his third supplement to INDEX FIL1CUM contains names of new genera 

 and species and new combinations of names published during the years 

 1917 — 1933, together with a few older names omitted from the Index and from 

 the two earlier supplements. I dare scarcely hope that the list is complete. 

 Botanical literature is much more scattered since the war than formerly and 

 a considerable number of new periodicals, several of which I have not seen, 

 have been issued during the last fifteen years, especially in extraeuropean coun- 

 tries. Nevertheless I hope that the overlooked names are only few, thanks to 

 the many writers who have kindly sent me separate copies of their papers and 

 to some colleagues who have furnished me with names from those papers to 

 which I have not had access. For this service I render my heartiest thanks, 

 to Mr. A. H. G. ALSTON, British Museum (Natural History), London, who has 

 helped me in different ways and lent me his manuscript list of new species, 

 and to Mr. R. C. CHING, Peiping, who sent me a long list of corrections, Pro- 

 fessor E. B. COPELAND, Berkeley (California), Mr. R. E. HOLTTUM, Singapore, 

 Senor G. LOOSER, Santiago de Chile, Dr. W. R. MAXON, Washington, Pro- 

 fessor E. D. MERRILL, New York and Mr. C. A. WEATHERBY, Gray Herbarium. 

 Besides the enumeration of new names this supplement — like the two 

 earlier ones — contains a considerable number of corrections and changes of 

 names. While such corrections were enumerated separately in the first two 

 supplements they are here incorporated in the list of new names. This arran- 

 gement is probably more convenient, as separate lists of Corrigenda are liable 

 to be overlooked. 



The corrections and changes are essentially of four kinds: 

 1). Simple corrections of wrong citations or of spellings of names in the Index. 

 2). Restoration of varieties to specific rank and reduction to synonyms of 

 species adopted as valid in the Index. Such changes are very numerous 

 and are due in part to the extensive taxonomic study of ferns during recent 

 years by competent pteridologists, but chiefly to my own studies in the 

 larger European herbaria. Such changes, as a rule, are listed only for the 

 chief entries in the Index and supplements, and not for changes in the 

 synonymy. 

 3). Changes of generic names. These are few, the most important being the 

 choice of Tectaria for Aspidium, which is warranted because most new 

 species of this genus have been decribed under that name, which is no 

 doubt the earlier one. On the other hand I cannot follow some American 

 writers in using Thelypteris for Dryopteris sens. lat. If the former name 

 is to be used at all it must replace Lastrea only, a single subgenus of Dryop- 

 leris sens. Ind., which I regard as a most natural genus, and cannot be 

 used for the hundreds of other species of Dryopteris. 



