172 STRUCTURAL HYBRIDS 



noticed. Were they all short they would all fail to pair and meiosis 

 would follow an entirely different course. 



Finally when, as in polyploid hybrids, pairing is seen to be 

 governed by " differential affinity " (Ch. VI), deductions from 

 pairing must have an enormous margin of error. The extensive 

 phylogenetic conclusions that have been based on observation of 

 pairing in hybrids, especially in Triticum and Nicotiana, must 

 therefore be regarded as little better founded than those based on 

 chromosome number in Crepis. 



The behaviour of unpaired chromosomes will be considered in 

 relation to the breakdown of genetic systems (Ch. X). 



Table 21 



CLASSIFIED OBSERVATIONS OF PAIRING OF CHROMOSOMES IN UNDEFINED HYBRIDS 



The haploid number is given after each species, and the number of pairs (;r") 

 formed by the hybrid where this is variable. 



(i) Potentially Complete Pairing. 



Lepidoptera. 

 Oporabia filigrammaria (37) X O. autumnata (38), 34-37". Harrison, 1920 a. 

 Pergesa porcellus (29) X P. elpenor (29). Federley, cit. Cretschmar, 1927. 

 Amorpha populi austauti (28) x A. p. populi (28). Federley, cit. Cretschmar, 



1927. 

 Celeris euphorbics (29) X C. galii (29). Bytinski Salz and Giinther, 1930. 



Pisces. 

 Platypoeciliis variatus {25) X P. maculatus (24) 24^^ + i^ or 23" + i^". 

 Friedman and Gordon, 1934. 



Angiosperms. 

 Primula Jforibunda (9) X P. verticillata (9) (= P. kewensis). Digby, 



191 2 ; cf. Newton and Pellew, 1929. 

 Digitalis lanata (28) X D. micrantha (28). Haase-Bessel, 1922. 

 Tragopogon pratense {6) X T. porr if olius [6)] Wing e, cit. Babcock and J. 

 Geum rivale (21) X G. urbanum (21). J Clausen, 1929. 



Primus persica (8) x P. Amygdalus (8) \ 

 P. triflora (8) x P. persica (8). [ D., 1930 a. 



P. triflora (8) x P. cerasifera (8) ) 



Fragaria vesca (7) X F. Helleri (7) \ 



F. bracteata (7) X F. Helleri (7) \ Ichijima, 1926. 



F. glauca (28) x F. virginiana (28) ) 



Sorbus Aria (17) x Aronia melanocarpa (17). Sax, 1929. 

 Ribes rubrum (8) x R. petrcsum (8) (= R. holosericeum) . Meurman, 1928. 

 Viola tricolor (13) X V. alpestris (13) | -r >-, 

 V. cornuta (ii) X V. orthoceras (11) f J' '-^ausen, 1931 c. 

 Salix viminalis (19) X 5. Caprea (19). HS.kansson, 19296. 

 Crepis rubra (5) X C. fcetida (5). Poole, 1931. 

 C. leontodontoides (5) X C. aiirea (5). Avery, 1930. 

 Triticum dicoccum (14) x T. persicum (14). Vakar, 1930. 



