THE GENUS DRTOPTERIS IN BRITAIN 



found first in relatively remote parts of the British Isles (central Ireland and Scotland) 

 and not, so far, in the more accessible parts of England or Wales. The other alternative 

 is that they have been formed de novo in each locality by an act of hybridization, but 

 here we are confronted with the dilemma that all the species with which a parental 

 relation has been suspected [D. spinulosa, D. dilatata, D. rigida, D. Filix-mas) are tetra- 

 ploids and could therefore not give rise at once to a triploid by a simple cross. 



A possible solution to this problem was detected in the summer of 1948 by the dis- 

 covery that a diploid form of D. dilatata exists on the Continent and, from its morpho- 

 logical characters, probably also in Great Britain, though a plant of British origin has 

 not yet been confirmed cytologically. Fig. 62 shows a complete frond, slightly reduced 

 but otherwise characteristic of a population of small individuals found growing m 

 profusion on the north face of a sheltered gully above the tree line on the frontier 



b 



Fig. 61. The cytology oi ' Dryopteris remota' from Ireland, for comparison with that of the Windermere 

 specimen. For description see text. From sections, x 1000. a, b. Two different focal levels 

 through the same group of mother cells showing a polar and a side view. Note the extreme 

 regularity and the large number of the chromosomes, c. Two focal levels of a mitotic metaphase 

 plate in a root. Note the lower chromosome number in comparison with Fig. 59^. 



between Norway and Sweden at Storlien in Jamtland. Its oval outline is distinctly 

 narrower than is normally shown by lowland forms of D. dilatata in Britain, and the 

 shape of the lowest pinna bears some resemblance to D. spinulosa (cf Fig. 54^); it has, 

 however, quite unmistakably the dark central streak to the scales [ramenta) which 

 is otherwise diagnostic of D. dilatata. Fig. 63 shows the central portion, natural size, 

 of a larger specimen found in a wood at sea-level at Trondheim in Norway, and Fig. 64 

 shows the lowest pinna only of a still larger plant of the same general character which 

 came from a high akitude at Arolla in Switzerland. All these plants agree in having 

 41 chromosomes instead of 82 in their spores, a feature which is perhaps sufficiently 

 demonstrated by a comparison between Fig. 53^, p. 67, from the Swiss plant with Fig. 53/ 

 of normal British D. dilatata placed immediately beside it. All agree also in their 

 more finely cut pinnation, as may be seen by comparing any of the three Figs. 62-64 

 with Fig. 54. This character is mentioned from time to time in the early British 

 literature in relation to various rather ill-specified 'varieties' of D. dilatata, which is one 



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