THE OTHER BRITISH FERNS 



(n = 126 and 84) and a great variety of different forms of leaves. We may be certain 

 of one thing only, which is that this degree of diversity cannot be all that will be found. 

 For one thing the cytology as it stands is manifestly incomplete. The relationship 

 between numbers as different as 126 and 84 may not at first leap to the eye, yet we 

 can hardly doubt that we are dealing with the upper members of a polyploid series, 

 the lower ones of which are still to seek. If a form with a gametic number of 42 could 

 be found we should have a simple series of 42, 84 and 

 1 26 in which the plants bearing them would be diploid, 

 tetraploid and hexaploid respectively. It may be that 

 the diploid is extinct. In a world-wide range it is, 

 however, scarcely necessary to postulate extinction ^ 

 as long as we are in ignorance of the nature of popula- 

 tions over vast regions. It is, therefore, desirable to '^ _ .^ 

 continue the search for cytogenetic data on a scale ^H^i^L^'T 



far greater than has so far been obtained, in the light ^ ^ 4 ^* 



of which the speciation of this most troublesome ^f ^^' ^ 



group may perhaps become clearer. - " ^m £a 



In the meantime perhaps enough has been said to / | ^^^ ^ 



give some indication as to why the pure taxonomy of 

 the Cystopteris populations of Europe is so intractably 

 entangled when studied without cytology, and to c. montana n - 64 



hope that more extensive collections, especially from Fig. 122. Explanatory diagram to 

 countries outside Britain, may ultimately bring order Fig. 120^. x 1500. 



out of chaos. 



The other British species, C. montana (Lam.) Desv., can be dealt with in one sentence. 

 The chromosome number (Fig. 122) is 84, a fact which is of importance merely in show- 

 ing that multiples of 42 are no innovation in the C. fragilis complex, but are probably 

 fundamental to the genus. In this respect therefore the genus Cystopteris, though 

 perhaps related to the Dryopteroids and to Woodsia, nevertheless stands somewhat alone. 



Leaving the Dryopteroids now aside, the next major group to be placed near them by 

 Bower (see diagram, p. 89) is that of the Blechnoids. The British representatives com- 

 prise two genera, Blechnum and Scolopendrium* [Phyllitis), each with one species only in 

 this country, namely Blechnum spicant (L.) With, and Scolopendrium vulgare Sm. ( = Phyllitis 

 Scolopendrium (L.) Newman). Both genera are commonly regarded as in some way 

 related to Asplenium, though the interpretation of the nature of the relationship varies 

 with different authors ; Bower himself regards Scolopendrium as the end-result of a series 

 of developments in the order Asplenium — Blechnum — Scolopendrium, but the alternate 

 order, namely, Asplenium — Scolopendrium — Blechnum, is that more commonly adopted in 

 Floras (cf also Copeland, 1947). 



The chromosome numbers of the British species are shown in the photographs (Fig. 

 123^,/). Blechnum spicant (Fig. 131/) has n = 34, the number having been established 



*The retention oi Scolopendrium instead of the technically more correct generic name Phyllitis for the 

 purpose of this chapter is a matter of convenience in equating it with the bulk of the literature dealing 

 with this species. 



122 



