370 



INTRODUCTION TO CYTOLOGY 



quadruple groupings sometimes occur, particularly when the species 

 crossed are nearly related. The fertile allotetraploid tends to breed 



18 R 



9R + 9B 







18R + 9B I8R+18B 27R + 18B 24R + 27B 



Fig. 211. — Correlation of seed pod characters with chromosome constitution in Rap- 

 hanus X Brassica. A, Raphanus sativus: upper, non-dehiscent seed-bearing part large; 

 lower part small and mostly seedless. B, Brassica oleracea: upper part nearly seedless; 

 lower part much elongated, with seeds. C, diploid Fi hybrid between A and B: upper and 

 lower parts about equal in size. D, F, triploid and pentaploid types derived from cross 

 of A and C: each has more Raphanus than Brassica chromosomes, and upper part of pod 

 is larger. E, fertile tetraploid type {Raphanobrassica) obtained by selfing C: two sets of 

 chromosomes from each grandparent; capsule parts about equal in size. G, hypohexaploid 

 type somewhat deficient in Raphanus chromosomes. {After Karpechenko, 1927b.) 



true, apparently because of the regular pairing between chromosomes 

 from similar sets (autosynapsis) and their regular distribution. The 

 occasional segregation of differing types, as in Primula and Aquilegia, is 



