I I.rH ll<)t)T OF ( lUl IKKltS 



95 



tioii from cell to itll. His ;u'COUllt was sllbscqucntlv 

 c'oiiririiicd liy K\inktl who holicvfil tliat a siiiitK' in- 

 foi'tioii may l»'a(l to tlif formation of tlioiisands of 

 sejtaratf and ilistiiu't " Kraiikluit>lurdc." Kiinkil as- 

 sumed that as a plasmodium migrates Irom cell to 

 cell it may divide, whereby portions are left inhind 

 and lieconK- established here and there in the tissue 

 and irive rise to siroiijjs of infected cells. 



Cclluliir Intenelfitions Hetweeii Host and 

 I'litliogeri 



Plasmotiuiphora lirassicaf has a iironouneed etfect 

 on infected and healthy cells. Infection may be tem- 

 Jjorary or permanent, and if the iilasniodium mi- 

 grates out of a cell before stimulatinn- mueli change, 

 the latter m.-iv recover and continue to function nor- 

 mally. Permanently infected cells, however, may ex- 

 |)and to more than 10 to 20 times their normal size. 

 In the early stages of infection the presence of the 

 jiarasite does not inhibit nuclear (PI. 2, fig. 5) and 

 cell division (fig. 6), so that some cells may function 

 normally in this respect for a short time. Other cells 

 m;iy begin to enlarge directly after infection with- 

 out dividing. Occasionally, cell division may be 

 affected to the extent that the cell wall is only partly 

 develo))ed across the mother cell (fig. 6). Even- 

 tually the jjower to divide is lost completely, and the 

 infected cell gradually expands to its large size. 

 Prowazek found that karyokinesis may continue 

 after cell division has ceased, resulting in binucle- 

 atc cells. I.utnian also found abnormal types of mito- 

 sis which al)l)eared to be a modified form of amitosis. 



The first visible effect of the parasite on the host 

 nucleus is an enlargement of the nucleus as a whole 

 followed by an increase in the number of nucleoli, 

 according to Lutman (fig. 8-11). By the time the 

 parasite is mature, the host nucleus has lost its regu- 

 lar outline, and the nucleoli lie (fig. 1 1 ) in clear 

 spaces surrounded by a distinct membrane, an ap- 

 pearance which led Prowazek to assume that smaller 

 nuclei may be formed in a mother nucleus. In the 

 final stages of degeneration the chromatic material 

 collects into irregular strands (fig. 12) and assumes 

 a peripheral jjosition in the distorted and hypertro- 

 phied nuclei. 



The relation between the protoplasts of host and 

 |)athogin appears to be very intimate, and little or 

 no visible antagonism is exhibited. The amoebae and 

 voung Plasmodia of the parasite lie embedded in the 

 host proto])lasm (fig. .■), (i. 2(5. 28). and in the living 

 condition the two are indistinguishable, according to 

 Woronin, Xawaschin, Lutman, and others. This 

 close association together with the fact that the in- 

 fected host cells may continue to divide and function 

 normally for some time led Xawaschin. f J.iylord. .and 

 Vanderyst to believe that there is a symbiotic rcl/i- 

 tionshi)) between the host and ])atliogcii during the 

 hitter's early developmental stages. The host cyto- 

 plasm has been described as becoming more vacuo- 

 late as the jilasmodium enlargj's, but part of the 

 early change is probably due to the great increase in 



xolumc of the host cell whcriby the cytopl;isui is 

 tliinni-d out. Later, iiowcx cr. .-is the plasmodia mature 

 .111(1 .ipproacli sporogeiicsis the proto))lasm is .ilmost 

 completely gone. Infected cells develo]) .m unusually 

 large amount of tr.insitory starch. ;iccording to Wal- 

 ker. H;ilsted, and Naw.ischin. whi<-li m.iy be grouped 

 .1 round the nucleus as l.utni.in h.is shown. These 

 grains may later be found in the plasmodium (fig. 

 7-i) and are apparently wholly or jiartly digested be- 

 fore sporogenesis. Reed ('11) noted an appreciable 

 iiu'rease in calcium, m.-ignesium, ])otassium, phos- 

 phoric acid, sulphuric acid, etc., in diseased cabbage 

 roots. The increase w.is greatest in the case of ))otas- 

 sium. which he attributed to an accumulation of jiro- 

 toi)lasm and starch in diseased tissues. Nicolotf and 

 Stefanova ('22), however, found that roots of dis- 

 eased cabbage plants were high in protein and lower 

 in phosphorus and potassium than those of healthy 

 plants. 



Noninfected cells are also stimulated to di\ ide by 

 the presence of the parasite and may often enlarge 

 considerably. This is jiarticularly true of medullary 

 rav cells, which may ex])and until they have lost all 

 characteristics as such. The nuclei of these cells en- 

 large also and keep pace to some extent with the in- 

 crease of cell size. According to Kunkel, the stimulus 

 travels in advance of the infection, so that increased 

 cell division may be noted before the parasite reaches 

 a particular, undifferentiated tissue, which suggests 

 that a growth-stimulating substance is released by 

 the causal organism and travels ahead of the plasmo- 

 dium. Nawaschin, on the other hand, believed that 

 the division of noninfected cells around the "Krank- 

 heitsherde" is due to the stimulus of mechanical out- 

 ward pressure exerted by the enlarging parasitized 

 cells. 



Kunkel suggested that the limitation of the para- 

 site in groups of cells might be due to a ijrotective 

 substance or antitoxin ))rodueed by the infected cell 

 which diffuses out into the adjoining healthy cells 

 and renders them imnmne to attack. Levine and I.e- 

 vine ('22) believed that the surrounding cells are 

 not only immune but present a reactive protective 

 barrier against the spread of the parasite. The ques- 

 tion of whether or not infected jjlants can recover 

 from club root and become immune has often been 

 debated. Woronin ('78), Eycleshymer ('91), Lau- 

 bert ('0.5a) and Miiller-Thurgau and Osterwalder 

 ('23) maintained that recovery is impossible, but 

 Massee ('96), Mathieu-Sanson ('97). Apjiel and 

 Schlumberger ('13). .Schlumberger ('1 !■), and Wahl- 

 ing ('22b) rejiorted varying degrees of recovery 

 when infected ))lauts were treated with a 2 jier cent 

 (jotash solution, milk of lime, planted in ore mud. and 

 sterile soil, and watered with sulfur and solibar 

 solutions. Miiller and Osterwalder transplanted in- 

 fected plants to heavily limed soil, but found no in- 

 hibitory effects or recovery. Honig ('31) believed 

 that if infected i)l:mts are transjjlanted to sterile and 

 d'sinfcctcd soil the progress of the disease may be 

 halted, but such ))lants can recover only if they are 

 sufficiently healthy to begin to grow anew. 



