THE MALE FERN DRTOPTERIS FILIX-MAS 



enjoyed the opportunity of conversing', again advocated very strongly that D. Filix- 

 mas and D. abbreviata should be regarded as distinct species and proposed the name of 

 Lastrea propinqua for the latter. 



It is perhaps unnecessary to add further details, since the position to-day is sub- 

 stantially the same as that reached in 1855. There is slight doubt whether the British 

 form is really the exact equivalent of Lamarck and de Candolle's French plant, since 

 their description of a single sorus only, at the base of each pinnule, certainly does not 

 apply in Britain, but 'var. abbreviata Newman' is a commonplace of British as of 

 continental floras, and Wollaston's preference for specific distinctness has either not 

 been known or has been generally disregarded by botanists. Among amateur fern 

 collectors it is otherwise. Wollaston's name ''propinqua^ was accepted at once and is 

 still in common use by members of the British Pteridological Society, and it figures in 

 many collector's handbooks, including one as recent as that by Druery (191 2). By the 

 modern International Rules of Nomenclature* the name itself is illegitimate, since, 

 among other things, it had been utilized for other plants on at least two previous 

 occasions, namely, in 1841 by J. Smith and in 1849 by Presl. Wollaston's view of 

 specific distinctness has, however, been fully borne out by the cytogenetical facts to be 

 recorded below, and the only necessary modification is to admit the prior claim of the 

 name abbreviata and to designate the species, if it is to be a species, as Dryopteris abbreviata 

 (Lam. & DC.) Newman. 



The cytogenetic confirmation of the correctness of the separation of D. abbreviata 

 from D. Filix-mas is based on several lines of evidence. In the first place the difference 

 of chromosome number, one being half the other, is very constantly displayed (cf. Figs, 

 34^, 36). The haploid complement of 41 chromosomes has been found in plants bearing 

 the morphology of Z). abbreviata from the following localities: 



Wales: near Bala and near Bettwys-y-Coed ; Lake District: Kentmere Valley and 

 Borrowdale; Scotland: Greenhill Dod near Glasgow; Ireland: Mourne Mountains 

 (east coast) and Brandon Mountain (west coast). 



An even stronger argument for the specific distinctions of D. abbreviata is that when 

 crossed with D. Filix-mas it forms a highly sterile hybrid. 



The setting up of species hybrids is not an easy matter in ferns and it is always 

 slow. The presence of both sexes on the same prothallus makes the risk of accidental 

 self-fertilization greater than is usual, though it can be minimized by using only old 

 prothalli which have been watered from below, to serve as females. The success 

 or otherwise of the cross cannot easily be determined for some months after an insemina- 

 tion has been made owing to the morphological similarity of all related young ferns in 

 the early stages. If a hybrid can be detected as such by its possession of a chromosome 

 number different from that of the female parent, it can be detected by a root-tip 

 count in about a year from its inception. Meiosis cannot be hoped for till the plant is 

 ab out 3 years old. 



* English-speaking botanists who are not professional taxonomists will find a very helpful introduc- 

 tion to the International Rules of Nomenclature in Bisby (1945), in which the Rules and Recommenda- 

 tions including those added at the 1935 International Congress at Amsterdam are reproduced verbatim. 

 I am much indebted to F. Ballard of Kew for drawing my attention to this very useful little book. 



48 



