11 



PLASMODIOPHORALES 



Table 1. Chromosome numbers in the Plusmodiophorales. 



Species Author 



Sorosphaera Veronicae Maire and Tison, '09 



S. Veronicae Webb, "35 



Tetramyxa -parasitica Maire and Tison, '11 



T. Elaeac/ni Yendo and Takase, '32 



Sorodisciis Callitrichis Winge, '13 



S. rudicicohis Cook, '31 



S. Heternntherae Wernham, '35 



Plasmodiiiphora Brassicae Maire and Tison, '09 



P. Brassicae Lutman, "13 



P. Brassicae Terby, 'H 4 



P. Brassicae Nawaschin, '34 ? 



P. Brassicae Tones, ^-2S ? 



Spongospora subterranea Osborn, '11 ? 



S. subterranea Home, '30 4 



6-8 

 8 



8(?) 

 8 



matic and recorded 16 individual cliromosomes asso- 

 ciated in eight pairs on the equatorial plate, which 

 separated and were distributed to the daughter nu- 

 clei. In the second division this number was halved 

 to four. Winge's confusion as to the nature of the 

 respective divisions has led to tlie belief that the 

 chromosome numbers in S. Callitrichis are 16 and 8. 

 but it is evident from Winge's report that 4 should be 

 recorded as the reduced number. In P. Brassicae four 

 workers have recorded 8 as the diploid number, and 

 curiously enough this is the number of bodies figured 

 earlier by Prowazek ('05) in the transitional phase. 

 In Spongospora subterranea, Osborn figured polar 

 views of the second division with 7 chromosomes, 

 which corresponds closely to the number later re- 

 corded by Home for the first division. It is not im- 

 probable, however, that Osborn's figure relates to the 

 first meiotic division. 



Schizogony and Cleavage 



Vegetative multiplication of young plasmodia by 

 division, segmentation or fragmentation has been re- 

 ported for all genera of the Plasmodiophorales ex- 

 cept Memhranosorus and Octomifxa. In Ligniera it is 

 said to be lacking entirely or reduced to the forma- 

 tion of a few daughter segments, while in T. Triglo- 

 chinis and P. graminis true "multiple division" has 

 been re])orted. Nawaschin did not observe segmenta- 

 tion in Plasmodiophora, but he believed that its oc- 

 currence is the only plausible explanation of the fre- 

 quent presence of numerous uni- and multinucleate 

 amoebae and plasmodia in a single host cell. Since 

 that time most cytologists have reported its occur- 

 rence, although none of them, with the ])ossible ex- 

 ception of I.edingham, actually observed it in liv- 

 ing material. Like Nawaschin, they found several 

 amoebae and plasmodia in the same cell and assumed 

 that the former were the products of fragmentation. 

 Maire and Tison ('10) found similar stages in Soro- 

 sphaera but interpreted them as fusion stages of 

 amoebae and young plasmodia in the formation of 

 the s))orogenous plasmodium. Brasil, however, sug- 

 gested that these stages relate instead to fragmenta- 

 tion or scliizogony — a suggestion which Maire and 



Tison adopted. These workers thus introduced the 

 protozoologists' term "schizogony" as descriptive of 

 the vegetative fragmentation of the plasmodium, and 

 since that time it has been rather widely adopted. 

 Pavillard ('10), however, contended that schizogony 

 in Sorosphaera, as described by Maire and Tison, 

 resembles plasmotomy instead of true schizogony as 

 in Trichosphaerium sieholdii (Doflein, '09, '27) and 

 Hepatazoon anis (Wenj'on, '26), for example. He 

 thus restricted the term schizogony to the "multiple 

 division" of Doflein, while Maire and Tison ('11) 

 interpreted it in the broad sense of most protozoolo- 

 gists to include the plasmotomy of Doflein as well as 

 all other methods of simple and multiple divisions. 



Schizogony in the Plasmodiophorales is reported 

 to occur most frequently during the 8- and 16-nucle- 

 ate stages of the plasmodia or schizonts. A few uni- 

 and multinucleate meronts may be formed as in Lig- 

 niera, or the whole plasmodium may undergo mul- 

 tiple division as in T. Triglochinis and P. graminis. 

 The latter type of complete fragmentation appears 

 to be limited as far as present-day knowledge goes. 

 Most cases so far reported involve primarily the con- 

 striction and cutting off of peripheral uni- and multi- 

 nucleate segments. No cases have yet been described 

 in which all or most of the nuclei migrate to the 

 periphery of the schizont and become enveloped in 

 cytoplasmic buds, which are subsequently pinched 

 off, leaving a central mass of degenerating cytoplasm 

 and nuclei, as in Hepatasoon anis, for example. The 

 mechanics of schizogony are unknown, because the 

 process has not been extensively observed in living 

 material. In Polymiioca graminis, Ledingham merely 

 reported that the pseudopodia are retracted and the 

 protoplasm becomes denser before the thallus splits 

 up into meronts. 



In cases in which only a few meronts arc formed 

 the remaining portion of the schizont may mature 

 directly into a sporogenous plasmodium or sporont. 

 The delimited meronts grow in size and become mul- 

 tinucleate and may in turn function as schizonts. 

 Otherwise, they develop into sporonts. The destiny 

 of the various portions depends to some extent on 

 the length and activity of the vegetative period. Inas- 



