoospores and gametes in the 

 Synehytriaceae jirecludes, in my opinion, any close 

 affinity. Furthermore, the presence of a membrane 

 around the mature tliallus, lack of amoebae and 

 naked plasmodia. and the absence of schizogony, as 

 well as the fact that the zygotic thallus does not seg- 

 ment and form numerous resting spores or cystosori 

 are other outstanding differences which are difficult 

 to reconcile. 



In certain members of the Olpidiaceae, particu- 

 larly species of Rozella, the thallus has been de- 

 scribed as naked, plasmodium-like, and indistin- 

 guishable from the host protoplasm. In the septi- 

 genous species of this genus, the thallus is further- 

 more reported to segment into numerous portions 

 which develoj) into zoosporangia or resting s))ores. 

 However, as the author ('1-2) has pointed out else- 

 where, the ))resencc of a plasmodium with this type 

 of development has not yet been conclusively dem- 

 onstrated for Rozella. In Prinffsheimella, on the 

 other hand, the evidence of segmentation of the thal- 

 lus and the formation of sjiorangiosori is more con- 

 clusive, according to Coucli's ('39) observations. 

 Certain genera of the Olpidiaceae like Rnzt'Ua and 

 Prinrishi-imi'Ua have thus been described as resem- 

 bling species of the Plasmodiophorales in the devel- 

 opment of s))orangiosori. On the other hand, they 

 differ fundamentally by their posteriorly uniflagel- 

 late aoos])ores. The contention of Winge that Sorol- 



pidiiim lU'tac, Rhlzomij.va hypoijaea, and Aiimomiixa 

 l*lanta<iinis are transition species between the Plas- 

 inodiojihorales and Chytridi;des is no longer ten.able, 

 bee.'iuse these species li.ave siiu'c been shown to be- 

 long to the former order. Therefore, the evidence of 

 rel.itionsiiip between these two grou))s is very mciger 

 ;ind inconelusi\e at ])resent. 



The family Woroninaceae is .'it present a conven- 

 ient dumping ground for all holocari)ic, Oomycete- 

 like species with biflagellate zoospores, and as such is 

 not a coherent group of closely related genera. In 

 light of |)resent-day knowledge it should be seiiarated 

 from tlie Chytridiales ])roper, which have uniHagel- 

 late zoos))ores. Therefore, a discussion of the rela- 

 tionship between the A\'oroniiiaeeae and Plasmodio- 

 phorales under the present heading is in a sense con- 

 tradictory. Nevertheless, it may be conveniently in- 

 serted here without offense to logic. The life cycle of 

 some species of IVoronina, particularly W . poli/- 

 ci/stis, as far as is now known, is strikingly similar 

 to that of several members of the Plasmodiophorales, 

 as Zopf, Maire and Tison (11), A\'inge, and others 

 have already eniiihasized. In light of the recent dis- 

 covery of Polyrntjjra and Octomyia by Ledingham, 

 Couch, ct al., these similarities have become more sig- 

 nificant and need to be emphasized again. With the 

 l)ur])ose of so doing I have reproduced in Plate 16 

 the life cycle of JV. poli/c//stis. In this species the 

 contents of the zoospore enters the host hypha as a 

 naked jjrotoplasmic mass (fig. 6-10). undergoes 

 amoeboid changes in shape, develops into a plasmo- 

 dium-like thallus as it feeds on the host protoplasm, 

 and causes local liy])ertrophy (fig. 11, 12). 



At maturity the thallus cleaves into segments (fig. 

 13. 1 1) which develop into zoosporangia (fig. 1.5, 16) 

 and form a typical sporangiosorus. As in Octomifxa, 

 the jieripheral zoosjjorangia are usually independent 

 with a single exit pa])illae, while the deeper lying 

 ones may be confluent with a common papilla for 

 zoospore emission. Each sporangium produces a 

 number of biflagellate zoospores (fig. 18—21) which 

 reinfect the host hyphae. As the culture becomes 

 older, the thalli cleave into small segments which be- 

 come the resting spores. These remain closely at- 

 tached and form compact cystosori of various sizes 

 and shajies (fig. 23-2.5). As in Lif/niera and Poh/- 

 mi/JTii, the cystosori may be elongate, irregular, flat- 

 tened, oval and almost spherical, and include a few 

 to numerous polygonal spores, whieh j)roduce zoo- 

 spores in germination. 



As to the structure of the zoospores of li'. poli/- 

 ci/xlis, there is. however, considerable disagreement 

 among students of tliis s))ecies. Fischer described and 

 figured them as ellipsoidal (fig. 1) with a slight in- 

 dentation at one side and two unequal flagella. The 

 shorter flagellum arises from the anterior end and ex- 

 tends forward in swimming, while the longer one is 

 inserted laterally and ))rojects backward. It must be 

 noted, however, that I''iseher's descrijition was not 

 .•ip|)lied directly to If ■ pi>li/ci/sti.i but relates to the 

 zoospores of Rozi'lla, Olpidiopsis, and IVoronina as a 

 group. Cook and Nicholson ('33), on the other hand, 



