I'l.ASMODIIU'lldH S 



25 



niovo. In vouiim: ))l.isiiuHii:i tlio psiiulo|)(i(ls .ire nl.i- 

 tivflv loni: .•iiul tt iiuous. but a> tin- i)l;iMii(i(liuin lu.i- 

 tiircs. tlu-v lu'coiuc Itss oxti-iisivc and more rouniloil 

 at till- ptri))li(r_v. I'ignri- 31 shows a mature Plasmo- 

 dium with several dense, opaque, iiseuihiixidial lobes 

 at the anterior end. The posterior end in eontrast is 

 quite vacuolate, thin, and relatively hyaline. 'I'lu 

 amoebae .-ind younji jdasmodia are hyaline, somewhat 

 transparent, viseous and slimy, and eomparativily 

 free of oil dro))lets and other bodies, but as the i)l;is- 

 modium inere.ises in size, the i)rotoplasm becomes 

 denser, more opacpu'. .md very rieh in oil jjlobuies. 

 Infected hypertrophied host cells are often rich in 

 starch grains, and according to Woronin. Xawaschin 

 ("99). Prowa/.ek ('05). and Lutman. these grains 

 may frequently be found in the folds of the Plasmo- 

 dium. N.iwasehin. I'avorsky ('10), and Henckel 

 ('23) did not believe tiiat amoebae and ))lasmodia 

 are capable of engulfing solid )iarticles, and Nawas- 

 cliin |)ointed out that starch grains, such as those 

 shown in figure 7 !■, are often caught between fusing 

 merouts and thus come to lie within the plasmodiuni. 

 Woronin, Eyeleshymer, and Lutman inferred that 

 the i)lasniodium feeds on these grains, because by 

 the time sporogenesis begins they have almost en- 

 tirelv disai)peared, although a few may occasionally 

 be found later scattered among the sjjores. Although 

 Honig did not observe the plasmodiuni engulfing 

 solid particles, lie nevertheless described it as nour- 

 ishing itself sai)roi)liytically outside of the host for 

 several weeks. In addition to oil globules, starch 

 grains, and other bodies, chondriosomes are quite 

 abundant in the i)lasmodia (fig. 48). according to 

 Von wilier ('18) and Milovidov ('31). They also 

 occur abundantly in the resting spores (fig. 86) and 

 amoebae. 



L'nder unfavorable environmental conditions plas- 

 modia and segments of the same in P. Brassicae may 

 encyst and develop thick walls, according to Prowa- 

 zek. Cook and .Schwartz, and Milovidov (fig. 46. 47). 

 Prowazek ('05) and .Milovidov regarded these cysts 

 as ))athological and involution forms. Cook and 

 Schwartz described the ])lasmodium as becoming en- 

 veIoi)ed by a distinct wall and then segmenting into 

 several portions which in turn develojied thick walls 

 (fig. 47). With the return of favorable conditions 

 the walls disa))pear, and the plasmodium continues 

 to function normally. Encysted ))lasniodia have also 

 been described in /'. Fici-repeniis by Andreucci 

 ('26). The cysts in this species are globular. 9.15- 

 73 n in diameter, with sculi)tured. thick w.-ills, and in 

 germination give rise again to plasniodia. The sig- 

 nificance of these cysts as a phase in the life cycle of 

 Plasmodiophora is not clearly understood, but they 

 are doubtles comparable with the sclerotia of the 

 niyxomycetes. 



The majority of resting spores are iniimuliatc, 

 but occasional globose and irregular ones (fig. 87) 

 have been reported by Prow.azek. Milovidov. and 

 others. Milovidov. in jtarticular. has figured numer- 

 ous tetra-. tri-. and binucleate spores. The binueleate 

 and nndtinucleate condition mav have resulted from 



the f;iilurc of large cleavage scgMuiits to (li\ ide .-iftcr 

 flu- comi)letion of the second nuclear division. On the 

 other hand, it is not altogether improb.-ible th.it it 

 may have arisen ;is the result of ;i third mitosis in 

 the inci))icut s))orc seguuMits in the maimer described 

 by Maire and Tison and Home in Soro.sphacra I't-ro- 

 iiirar and Sponrjospora siihicrranea, respectively. 

 I.utman ('13) and Tcrby ('2f) also figured biuuele- 

 .itc spores (fig. 95) and believed they had arisen as 

 tiu> result of division in the spore. After the spores 

 h.ive been formed they may remain stuck together for 

 .1 short time by the slimy intercellular substance left 

 from the jjlasmodiuui. Howc\er. they soon develo)j 

 hyaline walls, dehydrate, and sejiarate. .\t no stage 

 are they cnvelol)ed by a common membrane or form 

 a cystosorus of definite structure, size, and shape. 

 According to the rejiorts in the literature the resting 

 spores may vary up to and more than 200 per cent in 

 size. The early investigators found the siiores to be 

 quite small, but measurements by subsequent work- 

 ers have shown them to be considerably larger. 

 Woronin ('78) rejiorted them to be 1.6 /x in diam- 

 eter; Lowenthal ('05), 4 ;u ; Molliard ("09), 1.8- 

 2.2 /x: Chupp ('17) and Appel ('28), 1.9-4.3 /i, and 

 2.5-6.9 (u for the irregular ones; Esmarch ('24), 

 1-2 /J,; Pape ("25) and Honigmann ('26). 2.8-3.3 ix; 

 Wellman ('30), 1.7 /x; Cook and Schwartz ('30), 

 2-3 /x, and 4.6X6 /x for the oval ones; and Honig 

 ("31), 3.9 jx. The last-named worker made extensive 

 measurements from nimierous hosts grown in differ- 

 ent types of soil and under varying climatic condi- 

 tions and found that the spores did not differ more 

 than 0.5 /x in diameter. According to Wissenlingh 

 ('98) the spore wall consists of chitin and shows no 

 cellulose reaction when tested. 



The account given above is generally considered to 

 be the usual developmental cycle of P. Brassicae. 

 Henckel and P. M. .lones ('28b). on the other hand, 

 have reported life cycles for this species which vary 

 markedly from the orthodox type. In his study of 

 club root of radishes Henckel described the resting 

 spores as "aplanoamoebae" which by a jirocess of 

 gelatinization or softening give rise to "Umax amoe- 

 bae." These multi))ly outside of the host by budding, 

 and when this jirocess is eomijleted, the numerous 

 daughter amoebae enter the host and form a ))lasmo- 

 dium. At no stage iu the life cycle are zoos))ores or 

 flagellate gametes develojied. according to Henckel. 

 In connection with his account it may be noted that 

 Favorsky also figured and described spore germi- 

 nation in rotten tumors as a process of gelatiniza- 

 tion and softening of the s])ore wall, whereby large 

 /('ma.r-like amoebae are formed. P. .M. .lones re))orted 

 that he had isolated eight |)ure cultures of /'. Brassi- 

 cae from cabbage roots and ui.iintained them in ta]i 

 water under lal)oratory conditions for two months. 

 These cultures caused galls on turnips when used 

 as an inoculum and were subsequently recovered in 

 culture from the diseased roots. .Vccording to .Tones 

 (text-fig. 3). the following successive stages occur 

 within the host: gametes, zygotes, preplasmodia, 

 Plasmodia, cysts and spores ; while in culture outside 



