84 THE CHROMOSOMES 



TABLE VII 



Frequency of Quadrival.ent-formation in Auto- 

 tetraploids 



follows the usual eo«rse already described in the case 

 of bivalents. When they come to orientate them- 

 selves on the spindle of the first division they do so 

 in a way which can be explained if there is, in 

 addition to the general repulsion force between all 

 chromosome surfaces, an extra repulsion force 

 between spindle attachments. Thus in the case of 

 a trivalent it is usual for two spindle attachments to 

 go to one pole and the one between them to the 

 other. In the case of quadrivalents two spindle 

 attachments go to each pole. Which of the four 

 go to the same pole depends in part on whether they 

 lie in the middle of the chromosomes or almost at 

 one end and in part on the number of chiasmata 

 which have been formed in the quadrivalent. In 

 nuclei with only quadrivalents and bivalents an 

 equal number of chromosomes will go to the two 

 poles at the first division, but in those with uni- 

 valents, trivalents or quinquevalents the number of 

 chromosomes going to the poles will generally be 

 unequal. 



Meiosis in Complex Heterozygote 

 Organisms 29. 35, 21 



In many species of the genus Oenothera (Evening 

 Primroses) and in some other plants such as Hyperi- 



