OCCURREXCE OF HYBRIDS 



Table iS 

 Pairing in Tetraploid Interchange Heterozygotes 



159 



Similar behaviour is found in Tradescaniia virginiana (Stow, 1928 ; 

 D., 1929 c) and Campanula persicifolia (Gairdner and D., 1931). In 

 both of these tetraploid forms of various constitutions probably 

 occur. The constitution of the tetraploid forms of (Enothera can 

 be specified from knowledge of the behaviour of the diploids from 

 which they are derived, and they show the types of configuration 

 that are to be expected on these grounds (Hakansson, 1926 ; 

 Catcheside, 1932 and 1935 ; Seitz, 1935). 



Table 19 



Classification of Interchange Heterozygotes 



(a) Diploids. 



Artificial Hybrids. 

 Datura* (« = 12) . 



Pisitni {)i = 7) 



i 



Blakeslee, 192S, 1929. 

 (Hakansson, 1929, 1931, I934- 

 E. R. Sansome (Richardson), 

 1929, 1932, 1933 : Sutton, 

 1935- 



Polemonium reptans (race cross 

 P. mexicanum x P. pauciflorum 

 P.filicimim X ccBruleum 

 Canna* ..... 



Godetia amcena {n = 7) x G. Whitneyi 



{n = 7) 



(Enothera* (4) and (6) . 



Spontaneous Forms. 



Campanula persicifolia* {n = 8) 



(4) and (6) .... 



Oenothera spp.* {n == 7) (14) . 



J. Clausen, 1931 a. 



Honing, 1928. 



Hakansson, 1925, 1931 ^• 

 Catcheside, 1932. 



Gairdner and D., 1931- 

 Cleland, 1922-28 ; D., 1931 c. 



* Chiasmata all terminal apart from those arrested by change of homology, 

 cf. Ch. XII. Numbers in brackets are the numbers of chromosomes in a ring. 



