762 



SCIENCE. 



[N. S. Vol. XXIV. No. 624. 



tion and so to its type-locality. ' Synopsis 

 Filicum' served a useful purpose in its day, 

 but the days of indiscriminate ' lumping ' of 

 species are over, and the really serious-minded 

 who wish to attain accuracy in the scientific 

 delimitation of species must have, even for 

 the species known before 1874, a more accu- 

 rate and available guide than this work. Be- 

 sides this, the species that have been described 

 in the last thirty -two years nearly equal those 

 described before 1874, 



It is, therefore, with the greatest delight 

 that fern students of all lands will hail the 

 completion of a publication whose earlier 

 parts, already reviewed in this journal, have 

 proved only a fair sample of what is, without 

 question, the most useful single work on ferns 

 that has ever been published. 



'Index Filicum,' by Carl Christensen, now 

 completed in a volume of eight hundred oc- 

 tavo pages is the work in question.^ In this 

 work each described species is entered not only 

 under its original genus, but also under every 

 successive generic name to which it has been 

 referred in a century and a half of genus 

 making, unmaking and remaking. For ex- 

 ample the common male-fern of Europe is 

 cited as Polypodium filix-mas, under which 

 Linnaeus first described it, and successively 

 as Dryopteris fUix-mas, Polystichum filix-mas, 

 Aspidium filix-mas, Nephrodium filix-mas and 

 L&strea filix-mas, under which names it has 

 successively appeared commencing with Adan- 

 son (1763), and under each of which it is 

 known to-day in some part or other of Europe. 

 Each reference gives a full citation with date, 

 following almost exactly the American system 

 for citation, and each entry has a cross refer- 

 ence to the generic name adopted in the work. 

 Under the accepted one in the above case, 

 Dryopteris filix-mas, the principal synonymy 

 is given, together with the geographic distri- 

 bution of the species. Genera and species are 

 both included in one alphabetical series and 



^ Carl Christensen : Index Filicum ; sive enumer- 

 atio omnium generum specierumque Filicum et 

 Hydropteridum ab anno 1753 ad finem anni 1905 

 descriptorum ; adjeetis synonymis principalibu3, 

 area geographica, etc. 8vo, pp. Ix, 744. Hafniae, 

 1905-1906, apud H. Hagerup. 



selected forms of type readily distinguish ac- 

 cepted genera and species from synonyms, 

 and these in turn from names of horticultural 

 origin. Following this alphabetical index is 

 a bibliography containing titles of all the 

 works and papers in which genera and species 

 of ferns have been defined, arranged alpha- 

 betically by authors, followed in turn by a 

 systematic index of the bibliography by means 

 of which one can quickly ascertain the extent 

 of the literature bearing directly on the ferns 

 of any continent, country or island, or on 

 any genus or family of ferns. 



The summary of entries includes 819 gen- 

 eric names and 22,680 specific names, which 

 shows (1) the magnitude of the work, since 

 these names are all entered at least twice, and 

 (2) the extent of the synonymy, since the 

 number of accepted genera is 149 and the 

 number of accepted species is 5,940. To show 

 the growth of our knowledge during a genera- 

 tion, we give in the following table a list of 

 a few of the genera whose limits are alike in 

 all the works cited, with the number of species 

 in each as recognized in 1874 in Synopsis 

 Filicum, as estimated by Diels and others in 

 Die natiirlichen Pflanzenfamilien in 1898, 

 and as actually listed by Christensen in Index 

 Filicum to the end of 1905. 



In sixty preliminary pages issued with the 

 last part (12) of the work, Christensen gives 

 a concise systematic enumeration of the gen- 



