THE MALE FERN DRYOPTERIS FILIX-MAS 



morphological characters by Dr L. Praeger were pentaploids. A meiotic metaphase plate 

 of one of the latter is illustrated in Fig. 34^ with a comparable figure of a diploid 

 D. Borreri (Fig. 34^) added for comparison. Some photographs of the spores will be 

 found in Fig. 201, p. 192, Chapter 11. Reduced fertility, mixed morphology and 

 chromosome number all support a hybrid origin for these plants, the most probable 

 parentage for the tetraploids being diploid D. Borreri (male) xZ). Filix-mas (female), 

 while that of the pentaploids seems necessarily to be triploid D. Borreri (male) x D. Filix- 

 mas (female) . The fact that both types of hybrid can to a limited extent breed true 

 by means of the persistence of a few apogamously reproducing spores makes them 

 somewhat more conspicuous elements in our flora than is usually the case with newly 



Fig. 49. Map of the northern Hmits of Dryopteris Borreri Newm. in Europe. 



After Nordhagen (1947). 



formed species hybrids, and their existence is no doubt the chief reason why the specific 

 distinction of Z). Borreri has for so long been opposed by some taxonomists. 



Summarizing these conclusions, without going further at present into the mariy 

 interesting problems raised by D. Borreri Newman, it is sufficient for the moment to 

 have shown that on the simple criteria of morphological distinctions and genetical 

 discontinuity, three taxonomic species should be distinguished in the Male Fern popula- 

 tions of Great Britain. Two of these species show polyploidy and both of these can be 

 proved, or suspected, to have arisen as a result of hybridity. All three species can 

 probably cross with each other, though the subsequent fertility of such crosses is low. 



Confusing as all this may perhaps appear to a beginner and especially to an amateur 

 field collector, the choice of the Male Fern has turned out to be an unexpectedly 

 fortunate one for the purpose of the present inquiry. The use of the methods of 



61 



