ABSTRACTS OF SECTIONAL PROCEEDINGS 



pairing chromosomes at the prophase of meiosis, but each 

 type has a constant average behaviour. Four species, F. pon- 

 tica, F. citrina, F. ruthenica and F. Meleagris, have a concentra- 

 tion of the chiasmata near the attachment constriction, 

 whether this is median or sub-terminal. But in F. imperialis 

 chiasmata are formed at random along the whole length of 

 the chromosome with a mean frequency constant for each 

 clonal variety (taking the complement as a whole). Varieties 

 differ in their frequency, some having as low a mean as three, 

 others as high a mean as five. Fragment chromosomes one- 

 ninth the length of the ordinary chromosomes occur in these 

 varieties. These fragments fail to pair (either with one another 

 or with whole chromosomes) in a proportion of cases, and the 

 frequency of their pairing is lower in varieties with lower 

 chiasma formation. 



Comparison of Mean Frequencies of Chiasmata 

 and Fragment Pairing 



These two results show that the association of the fragments, 

 although usually terminal, is none the less essentially a chiasma. 

 Or it may be said that, in substance, they could be predicted 

 on the hypothesis that the pairing of chromosomes at meta- 

 phase is conditioned by the formation of chiasmata amongst 

 the associated chromosomes at prophase. 



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