COEFFICIENT OF MOVEMENT 



513 



Table y^ 



The Change in Chiasma Frequency from Diplotene to Metaphase 

 with Partial and with Complete Terminalisation 



1 . Stenohothrus paralldits * 

 Total number of chiasmata 



bivalent .... 

 Number of terminal chiasmata 



bivalent .... 

 Terminalisation coefficient 



2. Tulipa persica 



Total number of chiasmata 

 bivalent .... 



Number of terminal chiasmata 

 bivalent .... 



Terminalisation coefficient 



3. Rosa " Orleans " 



Total number of chiasmata 

 bivalent .... 



Number of terminal chiasmata 

 bivalent .... 



Terminalisation coefficient 



4. Campanula persicijolia 

 Total number of chiasmata 



bivalent .... 

 Number of terminal chiasmata 



bivalent .... 

 Terminalisation coefficient 



per 

 per 



per 

 per 



per 

 per 



per 

 per 



Metaphase. 



2-09 



I 04 

 0-50 



I '95 



0-91 

 0-47 



1-53 



i-i6 

 0-76 



1-90 



1-90 

 i-oo 



* Great size variation among the chromosomes. 

 t Observations of position at this stage uncertain. 



Terminalisation must then be regarded as the effect of unequal 

 forces of repulsion acting between the pairs of paired chromatids on 

 opposite sides of the chiasmata so that the association of the pair 

 that repel one another more gains at the expense of the other and 

 the chiasma moves along. 



There are seven kinds of conditions on the two sides of a chiasma, 

 five of them differential, according to whether the chromosomes are 

 in closed loops or lie free (with open arms), and according to whether 

 they have or have not the centromere in the loops or arms. These 

 show which differences are associated with movement and may 

 therefore be attributed to differential repulsion, as follows (c/. 

 Fig. 145) :— 



R.A. CYTOLOOy. 



17 



