THE OTHER BRITISH FERNS— POLTSTICHUM, ATHTRIUM, CETERACH 

 That they are distinct and vaHd species is, however, now the prevailing opinion among 

 systematists, ahhough much discussion of this will be found in older Floras, owing 

 probably to the fact that hybrids of intermediate morphology can sometimes be found. 



Cytological observations have been made on British and on 

 continental specimens of all three species. The Holly Fern, 

 P. Lonchitis, has been examined from Scotland, Ireland and 

 Switzerland with identical results; as shown in Figs. 78 and 

 jgc the reduced chromosome number is « = 41. This number 

 was found again in P. angulare from Devon, the Lake District 

 and north Italy, and is very clearly demonstrated in Fig. 79 a. 

 On the other hand, P. aculeatum from the Lake District, 

 Yorkshire and Switzerland has twice this number, as may be 

 seen in Figs. 79^, 79^ and 80. 



P./onchih's n=4l 

 Fig. 78. Explanatoiy dia 

 gram to Fig. 79c. x 2000. 





• ^ 



• . *j 



* *• 





¥ 

 « 



t^ 



^ 



^i»' 





Fig. 



79. Meiosis in British species of Polystichum. x 1000. a. Permanent acetocarmine squash of 

 P. angulare Presl. n — 4.1. b. Permanent acetocarmine squash of P. aculeatum (L.) Roth. « = 82. 

 For explanatory diagram see Fig. 80. c. Section of P. Lonchitis (L.) Roth. 71 = 41. For explanatory 

 diagram see Fig. 78. d. Section of P. angulare. n-J^i; cf. a. e. Section of P. aculeatum. 7j = 82; 

 cf. ^. 



Further information about this genus will be found in Chapter 9, and for the present 

 the only conclusions which need be drawn from these facts are that the close affinity 

 between Polystichum and the Male Fern section o{ Dryopteris is strongly confirmed by the 



92 



