1929] BahcocTc-Clausen : Meiosis in Crepis 407 



plate 58, figure 4 clearly shows at one end ; while the less clear parts 

 of the chromosomes in this and in several other pollen mother cells 

 appeared like a string of beads, the beads being much larger than in 

 the earlier stages. Also the beads here apparently were not chromo- 

 meres but short spiral coils. Real spirals with tight windings, giving 

 the impression of bars on a ribbon, might also sometimes mislead the 

 observer. 



As the diplophase proceeds, the paired chromosomes gradually 

 uncoil and the chromosomes become shorter and thicker. This is 

 probably due to the fact that the chromatic spiral of the chromosome, 

 the chromonema as Vejdovsky, Kaufmann, and others name it, 

 becomes larger in diameter. The four pairs of chromosomes in plate 

 58, figure 4 have not more than about two twists each. 



In a little later phase, the typical dia phase (or diakinesis) each 

 of the members contains two chromonemata or chromatids as shown 

 in plate 58, figures 5, 8, and 13. The splitting for the homotypic 

 division has here become visible, but the process of splitting may have 

 taken place in an earlier phase. In several cases the spiral structure 

 is very clear and regular, in other cases (perhaps a little later) the 

 spirals are not so regular and tight (fig. 12). Although here the 

 two chromonemata within one chromosome are a little twisted, we 

 might with poorer staining get the impression of a longitudinal split, 

 which is shown in so many pictures of chromosome division. This 

 might also, in other cases, be due to the fact that the two spiral 

 chromatids within the chromosome really have become separated from 

 each other (Kuwada, 1926, 1927). The two zigzag spirals crossing 

 one another within one chromosome also might sometimes give the 

 appearance of alveolized chromosomes or of a reticulum. 



As the chromosomes uncoil during the latter part of the diaphase 

 there is often seen a connection between the two members of a chromo- 

 some pair. In several cases it can be seen that one of the spiral 

 chromatids extends from one chromosome to its homologue while one 

 of the chromatids f?"om the latter chromosome extends to the former, 

 the two connecting chromatids sometimes forming a cross where they 

 change chromosomes (pi. 58, fig. 7). This phenomenon is very similar 

 to the chiasmas which Janssens (1909, 1924) saw in the nuclei of 

 insects and apparently is what Belling (1928a, p. 284) calls an X 

 chiasma; but in Crepis the outline of the chromosomes is much more 

 distinct than in Janssens' pictures, the nature of the connections, 

 therefore, much less questionable. 



