THE GENUS DRYOPTERIS IN BRITAIN 



We have also now a new possibility for the parentage of Z). remota. If the new diploid 

 were to hybridize with D. Filix-mas, or another of the suggested species of appropriate 

 morphology, a triploid would be formed at once which might or might not be apogamous 

 but which would be expected to show much the same mixtiue of characters that we find 

 in D. remota. Attempts to synthesize such a hybrid have already been begun though they 

 will take several years to mature. If they are successful a very long-standing problem 

 in the European flora will have been solved. 



Leaving these problems aside, we come next to two very distinct and well-known 

 species, D. Oreopteris Ehrh., the Sweet Scented Mountain Fern, and the Marsh Fern, 

 D. Thelypteris (L.) A. Gray. In habitat and in habit these two species are about as far 

 removed from each other as any in the genus. The Mountain Fern is never found far 

 from hills; it is of the ordinary Lastrea type, growing abundantly in exposed positions 



I 



^ * 





* y ♦ • 



Fig. 65. Explanatory diagram to Fig. 66. x 1500. 



up to 1680 ft. in England, 2000 ft. in Ireland and 2900 ft. in Scotland, sometimes 

 mixed with Dryopteris abbreviata, D. Borreri or D. dilatata at the lower levels but eventually 

 outstripping these as it ascends. The Marsh Fern has a creeping habit and grows sub- 

 merged in the wettest of lowland bogs to which it is absolutely confined. In nature these 

 two species probably never meet under present conditions, and that they are ancient 

 is indicated by a geographical distribution which includes America as well as Europe. 

 To a cytologist they show, however, several striking points of resemblance. Although 

 tlie Marsh Fern has a curiously inverted periodicity in putting up its fertile leaves after 

 its sterile leaves, at the end of July, the sori share with those of the Mountain Fern the 

 peculiarity that they are placed very near to the edge of the pinnules, and though an 

 indusium is present, the main protection for the sporangia at the stage of full meiosis 

 is the recurved margin of the leaf They also differ very markedly in chromosome 

 number from all other British species of the genus. 



Fig. 71a represents meiosis in D. Oreopteris as it appears in sections, and Figs. 65 and 66 

 show a similar stage in a squash preparation in which the number n = 34 is very clearly 

 displayed. 



Figs. 67 and 68 represent a squash preparation of the Marsh Fern, D. Thelypteris. 

 The number appears not to be 34 but still less is it 41. In this species, as nearly as can 

 be determined, n = 35. 



79 



