SCOLOPENDRIUM HTBRIDUM, WOODSIA AND POLTSTICHUM ILLTRICUM 



is sufficient demonstration that some at least of the putative hybrids are triploids, as 

 they should be if the interpretation of their nature has been correct. 



The relevance of this to our general field of inquiry is close. In spite of the imper- 

 fection of the cytology at this preliminary stage we are undoubtedly seeing a type of 

 behaviour which has much in common with the Male Fern story of Chapter 4. As in the 

 case of the artificial hybrid between Dryopteris abbreviata and D. Filix-mas, we have a 

 triploid in which two gametic sets of chromosomes have paired with each other and one 

 has remained unpaired. In the case of Woodsia the gametic sets which have paired 

 seem necessarily to be those of W. ilvensis, and we therefore reach the somewhat 

 surprising conclusion that the diploid species IV. ilvensis must be part-parental to the 

 tetraploid species W. alpina in the same sense that Dryopteris abbreviata has shown itself 

 to be part-parental to the Male Fern. 



Woodsia alpina seems therefore to be another member of the British flora for which a 

 hybrid origin must be assumed, though, as in the case of the Male Fern, we know one 

 parent but not the other. That W. glabella, the third European species, may perhaps be 

 the other parent of W. alpina is quite possible though the fact can only be determined 

 by experiment. This problem also must therefore be left undecided until some future 

 occasion. 



The last case to be discussed in this chapter is that oi Polystichum illyricum Hahne and 

 related forms. This is the name given to the putative hybrid between P. aculeatum and 

 P. Lonchitis. As already pointed out in Chapter 6 these two species in Britain occupy 

 rather different habitats, the Holly Fern, P. Lonchitis, being almost always an alpine 

 while P. aculeatum is a lowland or at most a montane rock plant. Under most normal 

 conditions they do not therefore encounter one another; occasionally, however, this 

 occurs. In Britain the only locality known to me where this happens is in the limestone 

 pavement of the Craven area in the northern Pennines, and comparable admixture 

 has been described from time to time from various parts of the Continent. Only 

 in such places is P. illyricum to be found. It is represented by single individuals 

 (as opposed to homogeneous populations), which betray their hybrid nature both by 

 the possession of morphological characters (cf. Fig. 155) intermediate between those of 

 the putative parents and also by marked spore sterility. 



The material of P. illyricum available to me was obtained on each of two visits 

 made in 1937 and 1947 respectively to one of the classic localities for this particular 

 mixture of species, namely, that adjacent to the alpine garden at Pont-de-Nant above 

 Bex in the Rhone Valley in Switzerland. I am greatly indebted to the authorities of the 

 University of Lausanne for facilitating both visits. 



The locality in question is a Picea wood on the south-facing slopes of a tributary valley 

 at an altitude of 4100 ft. The soil is calcareous and the floor of the wood is composed 

 of gigantic boulders, partly moss covered, in the cracks under which Polystichum 

 Lonchitis, P. aculeatum {P. lobatum), together with putative hybrids, grow in great pro- 

 fusion and in very close proximity to each other. Some characteristic old plants of all 

 three types had been transferred to the alpine garden some years before my visit, and 

 fixings of sporangia were made on all of these. Other plants of all three types were 

 collected on both occasions and posted alive to England for further study. 



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