Nuclear Divisions in the Rusts. 
335 
Sappin-Trouffy (’96) and Maire (’ 00 ), on the other hand, regard the two 
chromatin masses in each dividing nucleus, not as evidence of longitudinal 
splitting, but rather as showing that there are two chromosomes regularly 
present in the nuclei of the Rusts. While indirect division is described 
as the principal method of nuclear division, Sappin-Trouffy also finds cases 
of amitosis, especially in old mycelial cells. 
Juel (’98), studying the promycelial divisions in Coleosporium , obtained 
results quite different from the authors mentioned above. His figures of 
nuclear division resemble closely those of other fungi. While not able 
to distinguish individual chromosomes, Juel thinks it quite probable that 
there are many. 
Holden and Harper (’03) have recently shown that the process of 
division of the fusion nucleus of Coleosporium agrees in essential details 
with those described for higher plants. In the prophases, a spirem thread 
splits longitudinally. In the metaphases, polar radiations, centrosomes, 
spindle and chromosomes are all very sharply differentiated. The chromo- 
some number is somewhere between six and ten. Conjugate division, in 
which the chromatin is represented as solid, dumbbell-shaped masses in all 
stages of division, is also figured by these authors ; but they think it quite 
likely that poor fixation is responsible for the lack of differentiation. 
Blackman (’04) has also investigated the subject of nuclear division, 
particularly in the promycelial cells of Gymno sporangium , and he has 
further compared with this type the divisions in the spermogonium, as well 
as the conjugate divisions in the sporophytic cells. The two divisions in 
the promycelium are regarded as reduced, or simple, forms of indirect 
division, while in the spermogonium and in the binucleated cells ‘chromo- 
some-formation is in complete abeyance, so that the division actually par- 
takes of the nature of direct division (amitosis) ’ (p. 356 ). 
In the promycelial divisions, according to Blackman, a well-defined 
spindle, centrosomes, and polar radiations are present. In the first division 
many chromosomes — at least ten — are formed ; but in the second division 
the chromosomes appear to lose their individuality, and to form a solid 
mass. Blackman regards the spindle in the case of the second division 
of the promycelial nuclei, and apparently also in the case of the first, as 
formed free in the cytoplasm between the two portions of a divided extra- 
nuclear centrosome, and therefore as similar to the £ Centralspindel ’ of 
Hermann. His figures showing divisions in the spermogonium and in the 
binucleated cells merely repeat the poorly differentiated structures brought 
out by former authors. 
Finally, Christman (’05, ’07 ’) has figured the anaphases of the conjugate 
division, showing the two distinct spindles, the several chromosomes (the 
number was not determined), and a few short rays attached to each 
pole. 
