214 



THE BEHAVIOUR OF POLYPLOIDS 



to secure the degree of differentiation found between pairs of 

 homologues in any two. The different kinds of polyploid species 

 may therefore be classified, arbitrarily but conveniently, in three 

 groups. 



The first class includes those in which autosyndesis never occurs 

 in haploids, triploids or hybrids, or a fortiori in the normal species. 

 This extreme of differentiation, found in Nicotiana Tahacum and in 

 Triticiim compactum, is analogous to that in the Raphanus-Brassica 

 tetraploid. It is probably found most generally in old established 

 sexually-propagated annual species. 



The second class consists of those species with imperfect 

 differentiation. The pairing observed in Bromus eredus may serve 

 as a type of behaviour in this group. Table 31 shows pairing in 

 one plant ; in others a sexivalent and octavalent were found. The 

 occurrence of univalents in 9 per cent, of the cells is probably 

 due to mechanical interference with pairing at zygotene as in 

 tetraploid Primula sinensis, and is therefore a symptom of 

 autopolyploidy. 



Following is a list of similar species whose pairing is normally 

 and " legitimately," as we may say, that of diploids, but in which 

 multivalents are occasionally and illegitimately formed. In these, 

 more or less autosyndesis is found, or is to be expected, in haploids 

 and hybrids. Experimental breeders are treading on dangerous 

 ground when they treat such species as functional diploids. 



Table 30 

 Polyploid Species of an Intermediate Type 



Rumex Acetosella {6x, 42) 

 Triticum vulgare {6x, 42) 

 Avena saliva {6x, 42) 

 Bromus erectus eu-erectus {8x 

 Rubus thyrsiger {4X, 28) 

 Prunus domestica {6x, 48) 

 P. spinosa {4X, 32) 

 P. laurocerasus {22X, 176) 

 Pyrus Malus {4-6X, 34) 

 Cardamine pratensis {4X, 30) 

 Ly thrum Salicaria {6x, 30) 

 Tulipa stellata {4X, 48) 

 Veronica spp. {4X, 68) . 

 Helianthus tuberosus {6x, 102 



56) 



Kihara, 1927 ; Ono, 1930. 

 Winge, 1924 ; Huskins, 1928. 

 Huskins, 1927. 

 Kattermann, 1931. 

 Crane and D., 1927. 



D., 1930 a. 



Meurman, 1929 a. 



D. and Moffett, 1930 [v. p. 224). 



Lawrence, 1931 b. 



Shinke, 1929. 



D. and Janaki-Ammal, 1932. 



Graze, I935- 



Kostoff, 1934. 



