FUNCTIONAL DIPLOIDS 185 



hybrid with 5. luteum (2n = 48) gives an allotetraploid sport 

 (2n = 120), which is, in relation to the basic number of the genus, a 

 decaploid. 



Table 24A 

 Chromosome Association in Polyploids 



Species (giving auto-tetraploids) 



Datura Stramonium (12). Belling, 1927 ; 2x : 12" ; 4X : 12^^. 

 Primula sinensis (12). D., 1931 a] 2x : 12" \ 4X : g-ii^"^ ; 



6 - 2". 

 Solanum Lycopersicum (12). 2x : 12" ; ^x \y — 11^^', 10 — 2" 



Lesley, 1930 ; i - 8'\ 22 - 8", Upcott, 1935. 



Undefined Hybrids (giving allo-tetraploids) 



Crepis rubra x C. foetida (5). Poole, 1931 ; 2a; : 5" ; 4X : 



o - 5^\ 10 - o". 

 Primula kewensis {g) . {P.florihunda x P.verticillata.) Newton 



and Pellew, 1929 ; 2a; : 9" ; 4X \ o — 3'^, 18 — 12". 

 Triticum dicoccoides (14) x Mgilops ovata (14). Kihara and 



Nishiyama, 1930 ; 2a: : o — 3", 28 — 22^ ; 4x\ o^^ 28". 

 Digitalis mertonensis (28). (Z>. purpurea X Z). ambigua.) 



Buxton and Newton, 1928 ; 2x : ^ — 12", 46 — 32' ; ^a; : 



o^ 56". 

 Raphanus-Brassica (9). Karpechenko, 1927 ; 2x : 0", 18' ; 



4x : 0'^ 18". 



The mechanically diploid behaviour of the allotetraploid means 

 that the corresponding chromosomes that pair and pass to opposite 

 poles to yield identical gametes, must always be those from the same 

 ancestral diploid parent and not those from opposite parents. 

 Thus in hybrids of the Primula kewensis type, the diploid has 

 pairing of the homologues derived from opposite species, but its 

 tetraploid descendants have not. Such a difference in behaviour 

 may be described as due to a " differential affinity " (D., 1928) 

 whose significance in relation to prophase behaviour will be con- 

 sidered later. 



