1931 The secondary association of chromosomes 359 



shown in Fig. 2 g. Six pairs of bivalents are clearly associated and in 

 every case the members of each pair are similar in size and configura- 

 tion. Four of these pairs of bivalents are in a plane at right angles to 

 the line of vision, and although the components of each are very close 

 together, no obvious connections are to be seen as between the quad- 

 rivalents in D. variabilis. In four of these six associations (a—d) the 

 bivalents have two terminal chiasmata; the other two associations 

 (e, /) have single terminal chiasmata. 



Anaphase is mainly regular, but laggard univalents have been ob- 

 served occasionally. 



D. coronata (2n=32). 



At diakinesis there are regularly 16 bivalents. At metaphase 

 secondary association is of frequent occurrence. An account of the 

 cytology of meiosis in this species was given in my 1931 Dahlia paper. 



b c 



Fig. 3. 

 Fig. 3. Meiosis in D. variabilis (2n=64) 



o. polar view. Anaphase I (the bivalent in outline marked x has been displaced by 

 the microtome knife). &-c. polar views MI showing groups of 2 and 3 bivalents. 



