CONCLUSIONS 



Table 8. Statistical frequency of polyploidy among Flowering Plants in different 

 regions of north-western Europe, after Love and Love, 1943 



Table 9. Statistical frequency of polyploidy among the leptosporangiate ferns of the 



British Isles and Madeira 



British Isles 

 Madeira 



Km.2 

 316,000 

 635 



Latitude 

 50-61° N. 



32° N. 



Percentage 



of flora f 



determined Diploids 



Total number of 



Polyploids 



100 

 91 



22 



22 



25 

 16 



Percentage 

 polyploidy 



53 

 42 



Leaving this last conclusion aside for a moment we may compare the British ferns 

 with Love and Love's data for Flowering Plants. These are summarized in Table 8, in 

 the form presented in their 1943 paper which for the present purpose is the more 

 convenient to quote. The top part of Table 9 gives the comparable facts for the British 

 ferns compiled with the sole assumption that the three cases for which only non- 

 British specimens have been available {Cystopteris montana, diploid D. dilatata, Asplenium 

 Adiantum-nigrum var. acutum) will actually be found here in the form predicted. With 

 this assumption, the total frequency of polyploidy among British ferns is of the order 

 of 50 per cent, and though the exact figure obtained (Table 9) should not be taken too 

 seriously since it might easily have been slightly different had the search for relict 

 diploids been less thorough, or had others been found. As an order of magnitude it 

 nevertheless compares closely with Love and Love's estimate for Flowering Plants in 

 general and for Dicotyledons in particular at comparable latitudes in Scandinavia. 



Does this, however, mean that polyploidy as such is geographically determined either 

 in ferns or Flowering Plants as an adaptive response to cold? I personally think that 

 it does not, but rather that the historical incidence of recent glaciation has produced 

 this appearance locally and incidentally. If comparisons are conducted not within the 

 glaciated territories but outside them a somewhat different picture emerges which, 

 when it can be more fully seen, will almost certainly solve this particular problem. 

 The island of Madeira is an excellent starting point for such a comparison and though 

 the facts can at present only be quoted in a preliminary form they will be briefly 

 introduced at this point because they provide a valuable corrective against the hasty 

 acceptance of what may prove to be an incomplete, and therefore misleading, explana- 

 tion. 



282 



