SCOLOPENDRIUM HYBRIDUM, WOODSIA AND POLYSTICHUM ILLYRICUM 



Ceterach. This cannot lightly be dismissed, even though an intergeneric hybrid seems at 

 first sight improbable and the chromosome number hitherto found {n = 72) is too high. 

 We cannot, however, assume that a form of Ceterach with a lower chromosome number 

 may not exist, and the fact that if the known number were halved it would be identical 

 with that of diploid Scolopendrium may indicate a closer relationship than one might 

 otherwise have expected to find. Further investigation of this problem is therefore very 

 much to be desired. 



The second case to be discussed, that of Woodsia, came to my notice almost accident- 

 ally during the summer of 1948, and a full investigation has been impossible to carry 



Fig. 152. Hybrid Woodsia. Series of leaves from the island of Runmaro near Stockholm, each from 

 a different plant, grown in cultivation. Natural size. For description see text. 



out before going to press. Even in a preliminary form, however, the results are so 

 surprising to a British botanist that reference to them seems profitable. 



The extreme rarity and alpine associations of W. ilvensis and JV. alpina in Britain have 

 already been commented upon in Chapter 7, and it is therefore at first an unfamiliar 

 experience to find both species growing, often in great profusion, at sea-level in Scan- 

 dinavia. Once this experience has been gained it is perhaps not so surprising to learn 

 that both in Sweden, Norway and also in Alaska (Hulten, 1941) both species can some- 

 times be found together and that in some of these localities hybrids are formed. One of 

 the best known of such places is the island of Runmaro in the archipelago near Stockholm 

 which was described in detail by Qyarfort in the Svensk botanisk Tidskrift for 193 1 (vol. xxv, 

 p. 36). I was not able myself to visit the island, since in 1948 it was still included in 



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