80 



PLASMODIOPHORALES 



anteriorly uniflagellate zoospore in both groups as 

 evidence that they have originated from a common 

 ancestor. Considerable significance has also been at- 

 taclied to the reports that the plasmodia of Sponc/o- 

 spora (Kiinkel, '15) and Plasmodiophora (P. M. 

 Jones, '28) can live outside of the host and may be 

 cultivated on synthetic media like those of the Myxo- 

 mycetes. Careful analysis of Kunkel's paper, how- 

 ever, shows that the saprophytic plasmodia which 

 he described apparently do not relate to Spongo- 

 spora at all, because at maturity they form stalked 

 Dicti/osfelium-like sorocarps instead of spongy cys- 

 tosori. I>ike\vise, the peculiar and abnormal life cycle 

 described by P. M. Jones for P. Brassicae suggests 

 that he may have been studying some other plasmo- 

 dial organism instead of Plasmodiophora. It thus 

 remains to be seen whether or not the plasmodium of 

 the Plasmodiophorales can be cultivated saprophy- 

 tically outside of the host. 



As to the mode of nutrition, data are accumulat- 

 ing which suggest that it possibly may be very simi- 

 lar in both groups. The zoospores, amoebae, the 

 plasmodia of the Myxomycetes are capable of en- 

 gulfing food particles, digesting them, and discard- 

 ing the extraneous waste material. While this type 

 of nutrition is not particularly evident in the Plas- 

 modiphorales, claims have nonetheless been made 

 that the plasmodium at least engulfs starch grains 

 and masses of host protoplasm. According to Woro- 

 nin. Nawaschin, Prowazek, and Lutman, starch 

 grains may often be found in the folds and vacuoles 

 of the Plasmodium of P. Brassicae. Nawaschin 

 ('99), Favorsky, and Henckel did not believe these 

 had been engulfed, but Woronin, Eycleshymer, and 

 Lutman nevertheless inferred that the plasmodium 

 feeds on these grains. Maire and Tison (11) like- 

 wise reported that the small plasmodia of Ligniera 

 Junci may engulf algal cells. The zoospores of some 

 species also appear to be capable of taking in solid 

 bodies, but how generally it occurs is not known. In 

 Polymijxa (jraminis Ledingham reported that the 

 pseudopods of amoeboid zoospores may flow around 

 and engulf small objects. 



The evidence of relationship on the basis of simi- 

 larity in zoospore structure is not particularly con- 

 vincing in light of recent discoveries. Until 1931' it 

 was believed that the zoospores of the Plasmodio- 

 phorales were like those of the Myxomycetes in hav- 

 ing one anterior flagellum, but since that time it has 

 been clearly shown that the zoospores of six genera 

 of the former group are anteriorly biflagellate and 

 heterocont. Further study will doubtless show this to 

 be true in the remaining genera of the Plasmodio- 

 phorales also. The structure of the zoospores and 

 the number, position, and relative lengths of the 

 flagella are very significant phylogenetically, and it 

 would seem offhand that the presence of biflagellate, 

 heterocont zoospores in the Plasmodio])horales sepa- 

 rates this order very sharply from the Myxomycetes. 

 It must be remembered, however, that although the 

 majority are uniflagellate, zoospores with two fla- 

 gella are not uncommon in the Myxomycetes also. 



De Bary ('84) and Vouk ('11) early noted zoospores 

 with two flagella, and since that time numerous re- 

 ports of similar zoospores have appeared. Gilbert 

 ('27) found that 25 per cent of the zoospores of 

 Stemoiiitis fiisca are biflagellate, and his figures le 

 and If show that one of the flagella is considerably 

 shorter. Similar zoospores have been subsequently 

 described and figured by Smith ('29) for Dictyae 

 thalium plumheum, by Howard ('31) for Physarum 

 polycephalum, and by Sinoto and Yuasa ('St) and 

 Yuasa ('35) for Physarella ohlonga, Fuligo septica, 

 and Comatrichia longa var. ftaccida. In the latter 

 species 13 per cent of the zoospores were biflagel- 

 late, and in rare cases triflagellate. As is shown in 

 figures 2 to 5, Plate 17, the flagella are of equal as 

 well as of unequal length. Stosch ('35) also found 

 biflagellate zoospores in Didymium eunigripes, D. 

 xanthopus, D. squamosum, D. difforme, Physarum 

 cinereum, P. nutans, Trichia favoginea, Comatrichia 

 nigra, and Lycogola epidendrum. 



In most species which normally have uniflagellate 

 zoospores, bi- and multiflagellate cells are usually 

 the result of unequal or incomplete cleavage, and 

 are consequently large and bi- or multinucleate. 

 Such does not appear to be true of the zoospores 

 shown in figures 2 to 6, Plate 17, since there is but 

 one nucleus present regardless of the number of fla- 

 gella and the size of the zoospore. A more funda- 

 mental cause may perhaps be operating in these 

 cases. Of particular interest in these figures are the 

 basal bodies upon which the flagella are oriented. In 

 Ceratiomyxa fructiculosa var. flaccida, Physarella 

 ohlonga, and Fuligo septica, they are double regard- 

 less of whether one or more flagella are present. 

 E. A. Bessey, Professor of Botany, IMichigan State 

 College, believes that this double condition may per- 

 haps be significant phylogenetically. In correspond- 

 ence with the author concerning these zoospores, he 

 asks : "Are these two granules homologous to the 

 basal granules found in algae and .... sperm cells 

 of mosses or ferns, where each flagellum arises from 

 such a granule ? Then do the planocytes with but one 

 flagellum represent cases where there has been a 

 loss of one flagellum in progressive evolution from 

 a normally biflagellate condition, and do tlie biflag- 

 ellate cells of these slime molds represent the an- 

 cestral condition which has not been com])letely lost 

 in this grou]).'' In the Plasmodiophorales, which are 

 probably closely related to the slime molds, the bi- 

 flagellate condition has not yet been lost, though one 

 flagellum is smaller than the other." Bessey thus 

 suggests that the presence of a second basal granule 

 in uniflagellate zoospores may possibly be a relic of 

 the biflagellate condition and that the Plasmodio- 

 phorales are more primitive than the slime molds. 

 However, it remains to be seen how general the 

 double condition is in uniflagellate zoospores. Jahn 

 ('04), Wilson and Cadman ('28), and Cadman ('31) 

 figured and described only one basal granule, while 

 Cotner ('30) and Stosch reported the presence of 

 several bodies at the base of the flagellum. Sinoto 

 and Yuasa's accounts of the presence of two basal 



