1929] BabcocTc-Clausen : Meiosis in Crepis 409 



which have the fiber attachment. The disjunction of the spirally 

 coiled and intercrossed chromatids must be a little difficult and in 

 different organisms many anaphases show that the homologous chro- 

 mosomes adhere very tightly to each other, sometimes showing a long 

 connection between even rather widely separated homologues. It 

 would be expected that exchanged parts of chromatids during this 

 pulling would be straightened out and uncoiled to some extent. 



The four gemini, in the diaphase of the two Crepis species men- 

 tioned, assume different shapes according to whether there is any 

 connection between the two homologues or not, and according to where 

 an eventual chiasma has taken place. So sometimes they form Vs, 

 sometimes X's, sometimes K's, and sometimes they are just parallel 

 (pi. 58, figs. 5-9, 12-13). Figures 7 and 12 show gemini with pre- 

 sumably two connections (nodes, in Belling's terminology). Figure 

 8 shows a pair with a very conspicuous chiasma. 



The shape of the bivalents during disjunction in the heterotypic 

 meta-anaphase apparently is determined by their mode of connection 

 during the late prophase. Plate 58, figures 10-11, shows this stage 

 in C. aspera; figures 14 and 15, the corresponding ones in C. hursi- 

 folia. Only the small chromosome pair of hiirsifolia is rod-shaped 

 and always very conspicuously different from the other pairs. Plate 

 59, figures 16-18, shows heterotypic anaphase and homotypic meta- 

 phase and anaphase of C. hursifoUa in order to illustrate that the 

 short chromosome of this species can be distinguished from the other 

 three during all phases of division. During the phases following the 

 diaphase the chromosomes stained so dark that it was impossible to 

 see any structure in them. For the study of chromosome structure in 

 these phases objects with less heavily staining chromosomes than those 

 of Crepis should be used. 



The facts observed regarding the spiral structure of the chromo- 

 somes in Crepis are a new link in the chain of observations made by 

 many cytologists on different plants and animals, as for instance 

 Tradescantia (Baranetzky, 1880; Kaufmann, 1926fl; Kuwada and 

 Sugimoto, 1926; Sakamura, 1927) ; Ascaris (Bonnevie, 1908; Vejdov- 

 sky, 1911-12), PodophijUum (Kaufmann, 1926&), FritiUaria (New- 

 ton, 1927), and Vicia (Kuwada, 1926, 1927). Also the zigzag fila- 

 ments in chromosomes of Paris and Listera described by Martens 

 (1922, 1924) might be considered evidence for a spiral structure. 

 The occurrence of such structure very naturally explains how the 

 chromosomes in the course of a short time change in form from long, 



