Cytologia 2, 



The Secondary Association of Chromosomes 



By w. J. C. Lawrence 



John Innes Horticultural Institution, Merton, London 



Received Ap-il 2/, Jg3i 



Contents 



Page 



Introduction 352 



Methods 353 



Observations 353 



The Theory of Secondary Association ... 361 



Evidence from the Literature 364 



a) cases observed . . 364 



b) cases inferred 366 



Discussion 370 



a) Fixation 870 



b) Secondary association in relation to allopolyploids 371 



c) Secondary association as a criterion of homology .... . 373 

 Summary 377 



Introduction 



The association of more than two chromosomes at metaphase of 

 meiosis in polyploids was first clearly observed by Kuwada in Oryza 

 sativa (1910), ISHiKAWA in Dahlia variabilis (1911) and Marchal in 

 Amblystegium (1912). 



The nature of multivalent chromosome association at metaphase 

 was first described by Belling (1921) in triploid Canna. Darlington 

 (1928) working on Prunus, later distinguished two types of pairing, 

 namely a) multivalent, resulting from prophase pairing and b) secon- 

 dary, or post-synaptic association. The present writer described (1929) 

 the association of varying numbers of bivalents at the first and second 

 metaphases in Dahlia variabilis and other species. 



At this time the true nature of bivalent or multivalent as ociation of 

 chromosomes was not realised. The work of Newton and Darlington 



