PLASMOniOIMlOKA 



23 



Pta.imodiopliora iiirhulcs at prisciit live sjucics, 

 of wliicli only one, /'. lirassicae, is fairly well known. 

 Most of tlu' otluT spci'ics arc so little known that 

 tlu'ir validity as nu-nilnTs of tlu' genus has ht-i-n seri- 

 ously questioned. They nevertheless (jossi-ss the eoni- 

 nion ability of eaiisiiii; eonspieuous galls and malfor- 

 mations of the host tissues. Numerous other organ- 

 isms with )>lasmodial stages have been inehided in 

 the genus from time to time, but eareful reinvestiga- 

 tion has shown them to be invalid. Pla.imodiophora 

 is distinguished from the other genera of the family 

 by the laek of a distinet eystosorus. The resting 

 spores are not united or attaeiied to form a sorus of 

 definite size and sliajx' but lie loose in the host eell. 

 as is shown in figures 88 and 100. When the host eell 

 disintegrates, the spores are liberated into the soil 

 where they may germinate at onee, as in P. Brassi- 

 cae, or remain viable up to seven or eight years 

 (Jorstad, '23), So little is known about the other 

 species of Plasmodiophora that present day discus- 

 sions of the genus must necessarily be based princi- 

 pally on /'. lirassicae. .\lthough this species has been 

 intensively studied for more than .50 years, there 

 is still considerable disagreement and controversy 

 about its critical developmental stages, and doubt- 

 less much remains to be discovered. 



The resting spores of P. Brassicae normally give 

 rise to a single zoos])ore in germination (fig, 13-17), 

 but it is not imj)rob.ible that more than one may be 

 produced by the occasional large, bi- and multinu- 

 cleate resting spores. Some workers, including Pol- 

 lacei (12) and Honig ('31), have seriously ques- 

 tioned the production of zoospores in this species. 

 Honig, in particular, maintained that only non-flag- 

 ellate amoebae are formed in germination (fig. 16— 

 18). .\lso, most investigators have figured and de- 

 scribed the zoospores as anteriorly uniflagillate, but 

 Ledingham ('St) clearly demonstrated that they are 

 biflagellate and heterocont (fig. 22, 23). They have 

 also been described in tile literature as varying from 

 oval, pyriform, and fusiform to spherical in shape 

 (fig, 19-23). After emerging from the sjiore case 

 tliey may swim 'apidly away or become intermit- 

 tently amoeboid v ;. 19. 20), during which the ante- 

 rior end may double back and forth and thus jerk 

 the sjiore body along. 



.\ccording to most students, the zoospores come 

 to rest on the host and enter as amoebae through the 

 root hairs and e))idermal cells, where they soon cause 

 local hypertroi)hy (fig. 28, 29), A few workers, how- 

 ever, have questioned these observations. Kunkel 

 ('18) found nothing but thalli of Olpidium Brassicae 

 in the root hairs of the host sjieeies which he studied 

 and like F.ivorski (10) concluded that the ])revious 

 reports on the occurrence of /'. Brassicae in such host 

 cells were erroneous. However, subsequent investi- 

 gators, including Cook and .Schwartz ('30). Honig 

 ('31), Rochlin ('33). and Fedorintschik ('lio) have 

 clearly shown infection of root hairs. Honig ajipears 

 to have been the first to observe, describe, and figure 

 actual penetration of the parasite into root h.iirs (fig. 

 27). He maintained that the ))r<)toplasts derived 



from geruiin.iting resting sjiores are true .iiiioebae 

 without Hagella, a contention which has been re- 

 futed by subsequent observers. Honig found small 

 amoebae .as well as giant ones meas\iring l-2(i jx by 

 2l'-3(>/( abundant around root hairs and observed 

 tii.it both tyi)es may readily enter the host eell. In 

 so doing they become closely .iiiplicd to the root h.iir, 

 and soon thereafter a hole appe.irs in the wall at the 

 region of attachment, through which they then enter. 

 The hole closes u]> immediately afterwards, so that 

 it is no longer visible after the parasite has entered, 

 Honig also observed that amoebae may live sapro- 

 |)hytieally for weeks in the soil and increase mark- 

 edly in size (fig. 3.")). 



It is not imiirobable. ;is Hoelilin's ('33) study 

 suggests, that under certain enviroiiment.il condi- 

 tions and particularly when s])ores germinate in eon- 

 tact with the host cell, flagella are not formed, and 

 the jiarasite enters the host almost at once in the 

 amoeboid state. Rochlin found that the resting spores 

 become attached to the root hairs and e))idermal cells 

 of the root and cap and cause localized swelling of 

 the eell wall (fig. 21-26). These regions become 

 gelatinized and show no cellulose reactions when 

 tested with chloro-iodide of zinc, indicating that a 

 chemical change has taken place. .Small jjlastic, 

 spherical protoplasts which presumably emerge 

 from the attached sjiores, pass through these swollen 

 and gelatinized regions (fig. 26) and enter the host 

 cell.' 



The amoebae and young ))lasmodia in the host cell 

 may bud and divide repeatedly (fig. 30), according 

 to Gay lord (Ol), Chupp (17), Kunkel, Fedorints- 

 chik and others, and thus multiply in number. They 

 may also encyst and develop fairly thick hyaline 

 walls (fig. 44—46) under unfavorable conditions. As 

 the ))lasmodia grow in size and their nuclei multi))lv, 

 they penetrate the walls of the adjacent cells and 

 thus migrate from cell to cell (fig. 31-33), accord- 

 ing to W'oronin ('78), Lutman ('13), Chupp ('17), 

 Kunkel, Honig, Rochlin, Larson ('34), and Fedo- 

 rintschik ('3.5). As to the method of cell wall jiene- 

 tration, Rochlin noted that the plasmodium may be- 

 come closely a))plied to a region of the wall and 

 through lysic action cause localized swelling and 

 gelatinization (fig. 7) of the latter. Passages in the 

 walls are thus formed through which the plasmodium 

 enters. Kunkel believed that only young and small 

 Plasmodia free of oil bodies and other priidiicts are 

 cai)able of migration. Cook .-iiid Schwartz ('30) were 

 uncertain on this jihasc of develoi)ment and some- 

 what vague in their description of it. In one )iart of 

 their paper (p. 287) they stated that the amoebae 

 "have the ])ower of ]>enetr;iting the walls of the host 

 cells and in this way can tr.ivil through the cortical 

 tissues of the host, " but they thought it im))robable 

 ()). 297) that the plasmodia are able to do so. I'inally 

 (|). 301 ) they expressed the belief that oidy gametes 

 from sporangia have the ability of ))assing from cell 

 to cell, .ind after gametic fusion the zygote is dis- 

 tributed onlv bv division of infected host cells. 



