AUTOSYNDESIS 203 



with a diploid species and again 3'ield a hybrid with complete 

 pairing, thus : — 



lox X 2x = 6x (ja;"), 6x X 2x = 4X (2a:"). 



Here also pairing is occurring between all the sets of the polyploid. 

 5. In hybrids between two tetraploid species. Most of the 

 chromosomes may fail to pair altogether, but some quadrivalents 

 are found as in the first and fourth cases. Higher configurations 

 often occur in the hybrid than in its polyploid parent, although 



Fig. 71. — Side views of the pairing chromosomes at first metaphase : 

 a, in Primus cerasifera, n = 8; b, in P. domestica, n — 2^; c, in 

 the hybrid, P. domestica X P. cerasifera, n = 16. X 3000. {b, 

 from Mather, unpubHshed ; c, from D., 1930 a.) 



very little pairing occurs at all (Kihara and Nishiyama, 1930 ; 

 V. Fig. 72 ; Kattermann, 1931). This condition is found in hybrids 

 between two tetraploids {Triticum-^Egilops, Kihara, 1929) and in 

 Viola hybrids (e.g., V. nana and V . lutea, J. Clausen, 1931 c). The 

 formation of multivalents makes it possible to prove the occurrence 

 of autosyndesis in a hybrid between two tetraploids. Thus in the 

 cross jEgilops cylindrica (4% = 28) by ^. triuncialis (4X = 28) a 

 trivalent was sometimes found together with 6 to 11 bivalents 

 (Kagawa, 1931). The trivalent could only arise through pairing of 

 chromosomes derived from the same gamete, if not with one another 

 at least with the same chromosome derived from the other gamete. 



