STATISTICAL TREATMENT 169 



intermittent and appear complete as it sometimes does with localised 

 pairing, owing to the relational coiling of the chromosomes in their 

 intercalary unpaired parts. 



The second class is characterised by a unimodal curve in the 

 frequency of the pairing [v. Table 22). This curve shows some 

 variation even between different preparations of the same individual, 

 and a fortiori between sister individuals from the same cross. Such 

 variation is paralleled by that found in chiasma frequencies shown 



TA.80 





Fig. 57. — Percentage frequencies, T.A., of pairs of chromosomes 

 per nucleus in a Triticiim-JEgilops hybrid (Kihara, 1929 c) 

 from different preparations and V.f. of chiasmata per bivalent 

 in the m chromosomes of Vicia Faba (Maeda, 1930), also from 

 different preparations showing the effect of different develop- 

 mental conditions on these two variables. (From D., 1931 c.) 



by the same chromosome pair in different preparations in non- 

 hybrids (cf. D., 1931 c, on Maeda, 1930, and Fig. 57). 



In the second and third classes it is also found that wherever the 

 chiasma frequency of the parents is known or can be inferred, it is 

 found to be lower in the hybrid. Thus in Canna, Triticum and 

 Papaver two or three chiasmata are formed by the bivalents in the 

 parental species {cf. Table 23, and Peto, 1930 ; Goodspeed, 1934). 

 But in hybrids in these genera or between Triticum and Mgilops, 

 where the pairing is small and variable, such pairing as occurs is 



