PIIYI.OCJKNV AND HK.I-ATIOXSIIII'S 



81 



Inulifs in tin- M\ ictuzo.i Iiuve aocordiiiiily nut lucii 

 universiilly continnoil. .Ijiliii ( 30) sovcri'ly critiiizid 

 the belief tliat tlio presence of two H.ifjella aic nl 

 niueli sijrnilieaiiee, questioned the presence of more 

 than one liasal jirannle, and rejjarded all liiHauellate 

 zoospores as alinornial. 



In tlie I'lasniodiopliorales little is known about 

 the l)lei>haro])last and its eoinposition. 'Terhv (lil-a) 

 and Cook and Sehwartz ('30) tiirnred only oiu' t)lei)h- 

 aroplast in the uniHairellate zoospores of /'. Hras- 

 sicar, but later Terby ("'2t-b) reported that the 

 blepharojilast may divide and form two bodies in 

 the incipient spore. Neither Ledingiiain ('31, '35) 

 nor Couch. <-t al. ('39). showed basal fjranules in 

 their fifrures of the biflai;ellate zoosjiores of Plasmo- 

 diophora, Spoiifioxpora, and Octomi/.ra. In I'oli/- 

 mi/ja, on the otiier liand. I.ediniiham ('39. p. t2) 

 figured the two flagella attached directly to the nu- 

 clear membrane without the presence of blei)haro- 

 plasts or basal granules. It is thus obvious that but 

 little is known about the number of basal granules 

 in the zoosj)ores of this order and their relations to 

 the H.igell.i. Nevertheless. Bessey's suggestion con- 

 cerning the significance of basal granules and the 

 occasional occurrence of biflagellate zoosjiores in the 

 slime molds is very stinnilating and merits further 

 investigation. 



Turning now to other differences within the two 

 groups, it may be noted that sporangia and capil- 

 litia of the tyi)e found in the slime molds are lack- 

 ing in the Plasmodio]iliorales. As has been noted 

 before, mycologists and protozoologists have re- 

 garded this reduction as due to the jiarasitic mode 

 of life adojjted by the Plasmodiophorales. Cook 

 ('33) suggested that the membrane around the cys- 

 tosori in certain ))Iasmodiophoraceous genera, Soro- 

 discus, Sorosphaera, etc.. may be looked upon as 

 equivalent to the sporangium wall of the Myxomy- 

 cetcs. However, there is considerable doubt about 

 the jiresenee of a soral membrane in these genera. 

 The Myxomycetes. on the other hand, lack s])o- 

 rangiosori and thin-walled evanescent zoosporangia, 

 which have recently been shown to occur in most 

 genera of the Plasmodiophorales. These zoosporan- 

 gia may arise directly from zoos])ores which have 

 entered the host or later from small or large, seg- 

 mented, vegetative plasmodia. These differences — 

 lack of thin-walled, intramatrical zoos])orani!:ia in 

 one grou]) and sjiecialized sporangia and capillitia in 

 the other — are of fundamental significance, in the 

 author's opinion, and are difficult to ex))lain wliolly 

 by differences in mode of life. 



Other develojjmental phases and eytological dif- 

 ferences between the two groups are to be noted 

 here. Schizogony of the young plasmodiimi has been 

 described in most genera of the Plasmodiophorales, 

 but it a])pears to be lacking in tlie Myxomycetes. At 

 least, no conclusive evidence of its occurrence has 

 yet been presented. Furthermore, neither the so- 

 called "promitotic" nuclear divisions nor a marked 

 "akarvote " stage, which are rejiorted to be charac- 

 teristic developmental i)hases of the Plasmodiopho- 



rales, li.i\ e been found in the Myxomycetes. W'iiether 

 or not tliese (litl'erenees alone are of much phyloge- 

 nitie signiHc.incc, however, is questionable. 



Comp.-irisons of the two groups on the basis of 

 sexuality, alternation of generations, time and place 

 of meiosis, etc., are difficult to m.ake at present, be- 

 cause so little is kiu)wn about these ])rocesses in the 

 Plasm()dio|)!iorales. In the Myxomycetes also there 

 is considerable disagreement among workers about 

 these devclo|)mental phases. As far as is now known 

 the resting spores of the slime molds usually form 

 more than one zoospore in germination, and these in 

 turn divide once to several times before becoming 

 gametes. In the Plasmodiophorales, on the other 

 hand, it is claimed that only one zoospore is formed, 

 which functions directly as a gamete without di\ id- 

 ing. Cook ('33) empluisized this distinction and 

 stated that it is "the chief difference between the 

 two groups." In light of data in the literature, this 

 statement is obviously open to criticism. Maire and 

 Tison.and Home found an additional or third mitosis 

 after the two meiotic divisions in Sorosphaera and 

 .S' /;0H r/cs/jora, respectively, where by binucleate spores 

 were occasionally ))rodueed. I.utman and Terby also 

 figured binucleate sjjores in P. Brassicac and be- 

 lieved that these arise as tiie result of division of the 

 spore nucleus. It is not improbable that such spores 

 form more than one zoospore or gamete. In addition 

 to such spores, unusually large multinucleate ones 

 ha\e been found in several genera, and it is not un- 

 likely that they also give rise to several motile cells 

 in germination. Likewise. Cook's assertion "that di- 

 vision of the swarm cells does not take ])laee in the 

 Plasmodiophorales i)rior to fusion" is rather dog- 

 matic and premature in light of our meager present- 

 day knowledge of the behavior of the zoospores in 

 this order. The}- have never been cultured with cer- 

 tainty outside of the host, and very little is known 

 about their behavior within the host cells. Cook's 

 assertion is furthermore contradicted by Massee's 

 (PL 10, fig. 10). Osborn's. Home's and Fedorint- 

 schik's accounts of tin- multi))lieation of amoebae or 

 gametes in Spoiu/ospora and Pla.smodiophora by 

 equal division and budding. In maintaining that the 

 gametes are the direct ))roducts of the resting spores. 

 Cook further contradicted his own and Schwartz's 

 ('30) earlier assertion that the gametes of 1'. Kras- 

 sicae are produced in thin-walled zoos))orangia or 

 gametangia. The origin .-uid method of formation of 

 gametes in the Plasmodiophorales are thus some- 

 what doubtful at jircsent, and it seems jirematurc to 

 make definite comparison between the two groups on 

 this basis. 



Fusion in pairs of isomorphic amoeboid and flag- 

 ellate gametes has been reported to be characteristic 

 of both groui>s, but as noted elsewiiere actual fusion 

 has so far been seen very seldom in tlie Plasmodio- 

 phorales. The respective gametes are alike in size 

 and structure in both groups, but in the Myxomy- 

 cetes certain other differences between gametes of 

 the opposite sex have been reported, .\ccording to 

 Abe ('3f) the male gamete loses its Hagellum as it 



