POLYPLOIDY WITHIN SPECIES 



227 



forms which have presumably remained unaltered since their origin. 

 Amongst these are the sterile polyploid clone-species in Tulipa, 

 Lilium and Fritillaria, and probably the giant forms in Allium and 

 Portulaca. 



The rest, however, have changed in one or, as in the case of 

 Silene ciliata or Viola Kitaiheliana, in both of two ways : they have 

 lost their gigantism ; they have become allopolyploid. For 

 example, the hybrid between the two forms of the Viola species 

 shows no autosyndesis (Table 29). The loss of the gigantism may 

 be attributed to mutation and segregation as already suggested. 

 The loss of the autopolyploidy must be due to differentiation 

 arising between the different pairs of haploid sets. Structural 

 changes in the chromosomes might lead both to the differentiation 

 and to the loss of gigantism ; it would be advantageous to any race 

 to have pairs of chromosomes alike in regard to any new structural 

 change, for this would prevent the formation of larger associations 

 of chromosomes than twos. We shall see later, in the wide distribu- 

 tion of inversions, a means by which such differentiation could 

 arise without a genetic change that is physiologically expressed. 

 This method of differentiation is probably therefore the chief agent 

 of change in polyploid forms after their origin. It is, in general, 

 analogous in cause and effect to that which arises between particular 

 pairs of chromosomes in sex heterozygotes and between the two 

 whole sets in complex heterozygotes (Ch. IX). 



Table 37 

 Examples of Polyploidy within the Species 

 A. Not associated with systemMic differences (other than distribution 

 Rosa acicularis Lindl. 



Potentilla opaca L. . 

 Callitriche stagnalis . 

 Salix aurita L, 



Ranunculus acris 



Anemone montana 

 Nasturtium officinale. 



Draba magellanica Lam. 

 Crepis Bungei Ledeb. 



n = (7), 21, 28 



n = 7, 14 

 « = 5, 10 

 n = 19, 38 



n = (6), 7, 14 . 



w = 8, 16, 24 . 

 n = 16, 32 (and 

 16x32). 

 n = 24, 32, 40 

 M = 4, 8 



Tackholm, 1922 ; Erlanson, 



1929. 

 Tischler, 1928. 

 Jorgensen, 1923. 

 Blackburn and Harrison, 



1924 ; Hakansson, 1929 h. 

 Senjaninova, 1927 ; Sorokin, 



1927 ; Larter, 1932. 

 Moffett, 1932 b. 



Manton, 1932. 

 Heilborn, 1927. 

 Hollingshead and 

 1930. 



Babcock, 



