THE OTHER BRITISH FERNS 



nature and small size of these plants, coupled with their extreme rarity in Britain, 

 which makes a large-scale multiplication of preparations unusually difficult. Other 

 cells of both species have, of course, been seen, but none of better quality. 



Turning now to Cystopteris we come to what is in some ways the most remarkable 

 cytological problem yet raised in the ferns. C.fragilis (L.) Bernh. is a small rock plant of 

 world-wide distribution, being met with even in the southern hemisphere. It is a vari- 

 able plant, and it has often puzzled systematists to decide whether it should or should 

 not be subdivided into several species. A closely cognate problem is to decide whether 

 C. alpina Desv. (C. regia Desv.) from the central European mountains should be separated 

 from it as a species, and, if so, whether this species is present in the British Isles. Com- 

 parable difficulties concern the status of other extreme foliar types, C. Dickieana Sim, 

 once found near Aberdeen, being one of the most frequently debated. The difficulty 



1^1^^^ 





Fig. iio. Meiosis in Cystopteris fragilis (L.) Bernh. in section, x looo. 

 The chromosomes uncountable, but see Figs. 1 12-1 15. 



with all these plants is their extreme plasticity under different environmental conditions, 

 so that without experimental cultures it may be quite impossible to obtain sufficient 

 evidence from herbarium material alone, and even with experimental cultures it may 

 require far more difficult types of observation than mere comparison of foliage. 



In contrast to the host of problems raised by or round C.fragilis (L.) Bernh., the other 

 British species, C. montana (Lam.) Desv., is simplicity itself With its creeping rhizome and 

 deltoid leaves it is as distinct from the fragilis complex as is the Oak Fern from the Lastrea 

 type of Dryopteris. It is, however, excessively rare in the British Isles, being confined to 

 central Scotland. Although I have had a specimen from this region in cultivation, 

 I have not so far been able to obtain a cytological result from it. In the account 

 which follows I have had to be content with a specimen of garden origin, previously 

 collected in Switzerland. 



Before presenting what can only be regarded as a prehminary report on the cytology 

 of Cystopteris, a special note on technique is perhaps desirable. In my experience this 

 genus is more than usually difficult to study effectively by any of the older cytological 

 methods. In sections of roots the hundreds of thin and contorted chromosomes are 

 virtually uncountable, and the same is true of meiosis, as may perhaps be seen from Fig. 



1 12 



