HYBRIDS AND HAPLOIDS 205 



the ultimate diploid parents may be expected. This " secondary 

 segregation ' ' has been found in the progeny of similar crosses in 

 Triticum (cf D., 1928), and is probably characteristic of hybrids 

 between allopolyploids (cf. Philp, 1934). 



Finally there are hybrids (especially triploids) where the 

 relationships of the pairing chromosomes cannot be stated with 

 certainty. In the Drosera hybrid (Rosenberg, 1909) it was assumed 

 that the unpaired chromosomes were those of the tetraploid parent, 

 but they may (at least in part) be those of the diploid as a result of 

 autosyndesis. Similarly, in the Beta hybrid it is not possible to 

 know the provenance of the pairing chromosomes [cf. Table 28 D). 



The different kinds of autosyndesis may be summarised, giving 

 the same chromosome type the same capital letter, but a different 

 number when dissimilar, as follows : — 



1. Allotetraploid species {4X, 2x pairs) : A^^-A^, A^-A^, B^-B^, 

 B2-B2, etc., shows exceptional autosyndesis, A1-A1-A2-A2, 

 B^-B^, B2-B2, etc. 



2. " Haploid " derived from it by parthenogenesis, or diploid 

 hybrid giving rise to it by doubling {2x, x pairs) shows autosyndesis : 

 A1-A2, B1-B2, etc. 



3. " Triploid " derived from tetraploid by fusion of reduced and 

 unreduced gametes {6x) shows autosyndesis : — 



A I— A I, A I— A 2, A 2— A 2, B^—B^, etc. 

 or A ^-A ^-A ^-A 2, A 2-A 2, ^i-^i, etc. 

 or A i-A i-A i-A 2-A 2-A 2, B^-B^, etc. 



4. Hybrid with another tetraploid species (^3-^3, A^-A^, B^-B^, 

 etc.) (4%) shows autosyndesis : — 



A1—A2, A^—A^, B1—B2, BgrB^ 

 or A i-A 2-A ^-A 4, etc. 

 or yi J, A 2} ■^ 3 — ■^4> etc. 

 (allosyndesis being A ^-A 3, A 2-A 4, B^-B^, etc.;. 



5. Hybrid of a hexaploid species {6x, jx pairs) : A^-A^, A 2-A 2, 

 ^13-^3, B^-B^, etc., and a diploid species (2x, x pairs), A^-A^, B^-B^, 

 etc. (4x) shows autosyndesis : — 



A1-A2, A^-A^, ^1-^2. etc. 

 or A ^-A ^-A ^-A 4, etc. 



