54 



PLASMODIOPHORALES 



be effected at or near the tip. Cells of the periblem 

 are more frequently attacked, and the fungus occurs 

 most abundantly in a region approximately 0.5 cm. 

 back of the root tip. The cells of the central cylmder 

 apparently are never infected. According to Osten- 

 feld and "Petersen, the fungus first appears as a 

 small plastic granular body close by or attached to 

 the host nucleus (fig. 2), and as it grows in size and 

 becomes multinucleate it may envelop the host nu- 

 cleus and cytoplasm (fig. 3. 5. 6). There is thus a 

 close association of the protoplasts of host and 

 pathogen, and in Ostenfeld and Petersen's drawmgs 

 it is difficult to distinguish between them. The para- 

 site causes the infected cells to enlarge somewhat but 

 apparently does not stimulate cell division. Figure 3, 

 however, "suggests that infected cells may divide, 

 whereby the' parasites are passively distributed to 

 the daughter cells. 



The mature plasmodia vary greatly in size, and 

 the large extensive ones may often line the inner 

 periphery of the host cell (fig. 5) as in Tetramiixa. 

 According to Wernham, cruciform nuclear divisions 

 occur (fig. 7) during the vegetative phase of the 

 Plasmodium, and the nuclei undergo meiosis in the 

 first of the two divisions prior to cleavage into rest- 

 ing spores. Although he stated that he had observed 

 numerous meiotic stages and counted four to six 

 pairs of chromosomes, his figures (fig. 8, 9, 10) show 

 nothing of the process. 



SPONGOSPORA 



Brunchorst, 1887. Bergens Mus. Aarsberet. 



1886: 225. 

 Clathrosorus Ferdinandsen and Winge, 1920. Ann. 



Bot. 31.: 168. 



(plate 10) 



Resting spores usually arranged in hollow or 

 irregularly-channeled spongy, globose balls or cysto- 

 sori! Resting spores loosely or fairly closely packed 

 together, spherical, oval, pentagonal, hexagonal in 

 op'tical section with hyaline, yellowish to yellowish- 

 green, smooth, thin or fairly thick walls ; each spore 

 producing a single ( ?) zoospore; such zoospores giv- 

 ing rise to either plasmodia or zoosporangia. Plas- 

 modia usually large, irregular, amoeboid and multi- 

 nucleate ; partly or completely filling the host-cell ; 

 forming one or more spore balls. Zoosporangia sin- 

 gle or in clusters, variously-shaped. Zoospores from 

 resting spores and zoosporangia similar, small, bi- 

 flagellate and heterocont; flagella attached at or 

 near anterior end. 



Sponqospora includes at present three species, one 

 of whicii is poorly known and doubtful. The type spe- 

 cies, .S'. siibterraneaMs been repeatedly studied mor- 

 phologically and cytologically. but there is still con- 

 siderable disagreement concerning some of the criti- 

 cal stages of its life history. As noted in Chapter III. 

 these controversies have centered primarily around 

 the stages at which plasmogamy and karyogamy 



occur, and the manner by which the parasite invades 

 and spreads in the host tissue. Johnson ('07) de- 

 scribed the resting spores as one- to eight-nucleate 

 and giving rise to a corresponding number of zoo- 

 spores in germination, but subsequent workers in- 

 cluding Massee ('08), Kunkel ('15), Cook ('33) 



PLATE 10 



Spongospora sitbterranea 



(Fig. 7-9, 11 and 23 drawn from photographs) 



Fig. 1. Potato with shallow powdery scab lesions. 



Fig. 3. Malformed potato with deep cankerous lesions 

 and excrescences. 



Fig. 3. Powdery scab galls on roots of potato. 



Fig. i. Enlarged host cell with eight spongy spore balls 

 or cvstosori. Osborn, "11. 



Fig. 5. Section through a mature cystosorus. Osborn, I.e. 



Fig. 6. Uninucleate resting spores. Osborn, I.e. 



Fig. 7, 8. Zoospores from germinated resting spores. 

 Ledingham, '35. 



Fig. 9. Tetrafiagellate zoospore. Ledingham, I.e. 



Fig. 10. Dividing amoeba. Massee, '08. 



Fig. 11. Irregular ^oosporangium. Ledingham, I.e. 



Fig. 1:2. Uninucleate amoebae surrounded by host cyto- 

 plasm. Osborn, I.e. 



Fig. 13. Host cell with three amoebae and numerous 

 starch grains. Osborn, I.e. ,. , ., ^ , 



Fig. U. Dividing host cells with passively distributed 

 amoebae. Osborn. I.e. 



Fig. 15. Hypertrophied cells of S. xcarso-n-iczii which 

 have divided": amoebae aggregated around host nuclei. 

 Melhus, et al. "16. 



Fig. 16. Group of infected enlarged tomato cells; typi- 

 cal "Krankheitsherde." Melhus, et iil. l-c. 



Fig. 17. Infecting plasmodium pushing down between 

 host cells. Kunkel, "15. 



Fig. 18. Plasmodium entering host cell and enveloping 

 nucleus. Kunkel, I.e. 



Fig 19 Coalescence of amoebae to form plasmodium; 

 host nucleus enlarged, irregular, and densely chromatic. 



Osborn, I.e. 



Fig. 20. Plasmogamy of two amoebae derived from ger- 

 minated resting spores. Cook, '33. 



Fig. 21. Karyogamy. Cook, I.e. 



Fig. 22. Zygote. Cook, I.e. 



Fig. 23. S'aprophytic plasmodium (?) grown on nutrient 

 agar. Kunkel, I.e. 



Fig. 24, 25. Vegetative nuclei degenerating and extrud- 

 ing chromidia into cytoplasm. Osborn, I.e. 



Fig. 26. Akaryote and chromidial stage. Osborn, I.e. 



Fig. 27. Reconstructed nuclei emerging on new sites. Os- 

 born, I.e. , _ 1 f ■ 



Fig. 28, 29. Reconstructed nuclei pairing and fusing. 



Osborn. I.e. 



Fig. 30. Late stage in karyogamy. Osborn, I.e. 



Fig. 31. Diploid nuclei. Osborn, I.e. 



Fig. 32. I>ate prophase of meiosis with eight chromo- 

 somes. Home, '30. 



Fig. 33. Contraction stage and beginning ot pairing ot 

 homologous chromosomes. Home, I.e. 



Fig. 31. Dlakinesis. Home, I.e. 



Fig. 35. Metaphase, first division, showing three of the 

 chromosome pairs. Home, I.e. 



Fig. 36. Equatorial plate, second division, showing seven 

 chromosomes. Osborn, I.e. 



Fig. 37. Anaphase, second division, and cleavage. Os- 

 born, I.e. 



