PREFACE 



the facts are as fully authenticated and as firmly established as is the chromosome number 

 of the Broad Bean. 



In an extended inquiry all aids to accuracy which can relieve the observer of personal 

 fatigue are of great importance. In this connexion the photographic methods (Appendix 

 2) used for the making of black and white diagrams are perhaps of some interest. 

 Practically none of the numerous black and white illustrations of fern morphology and 

 of chromosomes has been based on a drawing of the usual type, and in dispensing 

 entirely with the old-fashioned camera lucida both speed and accuracy have been 

 greatly improved. 



With regard to the identification of material, this has not often been in any doubt, 

 although as a precaution close contact has been maintained with the herbaria at Kew 

 and the British Museum throughout the work. Since, however, it may perhaps be of 

 importance to later investigators to know more about the actual specimens used, a 

 herbarium specimen has been retained for almost every species, access to which may be 

 had on request either direct to the author or to the authorities at Kew. 



With regard to nomenclature, a perennial difficulty, this has become more acute 

 during the preparation of the manuscript owing to the numerous changes in taxonomic 

 usage regarding familiar species which have occurred since the work began. The 

 Check List of British Vascular Plants, published under the auspices of the British Ecological 

 Society (Clapham, 1946) in preparation for the compilation of new British Floras, has 

 emended terminology partly in accordance with preliminary communication of the 

 cytological results (as in the Male Fern complex, Manton, 1939) but in part inde- 

 pendently of this. More extended works, such as the Genera Filicum of Copeland (1947) 

 or th& Revised Classification of the Leptosporangiate Ferns by Holttum (1947), have similarly 

 affected the views previously current on questions of phylogeny. Since one of the aims 

 of the cytological study is to provide independent evidence on taxonomic matters it has 

 been felt that to revise the work constantly to incorporate these various developments as 

 they appeared was neither necessary nor desirable. As a basis of discussion any system of 

 classification and naming will suffice provided only that it is familiar and unambiguous. 

 Both these conditions are fulfilled by the very familiar phyletic views of F. O. Bower 

 and by the system of nomenclature of a standard Flora such as Babington's Manual of 

 British Botany (nth edition, 1922). At the time the work began these were all that were 

 available, and they still seem suitable as a framework on which the cytological facts 

 can be disposed. Emendations which seem necessary in the light of the cytology itself 

 can then be clearly distinguished and their agreement or disagreement with newer 

 views based on other evidence assessed. For ease of reference, however, the more 

 important cases in which the integrity of species has been disturbed by the cytological 

 facts are listed in Appendix 3, and a complete list of new chromosome numbers is 

 added in Appendix 4. 



That the work is incomplete is self-evident and a defect for which apology cannot be 

 made. The stopping place in an extended inquiry is in a sense arbitrary and could 

 be indefinitely postponed if it were made to wait upon completion of every item raised. 

 One can only repeat with Goethe that 'Die Kunst ist lang; und kurz ist unser 

 Leben', and since the ground which can be covered by the labours of one worker is 



