t YT()I.<)(iY 



11 



appc.-irs. ;in(l tlic k.'irvosdiiic (liiuinislios in size ;iikJ 

 finally disappoars also, so that wt- have a number of 

 vacuoles more or l<ss eireular in outline situated in 

 the spherieal mass of plasma." Osliorn likewise de- 

 serilied the disappearance of tlie nuclear membrane 

 in Spoil (/(IS pora and the formation dc iidfd of new 

 nuclei. F. M. Jones ('28) also maintained that the 

 nuclei disajjpear completely in P. Brassicae and that 

 the new nuclei are formed by the agfjre^ation and 

 fusion of chrouiidia within small vacuoles. Cook (''i(i, 

 "28) described a complete extrusion of chromatin 

 from the nuclei of L. Jiiiici, but later he and 

 Schwartz reported that in P. Brassicae a .small 

 amount of chromatin may remain within the nuclei. 

 They, nevertheless, refuted the reports of previous 

 workers that the nuclear membrane disappears. 

 However, in SoTodiscus radicicolus. Cook later ('31 ) 

 rejiorted that all of the chromatin is extruded during 

 the akarvote stage .-iiid later re-enters ( I ) the nucleus 

 in preparation for meiosis. Winge, on the other hand, 

 found no marked chromatin extrusion and akarvote 

 condition in S. Callitrichis and referred to the 

 changes which the nuclei undergo in preparation for 

 meiosis as the transitional stage, a term later adopted 

 by Home and Webb. In Spongospora, Home also 

 noted tliat the nuclear membrane remains clear and 

 distinct throughout this stage and the nuclei have a 

 well-defined chromatin reticulum, chromidia. and a 

 faintly-stainablc nucleole. Similar stages were found 

 bv Miss Terby ('21-) who denied the existence of an 

 akarvote stage in P. Brassicae. By using Newton's 

 gentian violet iodine stain on Sorosphaera, Webb 

 also found the normal interphase chromatin reticu- 

 lum and a large faintly-stainable nucleole present 

 in the nuclei during the transitional stage. His ob- 

 servations were later confirmed in part by I.eding- 

 ham's study of I'oli/mi/j-a. The latter worker ob- 

 served a well-difined reticulum in nuclei stained by 

 Newton's method, whereas in preparations stained 

 with iron-alum haematoxylin the nuclei appeared to 

 be devoid of chromatin. The latter four workers ac- 

 cordingly refuted previous cytologists on the pres- 

 ence of marked akarvote stage at the conclusion of 

 the vegetative divisions. 



With the excejjtion of Terby. Home, Milovidov. 

 Webb, and Ledingham. most workers have described 

 a definite reorganization of nuclei following the so- 

 called akarvote stage. As noted before. Schwartz, 

 Osborn. and .Jones contended that the generative nu- 

 clei arise de novo on new sites in the eyto])lasm from 

 extruded chromatin, while Blomfield and Schwartz 

 were uncertain about their origin in Sorosphaera. All 

 other workers, however, held that the nuclear mem- 

 branes persist and that the nuclei undergo certain 

 characteristic changes. During this process centro- 

 somes and astral rays become quite consj)icuous in 

 the cyto|)lasm. but it is not certain whether they arise 

 de novo and divide or originate from the karyosome, 

 as Maire and Tison contended. Whereas several 

 workers denied the ))resence of these structures dur- 

 ing the vegetative divisions, most of them agreed that 

 centrosomes and astral rays are conspicuous features 



of the reconstructed nuclei .and si)orogenous divi- 

 sions. However, Blomfield, Schwartz, and Cook .a))- 

 p.areiitly never found these structures in any of the 

 developmental stages of Li(/iiiera, Sorosphaera, and 

 Plasniodiaphora, since none of their figures show 

 centrosomes and asters. Concomitant with the devel- 

 opment of these cyt()))lasmie structures, chromatic 

 strands, granules, and other configurations appear 

 in the nuclei, which are generally regarded as i)ro- 

 |)hases of meiosis and will be discussed in greater de- 

 t.iil below. 



It is al)parent from this discussion that the ob- 

 servations of the early cytologists of the Flasmodio- 

 |)lii)r.ilcs were gre.itly iuHueneed by the chromidia 

 iiypothesis of Cioldsehmidt. Seiiaudin. Poiiott'. .md 

 other protozoologists of that jieriod. Its infiuence 

 is also evident in the more recent contributions of 

 P. M. Jones and to a large extent in the papers by 

 Cook and Schwartz. Lack of space does not allow a 

 detailed account of the chromidia hyjjothesis here. 

 Suttiee it to note that in .Ictinosphaeriiim, Arcella, 

 .irachnula, Eiitamoeha, and numerous other rhizo- 

 poda R. Hertwig, Sehaudin, Popoff, Dobell, and 

 others reported a gradual disajipearance of the nu- 

 cleus as chromidia are extruded into the cytoplasm 

 and the subsequent formation of new nuclei in repro- 

 ductive cells from chromidial granules. These obser- 

 vations among others were the foundation of (Jold- 

 schmidt's theory and eventually led to the "binu- 

 clearity hypothesis" of Sehaudin. Prowazek. Maire 

 and Tison. Blomfield and Schwartz, and others in- 

 terjjreted the akarvote and reconstruction stages of 

 the Plasmodiophorales in terms of this chromidia 

 hypothesis, while Schwartz, Osborn, and Jones ap- 

 pear to have adopted this theory completely as an 

 explanation of the changes undergone by the nuclei 

 during these phases. 



The chromidia hypothesis has been largely dis- 

 credited in the last three decades by researches in- 

 volving the use of mitochondrial fixatives. Feulgen's 

 nuclear stain, and other more specific fixatives and 

 staining techniques. In Arcella and Clami/dophrt/s, 

 for instance, the nuclei do not disintegrate as was 

 jireviously claimed, according to ,lollos, but instead 

 are masked during certain stages by a chromidial 

 network which can be dissolved away in trypsin and 

 pepsin, leaving the nuclei sharp and clear. That this 

 network is not com])osed of chromatin derived pos- 

 sibly from the nucleus is evident by its negative re- 

 action to Feulgen's stain. Likewise, in most of the 

 earlier reported cases of chromidia extrusion and 

 growth, the so-called chromidia have been found to 

 relate to chondriosomes, ergastic, reserve, and de- 

 generative products of metabolism, etc. In .Ictino- 

 sphaeriiim, classic exam])le of chromidia extrusion, 

 Rmnjantzew re))orted that the chromidia ajjpear to 

 be composed of a carbohydrate held in a mechanical 

 or perhaps adsorbtive imion with a protein. In Dif- 

 fliif/ia they a])pear to be com))osed of glycogen, ac- 

 cording to Zuelzer, while in Kimeria they are made 

 up of volutin or metachromatin which have a strong 

 affinity for basic dves. Additional cases of this na- 



