4). Changes in the conception of genera. We are still far from a thoroughly 

 natural classification of the genera of ferns on a real genetical basis, but 

 during recent years there have been several valuable contributions to a 

 much better classification and delimitation of really natural groups of spe- 

 cies and in many cases such groups have been raised to generic rank. I 

 am in agreement with these authors in most cases but I regret that I 

 cannot always follow them in this supplement. Since the Index has become 

 the standard work for the arrangement of ferns in most herbaria and the 

 splitting of big genera such as Dryopteris and Polypodium is hardly poss- 

 ible in the present state of our knowledge, I have confined myself in this 

 supplement to segregating from the larger groups such smaller natural 

 groups as are widely accepted and can be segregated easily in herbaria. 

 Even so, until these large genera are monographed, there will remain a 

 considerable number of species of which the taxonomic position will be 

 uncertain to all but trained pteridologists. 



In the Enumeratio generum systematica I follow as a whole the classifica- 

 tion of Diels, repeated in Index, in spite of it does not correspond to our 

 present knowledge of the natural relationship of the fern-genera. I find it, 

 however, less appropriate to publish in this supplement, which is a » supple- 

 ment t only, a thorough revision of the classification which is under prepara- 

 tion for another work, and I confine myself, therefore, to insert the new 

 genera listed in the three supplements and to replace some genera, the former 

 position of which was too unnatural. The generic number quoted in the 

 alphabetical Index refer to the systematical enumeration in this supplement. 



Copenhagen, March 1. 1934 



CARL CHRISTENSEN. 



Postscript. About a year before the printing of this supplement began 

 (April 1st 1934) I bad finished my part of the paper on the ferns of Mount 

 Kinabalu (see Cat. Litt., C. Chr. no. 61), in which several new species were 

 described and new combinations made. The paper was however first issued in 

 June and copies received in August and I could not therefore refer to it in the 

 supplement, in which most of the same new combinations are listed as new 

 ones, before the tenth sheet (pag. 160) was printed. The combinations are thus 

 first published in the said paper, but I have added the right citations in an 

 appendix to the supplement (v. pag. 196), in which also the new species, though 

 published in 1934, are listed. In the appendix are also included a number of 

 new species and new combinations overlooked by me, for references to which 

 I am indebted to Mr. F. BALLARD, Kew. 



October 19 34 - 





