Caroline Pellew and Eva Richardson Sansome 39 



Fritillaria imperialis (Darlington, 1930 a). In these species, the chiasmata 

 are relatively stationary, persisting from diplotene until anaphase. 



In many species which have been studied the chromosomes are only 

 attached by the ends at metaphase, by what Darlington describes as a 

 terminal chiasma. Also in some species which have been studied at 

 diplotene and at metaphase, a reduction in the number of chiasmata has 

 been observed to take place between the two stages. Darlington (1929 b) 

 puts forward the view that this reduction in number takes place by a 

 movement of the chiasmata away from the attachment constriction 

 towards the ends of the chromosomes, which movement he describes as 

 the terminalisation of chiasmata. TerminaKsation thus leads to the 

 formation of terminal chiasmata. 



Observations on Matthiola (Philp and Huskins, 1931) and on Rosa 

 (Erlansson, 1931), which show a greater concentration of the chias- 

 mata at the ends of the chromosomes at the later stages, leading to 

 complete terminaUsation, strongly support Darlington's views. Since it 

 has not been possible to study the early stages in Pisum, it is impossible 

 to determine exactly the extent of reduction of the number of chiasmata 

 in this particular instance. However, the percentage of terminal chias- 

 mata gives an indication of the extent of terminalisation. 



TABLE I. 



Chiasma frequency in bivalents. 



In the case of 696= the whole chromosome complement is included. 



The chiasma frequency of a semi-sterile F^ plant 696^/30 was estimated, 

 and for comparison pollen mother cells from Early Giant rogue 532^/30 



