196 



THE BEHAVIOUR OF POLYPLOIDS 



(Poole, 1931) and Aquilegia (Skalinska, 1935). It may therefore 

 be said that there is negative correlation between the fertility of 

 diploids and that of the tetraploids to which they give rise (D., 

 1928). The reason for this is evident. Two factors go to reduce 

 generational fertility : (i) the segregation of dissimilar chromosomes 

 (chiefly in the hybrid diploid) ; (ii) the unequal segregation of 

 multivalents (chiefly in the autotetraploid). And the greater the 

 dissimilarities in the diploid, the more regularly do the identical 



Non- 



H\/bricl 



Hybrid 



2oc 



J* 



fertile 



infertile 



4x 



•J- 



f 



infertile 



fertile 



Pairing ana Segregation 3t first JJiuision. 



Fig. 69. — Diagram showing the basis of the inverse correlation of 

 fertiHty of diploid and tetraploid. The fertile diploid gives 

 a tetraploid with quadrivalents having inherently irregular 

 division. The fertile tetraploid is derived from a diploid having 

 segregation of dissimilar chromosomes. 



chromosomes pair in the allotetraploid derived from it, and there- 

 fore the less frequent are the multivalents in the tetraploid. Multi- 

 valents are invariably liable to segregate unequally {e.g., Datura, 

 Belling and Blakeslee, 1924 ; Prunus, D., 1928 ; Primula, D., 

 1931 a), and give rise to gametes and zygotes of reduced viability. 

 The generalisation is therefore universally applicable subject to 

 three qualifications : — 



{a) The chromosomes must be capable of forming multivalents 

 as they universally appear to be. 



