( YTOl.OCY 



18 



nuiss is <'()iii))i)s((l (if fiiiir ilistiiu't clironiosoiius in 

 .S'/i()Hf/(».\7»()ro. Sonuwiiat siniil.ir c-irly clianuis wen- 

 riportcd \<\ M.iirc .uul Tisoii (11) and \\ iimc tor 

 Tftramtidti, W'injrc for Sorixliscitx (Fl. 7. (ij;. Ml, 2;i, 

 21), Wingc and W't'lib for Soro.iphnrra (Pi. (5, 

 fig. 29, 30), Terliv (21) for /'. lirassicai-, and Cook 

 ('31) for S. radicicolus. Winge fonnd tliat tlu- two 

 polar niassts may he arranged in tlu' form of gar- 

 lands with I'oiinci'ttd filanu-nts. an arrangtuu-nt jirc- 

 vioiisly reported by Frowazek for /'. Hrax.iicar, and 

 snl)se<iiiently by Terby (I.e.) and Cook (I.e.). The 

 nueleole may gradnally disaiJjiear dnring this st.ige 

 or beeome tjattened and aggregated with the eliro- 

 inatin ma.ssc.s and filaments at one .side of the nuelen.s. 

 Tlii.s nnelear eonfigiiration is strikingly similar to 

 the eollapsed .synizetie (zygotene) stage in higher 

 plants. In the Flasmodiophorales. however, it is gen- 

 erally referred to as synapsis and has been so far 

 rei)orted as sueh in PlasniotUophora (Terby, Cook 

 .and Sehwartz. .Milo\ idov), Spdiif/ospora (Osborn, 

 Home), SoTOsphaera (Maire and Tison, Webb), and 

 Sorodisciis (?) (Winge). In Spoiu/ospora, Home 

 found two contraction stages and designated the sec- 

 ond one as .synapsis. Each loop in the second contrac- 

 tion stage is converted directly into a heteroty|)ic 

 chromosome. Cook ('28) found no meiotic jirophases 

 in L. Jiinci, and in P. Brassicae he and .Schwartz re- 

 ])orted and figured only one stage wliieh might be 

 interpreted as such. The chromatin was arranged 

 in a thick thread with several globular nucleole- 

 like bodies distributed along its length. Cook and 

 .Schwartz regarded this stage as com))arable to syn- 

 apsis, but it bears little or no resemblance to the 

 synajitie stage figured by other workers. 



Before or during the contracted stage, the nueleole 

 disappears, while the chromatin threads loosen up 

 and take on the appearance of elongate chromo- 

 somes. According to Webb, in Sornsphaera the chro- 

 matin at this stage consists of beaded threads spread 

 over the |)eri))hery and has the ajipearanee of a nor- 

 mal ))aehytene. Tlie threads occasionally appear 

 double, and after further contraction four chromo- 

 somes become visible (PI. 6. fig. SJ). This stage 

 corresponds to diplotene in higher plants, according 

 to Webb. Then follows diakinesis (PI. (5. fig. 3.5). 

 during which four well-defined bivalents are visible. 

 In /'. Brnssicae, Cook and .Schwartz failed to find 

 comi)arable stages and merely reported that the 

 chromatin thread segments into chromosomes as the 

 nucle.ir membrane disa])i)ears. Miss Terby (^t), on 

 tlie other hand, found well-defined stre))sitene. early 

 and late diakinetic stages (PI. 3. fig. ()8-71) with 

 four bivalent chromosomes in P. lirassicae, which 

 indicates that Cook and Schwartz overlooked these 

 |)liases. \ diakinetic stage with thick broadly 

 \'-sha|ied ;ind ring diromosonies was also observed 

 by Home in SpDiKjospora. 



.Shortly after diakinesis the nuclear membrane dis- 

 appears, and tlie chromosomes become oriented in 

 the equator of a well-defined divi.sion sjjindle with 

 centrosomes and asters. .•\!1 other workers reported 

 that the nuclear membrane disajjpears during meta- 



phase. but in Plniiiunlidpliiira and Spoiiijospora, 

 Prowazek ,inil Ilorni' figured it as persisting until 

 tlu' telophases. The origin of the nuiotic spindle has 

 luit been sohcd, but \\ ilib lielie\cd tli.at it grows in- 

 ward from the Jioles to the equator. According to 

 most cytologists the heterotyi>ic ehronu)somes are 

 closely associated on the equatorial ])late and in 

 metai)hase and often appear as an irregular band or 

 row of connected globules, so that the ))rofile and 

 ))ol;ir views ;ire not very ciiaracteristic of hetero- 

 ty|)ie divisions. In Spiitifidxpora, however. Home 

 figured the chromosomes .-is short .-md thick with con- 

 s|)icu()us intervening ga))s in the t(i\iatorial jilate, 

 wliieli makes it possible to recognize and count the 

 individual members. At this stage tliey may often 

 show four blunt ends, which indicates their tetrad 

 nature, according to Home. 



With the excei)tion of Winge, most cytologists 

 held that the homologues separate at metapliase of 

 the first division and move to the ))oles where they 

 are incorporated in the daughter nuclei. In Soro- 

 xphnera, ^A'ebb found the late ana))hase and telo- 

 phase chromosomes to be double, which suggests that 

 the equatorial split for the homeotypic division oc- 

 curs quite early. Cook ('28) failed to see nuclear 

 membranes in the late telo)ihases of L. Jitnci and 

 thus concluded that they are no* formed between the 

 first and second divisions. All previous and subse- 

 quent workers, however, have shown that a well- 

 defined membrane develops around the telo))hase 

 groups of chromosomes and that daughter nucleoli 

 are subsequently formed. Interkinesis is usually 

 short in duration. In P. Brassicae Miss Terby ('2f) 

 reported that the telophase nuclei go directly into 

 the prophases of the next division, but in Spongo- 

 spora wheel-like resting nuclei and distinct pro- 

 ))hases may intervene between the two divisions. 



The second division is likewise mitotic or indi- 

 rect but considerably smaller in size than the first 

 one. Palling to count the chromosomes. Cook and 

 Schwartz regarded this size difference as ))roof that 

 these two divisions are res])eetively hetero- .ind ho- 

 meotypic. a criterion which is obviously of no critical 

 \alue in this respect. Osborn. Milovidow \\'ernham, 

 Whitf'en. and others also made the s.ime assuiu))tion 

 without counting the chromosomes. On the other 

 hand, Maire and Tison, Winge. Terby. Home, 

 Yendo and Takase. and Webb based their contention 

 on a numerical reduction in chronuisome nmnber dur- 

 ing these divisions. Whetlier or not their chromosome 

 counts are accurate remains, however, to be shown 

 from more intensive study of these divisions. 



The chromosomes of the PIasm(>dio|)hor.iles are 

 quite small and are not always clearly defined on the 

 equatorial plate, so that it is difficult to make accu- 

 rate counts. Xevertheless. numerous attempts have 

 been made, as is shown in table 1 . 



The numbers are low multi|)les of 2, with 8 )ire- 

 dominating as the di])loid inniiber. In .S. V iron'icae 

 Maire and Tison reported Hi .and 8 chromosomes, but 

 Webb later found only 8 and i. \\'inge. as noted be- 

 fore, described the first division as vegetative or so- 



