VI PBEFACE 



rrom 1934 onwards, F. Ballard had undertaken preliminary 

 work towards the continuation of the Index, and had assembled 

 a few thousand cards. He kindly sent me a copy of his records ; 

 this, with the data I had myself already collected, became the 

 foundation of the card-index for the fourth Supplement. But 

 as no complete record of journals searched had been kept, 

 it seemed necessary to re-check the possibly relevant literature. 

 A list of periodicals in which fern papers might be found was 

 prepared, and each member of the Committee was invited to 

 examine some of them, returning separate cards showing 

 (a) the full name of each periodical, (b) the title of each paper 

 containing any item for record in the Index, (c) each new 

 taxon, new status, new combination and new name. 



The cards so received did not all present the necessary in- 

 formation in precisely the same sequence j further, some omitted 

 details of one kind or another, and it appeared that in some 

 cases the publication did not comply with all the requirements 

 of the Code of Nomenclature. For these reasons I decided to 

 re-check all papers containing novitates. I also prepared new 

 cards for all basionyms. While doing this, I found that a certain 

 number of specific names in Chkistensejst's « Index Filicum », 

 cited as basionyms for new combinations, were nomina nuda and 

 thus not validly published. Consequently I undertook also a 

 revision of all basionyms to be cited in the fourth Supplement. 

 I further checked the original publications of all generic names. 

 I believe I have thus done everything necessary to prepare 

 the Supplement as accurately as possible, but I am aware 

 that, as with any work of this kind, it is not exempt from errors 

 and oversights. I am grateful to members of the Committee 

 for answering queries in connection with my work, and for 

 help with proof-reading. 



The research-work for the production of this supplement has 

 been very tedious and difficult ; it has required months and 

 months of work. IsTevertheless, I am very satisfied to have 

 served fern taxonomy and to have honoured Carl Christen- 

 SEN with the continuation of his monumental work. 



The help I have received from the members of the Committee 

 for the Index Filicum has been extremely valuable and I am 

 greatly indebted to them for their collaboration without which 

 the work would not have been done at all. My most sincere 

 thanks are due to the Directors and Librarians of the Royal 

 Botanic Gardens, Kew, of the British Museum (Natural His- 

 tory), of the Museum National d'Histoire Naturelle de Paris, 

 of the Conservatoire et Jardin Botaniques de Geneve, of the 

 Istituto Botanico dell'Universita di Firenze and other institu- 

 tions for the hospitality and facilities I have enjoyed during 



