8 



PLASMODIOPHORALES 



bodies in Tetramy.ra (PI. 5, fig. 5) and Sorodisciis 

 (PI. 7, fig. 12), which lends support to tiie later 

 views of Terby, Home, and Webb that definite 

 chromosomes are present in the vegetative divisions. 



The origin of the spindle has not been clearly dem- 

 onstrated in promitosis. Wiiether it originates frcmi 

 achromatic linin material, tropiiocliromatin, or in 

 relation to centrosomes and asters is not sufficiently 

 known. Nawaschin, Favorski, Osborn, Cook and 

 Schwartz, and Webb found no centrosomes and 

 asters during the vegetative divisions in Plasmodio- 

 phora, Lic/niera, and Sponc/ospora, but Prowazek, 

 Maire and Tison, Winge, Lutman, Nemec ('13), 

 Home, and Milovidov ('31) observed them in P/<i.v- 

 modiophora, Lif/niera, Tetrami/ja, Anisomyj:a (Lif/- 

 nieraf), Sorodisciis, and Sorospliaera (fig. 2, 10, 18, 

 3.5). Notliing is known concerning their presence or 

 absence in Membranosorus, Polymyjca. and Ocio- 

 myxa. Maire and Tison figured them in uninucleate 

 amoebae of S. Veronicae (fig. 3) and contended that 

 the centrosomes are derived from the karyosome and 

 may retain contact with this body by a slender chro- 

 matic strand. In P. Brassicae, however, instead of a 

 single body Miss Terby ('23) found a circle of five 

 to six granules around tlie poles of the nucleus from 

 which the aster-like filaments radiate. 



In the early equatorial ring stage, the globular 

 nucleole may often be found in the center of the spin- 

 dle (fig. 15) surrounded by the peripheral ring of 

 chromatin, according to Cook and others, and be- 

 cause of its characteristic ajipearance this pliase has 

 been described as the "saturn" stage of promitosis. 

 The nucleole or karyosome then begins to elongate 

 and constrict in the center (fig. 16-18). In longitu- 

 dinal view the ring of chromatin and elongate nu- 

 cleole present the appearance of a cross, and this 

 phase is accordingly referred to as the "cruciform" 

 stage. The chromatin rings then split lengthwise, ac- 

 cording to most workers, and the two daughter rings 

 move apart witli the ends of the elongating nucleole 

 (fig. 19). The latter may divide completely in the 

 early anaphase (fig. 20), or the two ends may remain 

 attached for some time by a chromatic strand (fig. 

 21). The latter condition is usually described as the 

 "double anchor" or "dumb-bell" stage of promitosis. 

 The nucleole finally divides into two daughter nu- 

 cleoli, and the curved, lialf-moon-shaped bands of 

 chromatin curve around them (fig. 21, 22) until they 

 are enclosed in a more or less complete sphere, ac- 

 cording to Cook. In this manner the karyosome of 

 the daughter nuclei is built up of a peripheral layer 

 of chromatin and a central core of strictly nucleolar 

 material. In the meantime, the spindle fibers dis- 

 appear, while the nuclear membrane becomes drawn 

 out, curved and somewhat crescentrie. It then con- 

 stricts sharply in the equator and pinches in two. 

 according to Cook (fig. 22), forming the daughter 

 nuclei (fig. 23) which soon move apart and become 

 spherical. 



Although variations in the jjrocess of promitosis 

 described above have been noted by some workers, 

 most of their views are in agreement about its fun- 



damental outlines. However, P. M. .Tones' ('28) de- 

 scription of division in what he believed to be P. 

 Brassicae is quite different, contradictory, and as 

 Milovidov characterized it, whollv fantastic. "After 

 the nucleus has become very large, the karyosome 

 moves to one side, and then escapes from the nucleus. 

 The karyosome, during this movement, assumes a 

 dumb-bell sliape and starts dividing by promitosis. 

 When the karyosome has completely left the nucleus, 

 it undergoes rapid division, by mitosis, until the Plas- 

 modium becomes filled with little nuclei. These nu- 

 clei increase in size to form a multinuclear Plasmo- 

 dium. The Plasmodium stops feeding and assumes a 

 frothy appearance. The nuclei becomes vacuolated, 

 chromidia are distributed around tlie vacuoles, and 

 collect into new vacuoles, to form new nuclei . . . . " 



It is to be particularly noted that the majority of 

 the early cytologists interpreted the karyosome in 

 terms of the duality concept of the cliromatin. They 

 believed that the chromatin which forms the equato- 

 rial ring and the division nucleole are derived from 

 the karyosome. This body is accordingly dual in 

 structure and consists of idio- and trophochromatin 

 which separates in the prophases, the latter forming 

 the dividing nucleole and the former the chromatin 

 ring. Maire and Tison described the division of the 

 tropochromatin as amitotic and that of the idiochro- 

 matin as indirect or mitotic. According to them, the 

 karyosome at rest is comparable with the nuclei of 

 Trypanosoma nociieae or Amoeba limaj:; during di- 

 vision it corresponds to the karyosome of Cari/otro- 

 pha mcsnilii, to tiie macronucleus of the Infusoria, to 

 the true chromidia of Goldschmidt, and to some ex- 

 tent to the nucleocentrosome of Euf/lena. 



The type of division illustrated in figures 1 to 31 is 

 obviously very similar to promitosis, in the strict 

 sense, which has been described in certain species of 

 amoebae. In order to compare the processes more 

 concretely, drawings by Nagler, Ciiatton, and Cal- 

 kins of successive promitotic stages in such species 

 have been brought together in figures 21 to 33. Both 

 the wheel-like (fig. 24) and "vacuolate" resting nu- 

 cleus (fig. 25) with large, conspicuous karyosomes 

 have been reported in Amoeba and these are strik- 

 ingly similar to the nuclei shown in figures 1, 2, l, 

 and 31 of tlie Plasmodiophorales. Division is like- 

 wise intranuclear. No sharply defined spindle and 

 chromosomes are formed, but instead the chromatin 

 aggregates into a more or less continuous band across 

 the equator (fig. 26—28). As the karyosome elon- 

 gates, constricts, and divides, tlie cliromatin band 

 splits lengthwise (fig. 29), and the daughter halves 

 migrate toward the opposite poles of the nucleus (fig. 

 30, 3 1 ) where they are incorporated with the daugli- 

 ter karyosome (fig. 32). As the nuclear membrane 

 disappears in the equator (fig. 32), new membranes 

 are develo])ed around the karyosome. and the daugli- 

 ter nuclei (fig. 33) are thus formed. 



To this extent the similarities are very striking — 

 so much so, in fact, that as one reads the accounts 

 of some students of the Plasmodiophorales it be- 

 comes obvious that their observations have been in- 



