I.KiXIKllA 



59 



Tliis jji-iuis was cstaMislKd l)_v Main- aiul 'rismi 

 for all i)lasiiio<lio|)liorjicfinis species cliaraeteri/.cd 

 by loosely and variously ajijirejiated restintr spores. 

 little or no seliizujiony of the iilasiuodiuiii. (■oni])lete 

 develo)>nu'nt within a sinirle host eell. and whieli 

 eause no hyiiertropliy of the iiost. As sueh. it is a 

 very questionahle i;eiuis and should iierhajis lie dis- 

 carded, since noiu- of its charai'ters are very distinc- 

 tive and diajjnostic. In the first |)lacc the shape and 

 character of the restinji spore clusters or cystosori 

 are too variable to be of nnich {generic value. Sec- 

 ondly, none of the si)ccies has yet been studied in- 

 tensivclv and sutHciently well to determine whether 

 or not sehizoiiony is well developed, redui'cd. or 

 lackinsr entirely. I'urthcrniore. it is not certain tli;it 

 the l);irasite completes its entire life cycle within one 

 host cell. Fin.illy. the Jircscnce or absence of host 

 hypertrophy is not a structural or eytological char- 

 acter of tlie jiarasite itself, but relates to the reac- 

 tions of host and ])athogen. Even if this latter charac- 

 ter were tenable, it would not be diagnostic for the 

 group as a whole, because I>. plloriim, according to 

 Fron and (iaillat. causes marked local enlargement 

 of the root hairs of Poa annua. t)n the basis of ])res- 

 ent-day knowledge. Lif/niera al)pears thus to be 

 scarcely more than a convenient dumping ground 

 for species which cause little or no hypertrophy. 

 Further intensive studies, however, may reveal a 

 more fundamental basis of distinction. 



The pyriform uninucleate zoosi)ores of Lif/niera 

 have been described by Cook as anteriorly uniHagel- 

 late (fig. 1). but more careful study will doubtless 

 show them to be biflagellate and heterocont as in 

 Plasmodiophora, Pol_i/mi/da, Sponr/ospora, and Ocfo- 

 mi/xa/ After penetrating root hairs and epidermal 

 cells, they may become flagellate and actively motile 

 again in the host ]iroto])lasm (tig. 2B). according to 

 Cook. The flagellum soon disap|)ears. however, and 

 the parasite becomes amoeboid in sha)3c and motion 

 (fig. 3). Nuclear divisions occur as the amoebae in- 

 crease in size (fig. K 8. 9). until a multinucleate 

 Plasmodium is formed. One or more amoebae and 

 Plasmodia may be present in a host cell, but so far 

 no conclusive evidence has been presented to show- 

 that they coalesce to form a larger structure. As 

 noted before Cook ('33) re))orted that the zoospores 

 are isogametes which fuse in i)airs to form zygotes. 

 but his evidence of plasmogamy or karyogamy is not 

 very conclusive. 



Host cells usually contain only one plasmodium. 

 which fills them almost eomjiletcly (fig. 12). Very 

 little is known about the feeding habits of the intra- 

 matrical plasmodia. They alijiarcntly absorb the host 

 cvtoijlasra. envelop the nucleus, and lead to the dis- 

 appearance of the starch grains, so that the infected 

 regions of the roots ap])ear quite pale in color. 

 Maire and Tison ('11). however, reported th.it the 

 Plasmodium is cal)able of engulfing large food pnr- 



• This is suppestrd by Rarretfs discovery of biflajrcllate 

 heterocont zoospores in Khhiinuij-a hiipoijea whieli is re- 

 garded as a combination of Liijniern sp., and another fun- 

 gus species. 



tides, .-iiid figured ;! yiiuiig p.'irasite with live en- 

 gulled algal cells (fig. .5). 



Whether or not schizogony incurs in Lii/nii'ra is 

 still questionable. Schwartz ('10) reported that the 

 young plurinuele.ite iil.ismodi.-i of /.. Jiinci function 

 .■IS schizonts. siilitting off smaller uni- or multiiiuele- 

 ;ite daughter segments. .M.iire and 'I'ison (lib), on 

 the other hand, believed that schizogony may be 

 l.iekiiig entirely or is reduci<l to the formation of two 

 or three iiieronts (fig. 10). Suiiseqiunt workers also 

 have doubted its occurrence or cl;iimed that, if pres- 

 ent at all. it takes place only in the young develoj)- 

 ment.il stages. 



With the doubtful exception of /,. plloriim (fig, 2.5. 

 2(). 38). species of Li(/)ticra ha\e no noticeable effect 

 oil the host tissues, according to most accounts in the 

 liter.iture. No galls are ))roduced, and the infested 

 cells arc not markedly enlarged or stinuil.ited to di- 

 vide. Schwartz (H), however, reported that para- 

 sitized cells of Poa annua are often considerably 

 elongated, due either to the failure of transverse wall 

 dev(lo])ment or the absorbtion of such walls by the 

 parasite. Subsequent workers, however, have not 

 confirmed these observations. The relation between 

 the ))rotoi)lasts of the host and ])athogen ap|)ears to 

 be very intimate, and no marked antagonism is ex- 

 liibited, according to the figures and descriptions in 

 the literature. Schwartz reported that tlie amoebae 

 are strongly attracted to the host nucleus and mi- 

 grate toward it as soon as they have entered the eell 

 (fig. 0. 7) like in .S'. subterranea. The amoebae shown 

 in these figures, however, look like nuclei of the 

 parasite, which suggests that the host nucleus in 

 these instances miglit )iossibly be envelojied by a 

 multinucleate plasmodium. Complete envelopment 

 of the host nucleus and a mixing of the two proto- 

 plasts has also been shown in root hairs of J uncus 

 articulatus (Schwartz. '10, fig. .5). Figure 37 shows 

 a host nucleus inside a mature eystosorus. The nu- 

 cleus of infected cells shows little or no enlargement, 

 and no conspicuous signs of degeneration are evi- 

 dent until the parasite is almost mature. Maire and 

 Tison's figures (11. 37) suggest that as degenera- 

 tion progresses the nucleus becomes more chromatic 

 and densely stainable. 



According to Cook ('2G, '28) the mature ))lasmo- 

 diuni may form either zoos]>orangia or cystosori. In 

 the former event uninucleate segments (fig. 20) are 

 delimited by ])rogressive cleavage, and their nucleus 

 divides twice and occasionally three times. Cook 

 claimed that the first division is heterotypic and the 

 second homeotypic, liut his evidence is not at all con- 

 clusive (see Chap, III). In resting spore develo])- 

 ment uninucleate amoebae may sometimes undergo 

 two nuclear divisions (fig. 22) and form tetrads of 

 resting spores, according to M;iire and Tison (1 lb). 

 It is not inijirobable. howe\er. that their figures m.iy 

 relate instead to sjioriingia and zoospore develo))- 

 ment. In larger ))lasmodia. the reconstructed nuclei 

 following the so-called "akaryote" stage also divide 

 twice. Following these divisions the jilasmodium 

 cleaves into uninueleate segments, which round u)). 



