CHAPTER 4 



THE MALE FERN DRTOPTERIS FILIX-MAS 



A very natural starting point to any inquiry involving observation of our native ferns in 

 the field is the Common Male Fern Dryopteris {=Lastrea = Nephrodium = Aspidium) 

 Filix-mas (L.) Schott. To quote a popular handbook (Step, 1908), it is said to be the 

 'commonest and best known British fern', and the inevitability of its recurrent use in 

 elementary classrooms may even at times have engendered that extreme measure of 

 superficial famiharity which breeds contempt. 



Little might one suspect that beneath this apparently famihar surface lies a welter 

 of so much concealed complexity that a beginner in cytological matters might well 

 be engulfed like Christian in the Slough of Despond and be tempted to abandon the 

 whole project in despair. D. Filix-mas (L.) Schott is in fact not a species in any legitimate 

 sense of the word, except perhaps the 'coenospecies' of Turesson.* It is an assemblage 

 of forms differing in morphology, genetical constitution and life history, and there 

 seems little doubt that, among the aggregate of forms found wild in Great Britain, 

 at least three taxonomic species should be separately distinguished, and more may be 

 expected to be found in other parts of the world. 



In order to unravel the position even in outline, cytological and other observations 

 have been made on about a hundred selected plants from the British Isles with a smaller 

 quantity of material from the continent of Europe. The scope of this inquiry had to be 

 somewhat restricted owing to the war, but enough of the necessary breeding work was 

 completed to reveal a position of unusual interest to the evolutionist, partly because 

 some of the larger problems raised have hope of solution. 



The form of the species to which the name D. Filix-mas should still adhere when all 

 necessary subdivision has been carried out is a large plant, common in hedgerows, 

 woods and ditches throughout Great Britain, though probably not quite so abundant as 

 the almost ubiquitous species, D. dilatata, which will be discussed in the next chapter. 

 Any large population will show numerous small variations in form, an index no doubt 

 of slight internal genetical diversity, but in addition to the broad morphological 

 features fisted below, which all of them share, must be added a sexual reproduction of 

 the usual type (Fig. 42<:, e), and chromosome numbers of 164 for the sporophyte and 

 82 for the gametophyte (Fig. 30). Forbidding as such numbers may perhaps at first 

 sight appear, they are established with complete numerical accuracy and will be met 

 with repeatedly on later occasions. 



The principal morphological characters by means of which D. Filix-mas in the 

 restricted sense can be distinguished in the field from the other species previously 

 amalgamated with it are fisted on the next two pages : 



* A definition of this will be found on p. 71. 



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