THE MALE FERN DRYOPTERIS FILIX-MAS 



The 'commonest and best known British fern' would therefore seem to be the first 

 case of an allopolyploid to be detected among ferns and to have owed its origin in the 

 first place to a cross between a species identical with or closely resembling D. abbreviata 

 and some other diploid species which has not yet been identified, followed in the 

 second place by chromosome doubling in the hybrid. 



If this diagnosis is correct it should be possible at some future time to resynthesize 

 the Male Fern from its component species. The identification of the second parent is, 

 however, hkely to be a matter of some difficulty. D. Filix-mas in the narrow sense is 

 common all over Europe, extending east at least as far as the Caucasus. It must there- 

 fore have been in existence for some time, and the second parent may in fact be extinct. 

 At least it may be expected to be non-British, since otherwise it seems likely to have 

 been detected in some way by the sharp eyes of the early collectors. This problem may 

 therefore be recommended to the interest of continental botanists. 



Fig. 39. Spores oi Dryopteris Filix-mas sens. strict. emend, x 100. 



The third species that should be separated from the old Filix-mas complex cannot 

 be fully dealt with until the cytological details accompanying apogamy have been 

 described (see Chapters 10 and 11). It is D. Borreri Newman, and its principal diagnostic 

 characters known to me in Great Britain are as follows : * 



( 1 ) Usually a large and handsome fern (except for certain local strains) and in both 

 respects more striking than D. Filix-mas. 



(2) Fronds tough and 'leathery', persisting long in the autumn and sometimes 

 surviving the winter, often of a more yellowish green than in the other two species. 

 The vernation of the unfolding fronds is usually more lax than in the other species. 



(3) Surface of the pinnae glossy when living. 



(4) Ramenta very abundant and more so than in either of the other two species. 

 Often, though by no means always, of a bright orange yellow, sometimes with some 

 darker cells at the base of the scale. 



(5) Indusium in most strains tucking under the sorus. 



(6) Shape of the pinnules very characteristic ; they are not completely separated at 

 the base; the sides of the pinnules are rather straight and the tips abruptly truncate 

 and not tapering (cf Fig. 29). 



(7) A very characteristic detail always present, even in putative hybrids, though 

 unfortunately lost in herbarium specimens, is the presence of a patch of dark pigment on 



* For further amplification, see Wollaston (1875). 



54 



