170 



STRUCTURAL HYBRIDS 



by single (usually terminal or sub-terminal) chiasmata (Figs. 58 

 and 72). The same is true in a less degree of a defined structural 

 hybrid in Lilium (Richardson, 1936, and Ch, VII). 



It will be observed that the difference between the two degrees 





Fig. 58. — First metapliase of meiosis in Triiicuni iurgidum {2n = 28), 

 T. durum {2n = 28) and the hybrid between them. The total 

 number of chiasmata and the number terminal is given at the 

 side of each plate. Cf. Table 23, smear preparations : The top 

 plate is fixed in aceto-carmine (x 1900), the rest in Flemming 

 (X 2800). (From D., 1931 d. Cf. Fig. 57.) 



of pairing is the same as that observed between the pairing of 

 fragments which form only one chiasma and their large sister 

 chromosomes which form two or more (e.g., in Fritillaria, D., 1930 c, 

 and Datura, Blakeslee, 193 1). The pairing found in undefined 

 hybrids is therefore in accordance with the assumption that a larger 

 or smaller fraction of the total length of chromosome threads is 



